Reconfigurable Vanadium Dioxide Nanomembranes and Microtubes with Controllable Phase Transition Temperatures

Abstract

Two additional structural forms, free-standing nanomembranes and microtubes, are reported and added to the vanadium dioxide (VO) material family. Free-standing VO nanomembranes were fabricated by precisely thinning as-grown VO thin films and etching away the sacrificial layer underneath. VO microtubes with a range of controllable diameters were rolled-up from the VO nanomembranes. When a VO nanomembrane is rolled-up into a microtubular structure, a significant compressive strain is generated and accommodated therein, which decreases the phase transition temperature of the VO material. The magnitude of the compressive strain is determined by the curvature of the VO microtube, which can be rationally and accurately designed by controlling the tube diameter during the rolling-up fabrication process. The VO microtube rolling-up process presents a novel way to controllably tune the phase transition temperature of VO materials over a wide range toward practical applications. Furthermore, the rolling-up process is reversible. A VO microtube can be transformed back into a nanomembrane by introducing an external strain. Because of its tunable phase transition temperature and reversible shape transformation, the VO nanomembrane-microtube structure is promising for device applications. As an example application, a tubular microactuator device with low driving energy but large displacement is demonstrated at various triggering temperatures.

Vanadium Dioxide: The Multistimuli Responsive Material and Its Applications

“…The MIT in VO 2 leads to the thermal expansion coefficient change between VO 2 and other materials, which make it can be used in some novel mechanical devices. Joule heating generated by current passing VO 2 can also cause a huge flexural and mechanical change of the VO 2 composite device …”

Inorganic Stimuli‐Responsive Nanomembranes for Small‐Scale Actuators and Robots

“…Lower panel: optical images of the rotation of the tube at various temperatures in a heating–cooling cycle. Reproduced with permission . Copyright 2018, American Chemical Society.…”

“…Recently, Tian et al reported a bimorph established on the basis of an ultra‐thin VO 2 NM (Figure e), which was constructed as a microtubular structure due to the low bending stiffness of the bilayer NM system . The rolled‐up tubular structure redistributes the strain inside the bilayer NM, resulting in an additional compressive strain in the outer layer consisting of VO 2 , which can be tuned via the deposition thickness of the structural layer.…”

“…Recently, an ultra-thin VO 2 NM was reported by Tian et al, who deposited VO 2 on a Si substrate with a sacrificial layer, SiO 2 , and thinned it into an NM by reactive-ion-etching (RIE). [43] The thinning process of the VO 2 NM reduces its flexural rigidities, which allows for the formation of 3D nanostructures. Interestingly, the temperature-resistance curves of VO 2 films are almost the same, whereas the thicknesses are quite different.…”

“…(Figure 3e), which was constructed as a microtubular structure due to the low bending stiffness of the bilayer NM system. [43] The rolled-up tubular structure redistributes the strain inside the bilayer NM, resulting in an additional compressive strain in the outer layer consisting of VO 2 , which can be tuned via the deposition thickness of the structural layer. On the one hand, through this strain engineering, the MIT voltage and temperature become lower by controlling the curvature of the tube.…”