Physical investigations on Cd doped NiO thin films along with ethanol sensing at relatively low temperature

Cadmium doped Nickel oxide thin films with ratio [Cd]/[Ni] = 0%, 1%, 2%, 2% and 4% were successfully prepared on glass substrates using spray pyrolysis technique at 460 °C. The effect of Cd doping on structural, morphological and optical properties was investigated. First, XRD studies reveal that all the films are polycrystalline with cubic structure and exhibit (111) as preferential orientation. Raman study shows the presence of bands corresponding to NiO structure. Cd is well incorporated in the host lattice without destroying the crystal structure. The surface topography of these films was performed by the atomic force microscopy. Second, the optical transmittance spectra of all films showed high transparency (∼80%) in the visible region. the band gap energy of the films varies from 3.89 to 3.80 eV with the cadmium content. Also, the effect of the cadmium incorporation in NiO matrix is studied in terms of Urbach energy. Finally, Cd-doped NiO thin films have been tested as sensitive films against ethanol vapor at different temperatures. The 3.0 wt% Cd-doped NiO based sensor showed excellent sensitivity toward 0.1% ethanol at the operating temperature of 100 °C.