Growth and Applications of Nanocomposite Carbon Films

• Main Authors: Liang-Chun Wang, 王亮鈞
• Other Authors: Franklin Chau-Nan Hong
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/20804533375786740816

博士 === 國立成功大學 === 化學工程學系碩博士班 === 93 === 　Multifunctional diamond-like carbon (DLC) nanocomposite films containing a high concentration of TiO2 nanoparticles are to be synthesized for optical, tribological and MEMS applications. The nanocomposite films had good hydrophilic property under ultraviolet (UV) radiation and hardness of 14 GPa. The XRD, XPS, Raman, and TEM analysis revealed that the films were incorporated TiO2 and TiC nanoparticles in the DLC matrix. The nanocomposite films were highly abrasion-resistant and had long-life hydrophilic surface. 　DLC films were deposited using benzene or acetylene with or without nitrogen doping at elevated temperatures by capacitive RF plasma chemical vapor deposition (CVD). The method for preparing DLC films with a high hardness and a good electrical conductivity was simultaneously achieved by combining the effects of nitrogen doping and raising deposition temperature. The film resistivity could reach 0.10 Wcm with hardness of 25 GPa. The film resistivity decreased with increasing N2 concentration or deposition temperature. At a lower deposition temperature, the hardness of films decreased with increasing the nitrogen content. Appropriate nitrogen content enhanced the hardness at a higher deposition temperature. However, a nitrogen concentration too high induced the formation of CºN bonds which obstructed the carbon-carbon cross-linking structure of DLC films. The formation of fullerene-like structure was observed in the DLC films using benzene as carbon source. According to TEM images, the microstructure of DLC films is significantly varied with the deposition temperature. By FT-IR, Raman, and residual stress analysis, we concluded that the formation of fullerene-like nanoparticles was attributed to the benzene structure and the induced local thermal spike at a high substrate bias of –1500 V. The growth mechanism was studied and will be discussed. 　To improve thermal resistance of DLC films, we incorporated a high concentration of silicon in the films. Acetylene was employed as the carbon source, and argon was used to sputter Si target for low temperature depositions. Low stress and thermally stable silicon-containing DLC films were deposited on the silicon wafer substrates. We found that the hardness decreased with increasing the concentration of silicon. When the atomic percent of silicon was higher than 50 %, the DLC films stress was only 0.48 GPa, and the films was stable up to 600℃, in comparison to the conventional undoped DLC films with a high stress of 2.13 GPa and thermal stability only below 400℃. However, the hardness was decreased from 18.6 GPa to 10.9 GPa when the atomic percent of silicon was increased from 0 % to 50 %. 　A new method in preparing carbon-based molecular sieve (CMS) membranes for gas separation has been proposed. Carbon-based films are deposited on porous Al2O3 disks using hexamethyldisiloxane (HMDSO) by remote inductively-coupled-plasma (ICP) CVD. After treating the film with ion bombardment and subsequent pyrolysis at a high temperature, carbon-based molecule sieve membranes can be obtained, exhibiting a very high H2/N2 selectivity around 100 and an extremely high permeance of H2 around 1.5x10-6 mol·m-2·s-1·Pa-1 at 298 K. The O2/N2 selectivity could reach 5.4 with the O2 permeance of 2x10-7 mol·m-2·s-1·Pa-1 at 423 K. 　During surface treatments, HMDSO ions were found to be more effective than CH4, Ar, O2 and N2 ions to improve the selectivity and permeance. Short and optimized surface treatment periods were required for high efficiency. Without pyrolysis, surface treatments alone greatly reduced the H2 and N2 permeances and had no effect on the selectivity. Besides, without any surface treatment, pyrolysis alone greatly increased the H2 and N2 permeances, but had no improvement on the selectivity, owing to the creation of large pores by desorption of carbon. A combination of surface treatment and pyrolysis is necessary for simultaneously enhancing the permeance and the selectivity of CMS membranes, very different from the conventional pore-plugging mechanism in typical CVD.