High quality single crystalline metastable phase VO_2 (A) ultra-long nanobelts were synthesized by hydrothermal method using inorganic V_2O_5 sol as precursor and polyethylene glycol (PEG) as both surfactant and reducing agent. It was found that the oriented attach growth mechanism is responsible for the formation of VO_2 (A) nanobelts. In addition to an endothermic peak, an unusual exothermic peak was detected in DSC curve of the nanobelts. The temperature dependence of the lattice parameters have been studied, and it was found that the a-axis expands while the c-axis contracts in the high-temperature XRD test. The VO_2 (A) nanobelt has a low turn-on field of 3.8 V μm~(-1) and a high field enhancement factor of 1739 in the field emission measurement. Electrical transport measurement of a single VO_2 (A) nanobelt gives a relative low hoping activation energy of 0.28 eV.
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