Scanning electron microscope 1

Scanning electron microscope

These pollen grains taken on an SEM show thecharacteristic depth of field of SEM micrographs.

SEM opened sample chamber

Analog type scanning electron microscope

A scanning electron microscope (SEM) is a type of electronmicroscope that images a sample by scanning it with a high-energybeam of electrons in a raster scan pattern. The electrons interact withthe atoms that make up the sample producing signals that containinformation about the sample's surface topography, composition, andother properties such as electrical conductivity.

The types of signals produced by an SEM include secondary electrons,back-scattered electrons (BSE), characteristic X-rays, light(cathodoluminescence), specimen current and transmitted electrons.Secondary electron detectors are common in all SEMs, but it is rarethat a single machine would have detectors for all possible signals. Thesignals result from interactions of the electron beam with atoms at ornear the surface of the sample. In the most common or standarddetection mode, secondary electron imaging or SEI, the SEM canproduce very high-resolution images of a sample surface, revealingdetails less than 1 nm in size. Due to the very narrow electron beam,SEM micrographs have a large depth of field yielding a characteristicthree-dimensional appearance useful for understanding the surfacestructure of a sample. This is exemplified by the micrograph of pollenshown to the right. A wide range of magnifications is possible, fromabout 10 times (about equivalent to that of a powerful hand-lens) tomore than 500,000 times, about 250 times the magnification limit ofthe best light microscopes. Back-scattered electrons (BSE) are beamelectrons that are reflected from the sample by elastic scattering. BSEare often used in analytical SEM along with the spectra made from thecharacteristic X-rays. Because the intensity of the BSE signal isstrongly related to the atomic number (Z) of the specimen, BSE imagescan provide information about the distribution of different elements inthe sample. For the same reason, BSE imaging can image colloidalgold immuno-labels of 5 or 10 nm diameter, which would otherwise bedifficult or impossible to detect in secondary electron images inbiological specimens. Characteristic X-rays are emitted when theelectron beam removes an inner shell electron from the sample,causing a higher energy electron to fill the shell and release energy. These characteristic X-rays are used to identifythe composition and measure the abundance of elements in the sample.

History

The first SEM image was obtained by Max Knoll, who in 1935 obtained an image of silicon steel showing electronchanneling contrast.[1] Further pioneering work on the physical principles of the SEM and beam specimeninteractions was performed by Manfred von Ardenne in 1937,[2] [3] who produced a British patent[4] but never madea practical instrument. The SEM was further developed by Professor Sir Charles Oatley and his postgraduate student

Scanning electron microscope 2

Gary Stewart and was first marketed in 1965 by the Cambridge Scientific Instrument Company as the "Stereoscan".The first instrument was delivered to DuPont.

Scanning process and image formation

Schematic diagram of an SEM.

In a typical SEM, an electron beam is thermionically emitted from anelectron gun fitted with a tungsten filament cathode. Tungsten isnormally used in thermionic electron guns because it has the highestmelting point and lowest vapour pressure of all metals, therebyallowing it to be heated for electron emission, and because of its lowcost. Other types of electron emitters include lanthanum hexaboride(LaB6) cathodes, which can be used in a standard tungsten filamentSEM if the vacuum system is upgraded and field emission guns (FEG),which may be of the cold-cathode type using tungsten single crystalemitters or the thermally assisted Schottky type, using emitters of

zirconium oxide.

The electron beam, which typically has an energy ranging from 0.2 keV to 40 keV, is focused by one or twocondenser lenses to a spot about 0.4 nm to 5 nm in diameter. The beam passes through pairs of scanning coils orpairs of deflector plates in the electron column, typically in the final lens, which deflect the beam in the x and y axesso that it scans in a raster fashion over a rectangular area of the sample surface.When the primary electron beam interacts with the sample, the electrons lose energy by repeated random scatteringand absorption within a teardrop-shaped volume of the specimen known as the interaction volume, which extendsfrom less than 100 nm to around 5 µm into the surface. The size of the interaction volume depends on the electron'slanding energy, the atomic number of the specimen and the specimen's density. The energy exchange between theelectron beam and the sample results in the reflection of high-energy electrons by elastic scattering, emission ofsecondary electrons by inelastic scattering and the emission of electromagnetic radiation, each of which can bedetected by specialized detectors. The beam current absorbed by the specimen can also be detected and used tocreate images of the distribution of specimen current. Electronic amplifiers of various types are used to amplify thesignals, which are displayed as variations in brightness on a cathode ray tube. The raster scanning of the CRT displayis synchronised with that of the beam on the specimen in the microscope, and the resulting image is therefore adistribution map of the intensity of the signal being emitted from the scanned area of the specimen. The image maybe captured by photography from a high-resolution cathode ray tube, but in modern machines is digitally capturedand displayed on a computer monitor and saved to a computer's hard disk.

Scanning electron microscope 3

Low-temperatureSEM magnification

series for a snowcrystal. The crystalsare captured, stored,and sputter-coatedwith platinum at

cryo-temperatures forimaging.

Magnification

An SEM micrograph of a house fly compoundeye surface at 450× magnification.

Magnification in a SEM can be controlled over a range of up to 6orders of magnitude from about 10 to 500,000 times. Unlike opticaland transmission electron microscopes, image magnification in theSEM is not a function of the power of the objective lens. SEMs mayhave condenser and objective lenses, but their function is to focus thebeam to a spot, and not to image the specimen. Provided the electrongun can generate a beam with sufficiently small diameter, a SEM couldin principle work entirely without condenser or objective lenses,although it might not be very versatile or achieve very high resolution.In a SEM, as in scanning probe microscopy, magnification results fromthe ratio of the dimensions of the raster on the specimen and the rasteron the display device. Assuming that the display screen has a fixed

size, higher magnification results from reducing the size of the raster on the specimen, and vice versa. Magnification is therefore controlled by the current supplied to the x, y scanning coils, or the voltage supplied to the x, y deflector

Scanning electron microscope 4

plates, and not by objective lens power.

Sample preparation

A spider coated in gold, having beenprepared for viewing with a scanning

electron microscope.

13mm radius aluminium stubs (the base tosupport and prepare a sample on) for sample

preparation and gold coating

All samples must also be of an appropriate size to fit in the specimenchamber and are generally mounted rigidly on a specimen holdercalled a specimen stub. Several models of SEM can examine any partof a 6-inch (15 cm) semiconductor wafer, and some can tilt an objectof that size to 45°.For conventional imaging in the SEM, specimens must be electricallyconductive, at least at the surface, and electrically grounded to preventthe accumulation of electrostatic charge at the surface. Metal objectsrequire little special preparation for SEM except for cleaning andmounting on a specimen stub. Nonconductive specimens tend tocharge when scanned by the electron beam, and especially insecondary electron imaging mode, this causes scanning faults and otherimage artifacts. They are therefore usually coated with an ultrathincoating of electrically conducting material, deposited on the sampleeither by low-vacuum sputter coating or by high-vacuum evaporation.Conductive materials in current use for specimen coating include gold,gold/palladium alloy, platinum, osmium,[5] iridium, tungsten,chromium, and graphite. Additionally, coating may increasesignal/noise ratio for samples of low atomic number (Z). Theimprovement arises because secondary electron emission for high-Zmaterials is enhanced.

An alternative to coating for some biological samples is to increase the bulk conductivity of the material byimpregnation with osmium using variants of the OTO staining method (O-osmium, T-thiocarbohydrazide,O-osmium).[6] [7] Nonconducting specimens may be imaged uncoated using specialized SEM instrumentation suchas the "Environmental SEM" (ESEM) or field emission gun (FEG) SEMs operated at low voltage. EnvironmentalSEM instruments place the specimen in a relatively high-pressure chamber where the working distance is short andthe electron optical column is differentially pumped to keep vacuum adequately low at the electron gun. Thehigh-pressure region around the sample in the ESEM neutralizes charge and provides an amplification of thesecondary electron signal. Low-voltage SEM of non-conducting specimens can be operationally difficult toaccomplish in a conventional SEM and is typically a research application for specimens that are sensitive to theprocess of applying conductive coatings. Low-voltage SEM of non-conducting specimens can be operationallydifficult to accomplish in a conventional SEM and is typically a research application for specimens that are sensitiveto the process of applying conductive coatings. Low-voltage SEM is typically conducted in an FEG-SEM becausethe FEG is capable of producing high primary electron brightness even at low accelerating potentials. Operatingconditions to prevent charging of non-conductive specimens must be adjusted such that the incoming beam currentwas equal to sum of outcoming secondary and backscattered electrons currents. I usually occurs at acceleratingvoltages of 0.5-4 kV.

Embedding in a resin with further polishing to a mirror-like finish can be used for both biological and materialsspecimens when imaging in backscattered electrons or when doing quantitative X-ray microanalysis.

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Biological samplesFor SEM, a specimen is normally required to be completely dry, since the specimen chamber is at high vacuum.Hard, dry materials such as wood, bone, feathers, dried insects, or shells can be examined with little furthertreatment, but living cells and tissues and whole, soft-bodied organisms usually require chemical fixation to preserveand stabilize their structure. Fixation is usually performed by incubation in a solution of a buffered chemical fixative,such as glutaraldehyde, sometimes in combination with formaldehyde[8] [9] [10] and other fixatives,[11] and optionallyfollowed by postfixation with osmium tetroxide.[8] The fixed tissue is then dehydrated. Because air-drying causescollapse and shrinkage, this is commonly achieved by replacement of water in the cells with organic solvents such asethanol or acetone, and replacement of these solvents in turn with a transitional fluid such as liquid carbon dioxideby critical point drying. The carbon dioxide is finally removed while in a supercritical state, so that no gas-liquidinterface is present within the sample during drying. The dry specimen is usually mounted on a specimen stub usingan adhesive such as epoxy resin or electrically conductive double-sided adhesive tape, and sputter-coated with goldor gold/palladium alloy before examination in the microscope.If the SEM is equipped with a cold stage for cryo-microscopy, cryofixation may be used and low-temperaturescanning electron microscopy performed on the cryogenically fixed specimens.[8] Cryo-fixed specimens may becryo-fractured under vacuum in a special apparatus to reveal internal structure, sputter-coated, and transferred ontothe SEM cryo-stage while still frozen.[12] Low-temperature scanning electron microscopy is also applicable to theimaging of temperature-sensitive materials such as ice[13] [14] (see e.g. illustration at left) and fats.[15]

Freeze-fracturing, freeze-etch or freeze-and-break is a preparation method particularly useful for examining lipidmembranes and their incorporated proteins in "face on" view. The preparation method reveals the proteins embeddedin the lipid bilayer.Gold has a high atomic number and sputter-coating with gold produces high topographic contrast and resolution.However, the coating has a thickness of a few nanometers, and can obscure the underlying fine detail of thespecimen at very high magnification. Low-vacuum SEMs with differential pumping apertures allow samples to beimaged without such coating and without the loss of natural contrast caused by the coating, but are unable to achievethe resolution attainable by conventional SEMs with coated specimens.[16]

MaterialsBack scattered electron imaging, quantitative X-ray analysis, and X-ray mapping of specimens often requires that thesurfaces be ground and polished to an ultra smooth surface. Specimens that undergo WDS or EDS analysis are oftencarbon coated. In general, metals are not coated prior to imaging in the SEM because they are conductive andprovide their own pathway to ground.Fractography is the study of fractured surfaces that can be done on a light microscope or commonly, on an SEM. Thefractured surface is cut to a suitable size, cleaned of any organic residues, and mounted on a specimen holder forviewing in the SEM.Integrated circuits may be cut with a focused ion beam (FIB) or other ion beam milling instrument for viewing in theSEM. The SEM in the first case may be incorporated into the FIB.Metals, geological specimens, and integrated circuits all may also be chemically polished for viewing in the SEM.Special high-resolution coating techniques are required for high-magnification imaging of inorganic thin films.

Scanning electron microscope 6

ESEMEnvironmental SEM allows use of hydrated specimens, omitting dehydration procedure. The accumulation ofelectric charge on the surfaces of non-metallic specimens can be avoided by using environmental SEM in which thespecimen is placed in an internal chamber at higher pressure, rather than the vacuum in the electron optical column.Positively charged ions generated by beam interactions with the gas help to neutralize the negative charge on thespecimen surface. The pressure of gas in the chamber can be controlled, and the type of gas used can be variedaccording to need. Coating is thus unnecessary. In ESEM mode X-ray analysis is prone to artifacts arose fromelectron beam scattering on gases of specimen chamber.

Detection of secondary electronsThe most common imaging mode collects low-energy (<50 eV) secondary electrons that are ejected from thek-orbitals of the specimen atoms by inelastic scattering interactions with beam electrons. Due to their low energy,these electrons originate within a few nanometers from the sample surface.[17] The electrons are detected by anEverhart-Thornley detector,[18] which is a type of scintillator-photomultiplier system. The secondary electrons arefirst collected by attracting them towards an electrically biased grid at about +400 V, and then further acceleratedtowards a phosphor or scintillator positively biased to about +2,000 V. The accelerated secondary electrons are nowsufficiently energetic to cause the scintillator to emit flashes of light (cathodoluminescence), which are conducted toa photomultiplier outside the SEM column via a light pipe and a window in the wall of the specimen chamber. Theamplified electrical signal output by the photomultiplier is displayed as a two-dimensional intensity distribution thatcan be viewed and photographed on an analogue video display, or subjected to analog-to-digital conversion anddisplayed and saved as a digital image. This process relies on a raster-scanned primary beam. The brightness of thesignal depends on the number of secondary electrons reaching the detector. If the beam enters the sampleperpendicular to the surface, then the activated region is uniform about the axis of the beam and a certain number ofelectrons "escape" from within the sample. As the angle of incidence increases, the "escape" distance of one side ofthe beam will decrease, and more secondary electrons will be emitted. Thus steep surfaces and edges tend to bebrighter than flat surfaces, which results in images with a well-defined, three-dimensional appearance. Using thesignal of secondary electrons image resolution less than 0.5 nm is possible.

Detection of backscattered electrons

Comparison of SEM techniques:Top: backscattered electron analysis -

compositionBottom: secondary electron analysis - topography

Backscattered electrons (BSE) consist of high-energy electronsoriginating in the electron beam, that are reflected or back-scattered outof the specimen interaction volume by elastic scattering interactionswith specimen atoms. Since heavy elements (high atomic number)backscatter electrons more strongly than light elements (low atomicnumber), and thus appear brighter in the image, BSE are used to detectcontrast between areas with different chemical compositions.[17] TheEverhart-Thornley detector, which is normally positioned to one sideof the specimen, is inefficient for the detection of backscatteredelectrons because few such electrons are emitted in the solid anglesubtended by the detector, and because the positively biased detectiongrid has little ability to attract the higher energy BSE electrons.Dedicated backscattered electron detectors are positioned above the sample in a "doughnut" type arrangement,concentric with the electron beam, maximising the solid angle of collection. BSE detectors are usually either ofscintillator or of semiconductor types. When all parts of the detector are used to collect electrons symmetrically

Scanning electron microscope 7

about the beam, atomic number contrast is produced. However, strong topographic contrast is produced by collectingback-scattered electrons from one side above the specimen using an asymmetrical, directional BSE detector; theresulting contrast appears as illumination of the topography from that side. Semiconductor detectors can be made inradial segments that can be switched in or out to control the type of contrast produced and its directionality.Backscattered electrons can also be used to form an electron backscatter diffraction (EBSD) image that can be usedto determine the crystallographic structure of the specimen.

Beam-injection analysis of semiconductorsThe nature of the SEM's probe, energetic electrons, makes it uniquely suited to examining the optical and electronicproperties of semiconductor materials. The high-energy electrons from the SEM beam will inject charge carriers intothe semiconductor. Thus, beam electrons lose energy by promoting electrons from the valence band into theconduction band, leaving behind holes.In a direct bandgap material, recombination of these electron-hole pairs will result in cathodoluminescence; if thesample contains an internal electric field, such as is present at a p-n junction, the SEM beam injection of carriers willcause electron beam induced current (EBIC) to flow.Cathodoluminescence and EBIC are referred to as "beam-injection" techniques, and are very powerful probes of theoptoelectronic behavior of semiconductors, in particular for studying nanoscale features and defects.

CathodoluminescenceCathodoluminescence, the emission of light when atoms excited by high-energy electrons return to their groundstate, is analogous to UV-induced fluorescence, and some materials such as zinc sulfide and some fluorescent dyes,exhibit both phenomena. Cathodoluminescence is most commonly experienced in everyday life as the light emissionfrom the inner surface of the cathode ray tube in television sets and computer CRT monitors. In the SEM, CLdetectors either collect all light emitted by the specimen or can analyse the wavelengths emitted by the specimen anddisplay an emission spectrum or an image of the distribution of cathodoluminescence emitted by the specimen in realcolour.

X-ray microanalysisX-rays, which are also produced by the interaction of electrons with the sample, may also be detected in an SEMequipped for energy-dispersive X-ray spectroscopy or wavelength dispersive X-ray spectroscopy.

Resolution of the SEMThe spatial resolution of the SEM depends on the size of the electron spot, which in turn depends on both thewavelength of the electrons and the electron-optical system that produces the scanning beam. The resolution is alsolimited by the size of the interaction volume, or the extent to which the material interacts with the electron beam.The spot size and the interaction volume are both large compared to the distances between atoms, so the resolutionof the SEM is not high enough to image individual atoms, as is possible in the shorter wavelength (i.e. higherenergy) transmission electron microscope (TEM). The SEM has compensating advantages, though, including theability to image a comparatively large area of the specimen; the ability to image bulk materials (not just thin films orfoils); and the variety of analytical modes available for measuring the composition and properties of the specimen.Depending on the instrument, the resolution can fall somewhere between less than 1 nm and 20 nm. By 2009, Theworld's highest SEM resolution at high-beam energies (0.4 nm at 30 kV) is obtained with the Hitachi S-5500. Atlow-beam energies, the best resolution (by 2009) is achieved by the Magellan XHR system from FEI Company(0.9 nm at 1 kV).

Scanning electron microscope 8

Environmental SEMConventional SEM requires samples to be imaged under vacuum, because a gas atmosphere rapidly spreads andattenuates electron beams. As a consequence, samples that produce a significant amount of vapour, e.g. wetbiological samples or oil-bearing rock, must be either dried or cryogenically frozen. Processes involving phasetransitions, such as the drying of adhesives or melting of alloys, liquid transport, chemical reactions, andsolid-air-gas systems, in general cannot be observed. Some observations of living insects have been possible,[19]

however.The first commercial development of the Environmental SEM (ESEM) in the late 1980s [20] [21] allowed samples tobe observed in low-pressure gaseous environments (e.g. 1-50 Torr) and high relative humidity (up to 100%). Thiswas made possible by the development of a secondary-electron detector [22] [23] capable of operating in the presenceof water vapour and by the use of pressure-limiting apertures with differential pumping in the path of the electronbeam to separate the vacuum region (around the gun and lenses) from the sample chamber.The first commercial ESEMs were produced by the ElectroScan Corporation in USA in 1988. ElectroScan was takenover by Philips (who later sold their electron-optics division to FEI Company) in 1996.[24]

ESEM is especially useful for non-metallic and biological materials because coating with carbon or gold isunnecessary. Uncoated Plastics and Elastomers can be routinely examined, as can uncoated biological samples.Coating can be difficult to reverse, may conceal small features on the surface of the sample and may reduce the valueof the results obtained. X-ray analysis is difficult with a coating of a heavy metal, so carbon coatings are routinelyused in conventional SEMs, but ESEM makes it possible to perform X-ray microanalysis on uncoatednon-conductive specimens. ESEM may be the preferred for electron microscopy of unique samples from criminal orcivil actions, where forensic analysis may need to be repeated by several different experts.

3D in SEM3D data can be measured in the SEM with different methods such as:• photogrammetry (2 or 3 images from tilted specimen)• photometric stereo (use of 4 images from BSE detector)• inverse reconstruction using electron-material interactive models[25] [26]

Possible applications are roughness measurement, measurement of fractal dimension, corrosion measurement andheight step measurement.

Scanning electron microscope 9

Gallery of SEM imagesThe following are examples of images taken using a scanning electron microscope.

Coloured SEM image of soybeancyst nematode and egg. The

colour makes the image easier fornon-specialists to view and

understand the structures andsurfaces revealed in micrographs.

Compound eye of Antarctickrill Euphausia superba.

Arthropod eyes are acommon subject in SEM

micrographs due to the depthof focus that an SEM image

can capture.

Ommatidia of Antarctic krilleye, a higher magnification

of the krill's eye. SEMscover a range from light

microscopy up to themagnifications available

with a TEM.

SEM image of normalcirculating humanblood. This is anolder and noisymicrograph of a

common subject forSEM micrographs:

red blood cells.

SEM image of ahederelloid from the

Devonian of Michigan(largest tube diameter is0.75 mm). The SEM is

used extensively forcapturing detailed images

of micro and macro fossils.

Backscattered Electron (BSE)image of an Antimony rich

region in a fragment of ancientglass. Museums use SEMs forstudying valuable artifacts in anondestructive manner. Many

BSE images are taken atatmospheric rather thandestructive high-vacuum

conditions.

SEM image of the corrosionlayer on the surface of an ancientglass fragment; note the laminarstructure of the corrosion layer.

SEM image of a photoresistlayer used in semiconductor

manufacturing taken on afield emission SEM at 1000

volts, a very lowaccelerating voltage for anSEM, but achievable withfield emission SEMs–thisone taken with a Schottkyfield-emission gun. TheseSEMs are important in thesemiconductor industry for

their high-resolutioncapabilities.

References[1] Knoll, Max (1935). "Aufladepotentiel und Sekundäremission elektronenbestrahlter Körper". Zeitschrift für technische Physik 16: 467–475.[2] von Ardenne, Manfred (1939). "Das Elektronen-Rastermikroskop. Theoretische Grundlagen" (in German). Zeitschrift für Physik 108 (9–10):

553–572. Bibcode 1938ZPhy..109..553V. doi:10.1007/BF01341584.[3] von Ardenne, Manfred (1938). "Das Elektronen-Rastermikroskop. Praktische Ausführung" (in German). Zeitschrift für technische Physik 19:

407–416.[4] von Ardenne M. Improvements in electron microscopes. GB 511204 (http:/ / worldwide. espacenet. com/ textdoc?DB=EPODOC&

IDX=GB511204), convention date (Germany) 18 Feb 1937[5] Suzuki, E. (2002). "High-resolution scanning electron microscopy of immunogold-labelled cells by the use of thin plasma coating of

osmium". Journal of Microscopy 208 (3): 153–157. doi:10.1046/j.1365-2818.2002.01082.x.[6] Seligman, Arnold M.; Wasserkrug, Hannah L.; Hanker, Jacob S. (1966). "A new staining method for enhancing contrast of lipid-containing

membranes and droplets in osmium tetroxide-fixed tissue with osmiophilic thiocarbohydrazide (TCH)". Journal of Cell Biology 30 (2):424–432. doi:10.1083/jcb.30.2.424. PMC 2106998. PMID 4165523.

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[7] Malick, Linda E.; Wilson, Richard B.; Stetson, David (1975). "Modified Thiocarbohydrazide Procedure for Scanning Electron Microscopy:Routine use for Normal, Pathological, or Experimental Tissues". Biotechnic and Histochemistry 50 (4): 265–269.doi:10.3109/10520297509117069.

[8] Jeffree, C. E.; Read, N. D. (1991). "Ambient- and Low-temperature scanning electron microscopy". In Hall, J. L.; Hawes, C. R.. ElectronMicroscopy of Plant Cells. London: Academic Press. pp. 313–413. ISBN 0123188806.

[9] Karnovsky, M. J. (1965). "A formaldehyde-glutaraldehyde fixative of high osmolality for use in electron microscopy". Journal of CellBiology 27: 137A.

[10] Kiernan, J. A. (2000). "Formaldehyde, formalin, paraformaldehyde and glutaraldehyde: What they are and what they do". Microscopy Today2000 (1): 8–12.

[11] Russell, S. D.; Daghlian, C. P. (1985). "Scanning electron microscopic observations on deembedded biological tissue sections: Comparisonof different fixatives and embedding materials". Journal of Electron Microscopy Technique 2 (5): 489–495. doi:10.1002/jemt.1060020511.

[12] Faulkner, Christine; et al. (2008). "Peeking into Pit Fields: A Multiple Twinning Model of Secondary Plasmodesmata Formation inTobacco". Plant Cell 20 (6): 1504. doi:10.1105/tpc.107.056903. PMC 2483367. PMID 18667640.

[13] Wergin, W. P.; Erbe, E. F. (1994). "Snow crystals: capturing snow flakes for observation with the low-temperature scanning electronmicroscope". Scanning 16 (Suppl. IV): IV88.

[14] Barnes, P. R. F.; Mulvaney, R.; Wolff, E. W.; Robinson, K. A. (2002). "A technique for the examination of polar ice using the scanningelectron microscope". Journal of Microscopy 205 (2): 118–124. doi:10.1046/j.0022-2720.2001.00981.x. PMID 11879426.

[15] Hindmarsh, J. P.; Russell, A. B.; Chen, X. D. (2007). "Fundamentals of the spray freezing of foods—microstructure of frozen droplets".Journal of Food Engineering 78 (1): 136–150. doi:10.1016/j.jfoodeng.2005.09.011.

[16] Heide Schatten, James B. Pawley (2007). Biological Low-Voltage Scanning Electron Microscopy (http:/ / books. google. com/?id=EDgFAJdzb4IC& pg=PA62). Springer. pp. 61–63. ISBN 0387729704. .

[17] Goldstein, G. I.; Newbury, D. E.; Echlin, P.; Joy, D. C.; Fiori, C.; Lifshin, E. (1981). Scanning electron microscopy and x-ray microanalysis.New York: Plenum Press. ISBN 030640768X.

[18] Everhart, T. E.; Thornley, R. F. M. (1960). "Wide-band detector for micro-microampere low-energy electron currents". Journal of ScientificInstruments 37 (7): 246–248. Bibcode 1960JScI...37..246E. doi:10.1088/0950-7671/37/7/307.

[19] http:/ / www. mnh. si. edu/ highlight/ sem/ newtool. html.[20] Danilatos, G,D (1988). "Foundations of environmental scanning electron microscopy". Advances in Electronics and Electron Physics 71:

109–250.[21] US patent 4823006 (http:/ / worldwide. espacenet. com/ textdoc?DB=EPODOC& IDX=US4823006), Gerasimos D Danilatos, George C

Lewis, "Integrated electron optical/differential pumping/imaging signal detection system for an environmental scanning electron microscope",issued 1989-4-18

[22] Danilatos, G,D (1990). "Theory of the Gaseous Detector Device in the ESEM". Advances in Electronics and Electron Physics 78: 1–102.[23] US patent 4785182 (http:/ / worldwide. espacenet. com/ textdoc?DB=EPODOC& IDX=US4785182), James F Mancuso, William B

Maxwell, Gerasimos D Danilatos, "Secondary Electron Detector for Use in a Gaseous Atmosphere", issued 1988-11-15[24] History of Electron Microscopy 1990s (http:/ / www. sfc. fr/ Material/ hrst. mit. edu/ hrs/ materials/ public/ ElectronMicroscope/ EM1990s.

htm)[25] Baghaei Rad, Leili (2007). "Computational Scanning Electron Microscopy". International Conference on Frontiers of Characterization and

Metrology.[26] Baghaei Rad, Leili (2007). "Economic approximate models for backscattered electrons". J. Vac. Sci. Technol. B 25.

External linksGeneral• HowStuffWorks - How Scanning Electron Microscopes Work (http:/ / www. howstuffworks. com/

scanning-electron-microscope. htm)• Notes on the SEM (http:/ / www. uga. edu/ caur/ semindex. htm) Notes covering all aspects of the SEM• Scanning Electron Microscopy basics (http:/ / virtual. itg. uiuc. edu/ training/ EM_tutorial/ ) an animated tutorial

on how SEM works• Preparing a Sample for the SEM (http:/ / virtual. itg. uiuc. edu/ training/ esem-prep. mov) preparing a

non-conducting subject for the SEM (QuickTime-movie)History• Microscopy History links (http:/ / bama. ua. edu/ ~hsmithso/ class/ bsc_656/ websites/ history. html) from the

University of Alabama Department of Biological Sciences• Environmental Scanning Electron Microscope (ESEM) history (http:/ / www. danilatos. com)Images

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• Rippel Electron Microscope Facility (http:/ / remf. dartmouth. edu/ imagesindex. html) Many dozens of (mostlybiological) SEM images from Dartmouth College.

• SEM micrographs carefully colored of daily objects, by Albert Lleal. (http:/ / albertlleal. com/ en/ reports/category/ 8-objects-at-scanning-electron-microscope-sem. html)

Article Sources and Contributors 12

Article Sources and ContributorsScanning electron microscope  Source: http://en.wikipedia.org/w/index.php?oldid=458778985  Contributors: 21655, 99of9, A. Carty, Acdx, Acroterion, Addhehe, Aharelick, Alchemy pete,Alohaaaa, Amaltheus, Aransil, Argon233, Aurelius173, Average Earthman, Awcga, Bender235, Blacksand, Blechnic, Blitterbug, Bobo192, Brian0918, Buzuk, Caltas, Camie, Carroy, Chasingsol,CheMechanical, Children of the dragon, Chris the speller, Christopher.booth, Chsh, CiaPan, Cjmnyc, Cleared as filed, Closedmouth, Cm the p, Cmichael, Cometstyles, CommonsDelinker,Conversion script, DMacks, DO11.10, Dandv, Dethme0w, Dgrant, Dhskep, Dicklyon, Diderot, Diliff, Dr bab, DrMikeF, Drosilia, Drphilharmonic, Duchoang81, Eaolson, Edward, Element16,Emvee, Eog1916, Epbr123, Esem0, Etan J. Tal, Facts707, Faradayplank, Fatcity7, Femto, Fhelmli, Fieldday-sunday, Filipi, Flcelloguy, ForrestFunk, Frap, Frecklefoot, GB fan, Gbrake, Gr8white,GreatWhiteNortherner, GreenLocust, Gspaul, Gterro, Gundeenz, HLHJ, Hakkasberra, Happy-melon, Heimstern, Hgrobe, Hugh2414, Ian Pitchford, IanOsgood, Ixfd64, JTN, JaGa, Jaccardi,JamesBWatson, Jamesc199244, Janderk, Jared lap, Jauerback, Jcwf, Jdheyerman, Jebus989, Jeffrey O. Gustafson, Jim Mikulak, Jjron, Karnesky, KaurJmeb, Kils, Kimsb0826, Kleopatra,Kmarinas86, Kopeliovich, Korath, KristianMolhave, La Pianista, Lancevortex, Lcmslutheran, LeaveSleaves, Lightmouse, Lmatt, Loupeter, Luna Santin, Lupin, Lyroussel, MC3DPCS, Malcolm,MarcoTolo, Markus Kuhn, Materialscientist, Meaty Weenies, Mgiganteus1, Mitaphane, Mwtoews, Nation kingdom, NellieBly, Nihiltres, Nima1024, Nono64, Nufy8, Ocatecir, Orangutan,Ozuma, Paul August, Pax:Vobiscum, Pengo, Penubag, Peterlewis, Plantsurfer, Pschemp, Pumbaa80, Quantumor, Qwyrxian, R.rommel, RGForbes, Raul654, Reyk, Richerman, Rjwilmsi, Rurik3,Sanders muc, Sbyrnes321, SchfiftyThree, Seervoitek, Skier Dude, Skmadhukar, Smith609, Snowmanradio, Snoyes, Sodium, Somearemoreequal, Spanyard, Spaully, Spinningspark, StealthFox,Steff, Stephan Schulz, Stephen Morley, Stevertigo, Stokerm, Sverdrup, Swerdnaneb, The High Fin Sperm Whale, The wub, TheParanoidOne, Timwi, Travelbird, Triwbe, Twisp, User A1,Vadmium, Vfranceschi, Viewfinder, Vivschmitt, Vniizht, WLU, Waldir, Wavelength, Whiner01, WikiLeon, Willking1979, Wilson44691, Yermih, Zephyris, 470 anonymous edits

Image Sources, Licenses and ContributorsFile:Misc pollen.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Misc_pollen.jpg  License: Public Domain  Contributors: Dartmouth Electron Microscope Facility, DartmouthCollegeFile:SEM chamber1.JPG  Source: http://en.wikipedia.org/w/index.php?title=File:SEM_chamber1.JPG  License: Creative Commons Attribution-Sharealike 2.5  Contributors: SteffFile:ScanningMicroscopeJLM.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:ScanningMicroscopeJLM.jpg  License: Creative Commons Attribution 3.0  Contributors: Etan J. TalFile:Schema MEB (en).svg  Source: http://en.wikipedia.org/w/index.php?title=File:Schema_MEB_(en).svg  License: Creative Commons Attribution-ShareAlike 3.0 Unported  Contributors:Schema_MEB_(it).svg: User:Steff, modified by User:ARTE derivative work: MarcoTolo (talk)Image:LT-SEM snow crystal magnification series-3.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:LT-SEM_snow_crystal_magnification_series-3.jpg  License: Public Domain Contributors: Brian0918, Coriolis ende, Howcheng, Ranveig, Saperaud, Steff, Tony Wills, Zzyzx11, 1 anonymous editsImage:FLY EYE.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:FLY_EYE.jpg  License: Creative Commons Attribution-Sharealike 3.0  Contributors: Nation kingdomImage:Gold Spider SEM sample.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Gold_Spider_SEM_sample.jpg  License: Creative Commons Attribution-Sharealike 3.0 Contributors: Toby HudsonFile:SEMStubs.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:SEMStubs.jpg  License: Creative Commons Attribution-Sharealike 3.0  Contributors: User:ZephyrisImage:SEM SE vs BE Zr Al.png  Source: http://en.wikipedia.org/w/index.php?title=File:SEM_SE_vs_BE_Zr_Al.png  License: Public Domain  Contributors: TwispImage:Soybean cyst nematode and egg SEM.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Soybean_cyst_nematode_and_egg_SEM.jpg  License: Public Domain  Contributors:Brian0918, Howcheng, Ies, Marac, Million Moments, Steff, 3 anonymous editsImage:Krilleyekils.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Krilleyekils.jpg  License: Creative Commons Attribution-ShareAlike 3.0 Unported  Contributors: User:uwe kilsFile:Antarctic krill ommatidia.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Antarctic_krill_ommatidia.jpg  License: GNU Free Documentation License  Contributors: Uwe Kils,aka Kils at en.wikipediaImage:SEM blood cells.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:SEM_blood_cells.jpg  License: Public Domain  Contributors: Bruce Wetzel (photographer). Harry Schaefer(photographer)Image:HederelloidSEM.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:HederelloidSEM.jpg  License: Public Domain  Contributors: Original uploader was Wilson44691 aten.wikipediaImage:BSEGlassInclusionSb.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:BSEGlassInclusionSb.jpg  License: Public Domain  Contributors: Original uploader was Alchemy peteat en.wikipediaImage:SEGlassCorrosion.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:SEGlassCorrosion.jpg  License: Public Domain  Contributors: Alchemy pete, Allen4names, Garion96,JkbeardsleeImage:Photoresist SEM micrograph.JPG  Source: http://en.wikipedia.org/w/index.php?title=File:Photoresist_SEM_micrograph.JPG  License: unknown  Contributors: EdC, EugeneZelenko,Tony Wills, 1 anonymous edits

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