Experimental Techniques available for Materials Research
One of the advantages of synchrotron radiation produced by the CAMD accelerator is the continuous spectrum of light from the infrared to hard X-rays. Beamlines allow one to select a particular energy of this light enabling a broad variety of experimental techniques to be applied to materials science. The techniques that are currently available at CAMD are described here and the acronyms are defined at the bottom of this page. CAMD also has the flexibility to implement new methods as the need arises.
X-ray Absorption Spectroscopy (XAS, EXAFS, XANES)
Each element has its own specific electronic energy levels and they absorb X-rays (XAS) at energies characteristic of those levels. Near the absorption edge, the spectra may contain fine structure (XANES) that reveals the chemical environment of the absorbing atom. Farther from the edge the spectra (EXAFS) reveals the spacings of neighboring atoms.
Soft X-ray Absorption Spectroscopy (NEXAFS, XANES)
This is a part of X-ray absorption spectroscopy, generally, for elements with absorption edges located below 1,000 eV. The spectrum is often called the near edge X-ray absorption fine structure (NEXAFS). Carbon K-edge, nitrogen K-edge, oxygen K-edge, and the first row of transition-metals' L-edges are often studied.
X-ray Fluorescence Spectroscopy
Each element has characteristic X-ray emission lines. The elemental composition of any material can be determined with X-ray Fluorescence Spectroscopy. The material is excited with an initial energy and all the fluorescence photons, originating from emission lines, are collected with an energy sensitive fluorescence detector. This XRF spectrum gives an overview of the energy and number of all detected photons in the selected energy range. The usual energy range at CAMD is 1-5 keV for low energy XRF, detecting Si, P, S, Cl, K, Ca, Ag etc., and 3-15 keV for high energy XRF, detecting all transition metals, Pb, Au, and others.
X-ray Diffraction (XRD)
X-ray diffraction (XRD) patterns provide interference patterns that allow one to evaluate the atomic structure of crystalline materials, powders, small molecules or larger ordered molecules like protein crystals.
Small Angle X-ray Scattering (SAXS, WAXS, GISAXS)
This technique provides structural information and dynamical processes of large molecular assemblies in non-crystalline materials. Many complex materials such as polymers and colloids, and living organisms can be investigated.
The atomic and molecular structure of protein crystals can be investigated by X-ray diffraction which is able to determine the three-dimensional structure of large biological molecules, proteins and enzymes. This is important in understanding the origin of disease and developing new drugs to combat it.
Microtomography is similar to a medical CAT scan but with about 1000 times better spatial resolution, and with synchrotron radiation it is elementally sensitive. It is accomplished by imaging by sections and reconstructing a 3D model of the object under analysis. It can be used in radiology, archaeology, biology, atmospheric science, geophysics, oceanography, plasma physics, materials science, and other sciences.
Ultraviolet (UV) Absorption Spectroscopy
Ultra-violet absorption spectroscopy of gas samples can be performed, providing information on electronic structure. In addition, UV and VUV photo irradiation effects on materials can be studied.
The energies and directions of electrons emitted from a sample are studied, providing information on the electronic structure (UPS), chemical adsorbates and reactions, and the electronic band structure (ARPES) as well as providing information on elemental oxidation states (XPS).
Infrared (IR) Spectromicroscopy
The determination of functional groups in organic and inorganic molecules can be performed by measuring transmission or reflection of IR energy. Special optics allows position-sensitive imaging of specimens. This method has broad applications in biology, chemistry, archaeology and environmental analyses.
Acronyms
- XAS = X-ray Absorption Spectroscopy
- XANES = X-ray Absorption Near-Edge Spectroscopy
- EXAFS = Extended X-ray Absorption Fine Structure
- NEXAFS = Near Edge X-ray Absorption Fine Structure
- XRF = X-ray Fluorescence Spectroscopy
- SAXS = Small Angle X-Ray Scattering
- WAXS = Wide Angle X-Ray Scattering
- GISAXS = Grazing-Incidence Small-Angle X-Ray Scattering
- UV = Ultra-Violet
- UPS = Ultraviolet Photoelectron Spectroscopy
- ARPES = Angle-Resolved Photoelectron Spectroscopy
- XPS = X-ray Photoelectron Spectroscopy
- IR = Infra-Red