Resonant inelastic soft x-ray scattering of Be chalcogenides

Abstract

Over the last few years it has been shown that information about the bulk band structure can be obtained by resonant inelastic X -ray scattering (RIXS) in the soft X -ray regime. However, conceptual differences exist about the underlying pictures involving keywords such as "resonant Xray emission" processes, "electronic resonant Raman scattering", and "core exciton formation". To understand and clarify the applicability of the different concepts, we have studied the properties of a new class of materials -beryllium chalcogenides (i.e., BeS, BeSe, and BeTe) -with soft X-ray K α emission following a resonant Be 1s core hole formation. Be chalcogenides constitute interesting candidates for several electronic applications of II-VIsemiconductors, e.g., in ZnSe-based blue light-emitting devices or Mn-containing spin aligner systems. We will show that even for such large band gap materials with an indirect gap, the observed spectral variations can be nicely correlated to the band structure derived from accompanying LDA-, EXX-, and GW-calculations taking the involved matrix elements into account. Furthermore, we observe Raman-like inelastic scattering features below the absorption threshold. Finally, "core excitonic" features above the valence band maximum can be observed for sufficiently high excitation energies. In the case of BeS, we will demonstrate that such information can even be obtained from insulating powder samples. The obtained results will be discussed in correlation with the above mentioned theoretical band structures, in view of the different conceptual approaches, and with a discussion of the underlying physical processes contributing to a loss of k-conservation and the appearance of a major non-coherent fraction in the observed spectra.The experiments were performed at beamline 8.0

Band structure of ZnO from resonant x-ray emission spectroscopy

“…20,21,22,23 However, to our knowledge there is no literature examining the K-edge electronic structure of a post transition metal oxide in the detail we present, or on any material using our image-based technique. Further, we show crystal anisotropy to be a useful tool, allowing a larger part of the Brillouin zone to be uniquely accessed via RXES.…”

The Be K-edge in beryllium oxide and chalcogenides: soft x-ray absorption spectra from first-principles theory and experiment

“…In both cases, the experimental XAS spectra are those shown in [28], but plotted in a wider energy window. Once again, as observed above for BeO and BeS, the two different theoretical approaches produce similar results.…”

“…The Be K-edge in zinc-blende BeTe. Experimental data (black line, top) [28]. The notation is the same as in figure 1.…”

“…As samples, BeS powder with 99 % purity and grain size up to 150 µm (Alfa Aesar) and a BeO ceramic piece on a carbon tape support were used. The preparation of the BeSe and BeTe samples is described in [28]. Note that the BeS powder exhibits some surface oxide as will be discussed below.…”

“…Experiments are carried out for BeO and BeS samples. Measurements for BeSe and BeTe were obtained previously, though only a range of ∼10 eV from the edge of the spectra were presented [28].…”