Influence of the Heating Protocol on the Crystallographic Texture and Electrical Properties of CuO Layers Formed by Thermal Oxidation of Cu

Abstract

CuO layers were formed by thermal oxidation of Cu sheets at 900 °C under static-air conditions using two different heating protocols: isothermal insertion into a preheated furnace and continuous ramp heating from room temperature. X-ray diffraction analysis revealed predominantly monoclinic CuO in both cases. The isothermal insertion protocol produced a distributed preferential orientation involving the (111), (020), and (311) planes, whereas the continuous ramp protocol promoted a pronounced texture along the (−202) plane, accompanied by larger crystallite size and reduced microstrain. Minor Cu₂O traces were detected in samples prepared under the continuous ramp protocol, indicating differences in oxidation kinetics. Raman peak positions were nearly identical (< 1.5 cm⁻¹ variation), indicating similar local bonding in both samples, while slightly broader full width at half maximum (FWHM) values for the isothermal insertion sample were consistent with the higher microstrain derived from XRD analysis. Photoluminescence measurements showed emission maxima at ~880 nm for the continuous ramp sample and ~887 nm for the isothermal insertion sample, with nearly identical FWHM values (~ 153 – 154 nm). The red shift observed for the isothermal insertion sample suggests minor variations in the local defect environment, while the comparable FWHM values indicate that the same dominant defect-related recombination mechanism governs the emission in both cases. Electrical transport properties were largely insensitive to the texture and microstructural variations induced by the heating protocol. The heating protocol therefore exerts a clear influence on the crystallographic texture of CuO layers formed by thermal oxidation of Cu, without significantly altering their electrical behavior.