DIFFRACTION

When X-rays strike a crystalline sample they are reflected by atomic planes to produce a diffraction pattern. This contains information about the structure of chemical compounds and composite materials at the nanometre level.

Powder diffraction

Many bulk solids are composed of microcrystals, which are hard to study by standard single-crystal techniques. Powder diffraction makes it possible to analyse the structures of such materials under a wide range of conditions, e.g. while heating or cooling, or under different atmospheric conditions. The positions, intensities and shapes of the peaks in the powder diffraction pattern reveal information about the microscopic structure and strain state of a sample, and can also be used to identify which substances are present in a (possibly complex) mixture. Such information is crucial for understanding the properties and behaviour of materials.

Macromolecular crystallography

The Macromolecular Crystallography (MX) beamlines allow scientists to investigate the fundamental structures of biological macromolecules. The ESRF is recognised as a world leader in MX. Its six MX beamlines, which are all equipped with automated and robotised sample handling, can process and analyse a great number of samples quickly and efficiently. Also, the ESRF has several micro-focus beamlines dedicated to MX, which means that scientists use a high-intensity microbeam with consistent performance characteristics. This is essential since macromolecules are difficult to prepare for diffraction (up to 1000 crystals may have to be screened to obtain a useful dataset) and, to be efficient, all samples must be exposed to a beam that matches the crystal size.‚Äč

Surface diffraction

It is a technique dedicated to surfaces and interfaces structural characterizations. It can be used for performing static surface crystallography studies or for studying processes at surfaces in real time. Even if several other techniques allow a structural determination of surfaces, X-ray diffraction offers unique possibilities. Surface X-ray diffraction is not limited to free surfaces under UHV conditions but it can be applied with success to study solid interfaces. Solid/liquid interfaces and high pressure gas/solid interfaces are well adapted to the technique. This is of particular importance in the case of heterogeneous catalytic reaction where the role of the catalyser can be studied under real working conditions. In addition to crystallographic studies, surface diffraction is also suited to dynamical studies such as epitaxial growth, ion patterning, surface kinetics and phase transitions. In particular, ion erosion with ion beams in combination with grazing-incidence small-angle scattering has been employed to study the dynamical evolution of medium-range correlations during nanopatterning. The possibility of tuning the energy allows to carry out experiments at resonance energies of particular elements. This is important to investigate surface magnetism in order to determine the depth distribution and magnetisation of the resonant atoms.

MICROSCOPY AND IMAGING

3D micro- and nano-tomography is possible by scanning the X-ray beam across a sample. The ESRF also offers complementary techniques such as X-ray diffraction topography and phase-contrast imaging, which exploits the coherence of the beam.

X-ray microtomography

X-ray microtomography extends the capacities of X-ray imaging to produce pictures of ultra-high resolution and contrast. Using the same principles as medical scanners, coupled to synchrotron radiation and phase-contrast imaging, scientists can produce 2D and 3D representations with micrometre resolution. Often, samples can be studied where classical techniques do not provide any useful image at all. The ESRF provides a unique sample environment, with temperature ranges from -60° to 1600°C, as well as tension, compression and fatigue stress devices.

X-ray fluorescence microscopy

X-ray fluorescence microscopy and microspectroscopy use very fine high-quality beams, focused on extremely small areas within heterogeneous materials. For example, irradiation of trace elements within hard or soft substances enables scientists to probe deeply and isolate minute quantities of substances within a large volume. This enables new investigations, such as access to elements of major interest in the biological and material sciences, identification of heavy metals and trace element mapping, with very little preparation needed for the materials being used.

SCATTERING

Scattering reveals key information about the structure and dynamics of large molecular assemblies in low-ordered environments, which include living organisms and complex materials such as polymers and colloids.

Small- and wide-angle X-ray scattering (SAXS and WAXS)

Small- and wide-angle X-ray scattering (SAXS and WAXS) use the high brilliance of an undulator source to study condensed matter samples in liquid or solid form. It offers sub-micrometre spatial resolution and deep penetration into materials, such as colloids, polymers, surfactant membranes and proteins, even when these are opaque or turbid. SAXS and WAXS can be combined with other techniques, such as rheology and light scattering, to provide better understanding of sample behaviour on short time scales (sub-milliseconds).

SPECTROSCOPY 

Since different atoms absorb X-rays sharply at certain wavelengths, absorption and fluorescence measurements provide information about the elemental composition and chemical bonding in samples.

X-ray Absorption Spectroscopy

X-ray absorption spectroscopy techniques provide information on the atomic organisation and chemical bonding around an absorbing atom in whatever medium it is embedded, i.e. solids and liquids. There are essentially two types of absorption spectroscopy: X-ray Absorption Fine Structure (EXAFS) and X-ray Absorption Near Edge Structure (XANES). Both techniques are element-selective, which means that scientists and researchers can study and characterise elements in their “working state” within compounds.