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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]

The sixth allowed family is $400$. For the two lattice constants, use $2{\theta }_{400}=2{\sin }^{-1}(2\lambda /a)$:ConsequentlyThe larger lattice constant shifts the AlAs reflection to lower scattering angle. As a differential check, $\Delta (2\theta )\simeq -2\tan \theta \Delta a/a$ in radians.

If the angular displacement is unresolved, use the intensity contrast. With the same $f\simeq Z$ model, a difference reflection has basis amplitude $13-33=-20$ for AlAs, versus $31-33=-2$ for GaAs. Its squared amplitude is therefore one hundred times greater before overall sample normalization. More robustly, compare a weak and a strong reflection within each specimen. Neglecting their almost identical angular corrections,The contrast in this internal ratio is about a factor $194$. Element-specific X-ray fluorescence, for example testing for a Ga characteristic line with a suitably energetic incident beam, or an X-ray absorption spectroscopy scan through an element-specific absorption edge, also distinguishes composition. Such scans can change incident energy; one must not assume every core shell can be excited by the original $8\mathrm{keV}$ beam.

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.