Aberration
An optical system's deviation from perfect imaging caused by imperfections in the lens or by non-uniformity of the electron beam.
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Accelerating voltage
The potential difference between cathode and anode over which electrons are accelerated in an electron gun. The higher the voltage, the faster the electrons and the more penetrating power they have. Voltages usually range from a few thousand volts up to several hundred thousand.
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Airlock
A specimen chamber within the electron microscope that can be isolated from the outside and from the rest of the system. The airlock is pumped out and the specimen is moved into the column vacuum, which reduces the amount of air and other contaminants brought into the column. Airlocks also facilitate the exchange of photographic material and the gun emitter.
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Amplitude
The maximum value attainable by a periodically changing physical magnitude. For electromagnetic waves, the intensity of the change is proportional to the square of their amplitude.
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Amplitude contrast
Image contrast caused when the specimen absorbs electrons (or light) from the electron beam.
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Ångström
Unit of length used in the early days of microscopy. 1 Å = 0.1 nm (nanometer). A nanometer is one millionth of a millimeter (10-9 meter). An intermediate measurement unit is the micrometer (abbreviated as µm,) which is one thousandth of a millimeter or 1,000 nm.
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Anode
In an electron gun, the negatively charged electrons are accelerated towards the anode which has a positive charge relative to the filament (cathode) from which they emerge. In practice (for ease of construction), the filament has a high negative charge and the anode is at earth (ground) potential.
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Aperture
A small hole in a disk of metal. The hole allows electrons from the beam to pass through to the sample, while the metal disk stops random and scattered electrons which are not required for image formation.
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Astigmatism
A lens aberration in which a circle in the specimen appears as an ellipse in the image.
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Atom
There are many ways of looking at the atom. The most useful one for electron microscopists is to think of it as consisting of a positively charged nucleus (containing positively charged protons and uncharged neutrons) surrounded by negatively charged electrons in discrete orbits.
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Atomic number
The unique number of protons in an element's atomic nucleus, which determines the chemical nature of the atom. For example, an atom of iron has 29 protons in its nucleus while an atom of oxygen has eight protons.
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Backscattered electrons
Primary electrons that have been deflected by the specimen through an angle generally greater than 180 degrees with little or no loss of energy.
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Binocular viewer
A light microscope built into a TEM for viewing a fine-grain fluorescent screen for critical focusing and astigmatism correction.
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Cathodoluminescence
The emission of light photons by a material under electron bombardment.
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Cleanroom
Room containing extremely low numbers of dust particles used for the manufacture of semiconductors and other nanoscale electrical items.
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Column
The electron beam path moves through, and is referred to as, a column. On electron microscopes, the electromagnetic lenses and the specimen and aperture mechanisms are engineered to work in a vertical column.
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Condenser lens
Part of the illumination system between the gun and the specimen, the condenser lens is designed to concentrate the electron beam into a finely focused spot on the specimen (or, in the case of the scanning electron microscope, into the objective lens).
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Cathode Ray Tube (CRT)
The screen of a conventional television set or PC monitor is the front-end of a cathode ray tube. Behind the screen is an electron gun producing an electron beam, lenses to focus the beam and a scanning system to make the beam rapidly scan a raster (lines of pixels) on the screen to produce an image.
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Crystal
A material in which the atoms are ordered into rows and columns (a lattice) and because of this consistency, electrons, whose wavelength is about the same size as the spacing between atoms, undergoes diffraction (spreading the light).
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Detector
A device for detecting particular electrons or photons in the electron microscope.
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Diffraction
Deviation of the direction of light or other waves' motion when the wavefront passes the edge of an obstacle and the wave is redirected or scattered.
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Diffraction contrast
Image contrast caused by the removal of electrons (or light) from the beam due to scattering by a periodic or crystalline structure in the specimen.
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Energy Dispersive X-ray Analysis (EDX)
(Also referred to as Spectrometry.) An EDX spectrometer makes a spectrum based on the energy emitted by a specimen in x-rays.
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EELS
Electron Energy Loss Spectroscopy (or Spectrometry) is a way of measuring the loss of energy in electrons as they travel through a specimen.
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Electron
Fundamental atomic particle rotating in an orbit around the nucleus of the atom. Free electrons can easily flow in a conductor and can be extracted into a vacuum by heat and/or an electrical field.
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Electron microscope
A microscope in which a beam of electrons is used to form a magnified image of the specimen.
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Environmental Scanning Electron Microscopy (ESEM)
ESEM involves an electron microscope with a specimen chamber that can be adjusted to different environmental conditions, typically to observe samples in a vacuum or to keep the sample "wet" and study it in equilibrium with water.
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Excitation
The input of energy into matter, leading to the emission of radiation.
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Excited atom
An atom which has lost one of its inner electrons (an ion) and has a higher energy value. The extra energy is that needed to remove the electron from the nucleus, which seeks to return to its ground state by rearranging its electrons and emitting the excess energy as an X-ray quantum.
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Fab line
A semiconductor production line that is located in a clean room.
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Field Emission Gun (FEG)
A FEG pulls heated electrons out of a very-fine tungsten tip using an extremely high electric field. With a FEG, users gain electron densities up to 1,000 times those of tungsten emitters without a FEG.
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Field Ion Beam (FIB)
A beam of ions replaces the beam of electrons on an electron microscope. DualBeam™ instruments may also have an ion beam column.
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Filament
Metal wire, usually formed like a hairpin, that, when heated in vacuum, releases free electrons and provides the source of the electron beam in an electron microscope.
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Fluorescent screen
Large plate coated with a material (phosphor) that gives off light (fluoresces) when bombarded by electrons. In transmission electron microscopes (TEMs), the image is formed on the fluorescent screen.
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Focal length of a lens
The distance (measured from the center of the lens) at which a parallel incident beam is brought to a focus.
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Focusing
Making the microscopy image as sharp as possible by adjusting the objective lens.
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Goniometer
Specimen stage that allows tilting and movement of the specimen in two or more directions, as well as rotation of the specimen in its own plane and tilting on one or more axes. In addition, goniometers can be used in specialized experiments to heat, cool or strain the specimen. Typically, the goniometer is mounted very close to the objective lens to minimize aberration while maximizing resolution.
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Ground state
The lowest energy state of an atom, typically achieved when all electrons are in place and the atom possesses no charge.
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Ion
An atom that has lost one or more of its outer electrons and has a positive charge.
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Lattice
Regular array, or pattern, of atoms in a crystal.
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Lens
In a light microscope, a piece of transparent material with one or more curved surfaces. The lens is used to alter the direction of light waves, typically to increase magnification or to sharpen resolution. In an electron microscope, a similar effect is achieved with a beam of electrons by using a magnetic (or electrostatic) field.
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Micrometer
Unit of length (distance). One micrometer (abbreviated to µm) is one thousandth of a millimeter or 1000 nm.
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Microscope
An instrument designed to extend humans' visual capability to make visible detail that is not seen with the naked eye.
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Microtome (ultramicrotome)
Instrument for cutting extremely thin sections from a specimen prior to examination in the microscope. In electron microscopy, the cutting instrument is often referred to as an ultramicrotome.
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Nanometer
Unit of length (distance). One nanometer (abbreviated as nm) is a millionth of a millimeter (10-9 meter).
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Objective lens
In a transmission electron microscope (TEM), this is the first lens after the specimen. In a scanning electron microscope (SEM) it is the last lens before the specimen and produces the extremely fine electron spot with which the specimen is scanned. With both SEMs and TEMs, the quality of the objective lens determines the performance of the microscope.
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Oil diffusion pump
A vacuum pump where the pumping action is produced by dragging a stream of oil vapor though a small orifice.
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Phase
Relative position in a cyclical or wave motion. Phase is expressed as an angle, one cycle or one wavelength corresponding to 180 degrees.
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Phase contrast
Image contrast caused by the conversion of phase differences in light leaving the object into amplitude differences in the image.
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Phase diagram
Graph of temperature and pressure showing the range of each under which a given material can exist in the solid, liquid or vapor phases.
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Photomultiplier
Electronic tube in which light is amplified without interference (noise) to produce an electrical signal.
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Photons
Discrete packets of electromagnetic radiation. A light beam is made up of a stream of photons.
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Primary electrons
Electrons in the beam as it leaves the gun and impinges on the specimen.
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Quantum
A discrete packet of X-radiation.
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Raster
The track of the beam in a SEM or S/TEM as it produces an image. Rastering moves the beam from left-to-right and top-to-bottom as it progresses line-by-line until the image is complete.
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Refraction
Changes in speed (and sometimes direction) when light or electrons pass through a specimen.
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Refractive index
The ratio of speed of light in a vacuum to that in a given medium, such as glass, water or oil.
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Resolving power
The ability to focus a microscope to see points or lines that are closely adjacent on an object or in an image.
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Resolution
The act or result of displaying fine detail in an image.
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Rotary pump
Vacuum pump in which the pumping action is produced by moving packets of air from one side of a rotating cylinder to another by means of an eccentric drum.
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Scanning
Process of investigating a specimen by moving a finely focused electron beam in systematic patterns over the surface. The technique results in an image that corresponds to the specimen.
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Scintillation detector
Electron detector used in scanning electron microscopy (SEM) or scanning/ transmission electron microscopy (S/TEM) in which electrons are accelerated towards a phosphor which fluoresces and is amplified by means of a photomultiplier to produce an electrical signal.
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Secondary electrons
Electrons that originate in the specimen and are emitted under influence of the primary beam.
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Scanning Electron Microscope (SEM)
An electron microscope that uses a focused electron beam to produce an image of the specimen's surface. Today, SEMs have a resolution of 1 nm and can magnify over 400,000x.
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Semiconductor detector
Electron detector used in a scanning electron microscope (SEM) or scanning transmission electron microscope (S/TEM) in which the electron to be detected causes a small change in the semiconductor material which is amplified by making the semiconductor part of an electrical circuit.
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Spectrometer
Instrument for obtaining a spectrum of light or X-rays.
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Spectrum
A display produced by the separation of a complex radiation into its component wavelengths or energies so that all wavelengths can be observed simultaneously.
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Spherical aberration
See Aberration. The magnification power in the center of a lens differs from the magnification possible at the len's edges.
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Sputter coater
Instrument for coating a non-conducting specimen with a very thin, uniform layer of a conducting element, such as gold, to make it suitable for examination in a scanning electron microscope (SEM).
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Scanning/Transmission Electron Microscopy (S/TEM)
A S/TEM combines the functionality of a SEM and a TEM by using both transmitted (direct) light and scanned (reflected) light.
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Transmission Electron Microscope (TEM)
With a TEM, an electron source (usually a vacuum-heated tungsten filament) bombards the sample as magnetic lenses produce images of the result on a fluorescent screen. To produce a good image, the sample must be thin enough to allow penetration by the electrons. As a result, not all specimens can be made thin enough to produce a detailed image with a TEM.
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Turbomolecular pump
Vacuum pump in which the centrifugal force of quickly- rotating disks forces molecules from the axis to the side of the pump.
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Vacuum
A space from which (most) gases and vapors have been removed.
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Wavelength
The distance on a periodic wave between two successive points with the same phase.
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Wehnelt cylinder
An electrode between the cathode (filament) and the anode (earth) in an electron gun which focuses and controls the electron current in the beam and keeps it constant.
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Working distance
The physical distance between the external, metal parts of the objective lens and the specimen's surface. This is the space available for placing certain electron, X-ray and cathodoluminescence detectors. To achieve the highest resolution, the working distance must be made as small as possible, which can lead to operational complications and engineering compromises.
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X-rays
Extremely short wavelength radiation. In the electron microscope, an X-ray photon is emitted when an excited atom releases its excess energy and returns to its ground state.
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