Sensing performance and mechanism of Fe-doped ZnO microflowers

Fe-doped ZnO microflowers have been hydrothermally synthesized without any surfactant at 120 °C for 10 h. The characteristics of products were examined by XRD, SEM, TG-DTA and XPS. The sensing tests reveal that the response is significantly enhanced by Fe doping, and the 3.0 wt%-Fe doped sample exhibits the highest response of 604 to 10 ppm NO2 at lower operating temperature of 125 °C. The intrinsic sensing characteristic is attributed to be native defects in ZnO, which has been confirmed by room temperature photoluminescence PL and XPS analysis. The response time is reduced disproportionately with the increase in NO2 concentration by modeling transient responses of the sensor using L-H reaction mechanism. The band structures and densities of states for undoped ZnO and two Fe-doped supercells of Zn0.9815Fe0.0185O and Zn0.9583Fe0.0417O have been calculated using the first-principles based on the density functional theory (DFT). The calculated results show that the band gap is significantly narrowed and the conductance is increased by Fe doping, which coincide with that of experimental results of gas sensing.