Effects of Lithium Incorporation on the Morphological, Optical, and Sensing Properties of ZnO Thin Films Synthesized By Chemical Spray Pyrolysis

This research explores the effect of lithium (Li) doping on the structural, morphological, optical, and gas-sensing characteristics of zinc oxide (ZnO) thin films, which were deposited onto glass substrates using the chemical spray pyrolysis technique. X-ray diffraction (XRD) analysis revealed that all the films are polycrystalline in nature with a hexagonal wurtzite structure, exhibiting a preferred orientation along the (100) plane. Li incorporation induced a shift in diffraction peaks and significantly influenced microstructural parameters; the crystallite size increased to a maximum of 23.34 nm for the 4% Li-doped film, while dislocation density and microstrain decreased, indicating improved crystallinity. Atomic force microscopy (AFM) analysis showed that Li doping leads to a more uniform and compact surface morphology, accompanied by a reduction in both average particle size and surface roughness. Optical analysis revealed that Li doping induced a red shift in the absorption edge and reduced the optical band gap from 3.38 eV in pure ZnO to 3.25 eV in the 4% Li-doped film, an effect attributed to the introduction of defect states within the band gap. Furthermore, the gas sensing response to nitrogen dioxide (NO₂) was evaluated, with the highest doped film showing the lowest response, Li doping serves as an effective approach for tailoring the physical properties of ZnO.