Unprecedented Insulator-To-Metal Transition Dynamics by Heterogeneous Catalysis in Pd-Sensitized Single Vanadium Oxide Nanowires

Abstract

In the part 1, Single crystal vanadium dioxide (VO2) nanowires were grown by physical vapor deposition (PVD) under atmospheric pressure and synthesized on a silicon dioxide (SiO2), a sapphire (Al2O3) C-plan and a sapphire R-plan as a substrate.The controllable spontaneous conversion of thin films into nanowires for large area production is investigated. The synthesis is found to depend critically on the thickness of V2O5 layer. We have controlled that the nanowires that are single crystal vanadium dioxide can be grown with thickness of V2O5 thin film and also we can synthesize VO2 nanowires to various directions on the substrate. By using the patterned substrate, we can not only control the numerous VO2 nanowire morphologies but also fabricate the guided growth of millimeter-long VO2 nanowires.

In the part 2, we report the high effective hydrogen gas sensor based on the metal-to-insulator transition (MIT) by the electro-thermally induced Palladium-nanoparticles-decorated VO2 nanowire prepared by the efficient and size-controllable growth method originated from V2O5 thin film driven.We have many experiments for improved hydrogen gas detector based on the MIT. First by doping the tungsten we showed that the MIT temperature was reduced to about 40°C. Second by irradiating a well-defined electron beam into the nanowires, we could considerably increase the conductivity up to 4 times with only a modest change in the MIT temperature (< 2°C). When exposed to trace amounts of hydrogen gas in a single nanowire configuration, the enhanced conductivity gave rise to about two times as fast transition to metallic phase even near room temperature (~35°C), by reaching much faster (~3x) a critical current density at which the self-heating initiates. Last, especially Palladium-VO2 nanowire near-corshell nanostructure shows remarkably large current increase at a temperature 10 °C lower than the MIT temperature in the bulk. This current increase occurs slowly over the duration of several seconds to several tens of seconds, depending on the Pd coverage, temperature, and hydrogen concentration. This novel finding thus mentions the capability of detecting selectively hydrogen of different three gases (O2, CO2, and ethylene) and has significant implications for the effective engineering the physicochemical properties of vanadium dioxide by a heterogeneous catalytic process.