Structural, optical, and electrical properties of Cu-doped NiO films synthesized by spray pyrolysis for potential gas sensing applications

Abstract: Cu-doped NiO thin films were deposited on ITO substrates via spray pyrolysis at 450 {\deg}C for 1.5 minutes. XRD confirmed a cubic NiO structure, with Cu incorporation reducing crystallite size, increasing interplanar spacing, and expanding the lattice parameter, indicating successful substitution of Cu ions. Optical analysis showed a slight bandgap reduction from 3.70 to 3.65 eV, while PL revealed lower emission intensity, suggesting enhanced defect states and suppressed carrier recombination. Raman spectroscopy exhibited redshifts in LO, 2TO, and 2LO modes and the disappearance of the TO mode, confirming lattice distortion from Cu doping. Gas sensing tests under ambient and LPG conditions demonstrated significantly improved sensitivity and voltage-dependent response for doped films. These results establish that Cu incorporation enhances charge transport and gas interaction mechanisms, making Cu-doped NiO films highly promising for efficient and reliable gas sensors.