Bandgap engineering of TiO₂ nanoparticles through MeV Cu ions irradiation

The effect of 5 MeV Cu⁺⁺ ions irradiation on structural and optical properties of Anatase TiO₂ nanoparticles (TiO₂-NPs) is investigated. For this purpose, TiO₂-NPs are irradiated with different Cu⁺⁺ ions fluences, ranging from 1 × 10¹⁵ to 1 × 10¹⁶ ions/cm² at room temperature. XRD results confirm the Ti₃O₇ phase appear at the dose of 5 × 10¹⁵ ions/cm² and peak intensity of Ti₃O₇ phase gradually increases with an increase of Cu⁺⁺ ions irradiation dose. At the dose of 1 × 10¹⁶ ions/cm² TiO₂ Anatase phase were transformed to Rutile phase. Same observations are confirmed from Raman spectroscopy. High resolution transmission electron microscopy (HRTEM) reveals that morphology converted into wavy shape and crystal structure detrioted with increase Cu ion irradiation dose to form vacancy loops and interstitial loops. Scanning electron microscopy (SEM) shows that TiO₂-NPs have been fused to form a cluster of nanoparticles at high Cu ion beam dose, while bandgap of TiO₂-NPs reduces from 3.19 eV to 2.96 eV as a function of Cu⁺⁺ irradiation fluence. These phase transformations and crystal damage are the responsible for optical bandgap reduction. The mechanism for the currently observed phase transformation of TiO₂ and coalescence of TiO₂-NPs are discussed in term of thermal spikes model.