Thin Colloidal Crystals

Colloidal crystals, made of large polystyrene particles (1.1 {μ}m in diameter), are confined into a thin layer between two glass boundaries. When the thickness h of the layer is increased progressively from zero, a sequence of structures $S(h)$ is detected from direct observations in an optical microscope. These structures are stacks of n square ({})---or triangular (Δ)---ordered layers. For $n<~7$, the sequence $S(h)$ is nΔ→(n+1)→(n+1)Δ→.