Delivered by Ingenta to: Nanyang Technological University IP: 146.185.204.204 On: Fri, 10 Jun 2016 23:52:15 Copyright: American Scientific Publishers RESEARCH ARTICLE Copyright © 2011 American Scientific Publishers All rights reserved Printed in the United States of America Journal of Nanoscience and Nanotechnology Vol. 11, 8251–8258, 2011 Optimization of Chemical Vapor Deposition Diamond Films Growth on Steel: Correlation Between Mechanical Properties, Structure, and Composition A. Laikhtman 1 * , L. Rapoport 1 , V. Perfilyev 1 , A. Moshkovich 1 , R. Akhvlediani 2 , and A. Hoffman 2 1 Sciences Department, Holon Institute of Technology, 52 Golomb St., Holon 58102, Israel 2 Schulich Faculty of Chemistry, Technion–Israel Institute of Technology, Haifa 32000, Israel In the present work we perform optimization of mechanical and crystalline properties of CVD micro- crystalline diamond films grown on steel substrates. A chromium–nitride (Cr–N) interlayer had been previously proposed to serve as a buffer for carbon and iron inter-diffusion and as a matching layer for the widely differing expansion coefficients of diamond and steel. However, adhesion and wear as well as crystalline perfection of diamond films are strongly affected by conditions of both Cr–N interlayer preparation and CVD diamond deposition. In this work we assess the effects of two parameters. The first one is the temperature of the Cr–N interlayer preparation: temperatures in the range of 500  C–800  C were used. The second one is diamond film thickness in the 0.5 m–2 m range monitored through variation of the deposition time from ∼30 min to 2 hours. The mechan- ical properties of so deposited diamond films were investigated. For this purpose, scratch tests were performed at different indentation loads. The friction coefficient and wear loss were assessed. The mechanical and tribological properties were related to structure, composition, and crystalline perfection of diamond films which were extensively analyzed using different microscopic and spec- troscopic techniques. It was found that relatively thick diamond film deposited on the Cr–N interlayer prepared at the temperature similar to that of the CVD process has the best mechanical and adhe- sion strength. This film was stable without visible cracks around the wear track during all scratch tests with different indentation loads. In other cases, cracking and delamination of the films took place at low to moderate indentation loads. Keywords: CVD Diamond Films, Steel, Friction, Adhesion. 1. INTRODUCTION Diamond coatings have attracted significant attention as they have a high potential for various applications includ- ing a wide range of tribological uses as bearings, seals, cutting tools, thin-film media for magnetic recording. 1 2 The adhesion of diamond films plays a crucial role on the mechanical and physical properties of the final prod- uct. In particular, the deposition of diamond films on steel surfaces is limited due to poor adhesion associated with formation of amorphous carbon on the steel surface under diamond deposition conditions. 3–6 At an earlier stage of our study of diamond deposition on steel, the adhesion problem was successfully solved through the use of a nitrided chromium interlayer which serves both as a buffer layer for carbon and iron inter-diffusion and, to a cer- tain extent, as a matching layer for the widely differing * Author to whom correspondence should be addressed. expansion coefficients of diamond and steel. 7–10 It was found that friction, wear, and adhesion properties of poly- crystalline diamond films are similar and in some cases even superior to these of homoepitaxial diamond. 11 Both chromium nitridation and subsequent diamond chemical vapor deposition (CVD) conditions were found to have major effect on tribological properties of the film, its crys- talline quality, amorphous sp 2 and sp 3 contents. 7 8 12 13 In the present study we worked on the optimization of process condition in order to achieve better adhesion prop- erties for continuous high purity diamond film. It is now generally accepted that good quality continuous diamond films, though composed of randomly oriented submicron crystallites and microcrystallites, with a minimal amor- phous carbon content, can be prepared during reasonable deposition times (up to several hours, mostly in a single step process), all when grown in the temperature range of 700  C–900  C using various pretreatment methods, J. Nanosci. Nanotechnol. 2011, Vol. 11, No. 9 1533-4880/2011/11/8251/008 doi:10.1166/jnn.2011.5046 8251