K. L. Håkansson

An angle-resolved photoemission study of ZrC0.92(100)

Abstract The (100) surface of a ZrC 0.92 single crystal has been studied using angle-resolved photoemission and synchrotron radiation in the energy range 15–40 eV. The experimental results are interpreted using the bulk band structure and theoretical photoemission spectra calculated for ZrC 1.0 . It is shown that most of the features in the recorded spectra can be explained as originating from direct bulk band transitions. Contributions from density of states (DOS) and a vacancy induced state are discussed. A mapping of the bulk band structure is presented and compared with the calculated LAPW band structure.

Comparison of calculated and experimental k-resolved inverse photoemission spectra from TiN(100) and TiC(100)

Calculated k-resolved inverse photoemission spectra from TiN(100) and TiC(100) are presented along the 〈011〉 and 〈010〉 azimuthal directions. Spectra were calculated utilising the same computational code and crystal potentials as used in earlier calculations of angle resolved photoemission spectra. A comparison with earlier published experimental results is made and the calculated spectra are found to reproduce the experimental spectra quite well.

A K-resolved inverse photoemission study of TiC0.93(100)

Abstract A K-resolved inverse photoemission study has been performed on a TiC0.93(100) crystal. Energy band dispersions for empty states recorded in the 〈010〉 and 〈011〉 azimuths for emitted photons at 9.8 eV are presented. The experimentally observed bands are compared to calculated transitions using free-electron initial state and LAPW calculated final state bands. Calculated dispersions are found to account for the experimentally determined bands quite well. Contribution from a previously predicted Shockley surface state close to \ gG is discussed.

Surface core level shift of Hf 4f in HfN and HfC

Photoelectron spectra of the Hf 4f core levels from a HfN(100) single crystal and a polycrystalline HfC sample have been measured and analysed. Surface-shifted 4f levels could be identified for both compounds, at a smaller binding energy than the bulk 4f levels in HfN and at a larger binding energy in HfC. The surface core level shifts were extracted by a curve fitting procedure and found to be −0.65 eV and +0.41 eV in HfN(100) and HfC. For HfC the shift is very similar to the previously published surface core level shift of +0.42 eV in polycrystalline Hf metal which agreed with theoretical calculations. For HfN however the results cannot be explained in terms of d-band narrowing effects, or by a simple electrostatic picture.

A K-resolved inverse photoemission study of the TiN0.83(100) surface

Abstract The first K-resolved inverse photoemission study of a transition metal nitride has been performed on the (100) face of TiN 0.83 . Energy band dispersions for empty states were recorded in the 〈011〉 and 〈010〉 azimuths for emitted photons at 9.8 eV. For the 〈011〉 azimuth, the recorded spectra were compared with direct transition models using free-electron or LAPW calculated empty bands. For the observed spectral features the latter model is slightly superior. In the 〈010〉 azimuth a surface sensitive feature was identified and is tentatively assigned to a Shockley surface state/resonance.

Core level photoemission study of Cr3Si(100)

High resolution photoemission studies of the core levels in Cr3Si have been carried out using synchrotron radiation. Investigations were performed both on the clean surface, cleaned in situ by sputter and annealing cycles, and after oxygen exposures. A surface shifted Si 2p component was observed on the annealed surface but no surface shifted component could be identified in the Cr3p spectrum. The surface shift was extracted using a curve fitting procedure and found to be −0.30(5) eV. The shift expected due to the loss of coordination at the surface is found to be negative but of about half the size of the observed shift. Upon oxygen adsorption at room temperature a chemically shifted Si 2p component appeared already after an exposure of < 1 L, indicating rapid silicon oxidation, while a chemically shifted Cr3p component could be resolved only after exposures of about 10 L. These findings are presented and discussed.

Core-level study of WSi2 (110)

Angle resolved core level studies of the Si 2p and W 4f levels have been carried out on the (110) surface of a WSi2 single crystal using synchrotron radiation. Surface shifted components have been revealed both in the Si 2p and W 4f spectra. Investigations were carried out at two different annealing temperatures. The results indicate Si enrichment at the surface, and a larger enrichment after the higher temperature anneals. The reactivity upon initial oxygen exposure was investigated. Strong Si oxidation was observed but chemically shifted W 4f components could also be detected.