Effect of growth conditions on the structure and properties of tungsten films prepared using a thermal evaporation process

Abstract

We report the fabrication and characterization of tungsten films obtained using a thermal evaporation method. Single phase α-tungsten films were obtained at higher substrate temperatures (520–680°C) than the single phase β-tungsten films (180–220°C). X-ray spectra show that both the α-tungsten films and the β-tungsten films are polycrystalline having unusual preferred (200) and (321) orientations, respectively. Poor adhesion was observed when the films were deposited on bare silicon substrate. The adhesion is greatly improved by the introduction of a carbon layer between the film and the substrate. The field emission properties of the α-tungsten films and the β-tungsten films were also examined. The α-tungsten films and β-tungsten films exhibit turn-on fields at 1.3 and 2.8V∕μm, respectively. Current densities in the order of 10−1mA∕cm2 were observed. These field emission properties are believed to be better or much better than that of both tungsten nanowires and nanorods. The relation between the field emission properties and the film structures is discussed.