Photon-Directed Colloidal Crystallization

We have recently shown that electric fields can be used to induce rapid three-dimensional colloidal crystallization from isotropic colloidal dispersions through a combination of dielectrophoretic and electro-osmotic mechanisms. In this letter we demonstrate that light itself can be used to drive colloidal crystallization in a local and directed fashion under applied electric fields, allowing one to effectively write colloidal crystals in arbitrary and reversible patterns. This ability will provide great flexibility in the construction of colloid-based devices and allow their reversible operation as a function of an applied optical or electric field. (C) 2004 American Institute of Physics.