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Single‐crystalline potassium tungsten bronze nanosheets were prepared by reducing potassium tungsten oxide nanosheets grown on a W foil. The nanosheets showed no evident shape change before and after reduction. Morphology, structure, and composition analyses revealed that a phase transformation from orthorhombic potassium tungsten oxide to hexagonal potassium tungsten bronze occurred. Better field emission with lower turn‐on field was measured from potassium tungsten bronze nanosheet film. The effects of reduction treatment on field emission performance are discussed.

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Large area tungsten trioxide (W03) nanosheets and nanoribbons were synthesized by directly heating tungsten plates covered with potassium iodide (KJ).The field emission properties of the as-grown samples were systematically measured.A 10 I1A/cm 2 current density was obtained from both samples under a 5.5 V/llm average field, while the average fields that extracted a current density of 1.0 mA/cm 2 were 8.2 and 11.1 V Illm for the nanosheets and nanoribbons, respectively. Also, the emission sites were found to distribute uniformly on the whole sample surface. In the preliminary test on the stability, the W03 nanosheets, which had larger surface area, exhibited better robustness than the W03 nanoribbons. These findings have demonstrated the application perspectives of nanometer-scale tungsten oxide as future cold electron sources. (a) Figure 1 SEM images ofW03 nanosheets and nanorods. (a) nanosheets, (b) nanoribbons. 978-1-4244-6644-3/10/$26.00 ©2010 IEEE 316 (b)