3D characterisation of individual grains of coexisting high-pressure H2O ice phases by time-domain Brillouin scattering

TL;DR

This study demonstrates the use of time-domain Brillouin scattering for 3D imaging of individual grains in high-pressure water ice phases, enabling phase identification and boundary localization at nanoscale resolution.

Contribution

It applies time-domain Brillouin scattering to image and analyze coexisting high-pressure ice phases in 3D, revealing grain-specific phase and orientation details.

Findings

Successful 3D imaging of ice grains with phase identification.

Simultaneous detection of quasi-longitudinal and quasi-shear waves.

Enhanced localization of grain boundaries.

Abstract

Time-domain Brillouin scattering uses ultrashort laser pulses to generate coherent acoustic pulses of picoseconds duration in a solid sample and to follow their propagation in order to image material inhomogeneities with sub-optical depth resolution. The width of the acoustic pulse limits the spatial resolution of the technique along the direction of the pulse propagation to less than several tens of nanometres. Thus, the time-domain Brillouin scattering outperforms axial resolution of the classical frequency-domain Brillouin scattering microscopy, which uses continuous lasers and thermal phonons and which spatial resolution is controlled by light focusing. The technique benefits from the application of the coherent acoustic phonons, and its application has exciting perspectives for the nanoscale imaging in biomedical and material sciences. In this study, we report on the application of the time-domain Brillouin scattering to the 3D imaging of a polycrystal of water ice containing two high-pressure phases. The imaging, accomplished via a simultaneous detection of quasi-longitudinal and quasi-shear waves, provided the opportunity to identify the phase for individual grains and evaluate their crystallographic orientation. Monitoring the propagation of the acoustic waves in two neighbouring grains simultaneously provided an additional mean for the localisation of the grain boundaries.