MECHANICAL-PROPERTIES OF DIAMOND MEMBRANES

Polycrystalline diamond films were deposited using the hot-filament chemical vapor deposition method. The fracture strength for these membranes was estimated in a bulge test and from Young's modulus measurement. These mechanical properties are changed by the substrate pretreatment conditions, the methane concentration, and the dc bias application between filaments and substrate. The maximum fracture strength was achieved at 2200 MPa, when 700 mA dc bias current was applied. The main characteristics for this film are a small grain size (0.3 mum) with relatively low nondiamond carbon content. It is concluded that the mechanical properties for diamond film are greatly affected by both grain size and nondiamond content in the film.