- Email: [email protected]
R.f. plasma-assisted deposition of diamond-like carbon films from methanol—water vapour mixture
DIAMOND AND RELATED MATERIALS ELSEVIER
Diamond and Related Materials 4 ( 1994} 15 19
R.f. plasma-assisted deposition of diamond-like carbon films from methanol-water vapour mixture Manoj Komath a, Madhukar Zambare
b S.A. Gangal b, S.K. Kulkarni c
a Department of Physics, Sardar Patel University, Vallabh Vidyanagar, Gujarat, India b Department of Electronic Sciences, University ofPoona, Pune-7, India c Department q['Physics, University ofPoona. Pune-7, India
Received 20 October 1993; accepted in final form 11 April 1994
Abstract Carbon films have been deposited in a parallel-plate r.f. CVD reactor using methanol-water vapour mixture as precursor, without any carrier or diluent gas. The various characterization tests showed that the films obtained at the optimum experimental conditions are typical DLC material. The notable feature of the experiment is that factors such as complexity of the set-ups, safety measures against hazards and costly precursor/carrier gases are avoided. This demonstration appears to be a positive step towards the more economical and convenient synthesis of DLC. Keywords: Diamond-like carbon; Electron spectroscopy; Transmission electron microscopy; X-ray diffraction
1. Introduction Hard, dense and amorphous carbon coatings, popularly known as diamond-like carbon (DLC) films, are materials of importance to both scientific and industrial communities [ 1,2]. Along with high values of hardness, these films possess very good thermal conductivity, large values of electrical resistivity, good optical transparency and chemical stability comparable to that of diamond. The unique combination of these properties opens up many potential avenues of application [2]. Generally, ion beam, sputtering and plasma processes yield DLC films at lower ion impact energies. Numerous methods for depositing DLC films have been developed based on the above processes, in which a variety of source gases, such as methane, butane and acetylene, are used along with hydrogen and argon [ 1,2]. During recent years research on DLC materials has showed remarkable progress [-3-5]. Various aspects of the structure, properties and application of DLC are being intensively studied. Also, the search is still going on to find more efficient and economical routes to synthesize diamond and DLC materials [4,5]. The present paper reports a more simple and straightforward way to synthesize good-quality DLC films. It describes the deposition of carbon films in a parallelplate r.f. CVD reactor with methanol water vapour 0925-9635,94/$07.00© 1994ElsevierScienceS.A. All rights reserved SSDI 0925-9635(94)00216-E
mixture as precursor, following the method pioneered by Rudder et al. [6]. Hydrogen, the indispensable carrier gas used in DLC film deposition, is avoided here, exploiting the fact that the decomposition of water in an r.f. field gives nascent hydrogen. The use of non-hazardous reagents ensures operational safety. Methanol, the starting material, mixes well with water and therefore a single solution in the right proportion can be evaporated and admitted to the reaction chamber. This avoids complexity of the experimental arrangement.
2. Experiment The experimental set-up is a parallel-plate reactor (flow type), similar to the one described in an earlier report [-7]. The chamber is a pyrolytic glass dome of 10 cm diameter and 40 cm length, with a capillary inlet at the apex. It is fitted horizontally on a vertical metal base using a metal flange and gasket. Two parallel electrodes (10 cm x 5 cm rectangular copper plates supported by brass rods) are inserted horizontally into the chamber through the base, with proper insulation. The vacuum outlet is given on to the base and connected to a rotary pump through foreline traps. The precursor solution (20% methanol in water, the proportion of which is decided by the partial vapour
16
M. Komath et al. / Diamond and Related Materials 4 (1994) 15-19
pressures) is taken in an airtight container and connected to the capillary inlet through a rotameter. A preevacuation of the container will produce the precursor vapour mixture. The vapours are admitted to the chamber at the required flow rates by using a needle valve. Pumping through the chamber base outlet will facilitate a lateral flow of vapours between the electrode plates. The r.f. power from a 13.56 MHz generator is fed to the lower electrode through a matching unit, and the upper electrode is grounded. Hard carbon deposition is observed particularly on the powered electrode because it develops a negative self-bias voltage, which enhances the settling of positively charged carbon species [8]. The cleaned substrates are kept fiat on the lower electrode. In the experimental runs, at higher values of RF power and vacuum, sputtering of the substrates was observed. This effect was employed to clean the substrate surfaces before starting the deposition. The experiments have been conducted for different combinations of r.f. power, flow rates and chamber pressures. The nature of the deposits varied according to the conditions: from sooty to graphitic and from polymeric to diamond-like. The appearance of the diamond-like properties can be identified by the scratch and corrosion resistance tests [9]. The deposition conditions were optimized so that optically transparent, scratch-resistant films that are passive to corrosive chemicals were obtained. The optimized conditions under which DLC films were prepared are given in Table 1.
presence of carbon only, except for traces of adsorbed oxygen. The carbon ls profile was centered at 285.8 eV, showing the richness of tetrahedrally bonded carbon (either C-C or C-H bonding). This value was close to the BE value for natural diamond, 285.7 eV. There was no notable component at 284.15 eV, which ruled out the possibility of free graphite incorporation in the film (Fig. 1). The films were analysed in a transmission electron microscope. The sample separation was achieved by dissolving the silicon substrate in hot HF-HNOa mixture. The floated film was then rinsed in distilled water and spread over the specimen grid. The film seemed uniform in texture with embedded particles inside, with sizes up to 60 nm. (The TEM image at a beam energy of 80 kV is shown in Fig. 2.) The particles showed good crystalline structure in transmission electron diffraction (TED), giving a hexagonal spot pattern (Fig. 3). The corresponding d-values of the material and the reported d-values of other crystalline forms of carbon [ 10] are given in Table 2. The rest of the film showed a highly diffused set of diffraction rings, usually seen in amorphous carbon coatings [ 11 ]. Analyses done in a low angle X-ray diffractometer at an incident angle of 0.5 o yielded peaks matching with the d-values shown by TED (Fig. 4). The presence of
3. Results and discussion The films were deposited for different lengths of time and the thicknesses were measured using multiple-beam interferometry. The average growth rate at the specified conditions was found to be 3 ,~ min- 1. Films on different substrates with appropriate thickness were subjected to various tests and analyses. The presence of carbon was tested by X-ray photoelectron spectroscopy (XPS). The binding energy (BE) spectrum of approx. 1000 ~, thick film on silicon was obtained using A1 K~ X-rays. Gold foil in firm contact with the sample and the holder served as a reference (Au 4f7/2 at 84.0 eV). The survey spectrum showed the
.o"
t/) Z hi Z
Table 1 The optimum conditions of deposition R.f. frequency (MHz) R.f. power (W) Precursor Vapour flow (cm 3 min-1) Substrates
13.56 50 20% CHaOH in H20 20 Si( 111 ), glass, quartz (unheated)
280 --
282
284
BINDING
286
288
290
ENERGY(eV}---~
Fig. 1. C(ls) XPS of the DLC film obtained at the optimum experimental conditions along with the spectra of graphite and natural diamond standards.
17
M. Komath et al. / Diamond and Related Materials 4 11994) 15 19
Table 2 Comparison of the d-values calculated from TED with that of the other crystalline forms of carbon Set of spots
Calculated Reported d-valuesa d-values (,~} Cubic L o n s d a l e i t e Graphite diamond d (A)
1
2.(!02
2.06
2 3
1.170 1.000
1.26 1.07
(170 ) d (A)
(l/io)
d (f~)
2.19 (100) 2.06 1.92 1.50 (25) (16)
3.36 (1001 (1001 2.03 (50) (25) 1.67 1.25 1.15
(I/Io)
(100) (50) (80) (39) (50)
a From JCPDS Data Cards. The d-values of peaks with insignificant intensities are not quoted.
Fig. 2. Transmission electron micrograph of the film. The scale mark corresponds to 200 nm.
20
30
40
50
60
70
BO
90
2. e ° ~
Fig. 4. XRD spectrum of the film.
Fig. 3. Transmission electron diffraction given by the particles seen in Fig. 2.
the a m o r p h o u s c a r b o n was seen as a b r o a d h u m p a r o u n d 25 ° of 20 value. The s c a n n i n g electron microscope (Fig. 5) revealed densely populated nucleation sites t h r o u g h o u t the surface, with sizes less than a micrometre. In a d d i t i o n to this roughness the overall surface m o r p h o l o g y is reticulated. An optical a b s o r p t i o n study has been done on a 500 a film deposited on quartz substrate in a U V - V i s spectrop h o t o m e t e r (the t r a n s m i s s i o n spectrum is shown in Fig. 6). The film was fairly t r a n s p a r e n t in the visible
Fig. 5. Scanning electron micrograph of the surface of the film.
region. A strong a b s o r p t i o n could be observed below 460 n m a n d the film went o p a q u e b e y o n d 300 rim. The optical a b s o r p t i o n data have been analysed to deduce the optical energy gap [12,13]. The energy gap
18
M. Komath et al. / Diamond and Related Materials 4 (1994) 15-19
80 /
11.0
f
60
/
e'
I0.0
¢
40
/
9.0
# # 0
/
8.o
A / /
r
i
250
350
450
i
i
550
650
/
i
750
850
/
7.0
A A
Fig. 6. UV-Vis transmission spectrum of the film. 6.0
l~S corresponding to indirect allowed transitions was calculated to be 2.35 eV. The infrared spectrum of the film did not give any appreciable absorption at about 2900 cm -1, where the various C-H stretching bands are expected [9]. This may probably be due to the low hydrogen concentration in the film. The relatively high optical gap of the film (the nominal value observed [3,5] for DLC is about 1.7 eV) also indicates the same [14]. Electrical measurements were done on films deposited on glass plates. Two evaporated silver contacts were made on both ends of a strip of the film and the resistance was measured. The films were found to be insulating, with a resistivity of about 2 x 106 ~ cm. The dependence of the resistivity on temperature has also been assessed by heating the sample in vacuum. The Arrhenius plot (Fig. 7) shows that the film possesses the typical behaviour of an intrinsic semiconductor. The thermal activation energy for the intrinsic conduction region was found to be 1.24 eV. This could be compared with the optical gap energy, which by theory should be double the thermal activation energy. The films have been tested against a wide range of corrosive chemicals: organic solvents (ether, acetone, benzene etc.), various kinds of acid (HC1, H2SO4, HNOs, HF and their mixtures) and alkalis (KOH, NaOH). The films were found to be passive to these reagents. To get an idea about the hardness, the scratch test was performed following Bierbaum's method [15]. In this method, the films are scratched with a diamond tip under a known load and, from the width of the groove, a rough estimation of the Vickers hardness is made. The value obtained was 3080 kg mm-2, nearer to that of SiC (3500 kg mm-2). The results of various characterization tests showed that the films obtained are comparable in many respects with the DLC films reported by other workers [3,53.
~'.o
2'.s
£o
3'.5
I0~'T Fig. 7. Arrhenius plot of the resistivity changes with temperature.
4. Conclusion The deposition of carbon films has been successfully done in a parallel-plate r.f. reactor using only methanolwater vapour mixture. At the optimized conditions, good DLC material was obtained. It showed high hardness and chemical stability. The optical transparency was fairly good. The material possessed a resistivity in the range of a few Mf~ cm and the electrical conduction properties were similar to that of an intrinsic semiconductor. The bandgap was found to be 2.35eV. Transmission electron microscopy showed crystalline particles of nanometer sizes embedded in the film. Thus the method demonstrated here, deposition in a parallel-plate r.f. reactor from methanol-water vapour mixture, proves to be a promising one in which DLC synthesis can be done economically and conveniently.
Acknowledgements The authors are grateful to Dr. Shubha Gokhle and Mr. K.D. Patel for their help in the experiment. M.K. acknowledges the CSIR, India, for Research Fellowship and S.K.K. thanks UGC, India for financial support.
References [1] R.C. DeVries, Ann. Rev. Mater. Sci., 17 (1987) 161. [2] J.C. Angus and C.C. Hayman, Science, 241 (1988) 913. [3] Y. Tzeng, M. Yoshikawa, M. Murakawa and A. Feldman (eds.), Applications of Diamond Films and Related Materials, Materials Science Monographs, Elsevier, New York, Vol. 73, 1991.
M. Komath et al. / Dh~mond and Related Mater&& 4 (1994) 15--19
[4] J.C. Angus, Thin Solid Films, 216 (1992) 126. [5] Proc. Diamond Films '93, 4th European Conf. on Diamond, Diamond-like and Related Materials, Algarve, Portugal, 20-.24 September 1993, Diamond Relat. Mater., 3 (1994). [6] R.A. Rudder, G.C. Hudson, J.B. Posthill, R.E. Thomas, R.C. Hendry, D.P. Malta, R.J. Markunas, T.P. Humphreys and R.J. Nemanich, Appl. Phys. Lett., 60 (1992) 329. [7] A. Joshi, S.K. Kulkarni and S.A. Gangal J. Appl. Phys., 64 (1988) 6668. E8] L. Holland and S.M. Ojha, Thin Solid Films, 58 (1979) 107. [9] P. Couderc and Y. Catherine, Thin Solid Films, 146 (1987) 93.
19
[10] X-Ray Diffraction Data Cards, Joint Committee on Powder Diffraction Standards, Philadelphia, PA, USA, 1974. [11] D.A. Anderson, Philos. Mag., 35 (1977) 17. [12] P.A. Lee, G. Said, R. Davies and T.H. Lira, J. Phys. Chem. Solids, 30 (1969) 2719. [131 J. Tauc, R~ Grigorovic and A. Vancu, Phys. Status Solidi, 15 ( 1966} 627. [14] R.H. Jarman, G.J. Ray, R.W. Standley and G.W. Zajac, Appl. Phys. Lett.. 49 (1986) 1065. [15] Hsiao chu Tsai and D.B. Bogy, J. ~tc. Sci. Technol.. A5 ( 19871 3287.
Diamond and Related Materials 4 ( 1994} 15 19
R.f. plasma-assisted deposition of diamond-like carbon films from methanol-water vapour mixture Manoj Komath a, Madhukar Zambare
b S.A. Gangal b, S.K. Kulkarni c
a Department of Physics, Sardar Patel University, Vallabh Vidyanagar, Gujarat, India b Department of Electronic Sciences, University ofPoona, Pune-7, India c Department q['Physics, University ofPoona. Pune-7, India
Received 20 October 1993; accepted in final form 11 April 1994
Abstract Carbon films have been deposited in a parallel-plate r.f. CVD reactor using methanol-water vapour mixture as precursor, without any carrier or diluent gas. The various characterization tests showed that the films obtained at the optimum experimental conditions are typical DLC material. The notable feature of the experiment is that factors such as complexity of the set-ups, safety measures against hazards and costly precursor/carrier gases are avoided. This demonstration appears to be a positive step towards the more economical and convenient synthesis of DLC. Keywords: Diamond-like carbon; Electron spectroscopy; Transmission electron microscopy; X-ray diffraction
1. Introduction Hard, dense and amorphous carbon coatings, popularly known as diamond-like carbon (DLC) films, are materials of importance to both scientific and industrial communities [ 1,2]. Along with high values of hardness, these films possess very good thermal conductivity, large values of electrical resistivity, good optical transparency and chemical stability comparable to that of diamond. The unique combination of these properties opens up many potential avenues of application [2]. Generally, ion beam, sputtering and plasma processes yield DLC films at lower ion impact energies. Numerous methods for depositing DLC films have been developed based on the above processes, in which a variety of source gases, such as methane, butane and acetylene, are used along with hydrogen and argon [ 1,2]. During recent years research on DLC materials has showed remarkable progress [-3-5]. Various aspects of the structure, properties and application of DLC are being intensively studied. Also, the search is still going on to find more efficient and economical routes to synthesize diamond and DLC materials [4,5]. The present paper reports a more simple and straightforward way to synthesize good-quality DLC films. It describes the deposition of carbon films in a parallelplate r.f. CVD reactor with methanol water vapour 0925-9635,94/$07.00© 1994ElsevierScienceS.A. All rights reserved SSDI 0925-9635(94)00216-E
mixture as precursor, following the method pioneered by Rudder et al. [6]. Hydrogen, the indispensable carrier gas used in DLC film deposition, is avoided here, exploiting the fact that the decomposition of water in an r.f. field gives nascent hydrogen. The use of non-hazardous reagents ensures operational safety. Methanol, the starting material, mixes well with water and therefore a single solution in the right proportion can be evaporated and admitted to the reaction chamber. This avoids complexity of the experimental arrangement.
2. Experiment The experimental set-up is a parallel-plate reactor (flow type), similar to the one described in an earlier report [-7]. The chamber is a pyrolytic glass dome of 10 cm diameter and 40 cm length, with a capillary inlet at the apex. It is fitted horizontally on a vertical metal base using a metal flange and gasket. Two parallel electrodes (10 cm x 5 cm rectangular copper plates supported by brass rods) are inserted horizontally into the chamber through the base, with proper insulation. The vacuum outlet is given on to the base and connected to a rotary pump through foreline traps. The precursor solution (20% methanol in water, the proportion of which is decided by the partial vapour
16
M. Komath et al. / Diamond and Related Materials 4 (1994) 15-19
pressures) is taken in an airtight container and connected to the capillary inlet through a rotameter. A preevacuation of the container will produce the precursor vapour mixture. The vapours are admitted to the chamber at the required flow rates by using a needle valve. Pumping through the chamber base outlet will facilitate a lateral flow of vapours between the electrode plates. The r.f. power from a 13.56 MHz generator is fed to the lower electrode through a matching unit, and the upper electrode is grounded. Hard carbon deposition is observed particularly on the powered electrode because it develops a negative self-bias voltage, which enhances the settling of positively charged carbon species [8]. The cleaned substrates are kept fiat on the lower electrode. In the experimental runs, at higher values of RF power and vacuum, sputtering of the substrates was observed. This effect was employed to clean the substrate surfaces before starting the deposition. The experiments have been conducted for different combinations of r.f. power, flow rates and chamber pressures. The nature of the deposits varied according to the conditions: from sooty to graphitic and from polymeric to diamond-like. The appearance of the diamond-like properties can be identified by the scratch and corrosion resistance tests [9]. The deposition conditions were optimized so that optically transparent, scratch-resistant films that are passive to corrosive chemicals were obtained. The optimized conditions under which DLC films were prepared are given in Table 1.
presence of carbon only, except for traces of adsorbed oxygen. The carbon ls profile was centered at 285.8 eV, showing the richness of tetrahedrally bonded carbon (either C-C or C-H bonding). This value was close to the BE value for natural diamond, 285.7 eV. There was no notable component at 284.15 eV, which ruled out the possibility of free graphite incorporation in the film (Fig. 1). The films were analysed in a transmission electron microscope. The sample separation was achieved by dissolving the silicon substrate in hot HF-HNOa mixture. The floated film was then rinsed in distilled water and spread over the specimen grid. The film seemed uniform in texture with embedded particles inside, with sizes up to 60 nm. (The TEM image at a beam energy of 80 kV is shown in Fig. 2.) The particles showed good crystalline structure in transmission electron diffraction (TED), giving a hexagonal spot pattern (Fig. 3). The corresponding d-values of the material and the reported d-values of other crystalline forms of carbon [ 10] are given in Table 2. The rest of the film showed a highly diffused set of diffraction rings, usually seen in amorphous carbon coatings [ 11 ]. Analyses done in a low angle X-ray diffractometer at an incident angle of 0.5 o yielded peaks matching with the d-values shown by TED (Fig. 4). The presence of
3. Results and discussion The films were deposited for different lengths of time and the thicknesses were measured using multiple-beam interferometry. The average growth rate at the specified conditions was found to be 3 ,~ min- 1. Films on different substrates with appropriate thickness were subjected to various tests and analyses. The presence of carbon was tested by X-ray photoelectron spectroscopy (XPS). The binding energy (BE) spectrum of approx. 1000 ~, thick film on silicon was obtained using A1 K~ X-rays. Gold foil in firm contact with the sample and the holder served as a reference (Au 4f7/2 at 84.0 eV). The survey spectrum showed the
.o"
t/) Z hi Z
Table 1 The optimum conditions of deposition R.f. frequency (MHz) R.f. power (W) Precursor Vapour flow (cm 3 min-1) Substrates
13.56 50 20% CHaOH in H20 20 Si( 111 ), glass, quartz (unheated)
280 --
282
284
BINDING
286
288
290
ENERGY(eV}---~
Fig. 1. C(ls) XPS of the DLC film obtained at the optimum experimental conditions along with the spectra of graphite and natural diamond standards.
17
M. Komath et al. / Diamond and Related Materials 4 11994) 15 19
Table 2 Comparison of the d-values calculated from TED with that of the other crystalline forms of carbon Set of spots
Calculated Reported d-valuesa d-values (,~} Cubic L o n s d a l e i t e Graphite diamond d (A)
1
2.(!02
2.06
2 3
1.170 1.000
1.26 1.07
(170 ) d (A)
(l/io)
d (f~)
2.19 (100) 2.06 1.92 1.50 (25) (16)
3.36 (1001 (1001 2.03 (50) (25) 1.67 1.25 1.15
(I/Io)
(100) (50) (80) (39) (50)
a From JCPDS Data Cards. The d-values of peaks with insignificant intensities are not quoted.
Fig. 2. Transmission electron micrograph of the film. The scale mark corresponds to 200 nm.
20
30
40
50
60
70
BO
90
2. e ° ~
Fig. 4. XRD spectrum of the film.
Fig. 3. Transmission electron diffraction given by the particles seen in Fig. 2.
the a m o r p h o u s c a r b o n was seen as a b r o a d h u m p a r o u n d 25 ° of 20 value. The s c a n n i n g electron microscope (Fig. 5) revealed densely populated nucleation sites t h r o u g h o u t the surface, with sizes less than a micrometre. In a d d i t i o n to this roughness the overall surface m o r p h o l o g y is reticulated. An optical a b s o r p t i o n study has been done on a 500 a film deposited on quartz substrate in a U V - V i s spectrop h o t o m e t e r (the t r a n s m i s s i o n spectrum is shown in Fig. 6). The film was fairly t r a n s p a r e n t in the visible
Fig. 5. Scanning electron micrograph of the surface of the film.
region. A strong a b s o r p t i o n could be observed below 460 n m a n d the film went o p a q u e b e y o n d 300 rim. The optical a b s o r p t i o n data have been analysed to deduce the optical energy gap [12,13]. The energy gap
18
M. Komath et al. / Diamond and Related Materials 4 (1994) 15-19
80 /
11.0
f
60
/
e'
I0.0
¢
40
/
9.0
# # 0
/
8.o
A / /
r
i
250
350
450
i
i
550
650
/
i
750
850
/
7.0
A A
Fig. 6. UV-Vis transmission spectrum of the film. 6.0
l~S corresponding to indirect allowed transitions was calculated to be 2.35 eV. The infrared spectrum of the film did not give any appreciable absorption at about 2900 cm -1, where the various C-H stretching bands are expected [9]. This may probably be due to the low hydrogen concentration in the film. The relatively high optical gap of the film (the nominal value observed [3,5] for DLC is about 1.7 eV) also indicates the same [14]. Electrical measurements were done on films deposited on glass plates. Two evaporated silver contacts were made on both ends of a strip of the film and the resistance was measured. The films were found to be insulating, with a resistivity of about 2 x 106 ~ cm. The dependence of the resistivity on temperature has also been assessed by heating the sample in vacuum. The Arrhenius plot (Fig. 7) shows that the film possesses the typical behaviour of an intrinsic semiconductor. The thermal activation energy for the intrinsic conduction region was found to be 1.24 eV. This could be compared with the optical gap energy, which by theory should be double the thermal activation energy. The films have been tested against a wide range of corrosive chemicals: organic solvents (ether, acetone, benzene etc.), various kinds of acid (HC1, H2SO4, HNOs, HF and their mixtures) and alkalis (KOH, NaOH). The films were found to be passive to these reagents. To get an idea about the hardness, the scratch test was performed following Bierbaum's method [15]. In this method, the films are scratched with a diamond tip under a known load and, from the width of the groove, a rough estimation of the Vickers hardness is made. The value obtained was 3080 kg mm-2, nearer to that of SiC (3500 kg mm-2). The results of various characterization tests showed that the films obtained are comparable in many respects with the DLC films reported by other workers [3,53.
~'.o
2'.s
£o
3'.5
I0~'T Fig. 7. Arrhenius plot of the resistivity changes with temperature.
4. Conclusion The deposition of carbon films has been successfully done in a parallel-plate r.f. reactor using only methanolwater vapour mixture. At the optimized conditions, good DLC material was obtained. It showed high hardness and chemical stability. The optical transparency was fairly good. The material possessed a resistivity in the range of a few Mf~ cm and the electrical conduction properties were similar to that of an intrinsic semiconductor. The bandgap was found to be 2.35eV. Transmission electron microscopy showed crystalline particles of nanometer sizes embedded in the film. Thus the method demonstrated here, deposition in a parallel-plate r.f. reactor from methanol-water vapour mixture, proves to be a promising one in which DLC synthesis can be done economically and conveniently.
Acknowledgements The authors are grateful to Dr. Shubha Gokhle and Mr. K.D. Patel for their help in the experiment. M.K. acknowledges the CSIR, India, for Research Fellowship and S.K.K. thanks UGC, India for financial support.
References [1] R.C. DeVries, Ann. Rev. Mater. Sci., 17 (1987) 161. [2] J.C. Angus and C.C. Hayman, Science, 241 (1988) 913. [3] Y. Tzeng, M. Yoshikawa, M. Murakawa and A. Feldman (eds.), Applications of Diamond Films and Related Materials, Materials Science Monographs, Elsevier, New York, Vol. 73, 1991.
M. Komath et al. / Dh~mond and Related Mater&& 4 (1994) 15--19
[4] J.C. Angus, Thin Solid Films, 216 (1992) 126. [5] Proc. Diamond Films '93, 4th European Conf. on Diamond, Diamond-like and Related Materials, Algarve, Portugal, 20-.24 September 1993, Diamond Relat. Mater., 3 (1994). [6] R.A. Rudder, G.C. Hudson, J.B. Posthill, R.E. Thomas, R.C. Hendry, D.P. Malta, R.J. Markunas, T.P. Humphreys and R.J. Nemanich, Appl. Phys. Lett., 60 (1992) 329. [7] A. Joshi, S.K. Kulkarni and S.A. Gangal J. Appl. Phys., 64 (1988) 6668. E8] L. Holland and S.M. Ojha, Thin Solid Films, 58 (1979) 107. [9] P. Couderc and Y. Catherine, Thin Solid Films, 146 (1987) 93.
19
[10] X-Ray Diffraction Data Cards, Joint Committee on Powder Diffraction Standards, Philadelphia, PA, USA, 1974. [11] D.A. Anderson, Philos. Mag., 35 (1977) 17. [12] P.A. Lee, G. Said, R. Davies and T.H. Lira, J. Phys. Chem. Solids, 30 (1969) 2719. [131 J. Tauc, R~ Grigorovic and A. Vancu, Phys. Status Solidi, 15 ( 1966} 627. [14] R.H. Jarman, G.J. Ray, R.W. Standley and G.W. Zajac, Appl. Phys. Lett.. 49 (1986) 1065. [15] Hsiao chu Tsai and D.B. Bogy, J. ~tc. Sci. Technol.. A5 ( 19871 3287.