Processes for suppressing the fractionation of chalcogenide alloys

A process for the preparation of chalcogenide alloy compositions which comprises providing a chalcogenide alloy; admixing therewith crystalline or amorphous selenium; and subsequently subjecting the resulting mixture to evaporation.

BACKGROUND OF THE INVENTION 
The present invention relates to processes for the preparation of 
chalcogenide alloys and to processes for suppressing the fractionation of 
chalcogenide alloys. More specifically, the present invention relates to 
processes for controlling the fractionation of chalcogenide alloys during 
the vacuum deposition thereof. In one embodiment, the present invention is 
directed to a process for controlling and suppressing the fractionation of 
chalcogenide alloys which comprises adding to the source material 
selected, such as the source alloy trigonal selenium thereby enabling, for 
example, desirable chalcogenide alloys possessing homogeneous 
distributions of the chalcogens throughout the product obtained. The 
products resulting from the process of the present invention can be 
selected as photoconductors in electrophotographic imaging systems, 
including xerographic imaging and printing methods. 
Chalcogens and chalcogenide alloys, and their use in electrophotographic 
processes, are well known. Generally, the aforementioned photoconductors 
are prepared by known vacuum deposition, flash evaporation, and chemical 
vapor deposition methods. These methods possess disadvantages in some 
instances, thus for example with vacuum deposited chalcogenide alloys the 
products obtained usually lack controllable reproducibility in their 
homogeneity thereby adversely effecting the electrophotographic electrical 
characteristics thereof. As the elements selected in the source alloy for 
vacuum deposition usually have different vapor pressures, such elements 
tend to separate during the vacuum deposition process causing undesirable 
inhomogeneity, or fractionation thereof. Also, with vacuum deposition 
processes the components with high selenium content tend to evaporate 
first and thus are not subsequently available for deposition. Accordingly, 
the final photoreceptor will contain less selenium at the top surface 
thereof which adversely affects the electrical characteristics thereof, 
and adds significantly to the cost of photoreceptor manufacturing or 
preparation primarily as a result of a reduction in total yield, or yield 
loss. With the processes of the present invention these and other 
disadvantages are avoided. 
Electrophotographic photoconductive imaging members containing amorphous 
selenium can be modified to improve panchromatic response, increase speed, 
and to improve color copyability. These members are usually comprised of 
binary and ternary chalcogenide alloys such as alloys of selenium with 
tellurium and/or arsenic with and without halogens. The selenium imaging 
members may be fabricated as single layered devices comprising a 
selenium-tellurium, selenium-arsenic, selenium antimony, selenium 
tellurium arsenic, selenium tellurium bismuth, selenium tellurium arsenic 
chlorine, selenium-tellurium-antimony or selenium-tellurium-arsenic alloy 
layer, which functions as a charge generation and charge transport medium. 
The selenium electrophotographic imaging members may also comprise 
multiple layers such as, for example, a selenium alloy transport layer and 
a selenium alloy generator layer. 
One known process for the preparation of photoconductors comprises the 
vacuum deposition of a selenium alloy on a supporting substrate such as 
aluminum. Tellurium can then be incorporated therein as an additive 
primarily for the purpose of enhancing the spectral sensitivity thereof. 
Also, arsenic can be incorporated as an additive for the primary purpose 
of improving wear characteristics, passivation against crystallization, 
and improving electrical performance of the resulting photoconductor or 
photoreceptor. Generally, the tellurium addition can be incorporated as a 
thin selenium-tellurium alloy layer deposited over a selenium alloy layer 
to achieve the benefits of the photogeneration and transport 
characteristics. Fractionation of chalcogenide alloys during the vacuum 
evaporation processes results in an undesirable concentration gradient of, 
for example, tellurium and/or arsenic in the deposited photoconductor. 
Accordingly, there results inhomogeneities (fractionation) in the 
stoichiometry of the vacuum deposited thin films. Fractionation occurs as 
a result of differences in the partial vapor pressure of the molecular 
species of the solid and liquid phases of binary, ternary and other 
multicomponent alloys. An important aspect in the fabrication of 
chalcogenide based photoreceptors resides in controlling the fractionation 
of alloy components such as tellurium and/or arsenic during the 
evaporation of source alloys. More specifically, tellurium and/or arsenic 
fractionation control is particularly important since the tellurium and/or 
arsenic concentration at the top surface of the resulting photoreceptor 
affects xerographic sensitivity, charge acceptance, dark discharge, copy 
quality, photoreceptor wear, cost of fabrication, crystallization 
resistance, and the like. For example, in single layer low arsenic 
selenium alloy photoreceptors arsenic enrichment at the top surface caused 
by fractionation can also cause severe reticulation of the evaporated 
film. Further, in single layer tellurium selenium alloy photoreceptors, 
tellurium enrichment at the top surface due to fractionation can cause 
undue sensitivity enhancement, poor charge acceptance and enhancement of 
dark discharge. Also, in two layer or multilayer photoreceptors where low 
arsenic alloys may be incorporated as a transport layer, arsenic 
enrichment at the interface with the layer above can lead to residual 
cycle up problems. Moreover, in two layer or multilayer photoreceptors 
where tellurium alloys may be incorporated as a generator layer, tellurium 
enrichment at the upper surface of the charge generator layer can result 
in similar undue sensitivity enhancement, poor charge acceptance, and 
enhancement of dark discharge. 
One specific method of preparing selenium alloys for evaporation comprises 
the grinding of selenium alloy shots (beads) and compressing the ground 
material into pellet agglomerates typically from about 150 to about 300 
milligrams in weight and having an average diameter of about 6 millimeters 
(6,000 micrometers). The pellets are then evaporated from crucibles in a 
vacuum coater in a manner designed to minimize the fractation of the alloy 
during evaporation. One disadvantage of the aforementioned vacuum 
deposited photoconductors, such as selenium-tellurium alloy layer, is the 
crystallization of the selenium-tellurium alloy at the surface of the 
layer when exposed to heat. To retard premature crystallization and extend 
photoreceptor life, the addition of up to about 5 percent arsenic to the 
selenium-tellurium alloy can be beneficial without impairment of 
xerographic performance. For example, when the photoreceptor comprises a 
single layer selenium arsenic alloy, about 1 to about 2.5 percent by 
weight arsenic, based on the weight of the entire layer, at the surface of 
the alloy layer there is provided protection against surface 
crystallization. When the concentration of arsenic is greater than about 
2.5 percent by weight, electrical instability risks increase. 
Also, in deposited layers of selenium tellurium alloys the amounts of top 
surface tellurium present can cause excessively high photosensitivity. 
This photosensitivity is variable and changes as the surface of the layer 
wears away. Surface injection of corona deposited charge and thermally 
enhanced bulk dark decay involving carrier generation cause the toner 
images in the final copies to exhibit a washed out, low density 
appearance. Excessive dark decay causes loss of high density in solid 
areas of toner images and general loss of image density. 
One known method for attempting to control fractionation is the selection 
of shutters for incorporation over the evaporation crucibles. Shutters are 
normally selected after evaporation is substantially completed to avoid 
the coating of, for example, tellurium and arsenic rich species on the 
photoreceptor. This results in a photoreceptor or photoconductor with a 
top surface containing desired levels of tellurium and arsenic. Further, 
shutters can be utilized at inititation of evaporation of elements from 
the crucible to avoid sputtering. The aforesaid shuttering is generally 
costly, usually requires incomplete evaporation, and further the crucibles 
selected have to be cleaned after each evaporation. Furthermore, with 
shuttering generally a substantial amount of the source material is lost 
during the process. 
Accordingly, a problem encountered in the fabrication of chalcogenide alloy 
photoreceptors, such as selenium alloy photoreceptors, is the 
fractionation or preferential evaporation of a component whereby the 
resulting film composition is not equivalent to the source component, such 
as the source alloy, thus the deposited film or layer does not have a 
uniform composition extending from one surface to the other. For example, 
with selenium tellurium alloys containing from about 10 to about 60 
percent by weight of tellurium, the tellurium concentration is high at the 
top surface and very low, that is it approaches almost zero, at the bottom 
of the vacuum deposited layer. This problem is observed with, for example, 
alloys of Se-Te, Se-As, Se-As-Te, Se-As-Te-Cl, mixtures thereof, and the 
like. 
In copending application U.S. Pat. No. 4,770,965, there is disclosed a 
process which includes heating an alloy comprising selenium and from about 
0.05 percent to about 2 percent by weight arsenic until from about 2 
percent to about 90 percent by weight of the selenium in the alloy is 
crystallized, vacuum depositing the alloy on a substrate to form a 
vitreous photoconductive insulating layer having a thickness of between 
about 100 micrometers and about 400 micrometers containing between about 
0.3 percent and about 2 percent by weight arsenic at the surface of the 
photoconductive insulating layer facing away from the conductive 
substrate, and heating the photoconductive insulating layer until only the 
selenium in the layer adjacent the substrate crystallizes to form a 
continuous substantially uniform crystalline layer having a thickness up 
to about one micrometer. A thin protective overcoating layer is applied on 
the photoconductive insulating layer. The selenium-arsenic alloy may be 
partially crystallized by placing the selenium alloy in shot form in a 
crucible in a vacuum coater and heating to between about 93.degree. C. 
(200.degree. F.) and about 177.degree. C. (350.degree. F.) for between 
about 20 minutes and about one hour to increase crystallinity and avoid 
reticulation. Preferably, the selenium-arsenic alloy material in shot form 
is heated until from about 2 percent to about 90 percent by weight of the 
selenium in the alloy is crystallized. The selenium-arsenic alloy material 
shot may be crystallized completely prior to vacuum deposition to ensure 
that a uniform starting point is employed. However, if desired, a 
completely amorphous alloy may be used as the starting material for vacuum 
deposition. In Examples II and V of this copending patent application, 
halogen doped selenium-arsenic alloy shot contained about 0.35 percent by 
weight arsenic, about 11.5 parts per million by weight chlorine, and the 
remainder selenium, based on the total weight of the alloy was heat aged 
at 121.degree. C. (250.degree. F.) for 1 hour in crucibles in a vacuum 
coater to crystallize the selenium in the alloy. After crystallization, 
the selenium alloy was evaporated from chrome coated stainless steel 
crucibles at an evaporation temperature of between about 204.degree. C. 
(400.degree. F.) and about 288.degree. C. (550.degree. F.). 
Copending application U.S. Pat. No. 4,780,386, discloses a process wherein 
the surfaces of large particles of an alloy comprising selenium, tellurium 
and arsenic, the particles having an average particle size of at least 300 
micrometers and an average weight of less than about 1,000 milligrams, are 
mechanically abraded while maintaining the substantial surface integrity 
of the large particles to form between about 3 percent by weight to about 
20 percent by weight dust particles of the alloy based on the total weight 
of the alloy prior to mechanical abrasion. The alloy dust particles are 
substantially uniformly compacted around the outer periphery of the large 
particles of the alloy. The large particles of the alloy may be beads of 
the alloy having an average particle size of between about 300 micrometers 
and about 3,000 micrometers or pellets having an average weight between 
about 50 milligrams and about 1,000 milligrams, the pellets comprising 
compressed finely ground particles of the alloy having an average particle 
size of less than about 200 micrometers prior to compression. In one 
preferred embodiment, the process comprises mechanically abrading the 
surfaces of beads of an alloy comprising selenium, tellurium and arsenic 
having an average particle size of between about 300 micrometers and about 
3,000 micrometers while maintaining the substantial surface integrity of 
the beads to form a minor amount of dust particles of the alloy, grinding 
the beads and the dust particles to form finely ground particles of the 
alloy, and compressing the ground particles into pellets having an average 
weight between about 50 milligrams and about 1,000 milligrams. In another 
embodiment of the copending application, mechanical abrasion of the 
surface of the pellets after the pelletizing step may be substituted for 
mechanical abrasion of the beads. The process includes providing beads of 
an alloy comprising selenium, tellurium and arsenic having an average 
particle size of between about 300 micrometers and about 3,000 
micrometers, grinding the beads to form finely ground particles of the 
alloy having an average particle size of less than about 200 micrometers, 
compressing the ground particles into pellets having an average weight 
between about 50 milligrams and about 1,000 milligrams, and mechanically 
abrading the surface of the pellets to form alloy dust particles while 
maintaining the substantial surface integrity of the pellets. 
In copending application U.S. Pat. No. 4,822,712, the disclosure of which 
is totally incorporated herein by reference, there are illustrated 
processes for controlling fractionation. More specifically, there are 
disclosed in this copending application processes for crystallizing 
particles of an alloy of selenium comprising providing particles of an 
alloy comprising amorphous selenium and an alloying component selected 
from the group consisting of tellurium, arsenic, and mixtures thereof, 
said particles having an average size of at least about 300 micrometers 
and an average weight of less than about 1,000 milligrams, forming crystal 
nucleation sites on at least the surface of said particles while 
maintaining the substantial integrity of said particles, heating the 
particles to at least a first temperature between about 50.degree. C. and 
about 80.degree. C. for at least about 30 minutes to form a thin, 
substantially continuous layer of crystalline material at the surface of 
the particles while maintaining the core of selenium alloy in said 
particles in an amorphous state, and rapidly heating said particles to at 
least a second temperature below the softening temperature of said 
particles, the second temperature being at least 20.degree. C. higher than 
the first temperature and between about 85.degree. C. and about 
130.degree. C. to crystallize at least about 5 percent by weight of said 
amorphous core of selenium alloy in the particles. 
In application U.S. Ser. No. 270,184 entitled Processes for Preparing and 
Controlling the Fractionation of Chalcogenide Alloys with the listed 
inventors of Geoffrey M. T. Foley, Paul Cherin, and Santokh S. Badesha, 
the disclosure of which is totally incorporated herein by reference, there 
is illustrated a process for the preparation of chalcogenide alloys which 
comprises providing a chalcogenide alloy source component; crystallizing 
the source component; and evaporating the source component in the presence 
of an organic component. 
Also, there is described in U.S. Pat. No. 4,205,098 a process wherein a 
powdery material of selenium alone or at least with one additive is 
compacted under pressure to produce tablets, the tablets being degassed by 
heating the tablets at an elevated temperature below the melting point of 
the metallic selenium, and thereafter using the tablets as a source for 
vacuum deposition. The tablets formed by compacting the powdery selenium 
under pressure may be sintered at a temperature between about 100.degree. 
C. and about 220.degree. C. Typical examples of sintering conditions 
include 210.degree. C. for between about 20 minutes and about 1 hour and 
about 1 to about 4 hours at 100.degree. C. depending upon compression 
pressure. Additives mentioned include Te, As, Sb, Bi, Fe, Tl, S, I, F, Cl, 
Br, B, Ge, PbSe, CuO, Cd, Pb, BiCl.sub.3, SbS.sub.3, Bi.sub.2, S.sub.3, 
Zn, CdS, CdSe, CdSeS, and the like. 
With further respect to the prior art, there is mentioned U.S. Pat. Nos. 
4,609,605, which illustrates a multilayered electrophotographic imaging 
member wherein one of the layers may comprise a selenium-tellurium-arsenic 
alloy prepared by grinding selenium-tellurium-arsenic alloy beads, with or 
without halogen doping, preparing pellets having an average diameter of 
about 6 millimeters from the ground material, and evaporating the pellets 
in crucibles in a vacuum coater; 4,297,424, which describes a process for 
preparing a photoreceptor wherein selenium-tellurium-arsenic alloy shot is 
ground, formed into pellets and vacuum evaporated; 4,554,230, which 
discloses a method for fabricating a photoreceptor wherein 
selenium-arsenic alloy beads are ground, formed into pellets and vacuum 
evaporated; 3,524,754 directed to a process for preparing a photoreceptor 
wherein selenium-arsenic-antimony alloys are ground into fine particles 
and vacuum evaporated; and 4,710,442 relating to an arsenic-selenium 
photoreceptor, wherein the concentration of arsenic increases from the 
bottom surface to the top surface of the photoreceptor, that the arsenic 
concentration is about 5 weight percent at a depth about 5 to 10 microns 
on the top surface of the photoreceptor and is about 30 to 40 weight 
percent at the top surface of the photoreceptor, which photoreceptor can 
be prepared by heating a mixture of selenium-arsenic alloys in a vacuum in 
a step-wise manner such that the alloys are consequentially deposited on 
the substrate to form a photoconductive film with an increasing 
concentration of arsenic from the substrate interface to the top surface 
of the photoreceptor. In one specific embodiment, a mixture of 3 
selenium-arsenic alloys are maintained at an intermediate temperature in 
the range of from about 100.degree. to 130.degree. C. for a period of time 
sufficient to dry the mixture. Further, in U.S. Pat. No. 4,583,608 there 
is disclosed the heat treatment of single crystal super alloy particles by 
using a heat treatment cycle during the initial stages of which incipient 
melting occurs within the particles being treated. During a subsequent 
step in the heat treatment process, substantial diffusion occurs in the 
particle. In a related embodiment, single crystal articles which have 
previously undergone incipient melting during a heat treatment process are 
prepared by a heat treatment process. In still another embodiment, a 
single crystal composition of various elements including chromium and 
nickel is treated to heating steps at various temperatures. Other prior 
art includes U.S. Pat. Nos. 4,585,621; 4,632,849; 4,484,945; 4,414,179; 
4,015,029, and 3,785,806; Swiss Patent CH 656486 A5; and Japanese Pat. 
Nos. 60-172346 and 57-91567. 
There is illustrated in U.S. Pat. No. 4,513,031 a process for the formation 
of an alloy layer on the surface of a substrate, which for example 
comprises forming in a vessel a molten bath comprising at least one 
vaporizable alloy component having a higher vapor pressure than at least 
one other vaporizable alloy component in the bath, forming a thin 
substantially inert liquid layer of an evaporation retarding film on the 
upper surface of the molten bath, the liquid layer of the evaporation 
retarding film having a lower or comparable vapor pressure than both the 
vaporizable alloying component having a higher vapor pressure and the 
other vaporizable alloying component, covaporizing at least a portion of 
both the vaporizable alloying component having a higher vapor pressure and 
the other vaporizable alloying component whereby the evaporation retarding 
film retards the initial evaporation of the vaporizable alloying component 
having a higher vapor pressure, and forming an alloy layer comprising both 
the vaporizable alloying component having a higher vapor pressure and the 
other vaporizable alloying component on the substrate, see column 3, lines 
33 to 54, for example. Examples of vaporizable alloying components include 
selenium-sulfur and the like, and examples of vaporizable alloying 
components having relatively low vapor pressures which include tellurium, 
arsenic, antimony, bismuth, and the like are illustrated in column 4, 
reference for example lines 41 to 50. Examples of suitable evaporation 
retarding film materials are outlined in column 4 at line 54, and 
continuing onto column 5, line 36, such materials including inert oils, 
greases or waxes at room temperature which readily flow less than the 
temperature of detectable deposition of the vaporizable alloying 
components having higher vapor pressures in the alloying mixture, and may 
include, for example, long chain hydrocarbon oils, greases, and waxes, 
lanolin, silicone oils such as dimethylpolysiloxane, branched or linear 
polyolefins such as polypropylene wax and polyalpha olefin oils, and the 
like, see column 5. According to the teachings of this patent, optimum 
results are achieved with high molecular weight long chain hydrocarbon 
oils and greases generally refined by molecular distillation to have low 
vapor pressure at the alloy deposition temperature, see column 5, lines 32 
to 36. It is believed with the aforementioned process that the levels of 
organics, which are incorporated into the resulting alloy film, are 
sufficiently high causing negative adverse effects in the electrical 
properties of the resulting photoreceptor, for example, dark decay and 
cyclic stability are adversely effected. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide processes for the 
preparation of chalcogenide alloys. 
Another object of the present invention is the provision of processes for 
the preparation of chalcogenide alloys wherein fractionation is minimized. 
Further, in another object of the present invention there are provided 
processes for the preparation of selenium alloys wherein fractionation is 
substantially avoided. 
It is a further object of the present invention to provide an improved 
process which controls arsenic and tellurium fractionation within specific 
ranges. 
It is a further object of the present invention to provide an improved 
process wherein additives such as trigonal selenium are added to a 
chalcogenide alloy source material prior to evaporation thereby 
controlling fractionation. 
Moreover, in a further object of the present invention there are provided 
processes wherein small amounts of amorphous, or crystalline selenium such 
as trigonal selenium are added to a chalcogenide alloy source material 
prior to evaporation thereby controlling fractionation. 
Also, in a further object of the present invention there are provided 
processes wherein small amounts of amorphous or crystalline selenium are 
added to a chalcogenide alloy source material prior to evaporation thereby 
controlling fractionation, and reducing the amount of, for example, 
arsenic at the top surface of the resulting photoconductor to from about 
0.5 to about 1 percent, and preferably 0.8 percent. 
Additionally, in another object of the present invention there are provided 
processes wherein amorphous or crystalline selenium are added to a 
chalcogenide alloy source material, such as selenium arsenic, prior to 
evaporation thereby forming, it is believed, a layer of crystalline 
selenium rich components with a lower vapor pressure than the source 
alloy. By selenium rich species is meant, for example, the chemical 
reaction of crystalline selenium as it contacts selenium-arsenic, or 
selenium-tellurium source alloys, with arsenic and/or tellurium components 
of the alloy. Further, mainly since the crystalline selenium with the 
process of the present invention is primarily added only at the surface, 
it induces only a surface reaction and as a result the surface thereof is 
richer in selenium containing species, that is its selenium content, for 
example, is higher than the selenium content present in the source alloy. 
Thus, with the process of the present invention high fractionation is 
avoided, that is, for example, there is not a substantial decrease in the 
amount of tellurium or arsenic present in the final selenium alloy product 
beginning at the top surface thereof and continuing to the bottom surface; 
in one example, a total thickness of about 55 microns as illustrated 
herein. 
In a another object of the present invention there are provided processes 
wherein amorphous, or crystalline selenium is added to a chalcogenide 
alloy source material, such as selenium-arsenic, prior to evaporation 
thereby, it is believed, chemically bonding the trigonal selenium on the 
surface of the source alloy, such as selenium-arsenic, and preventing the 
loss of this component during evaporation, primarily since the new species 
has a lower partial vapor pressure. 
It is a further object of the present invention to provide an improved 
process which increases photoreceptor yields. 
It is a further object of the present invention to provide an improved 
process which reduces the level of tellurium, or arsenic fractionation. 
Furthermore, it is another object of the present invention to provide an 
improved process which reduces the tellurium, or arsenic stoichiometric 
distribution variation throughout the thickness of a selenium-tellurium, 
or selenium-arsenic alloy photoconductive layer. 
Another object of the present invention is to provide an improved process 
which controls the mechanical wear characteristics of the photoreceptor 
surface. 
Also, in another object of the present invention there is provided a 
process which limits the loss of selenium rich species during the vacuum 
deposition process. 
It is a further object of the present invention to provide processes that 
provide evaporated films of selenium and its alloy with arsenic and/or 
tellurium which have superior photoconductive properties for extended time 
periods. 
Another object of the present invention is to provide processes for 
controlling the electrical cycling characteristics and photosensitivity 
within a narrow range. When fractionation is not controlled, that is when 
there results uneven distributions of tellurium or arsenic, for example, 
throughout the alloy photoreceptor or film product, it is very difficult 
to predict the photosensitivity, the cyclic characteristics, and the dark 
decay properties of the photoreceptor. This results from the variation in 
fractionation from photoreceptor to photoreceptor. However, once the 
distribution of the elements is controlled throughout the film or the 
alloy product with the process of the present invention there is obtained 
predictable and consistent desired characteristics. 
Moreover, in another object of the present invention there are provided 
processes for the preparation of chalcogenide alloys wherein the alloy 
product is richer in selenium than the source alloy, that is it contains, 
for example, from about 10 to about 20 weight percent more than the 
selenium in the source alloy. 
The above and other objects of the present invention are accomplished by 
providing process for the preparation of and for controlling the 
fractionation of chalcogenide alloys. More specifically, the present 
invention is directed to a process which comprises providing a 
chalcogenide alloy, adding thereto crystalline or amorphous selenium, such 
as trigonal selenium, and thereafter subjecting the resulting components 
to evaporation enabling the formation of a photoconductor with improved 
characteristics as illustrated herein. In one specific embodiment of the 
present invention, there is provided a process which comprises providing a 
chalcogenide alloy such as an alloy containing selenium, including 
selenium arsenic alloys; admixing therewith trigonal selenium in an amount 
of, for example, from about 0.1 to about 10, and preferably from about 2 
to about 5 percent by weight; subjecting the resulting components to 
evaporation by heating at a temperature of from about 250.degree. to about 
350.degree. C.; and depositing on a supporting substrate the desired 
chalcogenide alloy with reduced fractionation. Another specific embodiment 
of the present invention relates to a process which comprises providing a 
selenium tellurium alloy containing from about 95 to about 60 percent by 
weight of selenium; admixing therewith trigonal selenium in an amount of 
from about 0.1 to about 10, and preferably from about 2 to about 5 weight 
percent; subjecting the resulting components to evaporation by heating at 
a temperature of from about 300.degree. to about 400.degree. C.; and 
depositing on a supporting substrate the desired chalcogenide alloy with 
reduced fractionation, that is distribution of the elements in the alloy 
product in an almost substantially homogeneous manner throughout the 
photoreceptor. 
In a specific embodiment of the present invention, the process comprises 
adding to boats contained in a vacuum coater about 50 grams of selenium 
arsenic alloy steel shots containing about 98 weight percent of selenium, 
and 2 weight percent of arsenic. About one gram of trigonal selenium 
powder was then sprinkled by a powered funnel on the surface of the 
aformentioned alloy shots. After evaporation at 350.degree. C. at a vacuum 
of 10-.sup.5 Torr, there resulted a thin film, about 55 microns thick, of 
a selenium arsenic alloy (98/2). A surface analysis of the product alloy 
film by EMPA indicated that the arsenic content in the top 0.1 micron 
surface, averaged 1.5 percent. Repeating the above process without 
trigonal selenium resulted in a selenium arsenic alloy with a top surface 
arsenic content of from about 9 to about 23.5 weight percent. EMPA also 
indicated that the stiochiometric distribution of the arsenic was 
homogeneous throughout the evaporated film product in a situation when 
trigonal selenium is added, while with the control where no trigonal 
selenium was selected a highly fractionated alloy film resulted indicating 
that there was an arsenic content gradient beginning with the top of the 
film and moving toward the bottom of the alloy film product. 
The substrate, usually up to about 150 mils in thickness, and preferably 
from about 75 to about 100 mils in thickness, selected for the deposited 
chalcogenide alloy product for the process of the present invention may be 
opaque or substantially transparent and may comprise numerous suitable 
materials having the desired mechanical properties. The entire substrate 
may comprise the same material, such as an electrically conductive 
surface, or the electrically conductive surface may merely be a coating on 
the substrate. Various suitable electrically conductive materials may be 
employed as the substrate. Typical electrically conductive materials 
include, for example, aluminum, titanium, nickel, chromium, brass, 
stainless steel, copper, zinc, silver, tin, and the like. The optional 
conductive layer on the substrate may vary in thickness depending on the 
desired use of the electrophotoconductive member. Accordingly, this 
conductive layer may be of a thickness of from about 50 Angstrom to 5,000 
Angstroms. Generally, the substrate may be of any conventional material 
including organic and inorganic materials. Further substrate examples 
include insulating nonconducting materials such as various resins known 
for this purpose including polyesters, polycarbonates, polyamides, 
polyurethanes, and the like. The coated or uncoated substrate may be 
flexible or rigid and may have any number of configurations such as, for 
example, a plate, a cylindrical drum, a scroll, an endless flexible belt, 
and the like. The outer surface of the supporting substrate preferably 
comprises a metal oxide such as aluminum oxide, nickel oxide, titanium 
oxide, and the like. One fixed substrate selected is comprised of thick 
aluminum sheets, drums, and flexible substrates, such as Mylar, in 
suitable effective thickness as indicated herein, reference U.S. Pat. No. 
4,265,990, the disclosure of which is totally incorporated herein by 
reference, and the like. 
In some situations, intermediate adhesive layers between the substrate and 
subseuently applied layers, such as the alloy product, may be desirable to 
improve adhesion. Preferably, these layers have a dry thickness of between 
about 0.1 micrometer to about 5 micrometers. Examples of adhesive layers 
include film-forming polymers such as polyester, polyvinylbutyral, 
polyvinylpyrrolidone, polycarbonate, polyurethane, polymethylmethacrylate, 
and the like, and mixtures thereof. 
Any suitable photoconductive chalcogenide alloy, including binary, 
tertiary, quaternary, alloys and the like, may be employed as the source 
alloy to enable the formation of the vacuum deposited photoconductive 
layer. Preferred alloys include alloys of selenium with tellurium, 
arsenic, or tellurium and arsenic with or without a halogen dopant. 
Examples of photoconductive alloys of selenium include selenium-tellurium, 
selenium-arsenic, selenium-tellurium-arsenic, selenium-tellurium-chlorine, 
selenium-arsenic-chlorine, selenium-tellurium-arsenic-chlorine alloys, and 
the like. Generally, the selenium-tellurium alloy may comprise between 
about 5 percent by weight and about 40 percent by weight tellurium and a 
halogen selected from the group consisting of up to about 70 parts per 
million by weight of chlorine and up to about 140 parts per million by 
weight of iodine all based on the total weight of the alloy with the 
remainder being selenium. The selenium-arsenic alloy may, for example, 
comprise between about 0.01 percent by weight and about 40 percent by 
weight arsenic and a halogen selected from the group consisting of up to 
about 200 parts per million by weight of chlorine and up to about 1,000 
parts per million by weight of iodine all based on the total weight of the 
alloy with the remainder being selenium. The selenium-tellurium-arsenic 
alloy may comprise between about 5 percent by weight and about 40 percent 
by weight tellurium, between about 0.1 percent by weight and about 5 
percent by weight arsenic, and a halogen selected from the group 
consisting of up to about 200 parts per million by weight of chlorine and 
up to about 1,000 parts per million by weight of iodine all based on the 
total weight of the alloy with the remainder being selenium. The terms 
alloy of selenium and selenium alloy as presented herein are intended to 
include halogen doped alloys as well as alloys not doped with halogen. The 
thickness of the aforementioned photoconductive chalcogenide alloy layer 
is generally between about 0.1 microns and about 400 microns. Other 
thicknesses may be selected provided the objectives of the present 
invention are achieved. 
Illustrative examples of additives in an amount of, for example, from about 
0.1 to about 10, and preferably from about 10 to about 6 weight percent 
admixed with the source alloy prior to evaporation thereof include 
amorphous or crystalline selenium. Suitable forms of selenium include, for 
example, trigonal, hexagonal, and monoclinic selenium. Also, other amounts 
of additives can be selected providing the objectives of the present 
invention are achievable. 
Selenium-tellurium and selenium-tellurium-arsenic alloy photoconductive 
layers are frequently employed as a charge generation layer in combination 
with a charge transport layer. The charge transport layer is usually 
positioned between a supporting substrate and the charge generating 
selenium alloy photoconductive layer. Generally, a selenium-tellurium 
alloy photogenerating layer may comprise from about 40 percent by weight 
to about 95 percent by weight selenium, and from about 5 percent by weight 
to about 60 percent by weight of tellurium based on the stoichiometric 
amount of the alloy. The selenium-tellurium alloy may also comprise other 
components such as less than about 40 percent by weight arsenic to 
minimize crystallization of the selenium and less than about 1,000 parts 
per million by weight halogen. In a more preferred embodiment, the 
photoconductive charge generating selenium alloy layer comprises between 
about 5 percent by weight and about 25 percent by weight tellurium, 
between about 0.1 percent by weight and about 4 percent by weight arsenic, 
and a halogen selected from the group consisting of up to about 100 parts 
per million by weight of chlorine and up to about 300 parts per million by 
weight of iodine with the remainder being selenium. It is desirable, in 
general, to achieve uniformly homogeneous compositions within the 
evaporated layers, that is to evaporate the alloy source materials without 
significant fractionation. Elevated (that is the amount of tellurium or 
arsenic, which is usually higher, is present in the final alloy as 
compared to the initial source alloy) levels of tellurium on the top 
surface lead to excessive photoreceptor light sensitivity and high dark 
decay, and correspondingly reduced copy quality with, for example, 
undersirable background deposits. Elevated levels of arsenic in some 
applications above about, for example, 4 percent by weight can result in 
high dark decay to problems in cycling stability and to reticulation of 
the photoreceptor surface. 
Any suitable selenium alloy transport layer may be utilized in the 
aforementioned layered imaging member. Examples of these layers include 
pure selenium, selenium-arsenic alloys, selenium-arsenic-halogen alloys, 
selenium-halogen and the like. Preferably, the charge transport layer 
comprises a halogen doped selenium arsenic alloy. Generally, about 10 
parts by weight per million to about 200 parts by weight per million of 
halogen is present in a halogen doped selenium charge transport layer. 
When the halogen doped transport layer free of arsenic is utilized, the 
halogen content should normally be less than about 20 parts by weight per 
million. Inclusion of high levels of halogen in a thick halogen doped 
selenium charge transport layer free of arsenic may cause excessive dark 
decay. Imaging members containing high levels of halogen in a thick 
halogen doped selenium charge transport layer free of arsenic are 
described, for example, in U.S. Pat. Nos. 3,635,705 and 3,639,120, and 
Ricoh Japanese Patent Publication No. J5 61 42-537 published June 6, 1981. 
Generally, halogen doped selenium arsenic alloy charge transport layers 
comprise between about 99.5 percent by weight to about 99.9 percent by 
weight selenium, about 0.1 percent to about 0.5 percent by weight arsenic 
and between about 10 parts per million by weight to about 200 parts per 
million by weight of halogen, the latter halogen concentration being a 
nominal concentration. Halogen includes fluorine, chlorine, bromine, and 
iodine. Chlorine is preferred primarily because of its stability. 
Transport layers are described, for example, in U.S. Pat. Nos. 4,609,605 
and 4,297,424, the disclosures of which are totally incorporated herein by 
reference. 
The first layer of multiple layered photoreceptors, such as a transport 
layer, may be deposited by any suitable conventional technique, such as 
vacuum evaporation. Thus, a transport layer comprising a halogen doped 
selenium-arsenic alloy comprising less than about 1 percent arsenic by 
weight may be evaporated by conventional vacuum coating devices to form 
the desired thickness. The amount of alloy to be employed in the 
evaporation boats of the vacuum coater will depend on the specific coater 
configuration and other process variables to achieve the desired transport 
layer thickness. Chamber pressure during evaporation may be on the order 
of about 4.times.10-.sup.5 Torr. Evaporation is normally completed in 
about 15 to 25 minutes with the molten alloy temperature ranging from 
about 250.degree. C. to about 325.degree. C. Other times and temperatures 
and pressures outside these ranges may be used as well understood by those 
skilled in the art. It is generally desirable that the substrate 
temperature be maintained in the range of from about 50.degree. C. to 
about 70.degree. C. during deposition of the transport layer. Additional 
details for the preparation of transport layers are illustrated, for 
example, in U.S. Pat. No. 4,297,424, the disclosure of which is totally 
incorporated herein by reference. 
Fractionation control with the process of the present invention is 
sufficient to the extent that photoreceptors with acceptable and 
predictable electrical properties for extended time periods may be 
fabricated prepared with generator layers of selenium tellurium and 
selenium tellurium arsenic having thicknesses up to about 60 microns, 
other thicknesses as indicated herein, or other thicknesses providing the 
objectives of the present invention are achieved.

The following examples are being submitted to further define various 
species of the present invention. These examples are intended to be 
illustrative only and are not intended to limit the scope of the present 
invention. Also, parts and percentages are by weight unless otherwise 
indicated. 
EXAMPLE I 
Fifty (50) grams of selenium arsenic alloy shots with 0.5 percent arsenic, 
99.5 percent of selenium, and 20 parts per million of chlorine were 
charged into a crucible present in a vacuum deposition 18 inch bell jar 
coater. The alloy shots were evenly spread in the coater by a spatula. 
After evaporation at a crucible temperature of 300.degree. and a vacuum of 
4.times.10-.sup.5 Torr, there was coated on alloy product 99.5 percent 
selenium and 0.5 percent of arsenic over a period of 20 minutes on an 
aluminum substrate of a thickness of 10 mils and maintained at 55.degree. 
C. An EMPA (electron microprobe analysis) indicated that the alloy product 
was highly fractionated, that is the arsenic content decreased from the 
top surface down to the bottom surface of the film product which was of a 
thickness of 55 microns. More specifically, at the bottom surface of the 
alloy product film there was present about 0.02 percent by weight of 
arsenic. Also, the average amount of arsenic in the top 0.1 and 0.5 micron 
of the alloy was 3.1 and 2.6 weight percent, respectively. 
EXAMPLE II 
The process of Example I was repeated with the exception that one gram of 
trigonal selenium was sprinkled on the alloy shots present in the 
crucible. There resulted a selenium arsenic alloy (99.5/0.5) product. EMPA 
analysis evidenced a relatively flat arsenic profile, that is 
substantially no arsenic fractionation, and that the top 0.1 and 0.5 
micron of the alloy with a thickness of 55 microns had arsenic 
concentrations of 0.8 and 1.5 weight percent, respectively. 
EXAMPLE III 
The process of Example II was repeated with the exception that 3 grams of 
the trigonal selenium was sprinkled onto the surface alloy shots present 
in the crucible. EMPA analysis evidenced a relatively flat arsenic 
profile, that is substantially no arsenic fractionation, and that the top 
0.1 and 0.5 micron of the alloy had arsenic concentrations of 0.6 and 0.8 
weight percent, respectively. 
EXAMPLE IV 
The process of Example I was repeated with the exceptions that 50 grams of 
selenium tellurium alloy shots with 10.7 weight percent of tellurium were 
selected in place of the selenium arsenic alloy, the crucible temperature 
was maintained at 350.degree. C., and the coating was completed in 22 
minutes. The alloy product film, 89.3 percent selenium, 10.7 percent of 
tellurium, was of a thickness of 55 microns. EMPA analysis of the alloy 
indicated high fractionation and the top 0.1 and 0.5 micron of the alloy 
had tellurium concentrations of 17.6 and 17.7 weight percent, 
respectively. At the bottom of the 55 micron film product there was 
present about 2 weight percent of tellurium indicating a highly 
fractionated film alloy. 
EXAMPLE V 
The process of Example IV was repeated with the exception that 2.5 grams of 
trigonal selenium were sprinkled on the alloy shots present in the 
crucible. There resulted a selenium tellurium alloy film (89.3/10.7) 
product. EMPA analysis evidenced a relatively flat tellurium profile, that 
is substantially no tellurium fractionation, and that the top 0.1 and 0.5 
micron of the alloy had tellurium concentrations of 9.2 and 10.6 weight 
percent, respectively. At the bottom of the 55 micron film product there 
was present about 8.5 weight percent of tellurium, indicating that there 
was substantially no fractionation of the alloy product. 
EXAMPLE VI 
Fifty (50) grams of selenium arsenic alloy shots with 2 percent arsenic, 
and 98.0 percent of selenium were charged into a crucible present in a 
vacuum deposition coater. After evaporation at a crucible temperature of 
300.degree. C. and a vacuum of 4.times.10-.sup.5 Torr, there was coated 
over a period of 90 minutes a film of 55 microns on an aluminum substrate, 
10 mils in thickness. An EMPA indicated that the alloy product was highly 
fractionated. More specifically, the average amount of arsenic in the top 
0.1 and 0.5 micron of the alloy was 23.5 and 19.8 weight percent, 
respectively. 
EXAMPLE VII 
The process of Example VI was repeated with the exception that one gram of 
trigonal selenium was sprinkled on the alloy shots present in the 
crucible. There resulted a selenium arsenic alloy (98/2) product. EMPA 
analysis evidenced a relatively flat arsenic profile, that is 
substantially no arsenic fractionation, and that the top 0.1 and 0.5 
micron of the alloy had 1.5 and 2.6 weight percent concentration of 
arsenic, respectively. 
EXAMPLE VIII 
The process of Example VII was repeated with the exception that 3 grams of 
the trigonal selenium were sprinkled onto the surface alloy shots present 
in the crucible. EMPA analysis evidenced a relatively flat arsenic 
profile, that is substantially no arsenic fractionation, and that the top 
0.1 and 0.5 micron of the alloy had arsenic concentrations of 0.8 and 0.9 
weight percent, respectively. 
Thus, with the processes of the present invention the alloy products 
obtained are not highly fractionated as indicated herein. 
Although the invention has been described with reference to specific 
preferred embodiments, it is not intended to be limited thereto, rather 
those skilled in the art will recognize that variations and modifications 
made be made therein which are within the scope of the present invention 
and within the scope of the claims.