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Encyclopedia > Transmission electron microscopy
A section of a cell of Bacillus subtilis, taken with a Tecnai T-12 TEM. The scale bar is 200nm.

Transmission electron microscopy (TEM) is a microscopy technique whereby a beam of electrons is transmitted through an ultra thin specimen, interacting with the specimen as it passes through it. An image is formed from the electrons transmitted through the specimen, magnified and focused by an objective lens and appears on an imaging screen, a fluorescent screen in most TEMs, plus a monitor, or on a layer of photographic film, or to be detected by a sensor such as a CCD camera. The first practical transmission electron microscope was built by Albert Prebus and James Hillier at the University of Toronto in 1938 using concepts developed earlier by Max Knoll and Ernst Ruska. TEM is a TLA that could mean: Temiskaming and Northern Ontario railroad (AAR reporting mark TEM) Transmission electron microscopy Transverse electric and magnetic mode (see List of fiber optic terms) Telecommunications equipment manufacturer This page concerning a three-letter acronym or abbreviation is a disambiguation page — a navigational aid which... Image File history File linksMetadata Size of this preview: 800 × 600 pixel Image in higher resolution (1376 × 1032 pixel, file size: 73 KB, MIME type: image/jpeg) The Bacterium Bacillus subtilis taken with a Tecnai T-12 TEM. Taken by Allon Weiner, The Weizmann Institute of Science, Rehovot, Israel. ... Image File history File linksMetadata Size of this preview: 800 × 600 pixel Image in higher resolution (1376 × 1032 pixel, file size: 73 KB, MIME type: image/jpeg) The Bacterium Bacillus subtilis taken with a Tecnai T-12 TEM. Taken by Allon Weiner, The Weizmann Institute of Science, Rehovot, Israel. ... Binomial name Bacillus subtilis (Ehrenberg 1835) Cohn 1872 Gram-stained Bacillus subtilis Sporulating Bacillus subtilis Bacillus subtilis is a Gram-positive, catalase-positive bacterium commonly found in soil. ... A microscope (Greek: (micron) = small + (skopein) = to look at) is an instrument for viewing objects that are too small to be seen by the naked or unaided eye. ... For other uses, see Electron (disambiguation). ... An image that is partially in focus, but mostly out of focus in varying degrees. ... This article or section does not cite its references or sources. ... A charge-coupled device (CCD), is an integrated circuit containing an array of linked, or coupled, capacitors. ... James Hillier) James Hillier OC, Ph. ... The University of Toronto (U of T) is a public research university in the city of Toronto, Ontario, Canada. ... Max Knoll (17 July 1897 – 6 November 1969) was a German electrical engineer. ... Image:Ernstruska. ...

Contents

Background

An old model TEM, the HV source begins at the top, and the electromagnetic lenses focus the electrons from the HV source through the specimen and onto the viewing screen (bottom) A photographic emulsion can be loaded into the drawer at the base
An old model TEM, the HV source begins at the top, and the electromagnetic lenses focus the electrons from the HV source through the specimen and onto the viewing screen (bottom) A photographic emulsion can be loaded into the drawer at the base

Theoretically the maximum resolution that one can obtain with a light microscope has been limited by the wavelength of the photons that are being used to probe the sample and the numerical aperture of the system. Early twentieth century scientists theorized ways of getting around the limitations of the relatively large wavelength of visible light (wavelengths of 400–700 nanometers) by using electrons. Like all matter, electrons have both wave and particle properties (as theorized by Louis-Victor de Broglie), and their wave-like properties mean that a beam of electrons can be made to behave like a beam of electromagnetic radiation. Electrons are usually generated in an electron microscope by a process known as thermionic emission from a filament, usually tungsten, in the same manner as a light bulb, or by field emission. The electrons are then accelerated by an electric potential (measured in V, or volts) and focused by electrostatic and electromagnetic lenses onto the sample. The beam interacts variously with the sample due to differences in density or chemistry. The beam that is transmitted through the sample contains information about these differences, and this information in the beam of electrons is used to form an image of the sample. Download high resolution version (290x1212, 65 KB) Wikipedia does not have an article with this exact name. ... Download high resolution version (290x1212, 65 KB) Wikipedia does not have an article with this exact name. ... For other uses, see Wavelength (disambiguation). ... In physics, the photon (from Greek φως, phōs, meaning light) is the quantum of the electromagnetic field; for instance, light. ... Numerical aperture is a technical term of multiple uses: Numerical aperture of optical telecommunication fiber Numerical aperture in microscopy This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... Visible light redirects here. ... A nanometre (American spelling: nanometer) is 1. ... Louis-Victor-Pierre-Raymond, 7th duc de Broglie, generally known as Louis de Broglie (August 15, 1892–March 19, 1987), was a French physicist and Nobel Prize laureate. ... Closeup of the filament on a low pressure mercury gas discharge lamp showing white thermionic emission mix coating on the central portion of the coil. ... The light bulb is one of the most significant inventions in the history of the human race, illuminating the darkness of the evening and bringing light indoors at all times in order focus on the task at hand. ... Field emission, also known as Fowler-Nordheim tunneling, is a form of quantum tunneling in which electrons pass through a barrier in the presence of a high electric field. ... This article does not cite any references or sources. ... The volt is the SI derived unit for electric potential and voltage (derived from the ampere and watt). ...


Just as details of a light microscope sample can be enhanced by the use of stains, staining can be used to enhance differences in a sample for electron microscopy. Compounds of heavy metals such as osmium, lead or uranium can be used to selectively deposit heavy atoms in areas of the sample and to enhance structural detail by the dense nuclei of the heavy atoms scattering the electrons out of the optical path. The electrons that remain in the beam can be detected using a photographic film, or fluorescent screen among other technologies. So areas where electrons have been scattered in the sample can appear dark on the screen, or on a positive image due to this scattering. ... For other uses, see Heavy metal (disambiguation). ... General Name, Symbol, Number osmium, Os, 76 Chemical series transition metals Group, Period, Block 8, 6, d Appearance silvery, blue cast Standard atomic weight 190. ... General Name, Symbol, Number lead, Pb, 82 Chemical series Post-transition metals or poor metals Group, Period, Block 14, 6, p Appearance bluish gray Standard atomic weight 207. ... This article is about the chemical element. ... This article or section does not cite its references or sources. ...


Modifications

The capabilities of the TEM can be further extended by additional stages and detectors, sometimes incorporated on the same microscope. An electron cryomicroscope is a TEM with a specimen holder capable of maintaining the specimen at liquid nitrogen or liquid helium temperatures. This allows imaging specimens prepared in vitreous ice, the preferred preparation technique for imaging individual molecules or macromolecular assemblies. A tank of liquid nitrogen, used to supply a cryogenic freezer (for storing laboratory samples at a temperature of about -150 Celsius). ... Helium exists in liquid form only at very low temperatures. ... In physics and chemistry, vitreous ice is a difficult-to-achieve state of water formed by cooling it extremely rapidly in which crystallization does not occur. ...


A TEM can be modified into a scanning transmission electron microscope (STEM) by the addition of a system that rasters the beam across the sample to form the image, combined with suitable detectors. A scanning transmission electron microscope (STEM) is a type of transmission electron microscope. ...


An analytical TEM is one equipped with detectors that can determine the elemental composition of the specimen by analysing its X-ray spectrum or the energy-loss spectrum of the transmitted electrons. In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz...


Modern research TEMs may include aberration correctors, to reduce the amount of distortion in the image, allowing information on features on the scale of 0.1 nm to be obtained (resolutions down to 0.05 nm have been achieved [1]) at magnifications of 50 million times [2]. Monochromators may also be used which reduce the energy spread of the incident electron beam to less than 0.15 eV. Major TEM makers include JEOL, Hitachi High-technologies, FEI Company (from merging with Philips Electron Optics) and Carl Zeiss. Aberration (Latin ab, from or away + errare, to wander), a deviation or wandering, especially used in the figurative sense as: In ethics, a deviation from the truth. ... A monochromator is an optical device that transmits a mechanically selectable narrow band of wavelengths of light chosen from a wider range of wavelengths available at the input. ... The electronvolt (symbol eV) is a unit of energy. ... A manufacturer of scanning electron microscopes, transmission electron microscopes, electron microprobes, electron beam lithography systems. ... FEI Company (NASDAQ: FEIC), founded in 1971, is a supplier of electron microscopy tools to researchers, developers and manufacturers working on the nanoscale. ... Philips HQ in Amsterdam Koninklijke Philips Electronics N.V. (Royal Philips Electronics N.V.), usually known as Philips, (Euronext: PHIA, NYSE: PHG) is one of the largest electronics companies in the world, founded and headquartered in the Netherlands. ... Carl Zeiss (September 11, 1816 – December 3, 1888) was an optician commonly known for the company he founded, Zeiss. ...


Applications of the TEM

The TEM is used heavily in both material science/metallurgy and the biological sciences. In both cases the specimens must be very thin and able to withstand the high vacuum present inside the instrument. Materials science includes those parts of chemistry and physics that deal with the properties of materials. ... Georg Agricola, author of De re metallica, an important early book on metal extraction Metallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their compounds, which are called alloys. ... Biology studies the variety of life (clockwise from top-left) E. coli, tree fern, gazelle, Goliath beetle Biology is the science of life (from the Greek words bios = life and logos = word). ...


For biological specimens, the maximum specimen thickness is roughly 1 micrometre. To withstand the instrument vacuum, biological specimens are typically held at liquid nitrogen temperatures after embedding in vitreous ice, or fixated using a negative staining material such as uranyl acetate or by plastic embedding. Typical biological applications include tomographic reconstructions of small cells or thin sections of larger cells and 3-D reconstructions of individual molecules via Single Particle Reconstruction. Look up Vacuum in Wiktionary, the free dictionary. ... A tank of liquid nitrogen, used to supply a cryogenic freezer (for storing laboratory samples at a temperature of about -150 Celsius). ... Negative stain is an old-established method, often used in diagnostic microscopy, for contrasting a thin specimen with an optically-opaque fluid. ... Uranyl acetate (UO2(CH3COO)2Ë‘22H2O) or Uranium bis(acetato)-O)dioxo-dihydrate, is a yellow free-flowing crystalline solid of yellow rhombic crystals with a slight acetic odor. ... Tomography involves the generation of a two-dimensional image representing a slice or section through a three-dimensional object. ... Single particle reconstruction is a technique in which large numbers of images (10,000 - 1,000,000) of ostensibly identical individual molecules or macromolecular assemblies are combined to produce a 3 dimensional reconstruction. ...

SEM image of a thin TEM sample milled by FIB. The thin membrane shown here is suitable for TEM examination; however, at ~300-nm thick, it would not be suitable for high-resolution TEM without further milling.
SEM image of a thin TEM sample milled by FIB. The thin membrane shown here is suitable for TEM examination; however, at ~300-nm thick, it would not be suitable for high-resolution TEM without further milling.

In material science/metallurgy the specimens tend to be naturally resistant to vacuum, but must be prepared as a thin foil, or etched so some portion of the specimen is thin enough for the beam to penetrate. Preparation techniques to obtain an electron transparent region include ion beam milling and wedge polishing. The focused ion beam (FIB) is a relatively new technique to prepare thin samples for TEM examination from larger specimens. Because the FIB can be used to micro-machine samples very precisely, it is possible to mill very thin membranes from a specific area of a sample, such as a semiconductor or metal. Materials that have dimensions small enough to be electron transparent, such as powders or nanotubes, can be quickly produced by the deposition of a dilute sample containing the specimen onto support grids. The suspension is normally a volatile solvent, such as ethanol, ensuring that the solvent rapidly evaporates allowing a sample that can be rapidly analysed. Image File history File linksMetadata Download high-resolution version (1024x800, 205 KB)SEM micrograph of a wide-bandgap semiconductor prepared for TEM by focused-ion-beam milling. ... Image File history File linksMetadata Download high-resolution version (1024x800, 205 KB)SEM micrograph of a wide-bandgap semiconductor prepared for TEM by focused-ion-beam milling. ... SEM Cambridge S150 at Geological Institute, University Kiel, 1980 SEM opened sample chamber The scanning electron microscope (SEM) is a type of electron microscope capable of producing high-resolution images of a sample surface. ... Focused ion beam, also known as FIB, is a scientific instrument that resembles a scanning electron microscope. ... An ion beam is a stream of charged particles, which has many uses in electronics manufacturing (principally ion implantation) and other industries. ... Focused ion beam, also known as FIB, is a scientific instrument that resembles a scanning electron microscope. ...


The imaging techniques explained below are particularly important in materials science. Faults in crystals affect both the mechanical and the electronic properties of materials, so understanding how they behave gives a powerful insight. By carefully selecting the orientation of the sample, it is possible not just to determine the position of defects but also to determine the type of defect present. If the sample is orientated so that one particular plane is only slightly tilted away from the strongest diffracting angle (known as the Bragg Angle), any distortion of the crystal plane that locally tilts the plane to the Bragg angle will produce particularly strong contrast variations. However, defects that produce only displacement of atoms that do not tilt the crystal to the Bragg angle (i.e. displacements parallel to the crystal plane) will not produce strong contrast. The Bragg formulation of X-ray diffraction (also referred to as Bragg diffraction) was first proposed by William Lawrence Bragg and William Henry Bragg in 1913 in response to their discovery that crystalline solids produced surprising patterns of reflected X-rays (in contrast to that of, say, a liquid). ...


Furthermore, the HRTEM technique (see below) allows the direct observation of crystal structure and therefore has an advantage over other methods in that there is no displacement between the location of a defect and the contrast variation caused in the image. However, it is not always possible to interpret the lattice images directly in terms of sample structure or composition. This is because the image is sensitive to a number of factors (specimen thickness and orientation, objective lens defocus, spherical and chromatic aberration), and although quantitative interpretation of the contrast shown in lattice images is possible, it is inherently complicated and may require extensive simulation of the images. Computer modeling of these images has added a new layer of understanding to the study of crystalline materials. High Resolution Transmission Electron Microscopy (HRTEM) is an imaging mode of the transmission electron microscope (TEM) that allows the imaging of the crystallographic structure of a sample at an atomic scale. ...


Imaging in the TEM

Transmission Electron Micrograph of Dislocations
Transmission Electron Micrograph of Dislocations

The contrast in a TEM image is not like the contrast in a light microscope image. A crystalline material interacts with the electron beam mostly by diffraction rather than absorption, although the intensity of the transmitted beam is still affected by the volume and density of the material through which it passes. The intensity of the diffraction depends on the orientation of the planes of atoms in a crystal relative to the electron beam; at certain angles the electron beam is diffracted strongly from the axis of the incoming beam, while at other angles the beam is largely transmitted. Modern TEMs are often equipped with specimen holders that allow the user to tilt the specimen to a range of angles in order to obtain specific diffraction conditions, and apertures placed below the specimen allow the user to select electrons diffracted in a particular direction. TEM Micrograph of Dislocations 1 (precipitate and dislocations in austenitic stainless steel) Photomicrograph by Wikityke File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... TEM Micrograph of Dislocations 1 (precipitate and dislocations in austenitic stainless steel) Photomicrograph by Wikityke File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... In materials science, a dislocation is a crystallographic defect, or irregularity, within a crystal structure. ... The intensity pattern formed on a screen by diffraction from a square aperture Diffraction refers to various phenomena associated with wave propagation, such as the bending, spreading and interference of waves passing by an object or aperture that disrupts the wave. ... In physics, absorption is the process by which the energy of a photon is taken up by another entity, for example, by an atom whose valence electrons make transition between two electronic energy levels. ... For other uses, see Crystal (disambiguation). ...


A high-contrast image can therefore be formed by blocking electrons deflected away from the optical axis of the microscope by placing the aperture to allow only unscattered electrons through. This produces a variation in the electron intensity that reveals information on the crystal structure, and can be viewed on a fluorescent screen, or recorded on photographic film or captured electronically. Enargite crystals In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms in a crystal. ... Fluorescence induced by exposure to ultraviolet light in vials containing various sized cadmium selenide (CdSe) quantum dots. ... This article or section does not cite its references or sources. ...

Transmission Electron Micrograph of a cobalt catalyst (darker spots) supported on coal carbonized at 850 ºC and added by ion-exchange technique
Transmission Electron Micrograph of a cobalt catalyst (darker spots) supported on coal carbonized at 850 ºC and added by ion-exchange technique

This technique (known as Bright Field or Light Field) is particularly sensitive to extended crystal lattice defects in an otherwise ordered crystal, such as dislocations. As the local distortion of the crystal around the defect changes the angle of the crystal plane, the intensity of the scattering will vary around the defect. As the image is formed by the distortion of the crystal planes around the defect, the contrast in these images does not normally coincide exactly with the defect, but is slightly to one side. Image File history File links Metadata Size of this preview: 800 × 540 pixelsFull resolution (1320 × 891 pixel, file size: 705 KB, MIME type: image/jpeg) Fernando Vallejos Burgos Kaneko Labs. ... Image File history File links Metadata Size of this preview: 800 × 540 pixelsFull resolution (1320 × 891 pixel, file size: 705 KB, MIME type: image/jpeg) Fernando Vallejos Burgos Kaneko Labs. ... For other uses, see Cobalt (disambiguation). ... It has been suggested that this article or section be merged into Catalysis. ... Coal Example chemical structure of coal Coal is a fossil fuel formed in ecosystems where plant remains were saved by water and mud from oxidization and biodegradation. ... In materials science, a dislocation is a crystallographic defect, or irregularity, within a crystal structure. ...


It is also possible to produce an image from electrons deflected by a particular crystal plane. By either moving the aperture to the position of the deflected electrons, or tilting the electron beam so that the deflected electrons pass through the centred aperture, an image can be formed of only deflected electrons, known as a Dark Field image.


In the most powerful diffraction contrast TEM instruments, crystal structure can also be investigated by High Resolution Transmission Electron Microscopy (HRTEM), also known as phase contrast imaging as the images are formed due to differences in phase of electron waves scattered through a thin specimen. High Resolution Transmission Electron Microscopy (HRTEM) is an imaging mode of the transmission electron microscope (TEM) that allows the imaging of the crystallographic structure of a sample at an atomic scale. ...


Resolution of the HRTEM is limited by spherical and chromatic aberration, but a new generation of aberration correctors has been able to overcome spherical aberration. Software correction of spherical aberration has allowed the production of images with sufficient resolution to show carbon atoms in diamond separated by only 0.89 ångströms (89 pm, one ångström is 0.0000000001 of a meter or 100 picometers) and atoms in silicon at 0.78 ångströms (78 pm) at magnifications of 50 million times. Improved resolution has also allowed the imaging of lighter atoms that scatter electrons less efficiently — lithium atoms have been imaged in lithium battery materials[3]. The ability to determine the positions of atoms within materials has made the HRTEM an indispensable tool for nanotechnology research and development in many fields, including heterogeneous catalysis and the development of semiconductor devices for electronics and photonics. This article is about the optical device. ... This article is about the optical device. ... An Ã¥ngström or aangstroem (the official transliteration), or angstrom (symbol Ã…) is a non-SI unit of length that is internationally recognized, equal to 0. ... Picometre (American spelling: picometer) is an SI measure of length that is equal to 10−12 of a metre. ... Buckminsterfullerene C60, also known as the buckyball, is the simplest of the carbon structures known as fullerenes. ... Heterogeneous catalysis is a chemistry term which describes catalysis where the catalyst is in a different phase (ie. ... Semiconductor devices are electronic components that exploit the electronic properties of semiconductor materials, principally silicon, germanium, and gallium arsenide. ...


Limitations

There are a number of drawbacks to the TEM technique. Many materials require extensive sample preparation to produce a sample thin enough to be electron transparent, which makes TEM analysis a relatively time consuming process with a low throughput of samples. The structure of the sample may also be changed during the preparation process. Also the field of view is relatively small, raising the possibility that the region analysed may not be characteristic of the whole sample. There is potential that the sample may be damaged by the electron beam, particularly in the case of biological materials.


See also

Image File history File links Wikibooks-logo-en. ... Wikibooks logo Wikibooks, previously called Wikimedia Free Textbook Project and Wikimedia-Textbooks, is a wiki for the creation of books. ... SEM Cambridge S150 at Geological Institute, University Kiel, 1980 SEM opened sample chamber The scanning electron microscope (SEM) is a type of electron microscope capable of producing high-resolution images of a sample surface. ... An electron microscope is a type of microscope that uses electrons as a way to illuminate and create an image of a specimen. ... Transmission Electron Aberration-corrected Microscope or TEAM is a $100 million US Department of Energy research project being conducted at five US laboratories. ... Energy-filtered transmission electron microscopy (EFTEM) is a technique used in Transmission electron microscopy, in which only electrons of particular kinetic energies are used to form the image or diffraction pattern. ... This article is in need of attention from an expert on the subject. ...

References

  1. ^ TEAM Project Achieves Microscopy Breakthrough
  2. ^ The Scale of Things (Office of Basic Energy Sciences)
  3. ^ Imaging lithium atoms at sub-Ångström resolution pdf, 6Mb

External links


  Results from FactBites:
 
Transmission electron microscopy - Wikipedia, the free encyclopedia (1426 words)
Transmission electron microscopy (TEM) is an imaging technique whereby a beam of electrons is focused onto a specimen causing an enlarged version to appear on a fluorescent screen or layer of photographic film (see electron microscope), or can be detected by a CCD camera.
Electrons are generated by a process known as thermionic discharge in the same manner as the at the cathode in a cathode ray tube, or by field emission; they are then accelerated by an electric field and focussed by electrical and magnetic fields onto the sample.
A crystalline material interacts with the electron beam mostly by diffraction rather than absorption, although the intensity of the transmitted beam is still affected by the volume and density of the material through which it passes.
Transmission electron microscopy - definition of Transmission electron microscopy in Encyclopedia (799 words)
Like all matter, electrons have both wave and particle properties (as demonstrated by Louis-Victor de Broglie), and their wave-like properties mean that a beam of electrons can in some circumstances be made to behave like a beam of radiation.
Electrons are generated by a process known as thermionic discharge in the same manner as the at the cathode in a cathode ray tube, or by field emission; they are then accelerated by an electric field and focussed by electrical and magnetic fields on to the sample.
In the most powerful diffraction contrast TEM instruments, it is possible to produce a diffraction pattern image which is directly analogous to the planes of atoms in the crystal.
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