Total-reflection inelastic x-ray scattering from a 10-nm thick La _0.6Sr_0.4CoO₃ thin film

To study equilibrium changes in composition, valence, and electronic structure near the surface and into the bulk, we demonstrate the use of a new approach, total-reflection inelastic x-ray scattering, as a sub-keV spectroscopy capable of depth profiling chemical changes in thin films with nanometer resolution. By comparing data acquired under total x-ray reflection and penetrating conditions, we are able to separate the O K-edge spectra from a 10 nm La_0.6Sr_0.4CoO₃ thin film from that of the underlying SrTiO₃ substrate. With a smaller wavelength probe than comparable soft x-ray absorption measurements, we also describe the ability to easily access dipole-forbidden final states, using the dramatic evolution of the La N_4,5 edge with momentum transfer as an example.