BL10C beamline

Under construction

X-ray Absorption Spectroscopy

X-ray absorption fine structure, so-called acronym XAFS, has been used for electronic and local geometric structural refinement of interesting chemical materials under various in-situ and ex-situstates for general chemists and material scientists. The XAFS characterization is based on atomic-selective spectroscopy. Each element within the materials has an intrinsic X-ray energy for the X-ray absorption. Although several cations are positioned into same crystallographic sites, each independent geometric structure around each atom can be differentiated from another using corresponding atomic X-ray beam, Atomic-selectively. Also, crystalline-amorphous, gas- liquid-solid samples, and all kinds of material phases are possible in XAFS characterization, independent of atomic long-range ordering. Furthermore, real-time XAFS characterization is easily carried out under various external perturbed circumstances. For examples, under current or voltage for Li-ion rechargeable battery system, under UV-Vis light irradiation for photocatalyst, under applied magnetic field for spin-ordered magnetic materials. These additional devices can make your XAFS experiments much more valuable.

XAFS is modulation of X-ray absorption coefficient for increasing X-ray photon energy. XAFS can be classified into two sub spectra with respect to X-ray photon energy region, XANES and EXAFS spectra. Peak feature near absorption edge is called as XANES, X-ray Absorption Near Edge Structure, The oscillatory signal in the higher extended energy region is EXAFS, Extended X-ray Absorption Fine Structure. Basically, XANES spectra give electronic structure of material. In the K-edge spectrum, when monochromatic X-ray irradiates and photon energy gradually increases, the 1s core electron is excited to unoccupied molecular orbital or conduction band. Since the unoccupied molecular orbital is sensitive to local structural environments around central atom, the peak feature can show various electronic structure such as oxidation state, bond covalency, site symmetry of linear, tetrahedral, square planer, octahedral, asymmetric environment, and furthermore spin states, low spin and high spin states. On higher energy X-ray irradiation, 1s core electron is emitted from central atom beyond continuum level, as a form of photoelectron wave, with a proper kinetic energy, making outgoing wave. The outgoing photoelectron travel into condensed matter phase and can be scattered with neighboring atoms, generating incoming wave. Simultaneously, the outgoing wave can interfere with incoming wave. So the constructive and destructive interferences between two waves, make oscillatory signal of X-ray absorption coefficient in the extended energy region. This is EXAFS Because this EXAFS signal results from the scattering with neighboring atoms, the analysis of the oscillatory signal can give geometric structural information around central atom such as interatomicdistance between central and neighboring atoms, coordination number of neighboring atoms, Debye-Waller factor showing atomic disorder around central atom. EXAFS spectra gives information about neighboring atoms, Which atomic element, How long distance, How many numbers, How much disordered.

BL10C XAFS Beamline @ Pohang Accelerator Laboratory (PAL)

In current, Pohang Accelerator Laboratory has three operating XAFS beamlines(Bending BL7D XAFS, Undulator BL8CNanoprobe XAFS and Multipole-Wiggler BL10C XAFS beamlines), and plan to construct two new beamlines in the near future, Multipole-Wiggler ultrafast/energy-dispersive XAFS and Bending low-energy XAFS beamlines. XAFS beamline consists of three kinds of major optical components; Light Source, Optical component, and End-station equipped with various detection system. Double crystal monochromator(DCM) can make monochromatic X-ray. XAFS data is collected with transmittance mode in End-station which deserves to be your temporary Laboratory. Incident and transmitted X-ray intensities are monitored with proper gas-filled ionization chambers or fluorescence detector.

BL10C XAFS beamline in PLS welcomes all scientists who investigate structure-property relationship in energy-storage & conversion materials during an electrochemical or catalytic event, synthetic mechanism through nanochemistry, environmental (chemical/earth) materials before/after sample treatment, and active metal site in bio-inorganic materials. Thus, essential purpose of highly effective XAFS spectroscopy is to analyze electronic and local geometric structure of your materials, under Non-destructive, Atomic-selective, Time-resolved circumstances, especially most effective in the Li-ion rechargeable battery system. This XAFS spectroscopic approach helps your research much more improved and speeds your research processes.