Pyramid-like zinc oxide microstructures as humidity sensor

Detection of humidity is essential for human health monitoring, environmental control systems and various industries, including aviation and automobile industry. Herein, a facile, single-step method to synthesize pyramid-shaped ZnO microstructures is reported, which shows sensitivity as high as 480 against exposure to 70% relative humidity with a fast response and recovery times of 16 s and 7 s, respectively. The sensor shows good repeatability to several cycles and durability against aging over one month. When tested against different volatile organic compounds, the sensor is found sensitive to relative humidity and almost insensitive to non-alcoholic VOCs. Electron microscopy and X-ray diffraction analysis revealed uniformly distributed pyramid-like microstructures that are made of crystalline wurtzite phase of ZnO. UV-visible absorption spectroscopy revealed the existence of a strong absorption band at 375 nm, corresponding to a band gap of 3.32 eV as estimated from the Tauc plot. The sensing mechanism is described with the help of the formation of a favorable conduction pathway upon exposure to humid air leading to an increase in the electrical conductivity.