Metastable stage in porous silicon formation: the role of H-terminated low index faces

A combined photoclectrochemistry - atomic force microscopy (AFM) investigation on divalent silicon dissolution in dilute ammonium fluoride at pH 4.5 and 4 reveals the existence of over 200 nm large atomic terrace remnants from the original hydrogen termination. The mesa-type structures exhibit side walls which coincide with low index crystallographic orientations. All relevant observed features can be constructed from combinations of (110), (111) and (113) surfaces and facets. The surprising stability of the mesas is attributed to the property of (110), (111) and (113) faces to form (1 x 1) H-terminated surfaces. Since corrosion at kink sites (corners of terraces) and pitting continues for increased dissolution charge, the phenomenon has transitory character. (C) 2004 Elsevier B.V. All rights reserved.