Vanadium oxide on Rh(111) The growth and the atomic structure of epitaxial ultrathin vanadium oxide films on Rh(111) are investigated in our laboratory by various techniques. Here you can see scanning tunneling microscopy images of several oxide structures. Evaporating submonolayer amounts of vanadium oxide on the Rh(111) single crystal surface, results in a 2-dimensional film growth. Two Oxide structures can be found on the "as evaporated" surface: a (sqroot7 x sqroot7)R(19°) (left image) and a (sqroot13 x sqroot13)R(13°) (right image) structure. Click Image to enlarge... Scan over 1000x1000 Å of an annealed vanadium oxide film (T=250°C). The coverage chosen here is 0.25 MLE. Two oxide phases can be distinguished within the 2-dimensional islands: a disordered and a well ordered (5x5) phase. Additionally small white dots can be seen on the bare Rhodium patches. When one has a closer look at them (right picture) they appear as star-like features with a lateral dimension of about d = 1.5 Å . Click Image to enlarge... Upon further annealing this surface (T=400°C) the (5x5) phase transforms into a (5x3Ö3)rectangular phase. Still the star-like features are visible and from the picture below one can see that they represent the basic building units of the rectangular structure. Click Image to enlarge... Click Image to enlarge... Increasing now the coverage to about 0.8 MLE allows one to cover the surface entirely with the rectangular oxide phase. Beyond that additional structures are visible in the STM image to the left. The already mentioned (5x5) structure forms predominantly where domain boundaries of the rectangular phase come together (I,II and III are different domains of the same oxide structure). The new structure here is a striped oxide phase (picture on the right side), which run along the <1-10> direction of the substrate and have a (2x1) periodicity with respect to the rectangular phase in the <1-21> direction. Click Image to enlarge... Click Image to enlarge... At around 500°C annealing temperature the oxide film has predominantly a (9x9) internal structure, but also a "wagon-wheel"-like phase is recognizable. The wagon wheels are quite clearly visible in the left hand side bottom picture and the (9x9) phase on the right hand side. Click Image to enlarge... Click Image to enlarge... Increasing the coverage to ~ 1 ML results in an oxide film which consists of hexagonal shaped "nano-tiles", the latter presumably the results of strain-releasing effects. Finally, for thick layers (coverage > 3 MLE), one gets the bulk V2O3 phase as for Vanadium Oxides on a Pd(111) single crystal. Initially the surface is quite rough and the bulk V2O3 grows in small crystallites. Annealing helps to create a more flat surface as can be seen on the pictures below. The insets show images with atomic resolution and indicate that defects are formed during the annealing procedure (from left to right the annealing temperature increases. Left: as evaporated; middle: annealed to 350°C; right: annealed to 550°C). Click Image to enlarge... Click Image to enlarge...   STM-Movie, mpeg-1 video stream, 12.7 MB; shows the reduction of an ultrathin vanadium oxide layer grown on a Rh(111) surface The sample is held at 400°C and H2 is dosed during the measurement. The two dimensional oxide layer changes its internal structure and morphology throughout the entire reduction process. The sequence of structures observed is: (√7x√7)R19°, (5x5), (5x3√3)rect, (9x9), wagon-wheel.   STM-Movie, mpeg-1 video stream, 5.5 MB; back