Light and Small-Angle X-Ray Diffraction from Opal-Like Structures: Transition from Two- to Three-Dimensional Regimes and Effects of Disorder

Conclusions To summarize, in this chapter diffraction of light and x-rays on opal-like structures is considered. New methodological approaches to collection, processing, and interpretation of experimental data are presented. In particular, a novel representation of the light diffraction data in the “incident angle–registration angle” (θ, Θ) coordinates is shown to be an effective tool of data analysis. This representation allows one to easily distinguish the reflections originating from 2D diffraction from the ones governed by 3D Bragg diffraction. In addition, structural disorder becomes apparent in the (θ, Θ) representation. It is also demonstrated that the immersion spectroscopy method can be used to selectively switch diffraction reflections. This phenomenon is caused by inhomogeneity of the a-SiO2 particles that form synthetic opals. Furthermore, it is demonstrated that microradian x-ray diffraction is a powerful technique that is able to reveal the dominating structure and the presence of disorder in opallike structures. Short acquisition times, modern 2D detectors, and progress in computing techniques make 3D reconstructions of reciprocal space routinely available. This method provides extremely valuable information on the real structure of mesoscopic materials that cannot be easily obtained by other analytical approaches. K13299_