On-Chip Tungsten Oxide Nanowires Based Electrodes for Charge Injection

Abstract

Transition metal oxides are fundamental to the development of many potential applications in nanoelectronics, optoelectronics and sensor devices (Wang, 2003 and Simon et al., 2001). Nanostructured metal oxides are widely investigated for scientific and technological applications. For example, binary semiconducting oxides have distinctive properties as transparent conducting oxide materials (Pan et al., 2001). Nanowires, which are stimulated by carbon nanoubes, have attracted wide interest due to their potential for bringing basic issues like dimensionality and transport phenomena in nanoscale dimensions. Among the transition metal oxide nanowires, tungsten oxide nanorods/nanowires show good sensing and field emission (FE) properties. FE from tungsten oxide nanowires shows good stability and high emission current density due to large aspect ratio, low turn-on field and stability at high pressures of 10-6-10-3 Torr (Kim et al., 2005 and Seelaboyina et al., 2006). Synthesis methods for tungsten oxide nanowires include heating and oxidation of tungsten filaments (Liu et al., 2005), foils or films in vacuum at temperatures above 1000 C (Liu et al, 2003 and Cho et al., 2004). To the best of our knowledge, there are no studies atmospheric pressure FE performances of tungsten oxide nanowires. Synthesis of uniform and crystalline W18O49 nanowires on tungsten thin films by thermal annealing in ethane and nitrogen will be described in the first part of this chapter. Growth mechanism and atmospheric pressure FE analysis of a diode device based on nanowires will be discussed. The oxides have mixed cation valences and an adjustable oxygen deficiency which form the bases for tuning the electrical, chemical, optical and magnetic properties. In the second part of this chapter, application of tungsten oxide nanowires in a miniaturized plasma device will be demonstrated. Miniaturized plasma sources have generated wide interest, recently, due to a number of important applications, light sources and chemical reactors (Becker et al., 2006). Performing an atmospheric pressure plasma process in a microreactor leads to precise control of process parameters such as residence time and heat transfer, and also extreme quenching conditions, enabling control over the reactants to selectively produce desirable products (Nozaki et al., 2004). W18O49 nanowires gave outstanding field emission characteristics with low threshold voltages due to local field enhancement and high aspect ratio (Guillorn et al., 2001 and Zhou et al., 2005). Process of