X-ray absorption spectrometer (XAS) is an advanced spectroscopic technology based on synchrotron radiation sources. By analyzing the signal changes after the interaction between X-rays and matter, it reveals the elemental composition, electronic states, and microstructure information of materials. Its core lies in using X-rays to excite the inner layer electrons of atoms, and obtaining the "fingerprint" information of the local structure of the substance by detecting the fluorescence or Auger electron signals generated by electron transitions.
Technical principle: The "microscope" of electronic transitions
When the X-ray energy reaches the ionization threshold of the inner layer electrons of an atom, it triggers electron transitions and forms an absorption edge. According to different energy ranges, XAS is divided into two key regions:
X-ray Absorption Near Edge Structure (XANES): The absorption edge ranges from 10 eV to 50 eV, reflecting the electronic state and chemical environment. For example, by analyzing the position of the edge front peak in XANES spectra, the valence state of metal ions can be determined (such as the difference in absorption edge energy between Fe ² ⁺ and Fe ³ ⁺, which is about 2-3 eV).
Extended X-ray Absorption Fine Structure (EXAFS): 50 eV to 1000 eV behind the absorption edge, revealing structural parameters such as interatomic distance and coordination number. The interference effect generated by the scattering of photoelectrons and surrounding atoms causes the absorption coefficient to exhibit periodic oscillations, and the bond length (with an accuracy of 0.01 Å) and coordination number can be resolved through Fourier transform.
Technical advantages: Non destructive, in-situ, high sensitivity
XAS has no strict requirements for sample morphology and can analyze powders, films, liquids, and even gases without damaging the sample. By combining the high brightness and continuously adjustable wavelength characteristics of synchrotron radiation sources, XAS can achieve in-situ testing (such as high temperature, high pressure, electrochemical environment) and dynamically track the structural evolution of materials during reactions. For example, in lithium-ion battery research, XAS can monitor the valence state changes of transition metals during the charging and discharging process of electrode materials in real time, providing key data for optimizing battery performance.
Application Fields: From Catalysts to Biomacromolecules
XAS technology has been widely applied in fields such as materials science, chemistry, energy, and biomedical sciences
Catalyst research: Analyze the structure of the active center and reveal the reaction mechanism. For example, the coordination environment of metal sites in single atom catalysts can be discovered through XAS, guiding the design of efficient catalysts.
Energy materials: Analyze the ion deintercalation mechanism of battery electrode materials to improve energy storage efficiency.
Environmental Science: Tracking the transformation of pollutants in the environment to provide a basis for governance.
Biomedical: Investigating the active center structure of metalloproteins to aid in drug development.
Future prospects: Technological iteration and interdisciplinary integration
With the development of fourth generation synchrotron radiation sources such as free electron lasers, the energy resolution and time resolution of XAS will be further improved, enabling femtosecond level dynamic process observation. At the same time, the popularity of desktop XAS devices will promote the extension of this technology from large-scale scientific research facilities to conventional laboratories, providing stronger tools for material innovation, energy transformation, and breakthroughs in life sciences.