X-Ray Microscopy and Imaging: Coherent Scattering and Imaging

In recent years, materials research has increasingly sought to develop a better understanding of the disordered state of matter. However, measuring medium-range order (MRO) in disordered materials is still a long-standing problem. Based on fluctuation electron microscopy, which was applied successfully to the understanding of MRO in amorphous materials, we have developed fluctuation x-ray microscopy (FXM). This novel approach offers quantitative insight into medium-range correlations in materials at nanometer and larger length scales. It examines spatially resolved fluctuations in the intensity of a series of x-ray speckle patterns. The speckle variance depends on higher order correlations that are more sensitive to MRO. Systematically measuring the speckle variance as function of the momentum transfer and x-ray illumination size produces a fluctuation map that contains information about the degree of MRO and the correlation length, see for example Fig. 1.

Fig. 1: Mean (left) and variance (right) data from ~4000 speckle patterns obtained from a latex sphere sample (from [1]).

The current FXM experimental setup at 2-ID-B allows us to study ordering in systems with structural units on length scales of ~10 nm–2 µm. This approach can be used for the exploration of MRO and subtle spatial structural changes in a wide range of disordered materials from soft condensed matter to nanowire arrays, semiconductor quantum dot arrays and magnetic materials. It will also help us to understand the mechanisms of order-disorder transitions and may lead to control of ordering, which is important in developing ordered structures tailored for particular applications.

Questions ?

References

[1] L. Fan, I. McNulty, D. Paterson, M. M.J.Treacy, J. M. Gibson; "Characterization of medium-range order in noncrystalline systems
by fluctuation x-ray microscopy, " in Advanced Photon Source Activity Report 2003

last updated by Stefan Vogt - April 19, 2007