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# Probing bulk electronic structure with hard X-ray angle-resolved photoemission

## Abstract

Traditional ultraviolet/soft X-ray angle-resolved photoemission spectroscopy (ARPES) may in some cases be too strongly influenced by surface effects to be a useful probe of bulk electronic structure. Going to hard X-ray photon energies and thus larger electron inelastic mean-free paths should provide a more accurate picture of bulk electronic structure. We present experimental data for hard X-ray ARPES (HARPES) at energies of 3.2 and 6.0 keV. The systems discussed are W, as a model transition-metal system to illustrate basic principles, and GaAs, as a technologically-relevant material to illustrate the potential broad applicability of this new technique. We have investigated the effects of photon wave vector on wave vector conservation, and assessed methods for the removal of phonon-associated smearing of features and photoelectron diffraction effects. The experimental results are compared to free-electron final-state model calculations and to more precise one-step photoemission theory including matrix element effects.

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## Acknowledgements

The authors would like to thank O. D. Dubon (UC Berkeley) for providing the GaAs sample. The authors with LBNL affiliation acknowledge support from the Director, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, of the US Department of Energy under contract number DE-AC02-05CH11231, for salary and travel support. The measurements were performed under the approval of NIMS Beamline Station (Proposal Nos. 2008A4906, 2008B4800, 2009A4906). This work was partially supported by the Nanotechnology Network Project, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan. Financial support by the Deutsche Forschungsgemeinschaft (FOR 1346, EB-154/20 and MI-1327/1) and the Bundesministerium für Bildung und Forschung (05K10WMA) is also gratefully acknowledged.

## Author information

Authors

### Contributions

A.X.G., C.P., S.U. and B.B. carried out the experiments, with assistance from Y.Y. and under the supervision of K.K. and C.S.F. Data normalization and analysis were performed by C.P. and A.X.G. Free-electron final-state model calculations were performed by L.P., with assistance from C.M.S. One-step model calculations were performed by J.M., J.B. and H.E. DFT calculations were performed by E.R.Y. and W.E.P.

### Corresponding author

Correspondence to A. X. Gray.

## Ethics declarations

### Competing interests

The authors declare no competing financial interests.

## Supplementary information

### Supplementary Information

Supplementary Information (PDF 870 kb)

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Gray, A., Papp, C., Ueda, S. et al. Probing bulk electronic structure with hard X-ray angle-resolved photoemission. Nature Mater 10, 759–764 (2011). https://doi.org/10.1038/nmat3089

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