X-ray Absorption Spectroscopy (XAS)

What Is X-ray Absorption Spectroscopy (XAS)?

X-ray Absorption Spectroscopy is an element-specific technique that measures how a material absorbs X-rays as the incident energy is scanned across the absorption edge of a target element.

When X-rays interact with a material:

• Core electrons are excited to unoccupied states or ejected

• The absorption intensity changes as a function of X-ray energy

• These changes reveal detailed information about the local atomic structure and electronic state

XAS is especially valuable because it provides short-range structural information, even in amorphous or non-crystalline materials.

Components of XAS: XANES and EXAFS

XAS data is typically divided into two regions:

1. XANES (X-ray Absorption Near Edge Structure)

• Located close to the absorption edge

• Highly sensitive to:

  • Oxidation state

  • Chemical bonding

  • Electronic structure

  • Local symmetry

Applications of XANES:

• Identifying oxidation states of metals

• Tracking chemical reactions

• Studying electronic changes in batteries and catalysts

2. EXAFS (Extended X-ray Absorption Fine Structure)

• Found beyond the absorption edge

• Arises from interference between outgoing and back-scattered photoelectrons

• Provides quantitative information on:

  • Bond lengths

  • Coordination numbers

  • Disorder and local geometry

Applications of EXAFS:

• Determining atomic distances

• Studying short-range order

• Analyzing nanoparticles and amorphous materials

Why XAS Is Important in Laboratory Research

X-ray Absorption Spectroscopy offers several advantages over conventional analytical techniques:

• Element-specific analysis without interference from surrounding elements

• Works on solids, liquids, gases, and thin films

• No requirement for long-range crystalline order

• Non-destructive and highly sensitive

• Suitable for in-situ and operando studies

These capabilities make XAS indispensable for advanced material characterization.

Laboratory-Based XAS: A Game Changer

Historically, XAS experiments required access to synchrotron radiation sources, which limited routine usage. Modern laboratory-scale XAS systems now bring this capability in-house, offering:

• Faster access to data

• Improved research productivity

• Reduced dependence on external facilities

• Greater control over experimental conditions

This shift is enabling wider adoption of XAS across industrial R&D and academic laboratories.

Applications of X-ray Absorption Spectroscopy

XAS is widely used across multiple industries and research domains:

• Materials Science – alloys, nanomaterials, thin films

• Catalysis – active site identification and reaction mechanisms

• Energy Storage – batteries, fuel cells, supercapacitors

• Semiconductors – dopant behavior and defect analysis

• Environmental Science – speciation of pollutants and heavy metals

• Chemistry & Physics – electronic and structural studies

Key Advantages of XAS

• Atomic-level structural information

• Applicable to complex and disordered materials

• Supports both qualitative and quantitative analysis

• Enables time-resolved and in-situ experiments

• Complements techniques like XRD, XPS, and SEM

Conclusion

X-ray Absorption Spectroscopy (XAS) is a cornerstone technique for understanding materials at the atomic scale. By combining XANES and EXAFS, XAS delivers unparalleled insight into chemical states, bonding environments, and local structure—information that is often inaccessible through traditional methods.

With the advancement of laboratory-based XAS systems, this once specialized technique is now becoming an essential part of modern analytical laboratories, driving innovation across materials science, energy, chemistry, and industrial research.