Looking for Chemical Shifts with Energy Dispersive Spectroscopy

Energy dispersive spectroscopy (EDS), a commonly employed spectroscopic technique, identifies elements using their characteristic x-rays. Under energetic electron irradiation, each element emits x-rays with energies particular to its unique atomic structure. Peaks occurring at these specific energies in EDS spectra are used to quantify elemental composition and identify material phases. Due to shot noise in the number of electron hole pairs produced in standard x-ray detectors, the full width at half-maximum of each peak is approximately 100 eV throughout the periodic table. This relatively poor energy resolution renders EDS seemingly unsuitable for the measurement of single or sub-eV effects such as chemical shifts, in which local chemical bonding modifies an atom's energy levels and its radiative electronic transitions. However, by curve fitting high-count x-ray peaks, we are able to measure and map chemical shifts using EDS in a transmission electron microscope. EDS shows promise for extending chemical shift mapping to heavy elements that cannot be effectively probed using electron energy loss spectroscopy (EELS) and x-ray photoelectron spectroscopy (XPS).