Revealing stacking sequences in inverse opals by microradian X-ray diffraction

¹  Department of Materials Science, M.V. Lomonosov Moscow State University - 119991 Moscow, Russia
²  Saint-Petersburg State University - 198504 Saint-Petersburg, Russia
³  Petersburg Nuclear Physics Institute - Gatchina, 188300 Saint-Petersburg, Russia
⁴  European Synchrotron Radiation Facility - BP 220, F-38043 Grenoble Cedex, France, EU
⁵  Debye Institute, Utrecht University - 3584 CH Utrecht, The Netherlands, EU

Corresponding author: alexander.sinitskiy@rice.edu

Received: 30 September 2009
Accepted: 10 December 2009

Abstract

We present the results of the structural analysis of inverse opal photonic crystals by microradian X-ray diffraction. Inverse opals based on different oxide materials (TiO₂, SiO₂ and Fe₂O₃) were fabricated by templating polystyrene colloidal crystal films grown by the vertical deposition technique. Our results suggest that most inverse opal films possess dominating twinned face-centered cubic structure accompanied by some fragments of hexagonal close-packed and random hexagonal close-packed structures. The studied samples possessed individual structures with different ratios of the above fragments. By fitting the results of the angular-dependent X-ray diffraction by the Wilson model we estimate the stacking probability α in the studied samples to be ~ 0.7–0.8. Microradian X-ray diffraction therefore provides detailed structural information on opal-based photonic crystals and can be applied to opaque inverse opals or the samples with a periodicity < 300 nm, whose structure cannot be investigated by conventional optical methods.