Deep insights into the local structure of amorphous Ta2O5 thin films by X-ray pair distribution function analysis

TL;DR

This study uses X-ray pair distribution function analysis to reveal the local atomic arrangements in amorphous Ta2O5 films, showing similarities to high-pressure phases and effects of Ti doping and thermal treatment on structure.

Contribution

It provides detailed insights into the local structure of amorphous Ta2O5 and the impact of Ti doping and thermal processing, advancing understanding of its atomic-scale properties.

Findings

Ta atoms resemble high-pressure Z-Ta2O5 structure

Structural correlations vanish beyond 5 Å due to disorder

Ti doping preserves local structure after thermal treatment

Abstract

Amorphous films of tantalum oxide (Ta2O5) are widely applied to build highly reflective mirrors used in interferometric gravitational wave detectors, such as the Laser Interferometer Gravitational Wave Observatory (LIGO). Despite a large number of studies, the structural properties of amorphous Ta2O5 at the local scale still deserve several further investigations. Such information is essential to any attempt to understand the properties of this important material and no property modelling efforts can be expected to yield reliable information until the local structure in the amorphous phase is better understood. In this paper we report the results obtained by analysing the synchrotron X-ray pair distribution functions of pure and Ti-doped amorphous Ta2O5 film, deposited by ion beam sputtering, as prepared and after a thermal treatment. As a result, it is found that 1) the arrangement of Ta atoms in amorphous Ta2O5 strongly resembles that characterizing the high-pressure Z-Ta2O5 polymorph, whereas the topological properties of O atoms resembles that observed in delta-Ta2O5; 2) structural correlations in amorphous Ta2O5 start to vanish above ~ 5 Angstrom and are completely suppressed for r > 10 Angstrom on account of disorder; 3) Ti substitution retains the short-range topological ordering characterizing the as prepared Ta2O5 amorphous film even after thermal treatment; conversely, pure Ta2O5 films undergoes a significant rearrangement of the local structure after thermal treatment.