Surface reconstructions induced by reducing epitaxial WO3(100) thin films grown on LaAlO3(100) were studied using scanning tunnelling microscopy and low energy electron diffraction. When the WO3(100) surface was annealed in either O2 or NO2 at 620K, the surface was predominantly covered by a p(2 x 2) reconstruction with a low density of elongated (1 x 1) islands. Raising the annealing temperature to 800K reduced the film and the surface was dominated by p(4 x 2) and p(2 x 4) reconstructions, although a few small patches of the p(2 x 2) surface could still be detected. Annealing the p(4 x 2) surface in ultra-high vacuum at 800K resulted in a (1 x 1) low-energy electron diffraction pattern. The scanning tunnelling microscopic images of the p(4 x 2) surface were dominated by 0.1nm deep troughs separating bright rows. The appearance of the rows was sensitive to the imaging bias with a 2x periodicity along the rows seen at high biases and a 1x periodicity at low biases. These results could be explained by a structural model based on incomplete (1 x 1) terraces that formed as reduced W5+ ions migrate from the surface into the bulk.

The p(4 x 2) Surface Reconstruction on Epitaxial WO3 Thin Films. M.Li, E.I.Altman, A.Posadas, C.H.Ahn: Surface Science, 2003, 542[1-2], 22-32