NanoTerasu Coalition Beamlines: Glossary
GLOSSARY
Glossary
1. Analysis of Electronic/Chemical States and Local Structure (Spectroscopy)
XAFS / XAS (X-ray Absorption Fine Structure / X-ray Absorption Spectroscopy)
A technique that measures X-ray absorption while varying the X-ray energy. It is broadly divided into two regions:
- XANES: Region near the absorption edge. Provides information on the "valence (oxidation state)" and "chemical bonding" of the target element.
- EXAFS: Broad region on the high-energy side of the absorption edge. Provides precise information on the "local structure" (number, type, and distance of neighboring atoms) around the target element.
XAFS / XAS Measurement Modes (Detection Methods)
In XAFS measurements, the depth and precision of the information obtained depend on what is counted (transmitted light, electrons, or fluorescence) after X-ray irradiation.
Transmission Method
- Principle: Directly measures the intensity of X-rays transmitted through the sample.
- Provides: "Average information (bulk information)" of the entire sample. Yields the most standard and precise data.
- Note: Requires the sample to be processed "thinly and uniformly" to allow appropriate X-ray transmission. If too thick or uneven, correct data cannot be obtained.
TEY (Total Electron Yield)
- Principle: Measures "all electrons" emitted from the sample upon X-ray irradiation as a sample current.
- Provides: Information from a very shallow region, about a few nm (nanometers) from the surface.
- Features: Very commonly used in the soft X-ray region. While highly sensitive, it is strongly affected by surface contamination and oxidation, making sample cleaning crucial.
PEY (Partial Electron Yield)
- Principle: Selectively measures emitted electrons with specific energies (or above a certain energy).
- Provides: Highlights specific surface states even more than TEY.
- Features: By cutting off low-energy secondary electrons (noise), it improves the signal-to-noise (S/N) ratio and further enhances surface sensitivity.
FY (Fluorescence Yield)
- Principle: Measures the intensity of "fluorescent X-rays" emitted after X-ray absorption.
- Provides: Information from a relatively deep region, about a few hundred nm to several μm (micrometers) from the surface.
- Features: Looks slightly deeper into the interior compared to electron yield methods. It is also suitable for in-situ (operando) measurements in air or gas atmospheres, as it does not require a vacuum.
NanoTerasu Features:
- BL08W: Optimized for full-scale EXAFS analysis (e.g., interatomic distance calculation) in the tender to hard X-ray region.
- BL08U / BL14U: Excellent for observing the surface chemical states (XANES) of light elements and transition metals.
XPS / ESCA (X-ray Photoelectron Spectroscopy)
Measures "photoelectrons" emitted upon X-ray irradiation. Identifies element types and bonding states on the surface (a few nm).
- AP-XPS: Measurement under gas atmosphere. Enables "in-situ observation" such as during catalytic reactions.
- HAXPES: Uses hard X-rays to non-destructively investigate electronic states inside the material (tens of nm).
- Nano-ESCA: Visualizes chemical states in micro-regions using a nano-focused X-ray beam.
XRF (X-ray Fluorescence Analysis)
Measures element-specific light emitted upon X-ray irradiation. Reveals element types and their distribution (mapping).
- Features: At BL08W, combining it with XRD allows simultaneous evaluation of structure and elemental distribution.
ARPES (Angle-Resolved Photoemission Spectroscopy)
Measures the "angle" and "energy" of emitted photoelectrons. Reveals the mobility of electrons (band structure) within the material.
RIXS (Resonant Inelastic X-ray Scattering)
Precisely measures energy changes of scattered light. Dissects extremely low-energy electronic states such as spin and orbital excitations.
2. Analysis of Magnetic Properties
XMCD (X-ray Magnetic Circular Dichroism)
Measures the difference in absorption using left- and right-circularly polarized X-rays.
- Provides: "Magnetic properties (spin and orbital moments)" of a specific element.
- Methods: Magnetic domain imaging via microscopic observation, or average magnetic evaluation via non-focused beams.
3. Analysis of Crystal and Nano Structures (Diffraction / Scattering)
XRD (X-ray Diffraction)
Utilizes the diffraction phenomenon of X-rays by crystals. Investigates atomic arrangements and crystalline forms (phase identification) of materials.
⚠️ Note regarding BL08W: This instrument is configured with a powder diffractometer and XRF. It does not support residual stress measurements.
SAXS / WAXS (Small-Angle / Wide-Angle X-ray Scattering)
Measures the scattering angles of transmitted/scattered X-rays.
- SAXS: Evaluation of nano-sized structures (particle size, voids, self-assembled structures).
- WAXS: Evaluation of regularity at the atomic/molecular level (molecular orientation, aggregation state).
4. Morphology / 3D Imaging (Coherent Analysis)
CT (X-ray Computed Tomography)
Reconstructs 3D structures from multi-directional transmission images. Reveals 3D shapes, voids/cracks, heterogeneous mixing, and fracture processes.
- Use of Coherence: BL09W (white) and BL10U (monochromatic) use light coherence to clearly visualize complex structures with small density differences, which were difficult to see with conventional X-ray CT.
STXM / SXM (Scanning Transmission / Scanning X-ray Microscopy)
Scans with a focused X-ray beam to image nanoscale elemental distributions and chemical bonding states (microspectroscopy).
5. Nano / 3D Structures (Advanced Methods)
Ptychography
A lensless imaging technique that computationally reconstructs images from scattering patterns.
- Provides: Visualization of internal structures with extreme resolution on the scale of a few nanometers at best, surpassing the physical limits of X-ray microscopes. Although time-consuming, it is the method with the highest spatial resolution at NanoTerasu for visualizing irregular 3D structures. (Advanced Measurement)