Evidence of anisotropic structures of free-standing porous silicon films

Abstract

Optical and secondary electron beam images of free-standing porous silicon films reveal a pronounced layered structure. Films tend to split into sheets parallel to the 〈111〉 plane of the initial substrate and form steps and terraces at the broken edge of the film. We have investigated these layers by scanning and transmission electron as well as optical microscopy. We have not observed any significant differences in the microstructure of each layer. Film layering in the cross-section view, caused by these terraces, has a periodicity of about 1 μm. The origin of this effect is discussed and could arise from the electrochemical etching regime used, vertical inhomogeneities in the starting material or mechanical stress-related effect arising from electrolyte evaporation. © 1997 Elsevier Science S.A.