Reflectance anisotropy of the anatase Tio2(0 0 1)-(4 × 1) surface

The dielectric functions of bulk anatase TiO(2) and its (4 × 1) reconstructed (0 0 1) surface were calculated using a hybrid density functional theory method. The bulk dielectric function is compared to data obtained from synchrotron radiation reflectivity measurements in the energy range 0-20 eV and to dielectric functions from two Bethe-Salpeter calculations. There is agreement between predictions of the two theoretical methods, except at the absorption threshold, where there is some shift of spectral weight to lower energy in the Bethe-Salpeter calculations. All features observed in the dielectric function derived from synchrotron reflectivity data are reproduced in calculations. There are some differences in relative peak intensities for dielectric functions derived from experiment and theory. A dispersionless surface state is found which is localised on the topmost oxygen ion in the reconstructed surface. The reflectance anisotropy spectrum of the TiO(2)(0 0 1)-(4 × 1) surface shows strong features in the energy range to 12 eV but does not show any features caused by sub-bandgap surface state transitions.