  X-ray Compton spectroscopy is one of the few direct probes of the electron
momentum distribution of bulk materials in ambient and operando environments.
We report high-resolution inelastic X-ray scattering experiments with high
momentum and energy transfer performed at a storage-ring-based high-energy
X-ray light source facility using an X-ray microcalorimeter detector. Compton
profiles were measured for lithium and cobalt oxide powders relevant to
lithium-ion battery research. Spectroscopic analysis of the measured Compton
profiles shows high-sensitivity to the low-Z elements and oxidation states. The
lineshape analysis of the measured Compton profiles in comparison with computed
Hartree-Fock profiles is limited by the resolution of the energy-resolving
semiconductor detector. We have characterized an X-ray transition-edge sensor
microcalorimeter detector for high-resolution Compton scattering experiments
using a bending magnet source at the Advanced Photon Source (APS) with a double
crystal monochromator providing monochromatic photon energies near 27.5 keV.
The momentum resolution below 0.16 atomic units was measured yielding an
improvement of more than a factor of 7 over a state-of-the-art silicon drift
detector for the same scattering geometry. Furthermore, the lineshapes of
narrow valence and broad core electron profiles of sealed lithium metal were
clearly resolved using an X-ray microcalorimeter detector compared to smeared
and broadened lineshapes observed when using a silicon drift detector.
High-resolution Compton scattering using the energy-resolving detector shown
here presents new opportunities for spatial imaging of electron momentum
distributions for a wide class of materials with applications ranging from
electrochemistry to condensed matter physics.
