Influence of acetylene to argon flow rate ratios on structure and properties of hydrogenated amorphous carbon films prod
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Xun Cai and Qiulong Chen School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200030, People’s Republic of China
Jun Zhao Department of Physics & Materials Science, City University of Hong Kong, Kowloon, Hong Kong; and Southwestern Institute of Physics, Chengdu, 610041 Sichuan, People’s Republic of China
Paul K. Chua) Department of Physics & Materials Science, City University of Hong Kong, Kowloon, Hong Kong (Received 15 July 2006; accepted 8 December 2006)
Hydrogenated amorphous carbon (a-C:H) films were fabricated using mixed acetylene and argon plasma with various flow rate ratios of acetylene to argon. Raman scattering and x-ray photoelectron spectroscopy show that changing the flow rate ratios (FC2H2 to FAr) has a large impact on the structure of the films. Enhanced film hardness and reduced surface roughness were achieved at higher ratios attributable to the high ion flux and efficient etching by hydrogen. However, the film surface exposed to atomic hydrogen at a higher C2H2 flow rate becomes rougher. The sp3 content and film hardness also reach saturation combined with a fissile surface due to the high stress. I. INTRODUCTION
Amorphous carbon films have been extensively investigated in electrical, optical, thermal, and tribological applications on account of their unique combination of properties such as high chemical inertness, excellent tribological properties, and good thermal conductivity.1–5 They can be deposited using various techniques including ion beam deposition (IBD),6,7 chemical vapor deposition (CVD),8,9 pulsed laser deposition (PLD),10,11 and so on. Though many techniques have been used to deposit the materials, direct fabrication of a-C films on certain materials such as ferrous substrates still faces some technological difficulties. Besides, the film and interfacial quality synthesized by conventional deposition techniques depends on the deposition conditions. Plasma immersion ion implantation and deposition (PIII&D) has recently been utilized to produce a-C films.12–14 For example, carbon films were prepared on
II. EXPERIMENTAL DETAILS
a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0114 982
pure Al and Si substrates by PIII&D using sample bias voltages of 3–50 kV by Liao et al.15 Zeng et al. have also used PIII&D to prepare a-C films on stainless steel substrates, and an interfacial region in which carbon and the substrate elements are well mixed is accomplished.16 In Shinno’s studies, carbon coatings were deposited on glass substrates and surfaces ferrules, and the effects of the gas pressure, gas composition, and pulse voltage on the deposition rate were investigated.17 Most reports have hitherto focused on the effects of the negative bias voltage on the properties of the films.15,18 In contrast, the impact of the flow rates, for example, on the ratio of the acetylene to argon flow rates (FC2H2/FAr) or the deposition pressure have not been investigated as much, and based on our literature search, a sys
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