The following is a short summary on SAXS essentials. Are you just starting up in SAXS? Then this is perfect for you – lean back and enjoy this little introduction.
- 1 What SAXS is
- 2 SAXS parameters
- 3 Unique SAXS benefits
- 4 Different angles – different results
- 5 GI-SAXS: At grazing incidence
- 6 Different beam shapes – different benefits
- 7 Ultra-fast SAXS Measurements with Metal Jet
- 8 SAXS applications
- 9 External Links
What SAXS is
SAXS (Small-Angle X-ray Scattering) is a non-destructive method for investigating nanostructures in liquids and solids. Here’s the basic approach:
An X-ray beam is sent through or onto a sample containing nanostructures, such as proteins, macromolecules or quantum dots. The beam interacts with the electrons of the sample and is scattered. The detected scattering pattern is characteristic of the nanostructures and can be used to determine their size, shape, internal structure and more.
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SAXS is used to determine several parameters of nanostructured samples – the most common ones are:
• Internal Structure
Unique SAXS benefits
SAXS results are representative of an entire sample, so SAXS ideally complements methods that provide unique but local information, such as electron microscopy.
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Another essential benefit of SAXS is that it barely requires any sample preparation. This sets it apart from complementary techniques such as electron microscopy or NMR spectroscopy, which often require extensive sample preparation. And since SAXS allows in-situ measurements, preparation artifacts are avoided and the sample remains unchanged.
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SAXS also stands out for the fact that it can be used to investigate biological macromolecules in solution, under physiological conditions. This increasingly popular application known as Bio-SAXS is a vital tool in molecular biology, where the analysis of samples in their native state is essential for studying the dynamic processes the sample is involved in.
Different angles – different results
The scattered X-rays can be recorded at different angles. In SAXS, you analyze the scattering pattern at small angles, typically below <10° 2Θ, to probe nano-sized particles and domains in a size range from 1 nm to 200 nm, which scatter towards these small angles.
To investigate smaller structures, such as crystal lattices at the atomic level, you interpret the scattered X-rays at wider angles. This approach is called Wide-Angle X-ray Scattering (WAXS) or X-ray Diffraction (XRD). The obtained WAXS pattern enables you to analyze structures below nanometer size – as atoms and interatomic distances scatter towards wider angles.
GI-SAXS: At grazing incidence
GI-SAXS (GI = Grazing Incidence) is a rather new method used to investigate thin films with nanostructures on the substrate surface. For GI-SAXS analysis, the X-ray beam is set to graze a flat sample almost parallel to its surface. The scattered signal is a sampling of the structures on the surface or slightly below the surface, depending on the chosen angle of incidence.
Different beam shapes – different benefits
Before scattering, the X-rays are transformed into a well-defined line-shaped or point-shaped beam. This process is called collimation.
A line-collimated beam has the advantage that it combines a high photon flux with a high scattering volume – which means measurement times can be dramatically shorter than with point collimation. The drawback of a line-collimated beam is that it can only probe isotropic samples. Therefore, a line-shaped beam is preferable for analyzing weakly scattering samples, such as proteins and other soft matter. A point-collimated beam can be used to also analyze anisotropic samples, such as fibers or porous solids. Point collimation allows you to probe small sample areas and determine their local nanostructure, with the drawback of longer measuring times.
Ultra-fast SAXS Measurements with Metal Jet
The MetalJet x-ray source uses a high-speed jet of liquid gallium alloy as the target material with a wavelength close to copper radiation. The self-regenerating metal jet anode can accept very high power loads.
Combined with advanced electron optics the MetalJet delivers significantly higher brightness and power than any other microfocus X-ray source on the market.
Typical SAXS/WAXS/GISAXS applications over a broad range of diverse materials:
Surfactants and emulsions
Detergents, food and drug carrier materials, personal care products
Polymers and fibers
Semi-crystalline polymers, block copolymers, polymer blends, fibers
Nanostructured surfaces (GISAXS)
Layered thin-film samples, mesoporous thin films, nanoparticle superlattices
Catalysts, porous materials
Mesoporous materials, catalysts for polymerization, gas purification, fuel cell materials
Nano-filled polymer composites (carbon nanotubes, clay)
LC displays, food and drug delivery systems, membranes
Colloidal particle dispersions
Nanocrystals, pigments, quantum dots
Biomembranes, lipids, peptides, proteins in solution
Excipients, formulations, quality control