SULFUR-INDUCED C(4X4) RECONSTRUCTION OF THE SI(001) SURFACE STUDIED BY SCANNING-TUNNELING-MICROSCOPY

Scanning tunneling microscopy and low-energy electron diffraction have been used to study the adsorption and subsequent thermal desorption o f molecular sulfur from the Si(001) surface. Room-temperature adsorpti on of sulfur resulted in the formation of an overlayer, displaying a h igh density of vacancies or defects, with the underlying Si(001) surfa ce retaining the (2 X 1) reconstruction. Annealing this surface to 325 -degrees-C leads to the desorption of the sulfur overlayer and the app earance of coexisting c(4 X 4) and (2 X 1) surface reconstructions. Ou r data suggest that the c (4 X 4) reconstruction is an adsorbate-induc ed structure in which the sulfur creates defects during the desorption process. High-resolution filled- and empty-state images of the c(4 X 4) surface lead us to propose a missing-dimer defect model for this re construction.