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