Top view of the experimental setup. The angle between the x-ray beam and analyzing direction is fixed at 35. is the x-ray incidence angle and is the polar angle.
Upper panel: Nb spectra collected at at various conditions: (a) and photons, (b) (normal emission) and photons, and (c) and photons. Lower panel: GIXPS (filled circles) and ARXPS (open circles) results from the data measured at and using photons. Note that the ARXPS data are collected at the angles for . The solid lines are provided for eye guidance.
Nb spectrum measured using photons at and (circles). Simulation results obtained using the Doniach-Sunjic functions are shown as well. The full line indicates the fitting result and the dotted lines indicate various individual peaks as labeled by chemical formulas. The background is not shown for clarity.
Nb core-level (left) and valence-band (right) spectra collected using photons at (full lines) and (dotted lines) on a surface at , on the surface annealed for at , and on the surface further annealed at for .
Schematic for evolution of the oxide composition upon annealing at 430 and , respectively. The figure is presented from the vacuum/oxide interface to the Nb(100) surface as indicated.
ARXPS results obtained at various conditions as indicated. The results are displayed using the ratio of the metal peak to the oxide peak as a function of the polar angle. The dashed line is obtained for a flat surface covered with a uniform overlayer.
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