Ga-induced atom wire formation and passivation of stepped Si(112)

We present an in-depth analysis of the atomic and electronic structure of the quasi-one-dimensional 1D surface reconstruction of Ga on Si112 based on scanning tunneling microscopy and spectroscopy STM and STS, Rutherford-backscattering spectrometry RBS, and density functional theory DFT calculations. A new structural model of the Si1126 1-Ga surface is inferred. It consists of Ga zigzag chains that are intersected by quasiperiodic vacancy lines or misfit dislocations. The experimentally observed meandering of the vacancy lines is caused by the coexistence of competing 6 1 and 5 1 unit cells and by the orientational disorder of symmetry breaking Si- Ga dimers inside the vacancy lines. The Ga atoms are fully coordinated, and the surface is chemically passivated. STS data reveal a semiconducting surface and show excellent agreement with calculated local density of states LDOS and STS curves. The energy gain obtained by fully passivating the surface calls the idea of step-edge decoration as a viable growth method toward 1D metallic structures into question.