The electronic properties of tin dioxide single-crystalline (110) surfaces have been studied in correlation with their structure by low-energy electron diffraction, angle-integrated and resonant photoemission using synchrotron radiation [ultraviolet photoemission spectroscopy (UPS)]. Energy distribution curves were measured from the Sn 4d core levels and from the valence band. The experimental valence band is compared with the theoretical density of states (DOS) from perfect and defective surfaces. UPS difference curves, normalized to the Sn 4d intensity, reflect mainly the increase in the oxygen partial DOS when the sample is annealed at increasing temperatures up to 1000 K after sputtering. Their comparison with simulated theoretical difference curves favors a bridging oxygen termination for annealing temperatures above 900 K. After argon-ion bombardment, bandgap defect states that are not predicted by the calculations are found at a maximum density 1.4 eV above the valence-band maximum (VBM). Various degrees of resonant enhancement occur throughout the valence band when the photon energy crosses the Sn 4d~5p photoabsorption threshold, and these are used to establish the tin-derived character of the gap states, for which a tin Ss origin is proposed. Partial-yield spectra allow the localization of unoccupied Sn 5p states in the conduction band starting from 8 eV above the VBM with a maximum at 10 eV. The Sn 4d~5p absorption threshold also shows possible core exciton formation for sputtered surfaces only.
The magic angle solid-state NMR spectra of SnO, and SnO were recorded and analysed. The chemical shift tensor anisotropy is much smaller for SnO, (136 ppm) than for SnO (975 ppm). Simple calculations suggest that the latter is mainly due to the asymmetry in the valence electron cloud of the tin atom in SnO. An Sn-Sn indirect coupling of 8300 Hz was found in SnO, indicating the possibility of Sn 5s orbitals at the top of the valence band of SnO.
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