Formation energy and interaction of point defects in two-dimensional colloidal crystals

TL;DR

This study uses molecular dynamics simulations to analyze the formation and interaction energies of point defects in two-dimensional colloidal crystals, providing insights that align with experimental observations and similar 2D systems.

Contribution

It introduces detailed simulation results on defect energies in 2D colloidal crystals, comparing them with experimental data and other 2D systems like Wigner crystals.

Findings

Interstitial defects have lower formation energy than vacancies.

Defects exhibit strong short-range attractive interactions.

Bound defect pairs are likely the ground state configuration.

Abstract

The manipulation of individual colloidal particles using optical tweezers has allowed vacancies to be created in two-dimensional (2d) colloidal crystals, with unprecedented possibility of real-time monitoring the dynamics of such defects (Nature {\bf 413}, 147 (2001)). In this Letter, we employ molecular dynamics (MD) simulations to calculate the formation energy of single defects and the binding energy between pairs of defects in a 2d colloidal crystal. In the light of our results, experimental observations of vacancies could be explained and then compared to simulation results for the interstitial defects. We see a remarkable similarity between our results for a 2d colloidal crystal and the 2d Wigner crystal (Phys. Rev. Lett. {\bf 86}, 492 (2001)). The results show that the formation energy to create a single interstitial is $12% - 28%$ lower than that of the vacancy. Because the pair binding energies of the defects are strongly attractive for short distances, the ground state should correspond to bound pairs with the interstitial bound pairs being the most probable.