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We report measurements of the diffusion of atomic hydrogen in singlecrystalline VO2 micro/nanobeams by direct exposure to atomic hydrogen, withoutcatalyst. The atomic hydrogen is generated by a hot filament, and the dopingprocess takes place at moderate temperature (373 K). Undoped VO2 has ametal-to-insulator phase transition at ~340 K between a high-temperature,rutile, metallic phase and a low-temperature, monoclinic, insulating phase witha resistance exhibiting a semiconductor-like temperature dependence. Atomichydrogenation results in stabilization of the metallic phase of VO2micro/nanobeams down to 2 K, the lowest point we could reach in our measurementsetup. Based on observing the movement of the hydrogen diffusion front insingle crystalline VO2 beams, we estimate the diffusion constant for hydrogenalong the c-axis of the rutile phase to be 6.7 x 10^{-10} cm^2/s atapproximately 373 K, exceeding the value in isostructural TiO2 by ~ 38x.Moreover, we find that the diffusion constant along the c-axis of the rutilephase exceeds that along the equivalent a-axis of the monoclinic phase by atleast three orders of magnitude. This remarkable change in kinetics mustoriginate from the distortion of the "channels" when the unit cell doublesalong this direction upon cooling into the monoclinic structure. Ab initiocalculation results are in good agreement with the experimental trends in therelative kinetics of the two phases. This raises the possibility of aswitchable membrane for hydrogen transport.

Hydrogen Diffusion and Stabilization in Single-crystal VO2 Micro/nanobeams by Direct Atomic Hydrogenation