X-Ray Microscopy and Imaging: Ultra-Small-Angle X-Ray Scattering (USAXS) Imaging

Small Angle X-ray Scattering (SAXS) is a proven X-ray scattering technique to provide volume-averaged microstructural information, including morphology and size distribution. However it does not provide direct information about the shape and location of the scatters.

Ultra-Small-Angle X-ray Scattering (USAXS) imaging technique has been developed over the last few years to complement SAXS. It not only provides direct information about shape and 3-dimensional distribution of the scatterers, also it greatly expands the size range of USAXS from 1 to millimeter and above.

The USAXS imaging setup is based upon USAXS facility in Sector 32ID-B. Its layout is as following.

Si(111) monochromator is used to monochromize X-rays exiting from undulator. Depending on X-ray energy, different stripe (Si, Cr or Rh) of the mirror is used to suppress harmonic radiation. We collimate X-rays with two Bragg reflections of Si (111) or (220) crystals. The X-ray flux that enters the sample is monitored by a windowless ion chamber. After X-rays pass through the sample, a set of Si (111) or (222) analyzing crystals are utilized to select desired scattering vector. Only X-rays that satisfy the analyzing conditions could enter the scintillator, where X-rays are converted to visible light. The image data are captured with a CCD detector.

This setup operates best when the sample is nearly uniformly illuminated, which restricts the beam size at the sample to be about . Larger samples can be studied with an existing raster routine.

USAXS imaging has been shown as a promising new technique. When used to probe creep cavities in Cu, USAXS imaging showed that at different Qs, the same region of the sample displays strikingly different imaging features[1]. USAXS imaging also helped illustrate that the dramatic increase of electric conductivity in a Carbon Black/PMMA composite system is due to the development of nanowire network at triple junctions[2].

The instrumental setup of USAXS imaging is similar to that of Diffraction Enhanced Imaging (DEI). Therefore USAXS imaging facility is also capable of doing DEI studies.

[1] L. E. Levine, and G. G. Long, Journal of Applied Crystallography 37, 757 (2004).
[2] L. E. Levine et al., Applied Physics Letters 90 (2007).