Mn3O4 Nanomaterials Functionalized with Fe2O3 and ZnO: Fabrication, Characterization, and Ammonia Sensing Properties

The fabrication of metal oxide-based gas sensors with tailored structural design is of particular importance for the early recognition of poisonous/explosive analytes like ammonia, an irritating chemical occurring in a plethora of practical contexts. In this regard, the present work reports on the fabrication and gas sensing application of p-Mn3O4/n-MxOy nanocomposites with MxOy = Fe2O3 or ZnO. The target systems are developed by chemical vapor deposition of Mn3O4 nanosystems on alumina substrates and subsequent functionalization with iron or zinc oxides by sputtering under mild conditions. Material characterization reveals the formation of high purity composites with a controllable dispersion of Fe2O3 or ZnO into Mn3O4, and a close contact between the single constituents. The latter feature, resulting in the formation of p-n junctions and in a tailored modulation of Mn3O4 hole accumulation layer, is of strategic importance in obtaining promising responses to ammonia already at moderate temperatures. Furthermore, Fe2O3 or ZnO functionalization empowers the pristine Mn3O4 with good selectivity toward NH3 against other potential interferents. These results, along with the very favorable detection limits, provide new physical insights for the implementation of gas-sensitive devices with p-n junctions aimed at practical end uses.