Effects of bonding structure on the properties of plasma immersion ion processed diamondlike carbon films
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Effects of bonding structure on the properties of plasma immersion ion processed diamondlike carbon films X.M. He, K.C. Walter, and M. Nastasi Los Alamos National Laboratory, Materials Science and Technology Division, Los Alamos, New Mexico, 87545, USA (Received 28 April 1999; accepted 12 November 1999)
Hydrogenated diamondlike carbon (a-C:H DLC) films were prepared on different substrates by using C2H2–Ar plasma immersion ion processing (PIIP), and their bonding structure was modified by changing deposition parameters of the chamber pressure and the gas composition. The influence of the bonding structure on the properties of the DLC films was investigated by using ion-beam analysis techniques and Raman, infrared, and ultraviolet/visible spectroscopies and by analyzing the measured properties. The increases in density, hardness, and refractive index were found to correlate with the increase of the sp3-bonded structure and the concurrent decrease of both the C–H bonds and the average size of sp2-bonded domains in the films. An optimal combination of optical and mechanical properties was highly dependent on the hydrogen status existing in DLC films that can be adjusted by means of modulation of the synthesis parameters. The prepared DLC films exhibited desirable properties, which included a hardness above 28 GPa, a density above 2.3 g cm−3, a refractive index above 1.94, and band gap energies in the range of 1.8–1.85 eV.
I. INTRODUCTION
Amorphous hydrogenated carbon (a-C:H) films have been extensively studied because these materials can be prepared to exhibit unique diamondlike properties, such as high hardness, low electronic affinity, high transparency, etc.,1–3 and thus to have numerous potential applications as corrosion and wear resistant coatings,1,4 sensitive photoinduced electronic devices, and fieldemission devices.2,5,6 a-C:H films can be deposited at room temperatures at high deposition rates using different plasma-based deposition techniques where the hydrocarbon plasma is produced conventionally by radio frequency (rf) or direct current (dc) plasma sources and the film deposition is enhanced by the energetic ion bombardment induced by a negative voltage biased on the substrates.1–3 Depending on the deposition methods and other synthesis conditions, the quality of the a-C:H films can be changed from “soft” polymerlike to “hard” diamondlike carbon (DLC) films, which are substantially dependent on the mixed densities of sp3, sp2, and some sp1 bonding in the amorphous structure. The beneficial mechanical properties arise from sp3-bonded carbon sites, while the optical and electronic properties are dependent on the sp2 carbon sites.1–3 For several years we have been depositing a-C:H DLC films by the plasma immersion ion processing (PIIP) technique. The unique advantages of the PIIP technique, 564
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J. Mater. Res., Vol. 15, No. 2, Feb 2000 Downloaded: 16 Mar 2015
compared to most commonly used plasma-based deposition methods, are th
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