Axially Engineered Metal鈥揑nsulator Phase Transition by Graded Doping VO2 Nanowires

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• 作者：Sangwook Lee ; Chun Cheng ; Hua Guo ; Kedar Hippalgaonkar ; Kevin Wang ; Joonki Suh ; Kai Liu ; Junqiao Wu
• 刊名：The Journal of the American Chemical Society
• 出版年：2013
• 出版时间：March 27, 2013
• 年：2013
• 卷：135
• 期：12
• 页码：4850-4855
• 全文大小：378K
• 年卷期：v.135,no.12(March 27, 2013)
• ISSN：1520-5126

文摘

The abrupt first-order metal鈥搃nsulator phase transition in single-crystal vanadium dioxide nanowires (NWs) is engineered to be a gradual transition by axially grading the doping level of tungsten. We also demonstrate the potential of these NWs for thermal sensing and actuation applications. At room temperature, the graded-doped NWs show metal phase on the tips and insulator phase near the center of the NW, and the metal phase grows progressively toward the center when the temperature rises. As such, each individual NW acts as a microthermometer that can be simply read out with an optical microscope. The NW resistance decreases gradually with the temperature rise, eventually reaching 2 orders of magnitude drop, in stark contrast to the abrupt resistance change in undoped VO₂ wires. This novel phase transition yields an extremely high temperature coefficient of resistivity 10%/K, simultaneously with a very low resistivity down to 0.001 惟路cm, making these NWs promising infrared sensing materials for uncooled microbolometers. Lastly, they form bimorph thermal actuators that bend with an unusually high curvature, 900 m^鈥?路K^鈥? over a wide temperature range (35鈥?0 掳C), significantly broadening the response temperature range of previous VO₂ bimorph actuators. Given that the phase transition responds to a diverse range of stimuli鈥攈eat, electric current, strain, focused light, and electric field鈥攖he graded-doped NWs may find wide applications in thermo-opto-electro-mechanical sensing and energy conversion.