The electrical conductivity o (extrapolated to T=0) of uncompensated Si:P indicates a crossover as a function of P concentration TV at TV cr slightly above the metal-insulator transition at TV C . For TV > TV cr the exponent of a-(N-N c )' i is // ~ 0.64, while n « 1.3 for N c < TV < TV cr . At TV cr do/dT changes sign from negative for TV > TV cr to positive for TV < TV cr . o in a magnetic field also yields pi ~ 1. The apparent discrepancy between uncompensated and compensated semiconductors is traced back to a difference in the (nonuniversal) width of the critical region.
Natural type IIb diamond surfaces of (IOO), (110), and (111) orientation, as well as chemical vapor deposited (CVD) diamond thin films with (IOO), (110), or mixed orientation are probed by photoelectron spectroscopy in the ultraviolet (UPS) and X-ray (XPS) energy regimes. Dramatic changes can be observed in the valence band and core level spectra of these surfaces upon annealing, hydrogen-plasma exposure, or pulsed dye laser irradiation. The observed changes can be reversed by the exposure of the surfaces to atomic hydrogen (deuterium). The valence band spectra reveal specific surface reconstructions for all three surface preparation methods and moreover a cleaning effect is observed following laser irradiation of CVD diamond surfaces. A comparison to a multitude of theoretical and experimental studies on diamond surface reconstruction is made to elucidate the connection between electronic properties and atomic surface structures. I )
The electronic structure of liquid transition metals has been studied by time resolved photoelectron spectroscopy. Distinct changes in the valence band structure across the solid-liquid phase transitions have been observed for Pd, Mo and W. In the case of Pd the changes on melting are caused by a change in the photoemission process itself. For Nb, Mo, Ta and W we suggest a change in the atomic short range order from the bcc structure to an fcc-like short range order in the liquid state which causes a marked change in the valence band spectra of Mo and W due to the filling up of the pronounced gap in the density of states near the Fermi level. The measurements show that time resolved photoelectron spectroscopy can be used to study high temperature oxidation processes on the microsecond time scale.
The electronic structure of liquid tungsten has been studied by time-resolved photoelectron spectroscopy on laser pulse molten surface layers. The valence band spectra reveal distinct changes of the electronic structure across the solid-liquid phase transition which are interpreted by marked changes of the short-range order on melting which change qualitatively the valence electron density of states.
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