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(a) The Te core-level and valence band spectra for bulk with no nitrogen doping. The position of the valence band maximum is determined by linear extrapolation of the leading edge of the valence band spectrum to the base line, as illustrated in the plot. (b) Te core-level spectra obtained from samples with an ultrathin metal overlayer on bulk with no nitrogen doping.
Experimentally extracted effective work functions of Al, W, and Pt on undoped were plotted using squares against their respective vacuum work functions . The dashed line is given by , and represents the case where no pinning of metal Fermi level occurs on the surface. The intercept (indicated by shaded circle) of the dashed line and straight line represents the charge neutrality level of the undoped .
(a) The valence band spectra for with various nitrogen doping concentrations (0, 3.5, 6.2, 7.7, and 8.4 at. %). The reference for the spectra is the Te core-level spectra of the undoped sample. The Te core-level spectra for an ultrathin metal of (b) Al, (c) W, and (d) Pt deposited on the various nitrogen-doped films. The spectra have been referenced with respect to the Al , W , and Pt peak binding energies of bulk Al, W, and Pt in (b), (c), and (d), respectively.
Measured hole barrier height as a function of nitrogen doping concentration in the NGST films for various metals. The measured values are within the experimental error of ± 0.2 eV. Increasing nitrogen concentration generally gives a less negative hole barrier. Increasing the work function of the metal gives a more negative hole barrier. The slope parameter and charge neutrality level relative to the vacuum level (in eV) are also given for with various nitrogen concentrations. The valence band energies of NGST with 0, 3.5, 6.2, 7.7, and 8.4 at. % nitrogen relative to the vacuum level are 4.61, 4.64, 4.69, 4.70, and 4.88 eV, respectively.
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