SURFACE ROUGHENING AND METASTABLE SUPERSTRUCTURES ON WET-PROCESSED SI(111) SURFACE-INDUCED BY HYDROGEN DESORPTION

Scanning tunneling microscopy (STM) has revealed surface morphology ch anges of the hydrogen (H)-terminated Si(111) surface accompanied by hy drogen desorption. The atomically flat and H-terminated surface with r egular straight steps was prepared by NH4F anisotropic etching. These straight step edges became rough when the surface was annealed at 490 degrees C and then the H atoms were desorbed from the monohydride. Thi s phenomenon was compared with previous reports on the behavior of SiH x clusters on the Si(111)-1x1:H formed on the Si(111)-7x7 surface. It was found that the model of the preferential detachment of SiH species from the step edges proposed for the latter case can also explain the phenomenon observed in the current experiment. The SiH species migrat ed over T-4 sites on the surface and formed various superstructures, s uch as 2x2, c(2x4), and root 3x root 3, after the desorption of H atom s. These superstructures might be considered to be metastable ones, an d were converted into 7x7 structures with almost no defects after anne aling at 700 degrees C.