Chemical, Structural, and Electronic Characterization of the (010) Surface of Single Crystalline Bismuth Vanadate

We have structurally, chemically and electronically characterized the most stable (010) surface of a Mo-doped BiVO4 single crystal. Low energy electron diffraction (LEED) reveals that the surface is not significantly reconstructed from a bulk termination of the crystal. Synchrotron based X-ray spectroscopies indicate no surface enhancement of any of the crystal constituents and that the Mo dopant occupies tetrahedral sites by substituting for V at the surface. Using resonant photoemission to study the valence band structure as the V L-3 edge is scanned we observe an intraband gap state associated with reduced vanadium formed by the Mo doping. This state is likely associated with small polaron formation. This feature is enhanced at a photon energy that is not resonant with any of the main features in the absorption spectrum of the pristine BiVO4. This indicates that the additional electron from Mo doping likely induces further distortion of the VO4 tetrahedral units and generates a new conduction band state either by splitting of the V d(z)(2) states or by hybridization of V d(zx) and V d(z)(2). states. We measure a work function of 5.15 eV for the BiVO4(010) surface. Measurement of the work function allows us to recast the electronic energy levels onto the normal hydrogen electrode scale for comparison to the standard reduction and oxidation potentials of water. This detailed study should provide a basis for future work aimed at a molecular level understanding of BiVO4/electrolyte interfaces used for photoelectrochemical water splitting.