X-ray scattering methods

By X-ray small angle scattering the electron and size distribution in a system can be analyzed at a scale ranging from 2 nm – 2 µm.

The samples are irradiated by a (almost) parallel and monochromatic X-ray beam. This way the deviation from the parallel beam (scattering) can be analyzed by a detector behind the sample. X-ray small angle scattering is applied for the determination of form, concentration or electron density of artificial (e.g. nano powder, colloids, aero gels) or natural materials (e.g. collagen, wood, nacre). Also fluids (e.g. proteins in solution) can be analyzed this way.

System solution SAXS

Whereas wide angle scattering WAXS yields information about atomic lattices spacing, or the structure factor respectively, small angle scattering is applied for the analysis of the form factor, i.e. particle form and size, boundary surfaces and anisotropy, resp. orientation. When analyzing SAXS scattering images a purely elastic scattering is assumed. The entire intensity is dependent on the photon flux irradiating the sample, the dihedral angle of the detector and the scattering behavior of the sample, resp. the differential cross section.

Since the X-ray beam produced by an X-ray source does not have coherence it is monochromatized and parallelized by a Montel mirror. Thus, the beam can be formed and its divergence reduced (ca.0.24 mrad) by applying three collimators and two-axes hybrid blade systems. With the moveable Medipix detector the system can be used in SAXS or ultra-small scattering (USAXS) mode.

Since SAXS measurements are displaying the structure in reciprocal space smaller angles have to be used for imaging larger structures. Structural information in the range of 2 – 100 nm can be gained by conventional SAXS methods.

By applying USAXS sizes up to 2 µm can be analyzed at LRM. Due to the necessary collimation measurement periods for USAXS are considerably longer. As an example a sample of silver behenate usually used for calibration purposes was chosen. It is nano crystalline and has a large lattice spacing of 5.84 nm facilitating the precise assignment of the scattering angles (<100> and <200> in this case). Thus e.g. the detector-sample-distance can be calibrated.

  • Inspection of mesoscopic materials on a length scale of 2 nm to 2 µm
  • Artificial materials
  • Nano-powders
  • Colloids
  • Aerogels
  • Natural materials in solid phase, Collagen
  • Wood
  • Natural materials in liquid phase
  • Proteins

Source MicroMax-007HF with microfocus, rotating X-ray source
Multilayer Osmic Parabolic CMF infinity for Cu Ka line 1.54 Å
Collimator Three motorized collimator levels, each with 4 independently movable shutters
Detector

X-ray detector with semiconductor sensor, individual photo counting mode, 256x256 pixels with a pixel size of 55x55 µm2

Axes
  • Motorized detector level (0–2690 mm)
  • Motorized sampling level: TX (± 20 mm), TY (± 12.5 mm), RZ (± 180°)

Advantages and customer value

Due to the variable size of the incident X-ray beam large volumes can be analyzed simultaneously (compared to sample diameter). Thus, a direct statistical assessment of sample size distribution can be made. Additionally, large sample surroundings can be analyzed by a very small beam for determining local inhomogeneities. In contrast to imaging X-ray methods it is possible to obtain information from the nm regime by applying small angle scattering.