ENERGY-RESOLVED MOMENTUM DENSITY OF AMORPHOUS-GERMANIUM AND THE EFFECT OF HYDROGEN ADSORPTION BY (E,2E) SPECTROSCOPY

The energy-resolved momentum density rho(epsilon,q) of evaporated amor phous 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 german ium. The density consists of two main features: one disperses upwards from around - 13 eV at zero momentum to around - 6 eV at a momentum va lue of 0.85 a.u., the other appears throughout the momentum values inv estigated (0 to 1.6 a.u.) and is confined within 7 eV below the valenc e band maximum. The former is identified as being due to the lower val ence band of the germanium and agrees well with the LMTO calculation b oth in dispersion and in intensity, whereas only part of the intensity of the latter feature can be attributed to the upper valence bands. H ydrogen adsorption on the germanium surface reduces the intensity of t he upper feature, most noticeably at momenta from 0.65 to 0.85 a.u., a nd introduces features around energies of - 7 to - 13 eV between momen ta 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 hydrog en adsorption are estimated. These results are discussed in associatio n with early photoemission studies of the same material.