X-ray Absorbance Spectroscopy (XAS)

X-ray Absorbance Spectroscopy

X-ray absorption spectroscopy is a technique used to analyze the electronic structure of atoms and molecules by measuring the energy absorption of X-rays as they interact with a sample, providing insights into its chemical composition and bonding. 

X-ray Absorption Near Edge Spectroscopy

X-ray absorption near edge spectroscopy (XANES) is a technique that analyzes the fine structure of X-ray absorption spectra near the absorption edges of specific elements in a sample, providing detailed information about their chemical state and local atomic environment.

Strengths 

1. Chemical state analysis: XANES provides detailed information about the chemical and electronic states of specific elements in a sample, offering insights into oxidation states, coordination environments, and bonding.
2. Sensitivity to local structure: XANES is sensitive to the local atomic arrangement around the absorbing element, making it useful for studying the short-range order and structural changes in materials. 

Extended X-ray Absorption Fine Structure

Extended X-ray absorption fine structure (EXAFS) is a spectroscopic technique that analyzes the oscillations in the X-ray absorption spectrum beyond the absorption edge to provide information about the local atomic structure and coordination environment of specific elements within a sample.

Strengths 

1. Local structural information: EXAFS provides detailed information about the local atomic arrangement and coordination environment around a specific element within a sample, offering insights into bond distances, coordination numbers, and disorder
2. Versatility: EXAFS can be applied to a wide range of sample types, including solids, liquids, and gases, making it a versatile technique for studying the structural properties of various materials, from catalysts to biological molecules
3. Sensitivity to different elements: EXAFS is element-specific and can be used to study a variety of elements in the periodic table, allowing researchers to investigate the local structure of multiple elements within a single sample

Limitations

1. Bulk analysis 
2. Data analysis complexity: The interpretation of EXAFS data can be complex and requires advanced mathematical modeling and analysis techniques
3. Measurement time can be long with laboratory X-ray sources

X-ray Emission Spectroscopy

X-ray emission spectroscopy is a technique that analyzes the energy and intensity of X-rays emitted by a sample after it has been irradiated with X-rays providing information about the electronic structure and composition of the material.

Strengths

1. Element-specific information: X-ray emission spectroscopy provides element-specific insights into a sample’s electronic structure and chemical composition, making it particularly useful for analyzing complex materials containing multiple elements. 
2. Sensitivity: it can measure in samples with low concentration of the element of interest. 
3. Fast measurement time and easy sample preparation

Example plot from: easyXAFS.com
Fe Kβ spectra showing sensitivity to changes in oxidation state and local coordination environment for reference standards: Fe and Fe (III) [Fe2O3].

X-ray Pair Distribution Function

X-ray pair distribution function (PDF) analysis is a technique used to determine the three-dimensional atomic or molecular structure of amorphous or crystalline materials from their X-ray scattering patterns, providing insights into the arrangement of atoms in a sample without the need for long-range order.

Strengths

1. Amorphous and disordered materials: PDF analysis is highly effective in determining the structure of amorphous and disordered materials, which may lack the long-range order required for traditional crystallography techniques.
2. Nanoscale structures: It can provide structural information on nanoscale materials, such as nanoparticles, nanocrystals, and complex compounds, enabling researchers to study a wide range of materials.
3. Real-space information: PDF analysis directly yields real-space structural information, allowing for the visualization of atomic arrangements and providing insights into local bonding and coordination environments. 

Limitations

1. Limited long-range order: PDF analysis is less effective at characterizing materials with extensive long-range order, such as well-crystallized samples, as its strength lies in describing disordered or amorphous materials.

Example plot from:
Shyam, Badri & Stone, Kevin & Bassiri, Riccardo & Fejer, Martin & Toney, Michael & Mehta, Apurva. (2016). Measurement and Modeling of Short and Medium Range Order in Amorphous Ta2O5 Thin Films. Scientific Reports. 6. 32170. 10.1038/srep32170.