Surface treatment of ZnO:Sb microwires to improve their persistent photo-conductance response

Chemical and biological sensors based on ZnO microwires usually rely on the change in the wire conductance with the ambient gas composition. Yet, sensitivity and recovery time of the conductance are important limitations in these applications. We treated ZnO:Sb micro-wires with single droplets of solvents for very short times and found a significant enhancement of the persistent photo-conductance and a reduction of the recovery time of the resistance by more than an order of magnitude when treated with isopropanol droplets. Placing a solvent droplet on a ZnO:Sb micro-wire in situ during measurement allowed us to make a direct comparison between the behavior before, during, and after solvent treatment. Isopropyl alcohol (IPA) has the most significant response among the solvents that we studied. Two possible mechanisms have been proposed as possibly being responsible for this huge enhancement of the wire resistance: surface transformations of isopropanol and the catalyzing effect of Sb atoms. Both mechanisms seem to combine and enhance the oxygen adsorption to the wire surface causing a very large rise in the resistance.