Localized thermal spike driven morphology and electronic structure transformation in swift heavy ion irradiated TiO2 nanorods

Irradiation of materials by high energy (similar to MeV) ions causes intense electronic excitations through inelastic transfer of energy that significantly modifies physicochemical properties. We report the effect of 100 MeV Ag ion irradiation and resultant localized (similar to few nm) thermal spike on vertically oriented TiO2 nanorods (similar to 100 nm width) towards tailoring their structural and electronic properties. Rapid quenching of the thermal spike induced molten state within similar to 0.5 picosecond results in a distortion in the crystalline structure that increases with increasing fluences (ions per cm(2)). Microstructural investigations reveal ion track formation along with a corrugated surface of the nanorods. The thermal spike simulation validates the experimental observation of the ion track dimension (similar to 10 nm diameter) and melting of the nanorods. The optical absorption study shows direct bandgap values of 3.11 eV (pristine) and 3.23 eV (5 x 10(12) ions per cm(2)) and an indirect bandgap value of 3.10 eV for the highest fluence (5 x 10(13) ions per cm(2)). First principles electronic structure calculations corroborate the direct-to-indirect transition that is attributed to the structural distortion at the highest fluence. This work presents a unique technique to selectively tune the properties of nanorods for versatile applications.

Automated summary

The irradiation of TiO2 nanorods by 100 MeV Ag ions results in structural distortion and corrugated surface due to the rapid quenching of thermal spikes. The optical absorption study reveals changes in bandgap values with different fluences, and first principles calculations confirm the direct-to-indirect transition attributed to structural distortion at the highest fluence. This work demonstrates a unique technique to selectively tune the properties of nanorods for various applications.