Evolution of Electroless Cu/Cu_xO Nanostructured Thin Films: Study of Surface Fractal, Tuning Band Gap and Electronic Structure

Herein, the electroless deposition method was used to deposition Cu/Cu_xO thin films on Si substrates using Cu(NO₃)₂ concentration from 10 to 50 mL. The structural, morphological, surface fractal, chemical bonding, oxidation states, electronic structure core orbital and optical properties of the Cu/Cu_xO thin films were investigated. X-ray diffraction study revealed the existence of mixed phases of Cu and Cu₂O (cuprous oxide) cubic structure in the Cu/Cu_xO nanostructured thin films. The RMS roughness and crystallite size (D) varied from 23.99 to 30.71 nm and 15.91 to 9.01 nm in the Cu/Cu_xO films. The (111) and (220) planes of Cu₂O are the preferred grain orientation with the increasing Cu(NO₃)₂ concentration. The surface fractal was estimated to be 2.33 to 2.4, based on cube counting, triangulation, partition, and power spectrum statistical distribution. The I_Cu–O/I_O–Cu–O decreases with increasing Cu(NO₃)₂ concentration, confirming the interstitial Cu bonding increases in Cu/Cu_xO thin films. The B_g phonon modes of CuO and O–Cu–O bending were found at 566.46 cm⁻¹ and 573.78 cm⁻¹, respectively, from Raman and FTIR spectra. The average Cu and O content estimated from the XPS analysis were 69.18 and 30.81 at.%, respectively, on the surface of all the Cu/Cu_xO thin films. The optical bandgap decreased from 2.46 to 2.04 eV for Cu/Cu_xO thin films with increased Cu(NO₃)₂ concentration from 10 to 50 mL. Moreover, the semi-empirical estimation of various sub-orbital contributions of chemical bonds was mentioned.