From pore collapse to crystal growth: ultrafast laser-induced stishovite formation in nanoporous silica

TL;DR

This study demonstrates that nanopores in silica act as electromagnetic hotspots under ultrafast laser irradiation, enabling rapid, localized formation of high-pressure stishovite crystals through non-equilibrium phase transitions.

Contribution

The paper introduces a multiscale simulation framework revealing how nanopores enhance local electromagnetic fields to induce ultrafast crystallization of stishovite in silica.

Findings

Nanopores of 2 nm radius create higher local temperatures than smaller pores.

Ultrafast laser pulses induce stishovite formation within sub-nanoseconds.

Nanopores significantly accelerate phase transition compared to homogeneous silica.

Abstract

The crystallization of amorphous solids under ultrafast laser irradiation represents a paradigm of non-equilibrium phase transitions, where the interplay between electromagnetic energy localization and atomic-scale dynamics remains largely uncharted. By using a multiscale framework that couples Finite-Difference Time-Domain simulations of nonlinear light propagation with Molecular Dynamics of the atomic response, we demonstrate that field enhancement at nanopore interfaces confines laser energy and drives a rapid collapse of the surrounding matrix. In the silica structure containing a nanopore of 2 nm radius, corresponding to a porosity of approximately 7%, the enhanced local electromagnetic field led to a final equilibrium temperature 16% higher than for the 1-nm pore (1% porosity), and 20% higher than for the homogeneous medium. Particularly, the heterogeneous energy localization in the 2-nm-pore system created a preferential nucleation site within the dense glass network and led to the ultrafast formation of stishovite, a high-pressure crystalline phase of SiO2, on a sub-nanosecond timescale, significantly faster than in homogeneous silica at the same equilibrium temperature. Such accelerated crystallization enables the phase transition to outpace pressure relaxation, which would otherwise inhibit stishovite formation under identical thermal loading. These predictions align with experimental observations of laser-induced crystallization in confined geometries and establish nanopores as potent catalysts for controlling solid-state transformations via tailored electromagnetic hotspots.