Deformation behaviour of DLC coatings on (111) silicon substrates Ayesha J. Haq a, ⁎ , P.R. Munroe a , M. Hoffman a , P.J. Martin b , A. Bendavid b a School of Materials Sci. & Eng., University of New South Wales, Sydney, NSW 2052, Australia b CSIRO Industrial Physics, PO Box 218, Lindfield, NSW 2070, Australia Available online 14 June 2007 Abstract The deformation mechanisms operating in diamond-like carbon (DLC) coatings on (111) silicon substrates have been investigated. A hydrogenated amorphous carbon coating of ∼ 500 nm thickness was deposited by radio-frequency plasma-assisted chemical-vapour deposition onto a (111) oriented silicon substrate. Indentations were performed on the coatings using a spherical indenter with a radius of 5 μm for various loads up to a maximum of 150 mN. The coatings exhibited substantial elastic recovery on unloading. Minor pop-ins appeared for loads above 100 mN and a distinct pop-out was observed following indentation to 150 mN. Focused ion beam microscopy of cross-sections through the indentations revealed localized plastic compression of the coating beneath the indenter and bending at the coating-substrate interface. Although the coating was free from cracking or delamination, the substrate showed evidence of median cracks and lateral cracks for loads above 100 mN. Cross-sectional transmission electron microscopy examination of indentations revealed cracks in the coating, as well as cracks, crystalline defects and a transformation zone in the silicon substrate. These observations have been correlated with the deformation behaviour of the coating-substrate composite. Crown Copyright © 2007 Published by Elsevier B.V. All rights reserved. Keywords: Diamond-like carbon; Silicon; Nanoindentation; Deformation; Focussed ion beam microscopy; Cross-sectional transmission electron microscopy 1. Introduction Diamond like carbon (DLC) coatings are meta-stable amorphous films that exhibit a unique combination of properties like high hardness, elastic modulus, low friction coefficients, optical transparency, high chemical inertness, good wear resistance, and excellent corrosion resistance. Therefore they find applications as wear-resistant protective coatings in the magnetic storage, automobile, tooling and biomedical industries [1–3]. Nanoindentation is often employed in conjunction with a number of other surface characterization techniques to inves- tigate the cracking and deformation of DLC coatings [4–6]. Based on these studies, the discontinuities in the load– displacement curves of DLC coatings on silicon substrates have been attributed to the formation of through-thickness cracks and lateral cracks in the coating [4,5] rather than deformation of the Si substrate. In contrast, Beake and Lau [7] ascribed pop-outs in the load–displacement curves to pressure- induced phase transformations in the silicon substrate based on the observations on uncoated silicon. It is well known that during loading the diamond cubic silicon (Si-I) transforms to the metallic (Si-II) phase, accompanied by a volume reduction, which produces a displacement (or pop-in) in the loading curve. It is also well known that, on unloading, either amorphous silicon (a-Si) or a mixture of the crystalline Si-III and Si-XII phases form, depending on the indentation load and unloading rate, giving rise to either an elbow or a pop-out in the unloading curves [8–14]. Further, electrical resistance measurements have shown that the pressure required to induce transformation to the Si-II structure is lower in the [111] than in the [100] direction [15]. However, there are no there are no cross-sectional trans- mission electron microscopy (XTEM) studies on Si (111) in combination with investigations of the deformation mechan- isms by micro- or nanoindentation. In recent years, examination of subsurface microstructures has become possible due to the emergence of focused ion beam (FIB) technology as a tool for XTEM sample preparation [16,17]. Using this technique, in a recent investigation [18], the Available online at www.sciencedirect.com Thin Solid Films 516 (2007) 267 – 271 www.elsevier.com/locate/tsf ⁎ Corresponding author. Tel.: +61 2 9385 4435; fax: +61 2 9385 6400. E-mail address: ayesha@materials.unsw.edu.au (A.J. Haq). 0040-6090/$ - see front matter. Crown Copyright © 2007 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2007.06.032