REEXAMINATION OF THE SI(111)3 X 1-NA RECONSTRUCTION ON THE BASIS OF SI ATOM DENSITY AND UNIT CLUSTER DETERMINATION

Using scanning tunneling microscopy, features of the Si(111)3x1-Na rec onstruction have been found, namely, Si atom density of 4/3 ML and a u nit cluster that shows up in STM images as a group of four protrusions forming a (root 3a x 1a) rectangle. These findings led to the reexami nation of the atomic arrangement of a Si(111)3 x 1 phase. As a result, a double-pi-bonded chain model is proposed. The model incorporates tw o Si pi-bonded chains in faulted-unfaulted orientations connected thro ugh Na atoms.