2-D SMALL ANGLE X-RAY SCATTERING PATTERNS OF COLLOIDS AND PHOTONIC COLLOIDAL CRYSTALS M. Megens¹, W. L. Vos¹, C. M. van Kats¹, and P. Bösecke², ¹van der Waals-Zeeman Instituut, Universiteit van Amsterdam, 1018 XE Amsterdam, The Netherlands, ²European Synchrotron Radiation Facility, 38000 Grenoble, France.

We have started small angle x-ray scattering (SAXS) experiments on BL4/ID2 of the ESRF to study photonic colloidal crystals. These crystals have an as large as possible refractive index contrast in the optical regime, and are thus multiply scattering (photonic), which impedes optical diffraction experiments [1].

Monochromatic radiation (~0.1 nm) was focused on the samples. Scattered radiation was collected with a 2 dimensional gas detector at the maximum distance of ~10 m [2].

The diffraction patterns clearly reveal several features. 1) Sharp diffraction peaks are observed that originate from the colloidal crystals. The 2D nature of the information combined with rotation of the samples reveals a wealth of information on the structure and order of the samples than cannot be obtained from 1D diffraction patterns. Yet, we have observed lattice spacings on the order of several hundred nm. 2) The concentric ring pattern caused by the formfactor of the colloidal spheres is seen. It extends far into reciprocal space due to the high degree of monodispersity (single size). The possibility to measure the size distribution of the spheres for the first time in-situ will be discussed.

The information from the SAXS studies already proves to be essential for the interpretation of optical studies of the samples.

[1] W.L. Vos et al, in Photonic Band Gap Materials, ed. C. Soukoulis (Kluwer, Dordrecht, in press); Phys. Rev. B (submitted).

[2] P. Bsecke et al, Rev. Sci. Instr. 66, 1636 (1995).