Atomic layer deposition (ALD) is a versatile technique to deposit metals and metal oxide sensing materials at the atomic scale to achieve improved sensor functions. This article reviews metals and metal oxide semiconductor (MOS) heterostructures for gas sensing applications in which at least one of the preparation steps is carried out by ALD. In particular, three types of MOS-based heterostructures synthesized by ALD are discussed, including ALD of metal catalysts on MOS, ALD of metal oxides on MOS and MOS core–shell (C–S) heterostructures. The gas sensing performances of these heterostructures are carefully analyzed and discussed. Finally, the further developments required and the challenges faced by ALD for the synthesis of MOS gas sensing materials are discussed.

Metal oxide semiconductor (MOS) thin films are promising sensing layer for integration in gas sensor devices for detecting toxic and harmful molecules. Herein, tungsten oxide (WO₃) thin films are deposited on interdigital electrodes by vacuum thermal evaporation to realize batch fabrication of high-performance gas sensors. Subsequent annealing at different temperatures allows for regulation of the concentration of oxygen vacancies in the WO₃ films, which has been found to exert a great influence on the sensor properties. In addition, the surface structure of WO₃ films is also highly dependent on the annealing temperature. Gas sensing investigations show that the WO₃ sensor annealed at 500 °C possesses the best sensing properties for detecting triethylamine (TEA) including very high response, good selectivity, fast response, and low limit of detection (63 ppb). The excellent sensor performances are attributed to the enhanced adsorption of oxidative oxygen species due to the presence of abundant oxygen vacancies. The scalable fabrication of WO₃ thin film gas sensors and the oxygen vacancy engineering strategy proposed herein may shed some light to developing high performance environmental sensors.