Structure of the Ba-induced Si(111)-(3 x 2) reconstruction - art. no. 056104

The Ba/Si(111) surface, previously known as a 3 x 1 phase. is found to have a 3 x 2 periodicity and a semiconducting band gap. The substrate reconstru cts into the honeycomb chain-channel (HCC) structure with Ba atoms in the c hannel. as in the alkali-metal-induced Si(111)-(3 x 1). However, the metal coverage is determined to be 1/6 monolayers, half the alkali-metal coverage . We propose that the structure and the metal coverage determined for the B a adsorbate is universal for other alkaline-earth-metal adsorbates. With th e alkali-metal-induced 3 x 1 case, our results lead to a rule that one dona ted electron per 3 x 1 surface unit is necessary to stabilize the HCC recon struction of Si,