Crystal growth in confinement

TL;DR

This study reveals how confinement influences crystal growth mechanisms, showing that molecular layers can nucleate and propagate in confined spaces, with growth dynamics governed by 2D mass transport and specific morphological features.

Contribution

The paper introduces novel in situ optical observations of confined crystal growth, elucidating the mechanisms and predicting morphologies based on dimensionless parameters.

Findings

Molecular layers nucleate homogeneously in confinement.

Growth is controlled by 2D mass transport within the liquid film.

Distinctive features include skewed dislocation spirals and edge-localized nucleation.

Abstract

The growth of crystals confined in porous or cellular materials is ubiquitous in Nature and industry. Confinement affects the formation of biominerals in living organisms, of minerals in the Earth's crust and of salt crystals damaging porous limestone monuments, and is also used to control the growth of artificial crystals. However, the mechanisms by which confinement alters crystal shapes and growth rates are still not elucidated. Based on novel \textit{in situ} optical observations of (001) surfaces of NaClO$_3$ and CaCO$_3$ crystals at nanometric distances from a glass substrate, we demonstrate that new molecular layers can nucleate homogeneously and propagate without interruption even when in contact with other solids, raising the macroscopic crystal above them. Confined growth is governed by the peculiar dynamics of these molecular layers controlled by the two-dimensional transport of mass through the liquid film from the edges to the center of the contact, with distinctive features such as skewed dislocation spirals, kinetic localization of nucleation in the vicinity of the contact edge, and directed instabilities. Confined growth morphologies can be predicted from the values of three main dimensionless parameters.