Scanning tunneling microscopy study of hydrogen-terminated Si(001) surfaces after wet cleaning

A scanning tunneling microscopy (STM) study of the atomic structure of hydrogen-terminated Si(001) surfaces after wet cleaning is presented. Surface morphologies strongly depend on wet cleaning procedures. After being dipped into dilute HF solution, the surface is constructed by piling round, small terraces along the 〈110〉 direction. On the other hand, atomic rows along the 〈110〉 direction are clearly observed when the surface is subsequently rinsed by ultrapure water, and the corrugation pattern is identified as a 2×1 structure. With STM and Fourier-transform infrared attenuated total reflection (FTIR–ATR) observations, it is proposed that etching with ultrapure water proceeds in two steps. First, atomic steps perpendicular to dihydride rows of the upper layer are etched quickly to form step edges parallel to the dihydride rows and to produce large terraces with fewer steps. Second, etching occurs inside a terrace. Every other row of an ideally 1×1 dihydride terrace is removed preferentially in ultrapure water.