Vapour grown polycrystalline diamond films: Microscopic, mesoscopic and atomic surface structures

Abstract

A detailed analysis with scanning electron and electron tunnelling microscopy of microscopic, mesoscopic and atomic surface structures as well as the growth forms of vapour grown polycrystalline diamond films is presented. The growth form as a function of the substrate temperature Ts shifts from the octahedral shape at 990 K over the cubo-octahedral shape at ∼ 1100 K to the cubic shape at 1275 K. The major change appears in a very narrow temperature range around 1100 K—only an increase of Ts by 9% from 1050 to 1150 K is necessary to change the growth form from almost octahedral to cubic. Around this transition temperature, the microscopic (100) structure changes with increasing Ts from smooth to rough and the mesoscopic (100) structure vice versa from rough to smooth. In addition, there is evidence that the atomic (100) structure changes from the hydrogenated to the non-hydrogenated 2 × 1 reconstruction. A possible explanation for all these findings is a change from ineffective to effective surface migration caused by a surface transformation at ∼ 1100 K. This explanation is strongly supported by a diamond growth process described in the literature. For the 111 facets, a similar comprehensive surface structure characterisation was not possible due to the pronounced 100 texture formation at low Ts. On the microscopic scale, they appeared rough in either case. For Ts > 1050 K, mesoscopic images show triangular steps and islands. Regarding the atomic structures, at least three different structures were found by scanning tunnelling microscopy: A hexagon, row and ring-like structure are attributed to atomic 1 × 1, 2 × 1, and 2 × 2 or (√3 × √3)R30 ° structures.