Performance Limits of Microactuation with Vanadium Dioxide as a Solid Engine

Abstract

Miniaturization of the steam engine to the microscale is hampered by severe technical challenges. Microscale mechanical motion is typically actuated with other mechanisms ranging from electrostatic interaction, thermal expansion, and piezoelectricity to more exotic types including shape memory, electrochemical reaction, and thermal responsivity of polymers. These mechanisms typically offer either large-amplitude or high-speed actuation, but not both. In this work we demonstrate the working principle of a microscale solid engine (μSE) based on the phase transition of VO2 at 68 °C with large transformation strain (up to 2%), analogous to the steam engine invoking large volume change in a liquid-vapor phase transition. Compared to polycrystal thin films, single-crystal VO2 nanobeam-based bimorphs deliver higher performance of actuation both with high amplitude (greater than bimorph length) and at high speed (greater than 4 kHz in air and greater than 60 Hz in water). The energy efficiency of the devices is calculated to be equivalent to thermoelectrics with figure of merit ZT = 2 at the working temperatures, and much higher than other bimorph actuators. The bimorph μSE can be easily scaled down to the nanoscale, and operates with high stability in near-room-temperature, ambient, or aqueous conditions. On the basis of the μSE, we demonstrate a macroscopic smart composite of VO2 bimorphs embedded in a polymer, producing high-amplitude actuation at the millimeter scale.

Self-Assembly and Horizontal Orientation Growth of VO2 Nanowires

“…The combination of the low-melting-point source V 2 O 5 and lattice matched quartz substrates greatly facilitates the nucleation and enhances the growth rate. This approach is potentially a means for self-alignment of VO 2 NWs in the lithography industry to design novel metal-insulator transition devices based on VO 2 NWs such as near infrared linear polarizers27 and microactuators8.…”

“…For instance, the strain associated with grain boundary, dislocation, stoichiometry fluctuation and substrate clamping can broaden the phase transition temperature window3. Single-crystal nanowires offer an appealing alternative to thin films because they host single domains across their entire width, and thus support single or few domain MIT5678. Based on this unique single domain MIT characteristic of VO 2 NWs, different aspects of the physics of MIT were discovered91011, and a variety of applications in actuators58, gas sensors12, power meters6, and strain gauges13 were demonstrated.…”

Modulating Photoluminescence of Monolayer Molybdenum Disulfide by Metal–Insulator Phase Transition in Active Substrates

“…Fabrications : Poly‐crystalline VO 2 thin films and single‐crystal VO 2 microplates were prepared by pulsed laser deposition (PLD) and physical vapor deposition (PVD), respectively, on Si substrates with thermal SiO 2 (SiO 2 /Si). The details of syntheses were described in our previous work . Monolayer MoS 2 samples were synthesized by chemical‐vapor deposition (CVD) on SiO 2 /Si substrates using MoO 3 and S powders as precursors, which was also described in our previous work .…”

Vanadium Dioxide: The Multistimuli Responsive Material and Its Applications

“…Compared with other materials such as piezoelectric ceramics, polymers, and carbon nanotubes, VO 2 based thermal‐activated actuator is preferred because of its high work density (≈7 J cm −3 in theory) and fast phase changing time . A VO 2 /Cr bilayer structure actuator as shown in Figure a was employed to be the driving force of a solid engine . It should be mentioned that the thermal expansion mismatch between Cr and VO 2 is only 0.028% between room temperature and 68 °C.…”