Additional dimer-row structure of 3C-SiC(001) surfaces observed by scanning tunneling microscopy

Abstract

We present atomic-resolution images, obtained with scanning tunneling microscopy (STM), of 3C-SiC(001) surfaces with Si adlayers on the Si-terminated surface, formed by in situ cleaning. We propose a unified additional dimer-row model for the surface with extra Si atoms, which is consistent with structural features obtained by our STM and low-energy-electron-diffraction (LEED) observations. The unit cell of the Si-saturated (3×2) surface seen in LEED observations consists of a pair of additional Si dimers on the Si-terminated surface. The dimer pairs form a straight string along a direction through the centers of two constituent atoms of a dimer. Unit cells of (5×2) and a new reconstruction (7×2) also consists of a pair of additional Si dimers. The (5×2) and (7×2) surfaces have 5/3 and 7/3 wider distances between adjacent rows than that on the (3×2), respectively. This model predicts that even number phases such as (4×2), (6×2), . . . , which are so far unobserved, are unfavorable on the excess Si surfaces in terms of structural stability. Further, it is found that the saturation of Si adsorption on the (3×2) surface is derived from a steric hindrance caused by periodic dimer-vacancy strings between the adjacent dimer pairs.