By an extensive investigation of the principal growth parameters on the deposition process, we realized the epitaxial growth of crystalline wurtzite GaN thin films on single crystal (001) diamond substrates by metal organic chemical vapor deposition. From the influence of pressure, V/III ratio, and temperature, it was deduced that the growth process is determined by the mass-transport of gallium precursor material toward the substrate. The highest temperature yielded an improved epitaxial relationship between grown layer and substrate. X ray diffraction (XRD) pole figure analysis established the presence of two domains of epitaxial layers, namely (0001) h10 10i GaN k (001) [110] diamond and (0001) h10 10i GaN k (001) ½1 10 diamond, which are 90 rotated with respect to each other. The presence of these domains is explained by the occurrence of areas of (2 Â 1) and (1 Â 2) surface reconstruction of the diamond substrate. When applying highly misoriented diamond substrates toward the [110] diamond direction, one of the growth domains is suppressed and highly epitaxial GaN on (001) diamond is realized.

A method for the nucleation enhancement of nanocrystalline diamond ͑NCD͒ films on silicon substrates at low temperature is discussed. A sputter deposition of a Mo seed layer with thickness 50 nm on Si substrates was applied followed by an ultrasonic seeding step with nanosized detonation diamond powders. Hot-filament chemical vapor deposition ͑HF-CVD͒ was used to nucleate and grow NCD films on substrates heated up at 550°C. The nucleation of diamond and the early stages of NCD film formation were investigated at different methane percentages in methane/ hydrogen gas mixtures by atomic force microscopy, micro-Raman spectroscopy, scanning electron microscopy, and grazing incidence x-ray analyses in order to gain specific insight in the nucleation process of NCD films. The nucleation kinetics of diamond on the Mo-coated Si substrates was found to be up to ten times higher than on blank Si substrates. The enhancement of the nucleation of diamond on thin Mo interlayers results from two effects, namely, ͑a͒ the nanometer rough Mo surface shows an improved embedding of ultrasonically introduced nanosized diamond seeds that act as starting points for the diamond nucleation during HF-CVD and ͑b͒ the rapid carbonization of the Mo surface causes the formation of Mo 2 C onto which diamond easily nucleates. The diamond nucleation density progressively increases at increasing methane percentages and is about 5 ϫ 10 10 cm −2 at 4.0% methane. The improved nucleation kinetics of diamond on Mo interlayers facilitates the rapid formation of NCD films possessing a very low surface roughness down to ϳ6 nm, and allows a submicron thickness control.

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