Microcrystalline diamond deposition on a porous silicon host matrix

Porous silicon (PS) is a nanostructured material obtained by etching pores into crystalline Si wafers. In this paper, we report on the nucleation and growth of diamond on very thick PS films (130-220 mu m) of very high porosi ty (10-50%). The edges of the pores were in the form of small crosses, whic h followed the original directions of the [100] c-Si. The diamond coating w as made by chemical vapor deposition (CVD) in a hot-filament reactor. We ob served that the diamond nucleation occurs mainly at the edges of the pores but relatively few nuclei follow a preferential orientation axis. As the nu cleation density is very low, coalescence does not occur even after 11 h an d 30 min of deposition. Using a pre-deposition 'seeding' process with diamo nd grains, it was possible to produce a complete diamond CVD coating. A cro ss-section analysis of the diamond/PS/c-Si structure by scanning electron m icroscopy (SEM), micro-Raman and photoluminescence spectroscopies revealed interesting results: the luminescence of the PS under the diamond layer is preserved. There is no diamond deposition inside of the pores, but a small permeation of carbon was identified which forms diamond-like phases at the bottom of the ports. The Raman analyses indicated also a small contaminatio n of the diamond layer by Si nano-crystals. (C) 2000 Elsevier Science S.A. All rights reserved.