样品等（样品及制样）

TEM 用语集- 样品等（样品及制样）

ion etching keyword “ ion etching ”

"Ion etching" is a technique to selectively remove specific atoms and the atoms at lattice defects. This technique is used for observation of textures on a specimen surface. A technique of uniform and nonselective thinning for specimen preparation of TEM is ion milling. Sometimes, ion etching is confused with ion milling. Related term ion milling

ion cleaner keyword “ion cleaner ”

An ion cleaning tool that removes contaminants on a TEM specimen, which are residual substances deposited on a specimen at specimen pre-treatment, and contaminated substances deposited on a specimen in specimen storage. The specimen holder on which a specimen is set is inserted into an "ion cleaner." Then, a glow discharge due to residual gasses in the ion cleaner is generated and the ionized gasses by discharge irradiate the specimen. This chemical-reaction of the ionized gasses removes the contaminants (in particular, polymerized substances of hydrocarbons) deposited on the specimen. Related term contamination plasma cleaning

ion sputtering keyword “ion sputtering ”

"Ion sputtering" is a phenomenon where atoms are sputtered from a solid surface when ionized and accelerated atoms or molecules hit the solid surface. This phenomenon is utilized for formation of a thin film on a solid surface, specimen coating and ion etching. In the case of specimen coating, discharge is generated in a low vacuum or in an Ar gas environment under a vacuum, the ionized gas is accelerated and hits a target material (Au, Pt, etc.) at the anode. Then, the material is emitted from the target surface and deposit on a specimen at the cathode, specimen being coated. Related term focused ion-beam milling FIB

milling keyword “ milling “

"Milling" is a technique to mill and fabricate a specimen substance. In specimen preparation for TEM, an ion beam is used for milling. ion milling

ion milling keyword “ion milling ”

"Ion milling" is a specimen preparation technique that is used when electrolytic polishing or chemical polishing cannot be used to prepare a specimen. This technique is particularly effective for the specimen preparation when cross-section observations of layered materials are requested. A thin cross sectional film is prepared by milling surface layer atoms with the irradiation of an argon ion beam accelerated at 2 kV to 10 kV with a grazing incidence angle less than 10°. The disadvantage of ion milling is that damage to the specimen is unavoidable. Commercially-available ion-milling instruments are equipped with an optical microscope or a CCD camera with a magnification of several ten times to view the state of the specimen. Related term focused ion-beam milling FIB gentle milling electrolytic polishing chemical polishing

focused ion-beam milling

"Focused ion beam (FIB) milling" is a specimen preparation technique for TEM, which is used to mill a specific area on a specimen, such as a defective part on a semiconductor device. The specific area is fabricated to a wedge shape with a high accuracy of sub-micrometer scale. A focused gallium ion beam accelerated at several kV to 40 kV irradiates a specimen to mill the specific area while this area is monitored through a secondary ion image (a SEM image can also be viewed with some FIB instruments), resulting in formation of a thin section specimen. Since damage to the specimen caused by gallium ions is unavoidable, ion milling at a low accelerating voltage (gentle milling) may be applied afterwards to remove damaged layers on the specimen surface. Related term ion milling gentle milling 5-1. plating keyword “plating” "Plating" is a technique to form thin metal layers deposited on a surface of a solid. Related term ion plating electrolytic plating 5-2. ion plating keyword “ ion plating” "Ion plating" is a technique to form a thin metal layer deposited on a surface of a solid by ionizing metal. In this technique, discharge is generated in a low vacuum or a gas environment between the substrate acting as a cathode and a metal evaporation source acting as an anode. Then, metal atoms are evaporated and ionized, and accelerated by an electric field, then finally form a thin layer on the substrate. 5-3. electrolytic plating keyword “ electrolytic plating ” "Electrolytic plating" is a technique to form a thin metal layer on a surface of a solid specimen by electrolysis of a conductive solid (ex. metal) in a suitable electrolyte solvent. Actually, a specimen (acting as an anode) and a platinum (Pt) plate or a stainless-steel (acting as a cathode) are immersed in a suitable electrolyte solvent. By the flow of electric current between these electrodes, the eluted Pt or stainless-steel is deposited on the specimen surface. 6. liquid-metal ion source keyword “liquid-metal ion source” A "liquid-metal ion source" uses a metal that is at the liquid state at normal temperature. This ion source, normally liquid gallium, is used for an FIB instrument. Related term focused ion-beam milling FIB 7-1. etching keyword “ etching ” "Etching" is to selectively remove specific surface atoms of a specimen by utilizing chemical or physical reactions. Related term ion etching polishing 7-2. freeze etching keyword “ freeze etching “ Freeze etching is a technique to expose the structure under ice on a freeze-fractured surface of a biological specimen, by sublimating the ice under vacuum. After the structure is exposed, a replica is made from the fractured surface for TEM observation. This technique is mainly used to observe the structures of cytoskeletons, organelles, etc. Related term freeze fracturing freeze replication 7-3. ion etching "Ion etching" is a technique to selectively remove specific atoms and the atoms at lattice defects. This technique is used for observation of textures on a specimen surface. A technique of uniform and nonselective thinning for specimen preparation of TEM is ion milling. Sometimes, ion etching is confused with ion milling. Related term ion milling 8-1. Epitaxy keyword “ epitaxy ” "Epitaxy" is a technique to deposit and grow a crystalline film on a crystalline substrate using vacuum evaporation (deposition) or chemical vapor deposition (CVD), etc. In epitaxy, the crystalline film formed has a specific orientation relation with the substrate crystal. molecular beam epitaxy MBE 8-2. molecular beam epitaxy keyword “ molecular beam epitaxy ” "Molecular beam epitaxy (MBE)" is a technique to deposit and grow a crystalline film in an ultra-high vacuum. In MBE, target elements or target materials that will constitute a target crystal are heated and evaporated and then, the target crystalline film is deposited and grown on a heated crystalline substrate. MBE is similar to vacuum evaporation (deposition), but the technique accurately controls the molecular beam to prepare a crystalline specimen controlled at the atomic scale. MBE is used also for specimen preparation for a TEM. Related term vacuum evaporation (deposition) 9-1. Grid keyword “ grid ” A "grid" is a metal mesh with a thickness of 20 to 30 μm, which is used to support a supporting film of a specimen or a specimen itself for a TEM. The specimen on the grid is set on the specimen holder and inserted into the objective lens polepiece. The material of the grid is copper (Cu), molybdenum (Mo), or gold (Au). Related term supporting film micro grid 9-2. Microgrid keyword “ microgrid ” A "microgrid" is a supporting film used to support a fine specimen like powder for a TEM. The microgrid is made of cellulose aceto-butyrate and has many holes with the hole diameter of several μm or less. Related term grid supporting film 10-1. polishing keyword “ polishing ” "Polishing" is a mechanical or chemical treatment to prepare a smooth and uniform surface without selecting crystal orientations unlike etching and cleaving. Related term mechanical polishing chemical polishing electrolytic polishing etching 10-2. electrolytic polishing "Electrolytic polishing" is a technique used for preparing a thin film on metal, alloy, etc. In this technique, a specimen (acting as an anode) and a platinum (Pt) plate or a stainless-steel (acting as a cathode) are immersed in a suitable electrolyte solvent. Then, an electrostatic potential is applied between these electrodes to elute the atoms of the specimen surface, and finally the specimen surface is thinned with its surface kept smooth. The advantage of electrolytic polishing is that a thinned specimen can be prepared with no mechanical stress. Related term jet polishing chemical polishing ion milling 10-3. jet polishing "Jet polishing" is one technique in electrolytic polishing. In this technique, a jet-like polishing solution is sprayed onto a specimen to make a hole at its center. Spraying the solution makes it possible to keep the solution at the specimen surface fresh, thus a quick and smooth polishing is achieved. Related term electrolytic polishing chemical polishing ion milling 10-4. chemical polishing keyword “chemical polishing” "Chemical polishing" is a technique used for thinning inorganic materials of semiconductors and insulators. In this technique, a specimen is immersed in a polishing solution that is mainly composed of strong acid or strong alkali. Then, the specimen is thinned with its surface kept smooth. The advantage of chemical polishing is that thin specimens can be made with no mechanical distortion stress. Normally, a polishing solution that does not cause selective dissolution (etching) is used. When a particular layer in a multi-layer semiconductor is required to observe, a specified solution is used, which dissolves other layers while leaving the particular layer. Related term electrolytic polishing ion milling 10-5. mechanical polishing keyword “mechanical polishing” "Mechanical polishing" is a physical polishing technique used for specimen preparation of TEM. The common techniques are as follows: (1) Manual polishing using water-resistant paper (down to ～100 μm thick), (2) Rotational polishing device-based polishing using diamond or corundum particles (down to ～several 10 μm thick), (3) Dimple grinder-based polishing using corundum particles (down to <10 μm thick), and (4) Tripot polisher-based polishing using diamond particles (down to <10 μm thick). Related term tripot polisher dimple grinder 11-1. Coating keyword “ coating ” "Coating" is to form a thin layer (ex. metallic layer) on the surface of a target substance. Related term conductive coating 11-2. conductive coating "Conductive coating" is to coat a nonconductive specimen for TEM with conductive carbon by arc discharge so that charging on this specimen is prevented and observation is properly performed. Related term charging 12. ice embedding keyword “ ice embedding ” Ice embedding is one of rapid freeze fixation techniques used for biological specimen preparation in transmission electron microscopy. This technique embeds a suspended specimen of biological macromolecules (purified proteins, viruses, etc.) in an amorphous ice film with a few tens of nm to a few hundreds of nm. It enables us to observe a molecular state of the specimen in a liquid solution without staining. In an actual experiment, a few μL suspension liquid is dropped onto a micro grid subject to hydrophilic treatment, excessive liquid is removed with a filter paper, then the specimen is rapidly frozen by immersing it into a coolant as quickly as possible. Liquid ethane or liquid propane is used commonly as a coolant because these are easy to sublimate and have a large temperature difference between the melting point and the boiling point.

Schematic of ice embedding.

Cross sectional view of ice-embedded specimens, which are embedded in amorphous ice.

Cryo-TEM image of ice-embedded bacteriophage T4.

The morphology of the head and tail parts of the bacteriophage is well preserved. Related term cryo-electron microscopy rapid freeze fixation amorphous ice high pressure freezing metal mirror freezing (slam freezing) 13. top surface keyword “ top surface “ In a solid surface, the "top surface" is defined as an extremely thin surface (～0.5 to several nm from the surface). This term is used in the following manner. (1) The top surface of a specimen is fabricated. (2) Auger electrons are emitted from the top surface. 14. gentle milling keyword “ gentle milling “ A surface of a specimen milled by the focused ion beam (FIB) technique or a normal ion milling technique is likely to suffer damage. To remove the damaged layers on the specimen surface, an argon ion beam at a low accelerating voltage of 100 V to 2 kV is used to gently mill the specimen surface. This technique is termed "gentle milling." Related term focused ion-beam milling FIB ion milling 15. supporting film keyword “ supporting film “ A "supporting film" is a thin carbon, polyvinyl formal, or collodion film with a thickness of several 10 nm or less. It is pasted on a grid to support a specimen for a TEM on the specimen holder. Related term grid microgrid 16. focused ion-beam milling keyword “ focused ion -beam milling” "Focused ion beam (FIB) milling" is a specimen preparation technique for TEM, which is used to mill a specific area on a specimen, such as a defective part on a semiconductor device. The specific area is fabricated to a wedge shape with a high accuracy of sub-micrometer scale. A focused gallium ion beam accelerated at several kV to 40 kV irradiates a specimen to mill the specific area while this area is monitored through a secondary ion image (a SEM image can also be viewed with some FIB instruments), resulting in formation of a thin section specimen. Since damage to the specimen caused by gallium ions is unavoidable, ion milling at a low accelerating voltage (gentle milling) may be applied afterwards to remove damaged layers on the specimen surface. ion milling gentle milling 17. sintering keyword “ sintering “ "Sintering" is to heat a powder specimen until each powder in the specimen adheres to each other without melting. 18. filler keyword “ filler ” A material used for sintering. Yttria, etc., are used as "filler.". 19. radiation damage keyword “ radiation damage ” "Radiation damage" is defined as structure deterioration of a specimen due to the irradiation of an electron beam. The primary radiation damage includes the knock-on damage and the ionization damage. In the knock-on damage process, an atom that suffers the collision by an incident electron is ejected from its lattice site, forming an interstitial atom and an atomic vacancy at the corresponding lattice site. In the ionization damage process, outer-shell electrons of an atom are ejected and the atom is ionized. In a subsequent relaxation process after the primary radiation damage process, particular lattice defects or amorphous structures are created. This process is called the secondary radiation damage process. 20-1. contamination keyword “ contamination ” Hydrocarbons deposited on a specimen surface condense at an electron-beam irradiation area by the electrostatic force of the electron beam and are polymerized by the electron beam. This phenomenon is called "(specimen) contamination." Contamination is particularly severe when a small specimen area is irradiated with a focused, high-density electron beam, for example CBED or STEM. Related term hydrocarbon 20-2. anti-contamination device A device that is used for suppressing the deposition of hydrocarbons on a specimen in a TEM. By the condensation action of the cooled fin with liquid nitrogen which is set to surround the specimen holder, contamination on the specimen due to hydrocarbons is largely decreased. In this device, two small aperture holes are placed at the top and bottom to allow the electron beam to pass through the holes. The tip of the specimen holder (specimen part) is inserted into the fin through the opening at its lateral side. Related term contamination 21. specimen environment keyword “ specimen environment ” An environment when a specimen is observed or analyzed in TEM. Various specimen environments are used, which include a high-temperature environment, a low-temperature environment, an atmospheric pressure environment, and an environment with tensile force, electric fields or magnetic fields. 22. specimen preparation keyword “ specimen preparation ” "Specimen preparation" is to prepare a suitable specimen in observation and analysis of TEM. 23-1. deposition keyword “ deposition ” "Deposition" is to form a thin film on a solid surface by physical sputtering, chemical vapor deposition, etc. Related term ion sputtering ion plating vacuum evaporation (deposition) molecular beam epitaxy MBE 23-2. vacuum evaporation (deposition) keyword “ vacuum evaporation (deposition) ” "Vacuum evaporation (deposition)" is a technique to form a thin substance layer on a surface of a substrate by evaporating the substance in high vacuum. For a TEM, this technique is used for specimen preparation of a metal and an alloy with uniform thickness. Related term vacuum evaporator 24. vacuum evaporator keyword “ vacuum evaporator ” A "vacuum evaporator" is an instrument to form a thin substance layer on a surface of a substrate by vacuum evaporation (deposition). The vacuum evaporator consists of a heating element, a case and a substrate in a vacuum chamber. A substance (in most cases, a metal) that is placed in the case is evaporated by melting at high temperature, and a thin film (layer) is formed on the substrate. In specimen preparation for a TEM, a heating element, such as a tungsten (W) wire or a tantalum (Ta) plate, is resistively-heated and the substance is evaporated (deposited). Related term vacuum evaporation (deposition) 25. charging keyword “charging “ If a specimen has no conductivity, part of incident electrons accumulate on the specimen. This phenomenon is called "charging." Charging disturbs normal transmission and scattering of the incident electrons, thus abnormal contrast and distortion of the image occur. To prevent charging, conductive coating is performed. Related term conductive coating 26. diamond knife keyword “ diamond knife ” A diamond knife is used to prepare an ultrathin section in ultramicrotomy. The diamond knife was originally developed to cut hard inorganic materials, which cannot be cut with a glass knife. Today, the diamond knife is used also for resin specimens because the glass knife is damaged even by a resin specimen, that is, the blade edge of the knife is likely to become dull. Thus, the diamond knife currently plays an essential role in preparing a uniform ultrathin section. Related term ultramicrotomy glass knife ultrasonic knife ultrathin section 27. ultrasonic cleaning keyword “ ultrasonic cleaning “ "Ultrasonic cleaning" is a technique to remove contaminants on a specimen and parts of a TEM. In "ultrasonic cleaning," a cleaning solution is vibrated by an ultrasonic transducer and hits the object to clean. Since the cleaning solution can enter the fine gaps of the object, ultrasonic cleaning is suitable for precision components. Acetone is used as a cleaning solution in many cases. 28. dimple grinder keyword “ dimple grinder ” "Dimple grinder" is a mechanical polishing device. It creates a dimple (dip) with a thickness down to 10 μm or less on a parallel plate specimen prepared by polishing using a rotational polishing device (thickness: 100 μm or less). It uses a polishing agent, such as corundum particles having different particle sizes (0.1 μm to several μm). The specimen with the dimple is further thinned by ion milling. Related term tripot polisher ion milling 29. electrolytic plating keyword “ electrolytic plating” "Electrolytic plating" is a technique to form a thin metal layer on a surface of a solid specimen by electrolysis of a conductive solid (ex. metal) in a suitable electrolyte solvent. Actually, a specimen (acting as an anode) and a platinum (Pt) plate or a stainless-steel (acting as a cathode) are immersed in a suitable electrolyte solvent. By the flow of electric current between these electrodes, the eluted Pt or stainless-steel is deposited on the specimen surface. 30. freeze sectioning keyword “ freeze sectioning” Freeze sectioning is used to prepare a sectioned biological specimen of soft textures. The specimen is frozen under liquid-nitrogen temperature to cut the specimen easier with a cryo-microtome. A cryo-electron microscope is needed for specimen observation. Related term cryo-electron microscopy 31. conductive coating keyword “ conductive coating” "Conductive coating" is to coat a nonconductive specimen for TEM with conductive carbon by arc discharge so that charging on this specimen is prevented and observation is properly performed. Related term charging 32. tripot polisher keyword “ tripot polisher ” "Tripot polisher" is a mechanical polishing device that consists of three legs with micrometers and a leg for supporting a specimen. First, a bulk specimen is set on the leg for the specimen, and the polishing angle is finely adjusted by the micrometers, the tripot polisher is mounted on a rotational polishing device, and then the specimen is polished while the tripot polisher is supported with human fingers. A thinned specimen with a thickness of ～10 μm can be obtained from a bulk specimen (～3 mm × ～3 mm × ～2 mm thick). As a polishing material, lapping film coated with diamond of 0.1 μm to 30 μm is used. In the finishing process, the polished specimen with a mirror surface is fabricated using colloidal silica. For TEM observation, the specimen is usually polished to wedge-shaped. Normally, the specimen is finished by ion milling. Since the use of the tripot polisher enables preparation of a wedge-shaped specimen over a wide area, the device is particularly suitable for cross-sectional specimen preparation. Related term dimple grinder ion milling 33. thinning keyword “ thinning” "Thinning" is to fabricate a specimen to a thin film for a TEM. 34. crushing keyword “ crushing ” "Crushing" is a technique used for preparing a thin film on an oxide, a ceramic material, etc. In this technique, a bulk specimen is crushed in an agate mortor and the crushed specimen is dispersed in an organic solvent (methanol, acetone, etc.). After this process, an obtained suspending solution is dropped onto a microgrid for TEM and then thin specimen fragments are deposited. Related term electrolytic polishing chemical polishing ion milling 35. molecular beam epitaxy keyword “ molecular beam epitaxy” "Molecular beam epitaxy (MBE)" is a technique to deposit and grow a crystalline film in an ultra-high vacuum. In MBE, target elements or target materials that will constitute a target crystal are heated and evaporated and then, the target crystalline film is deposited and grown on a heated crystalline substrate. MBE is similar to vacuum evaporation (deposition), but the technique accurately controls the molecular beam to prepare a crystalline specimen controlled at the atomic scale. MBE is used also for specimen preparation for a TEM. Related term vacuum evaporation (deposition) 36. cleaving keyword “ cleaving “ "Cleaving" is a technique used for specimen preparation for a TEM, which cleaves a solid to expose a particular orientational section of a crystal. 37. ultramicrotomy keyword “ultramicrotomy “ A specimen preparation method that is used for thinning biological specimens, high-polymer specimens and composite materials. “Ultramicrotomy” is also used to prepare thin films of soft metals. The use of a diamond knife enables a specimen to be sequentially cut with a thickness of several 10 nm to 100 nm. Related term diamond knife electrolytic polishing chemical polishing ion milling 38. annealing keyword “ annealing” "Annealing" is a thermal treatment to heat metallic materials and others at an appropriate temperature and then to cool slowly them for obtaining uniform structures or for removing the internal stress of the materials. 39. coolant (refrigerant) keyword “ coolant(refrigerant)” A substance that is used for cooling components of instruments or other materials. For cooling, the latent heat of the "coolant" is used, which is emitted or absorbed at the transformation from the liquid state to the gas state or vice versa. 40-1. replica keyword “ replica” A "replica" is a reproduction of a topographic shape of the surface of a substance (specimen). To make a replica, a thin layer of a plastic material or an inorganic material is formed on the surface of the substance, and then, this thin layer is removed, the topographic shape of the surface being copied. The replica technique is used for a reproduction of a grating or observation of the topographic shape of the specimen. 40-2. freeze replication Freeze replication is a technique to make a metallic thin-film replica from a fractured surface of a biological specimen. When a lipid bilayer of the cell membrane is fractured, the extracellular leaflet of the freeze-fractured lipid bilayer is called the E face (or the extracellular face), whereas the cytoplasmic leaflet is called the P face (or the protoplasmic face). Thus, the technique is used to observe the morphology of membrane proteins. Related term freeze fracturing freeze etching 41. rapid freeze fixation keyword “rapid freeze fixation” Rapid freeze fixation is a technique to physically fix the morphology of biological tissues, biological cells, bacteria and suspended specimens composed of viruses, purified proteins, etc., by rapidly freezing the specimens. Chemical fixation, which is used in ordinary specimen preparation of biological tissues for TEM, may cause outflow of mineral salts, etc., in the tissues or deformation of the membrane structures of the tissues. On the other hand, rapid freeze fixation enables us to fix a specimen while preserving the morphology of the tissues. Rapid freeze fixation techniques include high pressure freezing, metal mirror freezing (slam freezing) and ice embedding. Related term high pressure freezing metal mirror freezing (slam freezing) ice embedding amorphous ice chemical fixation

42. high pressure freezing keyword “ high pressure freezing ” High pressure freezing, one of rapid freeze fixation techniques, is to fix biological specimens such as biological tissues, biological cells and bacteria. Rapid freezing under an about 2000 atm suppresses formation of ice crystals, which give rise to the destruction of the tissues, by decreasing the melting point of water by about -20 °C and increasing its viscosity. This technique provides a uniform freezing under amorphous ice with a depth more than one order of magnitude larger (about 200 μm) compared with the freezing depth at the atmospheric pressure. Specimen preparation for TEM observation of the frozen specimen is carried out by one of the following three procedures. (1) Applying freeze sectioning to the specimen, (2) Applying resin embedding and ultrathin sectioning to the specimen after the specimen is subject to freeze substitution and is returned to room temperature, and (3) Making a replica of the specimen by freeze fracturing. Related term rapid freeze fixation amorphous ice freeze substitution freeze fracturing 43. amorphous ice keyword “ amorphous ice” Amorphous ice means ice that does not take a crystalline state. When water is cooled below the melting point, ice crystal is formed and grows until its temperature reaches the re-crystallization temperature. Since formation of ice crystals can cause destruction of fine structures of a biological specimen, amorphous-ice formation without formation of ice crystals is required when rapid freeze fixation is applied. Thus, ice-crystal formation should be suppressed by cooling the specimen as rapid as possible down to the re-crystallization temperature. Related term rapid freeze fixation high pressure freezing freeze substitution metal mirror freezing (slam freezing) cryo-electron microscopy ice embedding 44. freeze substitution keyword “ freeze substitution “ Freeze substitution is a technique to replace amorphous ice with an organic solvent (acetone, etc.) (dehydration) in a biological specimen fixed by rapid freeze fixation, where the specimen is subject to rapid freeze fixation (high pressure freezing or metal mirror freezing (slam freezing)). To prevent destruction of fine structures of the specimen, the substitution is carried out by raising temperature step-by-step from -80 ℃ to 4 °C over a few days. In the course of the substitution, chemical fixation and electron staining are often performed by adding osmium tetroxide and/or uranium acetate. Then, the substituted specimen is returned to room temperature and is subject to resin embedding. A TEM specimen is made by ultrathin sectioning the specimen. Related term rapid freeze fixation metal mirror freezing (slam freezing) high pressure freezing amorphous ice 45. metal mirror freezing (slam freezing) keyword “metal mirror freezing (slam freezing) Metal mirror freezing (slam freezing) is one of rapid freeze fixation techniques. This technique punches and rapidly freezes a biological specimen against a metal block cooled by a coolant such as liquid nitrogen. In many cases, high-thermal-conductivity, high-purity copper with gold plating is used for a metal block. To increase a temperature drop efficiency of the specimen, the surface of the metal block is prepared into a flat mirror-surface. This technique can be performed using a relatively inexpensive device, but provides a smaller freezing depth suitable for TEM observation (about 20 µm) than the suitable depth produced by high pressure freezing. This technique is mainly used to fix tissues. Specimen preparation for TEM observation of the frozen specimen is carried out by one of the following three procedures. (1) Applying freeze sectioning to the specimen, (2) Applying resin embedding and ultrathin sectioning to the specimen after the specimen is subject to freeze substitution and is returned to room temperature, and (3) Making a replica of the specimen by freeze fracturing. Related term rapid freeze fixation high pressure freezing amorphous ice freeze fracturing 46. freeze fracturing keyword “ freeze fracturing ” Freeze fracturing is a technique to cut and expose the inner face of a biological specimen such as cells and tissues. This technique freezes the specimen with liquid nitrogen, etc., and then fractures the specimen under vacuum by giving an impact on the frozen specimen using a knife. After the specimen is fractured, a replica of a fractured surface is made for TEM observation. To observe the fractured surface with a TEM, either of two replication techniques is applied. One is freeze replication to make a replica of the fractured surface without any processing. Another is freeze etching by which ice on the fractured surface is sublimated, followed by making a replica of the exposed inner structure without ice. A replica is usually made under vacuum by depositing platinum or platinum palladium onto the specimen and then by depositing carbon onto the already deposited surface. The specimen is immersed and dissolved in an alkali reagent. Only the replica is mounted on a mesh (grid) for TEM observation. Related term freeze replication freeze etching 47. chemical fixation keyword “ chemical fixation ” Chemical fixation is a technique to fix a specimen with chemicals to prevent autolysis by the action of enzymes and deformation of morphologies during specimen preparation. Biological tissues start autolysis caused by their enzymes immediately after stopping the activities of them. For the TEM observation of a biological specimen, the specimen must be prepared by removing water to preserve its morphologies under vacuum in the microscope column, and by thinning the specimen to transmit an electron beam. For these requests, dehydration, resin embedding and thin sectioning are applied, but the procedures cause deformation of fine structures of the specimen. Chemical fixation is carried out to preserve the morphologies and physical properties at the living states of the specimen as much as possible. This technique prevents the autolysis and deformation by cross-linking the proteins or lipids of biological materials using chemicals. Chemical fixation for a TEM is performed by the two steps, prefixation and postfixation. Related term rapid freeze fixation prefixation postfixation cross-linking 48. cross-linking keyword “ cross-linking ” “Cross-linking” means that target chain-like macromolecules are additionally bounded to each other with other molecules by constructing inter- or intra-molecular bridges. Related term chemical fixation prefixation postfixation 49. prefixation keyword “ prefixation ” Prefixation is the first-step fixation technique of chemical fixation for biological specimens observed with a TEM. This technique aims at inactivation and preservation of proteins. In the preparation of a biological specimen for TEM observation, dehydration and resin embedding are applied. Under these procedures, a robust fixation of the fine structures of biological tissues is required. For such a fixation, it is effective to use strong oxidizing reagents (osmium tetroxide, potassium permanganate, etc.). However, these reagents have disadvantages that include slow permeation into the specimen and destruction of proteins in the specimen. To avoid these disadvantageous phenomena, the specimen is pre-fixed with paraformaldehyde or glutaraldehyde, which permeate quickly the specimen and cross-links the proteins to preserve the original morphologies. Related term chemical fixation postfixation cross-linking 50. postfixation keyword “ postfixation ” Postfixation is the second-step fixation technique of chemical fixation for biological specimens observed with a TEM. This technique aims at preservation of lipids or enhancement of a TEM image contrast. In the preparation of a biological specimen for TEM observation, dehydration and resin embedding are applied. In these procedures, fixation only with aldehyde (glutaraldehyde, paraformaldehyde, etc.) cannot fix lipids in the specimen. Thus, the membrane structures that consist of lipids flow out of the specimen when performing dehydration with ethanol or an organic solvent. In addition, aldehyde bounded to the specimen does not contribute to the enhancement of the image contrast because it consists of only light elements. These problems are solved by postfixation with heavy metal oxide reagents (osmium tetroxide, etc.) which is a subsequent process of prefixation with aldehyde. Osmium tetroxide fixes lipids by binding it to a double-binding region of unsaturated fatty acid and by constructing a cross-link for preventing outflow and deformation of the lipids. In addition, osmium is a heavy metal, thus enhancing the image contrast of the binding region. Osmium tetroxide is an effective reagent, but it has disadvantages that include slow permeation into the specimen and destruction of proteins in the specimen. To prevent these disadvantageous phenomena, fixation (prefixation) of proteins with aldehyde is required before applying fixation with osmium tetroxide. Related term chemical fixation prefixation cross-linking 51. ultrasonic knife keyword “ ultrasonic knife ” An ultrasonic knife is a diamond knife that thins a specimen while vibrating the blade head of the knife using ultrasonic wave. In ordinary thinning with a diamond knife, a pressure can be applied to the cutting direction of the specimen. This may cause “compression” (deformation of the specimen due to compression in the up-and-down direction) or falling of granules with different hardnesses such as lipid droplets. The ultrasonic knife which vibrates its blade head right-and-left in cutting, makes it possible to disperse the pressure to the specimen. Owing to this feature, the ultrasonic knife prevents “compression” or the falling of the granules. Related term ultrathin section diamond knife ultramicrotomy 52-1. ultrathin section keyword “ ultrathin section ” An ultrathin section means a section sliced thin enough to transmit an electron beam. In many cases, the ultrathin section has a thickness of 100 nm or less. Related term diamond knife ultramicrotomy 52-2. interference color of ultrathin section keyword “interference color of ultrathin section” Interference color of an ultrathin section is produced by the interference of light reflected from the top- and bottom-faces of the ultrathin section when white light is incident onto a section in the almost vertical direction. Since the interference color corresponds to the thickness of the section, the interference color enables us to know a rough thickness of the section. Sections with thicknesses of about 70 nm, about 100 nm and about 200 nm emit interference colors of silver gold, gold and blue, respectively. Related term ultrathin section ultramicrotomy diamond knife 53. glass knife keyword “ glass knife ” A glass knife is used for microtomy. The knife is made by fracturing a thick glass or a glass rod to use a fabricated edge line as the blade of the knife. The main role of the glass knife is to make a flat surface or to trim a specimen prior to ultrathin sectioning with a diamond knife. Related term diamond knife ultrathin section ultramicrotomy 54. electron staining keyword “ electron staining ” Electron staining means to adsorb heavy metals of a high scattering power to biological specimens or polymer materials composed of light elements which exhibit a small scattering power for electrons, for enhancing the TEM image contrast of these specimens. When observing a biological specimen, uranium or lead is adsorbed to proteins, etc., in the specimen. For a specimen of polymers (e.g. polypropylene, polyethylene) consisting of crystalline and amorphous states, ruthenium can be selectively adsorbed to the amorphous regions because ruthenium tetroxide enters only to the amorphous regions. Those heavy metals which strongly scatter incident electrons give rise to enhancement of the image contrast. Related term negative staining en bloc staining scattering contrast 55. negative staining keyword “negative staining ” Negative staining is one of electron staining techniques. This technique leaves heavy metals at the gaps in a specimen and on the supporting film at the surrounding regions of the specimen. Negative staining enables enhancement of the TEM image contrast. An aqueous solution of viruses or purified proteins, etc. is dropped onto a supporting film, and then excessive water is removed from the specimen with a filter paper. Immediately after the removal of excessive water, a staining solution containing heavy metals (uranium acetate, phosphotungstic acid, etc.) is dropped onto the specimen. Then, water is removed from the specimen with a filter paper to dry the specimen, leaving the heavy materials at the gaps and on the supporting film at the surrounding regions of the specimen. As a result, these regions appear dark due to strong scattering of incident electrons, and the morphology of the specimen is elucidated. Since the specimen itself is not stained, this technique is termed "negative" staining. related term electron staining scattering contrast 56. en bloc staining keyword “ en bloc staining” En bloc staining is one of electron staining techniques. A biological specimen (block tissue) is immersed in a solution of uranium acetate or an aqueous solution of lead aspartic acid after postfixation and before dehydration, for electron staining. En bloc staining enhances the TEM image contrast of membrane structures or fibrous structures in cells. Related term electron staining scattering contrast 57. shadowing keyword “shadowing” Shadowing is a technique to obliquely deposit metals (platinum, etc.) of a high scattering power with a low angle to the specimen surface of a biological specimen composed of proteins, DNA, viruses, etc., under vacuum. By shadowing, the TEM image contrast due to roughness of the surface of those specimens is enhanced. Biological molecules, such as proteins, DNA and viruses, are composed of light elements of carbon, nitrogen, oxygen or hydrogen. When a specimen of these molecules is observed with a TEM, most incident electrons pass through the specimen without suffering scattering. As a result, an obtained image hardly shows contrast. To solve this problem, metals (platinum, etc.) are vacuum-deposited onto the molecule particles. This deposition makes it possible to enhance the contrast of the surface roughness of fine structures. As the deposition angle is lower, the finer structures can be observed. When the deposition angle is higher, the fine structures are more embedded in the deposited metal. The technique is called "shadowing" or "shadow casting" because the metal-deposited part in the TEM image appears as a shadow. Related term electron staining scattering contrast 58. immunoelectron microscopy keyword “ immunoelectron microscopy” Immunoelectron microscopy is a technique to visualize the locations (localization) of specific proteins with a TEM, by utilizing antigen-antibody reactions where antibodies bind specifically to antigenic proteins. First, antibodies (primary antibodies) react with the target proteins. Then, the secondary antibodies labeled with gold colloid, etc., react with the primary antibodies, so that the target proteins can be detected with the TEM. Immunoelectron microscopy is classified into two methods depending on the timing of antibody reactions; pre-embedding (before resin embedding) and post-embedding (after resin embedding). Related term pre-embedding post-embedding 59. pre-embedding keyword “pre-embedding” Pre-embedding is a technique of embedding in the course of immunoelectron microscopy for the primary antibodies to react with the target antigenic proteins immediately after fixation of block tissues or cells. The name of “pre-embedding” originates from the fact that the immune-reaction is performed prior to resin embedding. The advantage of pre-embedding is that antibodies can react with the antigenic proteins in advance of the occurrence of denaturation or outflow of the antigenic proteins. However, pre-embedding has two major disadvantages. One is that antibodies do not stain uniformly the whole block tissue because staining is made for the block tissue prior to resin embedding. Another is that a large amount of expensive antibodies is needed for pre-embedding. In general, pre-embedding is a simpler technique than post-embedding. Related term immunoelectron microscopy post-embedding 60. post-embedding keyword “post-embedding” Post-embedding is a technique of embedding in the course of immunoelectron microscopy for the primary antibodies to react with the target antigenic proteins after ultrathin sectioning. The name of “post-embedding” originates from the fact that the immune-reaction is performed after ultrathin sectioning (subsequent to resin embedding). Post-embedding has two major advantages. One is that the locations (localization) of the target proteins are precisely elucidated because the primary antibodies react with the proteins exposed on an ultra-thin section. Another is that the structures of tissues, organelles, etc., are preserved better compared with the case of pre-embedding because post-embedding requires a few steps until embedding. However, post-embedding has a major disadvantage that antigens can be lost by dehydration or can be denatured by resin embedding, thus degrading the staining efficiency. Related term pre-embedding immunoelectron microscopy 61. Skyrmion keyword “ skyrmion” Skyrmion is a vortex-like magnetic structure formed by the magnetic moments of electron spins. The term “Skymion” is named after Skyrme, a theoretical physicist of UK, who proposed the quantum structure. “Skymion” is also called “magnetic vortex” or “spin vortex”. Its size ranges from approximately several nm to 100 nm, depending on materials and chemical compositions. Skymions align like a two-dimensional crystal by cooling the specimen temperature and controlling the external magnetic field.

Skyrmion was first observed as a real-space image by Lorentz electron microscopy. Since then, it was also imaged by STEM using the DPC (differential phase contrast) method.

Courtesy of figures: Senior Researcher T. Matsumoto and Associate Professor N. Shibata The University of Tokyo (as of August 2015)

Fig. (a) Schematic of the magnetic structure of skyrmions in a thin film. The directions of the magnetic moments of electron spins are indicated by arrows. The directions of those magnetic moments are perpendicular to the film plane at the core of the respective skyrmions, but swirl in the film plane at the peripheral region. Fig. (b) A real-space image of skymions acquired by the DPC (differential phase contrast) method (specimen: an Iron alloy). The colors in the figure depict the directions and magnitudes of the magnetic vectors in a two-dimensional plane. Related term Lorentz electron microscopy differential phase contrast imaging