Fine structure of swift heavy ion track in rutile TiO2

TL;DR

This study reveals the complex fine structure of swift heavy ion tracks in rutile TiO2, showing shape evolution and proposing a thermal spike model to explain the formation mechanisms of these tracks.

Contribution

First observation of detailed track morphology changes in rutile TiO2 and a new thermal spike model explaining their formation mechanisms.

Findings

Track shape evolves from cylinder to dumbbell to sandglass with depth

Molten phase outflow and recrystallization determine track morphology

Proposed radial-dependent molten phase duration and fluid flow distribution

Abstract

We report on the first observation of fine structure of latent tracks in rutile TiO2, which changes from cylinder to dumbbell-shape and then to sandglass-shape as a function of the ion path length. Based on inelastic thermal spike model, we show that Hagen-Poiseuille flow of molten phase produces the hillocks on surface and the void-rich zone near surface after epitaxial recrystallization due to material deficit, while at a deep depth, the lack of efficient outflow and recrystallization result in the absence of tracks. We propose that core-shell duration of transient molten phase induced by swift heavy ion and parabolic distribution of fluid velocity are radial-dependent. Moreover, the various morphologies of tracks are a consequence of the molten phase outflow and recrystallization during rapid cooling down. Our perspective provides a new interpretation in the track formation.