Visualization of Stacking Faults and their Formation in Colloidal Photonic Crystal Films

We demonstrate experimentally that stacking faults give rise to unique optical spectra in self-assembled colloidal crystal films. These defects are shown to affect only bands in the high frequency region, while leaving the fundamental 〈111〉 stopgap unaffected. Stacking faults are revealed to be caused by the incorporation of impurity spheres into the colloidal lattice during growth (pictured), a mechanism common to atomic crystallization.