Ion energy dependence of film properties for diamond-like carbon prepared with plasma-assisted deposition
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Hydrogen-free diamondlike carbon films were prepared on Si(100) with electron cyclotron wave-resonance plasma, which serves to sputter the graphite target and to simultaneously bombard the growing surface. Direct penetration of postionized carbon atoms (up to 140 eV) in addition to the momentum transfer from Ar plasma facilities the formation of the Ta–C structure. Surface morphology, mechanical, and optical properties of the deposits were examined with respect to the ion energy. Atomic force microscope images revealed island morphology in deposits with a typical root-mean-square roughness of 20 nm. A maximum content of about 70% for the fourfold-bonded structure was estimated from the Raman profiles, giving rise to a micro hardness of 60 ± 5 GPa.
The 1s22s22p2 electron configuration of carbon atom makes it unique among all the elements in the diversity of homoatomic and heteroatomic bonds it forms. In contrast to other amorphous materials such as SiO2, where the local bonding is quite uniform throughout the bulk, the amorphous carbon displays rather bewildering local configurations that the coordination (within a distance generally prescribed at 1.85 Å) can be either twofold, threefold, or fourfold at varying orientations.1 Consequently, there is not any typical local structure for the amorphous carbon. Those amorphous carbon samples of considerable content of fourfold-coordinated atoms demonstrate many extraordinary properties of a diamond and, thus, are termed diamondlike carbon (DLC).2 The DLC film has been subjected to intensive investigation in the past three decades due to its possible combination of those particular properties found in diamond and graphite including high hardness and elastic modulus, chemical inertness, good thermal conductance, low friction coefficient, and biocompatibility, to name only a few.3–5 In recent years, significant progress has been evidenced in all the directions regarding the understanding and control of DLC deposition as well as the research of beneficial DLC applications. The diverse bonding ability of carbon atoms renders the DLC films varying structures and properties in sensitive dependence upon the processing parameters. This implies the possibility of fine tuning the properties of the deposits by controllable growth. To enhance the deposition and to
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J. Mater. Res., Vol. 16, No. 11, Nov 2001 Downloaded: 27 Mar 2015
modify the deposit properties, a host of deposition techniques have been employed and considerable research performed to understand the growth mechanism with regard to a specific preparation method, as reviewed in Ref. 4. Among the various deposition techniques, ion-assisted deposition (IAD) and direct ion beam deposition (IBD) are most suitable for a rigorous study of the DLC deposition process, since in both cases the ion energy is well controlled. Although the deposition of DLC has reached a definitely mature stage, a tryout of novel growth techniques can still help the enterprise in s
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