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 μm) of very high porosity (10–50%). The edges of the pores were in the form of small crosses, which followed the original directions of the 〈100〉 c-Si. The diamond coating was made by chemical vapor deposition (CVD) in a hot-filament reactor. We observed that the diamond nucleation occurs mainly at the edges of the pores but relatively few nuclei follow a preferential orientation axis. As the nucleation density is very low, coalescence does not occur even after 11 h and 30 min of deposition. Using a pre-deposition ‘seeding’ process with diamond grains, it was possible to produce a complete diamond CVD coating. A cross-section analysis of the diamond/PS/c-Si structure by scanning electron microscopy (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 pores. The Raman analyses indicated also a small contamination of the diamond layer by Si nano-crystals.