Achieving Surface Sensitivity in Ultrafast XUV Spectroscopy: M_2,3-Edge Reflection–Absorption of Transition Metal Oxides

Ultrafast extreme ultraviolet (XUV) spectroscopy is a powerful tool for probing electronic structure and charge carrier dynamics in catalytic materials because of its elemental, oxidation, coordination, and electronic spin-state sensitivity. To extend the benefits of this technique to investigating charge carrier dynamics at surfaces, we have developed near grazing-angle XUV reflection–absorption (RA) spectroscopy. Because RA spectra probe both the real (i.e., reflection) and the imaginary (i.e., attenuation) parts of the refractive index, a general method is required to analyze RA spectra. Using semiempirical calculations, we demonstrate that XUV RA spectra of first row transition metal oxides retain the element and chemical state specificity of XUV absorption spectroscopy. We find that the imaginary part of the refractive index reports on the chemical state of the metal center, while the real part is additionally sensitive to the surface morphology of the material.