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DLC coating roughness as a function of film thickness
Surface & Coatings Technology 200 (2006) 5119 – 5122 www.elsevier.com/locate/surfcoat
DLC coating roughness as a function of film thickness M.C. Salvadori a,*, D.R. Martins b, M. Cattani a a
Institute of Physics, University of Sa˜o Paulo, Brazil Escola Polite´cnica, University of Sa˜o Paulo, Brazil
b
Received 23 November 2004; accepted in revised form 26 May 2005 Available online 23 June 2005
Abstract We have investigated the evolution of surfaces roughness of DLC-coated substrates as a function of film thickness. This is important for DLC applications having to do with friction and wear. We used substrates with three different roughnesses between several nanometers and hundreds of nanometers. The substrates were cut into a number pieces and each piece coated with a different DLC thickness. The coated samples were characterized by atomic force microscopy. The results show that the surface roughness changes with DLC coating thickness. For substrates with original roughness 393 and 278 nm, the coating roughness increased with DLC thickness up to a maximum and then decreased. For the substrate with original roughness around 4 nm, the coating roughness showed no systematic tendency to decrease or increase. These results are interpreted using our previous results and taking into account the thin film growth dynamics. D 2005 Elsevier B.V. All rights reserved. Keywords: DLC coating; Thin films; Roughness
1. Introduction Nanocoatings are increasingly important for a growing number of fundamental and technological applications [1,2]. In each particular case the specific coating properties must be carefully considered. These properties include the coefficient of friction, surface roughness, residual stress, adherence, pore density, etc. Diamond-like carbon (DLC) is an important nanocoating material because its chemical and physical properties can approximate those of diamond-hard, low thermal expansion, high thermal conductivity, low friction, and chemical inertness, etc. The characteristics of DLC and methods for forming thin films of this material have been widely discussed in the literature [3,4]. Here we consider an aspect of DLC coatings that has not previously been reported: the evolution of roughness of surfaces coated with DLC as a function of the DLC film thickness. This study explores substrates with initial roughness (rms) between several nanometers and hundreds of
* Corresponding author. E-mail address: [email protected] (M.C. Salvadori). 0257-8972/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2005.05.030
nanometers. The results are discussed taking into account the thin films growth dynamics [5].
2. Material and methods Three different substrates were used, two were polycrystalline diamond films and one was silicon. The three substrates had three different surface roughnesses. The diamond films were formed by microwave plasma assisted chemical vapor deposition (CVD) using facilities that have been described in detail elsewhere [6]. A silicon substrate 17 17 mm2 was polished by diamond powder, cut into pieces, and washed in an acetone ultrasonic bath. The silicon pieces were placed on the CVD substrate holder and diamond film grown using the following processing parameters: 300 sccm hydrogen flow rate, 1.5 sccm methane flow rate (0.5 vol.% methane in hydrogen), 1 104 Pa chamber pressure, 1128 K substrate temperature, and 700 W microwave power. The diamond films formed in this way then served as substrates for the subsequent DLC deposition and characterization experiments, and had roughness in the hundreds of nanometers range.
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M.C. Salvadori et al. / Surface & Coatings Technology 200 (2006) 5119 – 5122
Fig. 3. Typical AFM image of the silicon surface etched with acid used as substrate in this work. Fig. 1. Simplified schematic of the filtered vacuum arc plasma deposition set-up.
The silicon substrates were wet etched using a room temperature mixture of hydrofluoric acid, nitric acid and acetic acid, in which they were immersed for about 5 min. These silicon samples then served as substrates for the subsequent experiments, and had roughness of several nanometers. Each sample was characterized by atomic force microscopy (AFM) in contact mode. The microscope used was a Digital Instruments NanoScope IIIA scanning probe microscope. A silicon nitride tip was used with highest measurable angle of 65-. In our AFM images the measured angles are much smaller than 65- and the smallest pixel size was about 30 nm; thus it was not necessary to take into account the convolution of tip shape and surface profile. For each sample, three images were taken and an average roughness rms (root mean square) obtained. For each substrate sample, DLC films of different thicknesses were deposited using a filtered vacuum arc plasma deposition system that has been described in detail
elsewhere [7]. Carbon plasma is produced in abundance from a solid carbon cathode material by a high current vacuum arc, and it is this plasma that carries the arc current and is also used for the DLC deposition. For the work described here, a repetitively pulsed vacuum arc plasma gun [8] was used; the arc current was 200 A, the pulse length 5 ms, and the repetition rate 1 pulse per second. A 90magnetic filter was used to remove the Fmacroparticle_ flux (tiny droplets of cathode material) from the plasma stream [9]. The carbon plasma flux exiting the magnetic duct was deposited onto the substrate that was mounted on a grounded holder positioned about 10 cm from the duct exit. A simplified schematic of the filtered vacuum arc plasma deposition system is shown in Fig. 1. Note that the plasma deposition is performed perpendicularly to the substrate surface. A characteristic feature of vacuum-arc-produced plasma is the relatively high directed energy of the ions, in the range 20 – 150 eV depending on the ion species; for carbon the directed energy is about 20 eV. The film deposition is thus an energetic deposition, and for the case of carbon this results in the film material formed being a
rmscoated - rmsoriginal (nm)
300 250 200
rmsoriginal=393nm
150 100 50 0 20
40
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80
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120
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160
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200
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Film Thickness (nm) Fig. 2. Typical AFM image of the CVD diamond used as substrate in this work.
Fig. 4. Roughness shift as a function of DLC coating thickness, with CVD diamond substrate of original roughness 393 nm.
M.C. Salvadori et al. / Surface & Coatings Technology 200 (2006) 5119 – 5122
5121
250 200
↑
δ
rmsoriginal=278nm
150 100
DLC
↑
rmscoated - rmsoriginal (nm)
300
Si
50 0 -50 20
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100
120
140
160
180
200
220
Fig. 7. Schematic illustration of AFM tip extremity after DLC deposition, showing that the coating is thicker than on the lateral surfaces of the tip (y). From Ref. [7].
Film Thickness (nm) Fig. 5. Roughness shift as a function of DLC coating thickness, with CVD diamond substrate of original roughness 278 nm.
fairly high quality, hydrogen-free, diamond-like carbon [10,11]. We stress that the DLC deposition is a plasma deposition process, with relatively high ion energy, carried out in high vacuum and accompanied by no neutral particle flux. The DLC films on the samples were characterized by AFM. For each sample, three images were taken and an average roughness rms (root mean square) was obtained.
3. Results Typical AFM images of the substrates prior to DLC deposition are shown in Figs. 2 and 3. Fig. 2 shows the morphology of the CVD diamond surface, similar for both series (substrate roughness) used in this work; it is faceted, indicating good diamond quality. Fig. 3 shows the morphology of the silicon surface after being acid-etched. Importantly, note that in Fig. 3 the z-scale (height) is 200 nm per division while the scale in the plane of the surface is 5 Am per division; the image shown in Fig. 3 is expanded in the z
rmscoated - rmsoriginal (nm)
6 5 4
direction, emphasizing the film profile. The purpose in using these substrates was to have substrates with roughness (rms) varying from a few nanometers to hundreds of nanometers. Figs. 4– 6 show the measured surface roughness shifts as a function of DLC coating thickness. As can be seen, for substrates with original roughness 393 and 278 nm, the roughness shift increases with DLC thickness up to a maximum value and then decreases. For the substrate with original roughness around 4 nm, the roughness shift has no systematic tendency to decrease or increase. These results are consistent with our previous results [12,13]. In Ref. [12] we described work in which silicon AFM tips were coated with DLC to various thickness. We showed that there was a higher DLC deposition rate at the tip extremity than on the lateral surfaces of the tip, as illustrated in the schematic shown in Fig. 7. In this way, for sharply pointed structures as for the diamond films used here (see Fig. 2), DLC coating leads to a broadening of the sharp edges of the faceted crystals, increasing the roughness. Thus the roughness of the DLC-coated substrate increases for small DLC film thickness. However the roughness decreases for thicker coatings (see Figs. 4 and 5). In previous work [13], flat silicon (monocrystalline) substrates were coated with DLC of thickness between 30 and 200 nm, and in this case we showed that the DLC ˚ , corresponding to the original roughness was about 0.5 A substrate roughness. This result is consistent with the present observations for the wet-etched silicon substrate, as shown in Fig. 6. In this case there is no trend in roughness shift due to the DLC coating.
rmsoriginal=4nm
3 2
4. Discussion and conclusion
1
In previous work we have studied and reported [14,15] the growth dynamics of diamond films with different amorphous carbon concentrations. Note that the plasma deposition in our preceding papers [14,15] and in the present paper is performed perpendicularly to the substrate surface. In these conditions it was shown that the deposition process obeys the ballistic model (BD), which belongs to
0 20
40
60
80
100
120
140
160
180
200
220
Film Thickness (nm) Fig. 6. Roughness shift as a function of DLC coating thickness, with acidetched silicon substrate of original roughness 4 nm.
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thin films the dynamic growth process depends critically on the initial substrate roughness [17]. However, for thicker films [5,16] memory of the initial substrate roughness is lost and the film roughness increases with film thickness.
Acknowledgments Fig. 8. Illustration of a rough substrate with the successive DLC depositions.
the same universality class [5] of the stochastic equation of Kardar – Parisi –Zhang (KPZ). Since DLC films are basically amorphous carbon with diamond carbon bonds, we expect that their growth process also obeys the BD model. According to the BD model [5], in the early stages of the deposition process on a rough surface, the tops of the hills grow faster than the valleys are filled. This is illustrated by the first profile in Fig. 8. This figure is an illustration of a rough substrate with the successive overlaying DLC depositions, represented by the line profiles. Thus in the beginning of the deposition, the DLC film roughness tends to increase, becoming larger than the original roughness of the substrate surface. But as the DLC film grows thicker, the roughness growth decreases, as can be seen in Figs. 4 and 5. This is mainly due to filling of the valleys, generated by lateral growth of the surfaces characteristic of the BD model [5], and is illustrated by the second profile of Fig. 8. The decrease in roughness with increasing deposition thickness, as observed in our experimental results (Figs. 4 and 5), is expected according to the KPZ equation predictions [5,16]. This is illustrated in the successive profiles of Fig. 8. On the other hand, when DLC is deposited on a smooth surface such as the silicon substrate with low roughness, with very small hills and valleys, the roughness remains approximately constant with film thickness (Fig. 6). The roughness does not vary as it does for the case of rough diamond substrates (Figs. 4 and 5). Note that this roughness behavior, as seen in Figs. 4– 6, occurs only for thin DLC films, that is, for d < 200 nm, as used in the work described here. This is because for
We thank Professor Ian G. Brown from Lawrence Berkeley National Laboratory for valuable suggestions and for a critical reading of the paper. We are grateful to the FAPESP and the CNPq for financial support.
References [1] N.B. Dahotre, S. Nayak, Surf. Coat. Technol. 194 (2005) 58. [2] S.M. Spearing, Acta Mater. 48 (2000) 179. [3] See, for instance, Proceedings of the 10th European Conference on Diamond, Diamond-like Materials, Carbon Nanotubes, Nitrides and Silicon Carbide, in Diamond Relat. Mater. 9 (2000) pp. 231 – 1306 [Vol. 9, Nos.3 – 6, April/May, 2000]. [4] G. Thorwarth, C. Hammerl, M. Kuhn, W. Assmann, B. Schey, B. Stritzker, Surf. Coat. Technol. 193 (2005) 206. [5] A.-L. Baraba´si, H.E. Stanley, Fractal Concepts in Surface Growth, Cambridge University Press, 1995. [6] M.C. Salvadori, V.P. Mammana, O.G. Martins, F.T. Degasperi, Plasma Sources Sci. Technol. 4 (1995) 489. [7] A. Anders, Surf. Coat. Technol. 93 (1997) 158. [8] R.A. MacGill, M.R. Dickinson, A. Anders, O.R. Monteiro, I.G. Brown, Rev. Sci. Instrum. 69 (1998) 801. [9] A. Anders, S. Anders, I.G. Brown, J. Appl. Phys. 75 (1994) 4900. [10] G.M. Pharr, D.L. Callahan, et al., Appl. Phys. Lett. 68 (1996) 779. [11] O.R. Monteiro, Nucl. Instrum. Methods Phys. Res., B Beam Interact. Mater. Atoms 148 (1999) 12. [12] M.C. Salvadori, M.C. Fritz, C. Carraro, R. Maboudian, O.R. Monteiro, I.G. Brown, Diamond Relat. Mater. 10 (2001) 2190. [13] M.C. Salvadori, R.M. Galva˜o, O.R. Monteiro, I.G. Brown, Thin Solid Films 325 (1998) 19. [14] M.C. Salvadori, M.G. Silveira, M. Cattani, Phys. Rev., E Stat. Phys. Plasmas Fluids Relat. Interdiscip. Topics 58 (1998) 6814. [15] M.C. Salvadori, L.L. Melo, D.R. Martins, A.R. Vaz, M. Cattani, Surf. Rev. Lett. 9 (2002) 1409. [16] M. Kardar, G. Parisi, Y.C. Zhang, Phys. Rev. Lett. 56 (1986) 889. [17] T.J. da Silva, J.G. Moreira, Phys. Rev., E Stat. Phys. Plasmas Fluids Relat. Interdiscip. Topics 56 (1997) 4880.
DLC coating roughness as a function of film thickness M.C. Salvadori a,*, D.R. Martins b, M. Cattani a a
Institute of Physics, University of Sa˜o Paulo, Brazil Escola Polite´cnica, University of Sa˜o Paulo, Brazil
b
Received 23 November 2004; accepted in revised form 26 May 2005 Available online 23 June 2005
Abstract We have investigated the evolution of surfaces roughness of DLC-coated substrates as a function of film thickness. This is important for DLC applications having to do with friction and wear. We used substrates with three different roughnesses between several nanometers and hundreds of nanometers. The substrates were cut into a number pieces and each piece coated with a different DLC thickness. The coated samples were characterized by atomic force microscopy. The results show that the surface roughness changes with DLC coating thickness. For substrates with original roughness 393 and 278 nm, the coating roughness increased with DLC thickness up to a maximum and then decreased. For the substrate with original roughness around 4 nm, the coating roughness showed no systematic tendency to decrease or increase. These results are interpreted using our previous results and taking into account the thin film growth dynamics. D 2005 Elsevier B.V. All rights reserved. Keywords: DLC coating; Thin films; Roughness
1. Introduction Nanocoatings are increasingly important for a growing number of fundamental and technological applications [1,2]. In each particular case the specific coating properties must be carefully considered. These properties include the coefficient of friction, surface roughness, residual stress, adherence, pore density, etc. Diamond-like carbon (DLC) is an important nanocoating material because its chemical and physical properties can approximate those of diamond-hard, low thermal expansion, high thermal conductivity, low friction, and chemical inertness, etc. The characteristics of DLC and methods for forming thin films of this material have been widely discussed in the literature [3,4]. Here we consider an aspect of DLC coatings that has not previously been reported: the evolution of roughness of surfaces coated with DLC as a function of the DLC film thickness. This study explores substrates with initial roughness (rms) between several nanometers and hundreds of
* Corresponding author. E-mail address: [email protected] (M.C. Salvadori). 0257-8972/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2005.05.030
nanometers. The results are discussed taking into account the thin films growth dynamics [5].
2. Material and methods Three different substrates were used, two were polycrystalline diamond films and one was silicon. The three substrates had three different surface roughnesses. The diamond films were formed by microwave plasma assisted chemical vapor deposition (CVD) using facilities that have been described in detail elsewhere [6]. A silicon substrate 17 17 mm2 was polished by diamond powder, cut into pieces, and washed in an acetone ultrasonic bath. The silicon pieces were placed on the CVD substrate holder and diamond film grown using the following processing parameters: 300 sccm hydrogen flow rate, 1.5 sccm methane flow rate (0.5 vol.% methane in hydrogen), 1 104 Pa chamber pressure, 1128 K substrate temperature, and 700 W microwave power. The diamond films formed in this way then served as substrates for the subsequent DLC deposition and characterization experiments, and had roughness in the hundreds of nanometers range.
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M.C. Salvadori et al. / Surface & Coatings Technology 200 (2006) 5119 – 5122
Fig. 3. Typical AFM image of the silicon surface etched with acid used as substrate in this work. Fig. 1. Simplified schematic of the filtered vacuum arc plasma deposition set-up.
The silicon substrates were wet etched using a room temperature mixture of hydrofluoric acid, nitric acid and acetic acid, in which they were immersed for about 5 min. These silicon samples then served as substrates for the subsequent experiments, and had roughness of several nanometers. Each sample was characterized by atomic force microscopy (AFM) in contact mode. The microscope used was a Digital Instruments NanoScope IIIA scanning probe microscope. A silicon nitride tip was used with highest measurable angle of 65-. In our AFM images the measured angles are much smaller than 65- and the smallest pixel size was about 30 nm; thus it was not necessary to take into account the convolution of tip shape and surface profile. For each sample, three images were taken and an average roughness rms (root mean square) obtained. For each substrate sample, DLC films of different thicknesses were deposited using a filtered vacuum arc plasma deposition system that has been described in detail
elsewhere [7]. Carbon plasma is produced in abundance from a solid carbon cathode material by a high current vacuum arc, and it is this plasma that carries the arc current and is also used for the DLC deposition. For the work described here, a repetitively pulsed vacuum arc plasma gun [8] was used; the arc current was 200 A, the pulse length 5 ms, and the repetition rate 1 pulse per second. A 90magnetic filter was used to remove the Fmacroparticle_ flux (tiny droplets of cathode material) from the plasma stream [9]. The carbon plasma flux exiting the magnetic duct was deposited onto the substrate that was mounted on a grounded holder positioned about 10 cm from the duct exit. A simplified schematic of the filtered vacuum arc plasma deposition system is shown in Fig. 1. Note that the plasma deposition is performed perpendicularly to the substrate surface. A characteristic feature of vacuum-arc-produced plasma is the relatively high directed energy of the ions, in the range 20 – 150 eV depending on the ion species; for carbon the directed energy is about 20 eV. The film deposition is thus an energetic deposition, and for the case of carbon this results in the film material formed being a
rmscoated - rmsoriginal (nm)
300 250 200
rmsoriginal=393nm
150 100 50 0 20
40
60
80
100
120
140
160
180
200
220
Film Thickness (nm) Fig. 2. Typical AFM image of the CVD diamond used as substrate in this work.
Fig. 4. Roughness shift as a function of DLC coating thickness, with CVD diamond substrate of original roughness 393 nm.
M.C. Salvadori et al. / Surface & Coatings Technology 200 (2006) 5119 – 5122
5121
250 200
↑
δ
rmsoriginal=278nm
150 100
DLC
↑
rmscoated - rmsoriginal (nm)
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Si
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Fig. 7. Schematic illustration of AFM tip extremity after DLC deposition, showing that the coating is thicker than on the lateral surfaces of the tip (y). From Ref. [7].
Film Thickness (nm) Fig. 5. Roughness shift as a function of DLC coating thickness, with CVD diamond substrate of original roughness 278 nm.
fairly high quality, hydrogen-free, diamond-like carbon [10,11]. We stress that the DLC deposition is a plasma deposition process, with relatively high ion energy, carried out in high vacuum and accompanied by no neutral particle flux. The DLC films on the samples were characterized by AFM. For each sample, three images were taken and an average roughness rms (root mean square) was obtained.
3. Results Typical AFM images of the substrates prior to DLC deposition are shown in Figs. 2 and 3. Fig. 2 shows the morphology of the CVD diamond surface, similar for both series (substrate roughness) used in this work; it is faceted, indicating good diamond quality. Fig. 3 shows the morphology of the silicon surface after being acid-etched. Importantly, note that in Fig. 3 the z-scale (height) is 200 nm per division while the scale in the plane of the surface is 5 Am per division; the image shown in Fig. 3 is expanded in the z
rmscoated - rmsoriginal (nm)
6 5 4
direction, emphasizing the film profile. The purpose in using these substrates was to have substrates with roughness (rms) varying from a few nanometers to hundreds of nanometers. Figs. 4– 6 show the measured surface roughness shifts as a function of DLC coating thickness. As can be seen, for substrates with original roughness 393 and 278 nm, the roughness shift increases with DLC thickness up to a maximum value and then decreases. For the substrate with original roughness around 4 nm, the roughness shift has no systematic tendency to decrease or increase. These results are consistent with our previous results [12,13]. In Ref. [12] we described work in which silicon AFM tips were coated with DLC to various thickness. We showed that there was a higher DLC deposition rate at the tip extremity than on the lateral surfaces of the tip, as illustrated in the schematic shown in Fig. 7. In this way, for sharply pointed structures as for the diamond films used here (see Fig. 2), DLC coating leads to a broadening of the sharp edges of the faceted crystals, increasing the roughness. Thus the roughness of the DLC-coated substrate increases for small DLC film thickness. However the roughness decreases for thicker coatings (see Figs. 4 and 5). In previous work [13], flat silicon (monocrystalline) substrates were coated with DLC of thickness between 30 and 200 nm, and in this case we showed that the DLC ˚ , corresponding to the original roughness was about 0.5 A substrate roughness. This result is consistent with the present observations for the wet-etched silicon substrate, as shown in Fig. 6. In this case there is no trend in roughness shift due to the DLC coating.
rmsoriginal=4nm
3 2
4. Discussion and conclusion
1
In previous work we have studied and reported [14,15] the growth dynamics of diamond films with different amorphous carbon concentrations. Note that the plasma deposition in our preceding papers [14,15] and in the present paper is performed perpendicularly to the substrate surface. In these conditions it was shown that the deposition process obeys the ballistic model (BD), which belongs to
0 20
40
60
80
100
120
140
160
180
200
220
Film Thickness (nm) Fig. 6. Roughness shift as a function of DLC coating thickness, with acidetched silicon substrate of original roughness 4 nm.
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M.C. Salvadori et al. / Surface & Coatings Technology 200 (2006) 5119 – 5122
thin films the dynamic growth process depends critically on the initial substrate roughness [17]. However, for thicker films [5,16] memory of the initial substrate roughness is lost and the film roughness increases with film thickness.
Acknowledgments Fig. 8. Illustration of a rough substrate with the successive DLC depositions.
the same universality class [5] of the stochastic equation of Kardar – Parisi –Zhang (KPZ). Since DLC films are basically amorphous carbon with diamond carbon bonds, we expect that their growth process also obeys the BD model. According to the BD model [5], in the early stages of the deposition process on a rough surface, the tops of the hills grow faster than the valleys are filled. This is illustrated by the first profile in Fig. 8. This figure is an illustration of a rough substrate with the successive overlaying DLC depositions, represented by the line profiles. Thus in the beginning of the deposition, the DLC film roughness tends to increase, becoming larger than the original roughness of the substrate surface. But as the DLC film grows thicker, the roughness growth decreases, as can be seen in Figs. 4 and 5. This is mainly due to filling of the valleys, generated by lateral growth of the surfaces characteristic of the BD model [5], and is illustrated by the second profile of Fig. 8. The decrease in roughness with increasing deposition thickness, as observed in our experimental results (Figs. 4 and 5), is expected according to the KPZ equation predictions [5,16]. This is illustrated in the successive profiles of Fig. 8. On the other hand, when DLC is deposited on a smooth surface such as the silicon substrate with low roughness, with very small hills and valleys, the roughness remains approximately constant with film thickness (Fig. 6). The roughness does not vary as it does for the case of rough diamond substrates (Figs. 4 and 5). Note that this roughness behavior, as seen in Figs. 4– 6, occurs only for thin DLC films, that is, for d < 200 nm, as used in the work described here. This is because for
We thank Professor Ian G. Brown from Lawrence Berkeley National Laboratory for valuable suggestions and for a critical reading of the paper. We are grateful to the FAPESP and the CNPq for financial support.
References [1] N.B. Dahotre, S. Nayak, Surf. Coat. Technol. 194 (2005) 58. [2] S.M. Spearing, Acta Mater. 48 (2000) 179. [3] See, for instance, Proceedings of the 10th European Conference on Diamond, Diamond-like Materials, Carbon Nanotubes, Nitrides and Silicon Carbide, in Diamond Relat. Mater. 9 (2000) pp. 231 – 1306 [Vol. 9, Nos.3 – 6, April/May, 2000]. [4] G. Thorwarth, C. Hammerl, M. Kuhn, W. Assmann, B. Schey, B. Stritzker, Surf. Coat. Technol. 193 (2005) 206. [5] A.-L. Baraba´si, H.E. Stanley, Fractal Concepts in Surface Growth, Cambridge University Press, 1995. [6] M.C. Salvadori, V.P. Mammana, O.G. Martins, F.T. Degasperi, Plasma Sources Sci. Technol. 4 (1995) 489. [7] A. Anders, Surf. Coat. Technol. 93 (1997) 158. [8] R.A. MacGill, M.R. Dickinson, A. Anders, O.R. Monteiro, I.G. Brown, Rev. Sci. Instrum. 69 (1998) 801. [9] A. Anders, S. Anders, I.G. Brown, J. Appl. Phys. 75 (1994) 4900. [10] G.M. Pharr, D.L. Callahan, et al., Appl. Phys. Lett. 68 (1996) 779. [11] O.R. Monteiro, Nucl. Instrum. Methods Phys. Res., B Beam Interact. Mater. Atoms 148 (1999) 12. [12] M.C. Salvadori, M.C. Fritz, C. Carraro, R. Maboudian, O.R. Monteiro, I.G. Brown, Diamond Relat. Mater. 10 (2001) 2190. [13] M.C. Salvadori, R.M. Galva˜o, O.R. Monteiro, I.G. Brown, Thin Solid Films 325 (1998) 19. [14] M.C. Salvadori, M.G. Silveira, M. Cattani, Phys. Rev., E Stat. Phys. Plasmas Fluids Relat. Interdiscip. Topics 58 (1998) 6814. [15] M.C. Salvadori, L.L. Melo, D.R. Martins, A.R. Vaz, M. Cattani, Surf. Rev. Lett. 9 (2002) 1409. [16] M. Kardar, G. Parisi, Y.C. Zhang, Phys. Rev. Lett. 56 (1986) 889. [17] T.J. da Silva, J.G. Moreira, Phys. Rev., E Stat. Phys. Plasmas Fluids Relat. Interdiscip. Topics 56 (1997) 4880.