Current USAXS imaging results
show large promise for applications in materials science and biology. In this technique the photodiode is replaced by CCD camera.
The sample is positioned and then instrument is in steps tuned to various Q. The
image on the CCD camera reflects the parts of microstructure, which
scatter at teh tuned Q values . The beam needs to be at each step attenuated
appropriately, so the CCD is not damaged. Since the intensity drops roughly as Q^(-4), the exposure time ranges wildly. From heavily attenuated beam at around Q=0 to many minutes at larger Q values.
technique showed impressive results when combined for example with samples
which were strained and developed strain cracks. One can then observe crack
formation, orientation, location – depending on their size (selected by
selecting appropriate Q). This technique is available for II program only in
limited way, as we need to yet optimize parts of the instrumentation. However,
if you have problem appropriate for this instrument, please, contact me.
The resolution and field of view depends on the optics. The best
resolution we were able to achieve was about 1 micron. With 20X magnification, the field of view is
approximately 500 x 750 micron^2.
USAXS imaging is capable of showing inhomogeneities with sizes greater
than 1 micron, which is about where the USAXS effective range ends.
Scatterers with different scattering power show up in different part of
the Fourier spectrum. By analyzing the spectrum, we can distinguish the
intensity contributions from different scatterers and illustrate their
spatial distribution. It should benefit weak contrast and non-conductive
materials, which are difficult to image with traditional electron
microscope and X-ray radiography.
Few publications are available to help users to understand the USAXS imaging method.
Levine, L. E. and G. G. Long (2004). "X-ray imaging with ultra-small-angle X-ray scattering as a contrast mechanism." Journal of Applied Crystallography 37: 757-765. (pdf copy here)
A new transmission X-ray imaging technique using ultra-small-angle X-ray scattering (USAXS) as a contrast mechanism is described. USAXS imaging can sometimes provide contrast in cases where radiography and phase-contrast imaging are unsuccessful. Images produced at different scattering vectors highlight different microstructural features within the same sample volume. When used in conjunction with USAXS scans, USAXS imaging provides substantial quantitative and qualitative three-dimensional information on the sizes, shapes and spatial arrangements of the scattering objects. The imaging technique is demonstrated on metal and biological samples.
Levine, L. E., G. G. Long, et al. (2007). "Self-assembly of carbon black into nanowires that form a conductive three dimensional micronetwork." Applied Physics Letters 90(1).
The authors have used mechanical self-assembly of carbon-black nanoparticles to fabricate a three dimensional, electrically connected micronetwork of nanowires embedded within an insulating, supporting matrix of poly(methyl methacrylate). The electrical connectivity, mean wire diameter, and morphological transitions were characterized as a function of the carbon-black mass fraction. Conductive wires were produced with mean diameters as low as 24 nm with lengths up to 100 mu; 2007 American Institute of Physics.