Thermoluminescence properties of TiO2/Cu/TiO2 multilayer thin films fabricated by (RF/DC) sputtering for radiation dosimetry

Abstract

The most popular TLDs are composed of phosphors, ceramics, and crystals. Despite having a high light output per unit of absorbed dose, they suffer from rapid signal fading, light scattering, saturation at higher doses, and difficulties annealing for re-use. Here, we report the characteristics of a novel TiO2/Cu/TiO2 multilayer thin film dosimeter fabricated using radio-frequency (RF) and direct current (DC) sputtering methods with a faster deposition rate, high purity, and uniformity. The multilayer sequence was set to TiO2 (150 nm)/Cu (x)/TiO2 (50 nm), at varying Cu thicknesses (x = 5, 10, 25, 40, and 50 nm). The structure, morphology, elemental composition, and optical properties of the films were characterized by the XRD, FESEM, EDX, and UV–Vis, respectively. Next, the best TiO2 multilayer films with 5 nm Cu were tested for morphological, structural, and optical properties at 600 and 1200 mGy of x-ray radiation. The dosimetric properties of samples irradiated with X-ray doses ranging from 100 to 1500 mGy were then investigated. The best annealing time, reproducibility, fading, low minimum detectable dose as well as the effect of different heating rates on the TL glow curve have all been studied. Our results indicate that the films are amorphous, porous with spherically shaped nanoparticles, have a uniform distribution of elements, and are transparent in the visible region. The optimum TL intensity was found at TiO2 (445 nm)/14.2 nm Cu/TiO2 (130 nm) sequence. The dose-response has a good linear correlation to x-ray radiation with a sensitivity that is 0.444 times less than that of TLD-100 sensitivity within the dose range 100–1500 mGy. Upon irradiation, the band gap decreases, crystallinity increases, pores increase, films become rougher, and the absorption band edge extends to higher wavelengths. The single and multilayer TiO2 films have high-intensity peaks at 270 and 274 ∘C, respectively, which is typical of TL glow curve peaks used in TLD applications. There were no significant changes in the TL reading after six times of reuse, and the fading was observed at 49.57% after 15 days of irradiation. The findings indicate that TiO2/Cu/TiO2 multilayer films are appropriate for thermoluminescence dosimetric applications.