Direct observation of phase transitions in Archimedean trunctated tetrahedrons under quasi-2D confinement

TL;DR

This study demonstrates how Archimedean truncated tetrahedrons self-assemble into novel phases under quasi-2D confinement, revealing phase transitions driven by gravitational potential and particle rotations, advancing understanding of colloidal crystal formation.

Contribution

First experimental observation of phase transitions in Archimedean truncated tetrahedrons under quasi-2D confinement using two-photon lithography.

Findings

Particles form a hexatic phase under small gravitational potential.

Transition to a quasi-diamond phase occurs with increased gravitational potential.

Phase transition is triggered by out-of-plane particle rotation at defects.

Abstract

Colloidal crystals are used to understand fundamentals of atomic rearrangements in condensed matter and build complex metamaterials with unique functionalities. Simulations predict a multitude of self-assembled crystal structures from anisotropic colloids, but these shapes have been challenging to fabricate. Here, we use two-photon lithography to fabricate Archimedean truncated tetrahedrons and self-assemble them under quasi-2D confinement. Under a small gravitational potential, these particles self-assemble into a hexatic phase, which has not yet been observed or reported for this shape. Under additional gravitational potential, the hexatic phase transitions into a quasi-diamond two-unit basis. In-situ imaging reveal this phase transition is initiated by an out-of-plane rotation of a particle at a crystalline defect and causes a chain reaction of neighboring particle rotations. Our results provide a framework of studying different structures from hard-particle self-assembly and demonstrates the ability to use confinement to induce unusual phases.