CAREER: Synthesis, Phase Transitions, and Device Integration of Nanoscale Vanadium Oxides: A Research and Education Program

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Technical SummaryVanadium oxides have a rich and complex phase diagram originating from the facile accessibility of different vanadium oxidation states and the various structural distortions adopted to accommodate non-stoichiometry and point defects. The proposed research project focuses on understanding the influence of finite size on the properties of two intriguing vanadium oxides, VO2 and V2O5. Bulk VO2 shows a dramatic insulator?metal phase transition at ~67°C and represents a textbook problem in solid-state chemistry and physics. The proposed work is inspired by our preliminary results showing a strong size dependence of the phase-transition temperature and hysteresis for VO2 nanostructures prepared by hydrothermal methods. Chemical vapor deposition and hydrothermal approaches for the fabrication of VO2 nanostructures with controlled shape, size, and growth direction will be explored. A systematic investigation of the crystal growth mechanism will be performed to obtain rational and predictive control over the nanostructure dimensions. A combination of ensemble X-ray absorption spectroscopy, Raman spectroscopy, and X-ray diffraction measurements will be used in conjunction with single-nanowire electrical transport and Raman spectroscopy measurements to understand the influence of finite size on the insulator?metal phase transition in these nanostructures. Another aspect of the proposed CAREER proposal will involve the fabrication of V2O5 nanowires and their dielectrophoretic integration within device structures. Simultaneous electrical conductivity and Raman spectroscopy measurements of single nanowires will be performed within device geometries to understand the influence of finite size in modifying the electrical transport and surface conductance of these nanowires in the presence of alcohol vapors. The synthesis and device integration of anisotropic VO2 and V2O5 nanostructures will pave the way for their implementation in optical switching devices, thermochromic coatings, Mott field-effect transistors, alcohol sensors, and waveguides.Non-Technical SummaryNanoscale materials often show properties that are not exhibited by their bulk counterparts. The proposed research effort is focused on understanding how such properties can be harnessed for practical applications such as making faster electronic circuits for use in the next generation of computers, ?smart? window materials that change color with temperature, and accurate sensors for detecting low concentrations of vapors. Vanadium dioxide, one of the materials that will be explored in this project, is a transparent insulator at room temperature but upon heating to 67°C becomes an excellent conductor that is almost completely opaque. The proposed research will focus on shifting this transition closer to room temperature wherein this dramatic effect can be used to construct ultrafast nanoelectronic circuits and temperature-sensitive coatings. An integrated outreach and education program is also proposed emphasizing teacher professional development, classroom engagement, and curricular reform at the middle-school level at a local urban high-needs school. These activities will serve to build sustained mentoring relationships between faculty, graduate students, undergraduate students, and middle-school teachers and students. This effort will seek to actively engage Buffalo Public School middle-school students from economically disadvantaged backgrounds in appreciating science and technology at a critical and formative time period. The collaborative development of attractive curricular material and challenging laboratory experiments along with sustained classroom visitation and after-school science activities will form the cornerstone of this program. A freshman seminar course will be developed to discuss the broader societal implications of nanotechnology.