Analysis of the electronic structure of Hf(Si 0.5As 0.5)As by X-ray photoelectron and photoemission spectroscopy

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The ternary hafnium silicon arsenide, Hf(Si x As 1− x )As, has been synthesized with a phase width of 0.5⩽ x⩽0.7. Single-crystal X-ray diffraction studies on Hf(Si 0.5As 0.5)As showed that it adopts the ZrSiS-type structure (Pearson symbol tP6, space group P4/ nmm, Z=2, a=3.6410(5) Å, c=8.155(1) Å). Physical property measurements indicated that it is metallic and Pauli paramagnetic. The electronic structure of Hf(Si 0.5As 0.5)As was investigated by examining plate-shaped crystals with laboratory-based X-ray photoelectron spectroscopy (XPS) and synchrotron radiation photoemission spectroscopy (PES). The Si 2 p and As 3 d XPS binding energies were consistent with assignments of anionic Si 1− and As 1–. However, the Hf charge could not be determined by analysis of the Hf 4 f binding energy because of electron delocalization in the 5 d band. To examine these charge assignments further, the valence band spectrum obtained by XPS and PES was interpreted with the aid of TB-LMTO band structure calculations. By collecting the PES spectra at different excitation energies to vary the photoionization cross-sections, the contributions from different elements to the valence band spectrum could be isolated. Fitting the XPS valence band spectrum to these elemental components resulted in charges that confirm that the formulation of the product is Hf 2+[(Si 0.5As 0.5)As] 2−.