Journal of Materials Research
November 2005— Volume 20, Number 11

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Restructuring tungsten thin films into nanowires and hollow square cross-section microducts Prahalad M. Parthangal University of Maryland, College Park, Maryland 20742; and National Institute of Standards and Technology, Gaithersburg, Maryland 20899 Richard E. Cavicchi, Christopher B. Montgomery, and Shirley Turner National Institute of Standards and Technology, Gaithersburg, Maryland 20899 Michael R. Zachariah University of Maryland, College Park, Maryland 20742; and National Institute of Standards and Technology, Gaithersburg, Maryland 20899

We report on the growth of nanowires and unusual hollow microducts of tungsten oxide by thermal treatment of tungsten films in an RF H₂/Ar plasma at temperatures between 550 and 620 °C. Nanowires with diameters of 10-30 nm and lengths between 50 and 300 nm were formed directly from the tungsten film, while under certain specific operating conditions hollow microducts having edge lengths ~0.5 μm and lengths between 10 and 200 μm were observed. Presence of a reducing gas such as H₂ was crucial in growing these nanostructures as were trace quantities of oxygen, which was necessary to form a volatile tungsten species. Preferential restructuring of the film surface into nanowires or microducts appeared to be influenced significantly by the rate of mass transfer of gas-phase species to the surface. Nanowires were also observed to grow on tungsten wires under similar conditions. A surface containing nanowires, annealed at 500 °C in air, exhibited the capability of sensing trace quantities of nitrous oxides (NO_x).

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