Angle-resolved electron energy-loss spectra from Si(111)−7 × 7 surface under surface wave resonance condition for low-energy electrons

Abstract

Low-energy electron energy-loss spectra (LEELS) from Si(111)−7 × 7 surface were measured under surface wave resonance (SWR) conditions, under which (1) the electron beam forms a surface wave of the 1 7 -order superlattice reflections (SWR s), and (2) the beam forms the surface wave and another surface wave of fundamental lattice reflections (SWR b) simultaneously. The peak heights at 5, 7.5 and 15 eV in energy-loss value, Δ E, which are associated with a bulk band state and two surface states due to backbonds respectively, became slightly large under the SWR b condition. On the other hand, in the LEELS under the SWR s condition, the peak height at ΔE = 1–2 and 8–9 eV was enhanced. Since the peak at 1–2 eV is known to be associated with the surface state due to dangling-bonds, it is considered that LEELS measurement under the SWR s condition reflects some information on electronic structure of Si(111)−7 × 7 surface. Then it is also discussed that the peak at ΔE = 8–9 eV under the SWR s condition is due to excitation of a collective motion for electrons in the dangling-bonds out of the first plane of surface atoms.