Hydrogen-Induced Morphotropic Phase Transformation
of Single-Crystalline Vanadium Dioxide Nanobeams
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Abstract
We report a morphotropic phase transformation
in vanadium dioxide
(VO<sub>2</sub>) nanobeams annealed in a high-pressure hydrogen gas,
which leads to the stabilization of metallic phases. Structural analyses
show that the annealed VO<sub>2</sub> nanobeams are hexagonal-close-packed
structures with roughened surfaces at room temperature, unlike as-grown
VO<sub>2</sub> nanobeams with the monoclinic structure and with clean
surfaces. Quantitative chemical examination reveals that the hydrogen
significantly reduces oxygen in the nanobeams with characteristic
nonlinear reduction kinetics which depend on the annealing time. Surprisingly,
the work function and the electrical resistance of the reduced nanobeams
follow a similar trend to the compositional variation due mainly to
the oxygen-deficiency-related defects formed at the roughened surfaces.
The electronic transport characteristics indicate that the reduced
nanobeams are metallic over a large range of temperatures (room temperature
to 383 K). Our results demonstrate the interplay between oxygen deficiency
and structural/electronic phase transitions, with implications for
engineering electronic properties in vanadium oxide systems