X-ray linear dichroic ptychography

TL;DR

This paper demonstrates the first use of x-ray linear dichroic ptychography to map crystal orientations in coral skeletons with high spatial resolution, revealing detailed nano- and micro-scale structures.

Contribution

It introduces a novel application of x-ray linear dichroic ptychography for imaging crystal orientations in biominerals at nanometer resolution.

Findings

Mapped aragonite crystal c-axis orientations with 35 nm resolution

Identified narrow and wide c-axis angular spreads in coral particles

Corroborated ptychography results with electron nano-diffraction

Abstract

Biominerals such as seashells, corals skeletons, bone, and enamel are optically anisotropic crystalline materials with unique nano- and micro-scale organization that translates into exceptional macroscopic mechanical properties, providing inspiration for engineering new and superior biomimetic structures. Here we use particles of Seriatopora aculeata coral skeleton as a model and demonstrate, for the first time, x-ray linear dichroic ptychography. We map the aragonite (CaCO3) crystal c-axis orientations in coral skeleton with 35 nm spatial resolution. Linear dichroic phase imaging at the O K-edge energy shows strong polarization-dependent contrast and reveals the presence of both narrow (< 35{\deg}) and wide (> 35{\deg}) c-axis angular spread in sub-micrometer coral particles. These x-ray ptychography results were corroborated using 4D scanning transmission electron nano-diffraction on the same particles. Evidence of co-oriented but disconnected corallite sub-domains indicates jagged crystal boundaries consistent with formation by amorphous nanoparticle attachment. Looking forward, we anticipate that x-ray linear dichroic ptychography can be applied to study nano-crystallites, interfaces, nucleation and mineral growth of optically anisotropic materials with sub-ten nanometers spatial resolution in three dimensions.