Vibrational Excitation Mechanisms in Electron Energy Loss Spectroscopy Studies of Hydrogen Adsorbed on Si(100) and Ge(100)

Abstract

High-resolution electron energy loss spectroscopy (HREELS) has been used to investigate the inelastic electron scattering processes involved in the excitation of the normal modes of vibration of atomic hydrogen adsorbed on Si(100) and Ge(100). Detailed measurements as a function of incident electron beam energy allow a clear distinction to be made between dipole and nondipole excitation processes. The bending and scissor modes of adsorbed hydrogen are excited predominantly by dipole scattering, but the stretching modes show characteristic resonances between 3 and 6 eV. The mechanism for these scattering processes is discussed.

High resolution electron energy loss spectroscopy of clean and hydrogen covered Si(001) surfaces: First principles calculations

“…Furthermore, experimental HREELS data for Si(001)-(2×1)H from several groups are in good agreement. 3,8,12,13 Our calculations of loss energies and intensities are in very good agreement with loss energies and relative intensities from experiment for the hydrogen covered surfaces. This approach can therefore be expected to predict HREELS spectra for clean Si(001) surfaces reliably.…”

“…by Eggeling et al 3 We find four modes in the range 2147-2183(1550-1576) cm −1 in our calculations for the H(D) covered surfaces. The modes with the largest dipole activities are at 2179(1573) cm −1 .…”

“…In order to demonstrate a test of the method used to calculate HREELS spectra, we report spectra for hydrogen covered surfaces and compare them to experimental spectra. HREELS spectra for the Si(001)-(2×1)H and D surfaces have been measured by Eremtchenko et al 8 and by Eggeling et al 3 There is less experimental uncertainty in the composition of the hydrogenated surfaces than the clean surfaces. When a clean Si(001) sample is prepared for an HREELS measurement, (2×1), p(2×2), or c(4×2) domains may coexist and the chemical unsaturation of these surfaces means that they contaminate relatively quickly.…”

“…2 This is sometimes referred to as the surface dipole rule. 3 In early theoretical work, 1, 2 Mills and co-workers attributed the absence of scattering by modes with dynamic dipole moments oriented parallel to metal surfaces (or narrow band gap semiconductor surfaces, such as Si) to screening of those moments by the bulk response of the substrate.…”

“…8 These measurements followed earlier work on the Si(001)-(2×1)H surface. 3,[12][13][14] Assignment of H stretching and bending modes for the (2×1)H and D surfaces is straightforward and therefore provides a good test of a first principles calculation of HREELS spectra. Allan and Mele calculated the phonon dispersion relation for the Si(001)-(2×1)H surface 15 with one H atom per surface Si atom.…”