Crystal facet engineering and polarity control in ZnO gas sensors: advancements in sensing performance and operando surface analysis—secondary publication

Abstract This review examines zinc oxide (ZnO) gas sensors, which are widely recognized for their high sensitivity to flammable and toxic gases and for their cost-effectiveness. It emphasizes the importance of controlling crystal facets and polarity to enhance sensor performance. The synthesis of pyramid-shaped ZnO particles with well-defined crystal facets was performed for volatile organic compound (VOC) gas sensing. Additionally, the fabrication of polarity-controlled ZnO epitaxial thin films using pulsed laser deposition is examined, along with evaluations of their sensing properties for ethanol and hydrogen. The effect of additives on improving gas selectivity is also discussed. Operando surface analysis using low-energy He+ ion scattering (LEIS) was employed to elucidate the influence of crystal facets on ZnO single-crystal gas sensors. This review demonstrates that the selection and control of crystal facets greatly affect gas adsorption behavior and sensor sensitivity, particularly through enhanced adsorption capacity and increased surface oxygen deficiencies. Advanced surface analysis techniques, such as LEIS, provide deeper insights into interaction mechanisms at near-atmospheric pressure. These findings underscore the pivotal role of Zn and O polar surfaces in enhancing sensor response and selectivity, paving the way for high-performance gas sensors tailored to specific applications, such as the detection of isoprene in breath analysis. The ability to optimize crystal face exposure is expected to further advance the development of highly selective and sensitive gas sensor technologies.