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Valence electronic structure of the system as a function of film thickness. The vertical lines indicate the and Si band gaps, respectively. Left-hand side: Occupied states as probed with valence photoemission . The original spectra are denoted , whereas denotes difference spectra obtained by subtracting the spectrum for the clean surface. Spectrum denotes the spectrum after deposition shifted in binding energy in order to match the structure at . This gives information about the VBE for , which otherwise is obscured by the surface states. Right-hand side: Unoccupied states as probed with XAS. The XAS spectra are related in energy vs the Fermi level by comparing the XAS photon energy scale to the binding energy scale vs the Fermi level of the corresponding photoemission spectrum.
Silicon band edge positions for increasing film thickness. The VBE are both derived from the valence (VB, filled circles) and core level (CL, open circles) photoemission spectra. The CBEs are obtained by adding the silicon band gap value to the VBE values from the valence photoemission spectra.
Bottom: CL PES spectrum after deposition of . Top (dotted): The corresponding XAS spectrum. The PES and XAS spectra are put on a common energy scale for which the PES spectrum is referenced to the Fermi level while the XAS spectrum refers to the absolute photon energy. Top (solid line): The PES spectrum shifted in order to fit the low energy flank to the XAS edge. The excellent agreement indicates that this is a valid measure of the conduction band edge vs the Fermi level.
Integrated intensity ratios of the XAS peak and the XAS structure at lowest energy. These are relative measures and are not absolute stoichiometric values. The point at which the ratio starts to increase coincides with the completion of the interface and can be interpreted in terms of a change in the interaction.
Band offsets and band gap values for increasing film thickness.
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