Synthesis of Hexagonal Diamond Polytype in a Thermal Plasma

Abstract

Two kinds of diamond film were synthesized on Mo substrates using a plasma jet method, in which methane was injected as a reactant gas into the hydrogen plasma. One (type A) was cubic diamond film with clear habit planes, the other (type B) film with no habit plane. The latter was consisted mainly of a mixture of many kinds of higher hexagonal diamond polytypes, and deposited at a maximum growth rate of 250μm·h-1. These were determined through analyses of X-ray diffraction and selected-area electron diffraction patterns, and scanning electron microscopic observation.In order to find growth conditions for hexagonal diamond polytypes, we also synthesized the diamond film at the different temperature gradients of boundary layer above Mo substrates using an arc plasma reactor. It became clear that the polytypes were synthesized when the temperature gradient was greater than the gradient at which cubic diamond was synthesized.We also studied on the orientation of the hexagonal diamond polytypes deposited on the substrates, and suggested a growth model of the polytypes.