Growth of Ordered Ultrathin Tungsten Oxide Films on Pt(111)

Ordered ultrathin tungsten oxide films were prepared on a Pt(111) substrate at 700 K via direct sublimation of monodispersed cyclic (WO 3 ) 3 trimers. The surface composition, structure, and morphology were determined using a combination of atomically resolved imaging, ensemble-averaged surface-sensitive spectroscopies, and DFT. We find that half of the (WO 3 ) 3 tungsten atoms in the first layer get partially reduced to the (5+) oxidation state. The opening of the (WO 3 ) 3 ring leads to the formation of a tungsten oxide layer with a zigzag chain structure with a c(4 × 2) periodicity. In the second layer, the (WO 3 ) 3 clusters remain intact and form an ordered (3 × 3) array of molecularly bound (WO 3 ) 3 . DFT calculations provide a detailed understanding of the structure, oxidation states, and the vibrational frequencies for both the c(4 × 2) and (3 × 3) overlayers.