Characterization and optical properties of diamondlike carbon prepared by electron cyclotron resonance plasma
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Characterization and optical properties of diamondlike carbon prepared by electron cyclotron resonance plasma Xiao-Ming He,a) S-T. Lee, I. Bello, A. C. Cheung, and C. S. Lee Department of Physics and Materials Science, City University of Hong Kong, Hong Kong (Received 8 July 1997; accepted 13 July 1998)
Diamondlike carbon (DLC) films have been prepared on radio-frequency (rf) biased substrates maintained at low temperature using electron cyclotron resonance CH4 –Ar plasma. The effects of negative rf bias and reactant gas composition on the bonding structure, hardness, and resistivity of the films were systematically investigated. DLC films deposited on PMMA (polymethyl methacrylate) were examined by optical methods to determine the absorption coefficients and the optical band gap. It was found that DLC films synthesized at bias voltage of 2(80–100) V and FCH4 yFAr of 0.075–0.086 exhibit extreme hardness of more than 3000 kgf mm22 , high electrical resistivity up to 1014 V cm, band gap larger than 2.5 eV, and excellent optical transparency. The results indicate that ECR CH4 –Ar plasma with low negative rf bias and suitable CH4yAr gas ratio can process optically transparent and hard protective DLC films on PMMA plastics.
I. INTRODUCTION
The synthesis of diamondlike carbon (DLC) films has been a research focus in materials science with an increasing interest in recent years, especially of films which exhibit desirable properties comparable to diamond and are easy to prepare for some particular applications. DLC films are extremely hard, electrically insulating, optically transparent, and have a low friction coefficient, making them attractive candidates for applications such as tribological coatings,1–3 electronic devices,3 and infrared optical coatings.4,5 So far many low pressure deposition techniques, such as radiofrequency (rf) discharged plasma enhanced chemical vapor deposition (PECVD),6,7 ion beam assisted deposition (IBAD),2,8 and mass selected ion beam deposition (MSIBD) or filtered cathodic vacuum arc deposition (FCVAD),1,9 have been successfully used to prepare the hydrogenated (a-C : H) or hydrogen-free (a-C) DLC films. However, in comparison with these techniques, chemical vapor deposition (CVD) using an electron cyclotron resonance (ECR) plasma may be one of the favorable techniques for steady state growth of a-C : H films, since it combines a high plasma density, low substrate temperature, and independent control of ion energy under typical deposition conditions.10,11 Recently, a number of studies on DLC deposition by ECR plasma has been reported; in these works a negative substrate bias voltage of more than 2100 V and a microwave power in 50 –200 W were proved to be the conditions favorable for the growth of DLC films with a high sp 3 content.10 –17 It was found that the energetic ion a)
Present address: Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545. J. Mater. Res., Vol. 14, No. 3, Mar 1999
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