Formation of Free-Standing Inverse Opals with Gradient Pores

Abstract

We demonstrate the fabrication of free-standing inverse opals with gradient pores via a combination of electrophoresis and electroplating techniques. Our processing scheme starts with the preparation of multilayer colloidal crystals by conducting sequential electrophoresis with polystyrene (PS) microspheres in different sizes (300, 600, and 1000 nm). The critical factors affecting the stacking of individual colloidal crystals are discussed and relevant electrophoresis parameters are identified so the larger PS microspheres are assembled successively atop of smaller ones in an orderly manner. In total, we construct multilayer colloidal crystals with vertical stacking of microspheres in 300/600, 300/1000, and 300/600/1000 nm sequences. The inverse opals with gradient pores are produced by galvanostatic plating of Ni, followed by the selective removal of colloidal template. Images from scanning electron microscopy exhibit ideal multilayer close-packed structures with well-defined boundaries among different layers. Results from porometer analysis reveal the size of bottlenecks consistent with those of interconnected pore channels from inverse opals of smallest PS microspheres. Mechanical properties determined by nanoindentation tests indicate significant improvements for multilayer inverse opals as compared to those of conventional single-layer inverse opals.

Peculiarities of Eu3+ Photoluminescence in Opal Photonic Crystal Films and Heterostructures Based of Them

“…To vary the dielectric contrast and to enlarge the functionality of opal PhCs, the matrices are impregnated with magnetic clusters [20,21], active dielectrics [22][23][24], semiconductors [25][26][27],organic and laser-active materials [28][29][30]. Inverse opals are fabricated by removing PS or PMMA spheres from impregnated matrices [31,32]. For artificial opals, one should expect the formation of PhSBs, while, for inverted opals, the PhBG appearance is possible in the case of using a higher refractive index filler.…”