M. Seki

Electrical and optical properties of black phosphorus single crystals

Abstract Large single crystals of black phosphorus have been prepared by a large volume-high pressure technique at high temperature. Using the crystals, we have measured temperature dependences of the electrical conductivity and the Hall coefficient, the FIR cyclotron resonance absorption and the reflectance for synchrotron radiation. All samples obtained are p-type and the Hall mobility reaches 5×10 4 cm 2 v·sec around 20K. The anisotropies of the effective mass, the Hall mobility and the SOR reflectance along the three crystal directions, a, b, and c, have been observed.

Vacuum Ultraviolet Reflectance Spectra and Band Structures of Pyrites (FeS 2 , CoS 2 and NiS 2 ) and NiO Measured with Synchrotron Radiation

Reflectance spectra of FeS 2 , CoS 2 and NiS 2 pyrites have been measured in the photon energy region from 4 to 30 eV with synchrotron radiation and compared with the results of NiO and related compounds. Dielectric constants, optical constants, effective electron numbers as well as energy-loss functions are evaluated by means of the Kramers-Kronig analysis. Fine structures of the reflectance spectra are qualitatively interpreted providing information on band structures. Characteristic features of band structures related to the 3 d electrons in the low-spin state are experimentally elucidated.

Valence band and core-level photoemission spectra of black phosphorus single crystals

Abstract Valence band structures of black phosphorus have been measured by synchrotron-radiation photoemission spectroscopy. The excitation photon-energy dependence of the spectra has provided information about the 3s-3p hybridization. As for inner core-levels, binding energies of 2p and 2s core-levels, 2p 1 2 −2p 3 2 splitting, and the bulk plasmon energy are estimated from X-ray photoemission spectroscopy.

Surface core-level shifts of 4d states of (110) cleaved InSb

4d core levels of InSb(110) cleaved surface have been measured by ultraviolet photoemission spectroscopy with the aid of synchrotron radiation. The authors have recently observed surface core levels of In shifted to larger binding energies by +0.22 eV and those of Sb shifted to smaller binding energies by -0.29 eV, relative to their bulk components. The location of the cation-derived empty surface state is re-evaluated to be at 0.33 eV above the valence band maximum.

Core-exciton induced resonant photoemission in the covalent semiconductor black phosphorus

Abstract Valence band photoemission spectra of black phosphorus have shown anomalous behavior at the excitation of 2p core-excitons. The intensity of the 2.7 ev peak shows a clear Fano type interference due to a direct recombination of core-excitons leaving one hole in valence bands. Besides, strong enhancement of the 10.8 eV peak is interpreted as due to a core-exciton induced resonance with two-hole final states. The role of core-excitons as intermediate states for photoemission processes is newly revealed in the experiments.

Ultraviolet photoemission and 4d core reflectance spectra of SmSe(100)

Abstract Ultraviolet photoemission (UPS) and inner core reflectance spectra have been measured on SmSe(100) surface with synchrotron radiation. Besides the multiplet structures observed in UPS spectra for the Sm 4f, 5p and 5s excitations, the reflectance spectrum has revealed a multiplet structure associated with the Sm 4d→4f excitation. Each band of the UPS spectra has shown remarkably different hν dependence and the resonant behavior of the cross section. Sm 4f- and Se 4p-derived valence band features are unambiguously identified by the angle resolved UPS.

Reflectance and UPS studies of band structures and final state interactions of low-spin pyrites

Abstract Reflectance spectra of FeS 2 and NiS 2 have been measured with synchrotron radiation from 4 to 30eV. The intensity decrease of the p(valence)→p ∗ +dγ(conduction band) excitation from FeS 2 to NiS 2 is a characteristic feature of the low-spin configuration of the 3d electrons in pyrites. Photoelectron partial yield spectrum of FeS 2 has shown conspicuous multiplet structures in the region of the 3p core(M 2,3 ) excitation, which are quantitatively analyzed by a newly developed theory based on a localized model. The reduction factors κ F and κ G of the Coulomb and exchange interactions between the core p hole and the d electron are evaluated as 0.5 and 0.4, in agreement with the large covalency and itinerant nature of the d electrons in pyrites.

Resonant photoemission and Ta 5p core reflectance spectra of 1T- and 2H-TaSe2

Abstract Reflectance spectra of 2H- and 1T-TaSe2 have been measured at room temperature in the region between 20 and 60 eV. The multiplet structures in the Ta 5p core excitation region are analyzed on the localized excitation model. The ultraviolet photoemission spectra have revealed a resonant enhancement of the Ta 5d and Se 4p valence bands for the excitation of the Ta 5p core states. The difference of the multiplet structures as well as of the resonant behavior between 1T- and 2H-polytypes has elucidated the hybridization of the Se 4p states with the Ta 5d states in the valence bands of TaSe2.

Core-level reflectance spectroscopy of germanium by means of synchrotron radiation

Abstract Reflectance spectra due to 3d core-levels of Ge have been measured in the photon-energy region from 29 to 38 eV by means of synchrotron radiation. Second-energy-derivative spectra have newly shown pairs of doublet structures with energy separation of the Ge 3d 5 2 − 3 2 core-level splitting. The observed doublet structures are assigned to the transitions from the 3d 5 2 and 3d 3 2 core-levels to the flat regions of the conduction band around the particular symmetry points of Δ6c and L(3c(L6c, L4,5c).

Core-exciton spectra of AlxGa1−xAs studied with synchrotron radiation

Abstract Core-exciton spectra of Al x Ga 1− x As have been measured in the photon-energy region from 19 to 27 eV by use of synchrotron radiation. The core-excitons associated with the Ga 3 d core-hole and the conduction electron around the lowest L 6 and X 6 symmetry points are found to be coupled with each other through intervalley electron-hole interactions. Quantitative analyses have elucidated that intervalley Coulomb term is playing a dominant role for this coupling. Another higher energy doublet structure is interpreted as due to the transition from the Ga 3 d core-levels to the rather flat region in the second lowest conduction band around the L 6 and L 4, 5 symmetry points.