Fluctuation microscopy - a tool for examining medium-range order in noncrystalline systems

Fluctuation microscopy examines the spatial variations in coherent microdiffraction from an ensemble of small volumes in noncrystalline systems. The variance of scattered intensity into regions of reciprocal space can be used to give insight into three-body and four-body correlation functions, which are sensitive to medium-range order. The technique was originally developed for transmission electron microscopy and was successfully used to understand medium-range order in amorphous silicon and germanium. Applying this method to X-rays, we have developed a new approach: fluctuation X-ray microscopy (FXM). The approach offers quantitative insight into medium-range correlations in materials at nanometer and larger length scales. The FXM technique can be used to explore medium-range order and subtle structural changes in a wide range of disordered materials from soft matter to nanocomposites, nanowire and quantum dot arrays. We have demonstrated this new technique by studying films of polystyrene latex spheres.