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Friction and adhesion properties of fluorocarbon polymer thin films prepared by magnetron sputtering
Vacuum 84 (2010) 592–596
Contents lists available at ScienceDirect
Vacuum journal homepage: www.elsevier.com/locate/vacuum
Friction and adhesion properties of fluorocarbon polymer thin films prepared by magnetron sputtering Satoru Iwamori a, *, Norihiko Hasegawa a, Akihiro Uemura a, Tomoya Tanabe a, Itsuo Nishiyama b a b
Graduate School of Natural Science and Technology, Kanazawa University, Kakuma-machi, Kanazawa city 920-1192, Japan Daipla Wintes Co. Ltd, Japan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 16 October 2008 Received in revised form 13 February 2009 Accepted 15 April 2009
Fluorocarbon polymer thin films were deposited onto a SUS302 substrate with a poly(tetrafluoroethylene) (PTFE) target by three different types of r.f. magnetron sputtering systems with strong, weak and unbalanced magnetic fields. Friction and adhesion properties of these polymer thin films were evaluated. Friction coefficient of polymer thin films prepared with strong magnetic field, unbalanced magnetron and without magnetron (r.f. sputtering) was almost the same level, however, that prepared with the weak magnetic field was slightly lower than those of other thin films. Wear durability of polymer thin film increased with increase of the magnetic field. Adhesion strength between these thin films and SUS302 substrate and shear stress were measured by SAICAS. Both of the adhesion strength and shear stress of polymer thin films prepared with r.f. sputtering (without magnetron) were slightly higher than those prepared by magnetron sputtering systems. Crown Copyright Ó 2009 Published by Elsevier Ltd. All rights reserved.
Pacs: 61.82.Pv 68.55.-a 81.15.Cd Keywords: Poly(tetrafluoroethylene) Thin film Magnetic field Unbalanced magnetron sputtering Friction Wear Adhesion strength Shear stress
1. Introduction Sputtering is widely used in electrical and mechanical industries, because a sputtered thin film has a uniform structure and an excellent adhesion property to most substrates. Poly(tetrafluoroethylene) (PTFE) has been widely used in mechanical, electrical and medical industries because it has excellent thermal stability, lubricating properties, and chemical stability. Surfaces of metal, inorganic and organic material substrates can be modified by coating of fluorocarbon polymer thin films. However, poor adhesion to the metal and inorganic material substrates sometimes causes problems. Coating technologies for stronger adhesion are definitely needed. There are many reports on properties of the fluorocarbon polymer thin films prepared by r.f. sputtering or r.f. magnetron sputtering with a poly(tetrafluoroethylene) target [1–6]. We’ve already reported on the effects of magnetic fields in the sputtering systems on surface morphologies and chemical
* Corresponding author. Tel./fax: þ81 76 234 4950. E-mail address: [email protected] (S. Iwamori).
structures of the fluorocarbon polymer thin films [7]. However, mechanical and tribological properties of the polymer thin films prepared by these magnetron sputtering systems have not reported. In this paper, we report on the friction and wear properties, adhesion to metal substrate and shear stress of these fluorocarbon polymer thin films deposited by three types of r.f. magnetron sputtering systems with a strong, a weak and an unbalanced magnetic fields. 2. Experimental Fluorocarbon polymer thin films were prepared with an r.f. sputtering apparatus (SBR-1104E, ULVAC, Inc., Japan) used a poly(tetrafluoroethylene) (PTFE) target (100 mm B 5mmt). The r.f. sputtering apparatus equipped with a magnetic field beneath the PTFE target. Fig. 1 shows a schematic diagram of sputtering system. The PTFE target and substrates are equipped onto down and upper electrodes respectively. Distance between the upper electrode and top surface of the PTFE target was 40 mm. I, II and III show substrate positions. We’ve already reported that floating potentials of substrates in the r.f.
0042-207X/$ – see front matter Crown Copyright Ó 2009 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.vacuum.2009.04.044
S. Iwamori et al. / Vacuum 84 (2010) 592–596
Fig. 1. Schematic diagram of sputtering system.
sputtering without magnetic field and with weak, strong and unbalanced magnetic fields were 28, 44, 63 and 63 V, and ion current at the region I were 15, 48, 1210 and 705 mA respectively [7]. Further, the ion current at the surface of the substrate in these magnetron sputtering systems slightly decreased with increase of distance from the middle of substrate [7]. Tribological properties were evaluated with these polymer thin films deposited around the region I. Adhesion strength and shear stress of these polymer thin films were analyzed in each region. Fig. 2 shows a schematic diagram of magnetron sputtering system, and magnetic fields used in this experiment are also summarized. Detail sputtering conditions were described in previous paper [7]. Coating thickness of these polymer thin films was 0.4 mm for
593
evaluation of tribological properties and 0.1 mm for evaluation of adhesion property. After the SUS302 substrates were polished with different grades of sandpaper (#400, #800, #1200, #2000), these were grounded with a Green Silicon Carbide #8000Ò (FUJIMI Inc., Japan). An arithmetical mean roughness (Ra) of the SUS302 surfaces was measured using a surface roughness measurement instrument, Surfcom 1400A-6Ò (Tokyo Seimitsu, Inc., Japan). The Ra value of the substrate was 32 3 nm after these procedures. These polished substrates were washed with distilled water and ultrasonically cleaned in acetone. The Ra values in the regions I, II and III were 15 5 nm after the coating of these polymer thin films. A pin-on-disk type friction and wear test apparatus with a steel ball (2 mm in diameter) as the slider was used for evaluation of friction coefficient and wear durability [8]. Revolution speed of the disk was 5 revolutions/min and revolution diameter of the pin was 5 mm. The load on the steel ball was 10 g for measuring friction coefficient, and 100 g for evaluation of wear durability. The friction coefficient was determined by averaging the values within 15 revolutions in order to eliminate an effect of the transfer films onto the steel ball. At least five separate measurements were used in averaging the friction coefficients and wear durability. The wear durability was evaluated by measuring the extent of electric current flown between the substrate and polymer thin films [8]. When the thin film is worn out or peeled off from the SUS302 substrate, an electric current flows between the pin and the substrate. This system has twenty four measurement points on a scratch track. If the signals of electric current are detected at six points, the wear ratio is 25% [8]. Shear stress is one of the important mechanical properties of thin films, which indicates brittleness of the thin film. Adhesion strength between these thin films and SUS302 substrate and shear stress of these thin films were measured by SAICASÒ(Surface and Interface Cutting Analysis System: DAIPLA WINTES Co., Ltd., Japan). Adhesion strength and shear stress in small area can be analyzed with SAICAS. Vertical and horizontal reaction forces at a single crystal diamond blade during cutting the thin film were monitored. Fig. 3(A) and (B) show a schematic diagram of the SAICAS and a typical profile of the reaction forces of the SAICAS. The shear stress can be calculated with measuring the horizontal force reaction during cutting the thin films (cutting mode). After the tip of the blade gets to the interface between the thin film and substrate, it moves only in the horizontal direction (peel mode). The thin films are peeled off from the substrates due to the tip of the blade moving in the horizontal direction. This force means the adhesion strength between the thin film and substrate (Fig. 3 (B)). The adhesion strength, P, and shear stress, s, can be represented as follows [9];
P ¼ FH =w
ðN=mÞ
s ¼ FH =ð2w$d$cotfÞ ðMPaÞ
(1) (2)
FH, w, d and 4 denote the horizontal reaction force, width of the blade, coating thickness and shear angle, respectively. In this experiment, we assumed 4 as 45 degree and calculated s according to equation (2). At least four separate measurements were used in averaging the adhesion strength and shear stress. 3. Results and discussion 3.1. Tribological properties of polymer thin films prepared by r.f. magnetron sputtering systems
Fig. 2. Schematic diagram of magnetron sputtering system and magnetic fields used in this experiment.
Fig. 4 shows friction coefficients of polymer thin films prepared by r.f. magnetron sputtering systems with a strong, a weak and an unbalanced magnetic fields. Taking into consider that this
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Fig. 3. Schematic diagram of the SAICAS (A) and a typical profile of the reaction forces of the SAICAS (B).
measuring system has an error value of friction coefficient within 0.02, friction coefficient of polymer thin films prepared with strong magnetic field, unbalanced magnetron and without magnetron (r.f. sputtering) was almost the same level, however, that prepared with the weak magnetic field was slightly lower than those of other thin films. Fig. 5 shows wear ratios of these polymer thin films. Wear durability of polymer thin films prepared by r.f. magnetron sputtering systems with strong and unbalanced magnetic fields was higher than that prepared by r.f. sputtering. Fig. 6(A)–(D) show the optical micrographs of scratch tracks in these polymer thin films after the 300 revolutions. The scratch tracks can be observed in all of polymer thin films. Taking into consideration of the results shown in Fig. 5, we’ve interpreted whether the coating films are removed or not. The polymer thin films prepared by r.f. sputtering
(Fig. 6(A)) and r.f. magnetron sputtering with weak magnetic field (Fig. 6(B)) were worn, however, those with strong (Fig. 6(C)) and unbalanced (Fig. 6(D)) magnetic fields remained. These results indicate that the wear durability for the steel ball of the polymer thin film prepared by r.f. magnetron sputtering systems with strong and unbalanced magnetic fields is higher than those with r.f. sputtering and r.f. magnetron sputtering with weak magnetic field. Wear durability of polymer thin film increased with increase of the magnetic field.
Fig. 4. Friction coefficients of polymer thin films prepared by r.f. magnetron sputtering systems with a strong, a weak and an unbalanced magnetic fields.
Fig. 5. Wear ratios of polymer thin films prepared by these r.f. magnetron sputtering systems and r.f sputtering system.
3.2. Adhesion and mechanical properties of fluorocarbon thin films prepared by the magnetron sputtering systems Adhesion strength between these thin films and SUS302 substrate and shear stress of these thin films were measured by
S. Iwamori et al. / Vacuum 84 (2010) 592–596
595
Fig. 6. Optical micrographs of scratch tracks in these polymer thin films after the 300 revolutions; prepared by r.f. sputtering (A), magnetron sputtering with weak magnetic field (B), with strong magnetic field (C) and unbalanced magnetic field (D).
SAICAS. Fig. 7 shows the adhesion strength of fluorocarbon polymer thin films. Adhesion strength of fluorocarbon polymer thin film prepared by r.f. sputtering showed highest value of all the fluorocarbon polymer thin films, and it slightly decreased with increase of magnetic fields in the sputtering systems. Adhesion strength of the polymer thin films prepared with strong and unbalanced magnetic fields in the region III was higher than that in the regions I and II. Fig. 8 shows shear stress of fluorocarbon polymer thin films. Shear stress of fluorocarbon polymer thin film prepared by r.f. sputtering showed highest of all the fluorocarbon polymer thin films. Shear stress of the polymer thin films prepared with strong and unbalanced magnetic fields in the region III were higher than that in the regions I and II as well as adhesion strength shown in Fig. 7. Why the polymer thin films prepared with strong magnetic fields show poor adhesion and shear stress compared to those with weak or without magnetic fields? We’ve already reported that ion current at surface of substrate increased with increase of magnetic field [7]. Further, the ion current around the regions I and II was higher than that around the region III in the polymer thin film
prepared with strong and unbalanced magnetic fields [7]. Large amount of ion bombardment during deposition would interfere with good adhesion and high resistance to shear stress. However, these adhesion strength and shear stress are not proportion to the ion current. There would be some factors to effect on these properties except for the ion current. The peeling is one of important factors to effect on the wear durability. A decrease of wear durability is caused by the peeling. We’d already reported that a sputtered thin film used a polyimide target deposited onto copper substrate with nitrogen showed higher wear durability than that with argon [10]. This thin film with argon was worn with peeling, however that with nitrogen worn out without peeling. The adhesion strength of the sputtered thin film with nitrogen was higher than that with argon [10]. These fluorocarbon polymer thin films were worn out without peeling as shown in Fig. 6 as well as the sputtered thin film used a polyimide target deposited onto copper substrate with nitrogen. However the adhesion strength of these fluorocarbon polymer thin films was almost the same value as that of the thin film with argon. Not only
Fig. 7. Adhesion strength of fluorocarbon polymer thin films in regions I, II and III shown in Fig. 1.
Fig. 8. Shear stress of fluorocarbon polymer thin films in regions I, II and III shown in Fig. 1.
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adhesion strength but also some characteristics, e.g., surface morphologies, hardness, brittleness, may relate with the wear durability.
adhesion strength and shear stress of polymer thin films prepared with r.f. sputtering (without magnetron) were slightly higher than those prepared by magnetron sputtering systems.
4. Conclusions Fluorocarbon polymer thin films were deposited with a poly(tetrafluoroethylene) target by three different types of r.f. magnetron sputtering systems with a strong, a weak and an unbalanced magnetic fields and r.f. sputtering. Friction coefficient of polymer thin film prepared by r.f. magnetron sputtering systems with weak magnetic field showed lowest, and that with strong magnetic field showed highest of all the thin films. Wear durability of polymer thin films prepared by r.f. magnetron sputtering systems with strong and unbalanced magnetic fields was higher than that prepared by r.f. magnetron sputtering system with weak magnetic field and r.f. sputtering. Both of the
References [1] Yamada Y, Kurobe T. Jpn J Appl Phys 1993;32:5090. [2] Biederman H. Vacuum 2000;59:594. [3] Biederman H, Zeuner M, Zalman J, Bı´lkova´ P, Slavı´nska´ D, Stelmasuk V, et al. Thin Solid Films 2001;392:208. [4] Stelmashuk V, Biederman H, Slavı´nska´ D, Zemek J, Trchova´ M. Vacuum 2005;77:131. [5] Kezuka K, Uemura A, Iwamori S. J Vac Soc Jpn 2008;51:201. [6] Iwamori S, Kezuka K, Uemura A. J Soc Mater Sci Jpn 2008;57:611. [7] Iwamori S, Hasegawa N, Uemura A. Surf Coat Technol 2008;203:59. [8] Iwamori S, Uemura A, Yamada Y, Adhes J. Sci Technol 2004;18:1771. [9] Nishiyama I, Saito M. J Printing Sci Technol Jpn 2005;42:285. [10] Iwamori S, Uemura A. J Adhes Soc Jpn 2006;42:89.
Contents lists available at ScienceDirect
Vacuum journal homepage: www.elsevier.com/locate/vacuum
Friction and adhesion properties of fluorocarbon polymer thin films prepared by magnetron sputtering Satoru Iwamori a, *, Norihiko Hasegawa a, Akihiro Uemura a, Tomoya Tanabe a, Itsuo Nishiyama b a b
Graduate School of Natural Science and Technology, Kanazawa University, Kakuma-machi, Kanazawa city 920-1192, Japan Daipla Wintes Co. Ltd, Japan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 16 October 2008 Received in revised form 13 February 2009 Accepted 15 April 2009
Fluorocarbon polymer thin films were deposited onto a SUS302 substrate with a poly(tetrafluoroethylene) (PTFE) target by three different types of r.f. magnetron sputtering systems with strong, weak and unbalanced magnetic fields. Friction and adhesion properties of these polymer thin films were evaluated. Friction coefficient of polymer thin films prepared with strong magnetic field, unbalanced magnetron and without magnetron (r.f. sputtering) was almost the same level, however, that prepared with the weak magnetic field was slightly lower than those of other thin films. Wear durability of polymer thin film increased with increase of the magnetic field. Adhesion strength between these thin films and SUS302 substrate and shear stress were measured by SAICAS. Both of the adhesion strength and shear stress of polymer thin films prepared with r.f. sputtering (without magnetron) were slightly higher than those prepared by magnetron sputtering systems. Crown Copyright Ó 2009 Published by Elsevier Ltd. All rights reserved.
Pacs: 61.82.Pv 68.55.-a 81.15.Cd Keywords: Poly(tetrafluoroethylene) Thin film Magnetic field Unbalanced magnetron sputtering Friction Wear Adhesion strength Shear stress
1. Introduction Sputtering is widely used in electrical and mechanical industries, because a sputtered thin film has a uniform structure and an excellent adhesion property to most substrates. Poly(tetrafluoroethylene) (PTFE) has been widely used in mechanical, electrical and medical industries because it has excellent thermal stability, lubricating properties, and chemical stability. Surfaces of metal, inorganic and organic material substrates can be modified by coating of fluorocarbon polymer thin films. However, poor adhesion to the metal and inorganic material substrates sometimes causes problems. Coating technologies for stronger adhesion are definitely needed. There are many reports on properties of the fluorocarbon polymer thin films prepared by r.f. sputtering or r.f. magnetron sputtering with a poly(tetrafluoroethylene) target [1–6]. We’ve already reported on the effects of magnetic fields in the sputtering systems on surface morphologies and chemical
* Corresponding author. Tel./fax: þ81 76 234 4950. E-mail address: [email protected] (S. Iwamori).
structures of the fluorocarbon polymer thin films [7]. However, mechanical and tribological properties of the polymer thin films prepared by these magnetron sputtering systems have not reported. In this paper, we report on the friction and wear properties, adhesion to metal substrate and shear stress of these fluorocarbon polymer thin films deposited by three types of r.f. magnetron sputtering systems with a strong, a weak and an unbalanced magnetic fields. 2. Experimental Fluorocarbon polymer thin films were prepared with an r.f. sputtering apparatus (SBR-1104E, ULVAC, Inc., Japan) used a poly(tetrafluoroethylene) (PTFE) target (100 mm B 5mmt). The r.f. sputtering apparatus equipped with a magnetic field beneath the PTFE target. Fig. 1 shows a schematic diagram of sputtering system. The PTFE target and substrates are equipped onto down and upper electrodes respectively. Distance between the upper electrode and top surface of the PTFE target was 40 mm. I, II and III show substrate positions. We’ve already reported that floating potentials of substrates in the r.f.
0042-207X/$ – see front matter Crown Copyright Ó 2009 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.vacuum.2009.04.044
S. Iwamori et al. / Vacuum 84 (2010) 592–596
Fig. 1. Schematic diagram of sputtering system.
sputtering without magnetic field and with weak, strong and unbalanced magnetic fields were 28, 44, 63 and 63 V, and ion current at the region I were 15, 48, 1210 and 705 mA respectively [7]. Further, the ion current at the surface of the substrate in these magnetron sputtering systems slightly decreased with increase of distance from the middle of substrate [7]. Tribological properties were evaluated with these polymer thin films deposited around the region I. Adhesion strength and shear stress of these polymer thin films were analyzed in each region. Fig. 2 shows a schematic diagram of magnetron sputtering system, and magnetic fields used in this experiment are also summarized. Detail sputtering conditions were described in previous paper [7]. Coating thickness of these polymer thin films was 0.4 mm for
593
evaluation of tribological properties and 0.1 mm for evaluation of adhesion property. After the SUS302 substrates were polished with different grades of sandpaper (#400, #800, #1200, #2000), these were grounded with a Green Silicon Carbide #8000Ò (FUJIMI Inc., Japan). An arithmetical mean roughness (Ra) of the SUS302 surfaces was measured using a surface roughness measurement instrument, Surfcom 1400A-6Ò (Tokyo Seimitsu, Inc., Japan). The Ra value of the substrate was 32 3 nm after these procedures. These polished substrates were washed with distilled water and ultrasonically cleaned in acetone. The Ra values in the regions I, II and III were 15 5 nm after the coating of these polymer thin films. A pin-on-disk type friction and wear test apparatus with a steel ball (2 mm in diameter) as the slider was used for evaluation of friction coefficient and wear durability [8]. Revolution speed of the disk was 5 revolutions/min and revolution diameter of the pin was 5 mm. The load on the steel ball was 10 g for measuring friction coefficient, and 100 g for evaluation of wear durability. The friction coefficient was determined by averaging the values within 15 revolutions in order to eliminate an effect of the transfer films onto the steel ball. At least five separate measurements were used in averaging the friction coefficients and wear durability. The wear durability was evaluated by measuring the extent of electric current flown between the substrate and polymer thin films [8]. When the thin film is worn out or peeled off from the SUS302 substrate, an electric current flows between the pin and the substrate. This system has twenty four measurement points on a scratch track. If the signals of electric current are detected at six points, the wear ratio is 25% [8]. Shear stress is one of the important mechanical properties of thin films, which indicates brittleness of the thin film. Adhesion strength between these thin films and SUS302 substrate and shear stress of these thin films were measured by SAICASÒ(Surface and Interface Cutting Analysis System: DAIPLA WINTES Co., Ltd., Japan). Adhesion strength and shear stress in small area can be analyzed with SAICAS. Vertical and horizontal reaction forces at a single crystal diamond blade during cutting the thin film were monitored. Fig. 3(A) and (B) show a schematic diagram of the SAICAS and a typical profile of the reaction forces of the SAICAS. The shear stress can be calculated with measuring the horizontal force reaction during cutting the thin films (cutting mode). After the tip of the blade gets to the interface between the thin film and substrate, it moves only in the horizontal direction (peel mode). The thin films are peeled off from the substrates due to the tip of the blade moving in the horizontal direction. This force means the adhesion strength between the thin film and substrate (Fig. 3 (B)). The adhesion strength, P, and shear stress, s, can be represented as follows [9];
P ¼ FH =w
ðN=mÞ
s ¼ FH =ð2w$d$cotfÞ ðMPaÞ
(1) (2)
FH, w, d and 4 denote the horizontal reaction force, width of the blade, coating thickness and shear angle, respectively. In this experiment, we assumed 4 as 45 degree and calculated s according to equation (2). At least four separate measurements were used in averaging the adhesion strength and shear stress. 3. Results and discussion 3.1. Tribological properties of polymer thin films prepared by r.f. magnetron sputtering systems
Fig. 2. Schematic diagram of magnetron sputtering system and magnetic fields used in this experiment.
Fig. 4 shows friction coefficients of polymer thin films prepared by r.f. magnetron sputtering systems with a strong, a weak and an unbalanced magnetic fields. Taking into consider that this
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S. Iwamori et al. / Vacuum 84 (2010) 592–596
Fig. 3. Schematic diagram of the SAICAS (A) and a typical profile of the reaction forces of the SAICAS (B).
measuring system has an error value of friction coefficient within 0.02, friction coefficient of polymer thin films prepared with strong magnetic field, unbalanced magnetron and without magnetron (r.f. sputtering) was almost the same level, however, that prepared with the weak magnetic field was slightly lower than those of other thin films. Fig. 5 shows wear ratios of these polymer thin films. Wear durability of polymer thin films prepared by r.f. magnetron sputtering systems with strong and unbalanced magnetic fields was higher than that prepared by r.f. sputtering. Fig. 6(A)–(D) show the optical micrographs of scratch tracks in these polymer thin films after the 300 revolutions. The scratch tracks can be observed in all of polymer thin films. Taking into consideration of the results shown in Fig. 5, we’ve interpreted whether the coating films are removed or not. The polymer thin films prepared by r.f. sputtering
(Fig. 6(A)) and r.f. magnetron sputtering with weak magnetic field (Fig. 6(B)) were worn, however, those with strong (Fig. 6(C)) and unbalanced (Fig. 6(D)) magnetic fields remained. These results indicate that the wear durability for the steel ball of the polymer thin film prepared by r.f. magnetron sputtering systems with strong and unbalanced magnetic fields is higher than those with r.f. sputtering and r.f. magnetron sputtering with weak magnetic field. Wear durability of polymer thin film increased with increase of the magnetic field.
Fig. 4. Friction coefficients of polymer thin films prepared by r.f. magnetron sputtering systems with a strong, a weak and an unbalanced magnetic fields.
Fig. 5. Wear ratios of polymer thin films prepared by these r.f. magnetron sputtering systems and r.f sputtering system.
3.2. Adhesion and mechanical properties of fluorocarbon thin films prepared by the magnetron sputtering systems Adhesion strength between these thin films and SUS302 substrate and shear stress of these thin films were measured by
S. Iwamori et al. / Vacuum 84 (2010) 592–596
595
Fig. 6. Optical micrographs of scratch tracks in these polymer thin films after the 300 revolutions; prepared by r.f. sputtering (A), magnetron sputtering with weak magnetic field (B), with strong magnetic field (C) and unbalanced magnetic field (D).
SAICAS. Fig. 7 shows the adhesion strength of fluorocarbon polymer thin films. Adhesion strength of fluorocarbon polymer thin film prepared by r.f. sputtering showed highest value of all the fluorocarbon polymer thin films, and it slightly decreased with increase of magnetic fields in the sputtering systems. Adhesion strength of the polymer thin films prepared with strong and unbalanced magnetic fields in the region III was higher than that in the regions I and II. Fig. 8 shows shear stress of fluorocarbon polymer thin films. Shear stress of fluorocarbon polymer thin film prepared by r.f. sputtering showed highest of all the fluorocarbon polymer thin films. Shear stress of the polymer thin films prepared with strong and unbalanced magnetic fields in the region III were higher than that in the regions I and II as well as adhesion strength shown in Fig. 7. Why the polymer thin films prepared with strong magnetic fields show poor adhesion and shear stress compared to those with weak or without magnetic fields? We’ve already reported that ion current at surface of substrate increased with increase of magnetic field [7]. Further, the ion current around the regions I and II was higher than that around the region III in the polymer thin film
prepared with strong and unbalanced magnetic fields [7]. Large amount of ion bombardment during deposition would interfere with good adhesion and high resistance to shear stress. However, these adhesion strength and shear stress are not proportion to the ion current. There would be some factors to effect on these properties except for the ion current. The peeling is one of important factors to effect on the wear durability. A decrease of wear durability is caused by the peeling. We’d already reported that a sputtered thin film used a polyimide target deposited onto copper substrate with nitrogen showed higher wear durability than that with argon [10]. This thin film with argon was worn with peeling, however that with nitrogen worn out without peeling. The adhesion strength of the sputtered thin film with nitrogen was higher than that with argon [10]. These fluorocarbon polymer thin films were worn out without peeling as shown in Fig. 6 as well as the sputtered thin film used a polyimide target deposited onto copper substrate with nitrogen. However the adhesion strength of these fluorocarbon polymer thin films was almost the same value as that of the thin film with argon. Not only
Fig. 7. Adhesion strength of fluorocarbon polymer thin films in regions I, II and III shown in Fig. 1.
Fig. 8. Shear stress of fluorocarbon polymer thin films in regions I, II and III shown in Fig. 1.
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S. Iwamori et al. / Vacuum 84 (2010) 592–596
adhesion strength but also some characteristics, e.g., surface morphologies, hardness, brittleness, may relate with the wear durability.
adhesion strength and shear stress of polymer thin films prepared with r.f. sputtering (without magnetron) were slightly higher than those prepared by magnetron sputtering systems.
4. Conclusions Fluorocarbon polymer thin films were deposited with a poly(tetrafluoroethylene) target by three different types of r.f. magnetron sputtering systems with a strong, a weak and an unbalanced magnetic fields and r.f. sputtering. Friction coefficient of polymer thin film prepared by r.f. magnetron sputtering systems with weak magnetic field showed lowest, and that with strong magnetic field showed highest of all the thin films. Wear durability of polymer thin films prepared by r.f. magnetron sputtering systems with strong and unbalanced magnetic fields was higher than that prepared by r.f. magnetron sputtering system with weak magnetic field and r.f. sputtering. Both of the
References [1] Yamada Y, Kurobe T. Jpn J Appl Phys 1993;32:5090. [2] Biederman H. Vacuum 2000;59:594. [3] Biederman H, Zeuner M, Zalman J, Bı´lkova´ P, Slavı´nska´ D, Stelmasuk V, et al. Thin Solid Films 2001;392:208. [4] Stelmashuk V, Biederman H, Slavı´nska´ D, Zemek J, Trchova´ M. Vacuum 2005;77:131. [5] Kezuka K, Uemura A, Iwamori S. J Vac Soc Jpn 2008;51:201. [6] Iwamori S, Kezuka K, Uemura A. J Soc Mater Sci Jpn 2008;57:611. [7] Iwamori S, Hasegawa N, Uemura A. Surf Coat Technol 2008;203:59. [8] Iwamori S, Uemura A, Yamada Y, Adhes J. Sci Technol 2004;18:1771. [9] Nishiyama I, Saito M. J Printing Sci Technol Jpn 2005;42:285. [10] Iwamori S, Uemura A. J Adhes Soc Jpn 2006;42:89.