Characterization of Medium-Range Order in Noncrystalline Systems by Fluctuation X-ray Microscopy
- AZU
In recent years, materials research has increasingly focused on developing a better understanding of the disordered state of matter. Much of our understanding amorphous materials has depended upon the atomic pair distribution function (PDF) obtained from diffraction experiments. However, the PDF method has poor sensitivity to medium-range order (MRO), the characterization of which is a long standing problem. Recently, fluctuation electron microscopy (FEM) was developed and successfully used for probing MRO in amorphous materials. This technique gains its sensitivity to MRO by examining fluctuations in coherently scattered (speckle) intensity patterns from very small sample volumes, on a length scale determined by the illuminated radius or associated imaging resolution. The speckle variance depends on two-, three- and four-body atomic correlation functions, whereas the average, which is just the diffracted intensity, depends only on the two-body PDF. Higher order correlation functions are more sensitive to MRO. In the x-ray regime, many techniques exist to probe long- and short-range order in matter, in real space by imaging and in reciprocal space by diffraction and scattering. The average intensity obtained from scattering and diffraction experiments is routinely inverted to give the atomic PDF. At present, no x-ray technique effectively probes MRO. By comparison to electrons, x-rays provide access to longer length scales due to their longer wavelengths and offer greater sample penetration with less radiation damage, as well as elemental and chemical sensitivity through resonant effects. Consequently, we are developing fluctuation x-ray microscopy (FXM) at the 2-ID-B soft x-ray beamline to study MRO in bulk samples, solutions and films at nanometer and larger length scales. Compared to FEM, FXM is better suited to materials with larger characteristic length scales such as polymers, biological macromolecules and their complexes, as well as other nanostructured materials, nanocomposites and hybrids.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 1008989
- Resource Relation:
- Conference: 8th International Conference on X-ray Microscopy;26-30 July 2005;Himeji, Japan
- Country of Publication:
- United States
- Language:
- ENGLISH
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