Preparation of Molybdenum Trioxide Nanostructure by Reactive Magnetron Sputtering for Gas sensing Application

Abstract

In this research are separated into two parts. In first part, suitable sputtering conditions for the formation MoO3 nanostructures are studied and the MoO3 thin films prepared under different condition are tested toward ethanol gas sensing. Sputtering with oxygen flow rate are systematically varied in the range 8 sccm to16 sccm. It was found that molybdenum oxide nano-needle tend to form at high oxygen flow rate of 16 sccm. Under these conditions, MoO3 nano-needles are formed with different length ranging from 0.2-0.5 μm. In addition, MoO3 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 sensing. It was found that molybdenum oxide thin films exhibit n-type conductivity with decreased resistance when exposed to ethanol, which is reducing gas. In addition, the molybdenum oxide thin films are capable of detecting ethanol gas at concentrations lower than 100 at operating temperature 400 °C. In the second part, the structure of Tin oxide thin films with different oxygen flow rate are studied and the Tin oxide thin films prepared under different condition are tested toward ethanol gas sensing. It was found that the structure of Tin oxide changes from amorphous to crystalline as the oxygen flow rate increases from 12 to 24 sccm and the degree of crystallinity tends to improve as the oxygen flow rate increases further. From morphological characterization, all SnO2 films prepared with different oxygen flow rates comprise isolated columnar nanorod structures and the nanorod size tends to decrease as the oxygen flow rate increases. In addition, the deposition rate is found to decrease from 0.28 to 0.10 nm/s as the oxygen flow rate increases from 12 to 48 sccm. Gas sensing performances of sputtered SnO2 nanorod thin film have been characterized toward ethanol sensing. It was found that SnO2 nanorod thin film exhibit n-type conductivity with decreased resistance when exposed to ethanol, which is reducing gas. In addition, the SnO2 nanorod thin film are detecting ethanol gas at concentrations lower than 50 ppm at operating temperature 250 °C.