X-ray diffraction analysis of the silicon (111) surface during alkaline etching

Abstract

We present a surface X-ray diffraction determination of the silicon (111)-liquid interface structure during alkaline etching. Preparation of an atomically smooth surface was realized by an in-situ procedure using an aqueous NH 4F solution devoid of oxygen. Using diluted aqueous potassium hydroxide (KOH) and ammonium fluoride (NH 4F) etchant, we have observed that the crystal surface is hydrogen terminated and is not reconstructed at open circuit potential. In addition, a partial liquid ordering of two water layers on top of the crystal surface was found, indicating a weak interaction with the hydrophobic, hydrogen terminated surface. We have followed in-situ the development of the oxide layer by a birth and spread mechanism during anodic passivation of the silicon surface.