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A researcher and educator in X-ray absorption fine structure. His tutorial connects the measured X-ray absorption spectroscopy oscillations with the scattering of a photoelectron by neighboring atoms. The resulting analysis estimates neighboring distances and coordination, making the technique useful for studying local structure even when a sample lacks the long-range order needed for ordinary crystallography.^[ref]

X-ray absorption fine structure is the structured variation of an X-ray absorption spectrum near and above a core-electron edge. The excited electron interacts with the absorbing atom's environment, so the spectrum is sensitive to local electronic states and nearby atoms even when the material lacks long-range crystalline order.

Near-edge X-ray absorption fine structure probes the complicated threshold region and available electronic states. Farther above the edge, extended X-ray absorption fine structure can be interpreted using the interference between outgoing and neighboring-atom-scattered photoelectron waves. Distances affect their phases; coordination and disorder affect their amplitudes. Extracting an interatomic distance therefore requires a scattering model and phase information, rather than simply reading a raw Fourier transform peak as a bond length.

X-ray absorption spectroscopy measures a material's absorption response as the incident photon energy is scanned. Near a core-electron threshold, the X-ray can excite or remove a bound electron, creating an absorption edge. The edge position and surrounding spectral structure carry information about the absorbing element and its electronic and local atomic environment.

In a transmission experiment, upstream and downstream detectors measure $I_0(E)$ and $I(E)$. For a uniform sample of thickness $d$ obeying the simple attenuation model, $\mu (E)d=-\ln [I(E)/I_0(E)]$. A synchrotron radiation source and a tunable monochromator can supply the energy scan; energy calibration, sample thickness and detector response enter the measurement model. X-ray absorption fine structure studies the variations around and beyond the edge, rather than only its threshold position.