Metal-insulator transition on the Si(111)4 x 1-In surface with oxygen impurity

Abstract

We investigate with low-energy-electron diffraction (LEED) and angle-resolved photoelectron spectroscopy (ARPES) the effect of oxygen adsorbates on the phase transition of the Si(111)4 × 1-In surface. On this surface, oxygen was reported to increase the transition temperature (Tc) into the distorted 8 × 2 phase. We observed that while the Tc into the 8 × 2 phase increases up to 180 K, the substantial disorder is also induced on the surface. ARPES study reveals that the oxygen-induced 8 × 2 phase has the same insulating band structure with that on the pristine surface at a lower temperature. This indicates clearly that the oxygen-induced 4 × 1–8 × 2 transition is a consistent metal-insulator transition with that on the pristine surface. On the other hand, oxygen adsorbates slightly increase the band filling of the one-dimensional metallic bands of the 4 × 1-In surface. This contrasts with the expectation of the hole doping and the increased Tc, thus cannot be explained by the doping effect of adsorbates. A further study of the oxygen-induced 8 × 2 phase is requested to understand the microscopic mechanism of the adsorbate-induced elevation of the metal-insulator Tc.