Electron microscope 9730 226009695 2008-07-16T12:42:37Z II MusLiM HyBRiD II 7383430 [[WP:UNDO|Undid]] revision 226009312 by [[Special:Contributions/203.87.184.66|203.87.184.66]] ([[User talk:203.87.184.66|talk]]) {{Refimprove|date=November 2006}} An '''electron microscope''' is a type of [[microscope]] that uses [[electron]]s to illuminate a specimen and create an enlarged image. Electron microscopes have much greater [[Angular resolution|resolving power]] than [[Optical microscope|light microscopes]] and can obtain much higher [[magnification]]s. Some electron microscopes can magnify specimens up to 2 million times, while the best light microscopes are limited to magnifications of 2000 times. Both electron and light microscopes have resolution limitations, imposed by their wavelength. The greater resolution and magnification of the electron microscope is due to the wavelength of an [[electron]], its [[de Broglie wavelength]], being much smaller than that of a [[Light|light photon]], [[electromagnetic radiation]]. The electron microscope uses [[Electrostatic lens|electrostatic]] and [[electromagnetic]] lenses in forming the image by controlling the electron beam to focus it at a specific plane relative to the specimen in a manner similar to how a light microscope uses glass lenses to focus light on or through a specimen to form an image. ==History== [[Image:Ernst Ruska Electron Microscope - Deutsches Museum - Munich.jpg|thumb|right|Electron microscope constructed by [[Ernst Ruska]] in 1933]] [[Image:Ant SEM.jpg|thumb|right|An image of an [[ant]] from a scanning electron microscope]] The first electron microscope prototype was built in 1931 by the German engineers [[Ernst Ruska]] and [[Max Knoll]].<ref name="RuskaNobel">[http://nobelprize.org/nobel_prizes/physics/laureates/1986/ruska-autobio.html Ernst Ruska Nobel Prize autobiography]</ref>. Although this initial instrument was only capable of magnifying objects by four hundred times, it demonstrated the principles of an electron microscope. Two years later, Ruska constructed an electron microscope that exceeded the resolution possible using an optical microscope. <ref name="RuskaNobel"/> [[Reinhold Rudenberg]], the research director of [[Siemens AG|Siemens]], had patented the electron microscope in 1931, although Siemens was doing no research on electron microscopes at that time. In 1937 Siemens began funding Ruska and [[Bodo von Borries]] to develop an electron microscope. Siemens also employed Ruska's brother [[Helmut Ruska|Helmut]] to work on applications, particularly with biological specimens.<ref>{{cite web |url=http://nobelprize.org/nobel_prizes/physics/laureates/1986/ruska-autobio.html |title=Ernst Ruska Autobiography |accessdate=2007-02-06 |author=Ernst Ruska |year=1986 |publisher=Nobel Foundation |language=English }}</ref><ref>{{cite journal | author = DH Kruger, P Schneck and HR Gelderblom | date = 13 | year = 2000 | month = May | title = Helmut Ruska and the visualisation of viruses | journal = The Lancet | volume = 355 | issue = 9216 | pages = 1713–1717 | doi = 10.1016/S0140-6736(00)02250-9 | id = | language = English}} </ref> In the same decade of 1930s [[Manfred von Ardenne]] pioneered the [[scanning electron microscope]] and his universal electron microscope.<ref>{{cite journal | author = M von Ardenne and D Beischer | date = | year = 1940 | month = | title = Untersuchung von metalloxud-rauchen mit dem universal-elektronenmikroskop | journal = Zeitschrift Electrochemie | volume = 46 | issue = | pages = 270–277 | language = German}} </ref> Siemens produced the first commercial TEM in 1939, but the first practical electron microscope had been built at the [[University of Toronto]] in 1938, by [[Eli Franklin Burton]] and students Cecil Hall, [[James Hillier]], and Albert Prebus.<ref>[http://web.mit.edu/Invent/iow/hillier.html MIT biography of Hillier]</ref> Although modern electron microscopes can magnify objects up to two million times, they are still based upon Ruska's [[prototype]]. The electron microscope is an integral part of many laboratories. Researchers use it to examine biological materials (such as [[microorganisms]] and [[cell (biology)|cells]]), a variety of large [[molecules]], medical [[biopsy]] samples, [[metals]] and [[crystalline]] structures, and the characteristics of various surfaces. The electron microscope is also used extensively for inspection, quality assurance and failure analysis applications in industry, including, in particular, [[semiconductor device fabrication]]. == Electron microscope manufacturers == Major manufacturers include: * [[Aspex]] Corporation * [[Delong Group]] * [[FEI Company]] – USA (merged with [[Philips]] Electron Optics) * [[FOCUS GmbH]] – Germany * [[Hitachi, Ltd.|Hitachi]] – Japan * [[Nion Company]] - USA * [[JEOL|JEOL Ltd.]] – Japan (Japan Electro Optics Laboratory) * [[TESCAN]] – EU * [[Zeiss|Carl Zeiss NTS GmbH]] – Germany ==Types == ====Transmission Electron Microscope (TEM) ==== {{main|Transmission electron microscopy}} The original form of electron microscopy, [[Transmission electron microscopy]] (TEM) involves a high [[voltage]] electron beam emitted by a [[cathode]], usually a tungsten filament and focused by electrostatic and [[electromagnetic]] lenses. The electron beam that has been transmitted through a specimen that is in part transparent to electrons carries information about the inner structure of the specimen in the electron beam that reaches the imaging system of the microscope. The spatial variation in this information (the "image") is then magnified by a series of electromagnetic lenses until it is recorded by hitting a fluorescent screen, photographic plate, or light sensitive sensor such as a CCD ([[charge-coupled device]]) camera. The image detected by the CCD may be displayed in real time on a monitor or computer. Resolution of the TEM is limited primarily by [[spherical aberration]], but a new generation of aberration correctors have been able to partially overcome spherical aberration to increase resolution. Software correction of spherical aberration for the High Resolution TEM [[HRTEM]] has allowed the production of images with sufficient resolution to show carbon atoms in diamond separated by only 0.89 [[ångström]] (89 [[picometer]]s) and atoms in silicon at 0.78 ångström (78 picometers)<ref>[http://www.lbl.gov/Publications/Currents/Archive/May-18-2001.html#_Hlk514817949 OÅM: World-Record Resolution at 0.78 Å], (May 18, 2001) Berkeley Lab Currents.</ref><ref>{{cite journal | author = P. D. Nellist, M. F. Chisholm, N. Dellby, O. L. Krivanek, M. F. Murfitt, Z. S. Szilagyi, A. R. Lupini, A. Borisevich, W. H. Sides, Jr., S. J. Pennycook | date = 17 | year = 2004 | month = September | title = Direct Sub-Angstrom Imaging of a Crystal Lattice | journal = Science | volume = 305 | issue = 5691 | pages = 1741 | doi = 10.1126/science.1100965 | id = | url = http://www.sciencemag.org/cgi/content/abstract/305/5691/1741 | language = English | pmid = 15375260}} </ref> at magnifications of 50 million times.<ref>[http://www.sc.doe.gov/bes/scale_of_things.html The Scale of Things], DOE Office of Basic Energy Sciences (BES).</ref> The ability to determine the positions of atoms within materials has made the HRTEM an important tool for nano-technologies research and development. ====Scanning Electron Microscope (SEM) ==== {{Main|Scanning Electron Microscope}} Unlike the TEM, where electrons of the high voltage beam form the image of the specimen, the [[Scanning Electron Microscope]] (SEM)<ref>[http://www-g.eng.cam.ac.uk/125/achievements/mcmullan/mcm.htm SCANNING ELECTRON MICROSCOPY 1928 - 1965]</ref> produces images by detecting low energy secondary electrons which are emitted from the surface of the specimen due to excitation by the primary electron beam. In the SEM, the electron beam is rastered across the sample, with detectors building up an image by mapping the detected signals with beam position. Generally, the TEM resolution is about an order of magnitude greater than the SEM resolution, however, because the SEM image relies on surface processes rather than transmission it is able to image bulk samples and has a much greater depth of view, and so can produce images that are a good representation of the 3D structure of the sample. ===Reflection Electron Microscope (REM) ==== In addition there is a '''Reflection Electron Microscope''' (REM). Like TEM, this technique involves electron beams incident on a surface, but instead of using the transmission (TEM) or secondary electrons (SEM), the reflected beam is detected. This technique is typically coupled with [[RHEED|Reflection High Energy Electron Diffraction]] and ''Reflection high-energy loss spectrum (RHELS)''. Another variation is Spin-Polarized Low-Energy Electron Microscopy (SPLEEM), which is used for looking at the microstructure of [[magnetic domain]]s.<ref>[http://ncem.lbl.gov/frames/spleem.html NCEM National Center for Electron Microscopy: SPLEEM<!-- Bot generated title -->]</ref> ====Scanning Transmission Electron Microscope (STEM) ==== {{Main|Scanning Transmission Electron Microscope}} 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 STEM's use of SEM-like beam rastering simplifies [[annular dark-field imaging]], and other analytical techniques, but also means that image data is acquired in serial rather than in parallel fashion. == Sample Preparation == [[Image:Golden insect 01 Pengo.jpg|thumb|An insect coated in gold for viewing with a scanning electron microscope.]] 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: * Fixation for biological specimens. *''Cryofixation'' – freezing a specimen so rapidly, to [[liquid nitrogen]] or even [[liquid helium]] temperatures, that the water forms [[Amorphous ice|vitreous (non-crystalline) ice]]. This preserves the specimen in a snapshot of its solution state. An entire field called [[cryo-electron microscopy]] has branched from this technique. With the development of [[cryo-electron microscopy|cryo-electron microscopy of vitreous sections]] (CEMOVIS), it is now possible to observe virtually any biological specimen close to its native state. *''Dehydration'' – replacing [[water]] with organic solvents such as [[ethanol]] or [[acetone]]. *''Embedding'' – infiltration of the tissue with a [[resin]] such as [[araldite]] or [[epoxy]] for sectioning. After this embedding process begins, the specimen must be polished to a mirror-like finish using ultra-fine abrasives. The polishing process must be performed carefully to minimise scratches and other polishing artefacts that impose on image quality. *''Sectioning'' – produces thin slices of specimen, semitransparent to electrons. These can be cut on an [[ultramicrotome]] with a [[diamond]] knife to produce very thin slices. [[Glass knives]] are also used because they can be made in the lab and are much cheaper. *''Staining'' – uses heavy metals such as [[lead]], [[uranium]] or [[tungsten]] 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 are usually stained "en bloc" before embedding and also later stained directly after sectioning by brief exposure to aqueous (or alcoholic) solutions of the heavy metal stains. *''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 (cryofixed), then fractured by simply 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. A second coat of carbon, evaporated perpendicular to the average surface plane is often performed to improve 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 solution or SDS detergent. The still-floating replica is thoroughly washed from residual chemicals, carefully fished up on EM grids, dried then viewed in the TEM. *''Ion Beam Milling'' – thins samples until they are transparent to electrons by firing [[ions]] (typically [[argon]]) at the surface from an angle and sputtering material from the surface. A subclass of this is [[Focused ion beam]] milling, where [[gallium]] 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. Such coatings include gold, gold/palladium, platinum, tungsten, graphite etc. and are especially important for the study of specimens with the scanning electron microscope. Another reason for coating, even when there is more than enough conductivity, is to improve contrast, a situation more common with the operation of a FESEM (field emission SEM). When an osmium coater is used, a layer far thinner than would be possible with any of the previously mentioned sputtered coatings is possible.<ref>http://www.2spi.com/catalog/osmi-coat.html</ref> == Disadvantages == [[Image:Krillfilter2kils.jpg|thumb|Pseudocolored SEM image of the feeding basket of [[Antarctic krill]]. Real electron microscope images do not carry any color information, they are [[greyscale]]. The first degree [[filter setae]] carry in v-form two rows of second degree [[setae]], pointing towards the inside of the [[feeding basket]]. The purple ball is one micrometer in diameter. To display the total area of this structure one would have to tile this image 7500 times.]] Electron microscopes are expensive to build and maintain. They are dynamic rather than static in their operation: requiring extremely stable high-voltage supplies, extremely stable currents to each electromagnetic coil/lens, continuously-pumped high- or ultra-high-vacuum systems, and a cooling water supply circulation through the lenses and pumps. As they are very sensitive to vibration and external magnetic fields, microscopes aimed at achieving high resolutions must be housed in buildings (sometimes underground) with special services. Some desktop low voltage electron microscopes have TEM capabilities at very low voltages (around 5 kV) without stringent voltage supply, lens coil current, cooling water or vibration isolation requirements and as such are much less expensive to buy and far easier to install and maintain, but do not have the same ultra-high (atomic scale) resolution capabilities as the larger instruments. The samples largely have to be viewed in [[vacuum]], as the molecules that make up air would scatter the electrons. One exception is the environmental scanning electron microscope, which allows hydrated samples to be viewed in a low-pressure (up to 20 [[torr]]), wet environment. Scanning electron microscopes usually image conductive or semi-conductive materials best. Non-conductive materials can be imaged by an environmental scanning electron microscope. A common preparation technique is to coat the sample with a several-nanometer layer of conductive material, such as [[gold]], from a sputtering machine; however, this process has the potential to disturb delicate samples. The samples have to be prepared in many ways to give proper detail, which may result in ''[[Artifact (observational)|artifacts]]'' from such treatment. This raises the problem of distinguishing artifacts from material, particularly in [[biology|biological]] samples. It is generally believed by scientists working in the field that as results from various preparation techniques have been compared and that there is no reason that they should all produce similar artifacts, it is reasonable to believe that electron microscopy features correlate with living cells. In addition, higher-resolution work has been directly compared to results from [[X-ray crystallography]], providing independent confirmation of the validity of this technique.{{Fact|date=February 2008}} Since the 1980s, analysis of unfixed, vitrified specimens has also become increasingly used by scientists, further confirming the validity of this technique.<ref name="Adrian1984">{{cite journal |last=Adrian |first=Marc |authorlink= |coauthors=Dubochet, Jacques; Lepault, Jean; McDowall, Alasdair W. |year=1984 |month= |title=Cryo-electron microscopy of viruses |journal=Nature |volume=308 |issue=5954 |pages=32&ndash;36 |doi=10.1038/308032a0 |url= |accessdate= |quote= }}</ref><ref name="Sabanay1991">{{cite journal |last=Sabanay |first=I. |authorlink= |coauthors=Arad, T.; Weiner, S.; Geiger, B. |year=1991 |month= |title=Study of vitrified, unstained frozen tissue sections by cryoimmunoelectron microscopy |journal=Journal of Cell Science |volume=100 |issue=1 |pages=227&ndash;236 |id= |url=http://jcs.biologists.org/cgi/content/abstract/100/1/227 |accessdate= |quote= }}</ref><ref>{{cite journal |last=Kasas |first=S. |authorlink= |coauthors=Dumas, G.; Dietler, G.; Catsicas, S.; Adrian, M. |year=2003 |month= |title=Vitrification of cryoelectron microscopy specimens revealed by high-speed photographic imaging |journal=Journal of Microscopy |volume=211 |issue=1 |pages=48&ndash;53 |doi=10.1046/j.1365-2818.2003.01193.x |url= |accessdate= |quote= }}</ref> ==Electron microscopy application areas== :{| style="background-color: transparent; width: {{{width|60%}}}" | width="{{{width|}}}" align="{{{align|left}}}" valign="{{{valign|top}}}" | '''Semiconductor and data storage''' * [[Circuit edit]] * [[3D metrology]] * [[Defect analysis]] * [[Failure analysis]] '''Biology and life sciences''' *[[Cryobiology]] *[[Protein localization]] *[[Electron tomography]] *[[Cellular tomography]] *[[Cryo-electron microscopy]] *[[Toxicology]] *[[Biological production]] and [[viral load]] monitoring *[[Particle analysis]] *[[Pharmaceutical QC]] *[[3D tissue imaging]] *[[Virology]] *[[Vitrification]] | width="{{{width|}}}" align="{{{align|left}}}" valign="{{{valign|top}}}" | '''Research''' *[[Materials qualification]] *[[Materials and sample preparation]] *[[Nanoprototyping]] *[[Nanometrology]] *[[Device testing and characterization]] '''Industry''' *[[High-resolution imaging]] *[[2D & 3D micro-characterization]] *[[Macro sample to nanometer metrology]] *[[Particle detection and characterization]] *[[Direct beam-writing fabrication]] *[[Dynamic materials experiments]] *[[Sample preparation]] *[[Forensics]] *[[Mining]] ([[mineral liberation analysis]]) *[[Chemical]]/[[Petrochemical]] |} == See also == * [[:Category:Electron microscope images]] * [[Field emission microscope]] * [[Scanning tunneling microscope]] ==References== {{reflist}} ==External links== * [http://www.danilatos.com Environmental Scanning Electron Microscope (ESEM)] * [http://www.microanalyst.net/index_e.phtml X-ray element analysis in electron microscope] – Information portal with X-ray microanalysis and EDX contents * [http://www2.physics.utoronto.ca/overview/history/microsco/microscopy.htm John H.L. Watson: Very early Electron Microscopy in the Department of Physics, the University of Toronto – A personal recollection] * [http://americanhistory.si.edu/archives/d8452.htm Rubin Borasky Electron Microscopy Collection, 1930-1988] Archives Center, National Museum of American History, Smithsonian Institution. * [http://www.microscopy.ethz.ch electron microscopy] Website of the ETH Zurich: Very good graphics and images, which illustrate various procedures. * [http://www.albertlleal.com/microphotography.html Albert Lleal microphotography. Scanning Electron Microphotography Coloured SEM] [[Category:Microscopy]] [[Category:Scientific techniques]] [[Category:Nanotechnology]] [[ar:مجهر إلكتروني]] [[bs:Elektronska mikroskopija]] [[ca:Microscopi electrònic]] [[cs:Elektronový mikroskop]] [[da:Elektronmikroskop]] [[de:Elektronenmikroskop]] [[es:Microscopio electrónico]] [[eo:Elektrona mikroskopo]] [[fa:میکروسکوپ الکترونی]] [[gl:Microscopio electrónico]] [[hr:Elektronski mikroskop]] [[id:Mikroskop elektron]] [[it:Microscopio elettronico]] [[he:מיקרוסקופ אלקטרוני]] [[lv:Elektronmikroskops]] [[lt:Elektroninis mikroskopas]] [[hu:Elektronmikroszkóp]] [[mk:Електронски микроскоп]] [[ms:Mikroskop elektron]] [[nl:Elektronenmicroscopie]] [[ja:電子顕微鏡]] [[no:Elektronmikroskop]] [[pl:Mikroskop elektronowy]] [[pt:Microscópio eletrônico]] [[ro:Microscop electronic]] [[ru:Электронный микроскоп]] [[simple:Electron microscope]] [[fi:Elektronimikroskooppi]] [[sv:Elektronmikroskop]] [[ta:இலத்திரன் நுண்நோக்கி]] [[te:ఎలక్ట్రాన్ సూక్ష్మదర్శిని]] [[th:กล้องจุลทรรศน์อิเล็กตรอน]] [[vi:Kính hiển vi điện tử]] [[zh:電子顯微鏡]]