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1、Thin Solid Films 405 (2002) 3003030040-6090/02/$ - see front matter ? 2002 Elsevier Science B.V. All rights reserved. PII: S0040-609001.01727-8Control of frictional force on coating films of boron nitridecopper complex in ultra high vacuumMasahiro Goto*, Akira Kasahara, Masahiro Tosa, Kazuhiro Yoshi
2、haraNanomaterials Laboratory, National Institute for Materials Science, 3-13 Sakura, Tsukuba, Ibaraki 305-0003, JapanReceived 20 July 2001; received in revised form 15 November 2001; accepted 15 November 2001AbstractBoron nitridecopper complex (BNyCu) films were synthesized using a magnetron co-sput
3、tering method using different discharge times. The frictional force of the coating films of BNyCu was observed with a vacuum-friction measuring system with variable vacuum pressure. Scanning auger electron microscopy and contact angle measurements were carried out in order to characterize the BNyCu
4、films. Two elements of surface energy were estimated from the contact angle of two solutions. Frictional coefficients as low as 0.1 were achieved for the BNyCu films under ultra high vacuum (UHV) conditions. It was found that alteration of the composition of boron nitride with copper in the mixture
5、under different discharge times was effective in controlling the frictional force on the film surface under UHV. ? 2002 Elsevier Science B.V. All rights reserved.Keywords:Frictional force; Boron nitride; Ultra high vacuum; Magnetron co-sputter; Surface energy1. IntroductionMaterials with low frictio
6、nal force in ultra high vacuum have attracted much attention in recent years in disciplines such as space development and the vacuum industry w1x. Thin coating films of hexagonal boron nitride (h-BN) are good candidates for many UHV applications requiring low friction due to their promising properti
7、es such as low Van der Waals force, low fric- tional force, chemical inertness, etc. However, h-BN films have a tendency to crack and peel off due to the internal stress and their chemical reaction with water. Also the frictional coefficient of h-BN increases under UHV to larger values than in a hig
8、her pressure atmos- phere. In order to develop coating films with ultra low frictional force, it is important to solve these problems and further to control the film properties such as internal stress, surface energy and surface adhesion force, which have large effects on the frictional force. In th
9、is paper we describe how boron nitridecopper complex (BNyCu) films were synthesized on stainless steel substrates by a magnetron co-sputtering method using different sputter discharge times and how the film* Corresponding author. Fax: q81-298-59-5010. E-mail address: goto.masahironims.go.jp (M. Goto
10、).properties along with the frictional force were observed under variable vacuum pressure.2. ExperimentalBoron nitridecopper complex (BNyCu) films were prepared using a magnetron co-sputtering deposition system on stainless steel substrates (10 mm=10 mm=1 mm=20 mm=2 mm=20 mm). A copper disk (50 mm i
11、n diameter) covered with sintered BN plates (5 mm=5 mm=1 mm) with approximately 20% of the area coated was used for the sputter target. Argon gas used for sputteringintheseexperimentswasgreaterthan 99.999% pure and its pressure was 0.4 Pa. The frictional force of the samples was determined with a Bo
12、wden Lebenen type vacuum friction measuring system w2x. Scanning auger electron microscopy (SAM) (PHI SAM- model 680) was carried out to measure the surface morphology and the surface elemental map image of the BNyCu films. Internal stress (s) of the samples (20 mm=2 mm=20 mm size) was calculated fr
13、om the substrates deflection (d) measured with a conventional optical microscope, using Stonys equation w3x.22.ssdEh y3L 1yn twhere E and n are Youngs modulus and Poissons ratio,301M. Goto et al. / Thin Solid Films 405 (2002) 300303Fig. 1. SEM images of the surface of BNyCu complex films with differ
14、ent sputter discharge times: (a) 15 min, (b) 30 min, (c) 60 min, (d) 150 min.Fig. 3. SAM element mapping image of BNyCu film surfaces with discharge times of 150 min: (a) SEM image, (b) copper element map, (c) boron map, (d) nitrogen map.Fig. 2. Temperature rise of BNyCu films with different sputter
15、 dis- charge times (minutes).Fig. 4. Change in internal stress of BNyCu films with different sputter discharge times (min).h, L and t are the thickness and length of the substrate and the thickness of the coated thin film, respectively. Two elements of the surface energy, namely the disper- sion for
16、ce and polar interaction force, were estimated from the contact angle of two solutions of known polar (H O) and non-polar (CH I ) characters using a contact22 2 angle measuring system (Kyowa Interface Science CA- A) by assuming Young, Dupre and Forkes derivationw4,5x.3. Results and discussion3.1. Film properties of BNyCu complexThe high quality coating of the BNyCu complex was achieved by the magnetron co-sputter method. The films are quite stable both in an atmosphere and in ultra
