Deposition Of Diamond-Chromium Carbide Composite Film By Hot-filament CVD

Diamond films deposited by Chemical vapor deposition (CVD) techniques often offer an advantage of economically producing thin films on a wide variety of substrates, even with complex shapes. However, The main reason for the poor adhesion is the existence of high residual stresses in the diamond films resulting mainly from the thermally induced shear stresses (due to the large thermal mismatch between the diamond film and the substrate) that are developed and localized at the film-substrate interface during the cooling down process after the deposition. In this thesis, the basic objective was that to deposit diamond-chromium carbide composite films by hot-filament chemical vapor deposition (HFCVD) technique. In this work hydrogen-methane gas mixtures were used as gas source and chromium plated tungsten rod was employed as chromium source. Through diverting thermal stresses to the interlayer of diamond-chromium carbide composite film to reduce shear stress in the diamond films localized at the film-substrate interface and increasing adhesive force of diamond film on the substrate the adherence between diamond film and substrate will be improved basically.Firstly, we studied the conditions under which chromium can be evaporated and Cr films can be deposited; secondly, we deposited chromium carbide films under the conditions under which diamond can be deposited and characterized these films. XRD diffraction patterns of chromium carbide films showed that Cr3C2,Cr7C3,C23C6 were formed. Cr could not be evaporated continuously because the top-layer chromium converted to chromium carbide in hydrogen-methane gas mixtures. The problem was solved by decarburization of the chromium carbide.We found out Cr3C2 was the major cause that Cr could not be evaporated.To deposit diamond and chromium carbide alternately was proposed for the first time. Because diamond's growth rate is less than that of chromium carbide, we adopt new methods to let chromium evaporation for a short period of time and several times, at the same time to keep diamond deposition much more time than that of chromium carbide. The deposition of diamond and chromium carbide alternately was realized by controlling quantity of chromium carbide. We prepared diamond-chromium carbide composite films successfully and deposited diamond films on the composite interlayer. In addition, the structure, composition and surface topography of these films were characterized by XRD, EPMA and SEM.In the paper the innovations are as following:it is the first time that chromium and chromium carbide films were deposited by Hot-filament chemical vapor deposition. Secondly, it is the first time to realize the deposition of diamond and chromium carbide alternately by controlling the deposition rate of chromium.