Thin Colloidal Crystals

Colloidal crystals, made of large polystyrene particles (1.1 μm 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 $S\left(h\right)\mathrm{}$ is detected from direct observations in an optical microscope. These structures are stacks of $n$ square (□)—or triangular $\left(\Delta \right)$—ordered layers. For $n<~7$, the sequence $S\left(h\right)\mathrm{}$ is $\dots n\Delta \to \mathrm{}(n+1\mathrm{})\mathrm{}\square \to \mathrm{}(n+1\mathrm{})\mathrm{}\Delta \to \dots$.