Dictionary
4D CT
4D / Time-Resolved Computed Tomography
4D Computed Tomography (4D CT, or time-resolved tomography) means repeating tomographic acquisition fast enough to follow changes inside a sample over time, treating time as the fourth dimension alongside the three spatial ones. Synchrotron sources make this practical, with full 3D scans now achievable in seconds, sub-second timescales, or even faster for some samples. 4D CT is used to watch crack propagation under load, dendrite growth during solidification, foam formation, drying and infiltration, chemical reactions inside catalyst pellets, and the cycling of battery electrodes — any process where the question is not just what the structure is but how it evolves.
APXPS
Ambient Pressure X-ray Photoelectron Spectroscopy
Ambient Pressure X-ray Photoelectron Spectroscopy (APXPS) extends conventional XPS to work under gas pressures up to several millibar, enabling surface chemical analysis under realistic reaction, environmental, or processing conditions rather than the ultra-high vacuum that XPS normally requires. This makes it possible to study catalytic reactions, oxidation, corrosion, gas–surface interactions, and electrochemical interfaces as they actually happen. APXPS reveals how surface composition and chemical states evolve in response to changing gas atmosphere, temperature, or humidity — information critical for developing catalysts, coatings, sensors, batteries, fuel cells, and other energy materials.
ARPES
Angle Resolved Photoelectron Spectroscopy
Angle-Resolved Photoelectron Spectroscopy (ARPES) maps the electronic band structure of materials by measuring both the energy and the emission angle of photoelectrons ejected from a sample surface. It directly visualises how electrons are distributed and how they move through a material, giving fundamental insight into electrical conductivity, magnetism, superconductivity, and exotic quantum phases. ARPES is essential for characterising semiconductors, quantum materials, thin films, heterostructures, and surface electronic states, and underpins the development of next-generation electronics, spintronic devices, and quantum technologies.
BioSAXS
Biological Small-Angle X-ray Scattering
Biological Small-Angle X-ray Scattering (BioSAXS) characterises the size, shape, conformation, and interactions of proteins, nucleic acids, and other biomolecules directly in solution — no crystals required. It captures the native solution-state behaviour of macromolecules, including conformational flexibility, oligomeric states, and structural responses to changes in pH, temperature, ligand binding, or concentration. BioSAXS is valuable for validating computational models, assessing protein quality and stability in biopharmaceutical development, and studying disordered or flexible systems that resist crystallisation.
CT
Computed Tomography
Computed Tomography (CT) is the most common form of tomography and refers to the computational reconstruction of a three-dimensional volume from many two-dimensional projections acquired at different angles. The term originated in medical imaging but is now widely used for any X-ray-based or neutron-based tomographic measurement in materials science and engineering, typically with millimetre-to-micrometre resolution. Synchrotron CT extends laboratory CT by adding much higher flux, coherence, monochromatic beams, and access to alternative contrast mechanisms (phase, diffraction, fluorescence), allowing finer structures, dynamic processes, and chemically specific imaging that laboratory instruments cannot reach. CT is used across the full range of industrial R&D — quality control, failure analysis, inspection of joints and welds, characterisation of composites, batteries, additively manufactured parts, electronics, and biological tissue.
Diffraction
Diffraction (general)
Diffraction is the coherent elastic scattering of waves — X-rays, neutrons, or electrons — by long-range ordered arrangements of atoms or molecules, producing the characteristic Bragg patterns that reveal crystalline structure. It is one of the most powerful tools for determining how atoms are arranged: crystal structure, phase composition, crystallinity, texture, strain, and (with total scattering / PDF) local atomic order in disordered systems. Diffraction is technically a special case of the broader Scattering family (see separate entry), restricted to samples with crystalline order, but in practice the two are treated as distinct sets of techniques because they answer different structural questions and use different sample preparation and analysis methods. Common synchrotron-based variants include XRD, PXRD, SCXRD, GI-XRD, and PDF; macromolecular crystallography (MX) is a diffraction-based life-science workflow with its own beamlines; neutron diffraction and electron diffraction are complementary methods used at neutron and electron sources. For non-crystalline, partially ordered, or solution samples, see the Scattering family entry (SAXS, WAXS, BioSAXS, GISAXS / GIWAXS, XRR).
Electron Diffraction
Electron Diffraction
Electron Diffraction uses electrons rather than X-rays or neutrons to probe atomic structure, performed in transmission electron microscopes or dedicated instruments rather than at synchrotron beamlines. It is included here because users sometimes reach a synchrotron facility looking for it, but it sits outside the scope of synchrotron and neutron measurement. For nanocrystalline or single-particle samples below the size accessible to synchrotron SCXRD, microED (single-particle electron diffraction) and 3D electron diffraction at electron-microscopy facilities are the appropriate methods.
EXAFS
Extended X-ray Absorption Fine Structure
Extended X-ray Absorption Fine Structure (EXAFS) is the oscillatory part of an XAS spectrum that extends from roughly 50 eV above an element’s absorption edge out to several hundred or thousand eV. The oscillations encode the distances to neighbouring atoms, the number of neighbours, and the type of neighbour around the absorbing element, giving a quantitative picture of local atomic structure even in systems without long-range order. EXAFS is widely used to characterise catalysts (active-site coordination), batteries (local structure around the redox-active element), amorphous and dilute systems, and biological metal sites, and is routinely performed under realistic operating conditions.
Fragment Screening
Fragment Screening
Fragment Screening uses high-throughput X-ray crystallography to systematically test libraries of small chemical compounds against a protein target, identifying which fragments bind and exactly where they attach. The atomic-resolution structural data reveal binding modes and interactions that guide the design of larger, more potent molecules, making it a key early step in drug discovery and molecular design. The approach can also be used to map functional sites on enzymes and other biomolecular targets.
GI-XRD
Grazing-Incidence X-ray Diffraction
Grazing-Incidence X-ray Diffraction (GI-XRD) is XRD performed at a very shallow angle of incidence so that the X-rays interact mainly with the top few nanometres to micrometres of a sample. This makes it highly sensitive to surfaces, thin films, and multilayers, where the bulk material would otherwise dominate the signal. GI-XRD is used to characterise crystalline phases, texture, and strain in semiconductor thin films, photovoltaic stacks, OLED layers, hard coatings, battery electrode surfaces, and corrosion layers. Closely related grazing-incidence small- and wide-angle scattering methods (GISAXS and GIWAXS) extend the same geometry to longer length-scale ordering in thin films and self-assembled layers — see separate entry.
GISAXS / GIWAXS
Grazing-Incidence SAXS / WAXS
Grazing-Incidence Small- and Wide-Angle X-ray Scattering (GISAXS and GIWAXS) are surface-sensitive scattering techniques that use a very shallow incidence angle to probe ordering in thin films, surfaces, and self-assembled layers. GISAXS reveals nanoscale structure — particle sizes, repeat distances, pore structures, lateral and vertical ordering — while GIWAXS resolves atomic and molecular packing at wide angles. The combination is widely used for organic photovoltaics, OLEDs, perovskite solar cells, semiconductor processing, block-copolymer self-assembly, coatings, and any system where the structure of a thin film (rather than a bulk material) controls performance.
In-situ / Operando CT
In-situ and Operando Computed Tomography
In-situ and Operando Tomography refer to tomographic measurements performed while the sample is exposed to a real-world environment or actively functioning — under load, at elevated temperature, in a gas atmosphere, under flowing liquids, during chemical reaction, or during electrochemical cycling. The synchrotron flux makes these measurements practical by keeping scan times short, so the underlying process is not perturbed. In-situ and operando tomography are central to understanding how materials and devices fail, age, or perform in their actual operating conditions, with heavy industrial use in batteries, fuel cells, catalysts, metals processing, composites under load, and pharmaceuticals.
micro-CT
Micro-Computed Tomography (μCT / SR-μCT)
Micro-Computed Tomography (micro-CT or μCT) is X-ray CT with micrometre-scale resolution, typically in the 0.5–50 μm range. At a synchrotron (sometimes called SR-μCT, for Synchrotron-Radiation μCT) the high flux and monochromatic beam give much faster scans, better contrast, and higher resolution than laboratory μCT. It is the workhorse 3D imaging method for materials characterisation across porosity and pore networks, fibre orientation in composites, microstructure of additively manufactured parts, dendrites in metals, soft tissue, and food microstructure, and is well suited to in-situ studies under mechanical loading, heating, or fluid flow.
MX
Macromolecular X-Ray Crystallography
Macromolecular X-ray Crystallography (MX) is a diffraction-based method specialised for determining the three-dimensional atomic structure of proteins, enzymes, nucleic acids, and other biological macromolecules from crystallised samples. The resulting structural models reveal active sites, binding pockets, and conformational details essential for understanding biological function, designing drugs, and engineering enzymes. MX underpins much of structure-based drug design in the pharmaceutical and biotech industries and is supported by extensive sample-handling automation at modern synchrotron beamlines.
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nano-CT
Nano-Computed Tomography
Nano-Computed Tomography (nano-CT) is X-ray CT pushed to sub-micrometre and nanometre resolution, typically achieved through high-resolution X-ray optics, full-field zone plates, or ptychographic reconstruction. It allows non-destructive 3D imaging of internal structures down to tens of nanometres, accessing features that are far below the reach of conventional μCT — for example, individual particles inside a battery electrode, intergranular structure in alloys, network structure in catalyst supports, or organelles inside cells. Nano-CT is essential for understanding how nanoscale architecture controls macroscopic performance in energy materials, electronics, structural materials, and biological tissue.
Pair Distribution Function Analysis
Pair Distribution Function analysis (PDF) extracts the distribution of interatomic distances in a material directly from a diffraction pattern, by analysing both the Bragg peaks and the diffuse scattering between them. Because PDF works on amorphous, nanocrystalline, and disordered materials — not just well-ordered crystals — it accesses local atomic structure where conventional XRD cannot. It is the standard method for studying glasses, liquids, nanoparticles, battery cathode materials (especially during charge / discharge), amorphous pharmaceuticals, and any system where local order matters more than long-range crystallinity. Synchrotron sources provide the high-energy X-rays needed for high-quality PDF data.
PTYCHO-CT
Ptychographic Computed Tomography
Ptychographic Computed Tomography (PTYCHO-CT) extends X-ray ptychography to three dimensions by acquiring ptychographic projections of a sample at many rotation angles and combining them tomographically. Because ptychography recovers the phase of the transmitted beam without optical limits, PTYCHO-CT can reach nanometre-scale 3D resolution and produce quantitative images of internal structure throughout the sample. It is used to image battery materials, catalysts, integrated circuits, biological cells, and any sample where the internal nanostructure controls performance and would otherwise be inaccessible non-destructively.
Ptychography
X-ray Ptychography
X-ray Ptychography is a computational imaging technique that achieves nanometre-scale resolution by scanning a coherent X-ray beam across a sample and reconstructing both the amplitude and the phase of the transmitted beam from many overlapping diffraction patterns. Because it recovers the phase information directly, it produces quantitative images of internal structure and composition without the resolution limits of physical X-ray lenses. Ptychography can image interfaces, defects, and compositional gradients in thin films, coatings, biological tissue, and nanostructured materials, and is especially powerful for samples where conventional microscopy lacks contrast or resolution. It can be performed in 2D or extended to 3D through ptychographic tomography (see PTYCHO-CT).
PXRD
Powder X-ray Diffraction
Powder X-ray Diffraction (PXRD) is the form of XRD applied to powders and polycrystalline samples, where many small crystallites contribute simultaneously to the diffraction pattern. It is the standard technique for phase identification, quantitative phase analysis, crystallite-size and strain estimation, and detection of impurities or polymorphs. Synchrotron PXRD offers far higher resolution and signal-to-noise than laboratory diffractometers, making it possible to detect minor phases at low concentration, distinguish closely related polymorphs, and follow phase changes in real time during heating, gas exposure, or electrochemical cycling. It is heavily used in pharmaceuticals (polymorph screening), catalysts, battery materials, cement, ceramics, and minerals processing.
SAXS
Small-Angle X-ray Scattering
Small-Angle X-ray Scattering (SAXS) characterises structures at the nanometre scale (roughly 1–100 nm) by measuring how X-rays scatter at low angles. It reveals particle sizes and shapes, repeat distances, pore structures, surface areas, and how components self-organise within a material. SAXS works on a broad range of samples — solutions, suspensions, gels, films, fibres, powders, and bulk solids — and measurements are fast enough to follow structural changes in real time during processing, flow, heating, or chemical reactions. It is frequently combined with WAXS to cover both nanoscale and atomic-scale ordering in the same experiment, and is widely used in pharmaceuticals, polymers, coatings, food, and personal-care products.
Scattering
Scattering (general)
Scattering is the family of techniques that probe material structure by measuring how X-rays (or neutrons) deflect from their incoming path when they pass through a sample, without requiring the long-range crystalline order that diffraction needs. The angular distribution of the scattered radiation encodes structural information at different length scales — small angles for nanometre-scale features (particles, pores, biomolecules), wide angles for atomic and molecular packing, grazing incidence for thin-film and surface structure, and near-zero angles (reflectivity) for layered film thickness and density. Scattering techniques are widely used for solutions, suspensions, gels, films, fibres, and disordered or partially ordered materials where diffraction is not applicable. Common synchrotron variants include SAXS, WAXS, BioSAXS, GISAXS / GIWAXS, and X-ray Reflectivity (XRR), each described as a separate entry.
SCXRD
Single-Crystal X-ray Diffraction
Single-Crystal X-ray Diffraction (SCXRD) determines the atomic structure of a material from the diffraction pattern of a single crystalline sample, giving a complete three-dimensional structural model with bond lengths, bond angles, and atomic positions at high accuracy. It is the gold standard for solving the structure of new chemical compounds — pharmaceutical actives, organic semiconductors, metal-organic frameworks (MOFs), coordination complexes, energetic materials, and small biological molecules. Synchrotron SCXRD adds the ability to handle very small, weakly diffracting, or radiation-sensitive crystals that laboratory diffractometers cannot, and to track structural changes under temperature, pressure, light, or electric field.
STXM
Scanning Transmission X-ray Microscopy
Scanning Transmission X-ray Microscopy (STXM) creates spatially resolved images of thin samples by rastering a focused X-ray beam across the sample and measuring the transmitted intensity. By tuning the photon energy across elemental absorption edges, STXM maps not only where specific elements are located but also their oxidation states and chemical bonding, combining imaging with spectroscopy at nanoscale resolution. It is well suited to studying soft matter, polymers, biological tissue, environmental particles, catalysts, and energy materials where chemical heterogeneity at the micro- to nanoscale matters.
Tomography
X-ray Tomography
Tomography is a non-destructive imaging technique that reconstructs a three-dimensional representation of an object from a series of two-dimensional projections taken from different viewing angles. At a synchrotron, the high X-ray flux and coherence make it possible to acquire those projections at much higher resolution, faster, and with richer contrast mechanisms than laboratory CT, enabling internal imaging of structures down to the nanometre scale and in real time during processes. Variants of tomography are distinguished by the radiation source (X-ray, neutron, electron), the spatial resolution (CT, micro-CT, nano-CT), the contrast mechanism (absorption, phase, diffraction, fluorescence, ptychographic), and the experimental mode (static, 4D / time-resolved, in-situ / operando). Tomography is widely used across materials science, energy research, life sciences, engineering, and cultural heritage to reveal internal structures, density variations, elemental distributions, crystalline phases, defects, and how these evolve under realistic conditions.
WAXS
Wide-Angle X-ray Scattering
Wide-Angle X-ray Scattering (WAXS) probes atomic and molecular-scale ordering in materials by collecting X-rays scattered at wide angles. It reveals crystalline phases, degree of crystallinity, molecular packing, and short-range structural order. WAXS is often paired with SAXS in the same experiment to capture both nanoscale and atomic-scale structure simultaneously, which makes the combination especially useful for hierarchical materials such as cellulose, wood, fibres, polymers, and other bio-based materials. The technique applies to powders, films, fibres, liquids, and solutions, and is well suited to tracking structural transformations during processing, heating, stretching, or chemical reactions in real time.
XANES
X-ray Absorption Near-Edge Structure
X-ray Absorption Near-Edge Structure (XANES, sometimes called NEXAFS in the soft X-ray range) is the part of an XAS spectrum within roughly ±50 eV of an element’s absorption edge. The shape of this region is dominated by the oxidation state, coordination geometry, and electronic structure around the absorbing atom, making XANES the standard method for determining oxidation state in catalysts, batteries, environmental samples, and biological systems. It is element-specific, works on amorphous and dilute samples, and is routinely used in-situ and operando to track how the chemical state of a specific element changes during reaction, electrochemical cycling, corrosion, or processing.
XAS
X-ray Absorption Spectroscopy
X-ray Absorption Spectroscopy (XAS) probes the oxidation state, local atomic environment, and electronic structure around a selected element by measuring how a sample absorbs X-rays as a function of energy across the element’s absorption edge. It is element-specific and does not require crystalline order, which makes it applicable to amorphous, dilute, and operando systems where many other techniques struggle. XAS is conventionally divided into two regions of the absorption spectrum: XANES (X-ray Absorption Near-Edge Structure), the region close to the absorption edge that is most sensitive to oxidation state and electronic structure; and EXAFS (Extended X-ray Absorption Fine Structure), the oscillations further from the edge that give quantitative information on bond distances and the number and type of neighbouring atoms (each described as a separate entry). XAS is a core technique for studying catalysis, electrochemistry, environmental chemistry, corrosion, functional materials, and biological systems under realistic operating conditions.
XCT
X-ray Computed Tomography
X-ray Computed Tomography (XCT, or X-ray CT) is the X-ray-based form of computed tomography, in which X-rays passing through a sample at many angles are used to reconstruct a 3D image of its interior. It is by far the most widely used tomography modality and forms the basis for the sub-methods micro-CT, nano-CT, phase-contrast CT, XRD-CT, XRF-CT, and ptychographic CT (each described as a separate entry). Synchrotron XCT can image samples non-destructively from millimetre to nanometre resolution, with much higher signal-to-noise and shorter scan times than laboratory CT. It is widely used in industry for inspecting composites, battery electrodes, additively manufactured parts, electronics, geomaterials, pharmaceuticals, biological tissue, and food products.
XPCT
X-ray Phase-Contrast Tomography
X-ray Phase-Contrast Tomography (XPCT) reconstructs a 3D image of a sample using the phase shift induced in X-rays as they pass through the material, rather than (or in addition to) the absorption used by conventional CT. Because soft materials, polymers, low-density tissue, and other weakly absorbing samples produce strong phase shifts but little absorption contrast, XPCT can reveal internal structures in samples where standard X-ray CT would show essentially no contrast. It is particularly powerful for soft tissue, neural networks, fibre composites, paper and wood, foams, and any sample where the components are made of light elements with similar densities. XPCT relies on the coherence of synchrotron beams and is widely used in biomedical research, materials science, food science, and cultural heritage.
XPEEM
X-ray Photoemission Electron Microscopy
X-ray Photoemission Electron Microscopy (XPEEM) produces spatially resolved images of surface chemistry and electronic structure by collecting the photoelectrons emitted from a sample under X-ray illumination. It combines the chemical sensitivity of XPS and XAS with sub-micrometre imaging, and can map elemental, chemical, electronic, and magnetic contrast across a sample surface. XPEEM is used to study heterogeneous catalysts, magnetic and electronic thin-film devices, corrosion phenomena, and any system where surface chemical or electronic properties vary spatially on the micro- to nanoscale.
XPS
X-ray Photoelectron Spectroscopy
X-ray Photoelectron Spectroscopy (XPS) determines the elemental composition and chemical bonding of a material’s surface by measuring the kinetic energy of photoelectrons emitted when the sample is illuminated with X-rays. It is sensitive to the outermost few nanometres (typically ~10 nm) and can distinguish the same element in different chemical states — for instance, metallic versus oxidised forms of iron. XPS is widely used to characterise surface treatments, coatings, contamination, corrosion, adhesion interfaces, catalytic surfaces, and thin-film composition across metals, polymers, ceramics, and semiconductor materials.
XRD
X-ray Diffraction
X-ray Diffraction (XRD) is the X-ray-based branch of the Diffraction family, used to determine crystalline structure by analysing how X-rays scatter from ordered arrangements of atoms in a sample. It identifies crystalline phases, measures unit-cell dimensions, detects structural distortions, quantifies phase mixtures, and reveals texture and strain depending on the experimental geometry. Specialised variants address specific sample types and questions: PXRD for powders and polycrystalline materials, SCXRD for single crystals, GI-XRD for thin films and surfaces, MX for biological macromolecular crystals, and PDF for amorphous or nanocrystalline materials (each described as a separate entry). Synchrotron XRD provides far greater sensitivity, resolution, and speed than laboratory instruments, enabling in-situ and operando studies that track structural transformations during heating, gas exposure, electrochemical cycling, or chemical reactions in real time, with applications across pharmaceuticals, catalysts, battery materials, geology, and food science. For non-crystalline samples and structures on the 1–100 nm scale, see the Scattering family (SAXS, WAXS, BioSAXS, GISAXS / GIWAXS, XRR).
XRD Diffraction
X-ray Diffraction
Used for atomic structure determination of materials, e.g. pharmaceuticals, catalysts, battery materials, and proteins.
XRD-CT
X-ray Diffraction Computed Tomography
X-ray Diffraction Computed Tomography (XRD-CT) combines X-ray diffraction with tomographic reconstruction, producing 3D maps not just of where material is in a sample but of which crystalline phases are present at each voxel. A diffraction pattern is recorded for each beam position and rotation angle, and the reconstruction yields a spatially resolved 3D phase map of the sample interior. XRD-CT is uniquely suited to studying heterogeneous materials where the local crystalline composition matters and varies in three dimensions — operando catalyst pellets, working battery electrodes, pharmaceutical tablets with mixed polymorphs, geological samples, and additively manufactured parts.
XRF
X-ray Fluorescence Spectroscopy
X-ray Fluorescence Spectroscopy (XRF) determines the elemental composition of materials by detecting the characteristic fluorescent X-rays each element emits when excited by an incoming X-ray beam. Synchrotron-based XRF achieves high sensitivity and, when combined with focused beams, can map elemental distributions across surfaces and within thin sections at micro- to nanoscale resolution. It is non-destructive and applies to a wide range of sample types — metals, minerals, biological tissue, environmental samples, coatings, and devices — making it a versatile tool for composition analysis, trace-element detection, contamination mapping, and quality assurance.
XRF-CT
X-ray Fluorescence Computed Tomography
X-ray Fluorescence Computed Tomography (XRF-CT) combines XRF with tomographic reconstruction to produce 3D maps of elemental distributions inside a sample. By scanning the sample through a focused X-ray beam and recording the fluorescent X-rays emitted from each voxel as the sample is rotated, XRF-CT reconstructs where each element is located in three dimensions, often at sub-micrometre resolution. The technique is particularly valuable for trace-element analysis in biological tissue, soil and environmental samples, catalysts, electrochemical devices, geomaterials, and any system where the spatial distribution of specific elements drives function or degradation.
XRR
X-ray Reflectivity
X-ray Reflectivity (XRR) measures how X-rays reflect from a sample surface at very shallow angles to determine the thickness, density, and roughness of thin films and multilayers. The technique is non-destructive, works on amorphous and crystalline films alike, and routinely measures layer thicknesses from sub-nanometre to a few hundred nanometres with sub-Ångström precision on density and surface or interface roughness. XRR is a workhorse in semiconductor processing, hard-coating development, photovoltaics, magnetic recording media, and any application where the structure of thin films stacked on a substrate controls device performance. It is complementary to GI-XRD (which probes crystalline phases in the same films) and GISAXS / GIWAXS (which probe lateral nanostructure and molecular packing).
