A novel quartz-crystal microbalance humidity sensor based on solution-processible indium oxide quantum dots

摘要： Having a large surface area, like the quantum con?nement e?ect also caused by the nano-level size of quantum dots (QDs), creates fantastic potential for humidity sensing. A high concentration of surface adsorption sites initiates an increased response. Porosity between QDs allows fast water vapor penetration and out?ow. Here, a quartz-crystal microbalance (QCM) humidity sensor was prepared using indium oxide (In2O3) QDs, synthesized via a solvothermal method. After the In2O3 QDs were directly spin-coated onto the QCM, an annealing process removed organic long chains and exposed more moisture adsorption sites on the surfaces of the QDs. The annealed QCM humidity sensor exhibited high sensitivity (56.3 Hz per %RH at 86.3% RH), with a fast response/recovery time (14 s/16 s). Long carbon chains were broken down, and hydrogen-bonded hydroxyl groups were chemisorbed to the QDs. The chemical reaction was reduced by these chemisorbed hydrogen-bonded hydroxyl groups. Mass change was mostly caused by fast multilayer physisorption. Thus, the transducer can e?ectively and precisely monitor the moisture from a person's breath. In2O3 QD-modi?ed QCM sensors demonstrate promising humidity-sensing applications in daily life.