Highly sensitive and multidimensional detection of NO2 using In2O3 thin films

We report on the ultrasensitive and unique detection of NO2 with respect to common gaseous interferents through multi-dimensional signature analysis using In2O3 thin films as sensing layers. Sensor devices fabricated using interdigitated metal fingers of Ti/Au deposited on the In2O3 film resulted in extremely high sensitivity for NO2 molecules, producing 20% change in conductance for 20 ppb NO2 in atmospheric conditions. Molecular adsorption induced changes in conductance (G), capacitance (C), and surface work function (ϕ) upon exposure to various gases were measured to obtain their respective C–G and ϕ–G plots. We observed that the gradients of the (C–G) and (ϕ–G) plots are distinct for individual analytes and can thus can be utilized for the specific detection of molecules. Three dimensional G–C–ϕ signature plots for NO2 and NH3 were found to be even more effective than 2D plots in uniquely identifying the gases. Utilization of 2D signatures to analyze a binary gas mixture was found to be quite promising with a large application potential.