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Dr. Armin Hoell
Dr. Armin Hoell
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ASAXS - Anomalous Small Angle X-ray Scattering

Small-Angle X-ray Scattering (SAXS) is a technique of registering the intensity of X-rays scattered at angles below 5° [1 - 3]. It is applied for investigating structures with spatial dimensions in the nanometre range, typically 0.5-100 nm. SAXS proves the nano-structure of a variety of different materials which can be solid (also very porous or powdered) or liquid.

Anomalous Small-Angle X-ray Scattering (ASAXS) uses tuneable X-ray energy near, but below, X-ray absorption edges of the elements comprising in the investigated sample. Thus element specific information, composition and density fluctuation can be obtained [4 - 6].

While SAXS and ASAXS are transmission geometry experiments Grazing Incidence  Small-Angle X-ray Scattering (GISAXS) is performed in reflection geometry. Typical incidence and exit angles relative to the sample plane are near and below 1°. The X-ray penetration depth can be few nanometres, so that structures on and slightly below the sample surface can be investigated [3, 7, 8]. 

The structural information that can be obtained is particle size distribution or shape, particle composition, the internal surface area per unit volume, the volume fraction, and characteristic length of ordered structures.

A Small Angle X-ray Scattering (SAXS) instrument, that is under construction at HZB,

  • will be installed at the monochromatic beam of the HMI 7T Wiggler at BESSY
  • will run in time sharing with the Magnetic Scattering experiment
  • will be able perform standard user SAXS experiments and different sample environments will be available.

The instrument is constructed to perform two advanced scattering techniques:

  • SAXS - Anomalous Small Angle X-ray Scattering
  • GISAXS - Grazing Incidence Small Angle X-ray Scattering

Instrument specification

  • X-ray energy: 4.5 keV < E < 22 keV, ΔE/E < 2*10-4
  • 2D - Gas Detector: 200*200 mm², resolution 200 µm
  • sample - detector distance varies between 650 mm - 3600 mm
  • CCD camera
  • photon flux at sample: ~109 s-1 – 1011 s-1 (optics depending) Schematic view of the small angle chamber: figure 1

Schematic view of the small angle chamber (figure 1)

The sample is positioned in the goniometer centre, shown by the red sign on the left in front of the instrument. The sample-detector distance can be varied between 650 mm and 3600 mm as shown on the two pictures A and B. Four z-stages are used to align the optical bench and to lift up the detector support by up to 3° in case of GISAXS. The instrument is based on an air cushion system.


Sample environments

  • sample changer under vacuum conditions (figure 2)
  • sample changer under air
  • high-temperature furnace (T < 1300 K)
  • GISAXS furnace in reflection geometry

figure 1



figure 2





References

  1. L.A. Feigin, and D.I. Svergun, (1987). Structure Analysis by Small-Angle X-ray and Neutron Scattering, New York: Plenum Press.
  2. O. Glatter, and O. Kratky (1982). Small Angle X-ray Scattering, London: Academic Press.
  3. Modern aspects of small-angle scattering. Editor H.Brumberger, NATO ASI Series; Series C: Mathematical and Physical Sciences, Vol. 451, (Dordrecht, Kluwer Academic. 1995).
  4. Goerigk, H.-G. Haubold, O. Lyon, and J.-P. Simon, J. Appl. Cryst. 36, 425 (2003).
  5. H.-G. Haubold, J. Phys. 3 C8, 475 (1993).
  6. J.-P. Simon, and O. Lyon, Ann. Phys. 20 C3, C3-C3-134 (1995).
  7. J.A R. Levine, J. B. Cohen, Y. W. Chung and P. Georgopoulos J. Appl. Cryst. 22, 528 (1989).
  8. A. Naudon, and D. Thiaudiere, J. Appl. Cryst. 30, 822 (1997). Materials: ASAXS investigations