We investigated the inhomogeneous electronic properties at the surface and interior of VO 2 thin films that exhibit a strong first-order metal-insulator transition (MIT). Using the crystal structural change that accompanies a VO 2 MIT, we used bulk-sensitive X-ray diffraction (XRD) measurements to estimate the fraction of metallic volume p XRD in our VO 2 film. The temperature dependence of the p XRD was very closely correlated with the dc conductivity near the MIT temperature, and fit the percolation theory predictions quite well: σ ~ (p -p c ) t with t = 2.0±0.1 and p c = 0.16±0.01. This agreement demonstrates that in our VO 2 thin film, the MIT should occur during the percolation process. We also used surface-sensitive scanning tunneling spectroscopy (STS) to investigate the microscopic evolution of the MIT near the surface. Similar to the XRD results, STS maps revealed a systematic decrease in

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