JPS63237064A - Photoconductive amorphous carbon - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to novel photoconductive materials. For more details 1
The present invention relates to photoconductive amorphous carbon topped with sulfur and hydrogen.

DESCRIPTION OF THE PRIOR ART Amorphous semiconductors with the classical photosensitive material, constant selenium, have long been used as photoconductive elements in electrophotographic reproduction. For electrophotographic applications, monoconducting materials have very low dark conductivities (approximately 10-13 ohm-1) to prevent self-discharge in unirradiated areas of the material.
m-1 to IJ9; must have high photoconductivity to quickly discharge the irradiated area of the material; and high dielectric strength to minimize the required thickness of the material. .

A very hard material is also desirable since the material is abraded by the paper and toner it comes into contact with during the copying process.

Amorphous silicon containing up to about 30 atomic percent hydrogen, called hydrogenated amorphous silicon, is currently being developed as a replacement for amorphous selenium for electrophotographic applications. It is much harder and has a useful life that is probably about 10 times longer (from about 500,000 to 1,0 copies for hydrogenated amorphous silicon coatings versus about 50,000 copies for amorphous selenium coatings).
00,000 copies).

Unfortunately, the dark conductivity of hydrogenated amorphous silicon is too high to be used alone, thus requiring the use of complex multilayer films containing blocking contacts to prevent self-discharge in the dark. No.

Carbon films can be produced by electron beam vacuum evaporation, high-frequency sputtering, high-frequency plasma decomposition of hydrocarbon gas, direct current glow discharge in hydrocarbon gas, and coaxial ξ using methane gas.
They are produced by a variety of vacuum deposition methods, including russ plasma acceleration, vacuum arc deposition using a graphite cathode, ion beam deposition using argon and hydrocarbon fragment ions, and deposition using a pure carbon ion beam. However, this film is typically prepared using sputtering.

Electron beam evaporation and plasma evaporation are the most convenient methods. When made by decomposition of a hydrogen-containing starting material such as carbon-arsenide, carbon films typically contain significant amounts of hydrogen.

The carbon film described above is very hard (and typically has a Mohs hardness of about 6, low dark conductivity, and high dielectric strength. Furthermore, the optical bandgap of this film is 1 eV depending on the preconditions. The carbon in this film is described in the scientific literature as diamond-like or amorphous, unlike graphite.For the purposes of this invention All woody non-graphitic carbon produced by vacuum evaporation is hereinafter referred to as amorphous carbon.

Numerous studies using methods such as X-ray diffraction, electron microscopy, and electron beam diffraction have demonstrated that the carbon produced by vacuum evaporation is essentially amorphous in nature. Unlike graphitic carbon, which is an excellent electrical conductor, amorphous carbon is a semiconductor with a relatively high resistivity that decreases with increasing temperature.

Finally, amorphous carbon is essentially transparent to red and infrared radiation, whereas graphitic carbon is not. These properties suggest that a significant proportion of the carbon atoms in amorphous carbon are not three-coordinated, as in graphite, but four-coordinated, as in diamond.

Glow discharge initiated polymerization of various sulfur-containing organic monomers was described by A. Bradley and P. Hamme S.
1℃ (: J, Electrochem, So
c, , Vol. 110.

pp 15-22 and 543-548 (1963)), the monomers listed are thiourea, thianthrene.

One polymerization involving thioacetamide and thiophene was carried out under relatively high pressure (approximately 1 torr) using an alternating current voltage in the ultrasonic frequency range (10 to 50 kilohertz). Films obtained from polymerization of thioacetamide and thianthrene were reported to have negligible photoconductivity [J, E1
8CtrOCh8m, Soc, .

Vol. 110.543 (1963)]. More specifically.

The photoconductivity (corrected to an incident light intensity of 7 cm2) of the polymers obtained from thianthrene and thioacetamide (90 mW using the intensity dependence shown by the authors) to dark conductivity ratio is only 168 and 250, respectively.
Met.

Polymerization initiated by glow discharge of carbon disulfide (C82) was described by Asano [Jap, J, Appl.

Phys, Vol. 22.1618-1622
(1983)].

The polymerizations described by Mr. Asano were carried out at pressures ranging from about 2 x 10"2 to about 6 x 10"2 Torr in a glow discharge sustained by a high frequency generator operating at 13.56 MHz. The sulfur-to-carbon ratio (S/C) in the resulting M+7-r- was a function of RF power and curtain temperature and varied from 0.16 to 14.

Sarani, whose film was found to be photoconductive1-
It's 1t'1. More specifically, for a polymer with an S/C value of 4.0, the photoconductivity (corrected to an incident light intensity of 90 milliwatts/min using the intensity dependence presented by the authors) versus dark conductivity. The ratio was 1429. As the S/C value decreases, this photoconductivity to dark conductivity ratio decreases and S
It was reported that a value of 237 was reached when the /C value was 1.8.

SUMMARY OF THE INVENTION The present invention relates to Wc yellow and hydrogen doped amorphous carbon made by plasma glow deposition in a gas mixture consisting of at least one hydrocarbon and at least one sulfur source. The resulting doped amorphous carbon is photoconductive.

For example, light guides in electrophotography are often used as electromagnetic elements.

'One embodiment of the invention is made by a method comprising depositing doped amorphous carbon by plasma glow radiation at 11 cK in a gas mixture consisting of at least one hydrocarbon and at least one sulfur source. It is amorphous carbon doped with sulfur and hydrogen.

Other aspects of the invention include (a) initiating a plasma glow discharge in a gas mixture comprising at least one hydrocarbon and at least one sulfur source; and lbl doped by the plasma glow discharge. A method for preparing amorphous carbon doped with sulfur and hydrogen comprises depositing amorphous carbon onto a substrate.

One objective of the present invention is to provide a new photosensitive material.

Another object of the invention is to provide new materials that can be used as photosensitive elements in electrophotography.

Another object of the present invention is to provide a new method for producing sulfur and hydrogen doped amorphous carbon.

Yet another object of the present invention is to provide a sulfur and hydrogen doped amorphous carbon having photoconductivity superior to anything previously reported for amorphous carbon materials.

DETAILED DESCRIPTION OF THE INVENTION The present inventors have discovered amorphous carbon doped with sulfur and hydrogen that has excellent photoconductivity. This material is deposited by a plasma glow discharge initiated and sustained in a gas mixture of one hydrocarbon and one sulfur-containing material. The process of this invention requires the use of at least two separate starting materials. (a) sulfur-free hydrocarbons; and (b) sulfur-containing materials, referred to herein as sulfur sources. As a result of using these two starting materials, the sulfur content of the doped amorphous carbon can be varied simply by varying the partial pressure of the sulfur source in the gas mixture. Furthermore, by adjusting the amount of hydrogen doping,
The hydrocarbon starting material can be chosen individually to optimize the properties of the amorphous carbon product.

Sources of sulfur suitable for use in the practice of this invention include all volatile organic and inorganic materials containing sulfur. It will be appreciated, of course, that the sulfur source must be sufficiently volatile to be used in forming the gas mixture that undergoes the plasma glow discharge in accordance with the present invention. Desirably the vapor pressure of the sulfur source at a selected operating temperature is at least about
, ooit should be true. However, in order to minimize handling problems, it is preferred that the sulfur source is a gas. Although organic sulfur-containing compounds are suitable for use as sulfur sources, providing the total carbon content from one or more sulfur-free hydrocarbon starting materials is less advantageous than doped amorphous carbon products. Because excellent control is usually obtained.

Sulfur-containing organic compounds are undesirable. Volatile inorganic sulfur compounds are preferred sulfur sources, and more preferably the sulfur source is selected from the group consisting of hydrogen sulfide and sulfur hexafluoride.

Hydrocarbons suitable for use in the practice of this invention include all volatile hydrocarbons. Needless to say.

It will be appreciated that hydrocarbons are compounds containing only carbon and hydrogen. Suitable hydrocarbons used to form the gas mixture subjected to the plasma glow discharge according to the present invention must be as volatile as 1-14.

Desirably, the vapor pressure of the hydrocarbon at a selected operating temperature should be at least about 0.001) liters. However, in order to minimize handling problems, it is preferred that the hydrocarbon is a gas.

Suitable hydrocarbons are alkanes, alkenes, and algines.

and aromatic hydrocarbons. More preferably the hydrocarbon is selected from the group consisting of alkanes, alkenes and algines. Suitable hydrocarbons include, but are not limited to, methane, ethylene, and acetylene.

The gas mixture used in the practice of the present invention can contain other components in addition to the carbonaceous hydrogen and sulfur sources. For example, the gas mixture can further include inert gases such as helium, neon, argon, krypton, and xenon. If desired, in a gas mixture of hydrocarbons and sulfur sources.

Dopant elements other than sulfur and hydrogen can also be introduced into the sulfur- and hydrogen-doped amorphous carbon of the present invention by mixing gases containing elements other than sulfur and hydrogen. Such a moth.

B2H can provide both boron and hydrogen.
6, and PH3 which can give both phosphorus and hydrogen
However, it is not limited to this tllc. A preferred embodiment of the invention includes the use of a gas mixture that further includes hydrogen. This additional use of hydrogen gas allows variation of the hydrogen content of the doped amorphous carbon product by simply changing the partial pressure of hydrogen in the gas mixture.

The composition of the gas mixture used in the invention is preferably:
A sulfur and hydrogen doped mineral having a hydrogen to carbon atomic ratio ranging from about 0.1 to about 2.0 and a sulfur to carbon atomic ratio ranging from about 0.005 to about 0.20. Adjusted to give fixed carbon. However, more preferably the composition of the gas mixture is.

to provide a doped amorphous carbon having a hydrogen to carbon atomic ratio ranging from about 0.5 to about 1.5 and a sulfur to carbon atomic ratio ranging from about 0.01 to about 0.05. The pA is adjusted to

Because there are many suitable carbon-hydrogen and sulfur sources, and because hydrogen gas can also be used as a component of the gas mixture that undergoes the glow discharge, the precise identification and proportions of the components of this mixture depend on the specific amounts of sulfur and sulfur. It must be empirically tailored to create an amorphous carbon containing hydrogen dopant atoms. For example, hydrogen-poor hydrocarbons such as acetylene (C2H2) are doped with low hydrogen content.
Hydrogen-rich hydrocarbons such as methane (OH) can be used advantageously to make doped amorphous carbons containing relatively high hydrogen contents. be able to. If desired, hydrogen can also be used as a component in the gas mixture to increase the hydrogen content of the doped amorphous carbon product. For example, hydrogen can be mixed with a hydrogen-poor hydrocarbon such as acetylene to create a product with an even higher hydrogen content than is possible by using acetylene alone.

The use of a sulfur source containing either hydrogen and carbon, or both, allows for additional control over the hydrogen to carbon ratio in the product. For example, the use of hydrogen sulfide as a sulfur source provides a hydrogen dopant source for the amorphous carbon product. Similarly, carbon- and hydrogen-containing sulfur sources such as methyl mercaptan are a source of both carbon and hydrogen and therefore may influence the hydrogen-to-carbon ratio in the doped amorphous carbon product. Dew. However, since there is a relatively small amount of sulfur dopant source, any contribution of hydrogen and/or carbon from the sulfur source will usually be small. If desired, carbon- and hydrogen-free sulfur sources such as sulfur hexafluoride can be used.

The sulfur content of the doped amorphous carbon of the present invention is:

It can be adjusted by empirical selection of a suitable sulfur source and empirical adjustment of the partial pressure of the sulfur source in the gas mixture.

It will of course be appreciated that some sulfur sources are more effective than others in providing sulfur content to the doped amorphous carbon products of the present invention.

The plasma glow discharge of the present invention can be sustained using a DC voltage or an AC voltage having any frequency within the range of about 1 Hertz to microwave frequencies (up to about 10 GHz). but.

It is convenient to use an alternating current voltage having a frequency of about 13.56 MHz. The reason for this is the commercial availability of equipment designed to operate at this frequency. Desirably, the gas mixture subjected to the plasma glow discharge in the practice of the present invention is at a pressure in the range of about 0.001 to about 1 Torr, and preferably in the range of about 0,005 to about 0.5 Torr. .

The sulfur and hydrogen doped amorphous carbon of the present invention is conveniently deposited as a film on a substrate. However, the exact nature of this substrate is not important. In fact, the type of substrate will usually be dictated by the intended use of the film or for reasons of convenience and availability. However, it will be appreciated that the substrate must be relatively inert to the film formed thereon.

Suitable substrates include, but are not limited to, glass, fused silica, crystalline silicon, amorphous silicon, thermoplastic carbonate-bonded polymers made by reacting bisphenol A and phosgene, aluminum, and stainless steel. If desired, the substrate can be heated or cooled during the deposition process.

FIG. 1 schematically illustrates the use of an inductively coupled plasma reactor for the deposition of sulfur and hydrogen doped amorphous carbon according to the present invention. The substrates 1 and 2 to be coated with the doped amorphous carbon of the present invention are placed on an insulating support (not shown) in the reaction chamber 3, It is sealed. Next, by operating the vacuum pump 8, the pipe line 5
．． The reaction chamber 3 is evacuated by removing the °C gas through the exhaust valve 6 and the line 7. Hydrocarbon gas flows from storage cylinder 9 to pipe 10. Metering valve 11. It enters mixing manifold 13 through line 12. Similarly, the sulfur source is stored in storage cylinder 1.
4 to conduit 15. Metering valve 16 enters mixing manifold 13 through line 17. If required, additional gas, such as hydrogen, can be supplied from storage bomb 18 to line 19. Metering valve 2
0. and is sent to the mixing manifold 13 through the conduit 21 1-1
Five different gases, which can be mixed into a gas mixture at t'l, are mixed in a mixing manifold 13 and then passed to the reaction chamber 3 by a distribution manifold 22. The proportions of the various gases are adjusted by adjusting their respective flow rates via metering valves 11, 16 and 20.

The pressure in the reaction chamber 3 is monitored by a pressure gauge 23 and a 1° metering valve 11.16. and 20 and the exhaust valve 6. When the desired gas flow is obtained.

Turn on the high frequency power supply 25, adjust the desired output to
The high frequency coil 24 is then energized by adjusting the impedance matching network 26 to minimize the amount of power reflected from the high frequency coil 24. After the sulfur- and hydrogen-doped amorphous carbon film of the required thickness has been deposited on the substrates 1 and 2, the radio frequency power supply 25 is switched off and the metering valves 11.1 (S and 20 are closed). The reaction chamber 6 is evacuated. One reaction chamber 6 is then filled with a suitable gas such as argon, the access door 4 is opened, and the coated substrates 1 and 2 are removed.

FIG. 2 schematically illustrates the use of a capacitively coupled plasma reactor for the production of sulfur and hydrogen doped amorphous carbon of the present invention. The substrates 51 and 52 to be coated with the doped amorphous carbon of the present invention are placed in the lower part of the reaction chamber 54, but the lower electrode 56 is electrically isolated from the reaction chamber 54.
placed on top of

Next, an upper electrode 56 disposed directly above the lower electrode 56 that seals the access door 55 of one reaction chamber 54 is suspended from the access door 55, but is electrically isolated from the access door 55. I'm here. If necessary, lower electrode 56 and substrates 51 and 52 can be heated by a resistive heater to enable deposition of doped amorphous carbon under elevated temperatures. After sealing the access door 55, the vacuum pump 58 is activated to open the pipe line 58. Exhaust valve 59
A vacuum is applied to the reaction chamber 54 by removing the gas via the conduit 60 and conduit 60 . Hydrocarbon gas flows from storage cylinder 62 to conduit 63. Metering valve 64. and through line 65 to mixing manifold 66 . Similarly.

The sulfur source is from the storage cylinder 67 to the pipe 68. It passes through metering valve 69° and line 70 to mixing manifold 966. Additional gases such as hydrogen if required.

71 storage cylinders, pipe line 72, metering valve 76 and pipe line 7
4 and into a mixing manifold 66. The various gases are mixed in a mixing manifold 66.

It is then passed to reaction chamber 54 by distribution manifold 975. The proportions of the various gases are adjusted by adjusting their respective flow rates through metering valves 64, 69 and 76. The pressure in reaction chamber 54 is monitored by pressure gauge 76 and regulated by metering valves 64, 69 and 76 and exhaust valve 59. When the substrates 51 and 52 reach the required deposition temperature and the required gas flow is not obtained in the reaction chamber 54, the high frequency power supply 77 is turned on and adjusted to the required output level, and the impedance matching network 78 is adjusted. This energizes the upper electrode 56 by minimizing the amount of power reflected from the upper electrode 56. The lower electrode 53 is connected to the ground 79
and the upper electrode 56 is connected to a high frequency power source 77 and an impedance matching network 78 by a capacitor 8o.
I am isolated from the world.

The powered upper electrode 56 is called the cathode. This is because the upper electrode 56 generates a negative self-bias with respect to the grounded lower electrode 53, which is called an anode. If desired, the power supply to the electrodes can be reversed so that the lower substrate support electrode 56 is powered and a portion of the electrode 56 is grounded. However, the cathode undergoes a much more active bombardment 9 of ions than the anode, and the kneading affects the exact nature of the deposited film. After the doped amorphous carbon film of the required thickness is deposited on the substrates 51 and 52,
High frequency power supply 77 is turned off, metering valves 6469 and 73 are closed, and reaction chamber 54 is evacuated. The reaction chamber 54 is then filled with a suitable gas such as argon, and the access door 54 is filled with a suitable gas such as argon.
5 and take out the coated substrates 51 and 52.

The following examples are only intended to illustrate the invention and should not be construed as limiting the invention.

Example 1 Using a Barzers beam evaporator with Corning 7
A film of tantalum (approximately 100 Angstroms thick) was deposited onto a 059 microscope slide.

A substrate was then prepared by covering it with the tanky platinum film (approximately 400 angstroms thick). Next, the substrate is placed in the reaction chamber of an inductively coupled plasma reaction system of the type shown in Figure #1. The reaction chamber was made of fused silica and was about 20 mm in diameter and about 45 cIn in length. Ethylene, hydrogen, and sulfur hexafluoride were passed into the reaction chamber at flow rates that produced partial pressures within the reaction chamber of 100 millitorr of ethylene, 90 millitorr of hydrogen, and 10 millitorr of sulfur hexafluoride.

A plasma glow discharge was then initiated and sustained within the gas mixture of the reaction chamber using 10 watts of radio frequency power. After 100 minutes, the plasma glow discharge was stopped and the resulting sulfur and hydrogen-topped amorphous carbon film was found to have a thickness of 350 D Angstrom units. The atomic ratio of sulfur to carbon in the film was found to be 0.048 by photoelectron spectroscopy.

A thin, translucent metal contact (60 angstroms of tantalum followed by 30 angstroms of tantalum) was deposited on the surface of the sulfur and hydrogen doped amorphous carbon film by electron beam evaporation.
1 angstrom of platinum) was deposited. Then,
Using the metal deposit as an electrode, the conductivity and photoconductivity of the doped amorphous carbon film are determined by the overlap of the metal deposits above and below the doped carbon film through the thickness of the film. The temperature was measured over an area of 0.6 cm. In order to avoid spurious results due to adsorption of water or other species with its surface in the case of these measurements, the samples were placed in fused silica tubes that were evacuated and then filled with helium again. The sample is fixed inside a quartz tube by an insulating Teflon mounting block.

All conductors from the electrometer to the sample were made of fully protected triaxial conductors. These precautions helped reduce the leakage current in the measurement circuit to far less than the current flowing in the carbon film.

For photoconductivity measurements, the sample was illuminated with white light from a 150 watt xenon lamp coupled with an f/1.0 fused silica optical system that focused the light beam to a spot approximately 23 in diameter on the sample. The light beam from the xenon lamp was also passed through a length 103 water filter to avoid heating the sample during irradiation. The resulting intensity of white light incident on the sample was approximately 90 milliwatts/DII2 as measured by a thermoelectric radiometer placed at the same location. The top metal electrode was thin and translucent, so photoconductivity was measured by shining the topped amorphous carbon through this electrode.

Using the method described above, the one element conductivity was found to be 4.7 x 10"ohm-'?+1-'.Due to the leakage t1 flow problem, the dark conductivity must be measured accurately. 1.5X 10"ohm-"cIn-
It was found to be less than 1. Therefore, at 3°C, the photoconductivity ratio (ratio of photoconductivity to dark conductivity) of amorphous carbon doped with sulfur and hydrogen was 3) more than 0.

EXAMPLE 2 An amorphous carbon film was deposited by plasma glow discharge in a mixture of ethylene and hydrogen without any sulfur hexatide, and the ethylene and hydrogen were heated to a partial pressure of each gas of 100 μl. The method set forth in Example 1 was repeated, except that the mixture was passed through the reaction chamber at a ratio such that: The resulting hydrogen-doped amorphous carbon film was sulfur-free and 4300 Angstrom units thick. The dark conductivity of the film is 2 x i □”ohm-' cr
R-'', the photoconductivity was 7 x 10-16 ohms 'cIn-', and the photoconductivity ratio was 6.5. Comparison of this result with the results shown in Example 1 shows that the photoconductivity was 0.048. If we dope the film with just enough sulfur to give the atomic ratio of sulfur to carbon.

The photoconductivity ratio of the film is about 100 times (3,5 to 3
) was shown to increase by more than 0.

Example 6 Example 1 except that in the reaction chamber the partial pressures of ethylene, hydrogen and sulfur were 1[]0.18 and 2 millitorr, respectively.
The method described in was repeated. The resulting sulfur and hydrogen doped amorphous carbon film had a thickness of 8000 Angstrom units and a sulfur to carbon atomic ratio of 0.01. The film has a dark conductivity of 6.5 x 10" ohms (711-') and a photoconductivity of 2.3 x 10" ohms.
The ohm-'crn-' and photoconductivity ratio was 650. A contrast between these results and those shown in Examples 1 and 2 shows that the sulfur content of the doped amorphous carbon can be easily adjusted by simple variation in the amount of sulfur used. certified.

Example 4 The method set forth in Example 1 was repeated except that the amorphous carbon film was deposited by plasma arc discharge in a mixture of acetylene, hydrogen, and sulfur hexafluoride. These gases were passed through the reaction chamber at flow rates that produced partial pressures of 50 mTorr of acetylene, 45 mTorr of hydrogen, and 5 mTorr of sulfur hexafluoride in one reaction chamber. The resulting sulfur and hydrogen doping
The amorphous carbon film had a thickness of 1500 Angstrom units. The dark conductivity of the film is 3.4×10
-17 ohms 'm-', photoconductivity is 6.5 x 1
0-” ohm-’crn-’, and the photoconductivity ratio is 190
It was 0.

Example 5 A doped amorphous carbon film was deposited by plasma glow discharge in a mixture of methane, hydrogen, and sulfur hexafluoride, following the method described in Example 1 except that the RF power of the discharge was 350 watts. repeated. methane 100
mitorr, hydrogen 90 mIJ), and sulfur hexafluoride 1
Gas was passed through the reaction chamber at a flow rate that produced a partial pressure within the reaction chamber of 0 mTorr.

The resulting sulfur and hydrogen doped amorphous carbon film had a density of 3400 angstrom units.

Dark conductivity is 2.8 x 10"ohm-'crn-'
, photoconductivity is 8.5 x 10-12 ohm-1cr
It-' and photoconductivity ratio were 3000. Another sample of sulfur and hydrogen doped amorphous carbon prepared under the same processing conditions was subjected to combustion analysis and the hydrogen to carbon atomic ratio was determined to be 1.4.

Example 6 Create a Plasma Glow Discharge The method described in Example 1 was repeated except that the RF power was 200 watts and the substrate was placed in the etch tunnel within the reaction chamber. The etch tunnel is circumferential with the reaction chamber but has a smaller diameter (approximately 1
2.5 crn) and sealed by a circular end plate at the end closest to the gas outlet of one reaction chamber. The aluminum tube and end plates were perforated with a network of small holes that allowed gas phase species to enter the tunnel. Etched tunnel conductive aluminum has essentially zero electric field within the tunnel.

It acts as an equipotential surface so that the plasma is mainly confined to the annular region between the tunnel and the reaction chamber wall.

This allows the radicals and ions produced by the °C plasma to reach the substrate and form a °C film, but if the plasma were to come into contact with the substrate, they would probably be accelerated into the substrate by the plasma sheath that would form. The bombardment of the substrate by highly active ions, which are considered to be sacrificial, is reduced.

The resulting Ty'4 yellow and hydrogen doped amorphous carbon film has a thickness of 2800 angstrom units and a dark conductivity of 3.7 x 10-16 ohm, -rn
-', photoconductivity is 2.8x10. -13 ohm-'
LM-' and photoconductivity ratio were 760.

Example 7 The method described in Example 1 was repeated except that a capacitively coupled plasma reaction system of the type shown in FIG. 2 was used. The plasma reaction system used a stainless steel reaction chamber. Furthermore, the electrodes had a diameter of 15 cm and a mutual spacing of 5 cm. A high frequency power of 79 watts was applied to the glow discharge, and the substrate was maintained at a temperature of 600° C. during deposition.

The deposition differed from Example 1 in that the deposition was carried out for 135 minutes and the doped amorphous carbon film was deposited by electric discharge at 0.degree. C. in a mixture of acetylene, hydrogen and hydrogen sulfide. Each gas was passed through the reaction chamber at a flow rate that resulted in a partial pressure within the reaction chamber of 30 millitorr of acetylene, 9 millitorr of hydrogen, and 1 millitorr of hydrogen sulfide. The thickness of the obtained sulfur and hydrogen doped amorphous carbon film was 6
000 angstrom unit, dark conductivity is 5×10
Ohm-'tM-', photoconductivity is 4.3 x 10-1
3 ohm-1 crn" and the photoconductivity ratio was 860.

Example 8 Acetylene 10 mtorr, hydrogen 4.5 mtorr.

The procedure set forth in Example 7 was repeated except that each gas was passed through the reaction chamber at a flow rate that produced a partial pressure in the reaction chamber of 0.5 mTorr and hydrogen sulfide. The resulting sulfur and hydrogen doped amorphous carbon film had a thickness of 6000 angstrom units and a sulfur to carbon atomic ratio of 0.032. Dark conductivity is 1x10 ohm-1 sub-1, photoconductivity is 1. I
X 10-12 ohms-'ff1-''.

and photoconductivity ratio was 1100.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an inductively coupled plasma reactor system suitable for use in preparing the sulfur and hydrogen doped amorphous carbon of the present invention. FIG. 2 is a schematic diagram of a capacitively coupled plasma reactor system suitable for use in preparing the sulfur and hydrogen doped amorphous carbon of the present invention. (5 other people) FIG, 2

Claims (20)

[Claims] (1) prepared by a method comprising depositing amorphous carbon doped with sulfur and hydrogen by plasma glow discharge in a gas mixture consisting of at least one hydrocarbon and at least one source of sulfur; Amorphous carbon doped with sulfur and hydrogen. (2) The doped amorphous carbon of claim 1, wherein the gas mixture further contains hydrogen. (3) The doped amorphous carbon of claim 1, wherein the sulfur source is selected from the group consisting of volatile inorganic sulfur compounds. (4) The doped amorphous carbon according to claim 1, wherein the sulfur source is selected from the group consisting of hydrogen sulfide and sulfur hexafluoride. (5) The doped anatomical carbon of claim 1, wherein the hydrocarbon is selected from the group consisting of alkanes, alkenes, and algines. (6) The doped amorphous carbon according to claim 5, wherein the hydrocarbon is selected from the group consisting of methane, ethylene, and acetylene. (7) The composition of the gas mixture is adjusted to provide an atomic ratio of hydrogen to carbon in the doped amorphous carbon ranging from about 0.1 to about 2.0. The doped amorphous carbon according to item 1. (8) Adjusting the amount of the sulfur source in the gas mixture to provide a sulfur to carbon atomic ratio in the doped amorphous carbon ranging from about 0.005 to about 0.20. The doped amorphous carbon according to claim 1 in the range of . 9. The doped amorphous carbon of claim 1, wherein said gas mixture is at a pressure within the range of about 0.005 to about 0.5 torr. (10) (a) initiating and sustaining a plasma glow discharge in a gas mixture comprising at least one hydrocarbon and at least one sulfur source; and (b) amorphous doped by the plasma glow discharge. Depositing carbon onto a substrate; A method for producing an amorphous carbon film doped with sulfur and hydrogen, comprising the steps described above. (11) The method according to claim 10, wherein the gas mixture further includes at least one gas selected from the group consisting of hydrogen, helium, and argon. 12. The method of claim 11, wherein the gas mixture further comprises hydrogen. (13) The method according to claim 10, wherein the sulfur source is selected from the group consisting of volatile inorganic sulfur compounds. (14) The method according to claim 13, wherein the sulfur source is selected from the group consisting of hydrogen sulfide and sulfur hexafluoride. (15) The method according to claim 10, wherein the hydrocarbon is selected from the group consisting of alkanes, alkenes, and algines. (16) The method according to claim 15, wherein the hydrocarbon is selected from the group consisting of methane, ethylene, and acetylene. 17. Adjusting the amount of the sulfur source in the gas mixture to provide a film having an atomic ratio of sulfur to carbon within the range of about 0.005 to about 0.20. The method described in. (18) Adjusting the amount of the sulfur source in the gas mixture to form the doped amorphous carbon from about 0.005 to about 0.00.
11. A method according to claim 10, which provides a sulfur to carbon atomic ratio within the range of 20. (19) adjusting the amount of the sulfur source in the gas mixture so that the amount of sulfur in the doped amorphous carbon is from about 0.01 to about 0;
11. A method according to claim 10 which provides a sulfur to carbon atomic ratio within the range of 0.05. 20. The method of claim 10, wherein the gas mixture is at a pressure in the range of about 0.005 to about 0.5 torr.