Au/epsilon-Fe2O3 Nanocomposites as Selective NO2 Gas Sensors

A combined chemical vapor deposition (CVD)/radio frequency (rf) sputtering approach to Au/Fe2O3 nanocomposites based on the scarcely investigated epsilon-iron(III) oxide polymorph is reported. The developed materials, analyzed by field emission-scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDXS), X-ray photoelectron spectroscopy (XPS), and secondary ion mass spectrometry (SIMS), consisted of iron oxide nanorods decorated by gold nanoparticles (NPs), whose content and distribution could be tailored as a function of sputtering time. Interestingly, the intimate Au/epsilon-Fe2O3 interfacial contact along with iron oxide one-dimensional (1D) morphology resulted in promising performances for the selective detection of gaseous NO2 at moderate working temperatures. At variance with the other iron(III) oxide polymorphs (alpha-, beta-, and gamma-Fe2O3), that display an n-type semiconducting behavior, epsilon-Fe2O3 exhibited a p-type response, clearly enhanced by Au introduction. As a whole, the obtained results indicate that the sensitization of p-type materials with metal NPs could be a valuable tool for the fabrication of advanced sensing devices.