Equilibrium Configurations and Energetics of Point Defects in   Two-Dimensional Colloidal Crystals
  We demonstrate a novel method of introducing point defects (mono and di-vacancies) in a confined mono-layer colloidal crystal by manipulating individual particles with optical tweezers. Digital video microscopy is used to study defect dynamics in real space and time. We analyze the topological arrangements of the particles in the defect core and establish their connection with the energetics of the system. It is found that thermal fluctuations excite point defects into \textit{dislocation multipole} configurations. We extract the dislocation pair potential at near field, where cores overlap and linear elasticity is not applicable. 
Alexandros Pertsinidis and X. S. Ling