1 Optical properties differences across the Insulator-Metal Transition in VO 2 Thin Films grown on different substrates E. Radue, 1,* E. Crisman, 1 L. Wang, 1 S. Kittiwatanakul, 2 J. Lu, 3 S. A. Wolf, 2, 3 R. Wincheski, 4 R. A. Lukaszew, 1 and I. Novikova 1 1 Department of Physics, College of William and Mary, Williamsburg, VA 23187, USA 2 Department of Physics, University of Virginia, Charlottesville, VA 22904, USA 3 Department of Material Sciences and Engineering, University of Virginia, Charlottesville, VA 22904, USA 4 NASA Langley Research Center, Hampton, VA 23681 USA *Corresponding author: elradue@email.wm.edu Abstract: We have used Raman spectroscopy to investigate the optical properties of vanadium dioxide (VO 2 ) thin films deposited on different substrates during the thermally induced insulating to metallic phase transition. We observed a significant difference in transition temperature in VO 2 films similarly grown on quartz and sapphire substrates: the film grown on quartz displayed the phase transition at a lower temperature (T c =50 o C) compared a film grown on sapphire (T c =68 o C). We also investigated differences in the detected Raman signal for different wavelengths and polarizations of the excitation laser. We found that for either substrate, a longer wavelength (in our case 785 nm) yielded the clearest VO 2 Raman spectra, with no polarization dependence. I. Introduction Vanadium dioxide (VO 2 ) undergoes a well-known thermally induced phase transition, changing from an insulator with a monoclinic lattice structure to a conductor with a tetragonal lattice structure [1- 3]. This structural insulator-to-metal transition (IMT) is evidenced by strong changes in the electrical and optical properties between the two VO 2 phases. The fact that MIT in VO 2 occurs just above room temperature makes it an exciting prospect for many new technologies. For example, it offers a lower loss alternative to noble metals for plasmonic applications [4], development of smart window coatings