Fabrication of large-area face-centered-cubic hard-sphere colloidal crystals by shear alignment

We make hard-sphere colloidal crystals from polymethyl methacrylate spheres suspended in organic solvents at high volume fractions. The samples are crystallized between two glass plates separated by 10-mu m spacer beads. We study the optical scattering from these systems and describe methods for discriminating between the various crystal packings. Crystals formed simply by increasing the volume fraction beyond the liquid-solid phase transition tend to be small and predominantly random close packed. However, we find that by forming these crystals while applying controlled shear to the glass plates, large-area single crystals can be made. These crystals are much more regular and appear to be predominantly twinned face-centred cubic. The creation of single-orientation face-centred cubic crystals appears possible when shear is applied in one direction.