Construction and stability of a close-packed structure observed in thin colloidal crystals

We have characterized a close-packed structure of confined charged colloidal spheres, which has been recently discovered. Using different microscopy experiments, the vertically arranged hexagonal planes of n-hcp perpendicular to are found to continuously evolve from the horizontally oriented stacks of n hexagonal planes (n Delta) following the maximum packing criterion, but discontinuously transform to a stack of n+1 square planes [(n+1)square]. Large mechanically stable domains with threefold twin structures are regularly observed in the suspended state at packing fractions between 0.4 and 0.58.