Figure 1

(Color online) (a) STM image with two ${\mathrm{V}}_2{\mathrm{O}}_3$ islands on Au(111). The tunneling parameters are $U=1.2\mathrm{V}$ and $I=50\mathrm{pA}$. (b) High resolution STM image of a ${\mathrm{V}}_2{\mathrm{O}}_3$ island showing the typical vanadyl termination with some point defects. Tunneling parameters are $U=0.5\mathrm{V}$ and $I=50\mathrm{pA}$.Reuse & Permissions

Figure 2

(Color online) (a) STM topographic image of ${\mathrm{V}}_2{\mathrm{O}}_3$ taken at $240\mathrm{mV}$ and $50\mathrm{pA}$. Conductance images of the same region taken at (b) $240\mathrm{mV}$ and (c) $-240\mathrm{mV}$. All images are $5.5\times 5.5{\mathrm{nm}}^2$ in size. The white arrows in (c) mark the course of the two spectral series shown in (d) and (e). In this matrix representation, turquoise color represents vanishing conductance and marks the correlation band gap, whereas red color corresponds to a high density of ${\mathrm{V}}_2{\mathrm{O}}_3$ states. The flat structure of the conduction band edge is related to the positive set-point bias ($500\mathrm{mV}$ and $100\mathrm{pA}$) chosen for this spectral series, which causes a partial compensation of local conductance differences already by adjusting the tip height before spectral acquisition. (f) Two conductance spectra selected from (d) to visualize the gap size in regions with large (blue line) and small conductance (violet line). A spectrum taken on an overannealed film with strongly reduced gap size is shown for comparison (dashed line).Reuse & Permissions

Figure 3

(Color online) (a) Four $dI∕dV$ spectra taken on a vanadyl-terminated surface at the positions marked with the dots in the inset (color coded). The image size is $1.5\times 3{\mathrm{nm}}^2$. In the green and orange curves, the Fermi level is slightly shifted toward the conduction band ($n$-type characteristic), whereas in the blue and red curves, it is shifted toward the valence band edge ($p$-type characteristics). For spectroscopic measurements, the tip was stabilized at $-0.45\mathrm{V}$ and $100\mathrm{pA}$. (b) $dI∕dV$ spectra taken at a defect site (violet line) and above a $\mathrm{V}\mathrm{O}$ group (blue line). STM image is $4.5\times 4.5{\mathrm{nm}}^2$ in size. For spectroscopic measurements, the tip was stabilized at $1.4\mathrm{V}$ and $100\mathrm{pA}$. The additional $dI∕dV$ intensity above the $\mathrm{V}\mathrm{O}$ lattice is attributed to a $\mathrm{V}\mathrm{O}$ related electronic state.Reuse & Permissions

Figure 4

(Color online) (a) STM and (b) corresponding conductance image taken at $200\mathrm{mV}$ and $50\mathrm{pA}$. Both images are $2.8\times 2.8{\mathrm{nm}}^2$ in size.Reuse & Permissions