Epitaxial growth of a colloidal hard-sphere hcp crystal and the effects of epitaxial mismatch on crystal structure.

We demonstrate the epitaxial growth of hard-sphere hcp and double hcp crystals using a surface pattern that directly dictates the stacking sequence. A detailed three-dimensional analysis based on real-space measurements is performed on crystal structure as a function of template-crystal mismatch, which demonstrates the possibilities of colloidal epitaxy as a model system for studying the effects of a patterned substrate on crystal structure. Perfect template-induced hcp-crystal growth occurs at an isotropically deformed template. At deformed lattices we observe growth of a non-close-packed superstructure and of a perfect (100)-aligned fcc crystal. Small mismatches lead to increased out-of-plane displacements followed by a structural breakup in "crystal" grains where particle positions in successive layers are strictly periodic and "defect" grains where these positions are displaced with respect to each other. Large mismatches prevent crystallization in the surface layers. The volume fraction was found to vary drastically (up to about 20% ) as a function of template deformation.

Hard-sphere crystals with hcp and non-close-packed structure grown by colloidal epitaxy.

We demonstrate the epitaxial growth of a metastable (with respect to the bulk) hcp crystal as well as any other close-packed stacking sequence of colloidal hard spheres. At certain stretched and compressed lattices we furthermore observed growth of a non-close-packed superstructure and of a perfect (100)-aligned fcc crystal. Perfect template-induced hcp-crystal growth occurs at lattice spacings that are larger than for bulk crystallization, indicative of prefreezing. Small mismatches lead to increased out-of-plane displacements. Large mismatches prevent crystallization in the surface layers.

Epitaxial crystal growth of charged colloids.

A pattern of repulsive, charged lines is shown to direct three-dimensional (3D) crystallization in a system of long-range repulsive, density-matched colloids. At volume fractions where the bulk phase behavior leads to bcc crystallization, the 1D template was found to induce formation of a metastable fcc crystal. The bcc crystals were oriented with the (100) or the (110) plane, with twofold twinning, parallel to the template. The template further induced prefreezing of the (100) plane. At a large mismatch between template and interparticle spacing, 1D strings form in the surface layer of a 3D crystal.