Fabrication and Gas-Sensing Characterization of Molybdenum Oxide Nanostructure by Reactive RF Sputtering
Molybdenum oxide (MoOx) is an interesting metal oxide with promising properties for applications in the field of catalysts and chemical sensors. Its characteristics could be significantly enhanced by forming nanostructures. Recently, MoOx nanostructures, including nanobelt and nanorod prepared by thermal evaporation, chemical syntheses and sputtering have been reported. Sputtering is a practical method for MoOx nanostructure synthesis because it is a low temperature, well-controlled and IC-compatible process. However, the structure of MoOx material prepared by sputtering techniques is strongly depending process condition and thus far there has been no systematic investigation of the sputtering parameters on MoOx structure. In this work, suitable sputtering conditions for the formation MoOx nanostructures are studied and the MoOx thin films prepared under different condition are tested toward ethanol, acetone gas sensing. Sputtering pressure, radio frequency (rf) power and argon to oxygen flow ratio are systematically varied in the range of 2x10-3- 8x 10-3 mbar, 200 W and 1:2 to 1:4, respectively. It was found that molybdenum oxide nano-needle tend to form at high argon to oxygen ratio of 1:4 and rf power 200 W. Under these conditions, MoOx nano-needles are formed with different length ranging from 0.2-0.5 um. In addition, MoOx nano-needles are highly crystalline with MoO3 Orthorhombic crystal phase. Gas-sensing performances of sputtered molybdenum oxide nano-needle thin film have been characterized toward ethanol and acetone sensing. It was found that molybdenum oxide thin films exhibit n-type conductivity with decreased resistance when exposed to ethanol and acetone, which are reducing gases. In addition, the molybdenum oxide thin films are capable of detecting ethanol and acetone gases at concentrations lower than 100 and 200 ppm, respectively at operating temperature 400 °C.
C. Oros et al., "Fabrication and Gas-Sensing Characterization of Molybdenum Oxide Nanostructure by Reactive RF Sputtering", Advanced Materials Research, Vol. 213, pp. 98-102, 2011