First-principles Study of the One-dimensional Au Atomic Wire Formed on the Si(111) Surface

DoctorWe have studied the Au/Si(111)-(5×2) surface by using density functional calculations. The (5×2) surface has attracted great attention as a representative self-organized one-dimensional metal chain system. Particularly, a number of studies have been performed to identify its atomic structure, but completely reliable structural model is not yet established. The structural model proposed by Erwin et al. [Phys. Rev. B 80, 155409 (2009)], which is considered as the best one so far, has a critical problem. This model is basically a (5×1) structure and so has difficulty in explaining the measured (5×2) scanning tunneling microscopy images. Although Erwin et al. argued by density functional theory calculations that the (5×2) images may be possible from the (5×1) structure with the aid of a electron doping, the origin of such electron doping is not clarified yet. In this thesis, we propose a new structural model for the surface. The key feature of our model is the incorporation of one more Au atom per (5×2) cell on the Erwin’s model, which leads to distinct (5×2) periodicity. Our model is energetically favored over the Erwin’s model, and well reproduces the scanning tunneling microscopy images and angle-resolved photoemission spectra data. Our band calculations show that this surface is metallic with a prominent half filled band of surface states, mostly localized around the Au-chain area. The correct identification of the atomic and band structure of the clean surface further clarifies the adsorption structure of Si adatoms which are always present on the surface and the physical origin of the intriguing metal-to-insulator transition driven by Si adatoms. In addition, our structural model is found to well reproduce the Si 2p and Au 4f surface core-level shifts reported by previous x-ray photoelectron spectroscopy studies, thereby clarifying their atomic origins. In our quantitative electron-counting analysis, the higher-binding shifts of Si 2p and Au 4f core levels were attributed to a charge transfer from Si to Au atoms and a depletion of d electrons at the Au atoms, respectively, in support of earlier experimental interpretations