Investigate the annealing effect on structural, optical and surface morphological properties of NiO/Co/Zn thin films prepared by e-beam deposition

In this study the effect of annealing on structural, optical and surface morphological properties of NiO/Co/Zn thin films were investigated. NiO/Co/Zn thin films were deposited onto the glass substrate using e-beam deposition technique. The prepared thin films were then vacuum annealed at two different temperatures (300 °C and 400 °C) to assess the impact of annealing on their properties. The presence of the cubic NiO phase was verified using X-ray diffraction (XRD) analysis, with enhanced grain growth and improved crystallinity observed at higher annealing temperature (400 °C). UV–Vis spectroscopy was revealed a notable increase in emission intensity with annealing, particularly at 400 °C, suggesting reduced non-radiative recombination and improved electron–hole pair recombination efficiency. The energy bandgap of the films decreased from 4.34 eV (as-deposited) to 4.15 eV (annealing at 400 °C). This reduction into bandgap is attributed to improved crystallinity and fewer structural defects, enhancing photon absorption in the visible spectrum. Atomic force microscopy (AFM) provided insights into surface morphology. A noticeable transformation in grain size and surface features was observed as the annealing temperature increased. The FE-SEM images indicate that films were uniformly deposited across the substrate, exhibiting excellent adhesion. The presence of specific peaks in the EDX spectra for Ni, Co and Zn corroborates the successful deposition of Co and Zn alongside NiO. Hall Effect measurements were revealed the conductivity of the thin film experiences a notable rise from 1.38 Ω⁻¹ cm⁻¹ to 96.94 Ω⁻¹ cm⁻¹ after annealing. The findings confirm that annealing significantly enhances the structural, optical and surface morphological properties of NiO/Co/Zn thin films.