Hydrogen termination of Si(110) surfaces upon wet cleaning revealed by highly resolved scanning tunneling microscopy

The surface structure of the hydrogen-saturated Si(110) surfaces after wet cleaning is studied on an atomic scale by means of scanning tunneling microscopy. When a surface oxide layer is stripped using a HF-containing solution, the surface consists of nanometer-scaled terraces and atomic steps along various directions. Coupled monohydride lines are formed inside a small terrace, as predicted by infrared spectra. The Si(110) surface after subsequent rinsing for a short period is occupied by a long terrace along the $[1¯10]$ direction in which the ideal $1×1$ structure is formed. Atomic arrangements around step edges are determined in detail based on atomic images and first-principles calculations. A ridge-shaped structure is observed after excess rinsing with water, and infrared spectra indicate that the slope is composed of (111) microfacets. From these results, we present the mechanism underlying the formation of the hydrogen-terminated Si(110) surfaces during wet cleaning processes.