Electron compound nature in a surface atomic layer of a two-dimensional hexagonal lattice

摘要

The two-dimensional (2D) ordered phase of monovalent metal alloy, 21~(1/2)×21~(1/2) is formed on the Si(111) surface with the constant electron/atom ratio, indicating electron compound nature. Two conventional theories of the Hume-Rothery compounds, Jones model (nearly-free-electron model), and pseudopotential model (in-terionic interaction model), were applied to examine stability of the 2D phase. We found breakdown of the former and confirmation of the latter approaches with importance of medium-range interatomic interaction, mediated by the 2D surface-state electrons, in the latter approach.