Energy-resolved momentum density of amorphous germanium and the effect of hydrogen adsorption by (e,2e) spectroscopy

The energy-resolved momentum density ρ(Ε,q) of evaporated amorphous germanium has been studied using a surface-sensitive solid state (e,2e) spectrometer with estimated energy and momentum resolutions of about 2.0 eV and 0.15 a.u., respectively, and has been compared with a LMTO (linear muffin-tin orbitals) calculation for crystalline germanium. The density consists of two main features: one disperses upwards from around -13 eV at zero momentum to around -6 eV at a momentum value of 0.85 a.u., the other appears throughout the momentum values investigated (0 to 1.6 a.u.) and is confined within 7 eV below the valence band maximum. The former is identified as being due to the lower valence band of the germanium and agrees well with the LMTO calculation both in dispersion and in intensity, whereas only part of the intensity of the latter feature can be attributed to the upper valence bands. Hydrogen adsorption on the germanium surface reduces the intensity of the upper feature, most noticeably at momenta from 0.65 to 0.85 a.u., and introduces features around energies of -7 to -13 eV between momenta of 0.15 and 0.85 a.u. On this basis, contributions to the momentum density from the dangling bonds on the surface and those due to hydrogen adsorption are estimated. These results are discussed in association with early photoemission studies of the same material.