The adsorption geometry of Na on the Si(l00)2 x 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 x 1 dimerized structure, similar to that of the clean 2X1 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(l00)2 x 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(l00)2 x 1 surface.
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