The infrared dielectric property of monoclinic BaTeMo2O9 single crystals is studied by polarized IR reflectance spectra from 20 to 1800 cm−1. Based on the modified Lorentz model, the frequencies, strengths, and dampings of TO modes as well as the orientations of the dipole momenta are determined, agreeing well with Raman spectra and results from First-principles calculation. The observed modes are visually assigned to the specific atoms' motions in the primitive cell based on the theory calculations. A large shift of the internal modes of the anion groups relative to free anion co-ordination polyhedra is observed, which can be used to indicate the distortions of co-ordination polyhedra related to the nonlinear optical properties. Further, the experimental results of the strengths of the oscillators support the elimination and splitting of degenerate modes in free regular polyhedrons. These results offer a way to evaluate the nonlinear optical properties by use of traditional IR reflectivity spectra.

Based on first principle calculations, Ga rich and As(P) rich clean GaAs0.5P0.5(001) reconstruction surfaces and adsorbed surfaces with 0.125ML coverage of Cs at different sites are researched. Formation energy of Ga rich GaAs0.5P0.5(001) β2(4×2) reconstruction surface is smaller than that of As(P) rich one, and the work functions of Ga rich β2(4×2) and As(P) rich β2(2×4) surfaces are 4.657 eV and 5.187 eV, respectively. The adsorption energies of Cs adatoms on both surfaces are negative, showing that Cs adsorption is a stable exothermic process. The work functions of two surfaces both decrease after Cs adsorption, and the average variation of As(P) rich β2(2×4) surface is larger. Mulliken charge analysis shows that Cs adatoms transfer electrons to GaAsP substrate, resulting in Cs-GaAsP dioples which lower the work functions. When Cs atoms are located at D2 of Ga rich surface and D2' of As(P) rich surface, work function values of the two reconstruction surfaces reach the minimums, which are 2.834eV and 2.859eV, respectively. By calculating dipole moments, it can be found that Cs adatoms on the topmost layer form larger effective dipole moments with GaAsP substrate than the Cs atoms located in the trench.

Based on first principle calculations, Ga rich and As(P) rich clean GaAs0.5P0.5(001) reconstruction surfaces and adsorbed surfaces with 0.125ML coverage of Cs at different sites are researched. Formation energy of Ga rich GaAs0.5P0.5(001) β2(4×2) reconstruction surface is smaller than that of As(P) rich one, and the work functions of Ga rich β 2 (4×2) and As(P) rich β2(2×4) surfaces are 4.657 eV and 5.187 eV, respectively. The adsorption energies of Cs adatoms on both surfaces are negative, showing that Cs adsorption is a stable exothermic process. The work functions of two surfaces both decrease after Cs adsorption, and the average variation of As(P) rich β2(2×4) surface is larger. Mulliken charge analysis shows that Cs adatoms transfer electrons to GaAsP substrate, resulting in Cs-GaAsP dioples which lower the work functions. When Cs atoms are located at D 2 of Ga rich surface and D 2 ' of As(P) rich surface, work function values of the two reconstruction surfaces reach the minimums, which are 2.834eV and 2.859eV, respectively. By calculating dipole moments, it can be found that Cs adatoms on the topmost layer form larger effective dipole moments with GaAsP substrate than the Cs atoms located in the trench.