Structural, morphological, electrical and vapour sensing properties of Mn doped nanostructured ZnO thin films

The influence of dopant precursor (manganese (II) acetate tetrahydrate) concentration on structural, morphological, optical and vapour sensing properties of zinc oxide (ZnO) was studied by fabricating manganese (Mn) doped ZnO thin films with various Mn2+ concentration, using spray pyrolysis technique. The as-deposited films were found to be polycrystalline in nature, with hexagonal wurtzite structure. A rope-like morphology was observed through secondary electron (SE) image. The I–V characteristics depict a decrease in electrical resistance with an increase in concentration levels of Mn2+. The optical band gap decreased from 3.45 eV to 1.9 eV, on increase in Mn2+ concentration from 0.002 M, 0.004 M and 0.006 M (Mn1, Mn2 and Mn3 samples) in 0.05 M of zinc acetate dihydrate. The vapour sensing behaviour of the films was observed for various concentrations of trimethylamine (TMA) and ethanol at an optimized operating temperature of 373 K. The sensor response for TMA was found to be more appreciable in comparison with the response towards ethanol. The response of TMA at 75 ppm was calculated to be 300, with a response and recovery time of 11 s and 20 s respectively.