X-ray absorption spectroscopy (XAS) is a popular characterization technique for probing the local atomic structure and electronic properties of materials and molecules. Because atoms of each element absorb X-rays at characteristic energies, XAS is well suited for mapping out the spatial distribution of elements in a sample. Typically, scientists perform XAS experiments at synchrotron light sources—such as the National Synchrotron Light Source II (NSLS-II)—because they provide very bright, tunable X-rays. By measuring the absorbance in a sample at varying X-ray energies, scientists can generate a plot called an X-ray absorption spectrum.