Relationships between the structural, chemical, and mechanical properties of Si-aC:H thin films
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Relationships between the structural, chemical, and mechanical properties of Si-aC:H thin films Ryan D. Evans,1 Gary L. Doll,2 Philip W. Morrison, Jr.,1 James Bentley,3 Karren L. More,3 Jeffrey T. Glass1 1 Dept. of Chemical Engineering, Case Western Reserve University, 10900 Euclid Ave., Cleveland, Ohio 44106 2 Advanced Materials R & D, The Timken Company, 1835 Dueber Ave., S. W., Canton, Ohio 44706 3 Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 ABSTRACT Silicon-incorporated amorphous hydrocarbon (Si-aC:H) films with varying Si contents were deposited onto a Ti interlayer on Si and steel substrates by reactive sputtering in an unbalanced magnetron sputtering system. The objective of this study was to measure and relate the structural, chemical, and mechanical properties of these Si-aC:H films. Transmission electron microscopy revealed that the Si-aC:H phase is amorphous and TiC exists at the Si-aC:H/Ti phase boundary for all compositions. Mechanical properties such as hardness, indentation modulus, and intrinsic stress decreased with increasing Si and H content in the films, for Si/C ≥ 0.04. XPS measurements suggested that this is most likely due to the decreasing presence of a C-C sp3 interlinked network, accompanied by an increase in C-H and Si-H bonds. This conclusion was supported by radial distribution functions obtained using extended electron energy-loss fine structure analysis (EXELFS). INTRODUCTION Diamond-like carbon (DLC) coatings are known for being chemically inert and having low friction coefficients and high hardness. Such materials are desirable for use as coatings for mechanical components such as bearings, gears, and seals. A significant amount of research has already been conducted on hydrogenated (aC:H) and hydrogen-free (aC) varieties of these thin carbon films, as outlined in various literature reviews [1,2,3]. Furthermore, incorporation of atomic species such as Ti, Cr, W, N, and Si into DLC is a common technique in tribological coating design for enhancing specific film properties [4]. Si-aC:H films are a silicon-containing variety of aC:H, sometimes referred to in the literature as Si-DLC. Researchers have reported that PECVD-deposited Si-DLC films have lower intrinsic compressive stress [5], lower friction coefficients in humid environments [6], and better thermal stability [7] than undoped DLC films. These properties make Si-aC:H attractive for use in tribological applications, and worthy of investigation. Additionally, the reactive sputtering process used to deposit these Si-aC:H films involved the introduction of an organic precursor into the sputtering chamber, thereby demonstrating a means for expanding the flexibility of existing production sputtering equipment. EXPERIMENTAL The films for this study were deposited onto steel coupons and silicon wafers using a closedfield unbalanced magnetron sputtering system. Two titanium and two carbon targets were used P7.8.1
during the deposition process. Initially, a thin (~300 nm) Ti layer was sputtered onto
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