Analysis of photo-functional materials using momentum-resolved EELS.

Abstract

Momentum transfer (q)-resolved electron energy-loss spectroscopy (q-EELS) is a powerful tool for analyzing photo-functional materials. The technique's application has been demonstrated in several recent studies. This study first investigated the anisotropic plasmon oscillations in Cs-doped hexagonal WO3, a near-infrared (NIR) shielding material, to understand the origin of its highly efficient light-scattering properties. This revealed how plasmon energies differ along different crystallographic directions, contributing to the broad NIR absorption capabilities of the material. Second, the study measured the q dispersion of carrier plasmons and thus quantified interactions (exchange-correlation effect) between carrier electrons in LaB6 crystals, another NIR shielding filter. This analysis provides critical insights into many-body effects not captured by the ideal free-electron gas model. Finally, the spatial spread sizes of excitons in anatase TiO2 were determined, establishing a correlation between the exciton size and the anisotropic photocatalytic activity of anatase TiO2. Collectively, this research demonstrates that q-EELS provides unique, q-dependent information on electronic excitations, deepening our understanding of the properties governing the performance of advanced materials.