Figure 1

(a) Constant current topographic STM image of nanostructured islands of the vanadium oxide $(5\times 3\sqrt{3})\mathrm{\text{−}}\mathrm{rect}$ monolayer phase on Rh(111) ($1500\times 1500{\AA }^2$; sample bias $U=+2\mathrm{V}$; tunneling current $I=0.1\mathrm{nA}$). (b) Magnified STM view of the $(5\times 3\sqrt{3})\mathrm{\text{−}}\mathrm{rect}$ structure; the rectangular unit cell is indicated ($55\times 55{\AA }^2$; $U=+1\mathrm{V}$; $I=0.1\mathrm{nA}$). (c) DFT derived model of the $(5\times 3\sqrt{3})\mathrm{\text{−}}\mathrm{rect}$ structure. The ${\mathrm{V}}_{13}{\mathrm{O}}_{21}$ unit cell is indicated by the square, and a ${\mathrm{O}}_4\mathrm{V}\mathrm{O}$ unit is encircled (see text). (d) Simulated STM image of the $(5\times 3\sqrt{3})\mathrm{\text{−}}\mathrm{rect}$ structure, considering tunneling into empty states between 0 and $+1\mathrm{eV}$.Reuse & Permissions

Figure 2

(a) STM image of the $(5\times 3\sqrt{3})\mathrm{\text{−}}\mathrm{rect}$ vanadium oxide phase showing the 2D evaporation of the planar starlike vanadium oxide clusters under oxidizing conditions ($p_{{\mathrm{O}}_{\mathrm{2}}}=5\times {10}^{-8}\mathrm{mbar}$, 130 °C) ($200\times 200{\AA }^2$; $U=+1\mathrm{V}$; $I=0.1\mathrm{nA}$). (b) High-resolution STM image of the ${\mathrm{V}}_6{\mathrm{O}}_{12}$ starlike clusters ($63\times 63{\AA }^2$; $U=+0.5\mathrm{V}$; $I=0.1\mathrm{nA}$). The inset shows the STM simulation based on the model structure of (c). (c) Relaxed DFT model geometry of ${\mathrm{V}}_6{\mathrm{O}}_{12}$ clusters on Rh(111).Reuse & Permissions

Figure 3

(a) Section of the thermodynamic DFT phase stability diagram of vanadium oxide on Rh(111) in equilibrium with an O particle reservoir controlling the chemical potential ${\mu }_{\mathrm{O}}$. The chemical potential can be related to the oxygen partial pressure through ${\mu }_{\mathrm{O}}(T,p)={\mu }_{\mathrm{O}}(T,p^0)+1/2k_{B}T\ln (p/p^0)$ [20]. The energy zero ${\mu }_{\mathrm{O}}=0\mathrm{eV}$ corresponds to oxygen molecules condensating on the surface. Lines are drawn at the nominal V coverage $c_{\mathrm{V}}$ of each phase, if the corresponding phase is stable at a specific chemical potential ${\mu }_{\mathrm{O}}$. Stars were considered at various coverages but found to be stable only at low coverages corresponding to a $(7\times 7)$ supercell and $c_{\mathrm{V}}=0.122$. The structure “stars $+$ chem. O” was modeled in this supercell by adding between five and nine chemisorbed O atoms. (b) Schematic drawing illustrating a possible route for the formation of ${\mathrm{V}}_6{\mathrm{O}}_{12}$ stars from the $(5\times 3\sqrt{3})\mathrm{\text{−}}\mathrm{rect}$ structure.Reuse & Permissions

Figure 4

(a)–(c) STM images of ${\mathrm{V}}_6{\mathrm{O}}_{12}$ stars on Rh(111), recorded consecutively after the indicated time at 110 °C ($85\times 85{\AA }^2$; $U=+1\mathrm{V}$; $I=0.1\mathrm{nA}$). The arrows indicate the hopping directions. (d) Arrhenius plot of the tracer diffusion coefficient $D$ versus $1/T$. (e) Plot of the mean square displacement versus time at $T=110°\mathrm{C}$, from which $D$ has been evaluated.Reuse & Permissions