Nanocrystals as very active interfaces: Ultrasensitive room-temperature ozone sensors with In2O3 nanocrystals prepared by a low-temperature sol-gel process in a coordinating environment

In2O3 nanocrystals were prepared by injection of In2O3 sol in a hot (160 degrees C) solution of tetradecene and an an-Line. By properly controlling the amine chain length, the processing of the starting Sol and the heat-treatment temperature, In2O3 nanocrystals with a size ranging from 4 to 10 nm were obtained. The nanocrystals suspensions could be easily processed by drop-coating onto alumina substrates to obtain gas-sensing devices. The devices displayed an enormous response to ozone gas, with a response of several orders of magnitude even to 60 ppb of ozone. In particular, the monitoring of low ozone concentrations was possible even by operating at room temperature, where the ozone concentration profile could be rapidly and reversibly monitored. The enhanced gas-sensing properties were explained as the cooperative effect of the nanocrystal size and surface chemistry, characterized by high densities of oxygen vacancies.