Surface plasmon resonance study on the optical sensing properties of tin oxide (SnO2) films to NH3 gas

Abstract

Surface plasmon resonance (SPR) technique is an easy and reliable method for detecting very low concentration of toxic gases at room temperature using a gas sensitive thin film layer. In the present work, a room temperature operated NH3 gas sensor has been developed using a laboratory assembled SPR measurement setup utilising a p-polarized He-Ne laser and prism coupling technique. A semiconducting gas sensitive tin oxide (SnO2) layer has been deposited under varying growth conditions (i.e., by varying deposition pressure) over the gold coated prism (BK-7) to excite the surface plasmon modes in Kretschmann configuration. The SPR reflectance curves for prism/Au/SnO2/air system for SnO2 thin films prepared at different sputtering pressure were measured, and the SnO2 film deposited at 10 mT pressure is found to exhibit a sharp SPR reflectance curve with minimum reflectance (0.32) at the resonance angle of 44.7° which is further used for sensing NH3 gas of different concentration at room temperature. The SPR reflectance curve shows a significant shift in resonance angle from 45.05° to 58.55° on interacting with NH3. The prepared sensor is found to give high sensing response (0.11) with high selectivity towards very low concentration of NH3 (0.5 ppm) and quick response time at room temperature.