Adsorption Structure of the Na-Saturated Si(100)2×1 Surface Studied by Field-Ion Scanning Tunneling Microscopy/Spectroscopy

The adsorption geometry of Na on the Si(100)2×1 surface has been investigated using field-ion scanning tunneling microscopy/spectroscopy (FI-STM/STS). The high resolution STM image of the Na-saturated surface showed a 2×1 dimerized structure, similar to that of the clean 2×1 surface. Individual dimers were bifurcated in the filled state STM images, resembling to those of the empty state images for the clean surface. The STS data for this surface showed a large energy band gap of approximately 1 eV, suggesting that the Na/Si(100)2×1 surface was semiconductor-like. These observations are consistent with the results of Kono's group and a recent theoretical study by Terakura's group, supporting the double-layer model for Na on the Si(100)2×1 surface.