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Properties of amorphous carbon layers for bio-tribological applications
ARTICLE IN PRESS Microelectronics Journal 40 (2009) 650– 653
Contents lists available at ScienceDirect
Microelectronics Journal journal homepage: www.elsevier.com/locate/mejo
Properties of amorphous carbon layers for bio-tribological applications M. Vojs a,, E. Zdravecka´ b, M. Marton a, P. Boha´cˇ c, L. Franta d, M. Vesely´ a a
Department of Microelectronics, FEI STU in Bratislava, Ilkovicˇova 3, 812 19 Bratislava, Slovak Republic ¨siarska 74, 040 01 Kosˇice, Slovak Republic Department of Technologies and Materials, FME TU of Kosˇice, Ma c Institute of Physics AS CˇR, Na Slovance 2, 182 21 Prague, Czech Republic d ´ 4, 166 07 Prague, Czech Republic Department of Mechanics, Biomechanics and Mechatronic, FME CTU in Prague, Technicka b
a r t i c l e in f o
a b s t r a c t
Available online 15 August 2008
This paper analyses the influence of composition, structure and adhesion of amorphous coatings with high wear resistance, low friction coefficient and good adhesion to coated CrCoMo material for parts of implants. By different deposition techniques, different mechanical and tribological properties were obtained. This work reviews amorphous carbon (a-C) films deposited by magnetron sputtering and diamond-like carbon (DLC) films grown by glow arc discharge technology on CrCoMo substrates. Films were investigated under static load under dry conditions (nanohardness, elastic module), and also with dynamic load (coefficient of friction, wear resistance). The following topics were investigated: surfaces and subsurface properties of a-C films, namely adhesion in connection with different techniques, different film properties in dependence on various technology conditions. & 2008 Elsevier Ltd. All rights reserved.
Keywords: Tribology Diamond-like carbon (DLC) CrCoMo Friction Adhesion Raman spectroscopy
1. Introduction
2. Experimental setup
Diamond-like carbon (DLC) coatings cover a wide range of different types of carbon-based coatings, which generally have properties such as low friction and high wear resistance. The low friction coefficient and good wear resistance of DLC coatings make them suitable for many tribological applications such as wear-resistant coatings, e.g. cutting tools, magnetic storage systems [1]. Also many applications of amorphous carbon (a-C) films are permanent actual for biotribological applications. In order to use DLC coatings reliably in different applications, it is important to understand the coating tribological behaviour at different operating conditions. This has been studied intensively by many scientists during the last few years. The friction and wear performance of a-C coatings greatly depend on the deposition method and the deposition parameters used as well as the test environment [2,3]. As a general trend, a-C:H films can provide low friction performance in sliding conditions [4–6]. In particular, in a vacuum or in inert atmosphere (e.g. in dry nitrogen) the friction coefficient can be very low, namely in the range of 0.04–0.006 [7–9]. This contribution deals with the study of DLC films with different contents of Ar and N2 to grow as nanocomposite materials like b-C3N4 or nanocrystalline diamond particle in amorphous graphitic matrix.
The films were deposited by low arc discharge UVNIPA-1-001 vacuum system with three sources (gas ion source for cleaning, electric arc source for non-magnetic metal sputtering and pulse arc carbon source for DLC deposition). The pulse sputtering of graphite target is a possible setup in wide range. Entered samples were sputtered in one vacuum cycle. All substrates were cleaned for 10 min with Ar ions. DLC layer was deposited at temperature down to 150 1C. Nitrogen and Ar gasses were added during the DLC deposition into working chamber, which is described in Table 1. The substrates were planetary rotating through all the deposition steps to achieve homogeneity. The coatings were produced on a highly polished flat CrCoMo substrate material with Ra ¼ 0.05 mm. One fine polished face of each CrCoMo substrate was coated with DLC film. The hardness and other mechanical characteristics were determined from depth sensing indentation (DSI) curves measured with Nano TEST NT 600. Raman measurements were conducted in DILOR-JOBIN YVON-SPEX Raman spectrometer, type LabRam. The excitation source was a He–Ne laser with 632.8 nm wavelength operated at 15 mW. The spectrometer was calibrated to 520.7 cm1 band of single crystalline Si and 1332 cm1 band of natural diamond. Scanning electron microscope (SEM) LEO 1550 operating in the secondary electron mode was used to study the microtopography of DLC layers.
3. Results and discussion Corresponding author. Tel.: +421 2 602 91 365; fax: +421 2 654 23 480.
E-mail address: [email protected] (M. Vojs). 0026-2692/$ - see front matter & 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.mejo.2008.06.083
The adhesion behavior of carbon coatings has been characterized by scratch tests. Scratch experiments with diamond Rockwell
ARTICLE IN PRESS M. Vojs et al. / Microelectronics Journal 40 (2009) 650–653
Table 1 Deposition parameters of DLC layers deposited by UVNIPA-1-001 No.
Ar (sccm)
N2 (sccm)
Dep. technique
U II U III U IIII
70 80 80
60 60 50
Arc discharge Arc discharge Arc discharge
Table 2 Results from nanoscratch tests No.
Lc1 (nM)
Lc2 (nM)
Lc3 (nM)
U II U III U IIII
46.0 40.5 42.0
53.5 79.0 62.5
57.5 120.0 115.0
200
greater measure is marked as LC3. During scratch test the sample feed speed dx/dt was recorded at loads with continuously increasing force. The acoustic emission signal is also recorded with a camera. The hardness H, elastic modulus Eeff and mechanical characteristics were determined from depth sensitive indentations (DSI curves measured by the NanoTest NT 600 apparatus at different maximal loads from 5, 10, 20, 50, and 100 mN with diamond Berkovich tip using the analysis developed by the Oliver–Pharr procedure [8]. Each indentation cycle (uploading to the maximal load and downloading to 0) was repeated five times in slightly different places for each maximal load. The load dependence of Eeff and HIT (1/Eeff ¼ [(1n2)/E]+ [(1ni2)/Ei], where index i means material of the indenter; for diamond ni ¼ 0.07 and Ei ¼ 1141 GPa) is shown in Fig. 1a and b. Values of Eeff for all types of DLC coatings are almost constant (Fig. 1a). Values of HIT for coatings of type U III and U IIII deposited under conditions given in Table 1 are comparable, the lowest value was observed for coating U II, what can be connected with lower content of N. Values of H3IT/E2eff (Fig. 2a) and also of HIT/Eeff (Fig. 2b) for type of films marked U III and U IIII are almost similar. The lowest value for H3IT/E2eff and of HIT/Eeff was observed for coating marked U II. Friction tests were performed on the same samples as for indentations by applying a microtribometre dry sliding point
150 Sample: No- Ar/N U II - 70/60 U III - 80/60 U IIII - 80/50
125
100 0
20
40
60 Load [mN]
80
100
0.08 Sample: No- Ar/N U II - 70/60 U III - 80/60 U IIII - 80/50
0.07 H3/E2 [GPa]
Eeff [GPa]
175
651
0.06 0.05 0.04 0.03
12
0.02 Sample: No- Ar/N U II - 70/60 U III - 80/60 U IIII - 80/50
HIT [GPa]
10
0.01 0.00 0
20
40
60 80 Load [mN]
100
8 0.09 Sample: No- Ar/N U II - 70/60 U III - 80/60 U IIII - 80/50
0.08
4 0
20
40
60 Load [mN]
80
100
Fig. 1. (a) Resulted Eeff for tested coatings under different loads and (b) resulted HIT for tested coatings under different loads.
sphere–conical tip of + ¼ 25 mm with scratch length of 1 mm; load in the range from 0 to 150 mN; scan speed of 0.75 mN/s were conducted. The results from nanoscratch tests are in Table 2. Loading in location where the first failure of coating occurred (cracks) is marked as LC1, the first adhesive failure of coating (flaking) is marked as LC2, the first adhesive coating failure in
HIT/Eeff [-]
6
0.07 0.06 0.05 0.04 0.03 0.02 0
20
40
60 Load [mN]
80
100
Fig. 2. (a) Dependence of H3IT/E2eff on different loads and (b) dependence of HIT/Eeff on different loads.
ARTICLE IN PRESS 652
M. Vojs et al. / Microelectronics Journal 40 (2009) 650–653
contact between corundum ball (a-Al2O3) and coatings. The coefficient of friction (COF) was recorded during testing by increasing normal force Fn from 30 to 90 mN at temperature of T ¼ 23 1C, relative humidity 50%; normal force Fn was continuously increased from 30 to 90 mN, friction couple: a-C coatings Al2O3 and ball with d ¼ 5.5 mm. Material of the ball was Al2O3. Speed of ball movement was v ¼ 0.4 mm/s. Graphical output COFs at different loads during sliding line contact are drawn in Fig. 3. From point of view of COF, coating marked with U II (DLC) was the
Friction Coefficient [µ]
0.19 0.17 0.15 0.13
Sample: No- Ar/N U II - 70/60
0.11
Sample: No- Ar/N U IIII - 80/50
Sample: No- Ar/N U III - 80/60
0.09 0.07
best. The resistance to plastic deformation—the quantity which can more distinctly divide film materials [13]. Fig. 4 presents Raman spectra taken from DLC layers. The spectrum of the DLC layer contains typical broad peaks, the ‘G’ and ‘D’ peaks. The G-peak corresponds to the fundamental E2g mode of graphite at 1580 cm–1, and D-peak disordered graphite, i.e. a Raman-active, in-plane vibrational mode for an infinite hexagonal network. With N2 content increase in case of U III (N2 from 50 to 60 sccm) we can find another broad band centered at 1140 cm1, which corresponds to nanocrystalline diamond cluster with sp3-bonding [9,10]. With increasing content of Ar/N2 ratio we observe decreasing sp2 content in layer and increasing concentration of disordered graphite sp3 bonds, and thus the stress in the coating. The lowest values of friction coefficient were recorded for coatings with highest hardness and content of sp3 bonds for U II coating, and the highest values of friction coefficient were recorded for U IIII coating with lowest sp3/sp2 ratio and hardness, what does not match with the results published elsewhere [11]. The SEM images of DLC samples are shown in Fig. 5. All layers consist of nanocomposite (nanocrystalline diamond) microstructure character clearly recognized from SEM images of diamond layers with high content of sp3 bonds [12].
90 I_
70
III
50
I_
I_
III
30
III
0
I_ III
0
_9
_7
III
0
III
0
_5 III
90
_3 III
70
II_
II_
50 II_
II_
30
0.05
Load [mN] Fig. 3. Friction coefficient COF of different loads during sliding line contact.
D
G
Sample: No- Ar/N U II - 70/60 U III - 80/60 U IIII - 80/50
Intensity [a.u.]
nano-D
800
1000
1200 1400 1600 Raman shift [cm-1]
1800
Fig. 4. Raman spectra of DLC layers: U II, U III and U IIII.
2000
4. Conclusion Tribological properties of thin and hard layers are influenced by structure, chemical composition and deposition parameters. Adhesion of thin and hard layers is dependent on the character of coupling forces between layer and substrate. Tribological properties of thin and hard layers are influenced by structure, chemical composition and parameters of deposition. Adhesion of thin and hard layers is dependent on character of coupling forces between layer and substrate [14]. For DLC coatings deposited by UVNIPA-1-001 equipment the lowest value of hardness HIT was observed for U IIII coating with highest content of sp2 bonds (Ar: 80 sccm/N2: 50 sccm). U II and U IIII coatings have almost the same values of HIT and content of N2 (60 sccm), but the adhesion parameter Lc3 (first adhesive coating failure) for U III coating is two times better than for U II coating, which corresponds to increasing content of Ar/N ratio, decreasing sp3 content in layer and increasing concentration of disordered graphite sp3 bonds and thus the stress in the coating. The friction coefficient of DLC coatings was more stable over the wide range of normal loads from 30 to 90 mN against corundum ball used at microtribotests. Its lowest values was recorded for coatings with highest hardness and content of sp3 bonds for U II coating (Ar: 70 sccm/N2: 60 sccm) and the highest values of friction coefficient were recorded for U IIII coating (Ar: 80 sccm/N2: 50 sccm) with lowest sp3/sp2 ratio and hardness.
Fig. 5. SEM images from samples: (a) U II, (b) U III and (c) U IIII.
ARTICLE IN PRESS M. Vojs et al. / Microelectronics Journal 40 (2009) 650–653
Development and applications of thin hard DLC layers are open to further research and they always represent very attractive and challenging theme.
Acknowledgments This work has been supported by Grants: COST 533, AV 4/0124/ 06, VEGA 1/0857/08, VEGA 1/0390/08 of The Ministry of Education of the Slovak Republic and APVT-20-034404, LPP-0246-06 of The Slovak Research and Development Agency and Project no. OC097 of action COST 533 of Ministry for Education, Youth and Sports of the Czech Republic. Many thanks to M. Michalka from the International Laser Center for SEM measurements.
653
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]
K. Holmberg, A. Matthews, Tribology Series 28, Elsevier, Amsterdam, 1994, p. 442. A. Grill, Wear 168 (1993) 143. A. Grill, Surf. Coat. Technol. 94/95 (1997) 507–513. A. Erdemir, M. Switala, R. Wei, P. Wilbur, Surf. Coat. Technol. 50 (1991) 17. B. Marchon, M.R. Khan, N. Heiman, P. Pereira, A. Lautie, IEEE Trans. Magnet. 26 (5) (1990) 2670. D.S. Kim, T.E. Fischer, B. Gallois, Surf. Coat. Technol. 49 (1991) 537. C. Donnet, et al., Surf. Coat. Technol. 68/69 (1994) 626–631. W.C. Oliver, G.M. Pharr, J. Mater. Res. 7 (1992) 1564–1583. G. Sepold, et al., Diamond Relat. Mater. 8 (1999) 1677–1681. A. Kromka, et al., Carbon 43 (2005) 425–429. Y. Kusano, et al., Thin Solid Films 332 (1998) 56–61. M. Vojs, et al., Diamond Relat. Mater. 14 (2005) 613–616. M. Madej, D. Ozimina, I. Piwon´ski, Tribol. Lett. 22 (2006) 135. E. Zdravecka´, et al., 9–13 September 2007 Eurocorr 2007, Freiburg; 1–9.
Contents lists available at ScienceDirect
Microelectronics Journal journal homepage: www.elsevier.com/locate/mejo
Properties of amorphous carbon layers for bio-tribological applications M. Vojs a,, E. Zdravecka´ b, M. Marton a, P. Boha´cˇ c, L. Franta d, M. Vesely´ a a
Department of Microelectronics, FEI STU in Bratislava, Ilkovicˇova 3, 812 19 Bratislava, Slovak Republic ¨siarska 74, 040 01 Kosˇice, Slovak Republic Department of Technologies and Materials, FME TU of Kosˇice, Ma c Institute of Physics AS CˇR, Na Slovance 2, 182 21 Prague, Czech Republic d ´ 4, 166 07 Prague, Czech Republic Department of Mechanics, Biomechanics and Mechatronic, FME CTU in Prague, Technicka b
a r t i c l e in f o
a b s t r a c t
Available online 15 August 2008
This paper analyses the influence of composition, structure and adhesion of amorphous coatings with high wear resistance, low friction coefficient and good adhesion to coated CrCoMo material for parts of implants. By different deposition techniques, different mechanical and tribological properties were obtained. This work reviews amorphous carbon (a-C) films deposited by magnetron sputtering and diamond-like carbon (DLC) films grown by glow arc discharge technology on CrCoMo substrates. Films were investigated under static load under dry conditions (nanohardness, elastic module), and also with dynamic load (coefficient of friction, wear resistance). The following topics were investigated: surfaces and subsurface properties of a-C films, namely adhesion in connection with different techniques, different film properties in dependence on various technology conditions. & 2008 Elsevier Ltd. All rights reserved.
Keywords: Tribology Diamond-like carbon (DLC) CrCoMo Friction Adhesion Raman spectroscopy
1. Introduction
2. Experimental setup
Diamond-like carbon (DLC) coatings cover a wide range of different types of carbon-based coatings, which generally have properties such as low friction and high wear resistance. The low friction coefficient and good wear resistance of DLC coatings make them suitable for many tribological applications such as wear-resistant coatings, e.g. cutting tools, magnetic storage systems [1]. Also many applications of amorphous carbon (a-C) films are permanent actual for biotribological applications. In order to use DLC coatings reliably in different applications, it is important to understand the coating tribological behaviour at different operating conditions. This has been studied intensively by many scientists during the last few years. The friction and wear performance of a-C coatings greatly depend on the deposition method and the deposition parameters used as well as the test environment [2,3]. As a general trend, a-C:H films can provide low friction performance in sliding conditions [4–6]. In particular, in a vacuum or in inert atmosphere (e.g. in dry nitrogen) the friction coefficient can be very low, namely in the range of 0.04–0.006 [7–9]. This contribution deals with the study of DLC films with different contents of Ar and N2 to grow as nanocomposite materials like b-C3N4 or nanocrystalline diamond particle in amorphous graphitic matrix.
The films were deposited by low arc discharge UVNIPA-1-001 vacuum system with three sources (gas ion source for cleaning, electric arc source for non-magnetic metal sputtering and pulse arc carbon source for DLC deposition). The pulse sputtering of graphite target is a possible setup in wide range. Entered samples were sputtered in one vacuum cycle. All substrates were cleaned for 10 min with Ar ions. DLC layer was deposited at temperature down to 150 1C. Nitrogen and Ar gasses were added during the DLC deposition into working chamber, which is described in Table 1. The substrates were planetary rotating through all the deposition steps to achieve homogeneity. The coatings were produced on a highly polished flat CrCoMo substrate material with Ra ¼ 0.05 mm. One fine polished face of each CrCoMo substrate was coated with DLC film. The hardness and other mechanical characteristics were determined from depth sensing indentation (DSI) curves measured with Nano TEST NT 600. Raman measurements were conducted in DILOR-JOBIN YVON-SPEX Raman spectrometer, type LabRam. The excitation source was a He–Ne laser with 632.8 nm wavelength operated at 15 mW. The spectrometer was calibrated to 520.7 cm1 band of single crystalline Si and 1332 cm1 band of natural diamond. Scanning electron microscope (SEM) LEO 1550 operating in the secondary electron mode was used to study the microtopography of DLC layers.
3. Results and discussion Corresponding author. Tel.: +421 2 602 91 365; fax: +421 2 654 23 480.
E-mail address: [email protected] (M. Vojs). 0026-2692/$ - see front matter & 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.mejo.2008.06.083
The adhesion behavior of carbon coatings has been characterized by scratch tests. Scratch experiments with diamond Rockwell
ARTICLE IN PRESS M. Vojs et al. / Microelectronics Journal 40 (2009) 650–653
Table 1 Deposition parameters of DLC layers deposited by UVNIPA-1-001 No.
Ar (sccm)
N2 (sccm)
Dep. technique
U II U III U IIII
70 80 80
60 60 50
Arc discharge Arc discharge Arc discharge
Table 2 Results from nanoscratch tests No.
Lc1 (nM)
Lc2 (nM)
Lc3 (nM)
U II U III U IIII
46.0 40.5 42.0
53.5 79.0 62.5
57.5 120.0 115.0
200
greater measure is marked as LC3. During scratch test the sample feed speed dx/dt was recorded at loads with continuously increasing force. The acoustic emission signal is also recorded with a camera. The hardness H, elastic modulus Eeff and mechanical characteristics were determined from depth sensitive indentations (DSI curves measured by the NanoTest NT 600 apparatus at different maximal loads from 5, 10, 20, 50, and 100 mN with diamond Berkovich tip using the analysis developed by the Oliver–Pharr procedure [8]. Each indentation cycle (uploading to the maximal load and downloading to 0) was repeated five times in slightly different places for each maximal load. The load dependence of Eeff and HIT (1/Eeff ¼ [(1n2)/E]+ [(1ni2)/Ei], where index i means material of the indenter; for diamond ni ¼ 0.07 and Ei ¼ 1141 GPa) is shown in Fig. 1a and b. Values of Eeff for all types of DLC coatings are almost constant (Fig. 1a). Values of HIT for coatings of type U III and U IIII deposited under conditions given in Table 1 are comparable, the lowest value was observed for coating U II, what can be connected with lower content of N. Values of H3IT/E2eff (Fig. 2a) and also of HIT/Eeff (Fig. 2b) for type of films marked U III and U IIII are almost similar. The lowest value for H3IT/E2eff and of HIT/Eeff was observed for coating marked U II. Friction tests were performed on the same samples as for indentations by applying a microtribometre dry sliding point
150 Sample: No- Ar/N U II - 70/60 U III - 80/60 U IIII - 80/50
125
100 0
20
40
60 Load [mN]
80
100
0.08 Sample: No- Ar/N U II - 70/60 U III - 80/60 U IIII - 80/50
0.07 H3/E2 [GPa]
Eeff [GPa]
175
651
0.06 0.05 0.04 0.03
12
0.02 Sample: No- Ar/N U II - 70/60 U III - 80/60 U IIII - 80/50
HIT [GPa]
10
0.01 0.00 0
20
40
60 80 Load [mN]
100
8 0.09 Sample: No- Ar/N U II - 70/60 U III - 80/60 U IIII - 80/50
0.08
4 0
20
40
60 Load [mN]
80
100
Fig. 1. (a) Resulted Eeff for tested coatings under different loads and (b) resulted HIT for tested coatings under different loads.
sphere–conical tip of + ¼ 25 mm with scratch length of 1 mm; load in the range from 0 to 150 mN; scan speed of 0.75 mN/s were conducted. The results from nanoscratch tests are in Table 2. Loading in location where the first failure of coating occurred (cracks) is marked as LC1, the first adhesive failure of coating (flaking) is marked as LC2, the first adhesive coating failure in
HIT/Eeff [-]
6
0.07 0.06 0.05 0.04 0.03 0.02 0
20
40
60 Load [mN]
80
100
Fig. 2. (a) Dependence of H3IT/E2eff on different loads and (b) dependence of HIT/Eeff on different loads.
ARTICLE IN PRESS 652
M. Vojs et al. / Microelectronics Journal 40 (2009) 650–653
contact between corundum ball (a-Al2O3) and coatings. The coefficient of friction (COF) was recorded during testing by increasing normal force Fn from 30 to 90 mN at temperature of T ¼ 23 1C, relative humidity 50%; normal force Fn was continuously increased from 30 to 90 mN, friction couple: a-C coatings Al2O3 and ball with d ¼ 5.5 mm. Material of the ball was Al2O3. Speed of ball movement was v ¼ 0.4 mm/s. Graphical output COFs at different loads during sliding line contact are drawn in Fig. 3. From point of view of COF, coating marked with U II (DLC) was the
Friction Coefficient [µ]
0.19 0.17 0.15 0.13
Sample: No- Ar/N U II - 70/60
0.11
Sample: No- Ar/N U IIII - 80/50
Sample: No- Ar/N U III - 80/60
0.09 0.07
best. The resistance to plastic deformation—the quantity which can more distinctly divide film materials [13]. Fig. 4 presents Raman spectra taken from DLC layers. The spectrum of the DLC layer contains typical broad peaks, the ‘G’ and ‘D’ peaks. The G-peak corresponds to the fundamental E2g mode of graphite at 1580 cm–1, and D-peak disordered graphite, i.e. a Raman-active, in-plane vibrational mode for an infinite hexagonal network. With N2 content increase in case of U III (N2 from 50 to 60 sccm) we can find another broad band centered at 1140 cm1, which corresponds to nanocrystalline diamond cluster with sp3-bonding [9,10]. With increasing content of Ar/N2 ratio we observe decreasing sp2 content in layer and increasing concentration of disordered graphite sp3 bonds, and thus the stress in the coating. The lowest values of friction coefficient were recorded for coatings with highest hardness and content of sp3 bonds for U II coating, and the highest values of friction coefficient were recorded for U IIII coating with lowest sp3/sp2 ratio and hardness, what does not match with the results published elsewhere [11]. The SEM images of DLC samples are shown in Fig. 5. All layers consist of nanocomposite (nanocrystalline diamond) microstructure character clearly recognized from SEM images of diamond layers with high content of sp3 bonds [12].
90 I_
70
III
50
I_
I_
III
30
III
0
I_ III
0
_9
_7
III
0
III
0
_5 III
90
_3 III
70
II_
II_
50 II_
II_
30
0.05
Load [mN] Fig. 3. Friction coefficient COF of different loads during sliding line contact.
D
G
Sample: No- Ar/N U II - 70/60 U III - 80/60 U IIII - 80/50
Intensity [a.u.]
nano-D
800
1000
1200 1400 1600 Raman shift [cm-1]
1800
Fig. 4. Raman spectra of DLC layers: U II, U III and U IIII.
2000
4. Conclusion Tribological properties of thin and hard layers are influenced by structure, chemical composition and deposition parameters. Adhesion of thin and hard layers is dependent on the character of coupling forces between layer and substrate. Tribological properties of thin and hard layers are influenced by structure, chemical composition and parameters of deposition. Adhesion of thin and hard layers is dependent on character of coupling forces between layer and substrate [14]. For DLC coatings deposited by UVNIPA-1-001 equipment the lowest value of hardness HIT was observed for U IIII coating with highest content of sp2 bonds (Ar: 80 sccm/N2: 50 sccm). U II and U IIII coatings have almost the same values of HIT and content of N2 (60 sccm), but the adhesion parameter Lc3 (first adhesive coating failure) for U III coating is two times better than for U II coating, which corresponds to increasing content of Ar/N ratio, decreasing sp3 content in layer and increasing concentration of disordered graphite sp3 bonds and thus the stress in the coating. The friction coefficient of DLC coatings was more stable over the wide range of normal loads from 30 to 90 mN against corundum ball used at microtribotests. Its lowest values was recorded for coatings with highest hardness and content of sp3 bonds for U II coating (Ar: 70 sccm/N2: 60 sccm) and the highest values of friction coefficient were recorded for U IIII coating (Ar: 80 sccm/N2: 50 sccm) with lowest sp3/sp2 ratio and hardness.
Fig. 5. SEM images from samples: (a) U II, (b) U III and (c) U IIII.
ARTICLE IN PRESS M. Vojs et al. / Microelectronics Journal 40 (2009) 650–653
Development and applications of thin hard DLC layers are open to further research and they always represent very attractive and challenging theme.
Acknowledgments This work has been supported by Grants: COST 533, AV 4/0124/ 06, VEGA 1/0857/08, VEGA 1/0390/08 of The Ministry of Education of the Slovak Republic and APVT-20-034404, LPP-0246-06 of The Slovak Research and Development Agency and Project no. OC097 of action COST 533 of Ministry for Education, Youth and Sports of the Czech Republic. Many thanks to M. Michalka from the International Laser Center for SEM measurements.
653
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]
K. Holmberg, A. Matthews, Tribology Series 28, Elsevier, Amsterdam, 1994, p. 442. A. Grill, Wear 168 (1993) 143. A. Grill, Surf. Coat. Technol. 94/95 (1997) 507–513. A. Erdemir, M. Switala, R. Wei, P. Wilbur, Surf. Coat. Technol. 50 (1991) 17. B. Marchon, M.R. Khan, N. Heiman, P. Pereira, A. Lautie, IEEE Trans. Magnet. 26 (5) (1990) 2670. D.S. Kim, T.E. Fischer, B. Gallois, Surf. Coat. Technol. 49 (1991) 537. C. Donnet, et al., Surf. Coat. Technol. 68/69 (1994) 626–631. W.C. Oliver, G.M. Pharr, J. Mater. Res. 7 (1992) 1564–1583. G. Sepold, et al., Diamond Relat. Mater. 8 (1999) 1677–1681. A. Kromka, et al., Carbon 43 (2005) 425–429. Y. Kusano, et al., Thin Solid Films 332 (1998) 56–61. M. Vojs, et al., Diamond Relat. Mater. 14 (2005) 613–616. M. Madej, D. Ozimina, I. Piwon´ski, Tribol. Lett. 22 (2006) 135. E. Zdravecka´, et al., 9–13 September 2007 Eurocorr 2007, Freiburg; 1–9.