Condensed-Matter Physics & Materials Science Seminar

X-ray absorption (XAS) and electon energy loss spectroscopies (EELS)
are powerful tools for probing excited state electronic structure, which
can in turn be used to determine many aspects of element-specific local
structure and chemical bonding. However, both techniques are generally
limited to dipole-allowed transitions to final states, and furthermore
both techniques have significant constraints on sample preparation and
environments for initial states with low binding energies. An
alternative technique, non-resonant x-ray Raman scattering (XRS),
overcomes these limitations through measurement of the momentum-transfer
(q). I have designed and commissioned the LERIX user facility to
simultaneously measure 19 momentum transfer channels, rapidly mapping
the progression from dipole-limited low-q spectra to the full-multipole
limit measurements at high q. The LERIX spectrometer is the first
instrument designed for high-throughput measurement of q-dependent XRS,
and it is now available for general users at the APS. Here, I will
discuss a few illustrative applications. First, using results from the
L-edges from Al and Mg, the q-dependence of the atomic background is
seen to amplify fine structure and edges that are largely absent in
dipole-limited techniques. Second, the q-dependence of the fine
structure near the edge can be used to experimentally determine the
individual symmetry components of the final density of states, giving a
quantitative measure of the hybridization of final states. I will
demonstrate this new technique on two technologically relevant
materials: the diclosocarboranes C2B10H12 and the wide bandgap
semiconductor AlN.