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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.

Transmission electron microscopy accelerates electrons through a thin sample, then uses electron lenses to form an image or diffraction pattern. Elastic scattering encodes projected structure and potential; inelastic scattering carries excitation and chemical information. Thin specimens reduce unwanted multiple scattering and absorption, although coherent dynamical scattering can still matter in a crystal. High-resolution phase-contrast images depend on defocus and the transfer function as well as the specimen; they are not direct height maps.

The relativistic wavelength is $\lambda =h/\sqrt{2m_{e}eV[1+eV/(2m_e{c}^2)]}$. A shorter wavelength permits fine resolution but does not guarantee it. A schematic probe/image blur budget contains diffraction $\sim \lambda /\alpha$, spherical aberration $\sim C_s{\alpha }^3$ and chromatic aberration $\sim C_c\alpha \Delta E/E$, plus source size, instabilities, specimen motion and radiation damage. Optimizing the aperture angle balances these terms; increasing accelerating voltage can also alter damage and contrast.

Bright-field imaging accepts the central transmitted beam or its neighborhood. Regions that scatter electrons outside that acceptance can appear dark. Conventional dark-field imaging selects a diffracted beam. Annular dark-field electron imaging in a scanning TEM instead collects a range of scattered angles while a probe is scanned. A sufficiently high-angle detector often gives strong atomic-number sensitivity and more nearly incoherent contrast; thickness, channeling and detector geometry prevent a universal conversion of intensity to composition.

Electron energy loss spectroscopy measures energy lost by transmitted electrons. Core-ionization thresholds identify elements, while near-edge fine structure probes bonding and unoccupied states. At successive probe positions, one can record a spectrum image or form a map from a selected edge after background subtraction. Plural scattering, edge overlap, delocalization, specimen thickness and counting statistics limit the interpretation. Chemical specificity comes from excitation energies and spectral structure, not from brightness alone.

A development already established before this 2012 paper is aberration-corrected transmission electron microscopy: multipole correctors compensate leading lens aberrations, allowing useful larger angular acceptance and finer probes. Correction does not remove every chromatic, stability or specimen limit. A concrete application was atom-by-atom annular-dark-field analysis of monolayer boron nitride with substitutional defects, resolving chemical differences between sites in a nonuniform lattice.^[ref] Combining structural maps with spatially resolved core-loss spectra supplies another route to distinguish composition and bonding at interfaces. Both exploit a calibrated imaging or spectroscopy response rather than assuming every visible spot is chemically self-identifying.

Ultraviolet photoelectron spectroscopy probes occupied valence states through photoemitted electron energies. Angle-resolved photoemission spectroscopy adds emission direction and therefore parallel crystal momentum, revealing occupied band dispersions and Fermi contours. For a clean periodic surface, $k_{\parallel }=\sqrt{2m_e{E}_{\mathrm{kin}}}\sin \theta /\hslash$ modulo a surface reciprocal-lattice vector. A two-dimensional surface band has no intrinsic perpendicular dispersion; varying photon energy helps distinguish it from bulk bands, while allowing for matrix-element changes. A simple surface-state example is a parabolic band $E({\mathbf{k}}_{\parallel })=E_0+{\hslash }^2{k}_{\parallel }^2/(2m_{\ast })$.

Scanning tunneling spectroscopy measures local differential conductance. With a suitable featureless tip and weak tunneling, $dI/dV$ samples the local density of states, giving occupied and unoccupied features on opposite bias sides. It provides spatial localization, defects and standing-wave patterns, while ordinary spectroscopy at one point does not directly give the complete momentum-resolved band structure. For the parabolic two-dimensional band, the ideal density of states has a step at its onset, while spatial interference can supply information about allowed wavevectors. Inverse photoemission spectroscopy accesses unoccupied states by injecting electrons and measuring emitted photons. Optical absorption and electron energy loss spectroscopy instead probe allowed excitation energies and collective modes, with their own selection rules and momentum ranges. These methods supply complementary information; none automatically returns the full interacting band structure without matrix elements, resolution and surface effects.

For the Pt core-level spectra, electrons suffering inelastic losses emerge with reduced kinetic energy and appear at larger inferred binding energies. Loss tails and secondary-electron contributions therefore generate the background, principally on the high-binding-energy side of a core peak. The two clean-surface components correspond to different environments of the same Pt core-level branch. The stated values imply a surface core-level shiftReduced coordination at a surface narrows the $d$ band. In a simple almost-filled-band picture, maintaining its occupation moves the band center upward relative to the Fermi level; associated local-potential changes can move core levels upward too, reducing their binding energy. This is a plausible initial-state explanation of the negative shift. Final-state screening of the core hole also matters, so the measured shift alone does not uniquely determine a local charge or separate these mechanisms.

After adsorption, Pt atoms directly bonded to CO have a different local potential, hybridization and core-hole screening. In carbon monoxide adsorption on platinum, carbon-end donation and metal-to-molecule back-donation change the Pt–CO bond and hence the Pt core binding energy. The additional weak high-binding-energy component is naturally assigned to these chemically modified surface Pt atoms. Its small weight is compatible with only a minority of surface sites being occupied; a quantitative coverage estimate requires fitted areas and appropriate attenuation assumptions.

The new component is centered at approximately $71.9$–$72.0\mathrm{eV}$ in the supplied plot. Relative to bare surface Pt at $70.5\mathrm{eV}$, the core-level chemical shift is thereforeUsing the bulk peak as the reference would instead give about $+1.0$–$1.1\mathrm{eV}$, which answers a different comparison. The plotted axis runs toward decreasing binding energy to the right, so the additional peak on its left is a positive binding-energy shift. The estimate is a graphical reading, with no claim to sub-tenth-eV precision or a unique charge-transfer value.

A researcher who coauthored measurements of chemical bonding around individual impurity atoms in graphene. Scanning transmission electron microscopy located silicon impurities, while electron energy loss spectroscopy probed their electronic environment. Comparing differently coordinated sites with calculations connected an atom's visible position to its bonding, extending microscopy beyond identifying where the atoms are.^[ref]