Surface evolution and multifunctionality of NiO thin films grown by SILAR

Abstract

Nickel oxide (NiO) thin films were fabricated on glass substrates using the successive ionic layer adsorption and reaction (SILAR) method, and the influence of deposition cycles on their surface evolution and multifunctional properties was systematically investigated. The central objective of this work was to understand how a single fabrication parameter—the number of SILAR cycles—controls morphology, crystallinity, defect chemistry, electrical transport, and antibacterial activity. Structural analyses revealed the formation of cubic NiO with improved crystallinity at intermediate deposition cycles. Atomic force microscopy showed that surface roughness decreases initially and then increases at higher cycles due to grain agglomeration. X-ray photoelectron spectroscopy confirmed Ni²⁺ as the dominant oxidation state, with cycle-dependent variations in hydroxyl and oxygen-related surface species. Optical investigations indicated that defect-related emissions are minimized at intermediate cycles, while electrical measurements revealed a transition from n-type to p-type conductivity at higher cycle numbers. In addition, all films exhibited measurable antibacterial activity against E. coli under visible-light irradiation, with performance influenced by surface and structural characteristics. These findings demonstrate that controlled adjustment of SILAR cycles provides an effective strategy to tailor the structural quality and multifunctional behavior of NiO thin films, offering potential for applications in optoelectronics, surface coatings, and antimicrobial technologies.