HABIT MODIFICATION OF GAS-PHASE SYNTHESIZED DIAMOND PARTICLES IN THE C-H-O SYSTEM

Habit modification of gas phase synthesized diamond particles was investigated for the C-H-0 system. The tungsten-filament chemical vapour deposition (CVD) method was used for the synthesis. The temperature of the tungsten filament and the distance between the substrate and the filament were 2100-degrees-C and 10 mm respectively. The deposition temperature varied from 700-degrees-C to 1100-degrees-C. The methane and oxygen concentrations extended up to 3.0% and 1.2%. respectively. At deposition temperatures of 800-degrees-C and 850-degrees-C, diamond particles changed their shape from cubo-octahedron to octahedron and again to cubo-octahedron with increasing oxygen concentration. At 900-degrees-C and 1000-degrees-C the cubo-octahedral particle changed to a cube continuously with increasing oxygen: the ((100)/(111) area ratio of the particle increased continuously with increasing oxygen). The deposition rate showed an interesting relationship to the habit modification. The deposition rate increased within the oxygen concentration range where the ((111)/(100) area ratio of the particles increased, while it decreased in the oxygen range where the (111)/(100) area ratio decreased. The morphology maps of diamond particles with varying methane and oxygen concentrations and deposition temperatures are presented; these show an apparent habit modification tendency which has not been reported previously.