Study of humidity sensing properties in ZnO nanotubes grown via hydrothermal method

Here, we report investigations on the relative humidity (RH) sensing property of ZnO nanotubes synthesized via hydrothermal method. Grown nanotubes are formed with a hexagonal shape and possess a wurtzite crystal structure in conjunction with higher oxygen vacancies. ZnO nanotube-based RH sensor shows a small current increase in lower RH (<75% RH) region, due to the frozen motion of H[Formula: see text] ions, where electronic conduction dominates. The sensor conduction increases from 13 to 960 fold upon exposer of 65%–90% RH, respectively. The free motion of H[Formula: see text] ions steers the conduction mechanism to be protonic in higher level physisorbed water layer and is responsible for the observed sharp increase in response. The competitive adsorption and desorption of oxygen species and water molecules play a vital role in defining the conduction to be electronic or protonic during the experiment.