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

► We studied the silicon (111) surface during alkaline etching using X-ray diffraction. ► We prepared an atomically smooth surface using aqueous NH4F solutions free of oxygen. ► During etching we found the surface to be hydrogen terminated and not reconstructed. ► Two water layers on top of the silicon surface showed partial liquid ordering. ► We recorded in situ the formation of a surface oxide layer during anodic passivation.