A three-dimensionally (3D) large and close-packed face-centered cubic colloidal crystal is useful as a template for inverse opals with perfect three-dimensional photonic bandgap [1]. Although bulk close-packed colloidal polycrystals are easily fabricated by drying highly-concentrated colloidal crystals [2], controlled fabrication of the highly-concentrated colloidal crystals with sufficiently large and high quality grains for device applications is still difficult.

We developed effective enlargement [3] and annealing [4] methods to obtain such a colloidal crystal grain by applying a gravitational field.

For enlargement studies, a highly concentrated and 3D large colloidal crystal grain was obtained by centrifugation of polystyrene particles (Duke Scientific, diameter d = 200 nm, volume fraction of the dispersion φ = 0.1) at 21G with the control of the angle of substrates (walls of growth cell). We adjusted the angle of an optical cell with a rid using a specially-designed cell holder.

For annealing studies, a highly concentrated colloidal crystal was obtained by centrifugation of silica particles (Nippon Shokubai Seahoster KE-W10, d = 110 nm, φ = 0.0968)  at 9 G for 2 days. Polarized transmission image of a grain in the crystal showed some striations in the grain. The striations show the stacking disorders in the grain [5]. After the first observation, the crystal was centrifuged again at 50 G for 5 days. The number of the striations seemed to decrease after the additional centrifugation. The decrease shows the shrinkage of the stacking disorders under high gravity [4].

[1] A. Blanco, et al., Nature, 405, 437-440 (2001). [2] Y. Suzuki, et al., J. Cryst. Growth, 322, 109-113 (2011). [3] Y. Suzuki, et al., J. Cryst. Growth, 318, 780-783 (2011). [4] Y. Suzuki, et al., Defect & Diffusion Forum, 323-325, 555-558 (2012). [5] Y. Monovoukas, et al., Phase Transitions, 21, 183-195 (1990).

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1. Domain competition in deposition growth
2. Effect of immobile impurities on behaviors of a two-dimensional island
3. Appearance of a homochiral state in crystallization by random fluctuation
4. Ordering of Brownian Particles from Walls Due to an External Force
5. Step patterns induced by a line source of adatoms