- Email: [email protected]
Low vacuum MEVVA titanium and nitrogen co-ion implantation into D2 steel substrates
Surface & Coatings Technology 185 (2004) 264 – 267 www.elsevier.com/locate/surfcoat
Low vacuum MEVVA titanium and nitrogen co-ion implantation into D2 steel substrates Deyuan Zhang a,*, Qinyong Fei a, Haomin Zhao a, Man Geng a, Xuchu Zeng a,b, Paul K. Chu b a b
National R&D Center for Surface Engineering of China, 2/F, 531 Bldg, Bagua 3 Rd., Futian Dist., 518029 Shenzhen, PR China Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, PR China Received 26 June 2003; accepted in revised form 23 December 2003 Available online
Abstract Co-implantation of titanium and nitrogen into D2 steel was conducted using a conventional metal vapor vacuum arc (MEVVA) ion source under low vacuum. Nitrogen was introduced into the vacuum chamber to decrease the mean free path of the particles below the distance between the ion source and targets. The experimental results show that when the pressure goes up from 5103 to 5102 Pa by bleeding in nitrogen, the ion beam current density decreases by 30% and the surface hardness of the implanted specimen increases from 760 to 950 HV. Our results suggest that the optimal nitrogen pressure and implantation dose are 3.5102 Pa and 3.51017 ions/cm2, respectively. Depth profiles acquired by Auger electron spectroscopy (AES) reveal that the implantation depth is approximately 600 nm but the profiles do no resemble a Gaussian distribution. Instead, a surface plateau can be seen. Analyses of X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) indicate that metal nitrides form in the surface layer and the nitrogen concentration in the surface layer is as high as 13.4 at.%. D 2004 Elsevier B.V. All rights reserved. Keywords: Metal vapor vacuum arc (MEVVA); Ion implantation; Low vacuum; Characterization
1. Introduction High current MEVVA (metal vapor vacuum arc) ion implantation was developed to improve the properties of metals [1– 5] and it is potentially useful to enhance the surface hardness, wear resistance, and corrosion resistance of TiN coatings fabricated by PVD (physical vapor deposition) and CVD (chemical vapor deposition) [6 –8]. Graphite is usually used as a cathode and co-implanted with the metal ions to improve the surface hardness further by forming of metal carbides in the implanted zone [9 –11]. Nevertheless, a graphite arc is hard to stabilize in practice. It is of course possible to co-implant mixed metal and gas species by utilizing two independent ion sources and accelerator system, but the added expense and complexity is significant. The other approach employs the ion mixing approach in which metal is deposited on the surface via a low energy
process such as evaporation or sputtering, followed by gas ion bombardment at high incident energy. The gas species is implanted in the usual way while the metal species is recoiled implanted via knock-on collisions with the energetic gas ions [12]. Hence, efforts have been made to concoct a MEVVA ion source capable of delivering mixed ion species by the simple incorporation of the gas into the arcing zone [13] or installing an oil-cooled Penning chamber in the MEVVA ion source [14,15]. This, however, requires basic re-engineering of the MEVVA ion source. In this article, a simpler method and setup referred to as low vacuum MEVVA ion implantation is described to achieve the co-implantation of metal and gas species using conventional MEVVA ion implantation technology. The effects of the process parameters on the surface properties of implanted D2 stainless steel are also investigated.
2. Experimental * Corresponding author. Tel.: +86-755-82055680; fax: +86-75582410418. E-mail address: [email protected] (D. Zhang). 0257-8972/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2003.12.019
A gas introduction and flow control system was built and incorporated into a typical MEVVA ion implanter.
D. Zhang et al. / Surface & Coatings Technology 185 (2004) 264–267
Fig. 1. Relationship between surface hardness of implanted specimens and implantation dose.
Nitrogen was introduced into the vacuum system at various flow rates near the target whereas a titanium cathode was used in the MEVVA ion source. Due to the introduction of nitrogen, the pressure was altered from 5103 to 1 –5102 Pa. The other parameters were: triggering voltage = 3500 V, frequency = 25 Hz, arcing voltage = 100 V, accelerating voltage = 40 kV, ion current = 50 – 60 mA, ion beam diameter = f50 cm, implant dose = 2.4– 4.91017 cm2, and measured sample temperature = 250 – 280 jC (due to ion beam induced heating). A bias of approximately 80 V was applied to the specimens to mitigate secondary electron emission and to more accurately monitor the ion implantation dose. AISI D2 specimens in the quenched-and-tempered state with Vicker’s hardness of 760 and average roughness Ra 0.05 were cut into disks with diameter of 10 mm and thickness of 5 mm. Prior to implantation, the samples were rinsed ultrasonically in ethanol. The surface hardness was measured using the HXD1000TC micro-hardness tester under a normal load of 25 g for 15 s. The surface composition and depth profiles were determined by X-ray photoelectron spectroscopy (XPS) using a PHI-5300 instrument and Auger electron spectroscopy (AES) using a PHI-610 scanning Auger instrument. The sputtering rate during the AES analysis was estimated to be approximately 30 nm per minute. The phase structure was evaluated by X-Ray diffraction (XRD) X’pert Pro using parallel beam optics at a fixed incident angle of 2j.
265
when the implantation dose is 3.51017 cm2 and this value appears to be the optimal value for highest efficacy. The variation of the ion current and hardness variation with nitrogen pressure is displayed in Fig. 2. It can be seen that the ion current decreases slightly with increasing nitrogen pressure, while the hardness increases more substantially until the nitrogen pressure reaches 3.5102 Pa and then increases only slightly thereafter. When the nitrogen pressure is higher than 5102 Pa, a golden color can be observed on the sample. In these experiments, if the apparent hardness is 950 HV, the depth of penetration of the indenter of the micro-hardness tester is approximately 998.63 nm and the depth of stress zone caused by the indenter is approximately 10 times deeper, that is, 9986.3 nm, which is much bigger than the thickness of hardening layer. If the volume-mixing law of surface layer hardness [16] is employed to calculate the real hardness and assuming that the shape of stress zone is hemispherical and the hardened implantation layer is uniform, the estimated surface hardness was approximately 2700 HV, which was about the hardness of TiN films if calculation errors were taken into consideration. The AES spectrum of the implanted surface and depth profile of the specimens implanted with nitrogen and titanium at the pressure of 3.5102 Pa are depicted in Fig. 3. The implantation depth was approximately 600 nm. However, due to the overlapping nitrogen and titanium accurate elemental concentrations could not be derived. The XPS spectra and surface concentrations of the conventional and low vacuum implanted specimens are shown in Fig. 4 and Table 1, respectively. Much more nitrogen and titanium ions were implanted at higher nitrogen pressures. Further analysis of the nitrogen peak N1s indicates that the specimen exhibits two peaks at 404.79 and 401.69 eV instead of one peak at 405.10 eV observed conventionally implanted sample. The results indicate that at least one new nitrogen containing compound phase is formed in the surface layer of the implanted sample. The X-ray diffraction spectra are
3. Results The relationship between hardness and implantation dose is described in Fig. 1. Our results indicate that the surface hardness decreases after pure metal ion implantation at high doses, however, the surface hardness of the implanted surface increases substantially in concert with nitrogen incorporation. The surface hardness reaches a maximum
Fig. 2. Effects of nitrogen pressure on total ion current and hardness of the implanted surface.
266
D. Zhang et al. / Surface & Coatings Technology 185 (2004) 264–267 Table 1 Surface atomic concentrations of different specimens Specimen
Vacuum/Pa 3
310 3.5102
Conventional Low vacuum
Ti
N
Fe
2.38 41.17
4.35 13.40
93.27 45.44
the XPS results into consideration, it can be inferred that iron or/and titanium nitrides are formed during implantation to account for the elevation of the surface hardness.
4. Discussion In our implanter, the distance between the ion source and the center of the sample holder where the specimens are located is 1043 mm. At different nitrogen pressures, the mean free path E¯ between nitrogen atoms and titanium ions can be calculated as follows: kT k ¼ pffiffiffi 2pðr1 þ r2 Þ2 P
ð1Þ
where k is the Boltzmann constant, T is the temperature, P is the pressure, and r1 and r2 are radius of particles 1
Fig. 3. AES spectra acquired from the implanted surface and depth profiles of nitrogen and titanium in the implanted sample.
shown in Fig. 5. There are five peaks besides the four peaks assigned to the iron substrate (01-1267), in the range, 2h from 30 to 110j. The possible new phases are Fe0.988Ti (83-1636), Fe2N (73-2102) and TiN0.90 (71-0299). Taking
Fig. 4. Nitrogen XPS peaks and fittings for specimens implanted at different nitrogen pressures.
Fig. 5. XRD spectra and peak identification.
D. Zhang et al. / Surface & Coatings Technology 185 (2004) 264–267
267
5. Conclusion Titanium metal ions and nitrogen gas were successfully co-implanted into AISI D2 steel substrates using low vacuum MEVVA ion implantation. The optimal nitrogen pressure was 3.5102 Pa and the optimal implantation dose was 3.51017 ions/cm2. Increased surface hardness was achieved and can be attributed to the formation of complex iron and/or titanium nitrides in the implanted region. The depth profiles of the implanted species do not possess a Gaussian shape because of the energy loss of Ti during collisions and knock-on of adsorbed nitrogen.
Fig. 6. Effects of vacuum on the mean free path of N – N and Ti2+ – N.
and 2, respectively. The calculation results are shown in Fig. 6. When the nitrogen pressure is higher than 1.5102 Pa, k¯Ti2þ N will be shorter than the distance between the ion source and specimens. This means that the majority of the titanium ions will collide with nitrogen before they reach the specimens. In this case, nitrogen can obtain sufficient energy from the collisions with titanium ions and be implanted into the specimens as well. Another way that nitrogen implantation can occur is nitrogen adsorption on the sample surface. According to the Langmuir adsorption formula: bP G ¼ Gl ; 1 þ bP
ð2Þ
b is the adsorption coefficient, Gl is the saturation adsorptive power, G is the adsorptive power and P is the adsorbate pressure. When P is low enough and bP is much less than 1, Eq. (2) becomes: G ¼ Gl bP
ð3Þ
That is to say, nitrogen adsorption on the target surface is proportional to the nitrogen pressure in the vacuum chamber. Consequently, there is an order of magnitude larger amount of adsorbed nitrogen to be knocked into the material via the energetic titanium ions in our process. Based on our argument, when the nitrogen pressure is high enough, titanium ions collide with nitrogen many times before they reach the specimens. Coupled with the higher amount of adsorbed nitrogen, a substantial amount of nitrogen is co-implanted into the samples. Due to the fact that these nitrogen ions are not truly implanted from the gas phase, the nitrogen distribution does not resemble a Gaussian. In addition, the collisions reduce the incident energy of the Ti ions making the deposition more pronounced, as evidenced by our observation that the surface titanium concentration reaches almost 41 at.% and the surface color changes.
Acknowledgements This project was financially supported by National HighTech Research and Development Program (863 program) of China under the grant No. 2001-AA338010 and Shenzhen Municipal Program of Science and Technology, City University of Hong Kong Strategic Research Grant (SRG) #7001447, as well as Hong Kong Research Grants Council (RGC) Competitive Earmarked Research Grant (CERG) #CityU 1137/03E.
References [1] W. Miao, K. Tao, Mater. Res. Bull. 36 (10) (2002) 1759. [2] C. Ji, A. Wang, H. Liao, Surf. Coat. Technol. 128 – 129 (2000) 213. [3] J. Treglio, A. Elkind, R. Stinner, A. Perry, Surf. Coat. Technol. 96 (1) (1997) 1. [4] T. Zhang, H. Zhang, C. Ji, Surf. Coat. Technol. 128 – 129 (2000) 1. [5] H. Buscail, M.F. Stroosnijder, Y.P. Jacob, E. Sciora, Mater. Sci. Eng. A. 262 (1 – 2) (1999) 184. [6] R.R. Manory, S. Monica, L. Ward, K.P. Purushotham, P. Evans, J. Noorman, et al., Surf. Coat. Technol 155 (2002) 136. [7] A. Perry, R.R. Manory, L. Ward, P.P. Kavuri, Surf. Coat. Technol 133 – 134 (2000) 203. [8] K.P. Purushotham, L. Ward, N. Brack, P.J. Pigram, P. Evans, H. Noorman, et al., Wear 254 (2003) 589. [9] T. Zhang, X. Wang, H. Liang, H. Zhang, G. Zhou, G. Sun, et al., Surf. Coat. Technol. 83 (1 – 3 pt 1) (1996) 280. [10] Z. Yi, Z. Xiao, F. Ma, T. Zhang, Y. Li, Surf. Coat. Technol. 128 – 129 (2000) 186. [11] Y. Li, T. Zhang, X. Wang, Surf. Coat. Technol. 128 – 129 (2000) 205. [12] W. Ensinger, Nucl. Instrum. Meth. B 127 – 128 (1996) 796. [13] I.G. Brown, F. Liu, O.R. Monterio, K.M. Yu, P.J. Evens, N. Dytlewski, et al., Surf. Coat. Technol. 103 – 104 (1998) 293. [14] E. Oks, G. Yuskov, P. Schanin, A. Nikolaev, Rev. Sci. Instrum. 67 (1996) 1213. [15] S.P. Bugaev, A.G. Nikolaev, E.M. Oks, P.M. Schanin, G.Yu. Yuskov, Rev. Sci. Instrum. 63 (1992) 2422. [16] P.J. Burnett, O.S. Richard, Thin Solid Films 154 (1987) 403.
Low vacuum MEVVA titanium and nitrogen co-ion implantation into D2 steel substrates Deyuan Zhang a,*, Qinyong Fei a, Haomin Zhao a, Man Geng a, Xuchu Zeng a,b, Paul K. Chu b a b
National R&D Center for Surface Engineering of China, 2/F, 531 Bldg, Bagua 3 Rd., Futian Dist., 518029 Shenzhen, PR China Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, PR China Received 26 June 2003; accepted in revised form 23 December 2003 Available online
Abstract Co-implantation of titanium and nitrogen into D2 steel was conducted using a conventional metal vapor vacuum arc (MEVVA) ion source under low vacuum. Nitrogen was introduced into the vacuum chamber to decrease the mean free path of the particles below the distance between the ion source and targets. The experimental results show that when the pressure goes up from 5103 to 5102 Pa by bleeding in nitrogen, the ion beam current density decreases by 30% and the surface hardness of the implanted specimen increases from 760 to 950 HV. Our results suggest that the optimal nitrogen pressure and implantation dose are 3.5102 Pa and 3.51017 ions/cm2, respectively. Depth profiles acquired by Auger electron spectroscopy (AES) reveal that the implantation depth is approximately 600 nm but the profiles do no resemble a Gaussian distribution. Instead, a surface plateau can be seen. Analyses of X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) indicate that metal nitrides form in the surface layer and the nitrogen concentration in the surface layer is as high as 13.4 at.%. D 2004 Elsevier B.V. All rights reserved. Keywords: Metal vapor vacuum arc (MEVVA); Ion implantation; Low vacuum; Characterization
1. Introduction High current MEVVA (metal vapor vacuum arc) ion implantation was developed to improve the properties of metals [1– 5] and it is potentially useful to enhance the surface hardness, wear resistance, and corrosion resistance of TiN coatings fabricated by PVD (physical vapor deposition) and CVD (chemical vapor deposition) [6 –8]. Graphite is usually used as a cathode and co-implanted with the metal ions to improve the surface hardness further by forming of metal carbides in the implanted zone [9 –11]. Nevertheless, a graphite arc is hard to stabilize in practice. It is of course possible to co-implant mixed metal and gas species by utilizing two independent ion sources and accelerator system, but the added expense and complexity is significant. The other approach employs the ion mixing approach in which metal is deposited on the surface via a low energy
process such as evaporation or sputtering, followed by gas ion bombardment at high incident energy. The gas species is implanted in the usual way while the metal species is recoiled implanted via knock-on collisions with the energetic gas ions [12]. Hence, efforts have been made to concoct a MEVVA ion source capable of delivering mixed ion species by the simple incorporation of the gas into the arcing zone [13] or installing an oil-cooled Penning chamber in the MEVVA ion source [14,15]. This, however, requires basic re-engineering of the MEVVA ion source. In this article, a simpler method and setup referred to as low vacuum MEVVA ion implantation is described to achieve the co-implantation of metal and gas species using conventional MEVVA ion implantation technology. The effects of the process parameters on the surface properties of implanted D2 stainless steel are also investigated.
2. Experimental * Corresponding author. Tel.: +86-755-82055680; fax: +86-75582410418. E-mail address: [email protected] (D. Zhang). 0257-8972/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2003.12.019
A gas introduction and flow control system was built and incorporated into a typical MEVVA ion implanter.
D. Zhang et al. / Surface & Coatings Technology 185 (2004) 264–267
Fig. 1. Relationship between surface hardness of implanted specimens and implantation dose.
Nitrogen was introduced into the vacuum system at various flow rates near the target whereas a titanium cathode was used in the MEVVA ion source. Due to the introduction of nitrogen, the pressure was altered from 5103 to 1 –5102 Pa. The other parameters were: triggering voltage = 3500 V, frequency = 25 Hz, arcing voltage = 100 V, accelerating voltage = 40 kV, ion current = 50 – 60 mA, ion beam diameter = f50 cm, implant dose = 2.4– 4.91017 cm2, and measured sample temperature = 250 – 280 jC (due to ion beam induced heating). A bias of approximately 80 V was applied to the specimens to mitigate secondary electron emission and to more accurately monitor the ion implantation dose. AISI D2 specimens in the quenched-and-tempered state with Vicker’s hardness of 760 and average roughness Ra 0.05 were cut into disks with diameter of 10 mm and thickness of 5 mm. Prior to implantation, the samples were rinsed ultrasonically in ethanol. The surface hardness was measured using the HXD1000TC micro-hardness tester under a normal load of 25 g for 15 s. The surface composition and depth profiles were determined by X-ray photoelectron spectroscopy (XPS) using a PHI-5300 instrument and Auger electron spectroscopy (AES) using a PHI-610 scanning Auger instrument. The sputtering rate during the AES analysis was estimated to be approximately 30 nm per minute. The phase structure was evaluated by X-Ray diffraction (XRD) X’pert Pro using parallel beam optics at a fixed incident angle of 2j.
265
when the implantation dose is 3.51017 cm2 and this value appears to be the optimal value for highest efficacy. The variation of the ion current and hardness variation with nitrogen pressure is displayed in Fig. 2. It can be seen that the ion current decreases slightly with increasing nitrogen pressure, while the hardness increases more substantially until the nitrogen pressure reaches 3.5102 Pa and then increases only slightly thereafter. When the nitrogen pressure is higher than 5102 Pa, a golden color can be observed on the sample. In these experiments, if the apparent hardness is 950 HV, the depth of penetration of the indenter of the micro-hardness tester is approximately 998.63 nm and the depth of stress zone caused by the indenter is approximately 10 times deeper, that is, 9986.3 nm, which is much bigger than the thickness of hardening layer. If the volume-mixing law of surface layer hardness [16] is employed to calculate the real hardness and assuming that the shape of stress zone is hemispherical and the hardened implantation layer is uniform, the estimated surface hardness was approximately 2700 HV, which was about the hardness of TiN films if calculation errors were taken into consideration. The AES spectrum of the implanted surface and depth profile of the specimens implanted with nitrogen and titanium at the pressure of 3.5102 Pa are depicted in Fig. 3. The implantation depth was approximately 600 nm. However, due to the overlapping nitrogen and titanium accurate elemental concentrations could not be derived. The XPS spectra and surface concentrations of the conventional and low vacuum implanted specimens are shown in Fig. 4 and Table 1, respectively. Much more nitrogen and titanium ions were implanted at higher nitrogen pressures. Further analysis of the nitrogen peak N1s indicates that the specimen exhibits two peaks at 404.79 and 401.69 eV instead of one peak at 405.10 eV observed conventionally implanted sample. The results indicate that at least one new nitrogen containing compound phase is formed in the surface layer of the implanted sample. The X-ray diffraction spectra are
3. Results The relationship between hardness and implantation dose is described in Fig. 1. Our results indicate that the surface hardness decreases after pure metal ion implantation at high doses, however, the surface hardness of the implanted surface increases substantially in concert with nitrogen incorporation. The surface hardness reaches a maximum
Fig. 2. Effects of nitrogen pressure on total ion current and hardness of the implanted surface.
266
D. Zhang et al. / Surface & Coatings Technology 185 (2004) 264–267 Table 1 Surface atomic concentrations of different specimens Specimen
Vacuum/Pa 3
310 3.5102
Conventional Low vacuum
Ti
N
Fe
2.38 41.17
4.35 13.40
93.27 45.44
the XPS results into consideration, it can be inferred that iron or/and titanium nitrides are formed during implantation to account for the elevation of the surface hardness.
4. Discussion In our implanter, the distance between the ion source and the center of the sample holder where the specimens are located is 1043 mm. At different nitrogen pressures, the mean free path E¯ between nitrogen atoms and titanium ions can be calculated as follows: kT k ¼ pffiffiffi 2pðr1 þ r2 Þ2 P
ð1Þ
where k is the Boltzmann constant, T is the temperature, P is the pressure, and r1 and r2 are radius of particles 1
Fig. 3. AES spectra acquired from the implanted surface and depth profiles of nitrogen and titanium in the implanted sample.
shown in Fig. 5. There are five peaks besides the four peaks assigned to the iron substrate (01-1267), in the range, 2h from 30 to 110j. The possible new phases are Fe0.988Ti (83-1636), Fe2N (73-2102) and TiN0.90 (71-0299). Taking
Fig. 4. Nitrogen XPS peaks and fittings for specimens implanted at different nitrogen pressures.
Fig. 5. XRD spectra and peak identification.
D. Zhang et al. / Surface & Coatings Technology 185 (2004) 264–267
267
5. Conclusion Titanium metal ions and nitrogen gas were successfully co-implanted into AISI D2 steel substrates using low vacuum MEVVA ion implantation. The optimal nitrogen pressure was 3.5102 Pa and the optimal implantation dose was 3.51017 ions/cm2. Increased surface hardness was achieved and can be attributed to the formation of complex iron and/or titanium nitrides in the implanted region. The depth profiles of the implanted species do not possess a Gaussian shape because of the energy loss of Ti during collisions and knock-on of adsorbed nitrogen.
Fig. 6. Effects of vacuum on the mean free path of N – N and Ti2+ – N.
and 2, respectively. The calculation results are shown in Fig. 6. When the nitrogen pressure is higher than 1.5102 Pa, k¯Ti2þ N will be shorter than the distance between the ion source and specimens. This means that the majority of the titanium ions will collide with nitrogen before they reach the specimens. In this case, nitrogen can obtain sufficient energy from the collisions with titanium ions and be implanted into the specimens as well. Another way that nitrogen implantation can occur is nitrogen adsorption on the sample surface. According to the Langmuir adsorption formula: bP G ¼ Gl ; 1 þ bP
ð2Þ
b is the adsorption coefficient, Gl is the saturation adsorptive power, G is the adsorptive power and P is the adsorbate pressure. When P is low enough and bP is much less than 1, Eq. (2) becomes: G ¼ Gl bP
ð3Þ
That is to say, nitrogen adsorption on the target surface is proportional to the nitrogen pressure in the vacuum chamber. Consequently, there is an order of magnitude larger amount of adsorbed nitrogen to be knocked into the material via the energetic titanium ions in our process. Based on our argument, when the nitrogen pressure is high enough, titanium ions collide with nitrogen many times before they reach the specimens. Coupled with the higher amount of adsorbed nitrogen, a substantial amount of nitrogen is co-implanted into the samples. Due to the fact that these nitrogen ions are not truly implanted from the gas phase, the nitrogen distribution does not resemble a Gaussian. In addition, the collisions reduce the incident energy of the Ti ions making the deposition more pronounced, as evidenced by our observation that the surface titanium concentration reaches almost 41 at.% and the surface color changes.
Acknowledgements This project was financially supported by National HighTech Research and Development Program (863 program) of China under the grant No. 2001-AA338010 and Shenzhen Municipal Program of Science and Technology, City University of Hong Kong Strategic Research Grant (SRG) #7001447, as well as Hong Kong Research Grants Council (RGC) Competitive Earmarked Research Grant (CERG) #CityU 1137/03E.
References [1] W. Miao, K. Tao, Mater. Res. Bull. 36 (10) (2002) 1759. [2] C. Ji, A. Wang, H. Liao, Surf. Coat. Technol. 128 – 129 (2000) 213. [3] J. Treglio, A. Elkind, R. Stinner, A. Perry, Surf. Coat. Technol. 96 (1) (1997) 1. [4] T. Zhang, H. Zhang, C. Ji, Surf. Coat. Technol. 128 – 129 (2000) 1. [5] H. Buscail, M.F. Stroosnijder, Y.P. Jacob, E. Sciora, Mater. Sci. Eng. A. 262 (1 – 2) (1999) 184. [6] R.R. Manory, S. Monica, L. Ward, K.P. Purushotham, P. Evans, J. Noorman, et al., Surf. Coat. Technol 155 (2002) 136. [7] A. Perry, R.R. Manory, L. Ward, P.P. Kavuri, Surf. Coat. Technol 133 – 134 (2000) 203. [8] K.P. Purushotham, L. Ward, N. Brack, P.J. Pigram, P. Evans, H. Noorman, et al., Wear 254 (2003) 589. [9] T. Zhang, X. Wang, H. Liang, H. Zhang, G. Zhou, G. Sun, et al., Surf. Coat. Technol. 83 (1 – 3 pt 1) (1996) 280. [10] Z. Yi, Z. Xiao, F. Ma, T. Zhang, Y. Li, Surf. Coat. Technol. 128 – 129 (2000) 186. [11] Y. Li, T. Zhang, X. Wang, Surf. Coat. Technol. 128 – 129 (2000) 205. [12] W. Ensinger, Nucl. Instrum. Meth. B 127 – 128 (1996) 796. [13] I.G. Brown, F. Liu, O.R. Monterio, K.M. Yu, P.J. Evens, N. Dytlewski, et al., Surf. Coat. Technol. 103 – 104 (1998) 293. [14] E. Oks, G. Yuskov, P. Schanin, A. Nikolaev, Rev. Sci. Instrum. 67 (1996) 1213. [15] S.P. Bugaev, A.G. Nikolaev, E.M. Oks, P.M. Schanin, G.Yu. Yuskov, Rev. Sci. Instrum. 63 (1992) 2422. [16] P.J. Burnett, O.S. Richard, Thin Solid Films 154 (1987) 403.