The smoothness of tetrahedral amorphous carbon

C. Casiraghi, A. C. Ferrari, J. Robertson

    Research output: Contribution to journalArticlepeer-review

    Abstract

    Diamond-like Carbon (DLC) is the preferred coating material for magnetic storage disks and future optical storage devices. Tetrahedral amorphous carbon (ta-C) films are used to coat the read heads. Films with a thickness below 2 nm and roughness well below 1 nm are needed to achieve the desired storage densities. To reach these values, we must determine the minimum thickness for continuous and pin-hole free films. Here, we review the studies on the smoothness and the growth mechanism of ta-C. The film roughness R of every growing surface generally increases with the thickness z as R∼z β until saturation. For a fixed thickness, R increases with the lateral scale length L as R∼Lα. The exponents α and β are called roughness and growth exponents, respectively, and they are uniquely defined by the growth process. The roughness evolution of ta-C films grown at room temperature was measured by atomic force microscopy. The roughness is very low (∼0.12 nm) and the growth exponents are α∼0.39 and β∼0-0.1. These require the presence of surface diffusion and relaxation. We propose that the diffusion is local and it occurs during the thermal spike, which accompanies ion dominated depositions. Monte Carlo simulations confirm this and show low exponents consistent with experiments. Thus, the scaling analysis shows that the surface properties, for a fixed temperature and ion energy, are a separate process to subplantation, which determines the sp3 bonding of the bulk film. © 2005 Elsevier B.V. All rights reserved.
    Original languageEnglish
    Pages (from-to)913-920
    Number of pages7
    JournalDiamond and Related Materials
    Volume14
    Issue number3-7
    DOIs
    Publication statusPublished - Mar 2005

    Keywords

    • Nucleation
    • Surface properties
    • Tetrahedral amorphous carbon

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