Optical Studies on VO 2 Thin Films
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Optical Studies on VO2 Thin Films Lei Wang1, Melissa Beebe1, Scott E. Madaras1, John M. Klopf1, Elizabeth Radue1, Zhaozhu Li1, Russell A. Wincheski2, Jiwei Lu3, Stuart A. Wolf3,4, Irina Novikova1 and Rosa A. Lukaszew1 1
Department of Physics, College of William and Mary, Williamsburg, VA 23187, U.S.A. NASA Langley Research Center, Hampton, VA 23681, U.S.A. 3 Department of Material Sciences and Engineering, University of Virginia, Charlottesville, VA 22904, U.S.A. 4 Department of Physics, University of Virginia, Charlottesville, VA 22904, U.S.A. 2
ABSTRACT We have been interested in the plasmonic properties of alternative conducting materials to metals, such as conducting oxides, and we have recently expanded our studies to include highly correlated oxides, such as vanadium dioxide (VO2) thin films. VO2 exhibits a metalinsulator transition (MIT) just above ambient temperature at ~ 340K. Interestingly, this transition can be induced thermally, optically or applying electric fields. Across the MIT, the optical properties are completely modified over a broad frequency range. We will present our recent optical investigations on the photon induced transition studies on such films, as well as the surface plasmon resonance (SPR) modulation in nanopatterned Au gratings by the thermally induced MIT in VO2 thin films, addressing possibilities of ultrafast SPR modulation with VO2. INTRODUCTION Vanadium dioxide (VO2) is a well-known material, which can exhibit a metal-to-insulator phase transition (MIT) from a low temperature insulating state to a high temperature metallic state around 340K [1]. This MIT could also be induced by light pulses [2] or electric current [3]. Across the MIT, the electrical transport properties and optical transmissions of VO2 thin films show significant changes [4, 5]. Due to these unique properties, VO2 has been used in many applications, such as electrical switches [6], smart window coatings [7], etc. Besides, research into combinations of noble metal nanostructures and VO2 layers has been reported recently, including investigations into enhanced optical transmission (EOT) using nanoholes through Au or Ag/VO2 bilayers [8], frequency tunable near-infrared metamaterials based on VO2 phase transition [9], and other possible combinations [10], showcasing just a few of the implementations of active devices using this concept. Current interest in surface plasmon resonance (SPR) technology is focused on the development of nanoscale optical devices to control the propagation of light in sub-wavelength geometries [11]. The use of photons and electrons together in such technologies is desirable for developing opto-electronic protocols to speed up information processing and transmission, as
well as for biological sensing and new imaging techniques. VO2 provides a suitable platform for these applications due to its ultrafast switching speed [2]. As a result, it is of great interest to combine plasmonic materials with VO2 for SPR modulation. In our research group, we have investigated the plasmonic propertie
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