Momentum-dependent Resonant Inelastic X-ray Spectroscopy of Anatase TiO2 Thin Films on LaAlO3 (001)

Materials that host two-dimensional excitons exhibit a strong bonding of the electron-hole pair. Anatase TiO2 is an interesting host candidate, as it has recently been reported to support strongly bound 2D excitons, even in the bulk. In addition, exciton energies in single crystal anatase have been modulated by as much as 30 to 50 meV at room temperature using coherent acoustic phonons. We employ resonant inelastic X-ray scattering (RIXS) to characterize excitons and phonons in anatase TiO2 thin films grown on LaAlO3 (001) using molecular beam epitaxy. RIXS is an ideal tool to characterize excitations at multiple energy scales due to the momentum dependence of the scattering from both excitons and phonons simultaneously, which can be challenging to achieve with optical methods. Initial results show phonon features in the 50 ~ 300 meV range that exhibit polarization, momentum, and film thickness dependence, revealing the influence of confinement.