Microwave Gas Sensing with Hematite: Shape Effect on Ammonia Detection Using Pseudocubic, Rhombohedral, and Spindlelike Particles

Hematite alpha-Fe2O3 pseudocubes, rhombohedra, and spindlelike particles were prepared via a low cost and environmentally friendly microwave route. The structure and morphology were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Possible formation mechanisms of the particles are discussed. The design of the sensor includes a conductor-backed coplanar waveguide (CBCPW) on which a hematite sensitive layer is deposited. Hematite deposition was realized by doctor-blade on areas identified as the most responsive by near-field microwave microscopy (NFMM). A comparative microwave gas sensing study was conducted to evaluate the gas response of these morphologies upon ammonia exposure at room temperature. This paper represents a first look at the shape effect involved in microwave transduction, as each morphology presented a significant different behavior upon ammonia adsorption.