Hydrogen-adsorbed group-IV materials

Hydrogenations of monolayer group-IV systems clearly present the diverse quasiparticle phenomena in this chapter. The rich crystal symmetries are directly reflected in the planar or buckled honeycomb lattice, IV–IV bond lengths, their observable fluctuations, IV–H bonding angles, H-adatom hollow sites and heights. These featured geometries, which are largely enhanced by the various chemisorption cases, have successfully created the unique band structures, wave functions, spatial charge density distributions/their variations after hydrogenations, as well as, van Hove singularities. Optical properties, transverse dielectric functions, energy loss spectra, absorption coefficients and reflectance spectra, and absorption coefficients, clearly show the unusual interband electron-hole excitations and coherent carrier oscillations, in which the different plasmon modes come to exist in the specific energy ranges. The pronounced absorption peaks and excitonic effects are successfully combined with the joint van Hove singularities. Each prominent structure is thoroughly examined to be a special set of orbital hybridizations from the initial and final band-edge states. The lowest/lower excitonic peaks are due to the stable or quasi-stable electron-hole bound states. The red shifts of threshold absorption frequency indicates the fact that optical gaps are less than energy gaps.