We describe some of the recent advances in the fluctuation microscopy technique for probing medium-range structural correlations in disordered materials. In particular we show that fluctuation microscopy is a surprisingly sensitive method for detecting trace quantities of C60 in a disordered graphite matrix. This surprising sensitivity arises because C 60 does not have the same forbidden reflections as graphite. Modeling shows that the method should readily distinguish between C60, C 70 and C72. This result indicates that the technique can be used to discern dilute distributions of macromolecules in an otherwise disordered matrix. We also describe preliminary interferometric fluctuation microscopy studies using cross-correlations in diffraction between coherent double probes. This is a form of holography where the diffraction patterns from two neighboring regions are allowed to overlap and interfere. Young's fringes appear wherever both regions scatter strongly. The cross-correlation can be examined as a function of probe separation to estimate a structure correlation length. At present, the method is being applied to x-ray and optical microscopies, but could also be applied to TEM. Since it isolates the essential four-body terms underpinning the fluctuation microscopy technique, this method holds much promise for studying medium-range order.
ASJC Scopus subject areas
- Physics and Astronomy(all)