Relaxation and H coverage of ammonium fluoride treated Si(111)

Using medium energy ion scattering and elastic recoil detection, we have studied silicon surfaces prepared by ex situ NH₄F wet etching. We report direct measurements of relaxation and hydrogen coverage of the passivated Si(111)-(1×1) surface. For Si(111), nearly ideal, unreconstructed surfaces are obtained, terminated by a single atomic layer of hydrogen. Silicon backscatter yields agree closely with simulations of a bulk truncation, with an inward relaxation of the outermost layer of 0.075±0.03 Å. On the other hand, Si(001) prepared by NH₄F solution shows severe roughening.