DESCRIPTION

IMAGE FORMING METHOD

TECHNICAL FIELD

The present invention relates to an image forming method using an electrophotographic system (hereinafter, also referred to as an "electrophotographic process") .

BACKGROUND ART

Conventionally, various techniques have been proposed on an electrophotographic process for attaining high- quality image formation.

Japanese Patent Application Laid-Open No. H01-310383 discloses a technique for improving stability of charge voltage by using an electrophotographic photosensitive member having a dispersion-type photosensitive layer, in which a charge generating material is dispersed in a binder containing a charge transporting substance, and a binder resin and by defining the ratio of the distance of charge removing light invading into a photosensitive layer and the thickness of the photosensitive layer.

Japanese Patent Application Laid-Open No. H08-022229 discloses a technique for effectively preventing a ghost by controlling the surface potential of an electrophotographic photosensitive member immediately before or during charge remove (charge removing light of 620 ran or more) to be -100 V or more by use of an image exposure light having a wavelength of 670 ran.

Japanese Patent Application Laid-Open No. H06-083143 discloses a photosensitive member for photo-image back irradiation having a first photoconductive layer having a photosensitivity to image exposure light and a second photoconductive layer stacked on the first photoconductive layer and having photosensitivity to image exposure light, which is lower than the first photoconductive layer, and photosensitivity to charge removing light.

Japanese Patent Application Laid-Open No. H06-266138 discloses a technique for reducing a ghost without decreasing chargeability by controlling the local level density of a photoconductive layer, the electric field applied to an electrophotographic photosensitive member and the migration rate of the surface of the electrophotographic photosensitive member so as to have a specific relationship.

Japanese Patent Application Laid-Open No. H08-179663 discloses a technique for reducing a ghost without decreasing chargeability and potential shift by specifying the characteristic energy of the exponential function tail obtained from the light absorption spectrum of a sub-band gap in a light incident portion of a photoconductive layer, and local state density within a specific range and further specifying the wavelength and light intensity of charge removing light. As one of the electrophotographic photosensitive members used in an electrophotographic process, an electrophotographic photosensitive member (hereinafter, also referred to as an "a-Si photosensitive member") having a photoconductive layer formed of hydrogenated amorphous silicon (hereinafter, also referred to as "a-Si" is known.

When an a-Si photosensitive member is used as an electrophotographic photosensitive member, a residual image (hereinafter, referred to as a "ghost"), which is an appearance of an exposure history of a previous round, sometimes appears in an output image. The present inventors presume the cause of a ghost as follows. Some of the electrons, which are generated in a photoconductive layer by image exposure, are captured by defects in the photoconductive layer and accumulated in the photoconductive layer. The accumulated electrons bind to positive charges during the next-round image formation and affect an output image.

Conventionally, the ghost is improved by reducing the effect of the aforementioned accumulated electrons upon an output image by a large amount of charges, which are generated in a photoconductive layer by applying exposure light (hereinafter, referred to as a "pre-exposure light") to the entire surface of an electrophotographic photosensitive member before a primary charging step (sometimes referred to as a "main charging step" or sometimes simply as a "charging step") . Alternatively, in the conventional art, layer design has been studied as follows. The photoconductive layer of an a-Si photosensitive member is formed of a plurality of layers, which are functionally divided into layers for mainly improving electron migration and layers for mainly improving hole migration. In addition, layer design is controlled such that pre-exposure light is substantially absorbed by the photoconductive layer provided near the surface of the electrophotographic photosensitive member. In this way, a ghost has been improved while maintaining other electrophotographic characteristics satisfactorily.

However, a minor ghost, ^■ even though it was not deemed as a problem in the conventional art, is recently required for improvement . Particularly, when an a-Si photosensitive member is used in an electrophotographic process having a primary charging step for positively charging the surface of an electrophotographic photosensitive member and a secondary charging step (which is further provided different from the primary charging step) for negatively charging the surface of the electrophotographic photosensitive member, a sufficient effect cannot be always obtained even if the aforementioned ghost improving technique is used. As the secondary charging step as mentioned above, e.g., a transfer step (a transfer charging step) in which a toner image formed on the surface of an electrophotographic photosensitive member is transferred to a transfer material, and a pre-transfer charging step for improving stability of a toner image transfer process, are mentioned. The pre- transfer charging step is generally performed between a developing step and a transfer step. Furthermore, in the case where image output was repeatedly performed in an electrophotographic process having a secondary charging step, an image density sometimes decreases depending upon the image output conditions . There are various causes for this. As far as an electrophotographic photosensitive member is concerned, many causes are found in the surface of the electrophotographic photosensitive member frequently.

As one of the causes, a phenomenon where a substance is attached onto the surface of an electrophotographic photosensitive member may be mentioned. In a general electrophotographic process, A substance, which is attached onto the surface of an electrophotographic photosensitive member, is removed by a cleaning step. However, for example, in some cases of using a toner having an extremely low melting point, some cases where the contact pressure between an electrophotographic photosensitive member and a cleaning member is extremely low, and other cases where an original having a low printing ratio is repeatedly output, a substrate attached onto the surface of an electrophotographic photosensitive member is not always sufficiently removed. As such a substance, for example, paper dust and a resin component/wax component contained in toner are mentioned.

Furthermore, as another cause, denaturation of the surface layer of an electrophotographic photosensitive member, that is, formation of an oxide film on the surface of the electrophotographic photosensitive member, is mentioned. The oxide film is also removed by a cleaning step in a general use environment and a general electrophotographic process. However, depending upon abnormal operation of an electrophotographic apparatus and abrupt change of the environment, the current or voltage to be applied to an electrophotographic photosensitive member significantly varies and cleaning conditions sometimes significantly change. In this case, the oxide film may often remain on the surface of the electrophotographic photosensitive member.

DISCLOSURE OF THE INVENTION

An object of the invention is to provide an image forming method suppressed in a ghost and having a primary charging step of positively charging an electrophotographic photosensitive member and a secondary charging step of negatively charging the electrophotographic photosensitive member. The present invention provides an image forming method for forming an image by sequentially repeating a pre-exposure step of applying pre-exposure light to the surface of an electrophotographic photosensitive member, thereby removing charge from the surface of the electrophotographic photosensitive member; a primary charging step of positively charging the surface of the electrophotographic photosensitive member; an image exposure step of applying image exposure light to the surface of the electrophotographic photosensitive member to form an electrostatic latent image on the surface of the electrophotographic photosensitive member; a developing step of forming a toner image on the surface of the electrophotographic photosensitive member by visualizing the electrostatic latent image with toner; and a secondary charging step of negatively charging the surface of the electrophotographic photosensitive member, in this order, characterized in that the electrophotographic photosensitive member is formed by sequentially forming a lower photoconductive layer and an upper photoconductive layer formed of hydrogenated amorphous silicon, and a surface layer formed of hydrogenated amorphous silicon carbide on a substrate, in this order; the lower photoconductive layer is a layer further containing a boron atom; the upper photoconductive layer is a layer containing no boron atom or contains a boron atom but is smaller in atom density than the lower photoconductive layer; the surface layer is a layer in which the total of the atom density of a silicon atom and the atom density of a carbon atom is not less than 6.60 x 10 ²² atoms/cm ³ ; and the light intensity A [μJ/cm ² ] of pre-exposure light reaching the lower photoconductive layer out of the light intensity of pre-exposure light applied to the electrophotographic photosensitive member in the preexposure step satisfies the following expression (1) : -12.0 < Ln(A) < -4.5 (1) . According to the present invention, the light intensity of pre-exposure light and the layer structure of the electrophotographic photosensitive member are controlled such that the light intensity of pre-exposure light reaching the lower photoconductive layer falls in the predetermined value mentioned above. In this manner, a ghost can be suppressed while maintaining chargeability, even if secondary charging is performed to negatively charging the surface of the electrophotographic photosensitive member. At the same time, the surface layer of hydrogenated amorphous silicon carbide high in atom density is formed near the surface of the electrophotographic photosensitive member. With this structure, formation of an oxide film on the surface of an electrophotographic photosensitive member and substance attachment onto the surface of the electrophotographic photosensitive member are suppressed even in a long operational use. Therefore, a decrease of image density and a ghost caused by the formation of an oxide film and the substance attachment onto the surface are suppressed. By virtue of combination of these, an effect of suppressing a ghost and an effect of suppressing a decrease of image- density can be maintained for a long time. Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic structural view illustrating an electrophotographic apparatus according to the present invention;

FIG. 2A and FIG. 2B are schematic sectional views illustrating a layer structure of an electrophotographic photosensitive member according to the present invention;

FIG. 3 is a schematic view illustrating a plasma CVD apparatus for use in manufacturing an a-Si photosensitive member according to the present invention;

FIG. 4A and FIG. 4B are schematic views of a measuring unit for evaluating substance attachment onto a surface;

FIG. 5A is a schematic sectional view illustrating a cylindrical substrate and location of a sample used during sample preparation; FIG. 5B is a schematic side view illustrating a cylindrical substrate and location of a sample used during sample preparation; FIG. 6 is a test chart used in ghost evaluation;

FIGS. 7A, 7B, 7C, and 7D are explanatory views illustrating a conventional mechanism how to form a ghost; and FIGS. 8A, 8B, 8C, and 8D are explanatory views illustrating a mechanism how to form a ghost by secondary charging (pre-transfer charging) .

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors conducted studies for suppressing a ghost in a secondary charging step, particularly, in an electrophotographic process (image forming method using an electrophotographic system) having a pre-transfer charging step. In the following, a description will be principally made by taking, e.g., the case where a secondary charging step of negatively charging the surface of an electrophotographic photosensitive member, is a pre-transfer charging step.

As the results of studies, the present inventors found that a ghost, which is generated in an electrophotographic process employing a pre-transfer charging step of negatively (reversed polarity) charging the surface of the electrophotographic photosensitive member, which has been positively charged in a primary charging step, is a combination of a conventional ghost (hereinafter, referred to as an "image exposure ghost") mentioned above and a ghost (hereinafter, referred to as "pre-transfer charge ghost") caused by a pre-transfer charging. Then, the present inventors speculated generation mechanism how to generate the image exposure ghost and the pre-transfer charge ghost for a difference. First, referring to FIGS. 7A, 7B, 7C, and 7D, the mechanism how to generate the image exposure ghost in the aforementioned electrophotographic photosensitive member having a photoconductive layer functionally divided into two layers and to be positively charged (an electrophotographic photosensitive member used in an electrophotographic process employing a primary charging step of positively charging the surface of the electrophotographic photosensitive member) will be described. In the electrophotographic photosensitive member to be positively charged, the photoconductive layer provided near a substrate (hereinafter, referred to as a "lower photoconductive layer") mainly contributing to improving hole migration. Furthermore, the photoconductive layer provided near the surface layer (hereinafter, referred to as an "upper photoconductive layer") mainly contributes to improving electron migration. Note that, although electrons and holes generated by image exposure are both involved in generation of an image exposure ghost, we will discuss focusing upon electrons in the following. First, in a primary charging step, the surface of an electrophotographic photosensitive member is positively charged. Then, an electrostatic latent image is formed on the surface of the electrophotographic photosensitive member by image exposure. At this time, the image exposure light applied is absorbed by a photoconductive layer to generate holes and electrons (FIG. 7A) . Some of holes and electrons generated in the photoconductive layer are reunited and disappear; however, some of the electrons generated are united with positive charges applied to the surface of the electrophotographic photosensitive member in the primary charging step to form an electrostatic latent image (FIG. 7B) . Furthermore, some of the electrons generated by image exposure are captured by defects of a photoconductive layer and accumulated in the photoconductive layer (FIG. 7C) .

For the reason, many electrons are accumulated in the portion of the photoconductive layer irradiated with image exposure light rather than the portion not irradiated with image exposure light during the formation of an electrostatic latent image. Some of the electrons accumulated in the photoconductive layer are thereafter reexcited, migrate toward the surface of the electrophotographic photosensitive member when a potential difference is produced by application of positive charges in the next-round primary charging step, and are united with the positive charges applied in the primary charging step. Therefore, the portion having a larger number of electrons accumulated therein actually possess a lower number of positive charges in the surface of the electrophotographic photosensitive member after the primary charging step. As a result, a potential difference is produced between the portion not irradiated with image exposure light and the portion irradiated with image exposure light during electrostatic latent image formation time (FIG. 7D) .

The present inventors presume that the potential difference is visualized by toner and appears as the image exposure ghost. Next, the mechanism how to generate the pre-transfer charge ghost will be described with reference to FIGS. 8A, 8B, 8C, and 8D by taking, e.g., cases where the electrophotographic photosensitive member to be positively charged is used in an analog electrophotographic apparatus and a BAE digital electrophotographic apparatus (an electrophotographic process for forming a toner image in the portion not irradiated with an image exposure light) . FIGS. 8A, 8B, 8C, and 8D show members just involved in generation of the pre-transfer charge ghost. Note that, in the case of an analog electrophotographic apparatus, a toner image is formed in the portion of an electrophotographic photosensitive member not irradiated with image exposure light. On the other hand, when the electrophotographic photosensitive member to be positively charged is used in an IAE digital electrophotographic apparatus (a toner image is formed in the part of an electrophotographic process irradiated with image exposure light) , a ghost (transfer ghost) , which is generated in the same mechanism as in the pre-transfer charge ghost generated in BAE (described below) , may sometimes generated due to transfer charging in a transfer step. This is because, in the case of the IAE digital electrophotographic apparatus, if a step of positively charging the surface of the electrophotographic photosensitive member is a primary charging step, the transfer step is automatically determined as a step of negatively charging the surface of the electrophotographic photosensitive member.

In the case where the surface of the electrophotographic photosensitive member is first positively charged in the primary charging step, and an electrostatic latent image is formed by image exposure, the state of the photoconductive layer is the same as in the image exposure ghost as mentioned above (FIG. 7B) .

Next, an electrostatic latent image formed on the surface of an electrophotographic photosensitive member is visualized (developed) with toner (negatively charged toner) to form a toner image on the surface of the electrophotographic photosensitive member. The toner image is formed in the portion not irradiated with image exposure light (FIG. 8A) . Furthermore, in a pre-transfer charging step, the surface of the electrophotographic photosensitive member is positively charged, which is reverse in polarity to negative charge that is applied in the primary charging step, for the reason mentioned above. By virtue of this, mostly toner is charged in the portion not irradiated with image exposure light. On the other hand, in the portion irradiated with image exposure light, since the electrophotographic photosensitive member is negatively charged, the electrons provided in the pre-transfer charging step are accumulated within the electrophotographic photosensitive member (FIG. 8B) . As a result, the number of electrons accumulated within the portion of the electrophotographic photosensitive member irradiated with image exposure light is larger than the portion not irradiated with image exposure light. After a toner image is transferred to a transfer material and the surface of the electrophotographic photosensitive member is again positively charged in a primary charging step, a larger number of the positive charges applied in the primary charging step are consumed, since a large number of electrons are accumulated in the portion irradiated with image exposure light (FIG. 8C) . Consequently, after the primary charging step, the surface potential of the electrophotographic photosensitive member decreases more significantly in the portion irradiated with image exposure light in the previous-round. Accordingly, the potential difference between the portion irradiated with image exposure light and the portion not irradiated with image exposure light further increases compared to the case where a pre-transfer charging step is not employed (FIG. 8D) . As a result, the density difference of an output image becomes more significant compared to that of an image exposure ghost by itself. This is presumably because a pre-transfer charge ghost is superposed on the image exposure ghost, as the present inventors speculated. The present inventors conducted studies on the accumulation of charges within electrophotographic photosensitive member, as a cause of the pre-transfer charge ghost. As a result, they found that when a photoconductive layer of an electrophotographic photosensitive member is formed of a plurality of layers, the pre-transfer charge ghost sometimes significantly appears. From this, the charges accumulated within an electrophotographic photosensitive member are presumably accumulated mostly in the interface between the photoconductive layers.

As described above, the image exposure ghost is generated by accumulation of electrons generated by image exposure in a photoconductive layer. On the other hand, the pre-transfer charge ghost is generated by accumulation of electrons in the interface between photoconductive layers further by negatively charging the surface of the electrophotographic photosensitive member, which is reverse in polarity to negative charge that is applied in the primary charging step, by the a pre-transfer charging step. Likewise, since the mechanism how to generate an image exposure ghost differs from that how to generate a pre- transfer charge ghost, it is considered necessary to take measures to deal with them, respectively.

To improve the image exposure ghost, it is considered effective to improve migration of charges generated by image exposure. Simultaneously, it is considered effective to reduce the effect of charges used in the electrostatic latent image formation time and remaining in a photoconductive layer upon an output image by applying preexposure light to the entire surface of an electrophotographic photosensitive member. To improve the pre-transfer charge ghost, it is speculated effective to reduce the number of electrons accumulated in the interface between a plurality of photoconductive layers. Then, the present inventors considered that a pre-transfer charge ghost can be suppressed by removing the electrons accumulated in the interface by pre-exposure and conducted intensive studies.

As a result, they found that a ghost can be suppressed by controlling the light intensity of preexposure light reaching the lower photoconductive layer to fall within a predetermined range by controlling the light intensity of pre-exposure light to be absorbed in an upper photoconductive layer and a surface layer. Based on the finding, the present invention was accomplished.

The present inventors further conducted studies to solve occurrence of a ghost and a decrease of image-density that encounter when image formation is performed repeatedly by an electrophotographic process. As a result, it was found that when a substance is attached onto the surface of an electrophotographic photosensitive member by repeatedly forming an image, a substantial light intensity of pre-exposure light incident upon the electrophotographic photosensitive member is lower than the beginning of use of the electrophotographic apparatus. A ghost is thus generated in the portion of the surface of the electrophotographic photosensitive member, at which the substance is attached. Furthermore, when an oxide film is formed and remains on the surface layer, a substantial light intensity of pre-exposure light incident upon the electrophotographic photosensitive member is larger than that of the beginning of use of the electrophotographic apparatus. A decrease of image density occurs at the portion of the surface of the electrophotographic photosensitive member at which an oxide film remains .

The mechanism how to decrease image density by the oxide film remaining on the surface of an electrophotographic photosensitive member and the mechanism how to generate a ghost by a substance attached onto the surface of the electrophotographic photosensitive member are presumed as follows.

First, the mechanism how to decrease image density by the oxide film remaining on the surface of an electrophotographic photosensitive member will be described. The surface of the electrophotographic photosensitive member is denatured by a charged product to form an oxide film. Since the refractive index of the oxide film takes an intermediate value between the refractive index of air and the refractive index of a surface layer (hereinafter, also referred to as an "a-SiC surface layer" formed of hydrogenated amorphous silicon carbide (hereinafter, also referred to as "a-SiC"), the oxide film serves as an anti- reflection film. Therefore, if the formed oxide film is not sufficiently removed by a cleaning member, the reflection index of the pre-exposure light applied to the surface of an electrophotographic photosensitive member having the residual oxide film decreases. For the reason, even if a predetermined light intensity of pre-exposure light is applied to the electrophotographic photosensitive member, the light intensity of pre-exposure light incident upon the electrophotographic photosensitive member substantially increases as the area of residual oxide film increases. Accordingly, the light intensity of preexposure light reaching the lower photoconductive layer is larger than the light amount determined at the beginning of use of the electrophotographic apparatus and the amount of charges generated by the pre-exposure increases. As a result, the positive charges applied to the surface of the electrophotographic photosensitive member in a next-round primary charging step are consumed in a larger amount. Thus, a decrease of image density is presumably occurs. Next, the mechanism how to generate a ghost by a substance attachment to the surface of an electrophotographic photosensitive member will be described.

In the oxide film formed by denaturation of the surface of the electrophotographic photosensitive member due to a charged product, a large number of polar groups are present. Therefore, if the formed oxide film is not sufficiently removed by a cleaning member, the surface free energy of the surface of the electrophotographic photosensitive member also increases. Likewise, when an image is repeatedly output while keeping a high surface free energy of the surface of an electrophotographic photosensitive member, a substance may attach to the surface of the electrophotographic photosensitive member. When a substance attaches to the surface of an electrophotographic photosensitive member, light reflective index of the pre-exposure light on the surface of the electrophotographic photosensitive member increases. Therefore, even if a predetermined light intensity of preexposure light is applied to an electrophotographic photosensitive member, the light intensity of pre-exposure light incident upon the electrophotographic photosensitive member surface substantially decreases as the amount of substance attached onto the surface increases. Accordingly, since the light intensity of pre-exposure light reaching the lower photoconductive layer is deviated from the intensity determined at the beginning of use of the electrophotographic apparatus, suppression of a ghost is presumably insufficient.

Such a decrease of image density caused by the remaining oxide film and generation of a ghost caused by substance attachment to a surface often occur only in a part of an image formation region, presumably for the reasons below.

For example, in the electrophotographic process in which the contact pressure between an electrophotographic photosensitive member and a cleaning member is extremely reduced, the frictional force between the surface of the electrophotographic photosensitive member and the cleaning member tends to be locally reduced. In the region at which a large frictional force is not applied, the oxide film formed on the surface of the electrophotographic photosensitive member is not sufficiently removed andremains. In addition, a substance tends to attach to the surface of the electrophotographic photosensitive member. As a result, only the portion at which the oxide film remains and the surface portion to which a substance attached deviate from the pre-exposure conditions determined at the beginning of use of the electrophotographic apparatus. Accordingly, a decrease of image density and a ghost presumably occur locally in the longitudinal direction (the direction in perpendicular to the circumferential direction) of the electrophotographic photosensitive member.

From this, the present inventors considered that a decrease of image density and a ghost that locally occur can be suppressed by suppressing denaturation of the a-SiC surface layer by a charged product. Then, the present inventors conducted intensive studies on a-SiC surface layer excellently suppressing denaturation by a charged product .

As a result, they found that if a sum of the atom density of a silicon atom and the atom density of a carbon atom constituting the a-SiC surface layer is set to be larger than a predetermined value, a large effect is obtained in solving the aforementioned problems. Hereinafter the atom density of a silicon atom will be referred to as the "Si atom density", the atom density of a carbon atom will be referred to as the "C atom density" and the sum of the atom density of a silicon atom and the atom density of a carbon atom will be referred to as the "Si + C atom density".

Furthermore, in the present invention, it is characterized in that the lower photoconductive layer contains a boron atom; whereas the upper photoconductive layer contains no boron atom or contains a boron atom but the atom density of boron atom is lower than the atom density of boron atom in the lower photoconductive layer. Hereinafter, the atom density of boron atom will be referred to as the "B atom density".

As mentioned above, migration of holes is improved in the lower photoconductive layer than in the upper photoconductive layer and migration of electrons is improved in the upper photoconductive layer than in the lower photoconductive layer. Therefore, holes generated by image exposure are likely to migrate towards the substrate; whereas electrons are likely to migrate towards the surface of the electrophotographic photosensitive member. Thus, the number of holes and electrons accumulated in the photoconductive layer can be reduced. As a result, a ghost caused by charges generated by image exposure can be suppressed.

Furthermore, as described above, the image forming method of the present invention is characterized in that the light intensity of pre-exposure light A [μJ/cm ² ] reaching the lower photoconductive layer out of the light intensity of pre-exposure light applied to the electrophotographic photosensitive member in the preexposure step satisfies the following expression (1) , wherein Ln(A) is a natural logarithmic value of A. -12.0 < Ln(A) ≤ -4.5 (1) To improve the pre-transfer charge ghost, the electrons accumulated in the interface between the lower photoconductive layer and the upper photoconductive layer as shown in FIG. 8B must be consumed by pre-exposure. In this manner, the lower photoconductive layer is allowed to absorb a pre determined light intensity of pre-exposure light and generate charges, which can consume the electrons accumulated in the interface between the lower photoconductive layer and the upper photoconductive layer. The present inventors consider that the pre-transfer charge ghost can be suppressed in this manner.

On the other hand, when the light intensity of pre- exposure light reaching the lower photoconductive layer is excessively large, and thus the charges generated by preexposure sometimes consume positive charges applied to the surface of the electrophotographic photosensitive member in the next-round primary charging step. In this case, desired chargeability cannot be maintained.

Therefore, in the present invention, Ln(A) regarding the light intensity A of pre-exposure light reaching the lower photoconductive layer is set to fall within the aforementioned range and the light intensity of pre- exposure light reaching the deeper portion (on the side of the lower photoconductive layer) than the interface between the lower photoconductive layer and the upper photoconductive layer is set to be a predetermined value. In this way, the electrons accumulated within the electrophotographic photosensitive member in the pre- transfer charging step can be sufficiently consumed by preexposure, and the effect of charges generated in the upper photoconductive layer by pre-exposure upon positive charges to be applied to the surface of the electrophotographic photosensitive member in a primary charging step, can be suppressed. As a result, it is considered that the pre- transfer charge ghost can be suppressed while maintaining chargeability.

Furthermore, as described above, an electrophotographic photosensitive member according to the present invention is formed by forming a lower photoconductive layer and an upper photoconductive layer constituted of an a-Si (hydrogenated amorphous silicon) and an a-SiC surface layer on a substrate sequentially in this order. Moreover, the Si + C atom density in the a-SiC surface layer is not less than 6.60 x 10 ²² atoms/cm ³ . In an electrophotographic photosensitive member according to the present invention, since the a-SiC surface layer has a high atom density, the interatomic distance of a silicon atom and a carbon atom forming a skeleton of a film structure of a surface layer is short. For this reason, the binding force between atoms forming the skeleton is presumably improved.

When the electrophotographic photosensitive member having such a surface layer is used, it is possible to suppress denaturation (oxidation reaction) of the surface layer in the primary charging step employing e.g., corona discharge. Consequently, it is possible to suppress formation of an oxide film serving as an anti-reflection film on the surface of the electrophotographic photosensitive member, and suppress an increase of the light intensity of pre-exposure light incident upon the electrophotographic photosensitive member. By virtue of this, an increase of the light intensity of pre-exposure light reaching the lower photoconductive layer is suppressed and excessive charge generation in the lower photoconductive layer is suppressed. Therefore, a decrease of chargeability is suppressed. As a result, a decrease of image density caused by formation of an oxide film is suppressed.

Furthermore, since formation of an oxide film on the surface of the electrophotographic photosensitive member is suppressed, generation of a polar group in the oxide film is also suppressed. By virtue of this, an increase of surface free energy of the electrophotographic photosensitive member is suppressed, with the result that substance attachment onto the surface of the electrophotographic photosensitive member is suppressed. As a result, an increase of the reflection index of preexposure light on the surface of the electrophotographic photosensitive member is suppressed by substance attachment onto the surface of the electrophotographic photosensitive member, and thus a decrease of the light intensity of pre- exposure light applied to the electrophotographic photosensitive member is also suppressed. By virtue of this, a decrease of the light intensity of pre-exposure light reaching the lower photoconductive layer is suppressed. Therefore, the electrons accumulated in the interface between the lower photoconductive layer and the upper photoconductive layer can be stably consumed. As a result, occurrence of the pre-transfer charge ghost caused by partial attachment of a substance onto the surface of the electrophotographic photosensitive member is suppressed in the longitudinal direction of the electrophotographic photosensitive member, As described above, a layer structure is designed such that the light intensity of pre-exposure light reaching the lower photoconductive layer falls within the above range while controlling the content of a boron atom in the lower photoconductive layer and upper photoconductive layer. In addition, the a-SiC surface layer having a high atom density is employed as the surface layer. In this way, a ghost suppression effect can be maintained for a long time while keeping good chargeability . In the present invention, the following layer structure and image exposure conditions are employed. In this way, a more significant ghost suppression effect can be obtained while suppressing ^' a decrease of chargeability.

First, as shown in FIG. 2B, a lower photoconductive layer 2005 is constituted of two layers, namely, a first lower photoconductive layer 2007 near a substrate and a second lower photoconductive layer 2008 near an upper photoconductive layer 2006. The atom density of hydrogen atom each in the second lower photoconductive layer 2008, the upper photoconductive layer 2006 is set to be lower than the atom density of hydrogen in the first lower photoconductive layer 2007. Hereinafter, the atom density of hydrogen atom will be referred to as the "H atom density". Furthermore, in the present invention, it is designed that light intensity B [μj/cm ² ] of image exposure light reaching the first lower photoconductive layer out of the image exposure light applied in an image exposure step satisfies the following expression (4) : Ln(B) < -6.5 (4) .

In the film formed of a-Si, the larger the H atom density, the wider the optical bandgap. To improve chargeability, the larger the H atom density, the more preferable. Therefore, in the present invention, it is preferred that the H atom density of the first lower photoconductive layer is set to be larger than the H atom density of each of the second lower photoconductive layer and upper photoconductive layer. On the other hand, when the H atom density is large, defects in the film sometimes increases. Consequently, charges (photocarriers) generated by light exposure may be captured by the defects in the photoconductive layer and accumulated. Therefore, if the H atom density of each of the upper photoconductive layer and the second lower photoconductive layer which absorbs a large light intensity of image exposure light is set to be lower than the H atom density of the first lower photoconductive layer; at the same time, the light intensity of image exposure light reaching the first lower photoconductive layer is set to be a predetermined value or less, an image exposure ghost is further suppressed. To also obtain such a ghost suppression effect stably, the surface layer of the electrophotographic photosensitive member must satisfy the aforementioned conditions. As described above, the surface layer of the electrophotographic photosensitive member according to the present invention, formation of an oxide film on the surface of the electrophotographic photosensitive member is suppressed. Consequently, the light intensity of image exposure light reaching the first lower photoconductive layer is suppressed from increasing with operation time of the electrophotographic apparatus. As a result, the image exposure ghost is suppressed from deteriorating with the operation time of the electrophotographic apparatus.

Now, the embodiments of the present invention will be more specifically described below with reference to the drawings .

Electrophotographic apparatus according to the present invention>

The image forming method (electrophotographic process) by use of an electrophotographic apparatus employing an a-Si photosensitive member will be described with reference to FIG. 1.

First, in FIG. 1, an electrophotographic photosensitive member 1001 is rotated clockwise to positively charge the surface of the electrophotographic photosensitive member 1001 by a primary charger 1002. Thereafter, the surface of the electrophotographic photosensitive member 1001 is irradiated with light (image exposure light 1006) by an image exposure apparatus to form an electrostatic latent image on the surface of the electrophotographic photosensitive member 1001. Then, the electrostatic latent image is developed by use of toner supplied by a developer 1012. As a result, a toner image is formed on the surface of the electrophotographic photosensitive member 1001.

Next, in order to stably transfer the image, charges are applied to the surface of the electrophotographic photosensitive member 1001 by a pre-transfer charger 1013. In this way, charges are further supplied to the toner forming the toner image. The polarity of charges applied by the pre-transfer charger 1013 is reverse (i.e., negative) to the polarity of charges applied onto the surface of the electrophotographic photosensitive member 1001 by the primary charger 1002, in the case of BAE. The pre-transfer charger 1013 is arranged downstream of the developer 1012 and upstream of a pre-exposure apparatus 1003.

Furthermore, the toner image to which charges are supplied is transfer onto a transfer material 1010 by a transfer charger 1004. Note that the transfer material 1010 is conveyed by a conveying unit 1011. Thereafter, the transfer material 1010 is separated from the electrophotographic photosensitive member 1001 to fix the toner image onto the transfer material 1010. After the toner image is transferred to the transfer material 1010, toner remaining on the surface of the electrophotographic photosensitive member 1001 is removed by a cleaner 1009. Thereafter, to remove charges from the surface of the electrophotographic photosensitive member 1001, pre-exposure light is applied to the surface of the electrophotographic photosensitive member 1001 by the preexposure apparatus 1003 to reduce the effect of charges (residual carrier) on an output image during formation of the electrostatic latent image in the electrophotographic photosensitive member 1001. A series of steps above is sequentially repeated to form an image.

As described above, if Ln(A) is set at -12.0 or more, the electrons accumulated in the interface between the lower photoconductive layer and the upper photoconductive layer in the pre-transfer charging step can be sufficiently consumed by the charges generated by pre-exposure. On the other hand, if Ln(A) is set at —4.5 or less, the effect of the charges generated by pre-exposure upon positive charges to be applied to the surface of the electrophotographic photosensitive member in the next-round primary charging step is suppressed. As a result, the pre-transfer charge ghost can be suppressed while keeping chargeability and advantages of the invention can be sufficiently obtained. More preferably, if Ln(A) satisfies the following expression (2), a significant suppression effect of a pre- transfer charge ghost can be obtained. -11 . 0 < Ln (A) < -6 . 0 ( 2 )

As the step of applying charges, which have reverse polarity to the charges applied to the surface of the electrophotographic photosensitive member in the primary charging step and varies depending upon the conditions of the electrophotographic process, the aforementioned pre- transfer charging step using the pre-transfer charger 1013 and a transfer step using a transfer charger 1004, etc. are mentioned. In the present invention, charges applied in the secondary charging step has a reverse polarity to that of the charges applied to the surface of the electrophotographic photosensitive member in the primary charging step. The conditions of current to be supplied to a charger in the secondary charging step are the same as those used in a conventional electrophotographic apparatus having an a-Si photosensitive member installed therein. Such as direct current, alternate current and a combination of direct current and alternate current can be used without any problem. For example, when direct current is used, -10 μA to -600 μA current is preferred.

Furthermore, in the image forming method of the present invention, the wavelength of pre-exposure light is not particularly limited. The wavelength employed in a conventional electrophotographic apparatus having an a-Si photosensitive member installed therein can be used without any problem. As the wavelength of pre-exposure light, 600 nm to 700 nm is preferred. Furthermore, the wavelength of image exposure light is not particularly limited as long as sensitivity which allows formation of an electrostatic latent image can be obtained. The wavelength employed in a conventional electrophotographic apparatus having an a-Si photosensitive member installed therein can be used without any problem. The wavelength of image exposure light is preferably 630 nm to 750 nm.

Electrophotographic photosensitive member according to the present invention>

FIG. 2A and FIG. 2B are schematic views illustrating an electrophotographic photosensitive member according to the present invention. FIG. 2A illustrates an electrophotographic photosensitive member formed by stacking a charge injection blocking layer 2004, a photoconductive layer 2002 and a surface layer 2003 on a conductive substrate 2001 sequentially in this order. The photoconductive layer 2002 is formed of a-Si and further functionally divided into the lower photoconductive layer 2005 and the upper photoconductive layer 2006. In FIG. 2B, the lower photoconductive layer has a double-layer structure formed of a first lower photoconductive layer 2007 and a second lower photoconductive layer 2008. (Photoconductive layer) In the present invention, the photoconductive layer of an electrophotographic photosensitive member is formed of the lower photoconductive layer and the upper photoconductive layer formed of a-Si, as described above. The reason why the photoconductive layer is formed of two layers is because a ghost is suppressed by the layer structure designed to improve migration of electrons and holes, as described above. For this reason, the photoconductive layer 2002 is divided into two layers, i.e., the lower photoconductive layer 2005 and the upper photoconductive layer 2006 based on the content of boron atom by which migration of electrons and holes can be controlled.

To describe more specifically, the lower photoconductive layer 2005 of an electrophotographic photosensitive member according to the present invention contains a boron atom; whereas, the upper photoconductive layer 2006 does not contain a boron atom or contains a boron atom, but the B atom density is lower than the B atom density of the lower photoconductive layer. By this constitution, migration of holes in the lower photoconductive layer 2005 can be improved compared to the upper photoconductive layer 2006 and migration of electrons in the upper photoconductive layer 2006 can be improved compared to the lower photoconductive layer 2005. As a result, a ghost caused by charges generated by image exposure can be suppressed, as described above. Furthermore, if the relationship between the B atom density (X) [atoms/cm ³ ] in the upper photoconductive layer 2006 and B atom density (Y) [atoms/cm ³ ] in the lower photoconductive layer satisfies the following expression (3) , the effect of the present invention can be more significantly obtained.

0.00 < X/Y < 0.50 (3) Furthermore, the B atom density in the lower photoconductive layer 2005 is not less than 1 x 10 ^~2 atomic ppm relative to a silicon atom, particularly preferably not less than 5 x 10 ^~2 atomic ppm, and further preferably not less than 1 x 10 ^"1 atomic ppm. Furthermore, the B atom density is not more than 1 x 10 ⁴ atomic ppm, particularly preferably not more than 5 x 10 ³ atomic ppm, and further preferably not more than 1 x 10 ³ atomic ppm.

Furthermore, the lower photoconductive layer is formed of two layers, i.e., a first lower photoconductive layer provided near the substrate and a second lower photoconductive layer provided near the upper photoconductive layer. The H atom density of each of the second lower photoconductive layer and the upper photoconductive layer is controlled to be lower than the H atom density in the first lower photoconductive layer.

This is preferable in view of obtaining a more significant ghost suppression effect while suppressing a decrease of chargeability .

Furthermore, it is more preferred that the relationship between the average value (ex) of the H atom density in the first lower photoconductive layer and the average value (β) of the H atom density in the second lower photoconductive layer and upper photoconductive layer satisfies the following expression (5) :

0.5 < β/α <1 (5) .

It is further preferred that the H atom density in the upper photoconductive layer is controlled to be lower than the H atom density in the second lower photoconductive layer.

Based on the relationship of the H atom density, if the light intensity of image exposure light reaching the first lower photoconductive layer is controlled, it is possible to obtain more significant ghost suppression effect while suppressing a decrease of chargeability.

The total content of a hydrogen atom (the sum of hydrogen atom contents in the first lower photoconductive layer, the second lower photoconductive layer and the upper photoconductive layer) is preferably not less than 10 atomic % relative to the sum of a silicon atom and a hydrogen atom, and more preferably not less than 15 atomic %. Furthermore, the total content of a hydrogen atom is preferably not more than 30 atomic %, and more preferably, not more than 25 atomic %.

In the present invention, the thickness of the photoconductive layer of an electrophotographic photosensitive member (the total thickness of the lower photoconductive layer 2005 and the upper photoconductive layer 2006) is preferably 15 μm or more, particularly preferably 20 μm or more; and 60 μm or less, particularly preferably 50 μm or less, and further preferably 40 μm or less in view of obtaining e.g., desired electrophotographic characteristics and economic effect. If the thickness of the photoconductive layer is controlled to be 15 μm or more, the amount of passing current through a charging member can be suppressed from increasing to prevent deterioration of the charging member.

The photoconductive layer constituted of a-Si can be formed by a method such as a plasma CVD method, a vacuum deposition method, a sputtering method and an ion plating method. Of them, the plasma CVD method is most preferably employed in view of feasibility of a raw material supply.

Now, a method for forming a photoconductive layer, for example, by a plasma CVD method will be described, below.

To form a photoconductive layer, basically a raw- material gas for supplying a silicon atom and a raw- material gas for supplying a hydrogen atom are introduced into a reaction container capable of being reduced in pressure in predetermined gaseous conditions to cause glow discharge in the reaction container. The raw-material gases introduced are decomposed by glow discharge to form a layer formed of a-Si on a conductive substrate previously arranged at a predetermined position. In the present invention, as the raw-material gas for supplying a silicon atom, a silane compound such as silane (SiH ₄ ) and disilane (Si ₂ H ₆ ) can be suitably used. Furthermore, as the raw-material gas for supplying a hydrogen atom into the photoconductive layer, hydrogen (H2) can be suitably used in addition to the silane compounds as mentioned above. Furthermore, when an additive such as a halogen atom, a boron atom, a carbon atom, an oxygen atom and a nitrogen atom as mentioned above is introduced into the photoconductive layer, a gaseous substance containing each atom or a substance that is easily converted into a gas can be appropriately used. (Surface layer)

In the present invention, it is characterized in that the Si + C atom density in the a-SiC surface layer is controlled to be not less than 6.60 x 10 ²² atoms/cm ³ , as described above.

If the Si + C atom density in the a-SiC surface layer is controlled to be not less than 6.60 * 10 ²² atoms/cm ³ , formation of an oxide film on the surface of an electrophotographic photosensitive member and substance attachment on the surface can be suppressed. By virtue of this, variation in the light intensity of pre-exposure light incident upon the electrophotographic photosensitive member is reduced and thus variation in light intensity of pre-exposure light reaching the lower photoconductive layer can be suppressed. As a result, a decrease of chargeability and deterioration of a ghost, which are caused by a change such as formation of an oxide film on the surface of an electrophotographic photosensitive member and substance attachment onto the surface can be suppressed. The mechanisms how to suppress formation of an oxide film and substance attachment onto the surface are speculated as follows.

When the Si atom density and C atom density in the a- SiC surface layer are increased, it is considered that the bond between a silicon atom and a carbon atom becomes hard to be broken. In addition, since a porosity decreases, the reaction probability between a carbon atom and an oxidizing substance may presumably be reduced. This is because, a- SiC oxidation reaction is caused between an oxidizing substance and a dangling bond of a silicon atom, which is newly generated by breaking the bond between a silicon atom and a carbon atom by oxidation and dissociation of a carbon atom.

In the electrophotographic process, it is considered that oxidation and dissociation of a carbon atom occurs by the reaction between ion spices generated in a primary charging step and a carbon atom. Therefore, it is speculated that oxidation of a silicon atom is suppressed by suppressing oxidation of a carbon atom as much as possible. To attain this, it is necessary to render the bond between a silicon atom and a carbon atom to be hard- to-break or reduce a reaction probability of a carbon atom to suppress oxidation of the carbon atom. To realize this, it is conceivably required to reduce the interatomic distance between atoms and the porosity.

If the Si + C atom density of a-SiC surface layer is increased, the interatomic distance between atoms and the porosity can be reduced. Therefore, formation of an oxide film and generation of polar group on the surface of the a- SiC surface layer is conceivably suppressed. As a result, formation of an anti-reflection film on the surface of an electrophotographic photosensitive member can be suppressed and further attachment of a substance onto the surface of the electrophotographic photosensitive member can be suppressed. Therefore, variation in the light intensity of pre-exposure light incident upon the electrophotographic photosensitive member is suppressed. In this way, a decrease of chargeability in the longitudinal direction of the electrophotographic photosensitive member and deterioration of a ghost are presumably suppressed. Because of this, the effect of suppressing a ghost by controlling the light intensity of pre-exposure light reaching the lower photoconductive layer can be maintained for a long time.

For the reason, the higher Si + C atom density of the a-SiC surface layer, the more preferable. If the density is not less than 6.81 x 10 ²² atoms/cm ³ , a predetermined light intensity of pre-exposure light can be further stably incident upon an electrophotographic photosensitive member.

The a-SiC surface layer has the highest Si + C atom density, when the layer becomes a crystal. Therefore, in the present invention, the uppermost value of the sum of a Si atom density and a C atom density is considered as follow. The SiC-crystal atom density (9.64 x 10 ²² atoms/cm ³ ) and a diamond atom density (17.65 x 10 ²² atoms/cm ³ ) are used as criteria and the atom density of a crystal, which is calculated according to the ratio of the number of a carbon atoms relative to the total number of a silicon atoms and a carbon atoms, is specified as the uppermost value. Furthermore, if the ratio of the atomic (C) number of a carbon atom relative to the sum of the atomic (Si) number of a silicon atom and the atomic (C) number of a carbon atom in the a-SiC surface layer (hereinafter, referred to as "C/ (Si + C)") is set to be 0.61 or more and 0.75 or less, further excellent electrophotographic characteristics can be obtained.

In the a-SiC surface layer, when the value of C/ (Si + C) is set to be 0.61 or more, even if an a-SiC having a high atom density is manufactured, the resistance of a-SiC can be suppressed from decreasing. By virtue of this, a decrease of a discrete dot, which is caused by lateral flow of charges in the surface layer during the formation of an electrostatic latent image, can be suppressed. As a result, an electrophotographic photosensitive member excellent in gradation on the low density side of an output image can be manufactured.

Furthermore, when the value of C/ (Si + C) is set to be 0.75 or less, even if a-SiC having a high atom density is manufactured, the light absorbed by the a-SiC surface layer can be reduced. As a result, the light intensity of image exposure light required for forming an electrostatic latent image decreases and an electrophotographic photosensitive member excellent in sensitivity properties can be manufactured.

Furthermore, in the present invention, the ratio of number of a hydrogen atoms relative to the sum of atomic (Si) number of a silicon atom, atomic (C) number of a carbon atom and atomic (H) number of a hydrogen atom (hereinafter, referred to as "H/ (Si + C + H)") in the surface layer of an electrophotographic photosensitive member is preferably set to be 0.30 or more and 0.45 or less. By virtue of this, excellent electrophotographic characteristics can be obtained and formation of an oxide film and generation of a polar group in the surface of an electrophotographic photosensitive member can be suppressed. In the a-SiC surface layer having a high atom density, an optical band gap narrows and light absorption increases, with the result that sensitivity decreases in some cases. However, if H/ (SI + C + H) is 0.30 or more, an optical bandgap widens to improve sensitivity. Therefore, it is preferred that H/ (SI + C + H) is set to be 0.30 or more. On the other hand, when H/ (SI + C + H) is larger than 0.45, a terminal group rich in a hydrogen atom such as a methyl group tends to increase in the a-SiC surface layer. When a terminal group such as a methyl ^' group having a plurality of hydrogen atoms is present in the a-SiC surface layer, a large space is formed in the a-SiC structure; at the same time, distortion of a peripheral interatomic bond occurs. Such a structurally weak portion is considered to be very susceptible to oxidation. Furthermore, when a large amount of hydrogen atom is added in the a-SiC surface layer, it becomes difficult to promote formation of a network of skeleton atoms, namely, a silicon atom and a carbon atom, in the a-SiC surface layer. For the reason,

H/ (SI + C + H) is set to be 0.45 or less. If so, formation of a network of a silicon atom and a carbon atom in the a- SiC surface layer is promoted and the distortion of an interatomic bond may be reduced. As a result, denaturation of the a-SiC surface layer is further suppressed.

More specifically, if H/ (SI + C + H) is set to be 0.30 or more and 0.45 or less in the a-SiC surface layer having a high atom density, good electrophotographic characteristics can be obtained and formation of an oxide film and generation of a polar group in the surface of an electrophotographic photosensitive member can be suppressed.

Furthermore, in a Raman spectrum of the a-SiC surface layer, if the ratio (I _D /I _G ) of the peak intensity (I _D ) at 1390 cm ^"1 relative to the peak intensity (I _G ) at 1480 cm ^"1 is set to be 0.20 or more and 0.70 or less, a large effect can be further obtained in suppressing formation of an oxide film and generation of a polar group in the surface of the electrophotographic photosensitive member.

First, the Raman spectrum of the a-SiC surface layer will be described in comparison with diamond-like carbon (hereinafter, referred to as "DLC") . The Raman spectrum of DLC formed of a sp ³ structure and a sp ² structure has a main peak in the proximity of 1540 cm ^"1 and a shoulder band in the proximity of 1390 cm ^"1 . The Raman spectrum is observed to be asymmetric. The Raman spectrum of the a-SiC surface layer manufactured by the RF- CVD method has a main peak in the proximity of 1480 cm ^"1 and a shoulder band in the proximity of 1390 cm ^"1 . This Raman spectrum is observed to be analogous to Raman spectrum of DLC.

The main peak of the a-SiC surface layer appears on the lower wavelength side than that of DLC because the a- SiC surface layer contains a silicon atom. From this, it is found that the a-SiC surface layer manufactured by the RF-CVD method is formed of a material having a structure very analogous to DLC. Generally, in the Raman spectrum of DLC, it is known that as the ratio of the peak intensity of a low frequency band relative to the peak intensity of a high frequency band decreases, the ratio of sp ³ structure in DLC tends to be high. Therefore, in the a-SiC surface layer, which has a very analogous structure to DLC, it is considered that as the ratio of the peak intensity of a low frequency band relative to the peak intensity of a high frequency band decreases, the ratio of sp ³ structure tends to be high.

In the a-SiC surface layer of the present invention having a high atom density, if the ratio (I _D /I _G ) / which is the ratio of the peak intensity (I _D ) in the proximity of 1390cm ^"1 relative to the peak intensity (I _G ) in the proximity of 1480 cm ^"1 in the Raman spectrum, is set to be 0.70 or less, a great effect can be obtained in suppressing denaturation of the a-SiC surface layer.

Hereinafter, peak intensity (I _G ) is defined as the peak intensity at 1480 cm ^"1 and the peak intensity (I _D ) is defined as the peak intensity at 1390 cm ^"1 .

The reason is considered as follows. When the number of sp ³ structures increases, the number of secondary networks (sp ² ) decreases and the number of a three dimensional networks (sp ³ ) increases. As a result, the number of bonds of skeleton atoms increases to form a strong structure.

Because of this, the smaller the ratio (I _D /I _G ), which is the ratio of the peak intensity (I _D ) at 1390cm ^~1 relative to the peak intensity (I _G ) at 1480 cm ^"1 in the Raman spectrum of the a-SiC surface layer, the more preferable.

However, in the a-SiC surface layer of an electrophotographic photosensitive member manufactured in a large scale production, the sp ² structure cannot be eliminated completely. Therefore, in the present invention, as the lowermost value of the ratio (I _D /I _G ) , which is the ratio of the peak intensity (I ₀ ) at 1390cm ^"1 relative to the peak intensity (I _G ) at 1480 cm ^x in the Raman spectrum of the a-SiC surface layer, is set to be 0.2, which was confirmed in Examples as the good range in view of oxidation of the a-SiC surface layer and substance attachment to the surface.

(Charge injection blocking layer)

In the electrophotographic photosensitive member of the present invention, it is effective to form a charge injection blocking layer, which serves a function of blocking injection of charges from the substrate, between a substrate and a photoconductive layer. More specifically, the charge injection blocking layer has a function of blocking injection of charges from the substrate to the photoconductive layer when charges having a predetermined polarity are applied to the surface of the electrophotographic photosensitive member in a primary charging step. To play such role, relatively a large number of atoms for controlling conductivity are added to the charge injection blocking layer compared to the photoconductive layer. As the atoms to be contained in the charge injection blocking layer to control the conductivity, atoms of the Xlll-group can be used.

The atoms to be contained in the charge injection blocking layer to control the conductivity may be contained in the charge injection blocking layer in a uniformly dispersed state. Furthermore, it is acceptable if there is a nonuniformly dispersed portion in the thickness direction. When the distribution concentration is nonuniform, a large amount of atoms are suitably distributed near the substrate. However, in either case, the atoms controlling the conductivity are preferably contained in a uniform distribution state in a plane parallel to the surface of the substrate also in view of obtaining uniform characteristics .

Furthermore, if at least one type of atom selected from a carbon atom, a nitrogen atom and an oxygen atom is contained in the charge injection blocking layer, it is possible to improve the adhesion between the charge injection blocking layer and the substrate.

At least one type of atom selected from a carbon atom, a nitrogen atom and an oxygen atom contained in the charge injection blocking layer may be uniformly distributed in the layer. Furthermore, it is acceptable if there is a nonuniformly dispersed portion. However, in either case, the atom is preferably contained in a uniform distribution state in a plane parallel to the surface of the substrate also in view of obtaining uniform characteristics.

The thickness of the charge injection blocking layer, in view of obtaining desired electrophotographic characteristics and economic effect, is preferably 0.1 to 10 μm, more preferably, 0.3 to 5 μm, and further preferably 0.5 to 3 μm. If the thickness is 0.1 μm or more, charges injection from the substrate can be sufficiently blocked and a preferable chargeability can be obtained. On the other hand, when the thickness is 5 μm or less, it is possible to prevent an increase of manufacturing cost due to extension of manufacturing time.

(Substrate) As a substrate, a substrate having conductivity (conductive substrate) and capable of holding a photoconductive layer and a surface layer to be formed on the surface can be used. For example, a metal such as Al, Cr, Mo, Au, In, Nb, Te, V, Ti, Pt, Pd and Fe and alloys of these such as an Al alloy and stainless steel are mentioned. Furthermore, a film of a synthetic resin such as polyester, polyethylene, polycarbonate, cellulose acetate, polypropylene, polyvinyl chloride, polystyrene, polyamide or an electrically insulating substrate such as a sheet, glass and ceramic can be used. In this case, a conductive treatment can be applied at least to the surface of the electrical insulating substrate on which a photoconductive layer is to be formed.

<Apparatus and method for manufacturing an electrophotographic photosensitive member according to the present invention>

FIG. 3 schematically illustrates a plasma CVD apparatus for use in manufacturing an a-Si photosensitive member according to the present invention. The plasma CVD apparatus is formed mainly of a deposition apparatus 3100 having a reaction container 3110, a raw-material gas supply apparatus 3200 and an exhaust system (not shown) for reducing the pressure of the reaction container 3110.

In the reaction container 3110 of the deposition apparatus 3100, a conductive substrate 3112 grounded, a heater 3113 for heating the substrate and a raw-material gas inlet pipe 3114 are arranged. Furthermore, to a cathode electrode 3111, a high-frequency power source 3120 is connected by way of a high frequency wave matching box 3115. The raw-material gas supply apparatus 3200 is constituted mainly of bombs 3221 to 3225 for raw-material gases such as SiH ₄ , H ₂ , CH ₄ , NO and B ₂ H ₆ and valves 3231 to 3235, pressure adjusters 3261 to 3265, flow-in valves 3241 to 3245, flow-out valves 3251 to 3255 and mass-flow controllers 3211 to 3215. The gas bombs containing raw- material gases are connected to the raw-material gas inlet pipe 3114 in the reaction container 3110 by way of an auxiliary valve 3260.

Next, a method for forming a deposition film (layer) by use of the plasma CVD apparatus will be described.

First, a substrate 3112, which has been defatted and washed, is placed in the reaction container 3110 via a receiver 3123. Next, an exhaust system (not shown) is operated to evacuate the reaction container 3110. When the pressure of the reaction container 3110 reaches a predetermined pressure (for example, 1 Pa or less), which is confirmed by monitoring the display of a vacuum gauge 3119, electric power is supplied to the heater 3113 for heating a substrate to heat the substrate 3112 to a predetermined temperature (for example, 50 to 35O ⁰ C) . At this time, heating can be performed in an inert gas atmosphere by supplying an inert gas such as Ar and He from the gas supply apparatus 3200 to the reaction container 3110.

Next, a gas for use in forming a deposition film is supplied from the gas supply apparatus 3200 to the reaction container 3110. To describe more specifically, the valves 3231 to 3235 and the flow-in valve 3241 to 3245 and the flow-out valves 3251 to 3255 are opened as needed, and the flow rates are determined by mass-flow controllers 3211 to 3215. When the flow rates controlled by the mass-flow controllers are stabilized, main valve 3118 is operated while monitoring the display of the vacuum gauge 3119 to control the inner pressure of the reaction container 3110 to be a predetermined pressure. When the predetermined pressure is obtained, high-frequency power is applied from the high-frequency power source 3120; at the same time, a plasma discharge is generated in the reaction container 3110 by operating the high frequency wave matching box 3115 Thereafter, the high-frequency power is quickly controlled to be a predetermined electric power and a deposition film is formed.

After a predetermined deposition film is formed, the application of high-frequency power is terminated, and the valves 3231 to 3235, flow-in valves 3241 to 3245, flow-out valves 3251 to 3255 and auxiliary valve 3260 are closed to terminate supply of raw-material gases. Simultaneously, the main valve 3118 is fully opened, the reaction container 3110 is evacuated to a predetermined pressure (for example, 1 Pa or less) .

In this way, formation of a deposition film is completed. When a plurality of deposition films are formed, the aforementioned procedure may be repeated to form deposition films. A contact area can be formed by changing the raw-material gas flow rate and pressure to the conditions for forming a photoconductive layer for a predetermined time.

After formation of all deposition films is completed, the main valve 3118 is closed and an inert gas is introduced into the reaction container 3110 to return the pressure to the atmospheric pressure, the substrate 3112 is taken out.

The electrophotographic photosensitive member of the present invention has a film-structure surface layer having a high atom density compared to the surface layer of a conventional electrophotographic photosensitive member. As described above, when the a-SiC surface layer of the electrophotographic photosensitive member of the present invention, having a high atom density is formed, although it varies depending upon the surface layer formation conditions, the lower the amount of gas to be supplied to the reaction container, the better, the higher high- frequency power, the better, and the higher the inner pressure of the reaction container, the better. Further, the higher the temperature of the substrate, the better. First, when the amount of gas to be supplied to the reaction container is reduced and high-frequency power is increased, the decomposition of the gas can be facilitated. By virtue of this, it is possible to efficiently decompose a raw-material gas (for example, CH ₄ ) for supplying a carbon atom, which is more difficult to be decomposed than a raw-material gas (for example, SiH ₄ ) for supplying a silicon atom. As a result, active species less in hydrogen atom is produced. Since the amount of hydrogen atom in the film deposited on the substrate decreases, the a-SiC surface layer having a high atom density can be formed.

Furthermore, when the inner pressure of the reaction container is increased, the reaction time of raw-material gases supplied to the reaction container becomes long. Furthermore, a reaction for withdrawing hydrogen poorly connected is caused by a hydrogen atom produced by decomposition of the raw-material gas. Therefore, the present inventors consider that formation of a network between a silicon atom and a carbon atom is accelerated.

Furthermore, when the temperature of the substrate is increased, the surface migration distance of the active species reaching the substrate becomes long and thus a more stable bond can be formed. As a result, atoms can be bind to structurally stable positions as the a-SiC surface layer.

Now, the present invention will be more specifically described by way of Examples and Comparative Examples below; the present invention should not be particularly limited by these.

(Preparation method for upper photoconductive layer sample)

Using a plasma CVD apparatus employing the RF zone high-frequency power source and shown in FIG. 3, an upper photoconductive layer sample was prepared by forming an upper photoconductive layer alone in the conditions shown in the following Table 1-1 on a glass substrate having a width of 10 mm, a length of 38 mm and a thickness of 1 mm (#7059, manufactured by Corning Incorporated) . As shown in FIGS. 5A and 5B, four glass substrates 5002 were provided at the center of mounting sites in the longitudinal direction on a cylindrical substrate 5001, which are provided at intervals of 90° in an arbitrary circumference direction of the outer diameter thereof.

Table 1-1

With respect to the upper photoconductive layer sample prepared in the above conditions, the absorption coefficient of the upper photoconductive layer at a wavelength of 630 nm was calculated by the calculation method (described later) . The results are shown in Table 1-3.

Note that since B ₂ H ₆ is not introduced when the upper photoconductive layer is formed, the boron atom density (hereinafter referred to as B atom density) of the upper photoconductive layer is regarded as 0.00 atoms/cm ³ .

(Preparation method for surface layer sample)

In the same manner as in the preparation method for the upper photoconductive layer sample, a surface layer sample was prepared by forming a surface layer alone in the conditions shown in the following Table 1-2 by use of the plasma CVD apparatus shown in FIG. 3, on a glass substrate having a width of 10 mm, a length of 38 mm and a thickness of 1 mm (#7059, manufactured by Corning Incorporated) . In this way, the surface layer sample was manufactured.

Table 1-2

With respect to the surface layer sample manufactured in the above conditions, the absorption coefficient of the surface layer at a wavelength of 630 nm was calculated by the same calculation method as in the preparation method for the upper photoconductive layer sample. The results are shown in Table 1-3.

Table 1-3

(Calculation method for absorption coefficient) In a method for calculating an absorption coefficient, the relationship between a wavelength and a transmissivity of a sample manufactured in each film forming condition (layer formation condition) was obtained by a spectrophotometer for ultraviolet and visible region (Type V-570, manufactured by Nihon Denkei Co., Ltd.) . At this time, a glass substrate used in preparing a sample was used a reference substrate.

First, transmissivity T (%) at a wavelength of 630 nra was obtained from the relationship between a wavelength and a transmissivity obtained. Next, the sample manufactured in each film forming condition was taken out from the spectrophotometer for ultraviolet and visible region and the deposition film was partially removed from the grass substrate of the sample by use of a cutter knife. Thereafter, the step between the portion of the glass substrate from which the deposition film was removed and the portion of the glass substrate from which the deposition film was not removed was measured by a surface profiler (ALPHA STEP 500, manufactured by KLA-Tencor Corporation) . Based on the step, the thickness D (cm) of the deposition film of the sample prepared in each film forming condition was obtained. Subsequently, using the values of T and D, absorption coefficient α ^* (l/cm) was calculated according to the following expression (6) : α ^* = -1/D x Ln (T/100) (6) . The relationship between a wavelength and a transmissivity obtained by an absorption spectrophotometer was analyzed based on the spectrum analysis of a spectrum manager (Rev.1.00 manufactured by Nihon Denkei Co., Ltd.) . The measurement conditions at this time are shown below.

Measuring mode: %T

Response: Medium Band width: 0.5 nm

Scanning speed: 1000 nm/min

Wavelength range: 300 nm to 1500 nm

Interval of data input: 2 nm

Furthermore, as the measurement conditions for layer thickness, a stylus diameter: 5 μm was used. The length and speed for measurement were appropriately set depending upon the removal range ^* of the deposition film by a cutter knife.

<Example 1-1> Using a plasma CVD apparatus using an RF zone high- frequency power source and shown in FIG. 3, and using a cylindrical substrate (a cylinder made of aluminum having a diameter of 80 mm, a length of 358 mm and a thickness of 3 mm, to which specular working is applied) , layers were formed in the conditions shown in the following Table 1-4 to manufacture the electrophotographic photosensitive member to be positively charged (a-Si photosensitive member to be positively charged) . At this time, a charge injection blocking layer, a lower photoconductive layer, an upper photoconductive layer and a surface layer were formed sequentially in this order and the thicknesses of the upper photoconductive layer and the surface layer were controlled to be those shown in Table 1-5. Furthermore, the total thickness of the lower photoconductive layer and the upper photoconductive layer was controlled to be 28 μm.

Note that as the conditions (film forming conditions) for forming the upper photoconductive layer, the same conditions as in preparing the upper photoconductive layer sample except the thickness were employed. Furthermore, as the conditions (film forming conditions) for forming the surface layer, the same conditions as in preparing the surface layer sample except the thickness were employed.

Table 1-4

The electrophotographic photosensitive member of each film forming condition manufactured in Example 1 was evaluated for chargeability and a ghost in the evaluation conditions (described later) . The light intensity A (Ln(A)) of pre-exposure light reaching the lower photoconductive layer was calculated by the calculation method (described later) . These results are shown in Table 7.

Note that when the electrophotographic photosensitive member of each film forming condition manufactured in Example 1-1 was evaluated for chargeability and a ghost, the light intensity of pre-exposure light to be applied to the surface of the electrophotographic photosensitive member by an external power source connected to a preexposure LED are shown in Table 1-5. Note that when B ₂ H ₆ was introduced at a flow rate

(0.50 ppm) relative to SiH ₄ flow rate during the formation of the lower photoconductive layer, the B atom density of the lower photoconductive layer (which was obtained by the measurement of B atom density described later), was 2.41 x 10 ¹⁶ atoms/cm ³ . Furthermore, B ₂ H ₆ was not introduced during the formation of the upper photoconductive layer and the B atom density was the lowermost limit of detection or less. Therefore, the B atom density of the upper photoconductive layer is regarded as 0.00 atoms/cm ³ . Furthermore, with respect to the surface layer of the electrophotographic photosensitive member manufactured in each film forming condition shown in Example 1-1, C/ (Si + C) was obtained by the analysis method (described later) . It was 6.81 x 10 ²² atoms/cm ³ . Table 1-5

<Comparative Example 1-1>

An a-Si photosensitive member was manufactured according to the conditions shown in Table 1-4 and in the same manner as in Example 1-1. At this time, the thicknesses of the upper photoconductive layer and the surface layer were controlled to be those shown in Table 1- 6.

The electrophotographic photosensitive member of each film forming condition manufactured in Comparative Example 1-1 was evaluated for Ln(A), chargeability and a ghost in the same manner as in Example 1-1. These results are shown in Table 1-7.

Note that when the electrophotographic photosensitive member of each film forming condition manufactured in

Comparative Example 1-1 was evaluated for chargeability and a ghost, the light intensity of pre-exposure light applied to the surface of the electrophotographic photosensitive member by an external power source connected to a pre- exposure LED is shown in Table 1-6. Table 1-6

(Chargeability evaluation)

Chargeability was evaluated by a method of using a modified digital electrophotographic apparatus iR-5075 (BAE) manufactured by Canon Inc. In the electrophotographic apparatus, an external power source is connected to the wire and grit of the primary charger and pre-exposure LED having a wavelength of 630 nm.

The electrophotographic apparatus was set under the environment of 25°C/50%RH and a heater for a photosensitive member was turned on. Furthermore, light intensity of light emitted from the pre-exposure LED was controlled to be a predetermined value by an external power source connected to the pre-exposure LED. After the electrophotographic photosensitive member manufactured was installed in the above electrophotographic apparatus, a potential sensor was arranged at the position of a developer, that is, at the site corresponding to the center position of the electrophotographic photosensitive member in the longitudinal direction. Next, a pre-exposure light was turned on in the aforementioned conditions and an image exposure light was turned off. In this state, an external power source was connected to each of the wire and grit of the charger. The grit potential was set to be 820 V. The surface potential was measured at the position of the developer by supplying a current of + 750 μA to the wire of the charger. Based on the surface potential, chargeability was evaluated. Note that the evaluation results were shown as relative comparison based on the surface potential (1.00) of the case where the electrophotographic photosensitive member of film forming condition No. 4 manufactured in Example 1-1 was installed. When the chargeability of an electrophotographic photosensitive member is low, assuming that the current applied to the wire of the primary charger is constant, the surface potential decreases. Therefore, as the surface potential increases, a higher chargeability is obtained. In this evaluation, as the numerical value increases, a higher chargeability is obtained.

Note that in the electrophotographic apparatus using an electrophotographic photosensitive member having a low chargeability, it is sometimes difficult to realize a high speed operation of the electrophotographic apparatus, even if a process speed increases. For this reason, it was determined that the effect of the present invention is obtained if chargeability evaluation B or more is obtained. The surface potential ratio of 0.96 or more relative to the surface potential of the electrophotographic photosensitive member of film forming condition No. 4 manufactured in Example 1-1 was determined as A. A ratio of 0.92 or more and less than 0.96 was determined as B and a ratio of less than 0.92 as C. (Evaluation of a ghost)

A ghost was evaluated by a modified digital electrophotographic apparatus iR-5075 (BAE) manufactured by Canon Inc.

First, the light intensity of light emitted from the pre-exposure LED was controlled to be a predetermined light intensity by a external power source connected to the pre- exposure LED.

Next, after the electrophotographic photosensitive member manufactured was installed in the above electrophotographic apparatus, a potential sensor was arranged at the position of a developer, that is, at the site corresponding to the center position of the electrophotographic photosensitive member in the longitudinal direction. Next, a pre-exposure light was turned in the aforementioned conditions and an image exposure light was turned off. The grit potential was set to be 820 V and the current to be supplied to the wire of the charger was controlled to set the surface potential of the electrophotographic photosensitive member at the position of the developer to be +400 μA. Subsequently, image exposure light was applied and the irradiation energy was controlled. In this manner, the potential at the position of the developer was set to be 100 V. Thereafter, the potential sensor was taken out, and the developer was arranged .

A ghost was evaluated by using a test chart shown in FIG. 6 and formed as follows. A black square piece (40 ram squares) having a reflection density of 1.4 is placed such that the center of the piece corresponds to the position of 40 mm inward from the left side of the image, that is, the left short-side of A3 chart. A half tone (HT) piece having a reflection density 0.4 is formed ranging from the position of 80 mm inward- from the left edge to the position of 5 mm inward from the right side.

The test chart was placed on an original mounting plate regarding the left edge of the test chart as the leading edge of an original. The reflection density of the HT portion of a test chart of an output image was controlled to be 0.4 by controlling a developing bias. In this state, an A3 electrophotographic image was output. The reflection density of the output image was measured.

Note that output of the test chart was performed in the conditions where the surface of an electrophotographic photosensitive member was maintained at 40°C by placing the electrophotographic apparatus in the environment of 22°C/50%RH and turning on the heater for the photosensitive member.

Measurement was performed at a reference position, which is the center of the short side of the A3 image and a position of 291 mm inward from the left edge of the A3 image (the position corresponding to one round of the electrophotographic photosensitive member from the center of the above black square) and at 4 comparative points (±30 mm relative to the reference position in the short side of the A3 image and ±30 mm in long side direction) . Measurement was performed at 5 points in total. Next, an average G of reflection density values measured at 4 comparative positions was obtained. The reflection density was measured by a reflection densitometer (504 spectrodensitometer manufactured by X-Rite Inc) . Subsequently, the difference (F-G) between reflection density F measured at the reference position and the average G of reflection density values of comparative portions was obtained. Based on the difference, a ghost was evaluated. Note that the evaluation results were shown as relative comparison based on the difference F-G (1.00), where F is the reflection density measured at the reference position and G is an average of reflection density values of comparative portions in the case where the electrophotographic photosensitive member of film forming condition No. 9 manufactured in Comparative Example 1-1 was installed.

In the ghost evaluation, an image exposure ghost and a pre-transfer charge ghost are overlapped each other. This is observed on an output image. Therefore, the overlapped image of an image exposure ghost and a pre- transfer charge ghost affects evaluation of ghost.

When a ghost appears, reflection density F obtained at the reference position is higher than the average G of the reflection density values obtained in comparative portions. Therefore, in the evaluation, as the numerical value decreases, a more satisfactory ghost is obtained. Note that it was determined that the effect of the present invention is obtained if a ghost evaluation B or more is obtained.

When the above value (F-G) obtained by use of an electrophotographic photosensitive member of film forming condition No. 9 manufactured in Comparative Example 1-1 was less than 0.8, A was given. When the value was 0.8 or more and less than 1.0, B was given. When a value was 1.0 or more, C was given.

(Calculation method for Ln(A)) Ln (A) was calculated according to the following method. The reflective index of light having a wavelength of 630 nm at the surface of the electrophotographic photosensitive member immediately after manufacturing was measured at the center position of the electrophotographic photosensitive member in the longitudinal direction in an arbitrary circumferential direction and the points, which are positions rotated by an angle of 90°, 180°, 270° from the arbitrary circumferential direction. That is, measurement was made at 4 points in total. An average value a of the obtained reflective indexes of the light having a wavelength of 630 nm was obtained. The average value was regarded as the reflective index of the electrophotographic photosensitive member manufactured in each film forming condition.

The reflective indexes of the electrophotographic photosensitive member manufactured in Example 1-1 and Comparative Example 1-1 were measured were 10.8% ± 0.1.

Therefore, as the reflective index used in calculating

Ln(A), a = 0.108 was used.

Next, using the absorption coefficient (α ^* l) of the surface layer, the absorption coefficient (α ^* 2) of the upper photoconductive layer (shown in Table 1-3) , the thickness (dl μm) of the surface layer, the thickness (d2 μm) of the upper photoconductive layer and the light intensity I (μJ/cm ² ) of the pre-exposure light (shown in

Table 1-5 and Table 1-6) and the reflective index (a) , the light intensity A of pre-exposure light reaching the lower photoconductive layer was calculated according to the following expression (5) :

A = exp (-α ^* 2-d2-10 ^~4 ) -exp (-α ^* l-dl-10 ^~4 ) -I-(l-a) (5). Finally, the light intensity A of pre-exposure light reaching the lower photoconductive layer thus calculated was converted into a value in terms of natural logarithm to obtain Ln (A) .

(Measurement of B atom density)

In the electrophotographic photosensitive member manufactured, 5 mm-square piece was cut off from the center portion in the longitudinal direction in an arbitrary circumferential direction to prepare a measurement sample. The measurement sample was subjected to secondary-ion mass spectrometry (Model 6650 manufactured by Ulvac-Phi Inc. ) to measure B atom density in the depth direction of the electrophotographic photosensitive member. In the measurement, an oxygen ion is used as a primary ion spices and B ⁺ is detected as a secondary ion. Note that, after completion of the measurement, the depth of a portion sputtered by the primary ion irradiation was measured to obtain a sputtering rate. Based on the results, density was calculated. Furthermore, a predetermined amount of boron ion was doped in a Si wafer to prepare a standard sample. The standard sample was measured in the same measurement method as mentioned above. Based on the results, B atom density was quantitatively calculated.

Also in this case, an oxygen ion is used as a primary ion spices and B ⁺ is detected as a secondary ion.

With respect to Example 1 and Comparative Example 1-1, the results of Ln(A), chargeability and a ghost are shown in Table 1-7.

Table 1-7

From the results of Table 1-7, it was found that if Ln (A) , which is calculated from the light intensity A of pre-exposure light reaching the upper photoconductive layer, is set to be -4.5 or less, good chargeability is obtained. It was found that if Ln(A) is set to be -12.0 or more, a ghost is improved. Furthermore, it was found that if Ln(A) is set to be -6.0 or less, chargeability is further improved, and that if Ln(A) is set to be -11.0 or more, a ghost is further improved.

As the reason why the ghost is improved by setting Ln(A) within the aforementioned range, it is presumed that a pre-transfer charge ghost was improved in consideration of the aforementioned mechanism on an image exposure ghost and a pre-transfer charge ghost. <Example l-2> An a-Si photosensitive member was manufactured according to the conditions shown in the following Table 1- 8 and in the same manner as in Example 1-1. At this time, a B ₂ H ₆ flow rate during the formation of the upper photoconductive layer was set according to the condition shown in the following Table 1-9.

Table 1-8

Table 1-9

With respect to the electrophotographic photosensitive member of each film forming condition manufactured in Example 1-2, a ghost was evaluated and B atom density was obtained in the same manner as in Example 1-1. The results are shown in Table 1-11.

Note that the light intensity of light emitted from the pre-exposure LED during the ghost evaluation was controlled to be 2.4 μJ/crα ² . Note that when the B ₂ H ₆ was introduced at a flow rate (0.50 ppm) relative to the SiH ₄ flow rate during the formation of the lower photoconductive layer, the B atom density of the lower photoconductive layer obtained by the aforementioned B atom density measurement was 2.41 * 10 ^lβ atoms/cm ³ . Furthermore, in film forming condition No. 10, B ₂ H ₆ was not introduced during the formation of the upper photoconductive layer and thus, B atom density was the lowermost limit of detection or less. The B atom density of the upper photoconductive layer is regarded as 0.00 atoms/cm ³ .

<Comparative Example l-2>

An a-Si photosensitive member was manufactured according to the conditions shown in Table 1-8 and in the same manner as in Example 1-2. At this time, film forming time was controlled such that the thickness of the upper photoconductive layer fell within the conditions shown in the following Table 1-10.

Table 1-10

Film forming condition No. 15

B ₂ H ₆ supplied to upper photoconductive layer[ppm](relative toSiH ₄ ) With respect to the electrophotographic photosensitive member of each film forming condition manufactured in Comparative Example 1-2, a ghost was evaluated and B atom density was obtained in the same manner as in Example 1-1. The results are shown in Table 1-11 .

Note that, the light intensity of light emitted from the pre-exposure LED during the ghost evaluation was controlled to be 2.4 μj/cm ² . The electrophotographic photosensitive members of each film forming condition manufactured in Example 1-2, Comparative Example 1-2 were evaluated for the ratio (hereinafter, referred to as "X/Y") of the B atom density (X) of the upper photoconductive layer relative to the B atom density (Y) of the lower photoconductive layer and a ghost. The evaluation results are shown in Table 1-11.

Note that film forming condition No. 10 of Example 1- 2 is the same as film forming condition No. 4 in Example 1- 1. Thus, Ln(A) is -6.9. Even if a small amount of boron atom is added to the upper photoconductive layer, the effect of the absorption coefficient can be ignored. Thus, in film forming condition Nos. 11 to 14 of Example 1-2 and

Comparative Example 1-2, Ln(A) is -6.9 in the same as film forming condition No. 10 of Example 1-2. Furthermore, with respect to the electrophotographic photosensitive member of each film forming condition manufactured in Example 1-2, the value of C/ (Si + C) was obtained according to the analysis method (described later) It was 6.81 x 10 ²² atoms/cm ³ . Table 1-11

From the results shown in Table 1-11, it was found that a ghost is improved by reducing the B atom density of the upper photoconductive layer compared to the B atom density of the lower photoconductive layer.

Furthermore, a ghost was further improved by setting the value of X/Y to be less than 0.5. It was found that even if the value of X/Y is 0, the good state of a ghost can be maintained.

Note that the electrophotographic photosensitive members manufactured in film forming condition Nos. 10 to 14 and having a good state of a ghost were evaluated for chargeability in the condition that the light intensity of light emitted from the pre-exposure LED was 2.4 μJ/cm ² and in the same manner as in Example 1-1. The evaluation results were all A.

As the reason why a ghost was improved by setting the B atom density values of the lower photoconductive layer and the upper photoconductive layer within the aforementioned range, it is presumed that an image exposure ghost was improved in consideration of the mechanism of an image exposure ghost and a pre-transfer charge ghost.

From the results above, it was found that if Ln(A) calculated from the light intensity A of pre-exposure light reaching the lower photoconductive layer is set to be —12.0 or more and -4.5 or less and the B atom density of the upper photoconductive layer is reduced compared to the B atom density of the lower photoconductive layer, the improvement of chargeability and suppression of a ghost can be obtained in balance. <Example l-3>

An a-Si photosensitive member was manufactured according to the conditions shown in the following Table 1- 12 and in the same manner as in Example 1-1. At this time, high-frequency power, SiH ₄ flow rate and CH ₄ flow rate during the formation of a surface layer were set to be the conditions shown in the following Table 1-13. Furthermore, four electrophotographic photosensitive members were manufactured in each film forming condition.

Table 1-12

Table 1-13

Four electrophotographic photosensitive members of each forming condition were manufactured in Example 1-3. With respect to a first photosensitive member out of the electrophotographic photosensitive members of each film forming condition, C/ (Si + C), Si atom density, C atom density, a sum of Si atom density and C atom density (hereinafter, referred to as "Si + C atom density"), H/ (SI + C + H) , the H atom density and sp ³ ratio of the surface layer were obtained by the analysis method described later.

Next, a second electrophotographic photosensitive member of each film forming condition was evaluated for oxidation resistance in the evaluation conditions described later. A third electrophotographic photosensitive member of each film forming condition was evaluated for substance attachment to a surface by the evaluation method described later. Furthermore, a fourth electrophotographic photosensitive member of each film forming condition was evaluated for Ln(A) by the calculation method described above and evaluated for gradation and sensitivity in the evaluation conditions described later. The results are shown in Table 1-16. Note that when the B ₂ H ₆ flow rate relative to SiH ₄ flow rate was set to be 0.50 ppm during the formation of the lower photoconductive layer, the B atom density of the lower photoconductive layer obtained by the aforementioned measurement of B atom density was 2.41 * 10 ¹⁶ atoms/cm ³ . Furthermore, B ₂ H ₆ was not introduced during the formation of the upper photoconductive layer and the B atom density was the lowermost limit of detection or less. Thus, the B atom density of the upper photoconductive layer is determined as 0.00 atoms/cm ³ . Furthermore, Ln(A) was calculated as follows.

First, a surface-layer sample of the surface layer of each film forming condition manufactured in Example 1-3 was prepared in the same manner as in the aforementioned surface-layer sample preparation method. The absorption coefficient of each surface-layer sample was calculated by the aforementioned absorption coefficient calculation method. Next, using the absorption coefficient of each surface-layer sample, Ln(A) was obtained according to the Ln(A) calculation method. Note that the light intensity I of pre-exposure light used in the Ln (A) calculation was 2.4

<Comparative Example l-3>

Four a-Si photosensitive members were manufactured in the conditions shown in Table 1-12 and in the same manner as in Example 1-3. Note that, the high-frequency power, the SiH ₄ flow rate and CH ₄ flow rate during the formation of a surface layer were set to be the conditions shown in the following Table 1-14.

Table 1-14

With respect to the electrophotographic photosensitive members manufactured Comparative Example 1-3, C/ (Si + C) , Si atom density, C atom density, Si + C atom density, H/ (SI + C + H) , the H atom density and sp ³ ratio of the surface layer were obtained n the same manner as in Example 1-3 and thereby oxidation resistance, substance attachment onto a surface (surface attachment), Ln(A), gradation and sensitivity were evaluated. The results are shown in Table 1-16.

<Comparative Example l-4> Using the plasma CVD apparatus employing an RF zone high-frequency power source shown in FIG. 3, four a-Si photosensitive members to be positively charged each were manufactured on a cylindrical substrate in the conditions shown in the following Table 1-15.

Table 1-15

With respect to the electrophotographic photosensitive member manufactured Comparative Example 1-4, C/ (Si + C), Si atom density, C atom density, Si + C atom density, H/ (SI + C + H) , the H atom density and sp ³ ratio of the surface layer were obtained in the same manner as in Example 1-3, and thereby, oxidation resistance, substance attachment onto a surface (surface attachment), Ln(A), gradation and sensitivity were evaluated. The results are shown in Table 1-16. Note that the film forming condition of the electrophotographic photosensitive member was manufactured in Comparative Example 1-4 was No. 20.

Note that, during the formation of the lower photoconductive layer, if B ₂ H ₆ was introduced at a flow rate (0.50 ppm) relative to SiH ₄ flow rate, the B atom density of the lower photoconductive layer obtained by aforementioned measurement of B atom density was 2.41 * 10 ¹⁶ atoms/cm ³ . Furthermore, during the formation of the upper photoconductive layer, B ₂ H ₆ was not introduced and the B atom density was the lowermost limit of detection or less. Thus, the B atom density of the upper photoconductive layer is determined as 0.00 atoms/cm ³ . (Measurement of C/ (Si + C) , Si atom density, C atom density, Si + C atom density, H/ (SI + C + H) )

First, a charge injection blocking layer, a lower photoconductive layer and an upper photoconductive layer alone according to of Table 1-12 were stacked sequentially in this order on the substrate to manufacture a reference electrophotographic photosensitive member. A 15 mm-square piece was cut off from the center portion in the longitudinal direction in an arbitrary circumferential direction to prepare a reference sample. Next, a charge injection blocking layer, a lower photoconductive layer, an upper photoconductive layer and a surface layer were stacked on a substrate sequentially in this order to manufacture an electrophotographic photosensitive member. A piece was cut off from the photosensitive member similarly to form a measurement sample. The thickness of a surface layer each of the reference sample and the measurement sample was measured by spectroscopic eHipsometry (high speed spectroscopic ellipsometry M-2000, manufactured by J. A. Woollam Co., Inc.) .

Specific measurement conditions for the spectroscopic ellipsometry are as follows: Incident angle: 60°, 65°, 70°, measurement wavelength: 195 nm to 700 nm, and beam diameter: 1 mm * 2 mm.

First, the relationship between the wavelength, amplitude ratio ψ and phase difference Δ at each incident angle was obtained by spectroscopic ellipsometry with respect to a reference sample.

Next, the measurement results of the reference sample were used as a reference. The relationship between the wavelength, amplitude ratio ψ and phase difference Δ at each incident angle was obtained by spectroscopic ellipsometry with respect to the measurement sample in the same manner as in the reference sample.

Furthermore, a charge injection blocking layer, a lower photoconductive layer, an upper photoconductive layer and a surface layer were sequentially stacked in this order. The layer structure had a rough layer having a surface layer and an air layer copresent in the outermost surface. The layer structure was used as a calculation model. The relationship between the wavelength, ψ and Δ at each incident angle was obtained by calculation while varying the volume ratio of the surface layer and the air layer of the rough layer by use of analysis software. Then, a calculation model was selected by obtaining the case where the mean square error between the relationship of the wavelength, ψ and Δ at each incident angle and the relationship of the wavelength, ψ and Δ at each incident angle obtained from the measurement sample was a minimum value. Using the calculation model thus selected, the thickness of the surface layer was calculated. The obtained value was determined as the thickness of the surface layer. Note that analysis software used herein was WVASE32 manufactured by J. A. Woollam Co., Inc. Furthermore, the above calculation was made by varying the volume ratio of the surface layer and the air layer of the rough layer, more specifically, by changing the ratio of the surface layer: the air layer one by one stepwise from 10:0 to 1:9. In the a-Si photosensitive member to be positively charged manufactured in each film forming condition of this Example, when the volume ratio of the surface layer and the air layer in the rough layer was 8:2, the mean square error of the relationship between the wavelength, ψ and Δ obtained by the calculation and the relationship between the wavelength, ψ and Δ obtained by measuring took a minimum value.

After completion of measurement by spectroscopic ellipsometry, the above measurement sample was subjected to the number of atoms measurement. The numbers of silicon atoms and carbon atoms in the surface layer were measured within the RBS measurement area by RBS (Rutherford backscattering method) using a backscattering measurement apparatus (AN-2500 manufactured by NHV Corporation) . Based on the numbers of silicon atoms and carbon atoms thus measured, the value of C/ (Si + C) was obtained. Next, using the numbers of silicon atoms and carbon atoms obtained in the RBS measurement area and the thickness of a surface layer obtained from spectroscopic ellipsometry, Si atom density, C atom density and Si + C atom density were obtained.

In addition to RBS, using the aforementioned sample, the number of hydrogen atoms in a surface layer within an HFS measurement area was measured by HFS (hydrogen forward scattering method) using a backscattering measurement apparatus (AN-2500 manufactured by NHV Corporation) . Based on the number of hydrogen atoms obtained in the HFS measurement area and the number of silicon atoms and carbon atoms obtained in the RBS measurement area, the value of H/ (SI + C + H) was obtained. Next, using the number of hydrogen atoms obtained in the HFS measurement area and the thickness of the surface layer obtained from spectroscopic ellipsometry, H atom density was obtained.

Specific measurement conditions of RBS and HFS were as follows :

Incident ion: 4He ⁺

Incident energy: 2.3 MeV Incident angle: 75° Sample: 35 nA Incident beam diameter: 1 mm Conditions of the detector of RBS were as follows:

Scattering angle: 160° Aperture diameter: 8 mm

Conditions of the detector of HFS were as follows: Angle of rebound: 30°

Aperture diameter: 8 mm + Slit (Evaluation of oxidation resistance)

Evaluation of oxidation resistance was performed by a method of evaluating formation of an oxide film on the surface of an a-SiC surface layer.

The reflective index of light having a wavelength of 630 nm on the surface of the electrophotographic photosensitive member immediately after manufacturing was measured at 9 points in the longitudinal direction in an arbitrary circumferential direction of an electrophotographic photosensitive member (0 mm, ±50 mm, ±90 mm, ±130 mm, +150 mm from the center of the longitudinal direction of the electrophotographic photosensitive member) and 9 points in the longitudinal direction at the positions after rotation with an angle of

180° from the arbitrary circumferential direction. In short, 18 points were measured in total.

The measurement method was as follows . Light was applied vertically to the surface of an electrophotographic photosensitive member through a spot having 2 mm in diameter and a spectrum of the reflection light was measured by use of a spectrometer (MCPD-2000 manufactured by Otsuka Electronics Co., Ltd.

After measurement, the electrophotographic photosensitive member manufactured was installed in modified digital electrophotographic apparatus iR-5075 (manufactured by Canon Inc.) and placed in an environment of 30°C/80%RH.

In the modified electrophotographic apparatus, the wire and grit of the primary charger is connected to the external power source and a developer, a pre-transfer charger, a transfer charger, a detach charger and a cleaner are removed. Furthermore, the apparatus is modified so as not to feed a paper sheet.

After the electrophotographic photosensitive member manufactured was installed in the modified electrophotographic apparatus, a potential sensor was arranged at the position of the developer, that is, at the position corresponding to the center of the electrophotographic photosensitive member in the longitudinal direction. Next, pre-exposure light was turned on to set the grit potential to be 820 V. The potential sensor placed at the developer was controlled to be +600 V by the external power source connected to the wire of the primary charger. After compression of the control, the external power source was turned off and the potential sensor was removed. Then, the pre-exposure light was again turned on to set the grit potential to be 820 V, the current providing a potential of +600 V at the position of the developer was supplied from the external power source to the wire of the primary charger. The heater for a photosensitive member was turned off and the electrophotographic photosensitive member was continuously rotated for 50 hours.

After 50 hours, the electrophotographic photosensitive member was taken out form the electrophotographic apparatus. The reflective index of the light having a wavelength of 630 nm was measured on the same position of the electrophotographic photosensitive member as that measured immediately after manufacturing.

Next, the ratio of the reflective index measured after 50 hours relative to the reflective index measured immediately after manufacturing was obtained with respect to each measurement point. Using an average value of 18 points, the oxidation resistance was evaluated.

When an oxide film is formed on the surface of the electrophotographic photosensitive member, the reflective index decreases. Therefore, as the ratio of the reflective index of light having a wavelength of 630 nm measured after 50 hours relative to the reflective index measured immediately after manufacturing becomes closer to 100%, the oxidation resistance is improved. Note that it was determined that an effect of the present invention is obtained if the oxidation resistance evaluation of D or more is obtained.

The case where the ratio of the reflective index of light having a wavelength of 630 nm measured after 50 hours relative to the reflective index measured immediately after manufacturing is 95% or more and 105% or less was evaluated as A, the case of 90% or more and less than 95% was evaluated as B, the case of 85% or more and less than 90% as C, the case of 80% or more and less than 85% as D, the case of 75% or more and less than 80% as E, and the case of less than 75% as F.

(Evaluation of substance attachment to surface) Substance attachment to a surface was evaluated also by use of modified digital electrophotographic apparatus iR-5075 manufactured by Canon Inc. Furthermore, the light intensity of light emitted from the pre-exposure LED was controlled to be a predetermine value by the external power source connected to the pre-exposure LED.

After an electrophotographic photosensitive member immediately after manufacturing was installed in the modified electrophotographic apparatus mentioned above, a potential sensor was placed at the position at which a developer was positioned, that is, at the site corresponding to the center position of the electrophotographic photosensitive member in the longitudinal direction. Next, a pre-exposure light was turned on and an LED arranged at the image exposure position was turned off to set the grit potential to be 820 V. The current to be supplied to the wire of the charger was controlled to set the surface potential of the electrophotographic photosensitive member at the developer position to be 600 V.

Next, while charging was performed in the charging conditions previously set, the light of LED set at the image exposure position was applied. The potential at the developer position was controlled to be 100 V by controlling the irradiation energy of LED. The irradiation energy was determined as the irradiation energy before a continuous paper-feed endurance test. Next, using the electrophotographic apparatus having a structure shown in FIG. 1 (digital electrophotographic apparatus iR-5075 manufactured by Canon Inc.), a machine for the continuous paper-feed endurance test was prepared. The machine for the continuous paper-feed endurance test is an electrophotographic apparatus modified such that the contact pressure between the electrophotographic photosensitive member 1001 and a cleaning blade 1008 can be controlled.

Subsequently, in the measuring apparatus shown in FIGS. 4A and 4B, the contact pressure between the electrophotographic photosensitive member (serving as the machine for a continuous paper-feed endurance test) and the cleaning blade was set by means of an adjusting screw 1016 for fixing a cleaning blade holding member 1014 and a fixing member 1015.

The structure of the measuring apparatus 4000 shown in FIGS. 4A and 4B will be described below. The measuring apparatus 4000 has a structure formed of an assembly of a support 4005 and flanges 4002, 4003. To the flanges 4002, 4003, bearings 4001, 4004 are fixed, respectively. Owing to the bearings 4001, 4004, the measuring apparatus can be rotatably fixed in an electrophotographic apparatus in the same manner as in an electrophotographic photosensitive member unit. To the support 4005, a load cell 4007 (TC-PAR 200N manufactured by TEAC Corporation) is fitted to the position corresponding to the center of the electrophotographic photosensitive member in the shaft direction. Furthermore, load cells 4006, 4008 are fitted to the positions at a distance of 130 mm from the load cell 4007 (as the center) on either side (on the right and left sides) . Each of the load cells is connected to a display (TD-240A manufactured by TEAC

Corporation, not shown) , on which the load applied to load buttons 4009 to 4011 respectively positioned at the centers of the load cells 4006 to 4008 can be read.

Furthermore, on the tops of the load buttons 4009 to 4011, a pressure receiving plate 4012 is placed, which is formed of an aluminum plate having a width of 30 mm, a length of 300 mm and a thickness of 3 mm and a surface to which specular working is previously applied and curved at a curvature (in terms of radius) of 40 mm in the width direction. The pressure receiving plate 4012 mechanically connects the load buttons. The pressure-receiving plate is placed such that the center of the curve corresponds to the center axis of the flanges and the surface thereof is positioned at a distance of 40 mm apart from the center axis of the flanges.

The measuring apparatus was installed in the machine for a continuous paper-feed endurance test in place of an electrophotographic photosensitive member and the values of pressure to be applied to the three load cells were controlled such that the total of the pressure values were

150 g +5 g and the difference between a maximum pressure and a minimum pressure to be applied to the load cells was 10 g or less.

Subsequently, the measuring apparatus was removed and the electrophotographic photosensitive member removed from the modified electrophotographic apparatus mentioned above was installed in the above machine for a continuous paper- feed endurance test. Thereafter, a continuous paper-feed endurance test was performed under the environment of 30°C/80%RH in the condition where a heater for the photosensitive member was turned on. During the continuous paper-feed endurance test, more specifically, during the period in which a continuous paper-feed endurance test was performed by turning on the continuous paper-feed endurance test machine and during the period in which the machine for a continuous paper-feed endurance test was turned off, the heater for the 'photosensitive member was always turned on.

More specifically, the continuous paper-feed endurance test was performed using an A4 test pattern having a printing ratio of 1% until 100,000 sheets were printed at a rate of 25,000 paper sheets per day. Furthermore, the toner used for evaluating substance attachment onto the surface of an electrophotographic photosensitive member was manufactured in the following conditions. After the continuous paper-feed endurance test of 100,000 sheets was performed, the electrophotographic photosensitive member was taken out from the continuous paper-feed endurance test machine.

After completion of the continuous paper-feed endurance test, the electrophotographic photosensitive member was installed in the modified electrophotographic apparatus mentioned above and irradiation energy (after the continuous paper-feed endurance test) was measured in the same manner as that performed before the continuous paper- feed endurance test.

From the measurement value, the ratio of the irradiation energy before to after the continuous paper- feed endurance test to the irradiation energy (irradiation energy after continuous paper-feed endurance test/irradiation energy before continuous paper-feed endurance test) was obtained. Based on the ratio, substance attachment onto the surface of the electrophotographic photosensitive member was evaluated.

Note that the evaluation results were obtained by relative comparison to the irradiation energy ratio (1.00) before to after the continuous paper-feed endurance test of the electrophotographic photosensitive member of film forming condition No. 20 manufactured in Comparative Example 1-4.

When a substance is attached onto the surface of a electrophotographic photosensitive member, irradiation energy after the continuous paper-feed endurance test increases relative to the irradiation energy before the continuous paper-feed endurance test. Therefore, in the evaluation, as a numerical value decreases, substance attachment to a surface is improved, showing that an increase of the irradiation energy before and after the continuous paper-feed endurance test is small. Note that it was determined that the effect of the present invention is obtained if the substance attachment to the surface was evaluated as D or more.

The case where the irradiation energy ratio before to after the continuous paper-feed endurance test relative to the irradiation energy ratio before to after the continuous paper-feed endurance test of the electrophotographic photosensitive member of film forming condition No. 20 manufactured in Comparative Example 1-4 was less than 0.95 was evaluated as A, the case of 0.96 or more and less than 0.97 was evaluated as B, the case of 0.97 or more less than 0.98 as C, the case of 0.98 or more and less than 0.99 as D, the case of 0.99 or more and less than 1.00 as E and the case of 1.00 or more as F.

<Example of manufacturing toner for evaluating substance attachment onto surface>

First, a binder resin was produced in the following conditions .

• Propoxylated bisphenol A (2.2 mol added) : 25.0 mol% • Ethoxylated bisphenol A (2.2 mol added) : 25.0 mol%

• Terephthalic acid : 37.2 mol%

• Anhydrous trimellitic acid : 12.8 mol% An esterification solvent and the aforementioned monomers were placed in a 5-L autoclave and a reflux condenser, a moisture separation apparatus, a N ₂ gas inlet pipe, a thermometer and a stirrer were attached. A polycondensation reaction was performed at 23O ⁰ C while supplying N ₂ gas to the autoclave. After completion of the reaction, a reaction product was taken out form the container, cooled and pulverized to obtain a binder resin.

Next, an example of producing toner for use in evaluation of substance attachment to a surface will be described. Note that the "parts" shown below represents "parts by mass". • Binder resin: 100 parts

• Magnetic iron oxide particles (average particle size: 0.15 μm, Hc = 11.5 kA/m, σs = 88 Am ² /kg, σr = 14 AmVkg) : 70 parts

• Fischer-Tropsch wax (melting point: 101°C) : 4 parts • Charge control agent (structural formula described later) : 2 parts

The materials mentioned above were mixed by a Henschel mixer, melted and then kneaded by double-screw kneader/extruder .

The kneaded product thus prepared was cooled and roughly pulverized by a hammer mill followed by a turbo mill. The obtained fine pulverized powder was classified by a hyperfractionation classifier using the Coanda effect to produce negatively charged magnetic toner having a weight average particle size of 5.9 μm. To the toner particles (100 parts), 1.0 part of hydrophobic silica fine particles [BET specific surface area: 150 m ² /g, silica fine particles (100 parts) hydrophobically treated with 30 parts of hexamethyldisilazane (HMDS) and 10 parts of dimethylsilicone oil], 0.2 parts of titanium oxide fine particles (D50: 0.3 μm) serving as inorganic and 3.0 parts of strontium titanate fine particles (D50: 1.0 μm) were externally added and mixed, sieved by a mesh having a pore size of 150 μm to produce the toner for use in evaluation of substance attachment to a surface.

Note that the structure of the charge control agent is shown below.

(Evaluation of gradation)

^' Zi ^*

Gradation was evaluated also by modified digital electrophotographic apparatus iR-5075 manufactured by Canon Inc.

First, using an area-gradation dot screen having a line density of 45 degree 170 lpi (170 lines per inch) , area gradation (i.e., area gradation of a dot portion to which image exposure is applied) was performed. The whole gradation range was equally divided into 17 levels and gradation data was obtained. At this time, the densest gradation (tone) was determined as No. 16 and the thinnest gradation (tone) as No. 0. In this way, numbers were assigned to individual gradations and used as the gradation levels .

Next, an electrophotographic photosensitive member was installed in the modified electrophotographic apparatus mentioned above. An image was output onto an A3 paper sheet by use of the gradation data and a text mode. At this time, a heater for the photosensitive member was turned on in the environment of 22°C/50%RH, since if a high-humidity image deletion is generated, evaluation of blurred image is affected, and output was performed while keeping the surface of an electrophotographic photosensitive member at 4O ⁰ C.

The image density of the image obtained was measured by a reflection densitometer (504 spectrodensitometer manufactured by X-Rite Inc) for each gradation (level) . Note that in the reflection density measurement, three images were output per gradation (level) and an average of the densities of these was obtained and determined as an evaluation value.

The correlation coefficient between the evaluation value thus obtained and a gradation level was calculated. Difference of the correlation coefficient from the correlation coefficient (1.00) of the case where a complete linear relationship (change) was obtained between a reflection density and a gradation (level) was obtained. Evaluation was made based on the ratio of the difference of the correlation coefficient of the electrophotographic photosensitive member manufactured in each film forming condition from the correlation coefficient (1.00) relative to the difference of the correlation coefficient of the electrophotographic photosensitive member manufactured in film forming condition No. 16 from correlation coefficient (1.00), as an index of gradation. In the evaluation, it was demonstrated that as a numerical value decreases, the gradation becomes excellent and nearly linear gradation expression is obtained.

The case where the ratio of the difference of the correlation coefficient of an electrophotographic photosensitive member manufactured in each film forming condition from and correlation coefficient (1.00) relative to the difference of the correlation coefficient of the electrophotographic photosensitive member manufactured in film forming condition No. 16 from the correlation coefficient (1.00) was 1.80 or less was evaluated as A. The case of larger than 1.80 and 2.20 or less was evaluated as B, and the case of larger than 2.20 as C. (Sensitivity evaluation) Sensitivity was evaluated also by modified digital electrophotographic apparatus iR-5075 manufactured by Canon Inc.

The light intensity of light emitted from the preexposure LED was controlled to be a predetermined value by the external power source connected to the pre-exposure LED.

After the electrophotographic photosensitive member manufactured was installed in the electrophotographic apparatus, the potential sensor was arranged at the position of a developer, that is, at the site corresponding to a center position of the electrophotographic photosensitive member in the longitudinal direction. Next, pre-exposure light was turned on in the aforementioned conditions and image exposure light was turned off to control the grit potential to be 820 V. The current to be supplied to the wire of a charger was controlled to set the surface potential of the electrophotographic photosensitive member at the position of a developer to be 400 V.

Next, image exposure light was applied to the surface of the electrophotographic photosensitive member charged in the previously determined charging conditions to control the irradiation energy, thereby setting the potential at the developer position to be 100 V.

The image exposure light source of the electrophotographic apparatus used in sensitivity evaluation is a semiconductor laser having an oscillation wavelength of 658 nm. Evaluation results were obtained by relative comparison to the irradiation energy (1.00) where the electrophotographic photosensitive member manufactured in film forming condition No. 20 in Comparative Example 1-4 was installed.

The case where the ratio of irradiation energy relative to the irradiation energy of the electrophotographic photosensitive member of film forming condition No. 20 manufactured in Comparative Example 1-4 was less than 1.10 was evaluated as A, the case of 1.10 or more and less than 1.15 was evaluated as B, the case of 1.15 or more and less than 1.20 as C, and the case of 1.20 or more as D.

(Evaluation of sp ³ ratio) The ratio of sp ³ structure was obtained as follows. A 10-mm square sample was cut off from the center portion of an electrophotographic photosensitive member in the longitudinal direction in an arbitrary circumferential direction and subjected to calculation by a laser Raman spectrophotometer (NRS-2000 manufactured by JASCO Corporation) .

Specific measurement conditions are as follows: light source: Ar ⁺ laser (514.5 nm) , laser intensity: 20 mA, objective lens: 5OX, center wavelength: 1390 cm ^"1 , exposure time: 30 seconds, and multiplication: 5 times. Measurement was repeated three times. The obtained Raman spectrum was analyzed as follows . The peak wavelength of a shoulder Raman band was fixed at 1390 cm ^"1 and the peak wavelength of a main Raman band was set to be 1480 cm ^"1 but not fixed. Curve fitting was performed by use of the Gaussian distribution. At this time, the base line was obtained by linear approximation. Based on the peak intensity (I _G ) of the main Raman band and the peak intensity (I _D ) of the shoulder Raman band obtained by the curve fitting, the ratio of ID/I _G ^was obtained. An average value of three-time measurements was used for sp ³ -ratio evaluation.

With respect to Example 1-3 and Comparative Examples 1-3 and 1-4, the results of C/ (Si + C), Si atom density, C atom density, Si + C atom density, H/ (SI + C + H) , H atom density, sp ³ ratio, oxidation resistance, substance attachment to a surface (surface attachment) , gradation and sensitivity are shown in Table 1-16.

Table 1-16

O o

From the results of Table 1-16, it was found that if the Si + C atom density of a surface layer is set to be not less than 6.60 x 10 ²² atoms/cm ³ , oxidation resistance and substance attachment to a surface are improved. Furthermore, it was found that if the Si + C atom density is set to be not less than 6.81 x 10 ²² atoms/cm ³ , oxidation resistance and substance attachment to a surface are further improved.

From the results, it was found that if the Si + C atom density of the surface layer is set to fall within the aforementioned range, denaturation of the surface of the a- SiC surface layer is suppressed, an a-SiC surface layer excellent in stability of an light intensity of preexposure light incident upon an electrophotographic photosensitive member can be obtained.

Furthermore, the electrophotographic photosensitive members of film forming condition Nos.16 to 18, which exhibited good oxidation resistance and substance attachment to a surface, were further evaluated for chargeability in the same manner as in Example 1-1, after oxidation resistance evaluation. These electrophotographic photosensitive members were evaluated for a ghost after evaluation of the substance attachment to a surface. As a result, the evaluation results of a ghost and chargeability were both B or more. Note that the light intensity of light emitted from the pre-exposure LED during chargeability evaluation and ghost evaluation was controlled to be 2.4 μJ/cm ² .

From the results, it was found that if Ln(A), which is calculated from the light intensity A of pre-exposure light reaching the lower photoconductive layer is set to be -12.0 < Ln(A) < -4.5, the B atom density of the upper photoconductive layer is set to be lower than the B atom density of the lower photoconductive layer, and the Si + C atom density of a surface layer is set to be not less than 6.60 x 10 ²² atoms/cm ³ , the stability of light intensity of pre-exposure light incident upon an electrophotographic photosensitive member is enhanced and chargeability improvement and ghost suppression are obtained in balance. <Example l-4> An a-Si photosensitive member was manufactured according to the conditions shown in Table 1-12 and in the same manner as in Example 1-3. At this time, the high- frequency power, SiH ₄ flow rate and CH ₄ flow rate during surface layer formation were set to fall the conditions shown in the following Table 1-17. Furthermore, four electrophotographic photosensitive members were manufactured in each of the film forming conditions.

Table 1-17

With respect to the electrophotographic photosensitive member manufactured in Example 1-4, C/ (Si + C) , Si atom density, C atom density, Si + C atom density, H/ (SI + C + H) , H atom density and sp ³ ratio were obtained and oxidation resistance, substance attachment to a surface (surface attachment), Ln(A), gradation and sensitivity were evaluated in the same manner as in Example 1-3. The results are shown in Table 1-18.

Table 1-18

O

From the results of Table 1-18, it was found that if the C/ (Si + C) of the surface layer is set to be 0.61 or more, gradation is improved. Furthermore, it was found that the C/ (Si + C) of the surface layer is set to be 0.75 or less, light absorption is suppressed and sensitivity is improved.

Furthermore, electrophotographic photosensitive members of film forming condition Nos . 21 to 26 and manufactured in Example 1-4 were evaluated for chargeability in the same manner as in Example 1-1 after oxidation resistance evaluation and evaluated for a ghost after evaluation of the substance attachment to a surface. As a result, the evaluation results of chargeability and a ghost were both B or more. Note that the light intensity of light emitted from the pre-exposure LED during chargeability evaluation and ghost evaluation was controlled to be 2.4 μJ/cm ² .

From the results, it was found that if Ln(A), which is calculated from the light intensity A of pre-exposure light reaching the lower photoconductive layer is set to be

-12.0 < Ln(A) < -4.5, the B atom density of the upper photoconductive layer is set to be lower than the B atom density of the lower photoconductive layer, the Si + C atom density of a surface layer is set to be not less than 6.60 x 10 ²² atoms/cm ³ and C/ (Si + C) is set within the range, an electrophotographic photosensitive member excellent in gradation and sensitivity can be obtained. <Example l-5>

An a-Si photosensitive member was manufactured according to the conditions shown in Table 1-12 and in the same manner as in Example 1-3. At this time, the high- frequency power, SiH ₄ flow rate and CH ₄ flow rate during surface layer formation were set to fall within the conditions shown in the following Table 1-19. Furthermore, four electrophotographic photosensitive members were manufactured in each of the film forming conditions.

Table 1-19

With respect to the electrophotographic photosensitive member manufactured in Example 1-5, C/ (Si + C) , Si atom density, C atom density, Si + C atom density, H/ (SI + C + H) , H atom density and sp ³ ratio were obtained and oxidation resistance, substance attachment to a surface (surface attachment), Ln(A), gradation and sensitivity were evaluated in the same manner as in Example 1-3. The results are shown in Table 1-21.

<Example l-6>

An a-Si photosensitive member was manufactured according to the conditions shown in Table 1-12 and in the same manner as in Example 1-3. At this time, the high- frequency power, SiH ₄ flow rate and CH ₄ flow rate during surface layer formation were set to fall within the conditions shown in the following Table 1-20. Furthermore, four electrophotographic photosensitive members were manufactured in each of the film forming conditions.

Table 1-20

With respect to the electrophotographic photosensitive member manufactured in Example 1-6, C/ (Si + C) , Si atom density, C atom density, Si + C atom density, H/ (SI + C + H) , H atom density and sp ³ ratio of the surface layer were obtained and oxidation resistance, substance attachment to a surface (surface attachment), Ln(A), gradation and sensitivity were evaluated in the same manner as in Example 1-3. The results are shown in Table 1-21.

Table 1-21

O OO

From the results of Table 1-21, it was found that if the H/ (Si + C + H) of the surface layer is set to be 0.30 or more, light absorption is suppressed and thus sensitivity are improved. Furthermore, when the H/ (Si + C + H) of the surface layer was set to be 0.45 or less, oxidation resistance and substance attachment to a surface were further improved.

Furthermore, electrophotographic photosensitive members of film forming condition Nos . 27 to 34 manufactured in Example 1-5 and Example 1-6 were evaluated for chargeability in the same manner as in Example 1-1 after oxidation resistance evaluation and evaluated for a ghost after evaluation of the substance attachment to a surface. As a result, the evaluation results of chargeability and a ghost were both B or more. Note that the light intensity of light emitted from the pre-exposure LED during chargeability evaluation and ghost evaluation was controlled to be 2.4 μJ/cm ² .

From the results, it was found that if Ln(A), which is calculated from the light intensity A of pre-exposure light reaching the lower photoconductive layer is set to be -12.0 < Ln(A) ≤ -4.5, the B atom density of the upper photoconductive layer is set to be lower than the B atom density of the lower photoconductive layer, the Si + C atom density of a surface layer is set to be not less than 6.60 x 10 ²² atoms/cm ³ and H/ (Si + C + H) of the surface layer is set within the aforementioned range, it was found that an electrophotographic photosensitive member is excellent in sensitivity and the stability of light intensity of preexposure light incident upon the electrophotographic photosensitive member.

<Example 1-1>

An a-Si photosensitive member was manufactured according to the conditions shown in Table 1-12 and in the same manner as in Example 1-3. At this time, the high- frequency power, SiH ₄ flow rate and CH ₄ flow rate during surface layer formation were set to fall within the conditions shown in the following Table 1-22. Furthermore, four electrophotographic photosensitive members were manufactured in each of the film forming conditions .

Table 1-22

With respect to the electrophotographic photosensitive member manufactured in Example 1-7, C/ (Si + C) , Si atom density, C atom density, Si + C atom density, H/ (SI + C + H), H atom density and sp ³ ratio of the surface layer were obtained and oxidation resistance, substance attachment to a surface (surface attachment), Ln(A), gradation and sensitivity were evaluated in the same manner as in Example 1-3. The results are shown in Table 1-24.

<Example l-8>

An a-Si photosensitive member was manufactured according to the conditions shown in Table 1-12 and in the same manner as in Example 1-3. At this time, the high- frequency power, SiH ₄ flow rate and CH ₄ flow rate during surface layer formation were set to fall within the conditions shown in the following Table 1-23. Furthermore, four electrophotographic photosensitive members were manufactured in each of the film forming conditions.

Table 1-23

With respect to the electrophotographic photosensitive member manufactured in Example 1-8, C/ (Si + C) , Si atom density, C atom density, Si + C atom density, H/ (SI + C + H) , H atom density and sp ³ ratio of the surface layer were obtained and oxidation resistance, substance attachment to a surface (surface attachment), Ln(A), gradation and sensitivity were evaluated in the same manner as in Example 1-3. The results are shown in Table 1-24.

With respect to the electrophotographic photosensitive members manufactured in Example 1-7 and Example 1-8, the results of C/ (Si + C), Si atom density, C atom density, Si + C atom density, H/ (SI + C + H) , the H atom density, sp ³ ratio, oxidation resistance, substance attachment to a surface (surface attachment) , gradation and sensitivity of the surface layer are shown in Table 1-24. Table 1-24

H ¹

From the results of Table 1-24, when the sp ³ ratio of the surface layer was set to be 0.70 or less, oxidation resistance and substance attachment to a surface were further improved. Furthermore, it was found that if sp ³ ratio of the surface layer is 0.20 or more, oxidation resistance and substance attachment to a surface are satisfactory.

Furthermore, electrophotographic photosensitive members of film forming condition Nos . 35 to 42 manufactured in Example 1-7 and Example 1-8 were evaluated for chargeability in the same manner as in Example 1-1 after oxidation resistance evaluation, and evaluated for a ghost after evaluation of the substance attachment to a surface. As a result, the evaluation results of chargeability and a ghost were both B or more. Note that the light intensity of light emitted from the pre-exposure LED during chargeability evaluation and ghost evaluation was controlled to be 2.4 μJ/cm ² .

From the results, it was found that if Ln(A), which is calculated from the light intensity A of pre-exposure light reaching the lower photoconductive layer is set to be -12.0 < Ln(A) < -4.5, the B atom density of the upper photoconductive layer is set to be lower than the B atom density of the lower photoconductive layer, and the Si + C atom density of a surface layer is set to be not less than 6.60 x 10 ²² atoms/cm ³ and further the sp ³ ratio of the surface layer is set to fall within the range of 0.20 or more and 0.70 or less, it was found that an electrophotographic photosensitive member is excellent in stability of light intensity of pre-exposure light incident upon the electrophotographic photosensitive member.

(Method for manufacturing samples of second lower photoconductive layer and upper photoconductive layer)

In the same manner as in the aforementioned method for manufacturing an upper photoconductive layer sample, a second lower photoconductive layer was just formed in the conditions shown in the following Table 2-1 to manufacture a sample of a second lower photoconductive layer. Furthermore, an upper photoconductive layer sample was manufactured in the same manner.

Table 2-1

With respect to the second lower photoconductive layer and upper photoconductive layer sample manufactured in the above conditions, the absorption coefficient thereof was calculated by the aforementioned calculation method. Note that the wavelengths used in calculation of the absorption coefficient were 630 nm and 670 nm. The results are shown in Table 2-3.

Furthermore, using a surface-layer sample formed by depositing a surface layer alone by the aforementioned preparation method for a surface layer sample in the conditions shown in Table 1-2, the absorption coefficients of the surface layer at wavelengths of 630 nm and 670 nm were calculated in the same evaluation conditions as in the second lower photoconductive layer and the upper photoconductive layer samples. The results are shown in Table 2-3.

Table 2-3

<Example 2-l>

Using a plasma CVD apparatus (shown in FIG. 3) employing a high-frequency power source of RF zone as a frequency, an a-Si photosensitive member positively charged was manufactured on a cylindrical substrate. At this time, a charge injection blocking layer, a first lower photoconductive layer, a second lower photoconductive layer, an upper photoconductive layer and a surface layer were formed sequentially in this order in the conditions shown in the following Table 2-4, while controlling film formation time such that the total thickness of the first lower photoconductive layer, the second lower photoconductive layer and the upper photoconductive layer was 28 μm and further the thicknesses of the upper photoconductive layer and the surface layer were as shown in the following Table 2-5.

The Si + C atom density of the surface layer was not atoms/cm ³ . Table 2-4

Table 2-5

With respect to the electrophotographic photosensitive member of each film forming condition manufactured in Example 2-1, chargeability and a ghost were evaluated in the evaluation conditions (described later) and, Ln (A) , which is the light intensity A of pre-exposure light reaching the second lower photoconductive layer was calculated by the calculation method (described later) . The results are shown in Table 2-7.

Note that when the electrophotographic photosensitive member of each film forming condition manufactured in Example 2-1 was evaluated for a ghost, the light intensity I of pre-exposure light to be applied to the surface of the electrophotographic photosensitive member from an external power source connected to the pre-exposure LED fell within the conditions shown in Table 2-5.

Note that, during the formation of the first lower photoconductive layer and the second lower photoconductive layer, if B2H ₆ was introduced at a flow rate of 0.50 ppm relative to SiH ₄ flow rate, the B atom densities of the first lower photoconductive layer and the second lower photoconductive layer obtained by the measurement of B atom density (described later) were 2.41 * 10 ¹⁶ atoms/cm ³ and 2.48 x 10 ¹⁶ atoms/cm ³ , respectively. Furthermore, during the formation of the upper photoconductive layer, B ₂ H6 was not introduced and the B atom density was the lowermost limit of detection or less. Therefore, the B atom density of the upper photoconductive layer is regarded as 0.00 atoms/cm ³ .

Furthermore, the H atom densities of the first lower photoconductive layer, the second lower photoconductive layer and the upper photoconductive layer were measured by the method (described later) . As a result, the H atom densities of the second lower photoconductive layer and the upper photoconductive layer were equal. Next, the ratio (β/cx) of the H atom density average value (α) [atoms/cm ³ ] of the first lower photoconductive layer and the H atom density average value (β) [atoms/cm ³ ] of the second lower photoconductive layer and upper photoconductive layer was obtained. As a result, the value of β/α was 0.70. Furthermore, the light intensity Ln(B) of image exposure light reaching the first lower photoconductive layer was calculated by the method (described later) . The Ln(B) value was -6.5 or less.

<Comparative Example 2-l> An a-Si photosensitive member was manufactured according to the conditions shown in Table 2-4 above and in the same manner as in Example 2-1 while controlling film formation time such that the thicknesses of the upper photoconductive layer and the surface layer were those shown in the following Table 2-6.

Table 2-6

With respect to the electrophotographic photosensitive member of each film forming condition manufactured in Comparative Example 2-1, chargeability and a ghost were evaluated in the same manner as in Example 2-1. The results are shown in Table 2-7.

Note that when the electrophotographic photosensitive member of each film forming condition manufactured in Comparative Example 2-1 was evaluated for a ghost, the light intensity of pre-exposure light to be applied to the surface of the electrophotographic photosensitive member by the external power source connected to the pre-exposure LED was shown in the conditions of Table 2-6. (Evaluation of chargeability)

Chargeability was evaluated in the same manner as in Example 1-1.

Note that evaluation results were shown by relative comparison to the surface potential (1.00) of the case where the electrophotographic photosensitive member of film forming condition No. 104 manufactured in Example 2-1 was installed.

Note that in an electrophotographic apparatus using an electrophotographic photosensitive member having low chargeability, it is sometimes difficult to realize a highspeed operation of the electrophotographic apparatus by increasing a process speed. For the reason, it was determined that the effect of the present invention is obtained at chargeability evaluation B or more.

The case where the ratio of a surface potential relative to the surface potential of the electrophotographic photosensitive member of film forming condition No. 104 manufactured in Example 2-1 was 0.96 or more was evaluated as A, the case of 0.92 or more and less than 0.96 was evaluated as B, and the case of less than 0.92 as C.

(Evaluation of a ghost)

A ghost was evaluated in the same manner as in Example 1-1.

Evaluation results were shown by relative comparison to the difference (F-G) of 1.00, where F is the reflection density measured at the reference position and G is the average value of reflection densities obtained in comparative portions mentioned above in the case where the electrophotographic photosensitive member of film forming conditions No. 109 manufactured in Comparative Example 2-1 was installed.

In the evaluation, as the numerical value decreases, the more satisfactory ghost is obtained. Note that, it was determined that the effect of the present invention was obtained if evaluation B of a ghost was obtained.

The case where a difference (F-G) relative to the electrophotographic photosensitive member of film forming condition No. 109 manufactured in Comparative Example 2-1 was less than 0.8 was evaluated as A. The case of 0.8 or more and less than 1.0 was evaluated as B, and the case of 1.0 or more as C.

(Calculation method of Ln(A)) Ln (A) was calculated in the same manner as in Example 1-1.

Reflective indexes of the electrophotographic photosensitive members manufactured in Example 2-1 and Comparative Example 2-1 were measured. They were 10.8% ± 0.1. Therefore, as the reflective index in calculating Ln(A), a=0.108 was used.

Next, according to the following expression (7), the light intensity A of pre-exposure light reaching the second lower photoconductive layer was calculated. Finally, the light intensity A thus calculated was converted into a value in terms of natural logarithm to obtain Ln (A) .

A = exp(-α ^* 2-d2-10 ^~4 ) -exp (-α ^* l-dl-10 ^~4 ) -I-(l-a) (7) α ^* l: Absorption coefficient α ^* l of a surface layer at 630 nm shown in Table 2-3 α ^* 2 : Absorption coefficient α ^* 2 of the upper photoconductive layer at 630 nm dl (μm) : Thickness of the surface layer shown in Table 2-5, Table 2-6 d2 (μm) : Thickness of the upper photoconductive layer

I [μJ/cm ² ] : Light intensity of pre-exposure light a: Reflective index

Note that the photoconductive layer of the electrophotographic photosensitive member put in practice contains a boron atom; however, the effect thereof on absorption coefficient is low. Therefore, the absorption coefficient shown in Table 2-3 is used. (Measurement of B atom density)

B atom density was measured in the same manner as in Example 1-1.

An average of measurement values of B atom density in each layer in the depth direction is used as the B atom density of each layer.

(Measurement of H atom density)

In the electrophotographic photosensitive member manufactured, a 5 ram-square piece was cut off from the center portion in the longitudinal direction in an arbitrary circumferential direction to prepare a sample. The H atom density in the depth direction of the electrophotographic photosensitive member was measured by secondary ion mass spectrometry (Model 6650 manufactured by Ulvac-Phi Inc.) . In the measurement, a cesium ion was used as a primary ion spices and H ^~ was detected as a secondary ion.

Note that after completion of the measurement, the depth of a portion sputtered by the primary ion irradiation was measured to obtain a sputtering rate. Based on the results, a density was calculated. Furthermore, a predetermined amount of hydrogen ion was doped in a Si wafer to prepare a standard sample. Based on the results obtained by measuring the standard sample in the same measurement method as above, H atom density was quantitatively calculated.

Furthermore, an average of the measurement values of H atom density in each layer in the depth direction is regarded as the H atom density of each layer.

With respect to Example 2-1 and Comparative Example 2-1, the results of Ln(A), chargeability and a ghost are shown in Table 2-7.

Table 2-7

From the results of Table 2-7, it was found that when Ln(A), which is calculated from the light intensity A of pre-exposure light reaching the second lower photoconductive layer, is set to be -12.0 or more and —4.5 or less, a ghost is improved without lowering chargeability . <Example 2-2-l>

In the same manner as in Example 2-1, a charge injection blocking layer, a first lower photoconductive layer, a second lower photoconductive layer, an upper photoconductive layer and a surface layer were formed sequentially in this order in the conditions shown in the following Table 2-8, while controlling film formation time such that the thicknesses of the second lower photoconductive layer and first lower photoconductive layer were those shown in the following Table 2-9.

Note that, during the formation of the first lower photoconductive layer and the second lower photoconductive layer, B ₂ Hg is introduced at a flow rate of 0.50 relative to SiH ₄ flow rate. As a result, the B atom densities of the first lower photoconductive layer and the second lower photoconductive layer obtained by the aforementioned B atom density measurement were 2.41 * 10 ¹⁶ atoms/cm ³ and 2.48 x 10 ¹⁶ atoms/cm ³ , respectively. Furthermore, during the formation of the upper photoconductive layer, B ₂ H ₆ was not introduced and the B atom density was the lowermost limit of detection or less. Therefore, the B atom density of the upper photoconductive layer is regarded as 0.00 atoms/cm ³ . Furthermore, the H atom densities of the first lower photoconductive layer, the second lower photoconductive layer and the upper photoconductive layer were measured by the method described above. As a result, the H atom densities of the second lower photoconductive layer and the upper photoconductive layer were equal. Next, the ratio

(β/α) of the H atom density average value (α) [atoms/cm ³ ] of the first lower photoconductive layer and the H atom density average value (β) [atoms/cm ³ ] of the second lower photoconductive layer and the upper photoconductive layer was obtained. As a result, the value of β/α was 0.70.

Furthermore, with respect to the electrophotographic photosensitive member of each film forming condition manufactured in Example 2-2-1, Ln(A) was calculated in the same manner as in Example 2-1. Ln(A) fell within the range of -12.0 to -4.5.

Table 2-8

Table 2-9

The electrophotographic photosensitive member of each film forming condition manufactured in Example 2-2-1 was evaluated for a ghost in the evaluation conditions (described later) . The light intensity Ln(B) of image exposure light reaching the first lower photoconductive layer was calculated by the calculation method (described later) . The results are shown in Table 2-11.

<Example 2-2-2>

In the same manner as in Example 2-2-1, a charge injection blocking layer, first lower photoconductive layer, the second lower photoconductive layer, upper photoconductive layer and a surface layer were formed sequentially in this order in the conditions shown in Table 2-8 above, while controlling film formation time such that the thicknesses of first lower photoconductive layer and the second lower photoconductive layer were those shown in the following Table 2-10.

Table 2-10

The electrophotographic photosensitive member of each film forming condition manufactured in Example 2-2-2 was evaluated for a ghost in the evaluation conditions

(described later) . The light intensity Ln(B) of image exposure light reaching the first lower photoconductive layer was calculated by the calculation method (described later) . The results are shown in Table 2-11. (Evaluation of a ghost)

A ghost was evaluated based on the following criteria in the same manner as in Example 2-1.

As described above, the case where a value of (F-G) where F is a reflection density of an electrophotographic photosensitive member measured at the reference position and G is an average of reflection-density values obtained in comparative portions relative to that obtained in the electrophotographic photosensitive member of film forming condition No. 114 manufactured in Example 2-2-2 was less than 0.8 was evaluated as A. The case of 0.8 or more and less than 1.0 was evaluated as B, and the case of 1.0 or more as C.

(Calculation method for Ln(B)) Ln(B) was calculated by the following method. The reflective index of light having a wavelength of 670 nm on the surface of an electrophotographic photosensitive member immediately after manufacturing was measured at the center position of the electrophotographic photosensitive member in the longitudinal direction in an arbitrary circumferential direction and at the points, which are positions rotated by an angle of 90°, 180°, 270° from the arbitrary circumferential direction. That is, measurement was made at 4 points in total. An average value a of the obtained reflective indexes of the light having a wavelength of 670 nm was obtained. The average value was regarded as the reflective index of the electrophotographic photosensitive member of each film forming condition. The reflective indexes of the electrophotographic photosensitive member manufactured in Example 2-2-1 and Example 2-2-2 were measured. As the results, they were

12.0% ±0.1. Therefore, as the reflective index used in calculating Ln(B), a = 0.120 was used. Next, based on the following expression (7), the light intensity B of image exposure light reaching the first lower photoconductive layer was calculated. Finally, the light intensity B of image exposure light reaching the first lower photoconductive layer obtained by calculation was converted into a value in terms of natural logarithm to obtain Ln (B) .

Expression (7) : B = exp (-α 2- (d2+d3 ) -10 ^"4 ) -exp (-α ^* l-dl-10 ^~4 ) -I ( 1-a ) α ^* l: Absorption coefficient of a surface layer at 670 nm shown in Table 2-3 α ^* 2 : Absorption coefficient of the upper photoconductive layer (the second lower photoconductive layer) at 670 nm dl (μm) : Thickness of the surface layer shown in Table 2-8 d3 (μm) : Thickness of the second lower photoconductive layer shown in Table 2-9 or Table 2-10 d2 (μm) : The thickness of the upper photoconductive layer shown in Table 2-8 a: Reflective index

I [μJ/cm ² ] : Light intensity of image exposure light = 0.35 μJ/cm ²

Note that the photoconductive layer of the electrophotographic photosensitive member put in practice contains a boron atom; however, the effect thereof on absorption coefficient is low. Therefore, the absorption coefficient shown in Table 2-3 is used.

The results of Ln(B) and a ghost with respect to Example 2-2-1 and Example 2-2-2 are shown in Table 2-11. Table 2-11

From the results of Table 2-11, it was found that if Ln(B), which calculated from the light intensity B of image exposure light reaching first lower photoconductive layer is set to be -6.5 or less, a ghost is further improved.

<Example 2-3>

In the same manner as in Example 2-1, a charge injection blocking layer, a first lower photoconductive layer, a second lower photoconductive layer, an upper photoconductive layer and a surface layer were formed sequentially in this order in the conditions shown in the following Table 2-12, while controlling the B ₂ H ₆ flow rate during the formation of the upper photoconductive layer as shown in the following Table 2-13.

Table 2-12

Table 2-13

The electrophotographic photosensitive member of each film forming condition manufactured in Example 2-3 was evaluated for a ghost in the same manner as in Example 2-1 and B atom density was obtained. The results are shown in Table 2-15.

Note that the light intensity of light emitted from the pre-exposure LED during the ghost evaluation was controlled to be 2.4 μj/cm ²

Furthermore, in film forming condition No. 115, B ₂ H ₆ was not introduced during the formation of the upper photoconductive layer and thus the B atom density was the lowermost limit of detection or less. Therefore, the B atom density of the third photoconductive layer is regarded as 0.00 atoms/cm ³ .

Furthermore, the H atom densities of the first lower photoconductive layer, the second lower photoconductive layer and the upper photoconductive layer were measured by the method described above. As a result, the H atom densities of the second lower photoconductive layer and the upper photoconductive layer were equal. Next, the ratio (β/α) of the H atom density average value (α) [atoms/cm ³ ] of the first lower photoconductive layer and the H atom density average value (β) [atoms/cm ³ ] of the second lower photoconductive layer and upper photoconductive layer was obtained. As a result, the value of β/α was 0.70.

Furthermore, with respect to the electrophotographic photosensitive member of each film forming condition manufactured in Example 2-3, Ln(A) was calculated in the same manner as in Example 2-1. Ln(A) fell within the range of -12.0 to -4.5.

Furthermore, with respect to the electrophotographic photosensitive member of each film forming condition manufactured in Example 2-3, Ln(B) was calculated in the same manner as in Example 2-2. Ln(B) was —6.5 or less. <Comparative Example 2-3>

In the same manner as in Example 2-2, a charge injection blocking layer, a first lower photoconductive layer, a second lower photoconductive layer, an upper photoconductive layer and a surface layer were formed sequentially in this order in the conditions shown in Table 2-12 above, while controlling the B ₂ H ₆ flow rate during formation of the upper photoconductive layer as shown in the following Table 2-14

Table 2-14

Film forming condition No. 120

B ₂ H ₆ supplied to upper photoconductive layer[ppm](relative toSiH ₄ )

The electrophotographic photosensitive member of each film forming condition manufactured in Comparative Example 2-3 was evaluated for a ghost in the same manner as in

Example 2-3 and B atom density was obtained. The results are shown in Table 2-15.

Note that the light intensity of light emitted from the pre-exposure LED during the ghost evaluation was controlled to be 2.4 μJ/cm ² .

Furthermore, with respect to the electrophotographic photosensitive member of each film forming condition manufactured in Comparative Example 2-3, Ln(A) was calculated in the same manner as in Example 2-1. Ln(A) fell within the range of -12.0 to -4.5.

Furthermore, with respect to the electrophotographic photosensitive member of each film forming condition manufactured in Comparative Example 2-3, Ln(B) was calculated in the same manner as in Example 2-2. Ln(B) was -6.5 or less.

With respect to the electrophotographic photosensitive member of each film forming condition manufactured in Example 2-3 and Comparative Example 2-3, X/Y and a ghost in the second lower photoconductive layer were evaluated. The results are shown in Table 2-15.

Table 2-15

From the results shown in Table 2-15, when the B atom density of the upper photoconductive layer was smaller than the B atom density of the first lower photoconductive layer and the second lower photoconductive layer, a ghost was improved.

Furthermore, when Y/X was less than 0.5, a ghost was further improved. Furthermore, it was found that even if Y/X is 0, a satisfactory ghost is maintained. <Example 2-4-l>

In the same manner as in Example 2-1, a charge injection blocking layer, a first lower photoconductive layer, a second lower photoconductive layer, an upper photoconductive layer and a surface layer were formed sequentially in this order in the conditions shown in the following Table 2-16, while controlling the SiH ₄ flow rate and high-frequency power during formation of the second lower photoconductive layer and upper photoconductive layer as shown in the following Table 2-17.

Note that B ₂ H ₆ was introduced at a flow rate of 0.50 ppm relative to the SiH ₄ flow rate during the formation of the first lower photoconductive layer and the second lower photoconductive layer. As a result, the B atom density of the first lower photoconductive layer and the second lower photoconductive layer obtained by the measurement of B atom density (described later) fell within the range not less than 2.36 x 10 ¹⁶ atoms/cm ³ and not more than 2.56 x 10 ¹⁶ atoms/cm ³ . Furthermore, B ₂ Ee was not introduced during the formation of the upper photoconductive layer and the B atom density was the lowermost limit of detection or less.

Therefore, the B atom density of the upper photoconductive layer is regarded as 0.00 atoms/cm ³ .

With respect to the electrophotographic photosensitive member of each film forming condition manufactured by Example 2-4-1, Ln(A) was calculated in the same manner as in Example 2-1. Ln(A) fell within the range of -12.0 to -4.5.

With respect to the electrophotographic photosensitive member of each film forming condition manufactured by Example 2-4-1, Ln(B) was calculated in the same manner as in Example 2-2-1. Ln(B) was -6.5 or less. Table 2-16

Table 2-17

The electrophotographic photosensitive member of each film forming condition manufactured in Example 2-4-1 was evaluated for chargeability and a ghost by the following method. Furthermore, the H atom densities of the first lower photoconductive layer, the second lower photoconductive layer and the upper photoconductive layer were measured by the method described above. As a result, the H atom densities of the second lower photoconductive layer and the upper photoconductive layer were equal. Next, the ratio (β/α) of the H atom density average value (α) [atoms/cm ³ ] of the first lower photoconductive layer and the H atom density average value (β) [atoms/cm ³ ] of the second lower photoconductive layer and upper photoconductive layer was obtained. The results are shown in Table 2-19. <Example 2-4-2>

In the same manner as in Example 2-4-1, a charge injection blocking layer, a first lower photoconductive layer, a second lower photoconductive layer, an upper photoconductive layer and a surface layer were formed sequentially in this order in the conditions shown in the Table 2-16 ^' above, while controlling the SiJrU flow rate and high frequency power during the formation of the second lower photoconductive layer and the upper photoconductive layer as shown in the following Table 2-18. Furthermore, two electrophotographic photosensitive members were manufactured in each of the film forming conditions.

Furthermore, with respect to the electrophotographic photosensitive member of each film forming condition manufactured in Example 2-4-2, Ln(A) was calculated in the same manner as in Example 2-1. Ln(A) fell within the range of -12.0 to -4.5.

Furthermore, with respect to the electrophotographic photosensitive member of each film forming condition manufactured by Example 2-4-2, Ln(B) was calculated in the same manner as in Example 2-2. Ln(B) was -6.5 or less. Table 2-18

The electrophotographic photosensitive member of each film forming condition manufactured in Example 2-4-2 was evaluated for chargeability, a ghost and β/α by the following method similarly to Example 2-4-1. The results are shown in Table 2-19.

(Evaluation of chargeability)

In the same manner as in Example 2-1, a ghost was evaluated based on the following criteria.

The case where the ratio of a surface potential relative to the surface potential of the electrophotographic photosensitive member of film forming condition No. 125 manufactured in Example 2-4-2 was 0.96 or more was evaluated as A, the case of 0.92 or more and less than 0.96 was evaluated as B, and the case of less than 0.92 as C.

(Evaluation of a ghost)

In the same manner as in Example 2-1, a ghost was evaluated based on the following criteria. As described above, the case where a value of (F-G) where F is a reflection density of an electrophotographic photosensitive member measured at the reference position and G is an average of reflection-density values obtained in comparative portions relative to that obtained in the electrophotographic photosensitive member of film forming condition No. 125 manufactured in Example 2-4-2 was less than 0.8 was evaluated as A. The case of 0.8 or more and less than 1.0 was evaluated as B, and the case of 1.0 or more as C. Table 2-19

From the results of Table 2-19, it is found that if β/α is 0.5 or more and less than 1.0, a further satisfactory ghost can be obtained while maintaining chargeability .

<Example 2-5>

An a-Si photosensitive member was manufactured according to the conditions shown in the following Table 2- 20 and in the same manner as in Example 2-1. At this time, the high-frequency power, SiH ₄ flow rate and CH ₄ flow rate during the formation of the surface layer were set to be the conditions shown in the following Table 2-21. Furthermore, four electrophotographic photosensitive members were manufactured in each of the film forming conditions.

Note that when B ₂ H ₆ was introduced at a flow rate of 0.50 ppm relative to SiH ₄ flow rate during the formation of the first lower photoconductive layer and the second lower photoconductive layer. As a result, the B atom densities of the first lower photoconductive layer and the second lower photoconductive layer obtained by the measurement of B atom density (described above) were 2.41 * 10 ¹⁶ atoms/cm ³ and 2.48 x 10 ¹⁶ atoms/cm ³ , respectively. Furthermore, B ₂ H ₆ was not introduced during the formation of the upper photoconductive layer and the B atom density was the lowermost limit of detection or less. Therefore, the B atom density of the upper photoconductive layer is regarded as 0.00 atoms /cm ³ .

Furthermore, the H atom densities of the first lower photoconductive layer, the second lower photoconductive layer and the upper photoconductive layer were measured by the method described above. As a result, the H atom densities of the second lower photoconductive layer and the upper photoconductive layer were equal. Next, the ratio (β/α) of the H atom density average value (α) [atoms/cm ³ ] of the first lower photoconductive layer and the H atom density average value (β) [atoms/cm ³ ] of the second lower photoconductive layer or upper photoconductive layer was obtained. As a result, β/α was 0.70.

Furthermore, with respect to the electrophotographic photosensitive member of each film forming condition manufactured in Example 2-5, Ln(A) was calculated in the same manner as in Example 2-1. Ln(A) fell within the range of -12.0 to -4.5.

Furthermore, with respect to the electrophotographic photosensitive member of each film forming condition manufactured by Example 2-5, Ln(B) was calculated in the same manner as in Example 2-2. Ln(B) was -6.5 or less. Table 2-20

Table 2-21

With respect to a first one of four electrophotographic photosensitive members of each film forming condition were manufactured in Example 2-5, C/ (Si + C) , Si atom density, C atom density, Si + C atom density, H/ (SI + C + H) , H atom density and sp ³ ratio were obtained by the analysis method (described later) . Subsequently, a second one of the electrophotographic photosensitive members of each film forming condition was evaluated for oxidation resistance in the evaluation conditions (described later) . A third one of the electrophotographic photosensitive members of each film forming condition was evaluated for toner melt-adhesion in the evaluation conditions (described later) . Moreover, a fourth one of the electrophotographic photosensitive members of each film forming condition was evaluated for gradation and sensitivity in the evaluation conditions (described later) .

The results are shown in Table 2-24. <Comparative Example 2-5>

Four a-Si photosensitive members positively charged were manufactured according to the conditions shown in

Table 20 above and in the same manner as in Example 2-5.

Note that the high-frequency power, SiH ₄ flow rate and CH ₄ flow rate during the formation of the surface layer were controlled to be the conditions shown in the following

Table 2-22.

Furthermore, with respect to the electrophotographic photosensitive member of each film forming condition manufactured in Comparative Example 2-5, Ln(A) was calculated in the same manner as in Example 2-1. Ln(A) fell within the range of -12.0 to -4.5.

Furthermore, with respect to the electrophotographic photosensitive member of each film forming condition manufactured in Comparative Example 2-5, Ln(B) was calculated in the same manner as in Example 2-2-1. Ln(B) was —6.5 or less. Table 2-22

With respect to the electrophotographic photosensitive member manufactured in Comparative Example 2-5, C/ (Si + C), Si atom density, C atom density, Si + C atom density, H/ (SI + C + H) , H atom density and sp ³ ratio were obtained and oxidation resistance, toner melt-adhesion (surface attachment) , gradation and sensitivity were evaluated in the same manner as in Example 2-5. The results are shown in Table 2-24. <Comparative Example 2-6> Using a plasma CVD apparatus using a high-frequency power source having an RF zone frequency and shown in FIG. 3, four a-Si photosensitive members positively charged each were manufactured on a cylindrical substrate in the conditions shown in the following Table 2-23. Note that, B ₂ H ₆ was introduced at a flow rate of 0.50 ppm relative to the SiH ₄ flow rate during the formation of the first lower photoconductive layer and the second lower photoconductive layer. As a result, the B atom densities of the first lower photoconductive layer and the second lower photoconductive layer obtained by the measurement of B atom density (described above) were 2.41 x 10 ¹⁶ atoms/cm ³ , and 2.48 * 10 ¹⁶ atoms/cm ³ , respectively.

Furthermore, with respect to the electrophotographic photosensitive member of each film forming condition manufactured in Comparative Example 2-6, Ln(A) was calculated in the same manner as in Example 2-1. Ln(A) fell within the range of -12.0 to -4.5. Furthermore, with respect to the electrophotographic photosensitive member of each film forming condition manufactured in Comparative Example 2-6, Ln(B) was calculated in the same manner as in Example 2-2-1. Ln(B) was -6.5 or less. Table 2-23

With respect to the electrophotographic photosensitive members manufactured in Comparative Example 2-6, C/ (Si + C), Si atom density, C atom density, Si + C atom density, H/ (SI + C + H), H atom density and sp ³ ratio were obtained and oxidation resistance, toner melt-adhesion (surface attachment) , gradation and sensitivity were evaluated. The results are shown in Table 2-24. Note that, the number of the film forming condition of the electrophotographic photosensitive member manufactured in Comparative Example 2-6 was 130.

(Measurement of C/ (Si + C), Si atom density, C atom density, Si + C atom density, H/ (SI + C + H) ) First, a reference electrophotographic photosensitive member was manufactured by stacking only a charge injection blocking layer, a first lower photoconductive layer, a second lower photoconductive layer and an upper photoconductive layer of Table 2-20. A 15 mm-square piece was cut off from the center portion in the longitudinal direction in an arbitrary circumferential direction to prepare a reference sample. Next, a piece was cut off from an electrophotographic photosensitive member formed by stacking a charge injection blocking layer, a first lower photoconductive layer, a second lower photoconductive layer, an upper photoconductive layer and a surface layer to prepare a measurement sample. Using the reference sample and the measurement sample, the thickness of a surface layer, C/ (Si + C), Si atom density, C atom density, Si + C atom density and H/ (SI + C + H) were obtained in the same manner as in Example 1-2.

Note that as the calculation model employed in thickness calculation, a structure obtained by stacking a charge injection blocking layer, a first lower photoconductive layer, a second lower photoconductive layer, an upper photoconductive layer and a surface layer sequentially and having a rough surface in which a surface layer and an air layer are copresent at the outermost surface.

(Evaluation of oxidation resistance) Oxidation resistance was evaluated in the same manner as in Example 1-2.

(Evaluation substance attachment to surface) Substance attachment to a surface was evaluated in the same manner as in Example 1-2. Note that evaluation criteria were as follows .

The case where the irradiation energy ratio before to after the continuous paper-feed endurance test relative to the irradiation energy ratio before to after the continuous paper-feed endurance test of the electrophotographic photosensitive member of film forming condition No. 130 manufactured in Comparative Example 2-6 was less than 0.95 was evaluated as A, the case of 0.96 or more and less than 0.97 was evaluated as B, the case of 0.97 or more less than 0.98 as C, the case of 0.98 or more and less than 0.99 as D, the case of 0.99 or more and less than 1.00 as E and the case of 1.00 or more as F.

(Evaluation of gradation)

Gradation was evaluated in the same manner as in Example 1-2. Note that evaluation criteria were as follows. The case where the ratio of the difference between the correlation coefficient of the electrophotographic photosensitive member manufactured in each film forming condition and the correlation coefficient (1.00) relative to the difference between the correlation coefficient of the electrophotographic photosensitive members manufactured in film forming condition No. 126 and the correlation coefficient (1.00) was 1.80 or less was evaluated as A. The case of larger than 1.80 and 2.20 or less was evaluated as B, and the case of larger than 2.20 as C. (Evaluation of sensitivity)

Sensitivity was evaluated in the same manner as in Example 1-2. Note that the evaluation results were obtained by relative comparison to the irradiation energy (1.00) of the case where the electrophotographic photosensitive member of film forming condition No. 130 manufactured in Comparative Example 2-6 was installed. Note that it was determined that the effect of the present invention is obtained if sensitivity evaluation was C or more.

The case where the ratio of irradiation energy relative to the irradiation energy of the electrophotographic photosensitive member of film forming condition No. 130 manufactured in Comparative Example 2-6 was less than 1.10 was evaluated as A, the case of 1.10 or more and less than 1.15 was evaluated as B, the case of 1.15 or more and less than 1.20 as C, and the case of 1.20 or more as D.

(Evaluation of sp ³ ratio)

Evaluation of sp ³ ratio was made in the same manner as in Example 1-2.

With respect to Example 2-5 and Comparative Example 2-5, Comparative Example 2-6, C/ (Si + C), the results of Si atom density, C atom density, Si + C atom density, H/ (SI + C + H) , H atom density and sp ³ ratio as well as oxidation resistance, toner melt-adhesion (surface attachment) , gradation and sensitivity in a surface layer are shown in Table 2-24.

Table 2-24

M Cn o

From the results of Table 2-24, it was found that if the Si + C atom density of the surface layer is set to be not less than 6.60 ^χ lθ ²² atoms/cm ³ , oxidation resistance and toner melt-adhesion are improved. Furthermore, it was found that if the Si + C atom density is set to be not less than 6.81 ^χ lθ ²² atoms/cm ³ , oxidation resistance and substance attachment to a surface (toner melt-adhesion) is further improved.

From the results, it was found that if the Si + C atom density of the surface layer is set to fall within the aforementioned range, the surface denaturation of an a-SiC surface layer is suppressed and an a-SiC surface layer having excellent stability in the light intensity of preexposure light incident upon the electrophotographic photosensitive member can be obtained.

Note that the electrophotographic photosensitive members of film forming condition Nos. 126 to 128 having good oxidation resistance and toner melt-adhesion were evaluated for a ghost after oxidation resistance evaluation in the same manner as in Example 2-1. These photosensitive members were also evaluated for chargeability after toner melt-adhesion evaluation. As a result, the evaluation results of a ghost and chargeability were B or more. <Example 2-6> In the same manner as in Example 2-5, a charge injection blocking layer, a first lower photoconductive layer, a second lower photoconductive layer, an upper photoconductive layer and a surface layer were formed sequentially in this order in the conditions shown in Table 2-20 above, while controlling the high-frequency power, SiH ₄ flow rate and CH ₄ flow rate during the formation of the surface layer to be the conditions as shown in the following Table 2-25. Furthermore, four electrophotographic photosensitive members were manufactured in each of the film forming conditions.

Table 2-25

With respect to the electrophotographic photosensitive member manufactured in Example 2-6, C/ (Si + C) , Si atom density, C atom density, Si + C atom density, H/ (SI + C + H) , H atom density and sp ³ ratio of the surface layer were obtained and the oxidation resistance, toner melt-adhesion (surface attachment) , gradation and sensitivity were evaluated in the same manner as in Example 2-5. The results are shown in Table 2-26.

Furthermore, with respect to the electrophotographic photosensitive member of each film forming condition manufactured in Example 2-6, Ln(A) was calculated in the same manner as in Example 2-1. Ln(A) fell within the range of -12.0 to -4.5.

Furthermore, with respect to the electrophotographic photosensitive member of each film forming condition manufactured in Example 2-6, Ln(B) was calculated in the same manner as in Example 2-2-1. Ln(B) was —6.5 or less.

Table 2-26

From the results of Table 2-26, it was found that if the C/ (Si + C) of the surface layer is set to be 0.61 or more, gradation is improved. Furthermore, it was found that if the C/ (Si + C) of the surface layer is set to be 0.75 or less, light absorption is suppressed and sensitivity is improved.

From the results, it was found that if the Si + C atom density of the surface layer is set to be not less than 6.60 *10 ²² atoms/cm ³ and C/ (Si + C) is set to fall within the aforementioned range, an electrophotographic photosensitive member excellent in gradation and sensitivity can be obtained, in other words, an electrophotographic photosensitive member having excellent electrophotographic characteristics can be obtained. Note that the electrophotographic photosensitive members of film forming condition Nos . 131 to 136 manufactured in Example 2-6 were evaluated for a ghost after oxidation resistance evaluation in the same manner as in Example 2-1. These photosensitive members were also evaluated for chargeability after toner melt-adhesion evaluation. As a result, the evaluation results of a ghost and chargeability both were B or more. <Example 2-7> In the same manner as in Example 2-5, a charge injection blocking layer, a first lower photoconductive layer, a second lower photoconductive layer, an upper photoconductive layer and a surface layer were formed sequentially in this order in the conditions shown in Table 2-20 above, while controlling the high-frequency power, SiH ₄ flow rate and CH ₄ flow rate during the formation of the surface layer to be the conditions as shown in the following Table 2-27. Furthermore, four electrophotographic photosensitive members were manufactured in each of the film forming conditions.

Table 2-27

With respect to the electrophotographic photosensitive member manufactured in Example 2-7, C/ (Si + C) , Si atom density, C atom density, Si + C atom density, H/ (SI + C + H) , H atom density and sp ³ ratio were obtained, and the oxidation resistance, toner melt-adhesion (surface attachment) , gradation and sensitivity were evaluated in the same manner as in Example 2-5. The results are shown in Table 2-29.

Furthermore, with respect to the electrophotographic photosensitive member of each film forming condition manufactured in Example 2-7, Ln(A) was calculated in the same manner as in Example 2-1. Ln(A) fell within the range of -12.0 to -4.5.

Furthermore, with respect to the electrophotographic photosensitive member of each film forming condition manufactured in Example 2-7, Ln(B) was calculated in the same manner as in Example 2-2-1. Ln(B) was -6.5 or less.

<Example 2-8>

In the same manner as in Example 2-5, a charge injection blocking layer, a first lower photoconductive layer, a second lower photoconductive layer, an upper photoconductive layer and a surface layer were formed sequentially in this order in the conditions shown in Table 2-20 above, while controlling the high-frequency power, SiH ₄ flow rate and CH ₄ flow rate during the formation of the surface layer to be the conditions as shown in the following Table 2-28. Furthermore, four electrophotographic photosensitive members were manufactured in each of the film forming conditions.

Table 2-28

With respect to the electrophotographic photosensitive member manufactured in Example 2-8, C/ (Si + C) , Si atom density, C atom density, Si + C atom density, H/ (SI + C + H) , H atom density and sp ³ ratio were obtained and the oxidation resistance, toner melt-adhesion (surface attachment) , gradation and sensitivity were evaluated in the same manner as in Example 2-5. The results are shown in Table 2-29.

Furthermore, with respect to the electrophotographic photosensitive member of each film forming condition manufactured in Example 2-8, Ln(A) was calculated in the same manner as in Example 2-1. Ln(A) fell within the range of -12.0 to -4.5.

Furthermore, with respect to the electrophotographic photosensitive member of each film forming condition manufactured in Example 2-8, Ln(B) was calculated in the same manner as in Example 2-2-1. Ln(B) was —6.5 or less.

With respect to Example 2-7 and Example 2-8, the results of C/ (Si + C) , Si atom density, C atom density, Si + C atom density, H/ (SI + C + H) , the H atom density, sp ³ ratio, oxidation resistance, toner melt-adhesion (surface attachment) , gradation and sensitivity are shown in Table 2-29.

Table 2-29

Cn ID

From the results of Table 2-29, when the H/ (Si + C + H) of the surface layer was set to be 0.30 or more, light absorption was suppressed and thus sensitivity was improved. Furthermore, when the H/ (Si + C + H) of the surface layer was set to be 0.45 or less, oxidation resistance and substance attachment to a surface were further improved.

From the results, it was found that if the Si + C atom density of the surface layer is set to be not less than 6.60 ^χ lθ ²² atoms/cm ³ , and H/ (Si + C + H) of the surface layer is set to fall within the aforementioned range, not only an electrophotographic photosensitive member excellent in sensitivity but also an a-SiC surface layer excellent in stability of light intensity of pre-exposure light incident upon an electrophotographic photosensitive member can be obtained.

Note that the electrophotographic photosensitive members of film forming condition Nos. 137 to 144 manufactured in Example 2-7 and Example 2-8 were evaluated for a ghost after oxidation resistance evaluation in the same manner as in Example 2-1. These photosensitive members were also evaluated for chargeability after toner melt-adhesion evaluation. As a result, the evaluation results of a ghost and chargeability both were B or more. <Example 2-9>

In the same manner as in Example 2-5, a charge injection blocking layer, a first lower photoconductive layer, a second lower photoconductive layer, an upper photoconductive layer and a surface layer were formed sequentially in this order in the conditions shown in Table 2-20 above, while controlling the high-frequency power, SiH ₄ flow rate and CH ₄ flow rate during the formation of the surface layer to be the conditions as shown in the following Table 2-30. Furthermore, four electrophotographic photosensitive members were manufactured in each of the film forming conditions.

Table 2-30

With respect to the electrophotographic photosensitive member manufactured in Example 2-9, C/ (Si + C) , Si atom density, C atom density, Si + C atom density, H/ (SI + C + H) , H atom density and sp ³ ratio were obtained and the oxidation resistance, toner melt-adhesion (surface attachment) , gradation and sensitivity were evaluated in the same manner as in Example 2-5. The results are shown in Table 2-32.

Furthermore, with respect to the electrophotographic photosensitive member of each film forming condition manufactured in Example 2-9, Ln(A) was calculated in the same manner as in Example 2-1. Ln(A) fell within the range of -12.0 to -4.5.

Furthermore, with respect to the electrophotographic photosensitive member of each film forming condition manufactured in Example 2-9, Ln(B) was calculated in the same manner as in Example 2-2-1. Ln(B) was -6.5 or less.

<Example 2-10>

In the same manner as in Example 2-9, a charge injection blocking layer, a first lower photoconductive layer, a second lower photoconductive layer, an upper photoconductive layer and a surface layer were formed sequentially in this order in the conditions shown in Table 2-20 above, while controlling the high-frequency power, SiH ₄ flow rate and CH ₄ flow rate during the formation of the surface layer to be the conditions as shown in the following Table 2-31. Furthermore, four electrophotographic photosensitive members were manufactured in each of the film forming conditions.

Table 2-31

With respect to the electrophotographic photosensitive member manufactured in Example 2-10, C/ (Si + C) , Si atom density, C atom density, Si + C atom density, H/ (SI + C + H) , H atom density and sp ³ ratio were obtained and the oxidation resistance, toner melt-adhesion (surface attachment) , gradation and sensitivity were evaluated in the same manner as in Example 2-5. The results are shown in Table 2-32. Furthermore, with respect to the electrophotographic photosensitive member of each film forming condition manufactured in Example 2-10, Ln(A) was calculated in the same manner as in Example 2-1. Ln(A) fell within the range of -12.0 to -4.5.

Furthermore, with respect to the electrophotographic photosensitive member of each film forming condition manufactured in Example 2-10, Ln(B) was calculated in the same manner as in Example 2-2-1. Ln(B) was —6.5 or less. With respect to Example 2-9 and Example 2-10, the results of C/ (Si + C), Si atom density, C atom density, Si + C atom density, H/ (SI + C + H) , the H atom density, sp ³ ratio, oxidation resistance, toner melt-adhesion (surface attachment) , gradation and sensitivity are shown in Table 2-32.

Table 2-32

From the results of Table 2-32, it was found that if the sp ³ ratio of the surface layer is set to be 0.70 or less, oxidation resistance and toner melt-adhesion are further improved. Furthermore, it was found that if the sp ³ ratio is 0.20 or more, oxidation resistance and toner melt-adhesion are satisfactory.

As a result, it was found that if the Si + C atom density is set to be not less than 6.60 x 10 ²² atoms/cm ³ , and sp ³ ratio is set to fall within the range of 0.20 or more and 0.70 or less, an a-SiC surface layer excellent in stability of light intensity of pre-exposure light incident upon an electrophotographic photosensitive member can be obtained.

Note that the electrophotographic photosensitive members of film forming condition Nos. 145 to 152 manufactured in Example 2-9 and Example 2-10 were evaluated for a ghost after oxidation resistance evaluation in the same manner as in Example 2-5. These photosensitive members were evaluated for chargeability after toner melt- adhesion evaluation. As a result, the evaluation results of a ghost and chargeability both were B or more.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions .

This application claims the benefit of Japanese Patent Application No. 2009-042760, filed February 25, 2009, and Japanese Patent Application No. 2009-042759, filed February 25, 2009 which are hereby incorporated by reference herein in their entirety.