Fabrication of 3-D photonic band gap material of TiO2 by microtransfer molding and sol-gel processing

Abstract

<p>Photonic band gap (PBG) crystals are artificially engineered periodic dielectric structures which exhibit frequency regions in which electromagnetic (EM) waves cannot propagate in certain directions. By using the "master mold" with desired features, an elastomeric mold of poly (dimethylsiloxane) (PDMS) with a relief structure on its surface was shaped. From these elastromeric molds, one-, two-, and multi-layer PBG samples were formed using microtransfer molding. The sol-gel solutions with the precursor of titanium diisopropoxide bis (2, 4-pentadionate)(TDBP), tetraethyl orthotitanate (TEOT) and titanium isopropoxide (TIPP) were infiltrated into the samples, respectively by spin coating. The infiltrated samples were sintered at 5500C. The sintered samples were characterized by optical microscopy, SEM and FTIR. Results show that the sintered samples experience large shrinkage (up to 40%) during heat treatment and therefore the structures had a low filling ration. The filling ratio can be enhanced by increasing the concentration of the precursor in the sol-gel. FTIR data showed that there were strong absorption peaks around 1500 cm−1 with a transmittance of 92.5% due to the existence of the first band gap of PBG structures. A sintered 4-layer sample was successfully obtained by infiltrating the sol of TDBP (26wt%) six times into the pattern through spin coating. It is likely that this approach can yield high quality three-dimensional PBG structures of Ti02.</p>