We investigated the surface work function (WS) and its spatial distribution for epitaxial VO2/TiO2 thin films using Kelvin probe force microscopy (KPFM). Nearly grain-boundary-free samples allowed observation of metallic and insulating domains with distinct WS values, throughout the metal-insulator transition. The metallic fraction, estimated from WS maps, describes the evolution of the resistance based on a two-dimensional percolation model. The KPFM measurements also revealed the fractal nature of the domain configuration.
Bibliographical noteFunding Information:
A.S. and D.K. acknowledge the support from Basic Science Research Program and the Quantum Metamaterials Research Center (QMMRC) through the National Research Foundation of Korea Grant (NRF-2013R1A1A2063744, NRF-2008-0061893). T.K., K.S. and H.T. acknowledge the support from Grant-in-Aid for Scientific Research A (No. 26246013) and Grant-in-Aid for Scientific Research B (No. 25286058) from the Japan Society for Promotion of Science (JSPS), and the Nanotechnology Platform Project (Nanotechnology Open Facilities in Osaka University) of MEXT (F-14-OS-0010, S-14-OS-0007).
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