Theoretical study on photon–phonon coupling at (001)‐(2 × 1) surfaces of Ge and α‐Sn

Abstract

AbstractWe present a study of the far‐infrared reflectance anisotropy spectra for (001) surfaces of Ge and α‐Sn in the (2 × 1) asymmetric dimer geometry, which exhibit a resonance structure associated with the excitation of surface phonon modes. We have employed a theoretical formalism, based on the adiabatic bond‐charge model (ABCM), for computing the far‐infrared reflectance anisotropy spectra. In comparison with previous theoretical results for silicon and diamond surfaces, the resonance structure in the reflectance anisotropy spectrum for Ge(001)‐(2 × 1) turns out to be similar to that observed in the spectrum for the Si(001)‐(2 × 1) surface, whereas the spectrum for α‐Sn(001)‐(2 × 1) surface is noticeably different from the others. We have established a trend of far‐infrared reflectance anisotropy spectra for IV(001) surfaces: the weaker dimer strength, the stronger resonances of low‐frequency surface phonons.