Optical characterization of macroporous oxides: evolution of the photonic band gap

Summary form only given. It has recently been shown that a crystal of close-packed air spheres, with a high dielectric in the interstitial regions, exhibits a complete photonic band gap. An example of such a material has been difficult to fabricate because the dielectric required is higher than that of nearly all transparent solids. However, it is nonetheless valuable to study the optical properties of materials as they approach this interesting limit, to see how these properties evolve with increasing dielectric contrast. Although a variety of metal oxides possess reasonably high dielectrics and good transparency in the visible range, the synthetic challenges associated with the preparation of a well-ordered macroporous solid have been daunting. Recently, several groups have reported the fabrication of macroporous oxides, but their ability to characterize the optical properties of these materials has been limited by issues of sample quality such as grain size, inhomogeneity in thickness, etc. As a result, no studies of transmission spectra have been reported. Recently, we have developed a method for preparing well-controlled thin films of macroporous oxides that are uniform in thickness and contain few grain boundaries over regions as large as 1 cm/sup 2/, and are thus well suited for optical transmission experiments.