Data-Driven Sensing Analysis of Chromium-Doped Copper Oxide Nanostructured Thin Films

Abstract

This study examined the of Cr on nanostructured CuO thin films synthesized via chemical spray pyrolysis (CSP). XRD analysis confirmed a polycrystalline CuO phase, with Cr doping resulting in increased crystallite size and reduced dislocation density and microstrain, indicating improved crystallinity—especially at 3% Cr, where crystallite size reached 17.37 nm. AFM analysis showed significant changes in surface morphology with increasing Cr content, including reduced particle size and surface roughness, leading to smoother, more uniform films. These structural enhancements suggest improved surface-related functionalities. UV-Vis spectroscopy revealed a slight decrease in transmittance and an increase in absorbance in the visible range with Cr doping. The optical band gap decreased from 1.96 eV for pure CuO to 1.84 eV at 3% Cr doping. Additionally, variations in extinction coefficient and refractive index were observed. Pure CuO thin films showed optimal NO₂ sensing at 120 °C, while 3% Cr doping increased resistance and reduced sensitivity due to impaired charge transport. Increasing Cr doping in CuO reduces NO₂ sensitivity due to enhanced charge carrier recombination, lattice disruption, and decreased mobility, weakening sensor response.