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

Abstract

A combined photoelectrochemistry – 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 (1 1 0), (1 1 1) and (1 1 3) surfaces and facets. The surprising stability of the mesas is attributed to the property of (1 1 0), (1 1 1) and (1 1 3) faces to form (1 × 1) H-terminated surfaces. Since corrosion at kink sites (corners of terraces) and pitting continues for increased dissolution charge, the phenomenon has transitory character.