Axially Engineered Metal–Insulator Phase Transition by Graded Doping VO₂ Nanowires

Abstract

The abrupt first-order metal-insulator 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 Ω·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(-1)·K(-1) over a wide temperature range (35-80 °C), significantly broadening the response temperature range of previous VO2 bimorph actuators. Given that the phase transition responds to a diverse range of stimuli-heat, electric current, strain, focused light, and electric field-the graded-doped NWs may find wide applications in thermo-opto-electro-mechanical sensing and energy conversion.

Vanadium dioxide nanowire-based microthermometer for quantitative evaluation of electron beam heating

“…3c Having demonstrated this microthermometer's unique ability to measure electron absorbtion coefficients a, we now consider further broadening its range of use. Since the threshold temperature of the MIT was found previously 18,19 to be tunable by doping of the VO 2 NW with W, this general microthermometer measurement method is not limited to only temperatures above 68°C. As such, the setup could be modified to detect temperatures lower than the MIT temperature.…”

Controlling the Temperature and Speed of the Phase Transition of VO2 Microcrystals

“…Over the years, many research groups have invested massive efforts not only to identify the origin of the phase transition in VO2, but also to control the occurrence of the phase transition onset by varying many physical parameters, such as doping, [15,16] strain, [17,18] pulsed voltage, [19,20] and size, [21][22][23] . [15,16] Recently, Whittaker et al reported that the phase transition temperature can be decreased by oxygen vacancy doping, which is induced by reducing VO2 crystal size to nanoscale.…”

“…[15,16] Recently, Whittaker et al reported that the phase transition temperature can be decreased by oxygen vacancy doping, which is induced by reducing VO2 crystal size to nanoscale. [22] Variations of crystal dimensions also provide a way to control the onset of the phase transition in VO2.…”

“…Cr, Fe, Ga, Al, by at most ~10 °C. [15,16] Also, the hysteresis, the difference of phase transition onset temperature between heating and cooling processes, increases as w decreases, e.g. the hysteresis of 3.6 µm thick crystal reached a value as large as 43.9 °C.…”

Direct Observation of Nanoscale Peltier and Joule Effects at Metal–Insulator Domain Walls in Vanadium Dioxide Nanobeams

“…6−10 One-dimensionally aligned metal−insulator (M−I) domain configurations can be attained either by substrate-induced uniaxial strain 11−13 or nonuniform transition metal doping in a single-crystalline VO 2 nanobeam (NB). 14 In the former case, M R domains appear gradually upon heating, shifting T MIT depending on the nature of external stress. Given a strong adhesive interaction with the substrate, I M2 phase (with longer lattice constant along C R ) becomes thermodynamically stable and the alternating M−I heterostructures are spontaneously organized ( Figure 1a).…”