[100] versus [111] diamond growth from methyl radicals and/or acetylene

The goal of this study was to investigate the roles of methyl radicals and acetylene, either individually or together, during diamond growth by chemic al vapor deposition. We have nucleated and grown micron-sized diamond parti cles at 800 degreesC in a flow-tube apparatus that permits growth from only methyl radicals or acetylene in atomic hydrogen, in contrast to the comple x mixture of species found in a normal reactor. Growth from methyl radicals only produced cubo-octahedral crystals with an alpha value (root3 x the ra tio of growth rates in the [1 0 0] and [1 1 1] directions) near 1.8, indica ting that the absence of acetylene is not a significant impediment in nucle ating new (I 1 1) planes, in contradiction to recent modeling work. Diamond growth from pure acetylene produced octahedra (alpha = 3), indicating that (1 0 0) growth is much more facile than (1 1 1) growth in the absence of m ethyl radicals, and the (1 1 1) facets had a high concentration of contact twins. Diamond growth from acetylene plus methane produced cubo-octahedra c rystals but the highly defective [1 1 1] growth persisted. We propose that at steady state the (1 1 1) growth surface has a high coverage of adsorbed hydrocarbons, rather than resembling the simple hydrogen-terminated (1 1 1) -1 x 1 : H structure; that steric repulsion and rearrangements play a criti cal role in the growth mechanism; and that desorption and etching of adsorb ed hydrocarbons by atomic hydrogen is less facile than has been commonly su pposed. The ratio of C-2 and C-1 gas-phase precursors should be minimized f or high quality [1 1 1] epitaxy. (C) 2001 Elsevier Science B.V. All rights reserved.