Materials whose dielectric constant varies spatially with submicrometer per
iodicity exhibit diffractive optical properties which are potentially valua
ble in a number of existing and emerging applications. Here, such systems a
re fabricated by exploiting the spontaneous crystallization of monodisperse
silica spheres into close-packed arrays. By reliance on a vertical deposit
ion technique to pack the spherical colloids into close-packed silica-air a
rrays, high quality samples can be prepared with thicknesses up to 50 mu m.
These samples are planar and thus suitable for optical characterization. S
canning electron microscopy (SEM) of these materials illustrates the close-
packed ordering of the spherical colloids in planes parallel to the substra
te; cross-sectional SEM micrographs of the arrays as well as optical method
s are used to measure sample thickness and uniformity. Normal-incidence tra
nsmission spectra in the visible and near-infrared regions show distinct pe
aks due to diffraction from the colloidal layers. While these basic optical
characteristics are similar to thicker and polycrystalline gravity-sedimen
ted colloidal crystals, the systematic control over the number of colloidal
layers allows the effect of sample thickness on the optical spectrum to be
studied for the first time.