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Electron energy loss spectroscopy measures the energy transferred from incident electrons to a specimen. A transmitted-electron spectrometer separates nearly unscattered electrons from electrons that excited collective modes, atomic transitions or core-level processes.

The zero-loss feature supplies an energy reference, and losses can be reported as $E_{\mathrm{loss}}=E_{\mathrm{incident}}-E_{\mathrm{detected}}$. Element-specific edges and their energy-loss near-edge structure constrain composition and bonding. A thicker specimen can produce several losses in one trajectory, so the recorded electron energy loss spectroscopy response need not equal a single-interaction response. ^[ref]

Energy-loss near-edge structure is the detailed shape near an inner-shell excitation edge in an electron energy loss spectroscopy measurement. Transition probabilities sample accessible unoccupied electronic states, so local bonding and orientation affect the edge shape as well as elemental identity.

Comparing two specimens containing the same element can therefore reveal different electronic environments. Interpretation must account for instrumental energy resolution, the incident beam's energy spread and lifetime broadening of the states involved. ^[ref] A small peak difference alone does not uniquely determine one atomic arrangement.

Aberration-corrected scanning transmission electron microscopy with annular dark-field imaging and spatially resolved EELS can locate the Si atoms and test their chemical environment. silicon scatters much more strongly to high angles than carbon, so an isolated Si impurity can stand out in a thin graphene lattice. Neighboring carbon positions reveal whether a site is, for example, three- or four-coordinated in projection.

Acquire a spectrum image at the same time. A silicon core-loss edge identifies the element, while its energy-loss near-edge structure contains information about the unoccupied states and bonding. This combination has experimentally distinguished individual Si coordination environments in graphene.^[ref]

Advantages are atom-scale spatial localization, simultaneous structural and chemical evidence, and stronger chemical identification than brightness alone. Limitations include low counts at one atom, background subtraction, finite energy resolution, drift and the high dose needed for a useful spectrum. The beam can move or damage an impurity, and a two-dimensional projection does not by itself determine its out-of-plane geometry. Compare spectra and images with plausible structural calculations rather than assigning coordination solely from one bright pixel.