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An electron microscope is a
microscope A microscope () is a laboratory instrument used to examine objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small objects and structures using a microscope. Microscopic means being invisi ...
that uses a beam of accelerated
electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have n ...
s as a source of illumination. As the wavelength of an electron can be up to 100,000 times shorter than that of visible light
photon A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they alwa ...
s, electron microscopes have a higher resolving power than light microscopes and can reveal the structure of smaller objects. A scanning transmission electron microscope has achieved better than 50  pm resolution in
annular dark-field imaging Annular dark-field imaging is a method of mapping samples in a scanning transmission electron microscope (STEM). These images are formed by collecting scattered electrons with an annular dark-field detector. Conventional TEM dark-field imaging ...
mode and
magnification Magnification is the process of enlarging the apparent size, not physical size, of something. This enlargement is quantified by a calculated number also called "magnification". When this number is less than one, it refers to a reduction in si ...
s of up to about 10,000,000× whereas most light microscopes are limited by diffraction to about 200  nm resolution and useful magnifications below 2000×. Electron microscopes use shaped magnetic fields to form electron optical lens systems that are analogous to the glass lenses of an optical light microscope. Electron microscopes are used to investigate the ultrastructure of a wide range of biological and inorganic specimens including microorganisms,
cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Locations * Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery w ...
, large molecules,
biopsy A biopsy is a medical test commonly performed by a surgeon, interventional radiologist, or an interventional cardiologist. The process involves extraction of sample cells or tissues for examination to determine the presence or extent of a dise ...
samples,
metals A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typical ...
, and crystals. Industrially, electron microscopes are often used for quality control and
failure analysis Failure analysis is the process of collecting and analyzing data to determine the cause of a failure, often with the goal of determining corrective actions or liability. According to Bloch and Geitner, ”machinery failures reveal a reaction chain ...
. Modern electron microscopes produce electron
micrograph A micrograph or photomicrograph is a photograph or digital image taken through a microscope or similar device to show a magnified image of an object. This is opposed to a macrograph or photomacrograph, an image which is also taken on a m ...
s using specialized digital cameras and frame grabbers to capture the images.


History

In 1926, Hans Busch developed the electromagnetic lens. According to Dennis Gabor, the physicist Leó Szilárd tried in 1928 to convince him to build an electron microscope, for which he had filed a patent. The first prototype electron microscope, capable of four-hundred-power magnification, was developed in 1931 by the physicist Ernst Ruska and the electrical engineer Max Knoll at the Berlin Technische Hochschule or Berlin Technical University. The apparatus was the first practical demonstration of the principles of electron microscopy. In May of the same year, Reinhold Rudenberg, the scientific director of Siemens-Schuckertwerke, obtained a patent for an electron microscope. In 1932, Ernst Lubcke of Siemens & Halske built and obtained images from a prototype electron microscope, applying the concepts described in Rudenberg's patent. In the following year, 1933, Ruska built the first electron microscope that exceeded the resolution attainable with an optical (light) microscope. Four years later, in 1937, Siemens financed the work of Ernst Ruska and Bodo von Borries, and employed Helmut Ruska, Ernst's brother, to develop applications for the microscope, especially with biological specimens. Also in 1937, Manfred von Ardenne pioneered the scanning electron microscope. Siemens produced the first commercial electron microscope in 1938. The first North American electron microscopes were constructed in the 1930, at the
Washington State University Washington State University (Washington State, WSU, or informally Wazzu) is a public land-grant research university with its flagship, and oldest, campus in Pullman, Washington. Founded in 1890, WSU is also one of the oldest land-grant uni ...
by Anderson and Fitzsimmons and the
University of Toronto The University of Toronto (UToronto or U of T) is a public research university in Toronto, Ontario, Canada, located on the grounds that surround Queen's Park. It was founded by royal charter in 1827 as King's College, the first institution ...
, by
Eli Franklin Burton Eli Franklin Burton, (February 14, 1879 – July 6, 1948) was a Canadian physicist. Burton was born in Green River, township of Pickering, Ontario, Canada. He graduated from the University of Toronto in 1901. From 1904 to 1906 he studied ...
and students Cecil Hall, James Hillier, and Albert Prebus. Siemens produced a transmission electron microscope (TEM) in 1939. Although current transmission electron microscopes are capable of two million-power magnification, as scientific instruments, they remain based upon Ruska's
prototype A prototype is an early sample, model, or release of a product built to test a concept or process. It is a term used in a variety of contexts, including semantics, design, electronics, and software programming. A prototype is generally used to ...
.


Types


Transmission electron microscope (TEM)

The original form of the electron microscope, the transmission electron microscope (TEM), uses a
high voltage High voltage electricity refers to electrical potential large enough to cause injury or damage. In certain industries, ''high voltage'' refers to voltage above a certain threshold. Equipment and conductors that carry high voltage warrant sp ...
electron beam to illuminate the specimen and create an image. The electron beam is produced by an electron gun, commonly fitted with a
tungsten Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isol ...
filament
cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction in whi ...
as the electron source. The electron beam is accelerated by an
anode An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic is ...
typically at +100 k eV (40 to 400 keV) with respect to the cathode, focused by
electrostatic Electrostatics is a branch of physics that studies electric charges at rest ( static electricity). Since classical times, it has been known that some materials, such as amber, attract lightweight particles after rubbing. The Greek word for ...
and electromagnetic lenses, and transmitted through the specimen that is in part transparent to electrons and in part scatters them out of the beam. When it emerges from the specimen, the electron beam carries information about the structure of the specimen that is magnified by the objective lens system of the microscope. The spatial variation in this information (the "image") may be viewed by projecting the magnified electron image onto a fluorescent viewing screen coated with a phosphor or
scintillator A scintillator is a material that exhibits scintillation, the property of luminescence, when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate (i.e. re-emit the absorbe ...
material such as
zinc sulfide Zinc sulfide (or zinc sulphide) is an inorganic compound with the chemical formula of ZnS. This is the main form of zinc found in nature, where it mainly occurs as the mineral sphalerite. Although this mineral is usually black because of various ...
. Alternatively, the image can be photographically recorded by exposing a
photographic film Photographic film is a strip or sheet of transparent film base coated on one side with a gelatin emulsion containing microscopically small light-sensitive silver halide crystals. The sizes and other characteristics of the crystals determine ...
or plate directly to the electron beam, or a high-resolution phosphor may be coupled by means of a lens optical system or a fibre optic light-guide to the sensor of a digital camera. The image detected by the digital camera may be displayed on a monitor or computer. The resolution of TEMs is limited primarily by spherical aberration, but a new generation of hardware correctors can reduce spherical aberration to increase the resolution in high-resolution transmission electron microscopy (HRTEM) to below 0.5
angstrom The angstromEntry "angstrom" in the Oxford online dictionary. Retrieved on 2019-03-02 from https://en.oxforddictionaries.com/definition/angstrom.Entry "angstrom" in the Merriam-Webster online dictionary. Retrieved on 2019-03-02 from https://www.m ...
(50 picometres), enabling magnifications above 50 million times. The ability of HRTEM to determine the positions of atoms within materials is useful for nano-technologies research and development. Transmission electron microscopes are often used in
electron diffraction Electron diffraction refers to the bending of electron beams around atomic structures. This behaviour, typical for waves, is applicable to electrons due to the wave–particle duality stating that electrons behave as both particles and waves. S ...
mode. The advantages of electron diffraction over
X-ray crystallography X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...
are that the specimen need not be a single crystal or even a polycrystalline powder, and also that the Fourier transform reconstruction of the object's magnified structure occurs physically and thus avoids the need for solving the phase problem faced by the X-ray crystallographers after obtaining their X-ray diffraction patterns. One major disadvantage of the transmission electron microscope is the need for extremely thin sections of the specimens, typically about 100 nanometers. Creating these thin sections for biological and materials specimens is technically very challenging. Semiconductor thin sections can be made using a focused ion beam. Biological tissue specimens are chemically fixed, dehydrated and embedded in a polymer resin to stabilize them sufficiently to allow ultrathin sectioning. Sections of biological specimens, organic polymers, and similar materials may require staining with heavy atom labels in order to achieve the required image contrast.


Serial-section electron microscope (ssEM)

One application of TEM is serial-section electron microscopy (ssEM), for example in analyzing the connectivity in volumetric samples of brain tissue by imaging many thin sections in sequence. This may be achieved by introducing a milling method into the imaging pipeline, by which successive slices of a 3D volume are exposed to the beam and imaged. These methods include Serial Block Face SEM (SB-SEM) and Focused Ion Beam-SEM ( FIB-SEM). Pre-processing of volumes to create many slices which are imaged in an automated fashion have recently achieved high-throughput imaging of volumes up to 1 mm3. Using this method, entire local neuronal microcircuits may be resolved, though the equipment and time requirements for this are still significant: imaging a 1 mm3 block of brain tissue required 6 months of near-continuous imaging by six TEM running in parallel.


Scanning transmission electron microscope (STEM)

The STEM rasters a focused incident probe across a specimen that (as with the TEM) has been thinned to facilitate detection of electrons scattered ''through'' the specimen. The high resolution of the TEM is thus possible in STEM. The focusing action (and aberrations) occur before the electrons hit the specimen in the STEM, but afterward in the TEM. The STEMs use of SEM-like beam rastering simplifies
annular dark-field imaging Annular dark-field imaging is a method of mapping samples in a scanning transmission electron microscope (STEM). These images are formed by collecting scattered electrons with an annular dark-field detector. Conventional TEM dark-field imaging ...
, and other analytical techniques, but also means that image data is acquired in serial rather than in parallel fashion. Often TEM can be equipped with the scanning option and then it can function both as TEM and STEM.


Scanning electron microscope (SEM)

The SEM produces images by probing the specimen with a focused electron beam that is scanned across a rectangular area of the specimen ( raster scanning). When the electron beam interacts with the specimen, it loses energy by a variety of mechanisms. The lost energy is converted into alternative forms such as heat, emission of low-energy secondary electrons and high-energy backscattered electrons, light emission (
cathodoluminescence Cathodoluminescence is an optical and electromagnetic phenomenon in which electrons impacting on a luminescent material such as a phosphor, cause the emission of photons which may have wavelengths in the visible spectrum. A familiar example is ...
) or
X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10  nanometers, corresponding to frequencies in the range 30&nb ...
emission, all of which provide signals carrying information about the properties of the specimen surface, such as its topography and composition. The image displayed by an SEM maps the varying intensity of any of these signals into the image in a position corresponding to the position of the beam on the specimen when the signal was generated. In the SEM image of an ant shown below and to the right, the image was constructed from signals produced by a secondary electron detector, the normal or conventional imaging mode in most SEMs. Generally, the image resolution of an SEM is lower than that of a TEM. However, because the SEM images the surface of a sample rather than its interior, the electrons do not have to travel through the sample. This reduces the need for extensive sample preparation to thin the specimen to electron transparency. The SEM is able to image bulk samples that can fit on its stage and still be maneuvered, including a height less than the working distance being used, often 4 millimeters for high-resolution images. The SEM also has a great depth of field, and so can produce images that are good representations of the three-dimensional surface shape of the sample. Another advantage of SEMs comes with environmental scanning electron microscopes (ESEM) that can produce images of good quality and resolution with hydrated samples or in low, rather than high, vacuum or under chamber gases. This facilitates imaging unfixed biological samples that are unstable in the high vacuum of conventional electron microscopes.


Reflection electron microscope (REM)

In the reflection electron microscope (REM) as in the TEM, an electron beam is incident on a surface but instead of using the transmission (TEM) or secondary electrons (SEM), the reflected beam of elastically scattered electrons is detected. This technique is typically coupled with reflection high energy electron diffraction (RHEED) and ''reflection high-energy loss spectroscopy (RHELS)''. Another variation is spin-polarized low-energy electron microscopy (
SPLEEM Low-energy electron microscopy, or LEEM, is an analytical surface science technique used to image atomically clean surfaces, atom-surface interactions, and thin (crystalline) films. In LEEM, high-energy electrons (15-20 keV) are emitted from an el ...
), which is used for looking at the microstructure of magnetic domains.


Scanning tunneling microscopy (STM)

In STM, a conductive tip held at a voltage is brought near a surface, and a profile can be obtained based on the tunneling probability of an electron from the tip to the sample since it is a function of distance.


Colour

In their most common configurations, electron microscopes produce images with a single brightness value per pixel, with the results usually rendered in
greyscale In digital photography, computer-generated imagery, and colorimetry, a grayscale image is one in which the value of each pixel is a single sample representing only an ''amount'' of light; that is, it carries only intensity information. Gr ...
. However, often these images are then colourized through the use of feature-detection software, or simply by hand-editing using a graphics editor. This may be done to clarify structure or for aesthetic effect and generally does not add new information about the specimen. In some configurations information about several specimen properties is gathered per pixel, usually by the use of multiple detectors. In SEM, the attributes of topography and material contrast can be obtained by a pair of backscattered electron detectors and such attributes can be superimposed in a single colour image by assigning a different primary colour to each attribute. Similarly, a combination of backscattered and secondary electron signals can be assigned to different colours and superimposed on a single colour micrograph displaying simultaneously the properties of the specimen. Some types of detectors used in SEM have analytical capabilities, and can provide several items of data at each pixel. Examples are the energy-dispersive X-ray spectroscopy (EDS) detectors used in elemental analysis and cathodoluminescence microscope (CL) systems that analyse the intensity and spectrum of electron-induced
luminescence Luminescence is spontaneous emission of light by a substance not resulting from heat; or "cold light". It is thus a form of cold-body radiation. It can be caused by chemical reactions, electrical energy, subatomic motions or stress on a crys ...
in (for example) geological specimens. In SEM systems using these detectors, it is common to colour code the signals and superimpose them in a single colour image, so that differences in the distribution of the various components of the specimen can be seen clearly and compared. Optionally, the standard secondary electron image can be merged with the one or more compositional channels, so that the specimen's structure and composition can be compared. Such images can be made while maintaining the full integrity of the original signal, which is not modified in any way.


Sample preparation

Materials to be viewed under an electron microscope may require processing to produce a suitable sample. The technique required varies depending on the specimen and the analysis required: * ''Chemical fixation'' – for biological specimens aims to stabilize the specimen's mobile macromolecular structure by chemical crosslinking of
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
s with
aldehyde In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl gro ...
s such as
formaldehyde Formaldehyde ( , ) ( systematic name methanal) is a naturally occurring organic compound with the formula and structure . The pure compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde (refer to section ...
and glutaraldehyde, and
lipid Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids in ...
s with osmium tetroxide. * '' Negative stain'' – suspensions containing nanoparticles or fine biological material (such as viruses and bacteria) are briefly mixed with a dilute solution of an electron-opaque solution such as ammonium molybdate, uranyl acetate (or formate), or phosphotungstic acid. This mixture is applied to a suitably coated EM grid, blotted, then allowed to dry. Viewing of this preparation in the TEM should be carried out without delay for best results. The method is important in microbiology for fast but crude morphological identification, but can also be used as the basis for high-resolution 3D reconstruction using EM tomography methodology when carbon films are used for support. Negative staining is also used for observation of nanoparticles. * '' Cryofixation'' – freezing a specimen so rapidly, in liquid ethane that the water forms vitreous (non-crystalline) ice. This preserves the specimen in a snapshot of its solution state. An entire field called
cryo-electron microscopy Cryogenic electron microscopy (cryo-EM) is a cryomicroscopy technique applied on samples cooled to cryogenic temperatures. For biological specimens, the structure is preserved by embedding in an environment of vitreous ice. An aqueous sample so ...
has branched from this technique. With the development of
cryo-electron microscopy Cryogenic electron microscopy (cryo-EM) is a cryomicroscopy technique applied on samples cooled to cryogenic temperatures. For biological specimens, the structure is preserved by embedding in an environment of vitreous ice. An aqueous sample so ...
of vitreous sections (CEMOVIS), it is now possible to observe samples from virtually any biological specimen close to its native state. * ''Dehydration'' – or replacement of
water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...
with organic solvents such as
ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a ...
or
acetone Acetone (2-propanone or dimethyl ketone), is an organic compound with the formula . It is the simplest and smallest ketone (). It is a colorless, highly volatile and flammable liquid with a characteristic pungent odour. Acetone is miscibl ...
, followed by
critical point drying Supercritical drying, also known as critical point drying, is a process to remove liquid in a precise and controlled way. It is useful in the production of microelectromechanical systems (MEMS), the drying of spices, the production of aerogel, t ...
or infiltration with embedding resins. Also
freeze drying Freeze drying, also known as lyophilization or cryodesiccation, is a low temperature dehydration process that involves freezing the product and lowering pressure, removing the ice by sublimation. This is in contrast to dehydration by most conve ...
. * ''Embedding, biological specimens'' – after dehydration, tissue for observation in the transmission electron microscope is embedded so it can be sectioned ready for viewing. To do this the tissue is passed through a 'transition solvent' such as propylene oxide (epoxypropane) or
acetone Acetone (2-propanone or dimethyl ketone), is an organic compound with the formula . It is the simplest and smallest ketone (). It is a colorless, highly volatile and flammable liquid with a characteristic pungent odour. Acetone is miscibl ...
and then infiltrated with an
epoxy Epoxy is the family of basic components or cured end products of epoxy resins. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. The epoxide functional group is also co ...
resin In polymer chemistry and materials science, resin is a solid or highly viscous substance of plant or synthetic origin that is typically convertible into polymers. Resins are usually mixtures of organic compounds. This article focuses on nat ...
such as Araldite, Epon, or
Durcupan Durcupan is a water-soluble epoxy resin produced by the Fluka subsidiary of Sigma-Aldrich. It is commonly used for embedding electron microscope samples in plastic so they may be sectioned (sliced thin) with a microtome and then imaged. Durcup ...
; tissues may also be embedded directly in water-miscible acrylic resin. After the resin has been polymerized (hardened) the sample is thin sectioned (ultrathin sections) and
stained A stain is a discoloration that can be clearly distinguished from the surface, material, or medium it is found upon. They are caused by the chemical or physical interaction of two dissimilar materials. Accidental staining may make materials app ...
– it is then ready for viewing. * ''Embedding, materials'' – after embedding in resin, the specimen is usually ground and polished to a mirror-like finish using ultra-fine abrasives. The polishing process must be performed carefully to minimize scratches and other polishing artifacts that reduce image quality. * ''Metal shadowing'' – Metal (e.g.
platinum Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver". Pla ...
) is evaporated from an overhead electrode and applied to the surface of a biological sample at an angle. The surface topography results in variations in the thickness of the metal that are seen as variations in brightness and contrast in the electron microscope image. * ''Replication'' – A surface shadowed with metal (e.g. platinum, or a mixture of carbon and platinum) at an angle is coated with pure carbon evaporated from carbon electrodes at right angles to the surface. This is followed by removal of the specimen material (e.g. in an acid bath, using enzymes or by mechanical separation) to produce a surface replica that records the surface ultrastructure and can be examined using transmission electron microscopy. * ''Sectioning'' – produces thin slices of the specimen, semitransparent to electrons. These can be cut on an
ultramicrotome A microtome (from the Greek ''mikros'', meaning "small", and ''temnein'', meaning "to cut") is a cutting tool used to produce extremely thin slices of material known as ''sections''. Important in science, microtomes are used in microscopy, allow ...
with a glass or
diamond Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. Another solid form of carbon known as graphite is the chemically stable form of carbon at room temperature and pressure, b ...
knife to produce ultra-thin sections about 60–90 nm thick. Disposable
glass knives A glass knife is a knife with a blade made of glass, with a fracture line forming an extremely sharp cutting edge. Glass knives were used in antiquity due to their natural sharpness and the ease with which they could be manufactured. In modern el ...
are also used because they can be made in the lab and are much cheaper. * ''
Staining Staining is a technique used to enhance contrast in samples, generally at the microscopic level. Stains and dyes are frequently used in histology (microscopic study of biological tissues), in cytology (microscopic study of cells), and in th ...
'' – uses heavy metals such as
lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, ...
,
uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...
or
tungsten Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isol ...
to scatter imaging electrons and thus give contrast between different structures, since many (especially biological) materials are nearly "transparent" to electrons (weak phase objects). In biology, specimens can be stained "en bloc" before embedding and also later after sectioning. Typically thin sections are stained for several minutes with an aqueous or alcoholic solution of uranyl acetate followed by aqueous lead citrate. * ''Freeze-fracture or freeze-etch'' – a preparation method particularly useful for examining lipid membranes and their incorporated proteins in "face on" view. The fresh tissue or cell suspension is frozen rapidly (cryofixation), then fractured by breaking (or by using a microtome) while maintained at liquid nitrogen temperature. The cold fractured surface (sometimes "etched" by increasing the temperature to about −100 °C for several minutes to let some ice sublime) is then shadowed with evaporated platinum or gold at an average angle of 45° in a high vacuum evaporator. The second coat of carbon, evaporated perpendicular to the average surface plane is often performed to improve the stability of the replica coating. The specimen is returned to room temperature and pressure, then the extremely fragile "pre-shadowed" metal replica of the fracture surface is released from the underlying biological material by careful chemical digestion with acids,
hypochlorite In chemistry, hypochlorite is an anion with the chemical formula ClO−. It combines with a number of cations to form hypochlorite salts. Common examples include sodium hypochlorite (household bleach) and calcium hypochlorite (a component of ...
solution or SDS detergent. The still-floating replica is thoroughly washed free from residual chemicals, carefully fished up on fine grids, dried then viewed in the TEM. * ''Freeze-fracture replica immunogold labeling (FRIL)'' – the freeze-fracture method has been modified to allow the identification of the components of the fracture face by immunogold labeling. Instead of removing all the underlying tissue of the thawed replica as the final step before viewing in the microscope the tissue thickness is minimized during or after the fracture process. The thin layer of tissue remains bound to the metal replica so it can be immunogold labeled with antibodies to the structures of choice. The thin layer of the original specimen on the replica with gold attached allows the identification of structures in the fracture plane. There are also related methods which label the surface of etched cells and other replica labeling variations. * ''Ion beam milling'' – thins samples until they are transparent to electrons by firing ions (typically
argon Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice a ...
) at the surface from an angle and sputtering material from the surface. A subclass of this is focused ion beam milling, where
gallium Gallium is a chemical element with the Symbol (chemistry), symbol Ga and atomic number 31. Discovered by France, French chemist Paul-Émile Lecoq de Boisbaudran in 1875, Gallium is in boron group, group 13 of the periodic table and is similar to ...
ions are used to produce an electron transparent membrane in a specific region of the sample, for example through a device within a microprocessor. Ion beam milling may also be used for cross-section polishing prior to SEM analysis of materials that are difficult to prepare using mechanical polishing. * ''Conductive coating'' – an ultrathin coating of electrically conducting material, deposited either by high vacuum evaporation or by low vacuum sputter coating of the sample. This is done to prevent the accumulation of static electric fields at the specimen due to the electron irradiation required during imaging. The coating materials include gold, gold/palladium, platinum, tungsten, graphite, etc. * '' Earthing'' – to avoid electrical charge accumulation on a conductively coated sample, it is usually electrically connected to the metal sample holder. Often an
electrically conductive adhesive An electrically conductive adhesive is a glue that is primarily used for electronics. The electric conductivity is caused by a component that makes ca. 80% of the total mass of an electrically conductive adhesive. This conductive component is sus ...
is used for this purpose.


Disadvantages

Electron microscopes are expensive to build and maintain, but the capital and running costs of confocal light microscope systems now overlaps with those of basic electron microscopes. Microscopes designed to achieve high resolutions must be housed in stable buildings (sometimes underground) with special services such as magnetic field canceling systems. The samples largely have to be viewed in
vacuum A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or " void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often ...
, as the molecules that make up air would scatter the electrons. An exception is
liquid-phase electron microscopy Liquid-phase electron microscopy (LP EM) refers to a class of methods for imaging specimens in liquid with nanometer spatial resolution using electron microscopy. LP-EM overcomes the key limitation of electron microscopy: since the electron opti ...
using either a closed liquid cell or an environmental chamber, for example, in the environmental scanning electron microscope, which allows hydrated samples to be viewed in a low-pressure (up to ) wet environment. Various techniques for in situ electron microscopy of gaseous samples have been developed as well. Scanning electron microscopes operating in conventional high-vacuum mode usually image conductive specimens; therefore non-conductive materials require conductive coating (gold/palladium alloy, carbon, osmium, etc.). The low-voltage mode of modern microscopes makes possible the observation of non-conductive specimens without coating. Non-conductive materials can be imaged also by a variable pressure (or environmental) scanning electron microscope. Small, stable specimens such as
carbon nanotubes A scanning tunneling microscopy image of a single-walled carbon nanotube Rotating single-walled zigzag carbon nanotube A carbon nanotube (CNT) is a tube made of carbon with diameters typically measured in nanometers. ''Single-wall carbon na ...
, diatom frustules and small mineral crystals (asbestos fibres, for example) require no special treatment before being examined in the electron microscope. Samples of hydrated materials, including almost all biological specimens, have to be prepared in various ways to stabilize them, reduce their thickness (ultrathin sectioning) and increase their electron optical contrast (staining). These processes may result in '' artifacts'', but these can usually be identified by comparing the results obtained by using radically different specimen preparation methods. Since the 1980s, analysis of cryofixed, vitrified specimens has also become increasingly used by scientists, further confirming the validity of this technique.


Applications

;Semiconductor and data storage * Circuit edit * Defect analysis *
Failure analysis Failure analysis is the process of collecting and analyzing data to determine the cause of a failure, often with the goal of determining corrective actions or liability. According to Bloch and Geitner, ”machinery failures reveal a reaction chain ...
Biology and life sciences *
Cryobiology Cryobiology is the branch of biology that studies the effects of low temperatures on living things within Earth's cryosphere or in science. The word cryobiology is derived from the Greek words κρῧος ryos "cold", βίος ios "life", and λ� ...
*
Cryo-electron microscopy Cryogenic electron microscopy (cryo-EM) is a cryomicroscopy technique applied on samples cooled to cryogenic temperatures. For biological specimens, the structure is preserved by embedding in an environment of vitreous ice. An aqueous sample so ...
*
Diagnostic electron microscopy The transmission electron microscope (TEM) is used as an important diagnostic tool to screen human tissues at high magnification (the ultrastructural level), often in conjunction with other methods, particularly light microscopy and immunofluoresc ...
* Drug research (e.g. antibiotics) * Electron tomography * Particle analysis * Particle detection * Protein localization * Structural biology * Tissue imaging *
Toxicology Toxicology is a scientific discipline, overlapping with biology, chemistry, pharmacology, and medicine, that involves the study of the adverse effects of chemical substances on living organisms and the practice of diagnosing and treating e ...
*
Virology Virology is the scientific study of biological viruses. It is a subfield of microbiology that focuses on their detection, structure, classification and evolution, their methods of infection and exploitation of host cells for reproduction, the ...
(e.g. viral load monitoring) ;Materials research * Device testing and characterization * Dynamic materials experiments * Electron beam-induced deposition * In-situ characterisation * Materials qualification * Medical research * Nanometrology * Nanoprototyping ;Industry * Chemical/
Petrochemical Petrochemicals (sometimes abbreviated as petchems) are the chemical products obtained from petroleum by refining. Some chemical compounds made from petroleum are also obtained from other fossil fuels, such as coal or natural gas, or renewabl ...
* Direct beam-writing fabrication * Food science *
Forensics Forensic science, also known as criminalistics, is the application of science to criminal and civil laws, mainly—on the criminal side—during criminal investigation, as governed by the legal standards of admissible evidence and crimin ...
* Fractography * Micro-characterization *
Mining Mining is the extraction of valuable minerals or other geological materials from the Earth, usually from an ore body, lode, vein, seam, reef, or placer deposit. The exploitation of these deposits for raw material is based on the econom ...
(mineral liberation analysis) * Pharmaceutical QC


See also

*
Acronyms in microscopy This is a list of analysis methods used in materials science. Analysis methods are listed by their acronym, if one exists. Symbols * μSR – see muon spin spectroscopy * χ – see magnetic susceptibility A * AAS – Atomic absorption spect ...
*
Electron diffraction Electron diffraction refers to the bending of electron beams around atomic structures. This behaviour, typical for waves, is applicable to electrons due to the wave–particle duality stating that electrons behave as both particles and waves. S ...
* Electron energy loss spectroscopy (EELS) * Electron microscope images * Energy filtered transmission electron microscopy (EFTEM) * Environmental scanning electron microscope (ESEM) *
Field emission microscope Field-emission microscopy (FEM) is an analytical technique used in materials science to investigate molecular surface structures and their electronic properties. Invented by Erwin Wilhelm Müller in 1936, the FEM was one of the first surface-anal ...
* HiRISE * Immune electron microscopy * In situ electron microscopy *
Karnovsky fixative Karnovsky fixative, developed by M. J. Karnovsky, is a fixative for electron microscopy. Solution The stock solution for Karnovsky fixative is as follows: * 2.0 g paraformaldehyde * 25 ml distilled water * 1M sodium hydroxide 2 - 4 drops * 50% ...
* Microscope image processing *
Microscopy Microscopy is the technical field of using microscopes to view objects and areas of objects that cannot be seen with the naked eye (objects that are not within the resolution range of the normal eye). There are three well-known branches of micr ...
* Nanoscience *
Nanotechnology Nanotechnology, also shortened to nanotech, is the use of matter on an atomic, molecular, and supramolecular scale for industrial purposes. The earliest, widespread description of nanotechnology referred to the particular technological goal ...
* Neutron microscope *
Quantum microscopy Quantum microscopy allows microscopic properties of matter and quantum particles to be measured and imaged. Various types of microscopy use quantum principles. The first microscope to do so was the scanning tunneling microscope, which paved the way ...
* Scanning confocal electron microscopy * Scanning electron microscope (SEM) * Scanning tunneling microscope *
Surface science Surface science is the study of physical and chemical phenomena that occur at the interface of two phases, including solid– liquid interfaces, solid– gas interfaces, solid–vacuum interfaces, and liquid– gas interfaces. It includes th ...
* Transmission Electron Aberration-Corrected Microscope * X-ray diffraction *
X-ray microscope An X-ray microscope uses electromagnetic radiation in the soft X-ray band to produce magnified images of objects. Since X-rays penetrate most objects, there is no need to specially prepare them for X-ray microscopy observations. Unlike visible ...
*
Low-energy electron microscopy Low-energy electron microscopy, or LEEM, is an analytical surface science technique used to image atomically clean surfaces, atom-surface interactions, and thin (crystalline) films. In LEEM, high-energy electrons (15-20 keV) are emitted from an e ...
* Hemispherical electron energy analyzer


References


External links


An Introduction to Electron Microscopy
: resources for teachers and students
Cell Centered Database – Electron microscopy data


high school (GCSE, A Level) resource


General


Animations and explanations of various types of microscopy including electron microscopy
(Université Paris Sud)
Environmental Scanning Electron Microscopy (ESEM)

ETH Zurich website
graphics and images illustrating various procedures
Eva Nogales's Seminar: "Introduction to Electron Microscopy"

FEI Image Contest
FEI has had a microscopy image contest every year since 2008
Introduction to electron microscopy
by David Szondy
Nanohedron.com image gallery
images generated by electron microscopy
X-ray element analysis in electron microscopy
information portal with X-ray microanalysis and EDX contents


History


John H.L. Watson's recollections at the University of Toronto when he worked with Hillier and Prebus


(Archives Center, National Museum of American History, Smithsonian Institution)


Other


The Royal Microscopical Society, Electron Microscopy Section (UK)

Albert Lleal. Natural history subjects at Scanning Electron Microscope SEM

EM Images
{{Authority control Microscopes Accelerator physics Anatomical pathology Pathology Scientific techniques German inventions Protein imaging 20th-century inventions