Grain size dependent physical and chemical properties of thick CVD diamond films for high energy density physics experiments

We report on the grain size dependent morphological, physical and chemical properties of thick microwaveplasma assisted chemical vapor deposited (MPCVD) diamond films that are used as target materials for high energy density physics experiments at the Lawrence Livermore National Laboratory. Control over the grain size, ranging from several µm to a few nm, was achieved by adjusting the CH(4) content of the CH(4)/H(2) feed gas. The effect of grain size on surface roughness, morphology, texture, density, hydrogen and graphitic carbon content was systematically studied by a variety of techniques. For depositions performed at 35 to 45mbar and 3000W microwave power (power density ~10 W cm(-3)), an abrupt transition from micro-crystalline diamond to nanocrystalline diamond was observed at 3% CH(4). This transition is accompanied by a dramatic decrease in surface roughness, a six percent drop in density and an increasing content in hydrogen and graphitic carbon impurities. Guided by these results, layered nano-microhybrid diamond samples were prepared by periodically changing the growth conditions from nano- to microcrystalline.