Unusual Dependence of the Diamond Growth Rate on the Methane Concentration in the Hot Filament Chemical Vapor Deposition Process.

Although the growth rate of diamond increased with increasing methane concentration at the filament temperature of 2100 °C during a hot filament chemical vapor deposition (HFCVD), it decreased with increasing methane concentration from 1% CH -99% H to 3% CH -97% H at 1900 °C. We investigated this unusual dependence of the growth rate on the methane concentration, which might give insight into the growth mechanism of a diamond. One possibility would be that the high methane concentration increases the non-diamond phase, which is then etched faster by atomic hydrogen, resulting in a decrease in the growth rate with increasing methane concentration.

Various Allotropes of Diamond Nanoparticles Generated in the Gas Phase during Hot Filament Chemical Vapor Deposition.

Diamond nanoparticles have been synthesized using various methods. Nanodiamonds generated in the gas phase were captured on the membrane of a transmission electron microscope grid during a hot filament chemical vapor deposition (HFCVD) diamond process. In total, ~600 nanoparticles, which were captured for 10 s in six conditions of the capture temperatures of 900 °C, 600 °C and 300 °C and the gas mixtures of 1% CH-99% H and 3% CH-97% H, were analyzed for phase identification using high-resolution transmission electron microscopy and fast Fourier transformation.

Stabilization of a Ga-adlayer structure with the zincblende stacking sequence in the GaN(0 0 0 -1) surface at the nanoscale.

Profile imaging by in situ high-resolution transmission electron microscopy is used to elucidate reconstructions of the GaN(0 0 0 -1) surface during annealing in the TEM. We have successfully captured a detailed process of a change from the stacking sequence of the wurtzite to that of the zincblende structure in the topmost three Ga layers for the surface with nanoscale hill-and-valley structures. For ab initio calculations of the change in the sequence, a model structure is approximated by the addition of a 1 × 1 Ga layer on the GaN(0 0 0 -1) surface (i.