Hydrogen-Induced Morphotropic Phase Transformation of Single-Crystalline Vanadium Dioxide Nanobeams

• Published in: Nano letters Vol. 13; no. 4; pp. 1822 - 1828
• Main Authors: Hong, Woong-Ki, Park, Jong Bae, Yoon, Jongwon, Kim, Bong-Joong, Sohn, Jung Inn, Lee, Young Boo, Bae, Tae-Sung, Chang, Sung-Jin, Huh, Yun Suk, Son, Byoungchul, Stach, Eric A, Lee, Takhee, Welland, Mark E
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 10.04.2013
• Subjects: Annealing; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Crystallization; Electric Conductivity; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Electronics; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; Hydrogen - chemistry; Materials science; Nanocrystalline materials; Nanoparticles - chemistry; Nanoscale materials and structures: fabrication and characterization; Nanoscale materials: clusters, nanoparticles, nanotubes, and nanocrystals; Nanostructure; Oxides - chemistry; Phase transformations; Phase Transition; Physics; Reduction; Specific phase transitions; Stabilization; Structural transitions in nanoscale materials; Structure of solids and liquids; crystallography; Surface double layers, schottky barriers, and work functions; Surface Properties; Vanadium Compounds - chemistry; Vanadium dioxide; Vanadium oxides; Morphotropic transformation; vanadium dioxide; compositional variation; hydrogen annealing; metal−insulator transition; reduction; Temperature dependence; Electronic properties; Annealing; Work functions; Phase transformations; Monoclinic lattices; Phase transitions; High pressure; Time dependence; Monocrystals; Hexagonal crystals; Electric resistivity; Vanadium oxide; Electronic transition; Nanostructured materials; Structural analysis; Crystal structure
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/nl400511x

We report a morphotropic phase transformation in vanadium dioxide (VO2) nanobeams annealed in a high-pressure hydrogen gas, which leads to the stabilization of metallic phases. Structural analyses show that the annealed VO2 nanobeams are hexagonal-close-packed structures with roughened surfaces at room temperature, unlike as-grown VO2 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.