The influence of annealing temperature on the gas sensing properties of multifunctional hematite (α-Fe₂O₃) films

In this study, hematite (alpha-Fe2O3) were prepared using direct solution spin coating and the changes of some physical properties with annealing temperature (400, 500 and 600 degrees C) for 2 h were investigated. The sensors annealed at 400 degrees C, 500 degrees C and 600 degrees C are referred to as F400, F500 and F600 respectively. The X-ray diffraction patterns of the prepared samples confirm the polycrystalline nature of the rhombohedral crystal structure of hematite (alpha-Fe2O3). The surface roughness parameters (SA-SQ) of the alpha-Fe2O3 films decreased drastically with increasing annealing temperature from 400 to 600 degrees C (57.47-68.08/13.63-17.13). The direct optical band gap values were estimated from absorption measurements and ranged from 2.77 to 2.52 eV. The electrical resistivity measurement at room temperature of the samples decreased with increasing annealing temperature from 400 to 600 degrees C. The response of the CO sensor of F400, F500 and F600 was found at 180 degrees C. The response to 1 ppm CO gas was calculated to be 1.45%, 8% and 10% for F400, F500 and F600 respectively. The wettability test of the samples showed a water contact angle (WCA) of less than 90 degrees, demonstrating the hydrophilic surface especially for the samples annealed at 500 degrees C.