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 (WO₃) 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 (WO₃) 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 (WO₃)₃ clusters remain intact and form an ordered (3×3) array of molecularly bound (WO₃)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.