Epitaxial Ir layers on SrTiO3 as substrates for diamond nucleation:: deposition of the films and modification in the CVD environment

Iridium films on SrTiO3(001) have recently proven to be a superior substrate material for the heteroepitaxy of diamond thin films by chemical vapour deposition in the effort towards the realization of single crystal diamond films. In this paper we report on the growth and structural properties of iridium (Ir) films deposited by electron-beam evaporation on SrTiO3(001) surfaces varying the deposition temperature between 280 and 950 degrees C. The films were studied by scanning electron microscopy, atomic force microscopy and X-ray diffraction. At the highest temperature film growth proceeds via three-dimensional nucleation, coalescence and subsequent layer-by-layer growth. The resulting films show a cube-on-cube orientation relationship with the substrate and a minimum mosaic spread of 0.15 degrees. Towards lower deposition temperatures the orientation spread increases only slightly down to similar to 500 degrees C while the surface roughness, after passing through a maximum at similar to 860 degrees C, decreases significantly. For the lowest temperatures (below 500 degrees C) the mosaic spread rises accompanied by the occurrence of twins until the epitaxial order is lost. plasma treatment in the diamond deposition reactor at high temperature (920 degrees C) yields low nucleation densities and modifies the Ir surface. At the same time {111} facets show a significantly higher structural stability as compared with {001} facets. Nucleation at 700 degrees C results in highly aligned diamond grains with low mosaic spread and a vanishing fraction of randomly oriented grains, proving the superior properties of Ir films on SrTiO3 for diamond nucleation as compared with pure silicon substrates. (C) 2000 Elsevier Science S.A. All rights reserved.