X-ray Absorption Spectroscopy (XAS)
X-ray absorption spectroscopy (XAS) is a chemical state analysis technique used for research in a broad range of disciplines. This technique involves measuring the transmission (or fluorescence) of x-rays as a function of incrementing x-ray energy in small steps at energies close to the absorption edge. The absorption edge energy corresponds to the energy required to eject an electron from an electron shell) of an element of interest (e.g. Fe). Small changes in how x-rays are absorbed near an atom’s absorption edge provide insight into the state of the electrons.
XAS is comprised of two regions:
- X-ray absorption near edge structure (XANES/NEXAFS): Comprising x-ray energies nearest to the absorption edge (~100 eV around the edge), this region exhibits sharp resonance peaks. Generally, the region is sensitive to local atomic states such as oxidation states and symmetry.
- Extended fine structure (EXAFS): This region contains features appearing after the XANES region and up to ~1000 eV or greater than the absorption edge. EXAFS appears as gentle oscillations in the measured signal and is caused by scattering of the ejected electron by surrounding atoms. EXAFS measurements can be used to measure neighboring atom information, including bond lengths and chemical coordination environments.
Sigray produces two laboratory XAS systems, both with capabilities rivaling synchrotron beamlines. The first is the V210, an optics-based transmission XAS with low Z (atomic number) capabilities down to phosphorus and with micro-XAS mapping capabilities at 100 µm spot sizes. The second is the H2000, an XAS system with both transmission and fluorescence XAS capabilities. Both systems offer excellent throughput.