Hard X-ray Photon-in Photon-out Spectroscopy as a Probe of the Temperature-Induced Delocalization of Electrons in Nanoscale Semiconductors

Abstract

Hard X-ray photon-in photon-out spectroscopy has so far mainly been applied to investigate fundamental physical phenomena in superconductors and chemical reactivity of bioinorganic, photocatalytic, and catalytic materials. Here, we show, with the example of Pr6O11 nanoparticles, an n-type semiconductor, how high-energy resolution fluorescence detected (HERFD) X-ray absorption near edge structure (XANES) can be used to track the changes of partially filled f-bands. We observe a reversible variation of the spectral features related to the tetravalent Pr ions upon heating and cooling, whereas structural and chemical transformations can be excluded. We assign these changes to the occupancy of the O 2p-Pr 4f band and show that they directly relate to changes in the electrical conductance. Our results demonstrate how HERFD-XANES can be used to particularly study in situ the electronic properties of f-electrons in a semiconductor and how this method can be further extended to other classes of semiconducting nanomaterials.