Structural, electrical, and optical properties of NiO films for surface-enhanced Raman spectroscopy applications

This study investigates the structural, electrical, and optical properties of NiO thin films deposited by DC sputtering in an Ar/O₂ atmosphere with varying oxygen concentrations. As the O₂ content increases, energy-dispersive X-ray (EDX) analysis reveals a higher concentration of Ni vacancies and Ni³⁺ ions, resulting in lower resistivity and a slight reduction in crystal quality. Among the samples, the film grown at 50% oxygen (NiO-50) exhibits the best combination of properties for Surface-Enhanced Raman Spectroscopy (SERS), including balanced crystallinity, surface roughness, and high hole concentration. Current-voltage (<i>I</i>-<i>V</i>) measurements and Raman spectra using Rhodamine 6G (10^-9 M) confirm that the SERS enhancement is driven by an electron transition mechanism. The calculated enhancement factor of 9.6 × 10⁸ for the NiO/Si substrate surpasses previously reported values. These results position NiO-50 as a promising SERS-active material and provide insights into tuning NiO film properties for enhanced sensing applications.