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Abstract:
The Si(111)4x1-In surface is composed of metallic atomic wires, which undergo a transition into a charge density wave phase at a transition temperature (T-c) of 125 K. This T-c was reported recently to substantially increase upon the oxygen adsorption, for which the underlying mechanism is not understood. We investigate the structures of oxygen adsorbates on the Si(111)4x1-In surface by scanning tunneling microscopy (STM) and density-functional theory calculations. We identify three distinct atomic-scale structures induced by the oxygen adsorption with high-resolution STM topography. The calculations find two energetically favorable adsorption sites on and between In zigzag chains, respectively. In conjunction with an additional adsorption configuration, where O is buried underneath the In chain, three stable structures are thus identified that reproduce very well the characteristic bias-dependent STM images. Experimentally, a switching between two specific adsorption structures is observed and is consistent with the structure models proposed. The structural distortions and the charge transfer of In atomic wires around the adsorbates are also characterized. This work provides a solid basis for the microscopic understanding of the intriguing oxygen impurity effect on the phase transition.
