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Nitrogen ion implantation of silicon-containing diamond-like carbon (Si-DLC) coatings synthesized by ion beam assisted deposition
Surface and Coatings Technology 103–104 (1998) 104–108
Nitrogen ion implantation of silicon-containing diamond-like carbon (Si-DLC ) coatings synthesized by ion beam assisted deposition Costas G. Fountzoulas *, J. Derek Demaree, James K. Hirvonen, James D. Kleinmeyer Weapons and Materials Research Directorate, Army Research Laboratory, Aberdeen Proving Ground, MD 21005-5069, USA
Abstract Hard, adherent, and low-friction silicon containing diamond-like carbon coatings (Si-DLC ) have been synthesized by 40 keV Ar+ ion beam assisted deposition (IBAD) of tetraphenyl-tetramethyl-trisiloxane oil, on 8.90 cm (3.5 in) diameter aluminum alloy substrates. The Si-DLC coatings were implanted with nitrogen ions to doses of 3×1015, 3×1016, and 3×1017 ions/cm2. The Si-DLC coating synthesis and the subsequent nitrogen ion implantation at 80 keV took place in a non-mass analyzed ion implanter. The thickness of the implanted coatings, measured with the aid of a profilometer, remained equal to the thickness of the unimplanted coating, and photon tunneling microscopy showed some surface roughening from the implantation process. The unlubricated steel ball-on-disk friction coefficient increased with increasing implant dose. However, the wear rate of the coating, determined with the aid of an optical microscope and a stylus profilometer, decreased with increasing implant dose. © 1998 Elsevier Science S.A. Keywords: Ion implantation; Nitrogen; Si-DLC
1. Introduction The technique of ion implantation is now a well established process in the semiconductor industry and was developed during the early 1960s as a method to introduce precise quantities of dopant ions into semiconductor materials. Since the early 1970s the modification of the surface properties of materials, particularly metals, by ion implantation has been an active field of investigation in numerous laboratories all over the world as documented by the past and present papers from this conference series. It has been demonstrated that properties such as hardness, wear resistance, coefficient of friction, fatigue strength, film adhesion, and corrosion resistance, may be significantly improved by ion implantation [1–6 ]. Coatings of many materials, including conventional diamond-like carbon (DLC ), have been successfully deposited by ion beam assisted deposition (IBAD) and are highly promising for tribological applications requiring high hardness and low friction coefficients. The friction coefficient of unlubricated DLC films in dry gases can be as low as 0.01 but generally increases with * Corresponding author. Fax: +1 410 306 0829; e-mail: [email protected] 0257-8972/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved. PII S 02 5 7 -8 9 7 2 ( 9 8 ) 0 0 38 1 - 8
increasing humidity, reaching values between 0.10 and 0.20 in a 10% relative humidity [7–9]. It has been shown by various researchers [7–9] that conventional DLC films containing silicon or various metallic elements such as Ti exhibit low friction coefficients even in humid environments. Si-DLC films exhibit friction coefficients as low as 0.04 at ambient humidity and temperature and have promise for tribological applications. The effect of ion implantation on single-crystalline and on polycrystalline diamond films solely for electronic applications has been examined by many researchers [10–14], but this is, to our knowledge, the first investigation of implantation Si-DLC for tribological applications. The goal of this investigation was to describe the effect of nitrogen ion implantation on the wear properties of Si-DLC; properties of these coatings without ion implantation have been described previously [15].
2. Experimental details A ZYMET 100 non-mass analyzed ion implanter was used for the synthesis and subsequent nitrogen ion implantation of Si-DLC coated specimens using ener-
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Fig. 1. (a) TRIM simulation of nitrogen ion implantation (60% N2++40% N+) of Si-DLC coating; (b) actual implantation profile obtained by RBS.
getic Ar+ ion bombardment of a vapor deposited tetraphenyl-tetramethyl-trisiloxane (Dow-Corning 704) diffusion pump oil [15]. The diffusion pump oil precursor was evaporated from a copper oil container through a 3 mm diameter aperture. The substrates were initially cleaned in methanol and acetone and then sputtercleaned with a 40 keV Ar+ beam (40 mA/cm2) for 10 min. The temperature of the substrate for both the synthesis and implantation was maintained close to room temperature using conducting grease to hold the sample on a water-cooled sample stage. The substrate was inclined at 45° with respect to both the horizontal ion beam and the vertical flow direction of the vaporized oil. The aperture to substrate distance was 0.15 m. A shutter was placed above the oil container to start and stop the oil deposition. The growing film surface was continuously bombarded by an Ar+ ion beam at 40 keV. The base pressure was 2.66×10−4 Pa (2×10−6 Torr) and the deposition/implantation was carried out at 4×10−3 Pa (3×10−5 Torr) pressure. Three aluminum alloy substrates coated with Si-DLC were cleaned in methanol and acetone and then implanted at 80 keV with nitrogen ions to doses of 3×1015, 3×1016, and 3×1017 ions/cm2 at an approximate current density of 10 mA/cm2. The nitrogen beam was not mass analyzed, and consisted of a mixture of roughly 40% N+ and 60% N+ , yielding about 1.6 2 nitrogen atoms per unit charge. The thickness of the films was measured before and after the implantation with the aid of a Dektak II profilometer, and the surface roughness was measured
with a photon tunneling microscope (Dyer Energy Systems). The microhardness values of the coatings were measured using a Knoop microhardness tester with a 15 g load. An Implant Sciences ball-on-disk tribometer with a 1.27 cm (1/2 in) diameter AISI 52100 chrome alloy steel ball under 0.5 N load was used to determine the unlubricated sliding coefficient of friction. Rutherford backscattering spectrometry (RBS) was performed on some of the films using 2 MeV He+ ions to determine their elemental composition.
3. Results and discussion 3.1. Compositional analysis and TRIM simulation The composition of the Si-DLC films was measured using Rutherford backscattering and forward elastic recoil spectrometry (2 MeV He+, 170° and 22° scattering angles). Using the simulation program RUMP [16 ], the coating composition was determined to be C Si O H Ar [15], which is nearly identical to that 67 9 6 15 3 of the hydrocarbon precursor, except for a decrease in H content and the presence of implanted Ar. This strongly suggests that the siloxane backbone (Si–O–Si–O–Si) of the precursor molecule remains intact during the ion irradiation process, and only C:H and C:C bonds are broken to convert the oil to hard, diamond-like carbon. The presence of the siloxane chains scattered throughout the carbon matrix after deposition is thought to have a strong effect on the
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(a)
(b)
(c)
(d)
Fig. 2. Surface topography of Si-DLC shown by photon tunneling microscopy: (a) unimplanted; (b) 3×1015 nitrogen ions/cm2; (c) 3×1016 nitrogen ions/cm2; (d) 3×1017 nitrogen ions/cm2.
ability of the material to maintain low friction in the presence of humidity. The TRIM Monte Carlo code was used to predict the implanted nitrogen distribution and to calculate the sputtering rate of Si-DLC coating. According to the TRIM simulation results the implanted zone should be about 250 nm thick, with a maximum concentration around 100 nm below the surface ( Fig. 1a). RBS analysis (Fig. 1b) of the implanted Si-DLC showed a retained
nitrogen implant dose of 1.8×1017 ions/cm2 for a delivered dose of 3×1017 ions/cm2, and a peak concentration of 22–27 at% nitrogen at a depth of 70–120 nm. This is in rough agreement with the TRIM prediction for ion range, although RBS was not able to distinguish the expected second peak from 80 keV nitrogen ions. The thickness of the implanted coatings, measured with the aid of a profilometer, remained equal to the thickness of the unimplanted coating, verifying indirectly the low
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107
Fig. 3. Unlubricated ball-on-disk friction coefficient of unimplanted and ion nitrogen implanted Si-DLC coating (dose 3×1016 nitrogen ions/c m2).
scopy revealed that implantation roughened the surface of the Si-DLC (Fig. 2a–d), which probably caused the change in coating color and friction coefficient. X-ray analysis showed that all films were amorphous, both before and after implantation. The resistivity of all coatings, implanted and non-implanted, was above 30 kV cm, that was beyond the maximum measurable value of the four-point probe apparatus used. 3.3. Sliding friction coefficient
Fig. 4. Wear rate and the unlubricated ball-on-disk friction coefficient of ion implanted Si-DLC.
sputtering rate of the Si-DLC coating predicted by TRIM (~0.03) and the absence of further densification by the ion beam.
The unlubricated friction coefficient of the unimplanted Si-DLC coating was 0.12 ( Fig. 3), while the friction coefficient of the implanted Si-DLC coatings increased to 0.18 for a dose of 3×1015 ions/cm2 and to 0.22 for doses of 3×1016 and 3×1017 ions/cm2. The increase of the friction coefficient with increasing ion implantation dose indicates that nitrogen implantation did not lead to graphitization of the implanted coatings. The higher friction coefficient was probably caused by the increased surface roughness.
3.2. Microstructure
3.4. Adhesion, wear and microhardness
The average film thickness was about 1 mm at 3.57 nm/min (0.06 nm/s) growth rate. All Si-DLC coatings, unimplanted and implanted, appeared to be featureless when examined under an ordinary optical microscope (200×). Visual observation revealed that the nitrogen ion implantation discolored the coating from its initial black color to brown, brown–gray, and gray for ion doses of 3×1015, 3×1016, and 3×1017 ions/cm2, respectively. Photon tunneling micro-
The adhesion of the coatings to the aluminum alloy substrates, tested directly by the so-called Scotch-Tape test and indirectly during ball-on-disk wear test measurements, showed no delamination. The wear rate of the coating, determined with the aid of an optical microscope and a stylus profilometer, is very low in the unimplanted case, and decreased further with increasing ion dose. The wear rate for implant doses of 3×1015, 3×1016, and 3×1017 ions/cm2 was determined to be
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95%, 78%, and 67% of the unimplanted wear rate, respectively ( Fig. 4). The decrease of the wear rate with increasing ion implantation dose is an indication of the surface hardening of the implanted Si-DLC coating, an effect seen by others following ion implantation of polymeric surfaces [17]. The average Knoop microhardness of the coatings was 10 GPa, in agreement with our previous results [15]. This is undoubtedly a significant underestimate of the hardness of the implanted material, however, since the implanted zone is roughly 250 nm thick, the coating is 1000 nm thick, and the penetration of the Knoop indenter into the sample is roughly the same as the coating thickness (and is strongly affected by deformation of the softer aluminum alloy substrate underneath).
4. Conclusions Nitrogen ion implantation of amorphous Si-DLC coatings described above yields amorphous, non-conductive coatings with a slightly higher friction coefficient and a significantly lower wear rate than the unimplanted material. Implantation of these coatings, at 80 keV and doses of 3×1015, 3×1016, and 3×1017 ions/cm2 did not cause any graphitization, densification, or other softening of these coatings. Visual and optical microscopy, including photon tunneling microscopy, of these coatings in conjunction with the increase of the unlubricated ball-on-disk friction indicate that nitrogen ion implantation increases the coating surface roughness, but decreases the wear rate of the Si-DLC coating by nearly a factor of 2. Nanohardness measurements of the implanted Si-DLC coating will be conducted in the near future to better understand the effect of ion implantation on the surface of this coating. Ion implantation at higher doses will also be tested in the near future in order to fully understand its impact on the Si-DLC wear properties.
Acknowledgement The authors would like to thank Mr. Jack S. Mullin (ARL) for his help in the optical microscopy of our coatings, and Mr. Dimitar Dimitrov (Dept. of Physics and Astronomy, University of Delaware, Newark, DE 19711) for his help in the X-ray and surface resistivity studies.
References [1] G. Dearnaley, Mater. Sci. Eng. 69 (1985) 139. [2] H. Dimigen, K. Kobs, R. Leutenecker, H. Ryssel, P. Eichinger, Mater. Sci. Eng. 69 (1985) 181. [3] G.K. Hubler, F.A. Smidt, Nucl. Instrum. Meth. B7/8 (1985) 151. [4] B.D. Sartwell, in: R.F. Hochman ( Ed.), Ion Plating and Implantation: Application to Materials, ASM, Materials Park, OH, 1986, pp. 81–89. [5] R.B. Alexander, Nucl. Instrum. Meth. B40/41 (1989) 575. [6 ] J.K. Hirvonen, B. Sartwell, Ion Implantation, ASM Handbook, Vol. 5, Surface Engineering, 1994, p. 605. [7] K. Enke, H. Dimingen, H. Huebsch, Appl. Phys. Lett. 36 (1980) 291. [8] T. Hioki, S. Hibi, T. Hioki, J. Kawamoto, Surf. Coat. Technol. 46 (1991) 233. [9] K. Oguri, T. Arai, J. Mater. Res. 7 (1992) 1313. [10] G.W. Malaczynski, A.H. Hamdi, A.A. Elmoursi, X. Qiu, J. Mater. Eng. Perform. 6 (2) (1997) 223. [11] J.C. Pivin, J. Mater. Sci. 27 (1992) 6735. [12] J.C. Pivin, T.J. Lee, J.H. You, H. Park, F. Davanloo, C.B. Collins, P. Catania, Y. Sampeur, H. Bernas, Nucl. Instrum. Meth. Phys. Res. B80/81 (1991) 1499. [13] K.X. Xhang, J.G. Guo, Y.F. Yao, F. Fang, Vacuum 43 (11) (1992) 1047. [14] A.M. Zaitsev, Nucl. Instrum. Meth. Phys. Res. B62 (1991) 81. [15] C.G. Fountzoulas, J.D. Demaree, W.E. Kosik, W. Franzen, W. Croft, J.K. Hirvonen, Mater. Res. Soc. Symp. Proc. 279 (1993) 645. [16 ] L.R. Doolittle, Nucl. Instrum. Meth. B15 (1980) 227. [17] G.P. Rao, E.H. Lee, J. Mater. Sci. 11 (1996) 2661.
Nitrogen ion implantation of silicon-containing diamond-like carbon (Si-DLC ) coatings synthesized by ion beam assisted deposition Costas G. Fountzoulas *, J. Derek Demaree, James K. Hirvonen, James D. Kleinmeyer Weapons and Materials Research Directorate, Army Research Laboratory, Aberdeen Proving Ground, MD 21005-5069, USA
Abstract Hard, adherent, and low-friction silicon containing diamond-like carbon coatings (Si-DLC ) have been synthesized by 40 keV Ar+ ion beam assisted deposition (IBAD) of tetraphenyl-tetramethyl-trisiloxane oil, on 8.90 cm (3.5 in) diameter aluminum alloy substrates. The Si-DLC coatings were implanted with nitrogen ions to doses of 3×1015, 3×1016, and 3×1017 ions/cm2. The Si-DLC coating synthesis and the subsequent nitrogen ion implantation at 80 keV took place in a non-mass analyzed ion implanter. The thickness of the implanted coatings, measured with the aid of a profilometer, remained equal to the thickness of the unimplanted coating, and photon tunneling microscopy showed some surface roughening from the implantation process. The unlubricated steel ball-on-disk friction coefficient increased with increasing implant dose. However, the wear rate of the coating, determined with the aid of an optical microscope and a stylus profilometer, decreased with increasing implant dose. © 1998 Elsevier Science S.A. Keywords: Ion implantation; Nitrogen; Si-DLC
1. Introduction The technique of ion implantation is now a well established process in the semiconductor industry and was developed during the early 1960s as a method to introduce precise quantities of dopant ions into semiconductor materials. Since the early 1970s the modification of the surface properties of materials, particularly metals, by ion implantation has been an active field of investigation in numerous laboratories all over the world as documented by the past and present papers from this conference series. It has been demonstrated that properties such as hardness, wear resistance, coefficient of friction, fatigue strength, film adhesion, and corrosion resistance, may be significantly improved by ion implantation [1–6 ]. Coatings of many materials, including conventional diamond-like carbon (DLC ), have been successfully deposited by ion beam assisted deposition (IBAD) and are highly promising for tribological applications requiring high hardness and low friction coefficients. The friction coefficient of unlubricated DLC films in dry gases can be as low as 0.01 but generally increases with * Corresponding author. Fax: +1 410 306 0829; e-mail: [email protected] 0257-8972/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved. PII S 02 5 7 -8 9 7 2 ( 9 8 ) 0 0 38 1 - 8
increasing humidity, reaching values between 0.10 and 0.20 in a 10% relative humidity [7–9]. It has been shown by various researchers [7–9] that conventional DLC films containing silicon or various metallic elements such as Ti exhibit low friction coefficients even in humid environments. Si-DLC films exhibit friction coefficients as low as 0.04 at ambient humidity and temperature and have promise for tribological applications. The effect of ion implantation on single-crystalline and on polycrystalline diamond films solely for electronic applications has been examined by many researchers [10–14], but this is, to our knowledge, the first investigation of implantation Si-DLC for tribological applications. The goal of this investigation was to describe the effect of nitrogen ion implantation on the wear properties of Si-DLC; properties of these coatings without ion implantation have been described previously [15].
2. Experimental details A ZYMET 100 non-mass analyzed ion implanter was used for the synthesis and subsequent nitrogen ion implantation of Si-DLC coated specimens using ener-
C.G. Fountzoulas et al. / Surface and Coatings Technology 103–104 (1998) 104–108
105
Fig. 1. (a) TRIM simulation of nitrogen ion implantation (60% N2++40% N+) of Si-DLC coating; (b) actual implantation profile obtained by RBS.
getic Ar+ ion bombardment of a vapor deposited tetraphenyl-tetramethyl-trisiloxane (Dow-Corning 704) diffusion pump oil [15]. The diffusion pump oil precursor was evaporated from a copper oil container through a 3 mm diameter aperture. The substrates were initially cleaned in methanol and acetone and then sputtercleaned with a 40 keV Ar+ beam (40 mA/cm2) for 10 min. The temperature of the substrate for both the synthesis and implantation was maintained close to room temperature using conducting grease to hold the sample on a water-cooled sample stage. The substrate was inclined at 45° with respect to both the horizontal ion beam and the vertical flow direction of the vaporized oil. The aperture to substrate distance was 0.15 m. A shutter was placed above the oil container to start and stop the oil deposition. The growing film surface was continuously bombarded by an Ar+ ion beam at 40 keV. The base pressure was 2.66×10−4 Pa (2×10−6 Torr) and the deposition/implantation was carried out at 4×10−3 Pa (3×10−5 Torr) pressure. Three aluminum alloy substrates coated with Si-DLC were cleaned in methanol and acetone and then implanted at 80 keV with nitrogen ions to doses of 3×1015, 3×1016, and 3×1017 ions/cm2 at an approximate current density of 10 mA/cm2. The nitrogen beam was not mass analyzed, and consisted of a mixture of roughly 40% N+ and 60% N+ , yielding about 1.6 2 nitrogen atoms per unit charge. The thickness of the films was measured before and after the implantation with the aid of a Dektak II profilometer, and the surface roughness was measured
with a photon tunneling microscope (Dyer Energy Systems). The microhardness values of the coatings were measured using a Knoop microhardness tester with a 15 g load. An Implant Sciences ball-on-disk tribometer with a 1.27 cm (1/2 in) diameter AISI 52100 chrome alloy steel ball under 0.5 N load was used to determine the unlubricated sliding coefficient of friction. Rutherford backscattering spectrometry (RBS) was performed on some of the films using 2 MeV He+ ions to determine their elemental composition.
3. Results and discussion 3.1. Compositional analysis and TRIM simulation The composition of the Si-DLC films was measured using Rutherford backscattering and forward elastic recoil spectrometry (2 MeV He+, 170° and 22° scattering angles). Using the simulation program RUMP [16 ], the coating composition was determined to be C Si O H Ar [15], which is nearly identical to that 67 9 6 15 3 of the hydrocarbon precursor, except for a decrease in H content and the presence of implanted Ar. This strongly suggests that the siloxane backbone (Si–O–Si–O–Si) of the precursor molecule remains intact during the ion irradiation process, and only C:H and C:C bonds are broken to convert the oil to hard, diamond-like carbon. The presence of the siloxane chains scattered throughout the carbon matrix after deposition is thought to have a strong effect on the
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(a)
(b)
(c)
(d)
Fig. 2. Surface topography of Si-DLC shown by photon tunneling microscopy: (a) unimplanted; (b) 3×1015 nitrogen ions/cm2; (c) 3×1016 nitrogen ions/cm2; (d) 3×1017 nitrogen ions/cm2.
ability of the material to maintain low friction in the presence of humidity. The TRIM Monte Carlo code was used to predict the implanted nitrogen distribution and to calculate the sputtering rate of Si-DLC coating. According to the TRIM simulation results the implanted zone should be about 250 nm thick, with a maximum concentration around 100 nm below the surface ( Fig. 1a). RBS analysis (Fig. 1b) of the implanted Si-DLC showed a retained
nitrogen implant dose of 1.8×1017 ions/cm2 for a delivered dose of 3×1017 ions/cm2, and a peak concentration of 22–27 at% nitrogen at a depth of 70–120 nm. This is in rough agreement with the TRIM prediction for ion range, although RBS was not able to distinguish the expected second peak from 80 keV nitrogen ions. The thickness of the implanted coatings, measured with the aid of a profilometer, remained equal to the thickness of the unimplanted coating, verifying indirectly the low
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107
Fig. 3. Unlubricated ball-on-disk friction coefficient of unimplanted and ion nitrogen implanted Si-DLC coating (dose 3×1016 nitrogen ions/c m2).
scopy revealed that implantation roughened the surface of the Si-DLC (Fig. 2a–d), which probably caused the change in coating color and friction coefficient. X-ray analysis showed that all films were amorphous, both before and after implantation. The resistivity of all coatings, implanted and non-implanted, was above 30 kV cm, that was beyond the maximum measurable value of the four-point probe apparatus used. 3.3. Sliding friction coefficient
Fig. 4. Wear rate and the unlubricated ball-on-disk friction coefficient of ion implanted Si-DLC.
sputtering rate of the Si-DLC coating predicted by TRIM (~0.03) and the absence of further densification by the ion beam.
The unlubricated friction coefficient of the unimplanted Si-DLC coating was 0.12 ( Fig. 3), while the friction coefficient of the implanted Si-DLC coatings increased to 0.18 for a dose of 3×1015 ions/cm2 and to 0.22 for doses of 3×1016 and 3×1017 ions/cm2. The increase of the friction coefficient with increasing ion implantation dose indicates that nitrogen implantation did not lead to graphitization of the implanted coatings. The higher friction coefficient was probably caused by the increased surface roughness.
3.2. Microstructure
3.4. Adhesion, wear and microhardness
The average film thickness was about 1 mm at 3.57 nm/min (0.06 nm/s) growth rate. All Si-DLC coatings, unimplanted and implanted, appeared to be featureless when examined under an ordinary optical microscope (200×). Visual observation revealed that the nitrogen ion implantation discolored the coating from its initial black color to brown, brown–gray, and gray for ion doses of 3×1015, 3×1016, and 3×1017 ions/cm2, respectively. Photon tunneling micro-
The adhesion of the coatings to the aluminum alloy substrates, tested directly by the so-called Scotch-Tape test and indirectly during ball-on-disk wear test measurements, showed no delamination. The wear rate of the coating, determined with the aid of an optical microscope and a stylus profilometer, is very low in the unimplanted case, and decreased further with increasing ion dose. The wear rate for implant doses of 3×1015, 3×1016, and 3×1017 ions/cm2 was determined to be
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95%, 78%, and 67% of the unimplanted wear rate, respectively ( Fig. 4). The decrease of the wear rate with increasing ion implantation dose is an indication of the surface hardening of the implanted Si-DLC coating, an effect seen by others following ion implantation of polymeric surfaces [17]. The average Knoop microhardness of the coatings was 10 GPa, in agreement with our previous results [15]. This is undoubtedly a significant underestimate of the hardness of the implanted material, however, since the implanted zone is roughly 250 nm thick, the coating is 1000 nm thick, and the penetration of the Knoop indenter into the sample is roughly the same as the coating thickness (and is strongly affected by deformation of the softer aluminum alloy substrate underneath).
4. Conclusions Nitrogen ion implantation of amorphous Si-DLC coatings described above yields amorphous, non-conductive coatings with a slightly higher friction coefficient and a significantly lower wear rate than the unimplanted material. Implantation of these coatings, at 80 keV and doses of 3×1015, 3×1016, and 3×1017 ions/cm2 did not cause any graphitization, densification, or other softening of these coatings. Visual and optical microscopy, including photon tunneling microscopy, of these coatings in conjunction with the increase of the unlubricated ball-on-disk friction indicate that nitrogen ion implantation increases the coating surface roughness, but decreases the wear rate of the Si-DLC coating by nearly a factor of 2. Nanohardness measurements of the implanted Si-DLC coating will be conducted in the near future to better understand the effect of ion implantation on the surface of this coating. Ion implantation at higher doses will also be tested in the near future in order to fully understand its impact on the Si-DLC wear properties.
Acknowledgement The authors would like to thank Mr. Jack S. Mullin (ARL) for his help in the optical microscopy of our coatings, and Mr. Dimitar Dimitrov (Dept. of Physics and Astronomy, University of Delaware, Newark, DE 19711) for his help in the X-ray and surface resistivity studies.
References [1] G. Dearnaley, Mater. Sci. Eng. 69 (1985) 139. [2] H. Dimigen, K. Kobs, R. Leutenecker, H. Ryssel, P. Eichinger, Mater. Sci. Eng. 69 (1985) 181. [3] G.K. Hubler, F.A. Smidt, Nucl. Instrum. Meth. B7/8 (1985) 151. [4] B.D. Sartwell, in: R.F. Hochman ( Ed.), Ion Plating and Implantation: Application to Materials, ASM, Materials Park, OH, 1986, pp. 81–89. [5] R.B. Alexander, Nucl. Instrum. Meth. B40/41 (1989) 575. [6 ] J.K. Hirvonen, B. Sartwell, Ion Implantation, ASM Handbook, Vol. 5, Surface Engineering, 1994, p. 605. [7] K. Enke, H. Dimingen, H. Huebsch, Appl. Phys. Lett. 36 (1980) 291. [8] T. Hioki, S. Hibi, T. Hioki, J. Kawamoto, Surf. Coat. Technol. 46 (1991) 233. [9] K. Oguri, T. Arai, J. Mater. Res. 7 (1992) 1313. [10] G.W. Malaczynski, A.H. Hamdi, A.A. Elmoursi, X. Qiu, J. Mater. Eng. Perform. 6 (2) (1997) 223. [11] J.C. Pivin, J. Mater. Sci. 27 (1992) 6735. [12] J.C. Pivin, T.J. Lee, J.H. You, H. Park, F. Davanloo, C.B. Collins, P. Catania, Y. Sampeur, H. Bernas, Nucl. Instrum. Meth. Phys. Res. B80/81 (1991) 1499. [13] K.X. Xhang, J.G. Guo, Y.F. Yao, F. Fang, Vacuum 43 (11) (1992) 1047. [14] A.M. Zaitsev, Nucl. Instrum. Meth. Phys. Res. B62 (1991) 81. [15] C.G. Fountzoulas, J.D. Demaree, W.E. Kosik, W. Franzen, W. Croft, J.K. Hirvonen, Mater. Res. Soc. Symp. Proc. 279 (1993) 645. [16 ] L.R. Doolittle, Nucl. Instrum. Meth. B15 (1980) 227. [17] G.P. Rao, E.H. Lee, J. Mater. Sci. 11 (1996) 2661.