• 3-window mapping

    An energy-filtering transmission electron microscopy (EFTEM) mapping method that uses two filtered images, prior to the edge of interest, to determine the background that is subtracted from a third image that is acquired after the edge of interest.


  • Absolute quantification

    Use of an analytical technique to determine the absolute number of atoms per area, as opposed to a relative or percent composition.

  • Accompanying edges

    Minor, less intense edges that follow a major edge.

  • Argon gas

    Argon (Ar) is widely used as the process gas during ion milling for transmission electron microscope (TEM) specimen preparation. It is also an important carrier gas during plasma cleaning to remove carbon (C) contamination from TEM samples.


  • Beam current

    Number of electrons in the transmission electron microscope's (TEM) electron beam and is usually measured in pA or nA.

  • Bragg angle

    The angle between an incident beam and a set of planes in the crystal where scattering shows the maximum intensity due to constructive interference.

  • Bright field / dark field (BF/DF)

    An imaging technique where only the unscattered electrons (bright field) or the scattered electrons (dark field) are collected to form an image. The term also refers to a bright field (BF)/dark field (DF) scanning transmission electron microscope (STEM) detector mechanism that allows you to insert the DF and BF detectors one at the time.


  • Charge-coupled device (CCD)

    An imaging device where the charge is moved to an area within the same device where it can be digitized.

  • Chemical state

    The chemical or electronic state of a particular element in a sample. This can change depending on the element’s bonding or local coordination.

  • Collection angle

    The angle that electrons are collected in the electron energy loss spectrometer.

  • Convergence angle

    The angle that the probe forms on the specimen.

  • Core-loss

    The region of the electron energy loss spectrum with signatures coming from the ionization edges.

  • Crossover

    The point in between two lenses at that the electrons from different paths converge.

  • Current drift

    Slow (10 – 100 s) changes in electron current.


  • Delayed edge

    When the maximum intensity is far from the edge onset.

  • Diffraction contrast

    Features in imaging caused by variations of intensity of diffraction across the image.

  • Drift tube voltage

    In DigitalMicrograph® (DM) software from Gatan, a control that applies a precise voltage to temporarily accelerate the beam as it passes through the prism, and thereby results in a net downward deflection of the dispersed beam. See also Spectrum offset and Energy shift.

  • DualEELS

    The (nearly) simultaneous acquisition of two different energy regions of the electron energy loss spectrum under the same experimental conditions. For more information see DualEELS™.

  • Dynamic range

    The intensity range that a particular device can handle.


  • Edge threshold energy

    The difference in energy between a core level initial state and the lowest unoccupied energy state in an excited atom.

  • Elastic scattering

    Scattering event that results in no loss of energy.

  • Electron energy loss spectroscopy (EELS)

    A method of measuring the loss of energy in electrons as they travel through a specimen.

  • Electron gun

    A component that generates a beam of electrons in vacuum.

  • Electron microscope

    A microscope that uses accelerated electrons to illuminate a specimen.

  • Electron scattering

    Deviation of the original electron path as result of the interaction with matter.

  • Electron transparent

    A specimen that is thin enough that electrons can travel through it.

  • Emission current

    Measurement of the number of electrons emitted by a filament (electron gun).

  • Energy dispersive x-ray spectroscopy (EDS)

    An analytical technique used for analysis and characterization of a sample; also referred to as EDX, XEDS, etc.

  • Energy drift

    Slow (10 – 100 s) energy fluctuations in the electron beam due to some instrumental instabilities.

  • Energy filter

    A device capable of imaging electrons that have lost a selected range of energy.

  • Energy loss

    The transfer of energy by the incoming electron to the sample as a result of the interaction with the matter.

  • Energy loss near edge structure (ELNES)

    The region of the energy loss spectrum that represents transitions from core level states to empty states just above the Fermi level. ELNES gives hints about the band structure (density of unoccupied states). For more information see ELNES.

  • Energy shift

    In DigitalMicrograph® software from Gatan, a control that offsets the energy loss spectrum by changing the magnetic field in the energy dispersing prism. See also Spectrum offset and Drift tube voltage.

  • Energy-filtered transmission electron microscopy (EFTEM)

    An analytical technique used in transmission electron microscopy, by which electrons of particular energies are used to form a diffraction pattern or image. For more information, please see EFTEM.

  • Energy-filtering transmission electron microscope spectrum imaging (EFTEM SI)

    The use of energy-filtered transmission electron microscope images to form a data cube containing two spatial dimensions (images) and a third energy dimension (spectra). For more information, please see EFTEM, Spectrum Imaging, and EFTEM SI.

  • Excited atom

    An atom that has absorbed energy and is now at a higher energy level.


  • Field emission gun (FEG)

    An electron source where the electrons are generated by the application of a strong electric field. The electrons tunnel, quantum mechanically, through the remaining energy barrier into the vacuum.

  • Filament

    The heated source of electrons in a themionic electron emitter.

  • Fluorescent screen

    A screen coated on one side by a material that emits light when exposed to electrons. Used for viewing electron images, diffracting patterns, or spectra.

  • Flyback time

    Time needed to ensure that the beam goes to the selected spot at the end of each sweep.

  • Focal length of lens

    The measurement of how a lens converges or diverges the electrons.

  • Forward scattering

    When scattering occurs mainly along the same direction as the incoming beam.

  • Fourier transform (FT)/Fast Fourier transform (FFT)

    An algorithm that converts a signal from its original domain (commonly spatial or time) into a frequency domain.

  • Fourier-log deconvolution

    Mathematical process used to remove the effects of plural scattering in the electron energy loss spectrum. It requires presence of the low-loss portion with the zero-loss peak (ZLP) in the same spectrum.

  • Fourier-ratio deconvolution

    Mathematical process used to remove the effects of plural scattering in the electron energy loss spectrum. It requires presence of the low-loss portion with the zero-loss peak (ZLP) but not necessarily in the same spectrum.

  • Frame time

    Time used for the acquisition of each frame of spectrum or image.


  • Gatan imaging filter (GIF)

    An imaging filter designed and manufactured by Gatan. For more information please visit the GIF Quantum® energy filters page on

  • Gaussian peak

    Peak that has the symmetric shape of the Gaussian function.

  • Goniometer

    Allows the specimen to be traversed and tilted.

  • Ground state

    Electron configuration of an atom at the lowest possible energy.


  • High resolution imaging

    Allows direct imaging of the atomic structure.

  • High vacuum

    Pressure ranging from 10-6 – 10-9 Pa.

  • High-loss region

    Region of the electron energy loss spectrum with signatures coming from the ionization edges.

  • Holey grid

    A TEM sample support where a coarse support mesh (typically Cu) supports a fine film (typically C) with the presence of much smaller circular or square holes.

  • Hydrogenic edge shape

    Edges with a sharp onset that resemble the ionization from a single hydrogen atom.


  • Inelastic scattering

    When there is a loss of energy accompanying the scattering event.

  • Intermediate lens

    Lenses that are used to magnify the image from the objective lens. Typically these are not the final stage of magnification.


  • Jump-ratio imaging

    The process used for energy-filtering transmission electron microscopy (EFTEM) mapping where one filtered image before the edge of interest and one filtered image after the edge of interest are collected. The ratio of the images forms the jump-ratio image.


  • Lens

    Magnetic fields in the TEM that are used to control the beam, and form and magnify images.

  • Low angle scattering

    Scattering that occurs at relatively low angle compared to the characteristic scattering angle for the material.

  • Low-loss signal

    Analysis of the electron energy loss spectrum at low energy, generally including the zero-loss peak (ZLP).


  • Magnetic lens

    Lenses that are used to focus and deflect charged particles such as electrons in the case of transmission electron microscopy (TEM).

  • Major edge

    A strong edge that represents the main signature for a particular element in the electron energy loss spectrum.

  • Mapping

    A record of the spatial distribution of selected features or signals.

  • Mean free path (MFP)

    Average distance electrons undergo between scattering events.

  • Minor edge

    An edge that is quite weak in intensity. Often invisible in the electron energy loss spectrum.

  • Monochromatic

    A beam of electrons with a range of energies that are narrower than the original electron source.

  • Multiple linear least square fitting (MLLS)

    A technique used to separate overlapping edges. For more information please see Advanced.


  • Non-linear least squares (NLLS)

    NLLS involves fitting models to spectral features to quantify the spectral peak properties. For more information, please see Advanced.


  • Objective aperture

    An aperture in the back focal plane of the objective lens that is used to enhance contrast as well as change the collection angle in filtered images.

  • Objective lens

    The primary magnifying lens in a microscope.


  • Phase contrast

    Contrast given by phase changes as electrons go through the sample.

  • Pixel

    Smallest element in an image.

  • Plasmon energy

    The most likely energy that will be absorbed by an electron that creates an oscillation of the charge density of a sample.

  • Plasmon loss

    Energy loss due to plasmon excitation. Also refers to the energy region of the spectrum where the plasmon excitation are typically observed.

  • Plural scattering

    When the incoming electrons, as they travel through the sample, go through many inelastic scattering events.

  • Pole piece gap

    The distance between upper and lower magnet yokes of the lens.

  • Precipitates

    The presence of an isolated cluster or grain of elements or material different from the matrix.

  • Projector lens

    The lenses that produce the final magnification of the beam onto the transmission electron microscope (TEM) viewing screen. They are used to control the magnification and camera length.


  • Refraction

    The bending of a wave when it enters a medium.

  • Refractive index

    Describes how the light or radiation propagate through the medium.

  • Ronchigram

    A shadow image that contains both real and reciprocal space information.


  • Scan space

    An area that is being scanned by the beam.

  • Scanning

    It is the action of moving the electron beam across the sample typically in a square raster pattern.

  • Scanning transmission electron microscope (STEM)

    A STEM is distinguished by the fact that the electron beam is focused into a narrow spot within the TEM, and then scanned over the specimen.

  • Scanning transmission electron microscope spectrum imaging (STEM SI)

    When the beam is scanned point by point across the specimen and spectra are acquired at each position and stored to form a data cube. For more information, please see STEM SI.

  • Scherzer focus

    When a high resolution image of a phase object is taken in the transmission electron microscope (TEM) mode, Scherzer focus is used as the defocus condition that ensures the phase of diffracted waves to be shifted by 1/4 wavelength of the electron wave over a wide range of spatial frequencies.

  • Scintillation detector

    A detector that emits photons/light when exposed to electrons.

  • Secondary electrons

    Electrons that originate in the specimen and are emitted under influence of the primary beam.

  • Selected area electron diffraction (SAED)

    A diffraction pattern formed from a sample region defined using an aperture in an image plane conjugate to the sample.

  • Signal-to-background ratio (SBR)

    A ratio between the intensity of the signal of interest and the background under that signal.

  • Signal-to-noise ratio (SNR)

    A ratio between the intensity of the signal of interest to that of all the noise sources in the measurement of that signal.

  • Spatial drift

    Physical sample drift.

  • Spectrometer

    An instrument used to measure a spectrum.

  • Spectrum

    A graph where the intensity is plotted against other dimensions such as energy, wavelength, etc.

  • Spectrum imaging

    A data set that mixes spatial and spectral information. Typically a data cube with two spatial dimensions and a third spectral dimension.

  • Spectrum offset

    In DigitalMicrograph® software from Gatan, a control that increases the high tension of the TEM by an amount equal to the average energy loss you wish to have in an EFTEM image. See also Energy shift and Drift tube voltage.

  • Spherical aberration

    When parallel electrons that travel through the center of a lens are in different focus than those from the edges of the lens.

  • Sputter coater

    An instrument used to create a fine coating of a material on to the substrate of interest by physical ablation.

  • Stigmate

    A process that will correct the effects of astigmatism in an image.


  • Tomography

    A technique that shows all the dimension of an object being imaged.

  • Transmission electron microscope (TEM)

    A microscopy technique where a beam of electrons is transmitted through a specially prepared specimen.

  • Transmission electron microscope (TEM) staining

    The process of adding heavy metals to the TEM sample in order to increase contrast in the image.


  • X-rays

    In the electron microscope, an x-ray photon is emitted when an excited atom releases its excess energy and returns to its ground state.


  • Zero-loss peak (ZLP)

    The ZLP appears at an energy loss of zero. It contains all electrons that have passed the specimen without any interaction or with an elastic interaction only. If the sample is thin, the ZLP is by far the most intense signal.