1. Department of Physics and
2. Department of Chemical Engineering, Princeton University, Princeton, New Jersey 08540, USA

Correspondence to: P. M. Chaikin¹ Correspondence and requests for materials should be addressed to P.M.C. (e-mail: Email: chaikin@pupgg.princeton.edu).

Abstract

Three-dimensional ordered colloidal systems with lattice constants comparable to the wavelength of visible light might find important application as photonic crystals¹, optic filters and switches², and chemical sensors³. Colloidal crystallization has been actively studied^{4, 5, 6, 7, 8}, leading to the development of several methods to control the self-assembly of the colloidal particles; examples include colloidal epitaxy⁹ and space-based reduced-gravity techniques^{10, 11}. Here we report a method to control the nucleation and growth of hard-sphere colloidal crystals that relies on the use of temperature gradients to define a density gradient. This is somewhat counterintuitive as temperature does not play a role in determining the hard-sphere phase diagram. We obtain hard-sphere single crystals (size 3 mm) from a sample in a concentration regime that would remain in the liquid state in the absence of a temperature gradient. We expect the method to have applications in controlling the ordering and growth of various 'soft' systems including colloids, copolymers, emulsions and proteins.