Structural characterization and evaluation of radiation-shielding performances of layered and composite ZnO–CdO thin films

Abstract In this study, ZnO, CdO, and ZnO–CdO composite and layered thin films were synthesized by spray pyrolysis, and their structural, optical, and radiation-shielding properties were systematically investigated. The crystal structures of the obtained thin films were analyzed by X-ray diffraction (XRD), and their surface morphologies and elemental compositions were determined using field-emission scanning electron microscopy and energy-dispersive X-ray spectroscopy (FESEM/EDX). Optical properties were investigated using a UV–Vis spectrophotometer. As a result of optical analyses, the direct band gap of the pure ZnO thin film was determined to be 3.26 eV, while in CdO thin films, the band gap was found to be broadened to approximately 3.8 eV due to the Burstein–Moss effect. In contrast, the changes in the band gap in ZnO–CdO composite and layered thin films were investigated in detail. Furthermore, the gamma radiation-shielding properties of the synthesized thin films were investigated using gamma energies of 81 and 356 keV and a NaI(Tl) detector system. The measurements yielded linear attenuation coefficient (LAC), mass attenuation coefficient (MAC), half-value layer (HVL), tenth-value layer (TVL), and mean free path (MFP) parameters. These results showed that the shielding performance varied depending on both gamma energy and film composition. In particular, the LAC values ​​showed a significant increasing trend among the samples, rising from 0.1851 ± 0.0400 to 3.9519 ± 0.9316 cm⁻ 1 at 81 keV gamma energy. At higher energy levels, the attenuation coefficients decreased relatively due to the increased photon penetration. A significant decrease in HVL, TVL, and MFP parameters was observed in parallel with the increase in MAC values, revealing that some thin-film structures can effectively attenuate gamma photons over shorter distances. Overall, the findings demonstrate that ZnO–CdO-based composite and layered thin-film structures have significant potential not only in terms of optoelectronic properties but also as thin and lightweight radiation-shielding coatings. These results reveal that such multilayered thin-film systems are promising candidates, especially for compact, high-performance radiation-shielding applications.