Sb-induced passivation of the Si(100) surface

The passivation of the Si(100)(2×1) surface upon chemisorption of Sb is investigated using the first-principles local-density dmol method with analytic gradients and cluster models containing up to 62 atoms. Sb adsorbed on the bridge site of Si(100)(2×1) is found to saturate the dangling bonds of the underlying two dimer atoms, resulting in an unusual chemisorption site for this system. The (2×1) reconstruction is removed when Sb adsorbs on the cave site between two nearest bridge sites of the Si(100)(2×1) surface that are already occupied by Sb atoms. The formation of an Sb dimer is found to be more stable than single atom adsorption; thus Sb dimers are the essential structure on the Si(100) surface. The calculated bond lengths of Sb-Si and Sb-Sb are 2.61 and 2.93 , respectively, in excellent agreement with a recent surface-extended x-ray-absorption fine-structure analysis.