Thickness measurement of colloidal opal crystal growth by Bragg reflection

This study investigates a simple method for thickness estimation with single layer accuracy for self-assembling opal crystals prepared by the dip-coating method. The thickness (number of layers) of the opal crystals was estimated by an analysis of the optical reflectance from s-polarization incident light, and then verified with SEM. The opal crystals were considered as periodic dielectric layers and were analyzed with the transfer matrix method. The reflectance simulation showed a good agreement with the experimental results. The lattice constant and the thickness were determined at the peak position and by the fringes of the reflection spectra, respectively.