Room-temperature NH3 gas-sensing characteristics of spray-deposited transition metal ions substituted CoFe2O4 thin films

We report here the structural, morphological and gas-sensing characteristics of 1, 3 and 5 wt. % Cr 3+ - and Zn 2+ -substituted CoFe 2 O 4 thin films prepared using the facile solution-based spray pyrolysis experimental method. Structural study confirms the polycrystalline nature and single-phase cubic spinel structure of the deposited films. Atomic force microscopy (AFM) study demonstrates that the substitution of transition metal ions significantly influences the surface topography of pristine CoFe 2 O 4 thin films. Results from the gas sensor analysis reveal an excellent sensing behavior of Cr 3+ -substituted CoFe 2 O 4 at room temperature, in particular, the maximum gas response is observed for 1 wt. % Cr 3+ -substituted CoFe 2 O 4 thin films than that of pristine and other substituted CoFe 2 O 4 thin films, which is due to the substitution of Fe 3+ by Cr 3+ provides more reactive sites, at this particular concentration, and thus relatively higher response. In addition, the selectivity, gas response, response time and recovery time of CoFe 2 O 4 thin films have been explored in the present study, and the deposited thin films show high selectivity for NH 3 gas than that of other tested toxic gases. Hence, based on the results obtained, spray-deposited Cr 3+ -substituted CoFe 2 O 4 thin films would act as potential candidates for the fabrication of NH 3 sensor devices even for detecting low ppm gas concentrations at room temperature.