Lanthanum-induced quasi-one-dimensional reconstructions on Si(111).

Various quasi-one-dimensional (1D) structures on Si(111) surface induced by submonolayer La are investigated by scanning tunneling microscopy/spectroscopy (STM/STS) and density-functional theory (DFT) calculations. Three types of reconstructions, 5 × 2, (2  m  + 1) × 6 ( m  > 2, integer) and 2 × 3, in which rows of La adatoms are separated by Si honeycomb chain-channels (HCCs) or Seiwatz chains (SCs), are formed and their stability can be controlled by the La coverage. In 5 × 2 reconstruction, the Si HCCs and SCs are arranged alternatively with La atoms in between, while the 2 × 3 reconstruction consists of SCs only. The (2  m  + 1) × 6 is an intermediate phase, in which each unit cell consists of a single HCC and ( m −1) SCs depending on the La coverage. The weak inter-chain interactions in 5 × 2 and 2 × 3 evidence the 1D character of the reconstructions. STS results and DFT calculations indicate these chains are semiconducting. The thermodynamic evolution of the surface is also investigated, providing important information for the growth of LaSi 2 films on Si during the initial stage. [ABSTRACT FROM AUTHOR]