Fabrication and temperature-dependent field-emission properties of bundlelike VO₂ nanostructures

Bundlelike VO₂(B) nanostructures were synthesized via a hydrothermal method, and VO₂(M₁/R) nanobundles were obtained after a heat-treatment process. Structural characterization shows that these nanobundles are selfassembled by VO₂ nanowires, and VO ₂(M₁/R) nanobundles have better crystallinity. Temperature-dependent field-emission (FE) measurement indicates that FE properties of these two phases of nanobundles can both be improved by increasing the ambient temperature. Moreover, for the VO₂(M₁/R) nanobundles, their FE properties are also strongly dependent on the temperature-induced metal-insulator transitions process. Compared with poor FE properties found in the insulating phase, FE properties were significantly improved by increasing the temperature, and about a three-orders-of-magnitude increasing of the emission current density has been observed at a fixed field of 6 V/μm. Work function measurement and density-functional theory calculations indicated that the decrease of work function with temperature is the main reason that caused the improvement of FE properties. These characteristics make VO₂(M₁/R) a candidate material for application of new type of temperature-controlled field emitters, whose emission density can be adjusted by ambient temperature.