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

SEM opened sample chamber

The scanning electron microscope (SEM) is a type of electron microscope that images the sample surface by scanning it with a high-energy beam of electrons in a raster scan pattern. An electron microscope is a type of Microscope that uses Electrons to illuminate a specimen and create an enlarged image The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J A Raster scan, or raster scanning, is the pattern of image detection and reconstruction in television and is the pattern of image storage and transmission used in most computer The electrons interact with the atoms that make up the sample producing signals that contain information about the sample's surface topography, composition and other properties such as electrical conductivity. Topography ( topo-, "place" and graphia, "writing" is the study of Earth 's Surface features or those of Planets Electrical conductivity or specific conductivity is a measure of a material's ability to conduct an Electric current. This particular type of microscope is exceedingly useful.

The types of signals made by an SEM can include secondary electrons, back scattered electrons, characteristic x-rays and light (cathodoluminescence). Secondary electrons are electrons generated as ionization products Energy dispersive X-ray spectroscopy (EDS EDX or EDXRF is an analytical technique used for the elemental analysis or chemical characterization of a sample Cathodoluminescence is an optical and electrical Phenomenon whereby a beam of Electrons is generated by an Electron gun (e These signals come from the beam of electrons striking the surface of the specimen and interacting with the sample at or near its surface. In its primary detection mode, secondary electron imaging, the SEM can produce very high-resolution images of a sample surface, revealing details about 1 to 5 nm in size. Due to the way these images are created, SEM micrographs have a very large depth of focus yielding a characteristic three-dimensional appearance useful for understanding the surface structure of a sample. Depth of focus is a lens Optics concept that measures the tolerance of placement of the image plane (the Film plane in a camera in relation to the lens This great depth of field and the wide range of magnifications (commonly from about 25 times to 250,000 times) are available in the most common imaging mode for specimens in the SEM, secondary electron imaging, such as the micrograph taken of pollen shown to the right. In Optics, particularly as it relates to Film and Photography, the depth of field (DOF is the portion of a scene that appears sharp in the image Magnification is the process of enlarging something only in appearance not in physical size Characteristic x-rays are the second most common imaging mode for an SEM. X-rays are emitted when the electron beam removes an inner shell electron from the sample, causing a higher energy electron to fill the shell and give off energy. X-radiation (composed of X-rays) is a form of Electromagnetic radiation. An electron shell may be crudely thought of as an Orbit followed by Electrons around an Atom nucleus. A quantum mechanical system or particle that is bound, confined spacially can only take on certain discrete values of energy as opposed to classical particles which These characteristic x-rays are used to identify the elemental composition of the sample. Back-scattered electrons (BSE) that come from the sample may also be used to form an image. BSE images are often used in analytical SEM along with the spectra made from the characteristic x-rays as clues to the elemental composition of the sample.

History

The first SEM image was obtained by Max Knoll, who in 1935 obtained an image of silicon steel showing electron channeling contrast. Electrical steel, also called lamination steel, silicon electrical steel, silicon steel or transformer steel, is specialty Steel tailored ^[1] Further pioneering work on the physical principles of the SEM and beam specimen interactions was performed by Manfred von Ardenne in 1937^[2][3], who produced a British patent^[4] but never made a practical instrument. Manfred von Ardenne ( January 20, 1907 in Hamburg - May 26, 1997 in Dresden) was a German research and applied The SEM was further developed by Professor Sir Charles Oatley and his postgraduate student Gary Stewart and was first marketed in 1965 by the Cambridge Instrument Company as the "Stereoscan". Sir Charles Oatley (1904–1996 was Professor of Electrical Engineering University of Cambridge, 1960–1971 and developer of one of the first commercial Scanning electron The first instrument was delivered to the DuPont.

Scanning process and image formation

In a typical SEM, electrons are thermionically emitted from a tungsten filament cathode and are accelerated towards an anode. Thermionic emission is the flow of Charge carriers from a surface or over some other kind of Electrical potential barrier caused by thermal vibrational energy Tungsten (ˈtʌŋstən also known as wolfram (/ˈwʊlfrəm/ is a Chemical element that has the symbol W and Atomic number 74 A cathode is an Electrode through which (positive Electric current flows out of a polarized electrical device An anode is an Electrode through which Electric current flows into a polarized electrical device Tungsten is normally used in thermionic electron guns because it has the highest melting point and lowest vapour pressure of all metals, thereby allowing it to be heated for electron emission. An electron gun (also called electron emitter) is an electrical component that produces an Electron beam that has a precise Kinetic energy and is most often Other electron sources include lanthanum hexaboride (LaB₆) cathodes, which can be used in a standard tungsten filament SEM if the vacuum system is upgraded. Lanthanum hexaboride ( La[[Boron B]]6, also called lanthanum boride and LaB) is an inorganic chemical a Boride of Lanthanum A cathode is an Electrode through which (positive Electric current flows out of a polarized electrical device Electrons can also be emitted using a field emission gun (FEG), which may be of the cold-cathode type or the thermally-assisted Schottky type. A field emission gun is a type of Electron gun in which the emitter tip is held at several kilovolts negative Potential relative to a nearby Electrode, A cold cathode is an element used within some Nixie tubes Gas discharge lamps Gas filled tubes and Vacuum tubes Cold cathodes do not Walter Hermann Schottky ( 23 July 1886, Zürich, Switzerland – 4 March 1976, Pretzfeld, West Germany

The electron beam, which typically has an energy ranging from a few hundred eV to 40 keV, is focused by one or two condenser lenses into a beam with a very fine focal spot sized 0. In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός 4 nm to 5 nm. The beam passes through pairs of scanning coils or pairs of deflector plates in the electron column, typically in the final lens, which deflect the beam horizontally and vertically so 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 scattering and absorption within a teardrop-shaped volume of the specimen known as the interaction volume, which extends from less than 100 nm to around 5 µm into the surface. The size of the interaction volume depends on the electron's landing energy, the atomic number of the specimen and the specimen's density. The energy exchange between the electron beam and the sample results in the reflection of high-energy electrons by elastic scattering, emission of secondary electrons by inelastic scattering and the emission of electromagnetic radiation which can be detected to produce an image, as described below. In Scattering theory and in particular in Particle physics, elastic scattering is one of the specific forms of scattering In Particle physics and Chemistry, inelastic scattering is a fundamental Scattering process in which the kinetic energy of an incident particle is not conserved Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter.

Electronic devices are used to detect and amplify the signals and display them as an image on a cathode ray tube in which the raster scanning is synchronised with that of the microscope. Electronics refers to the flow of charge (moving Electrons through Nonmetal conductors (mainly Semiconductors, whereas electrical The cathode ray tube (CRT is a Vacuum tube containing an Electron gun (a source of electrons and a Fluorescent screen with internal or The image displayed is therefore a distribution map of the intensity of the signal being emitted from the scanned area of the specimen. The image may be captured by photography from a high resolution cathode ray tube, but in modern machines is digitally captured and displayed on a computer monitor. A photograph (often shortened to photo) is an Image created by Light falling on a light-sensitive surface usually Photographic film or an electronic A visual display unit, often called simply a monitor or display, is a piece of Electrical equipment which displays images generated from the Video

Magnification

Magnification in a SEM can be controlled over a range of about 5 orders of magnitude from x25 or less to x 250,000 or more. Magnification is the process of enlarging something only in appearance not in physical size An order of magnitude is the class of scale or magnitude of any amount where each class contains values of a fixed ratio to the class preceding it Unlike optical and transmission electron microscopes, image magnification in the SEM is not a function of the power of the objective lens. An objective in Optics is the lens or Mirror in a Microscope, Telescope, camera or other optical instrument SEMs may have condenser and objective lenses, but their function is to focus the beam to a spot, and not to image the specimen. A condenser is one of the main components of the optical system of many transmitted light Compound microscopes A condenser is a lens that serves to concentrate Provided the electron gun can generate a beam with sufficiently small diameter, an SEM could in principle work entirely without condenser or objective lenses, although it might not be very versatile or achieve very high resolution. An electron gun (also called electron emitter) is an electrical component that produces an Electron beam that has a precise Kinetic energy and is most often In an SEM, as in scanning probe microscopy, magnification results from the ratio of the dimensions of the raster on the specimen and the raster on the display device. Scanning probe microscopy (SPM is a branch of Microscopy that forms images of surfaces using a physical probe that scans the specimen 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, and not by objective lens power.

Sample preparation

An insect coated in gold, having been prepared for viewing with a scanning electron microscope.

For conventional imaging, the SEM requires that specimens be conductive for the electron beam to scan the surface and that the electrons have a path to ground. All samples must also be trimmed to an appropriate size to fit in the specimen chamber and generally mounted on some sort of holder.

Metals require little special preparation for SEM except for mounting on an appropriate speciment holder.

Nonconductive solid specimens are coated with a layer of conductive material. An ultrathin coating of electrically-conducting material such as, gold, gold/palladium alloy, platinum, tungsten or graphite is deposited on the sample either by low vacuum sputter coating or by high vacuum evaporation. Gold (ˈɡoʊld is a Chemical element with the symbol Au (from its Latin name aurum) and Atomic number 79 Palladium (pronounced \pəˈleɪdiəm\ is a rare and lustrous silvery-white metal that was discovered in 1803 by William Hyde Wollaston, who named it palladium after the Platinum (ˈplætɪnəm is a Chemical element with the Atomic symbol Pt and an Atomic number of 78 Tungsten (ˈtʌŋstən also known as wolfram (/ˈwʊlfrəm/ is a Chemical element that has the symbol W and Atomic number 74 The Mineral graphite, as with Diamond and Fullerene, is one of the Allotropes of carbon. Sputter deposition is a Physical vapor deposition (PVD method of depositing Thin films by Sputtering, i This is done to prevent the accumulation of static electric charge on the specimen during electron irradiation. Electric charge is a fundamental conserved property of some Subatomic particles which determines their Electromagnetic interaction. Another reason for coating, even when there is more than enough conductivity, is to improve contrast and resolution, a situation most common when using a FESEM (field emission SEM) and samples with low atomic number.

Nonconducting specimens may be imaged uncoated using specialized SEM instrumentation such as the "Environmental SEM" (ESEM) or in field emission gun (FEG) SEMs operated at low voltage. Environmental SEM instruments place the specimen in a relatively high pressure chamber where the working distance is short and the electron optical column is differentially pumped to keep vacuum adequately low at the electron gun. The high pressure region around the sample in the ESEM facilitates charge neutralization and provides an amplification of the secondary electron signal. Low voltage (LV) SEM can be operationally difficult to accomplish and is typically a research application for specimens that are sensitive to the process of applying conductive coatings. LV-SEM is typically conducted in an FEG-SEM because the FEG is capable of producing high primary electron brightness even at low accelerating potentials. Operating conditions must be adjusted such that the local space charge is at or near neutral with adequate low voltage secondary electrons being available to neutralize any positively charged surface sites. This requires that the primary electron beam's potential and current be tuned to the characteristics of the sample specimen.

Embedding in a resin with further polishing to a mirror-like finish can be used for both biological and materials specimens when imaging in backscattered electrons or when doing quantitative X-ray microanalysis. Resin, not to be confused with Rosin, is a Hydrocarbon Secretion of many Plants particularly coniferous trees.

Biological samples

A biological specimen normally requires fixation to preserve its structure. This is usually performed by incubation in a solution of a buffered chemical fixative, such as glutaraldehyde or paraformaldehyde. For an individual weak acid or weak base component see Buffering agent. Glutaraldehyde is a colorless liquid with a pungent odor used to sterilize medical and dental equipment Formaldehyde is a Chemical compound with the formula H2CO It is the simplest Aldehyde —an organic compound containing a terminal Carbonyl Biological specimens are dehydrated, usually by replacing water in the cell with organic solvents such as ethanol or, and then by replacing these solvents in turn with a transitional fluid such as liquid carbon dioxide in critical point drying. Water is a common Chemical substance that is essential for the survival of all known forms of Life. Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single If the SEM is equipped with a cold stage for cryo-microscopy, cryofixation may be used and low-temperature scanning electron microscopy performed on the cryogenically fixed specimens. ^[5] Cryo-fixed specimens may be cryo-fractured under vacuum in a special apparatus to reveal internal structure, sputter coated and transferred onto the SEM cryo-stage while still frozen.

Freeze-fracturing, freeze-etch or freeze&break is a preparation method particularly useful for examining lipid membranes and their incorporated proteins in "face on" view. The preparation method reveals the proteins embedded in the lipid bilayer.

Sputter-coated gold has a high atomic number and produces high topographic contrast and resolution but the coating has finite thickness, and can obscure the underlying fine detail of the specimen for very high magnification images. Low-vacuum SEMs with differential pumping apertures allow samples to be imaged without such coating and without the loss of natural contrast caused by the coating.

Materials

Back scattered electron imaging, quantitative x-ray analysis, and x-ray mapping of geological specimens and metals requires that the surfaces be ground, mounted, sanded, and polished to an ultra smooth surface. Geological specimens that undergo WDS or EDS analysis are often carbon coated. Metals are not generally coated prior to imaging in the SEM because they are conductive and provide 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. Fractography is the study of fracture surfaces of materials Fractographic methods are routinely used to determine the cause of failure in engineering structures especially in product The fractured surface is cut to a suitable size, cleaned of any organic residues, and mounted on a specimen holder for viewing in the SEM.

Integrated circuits may be cut with a FIB or other ion milling instrument for viewing in the SEM. Focused ion beam, also known as FIB, is a technique used particularly in the semiconductor and materials science fields for site-specific analysis deposition and ablation of 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.

ESEM

The accumulation of electric charge on the surfaces of non-metallic specimens can be avoided by using environmental SEM in which the specimen is placed in an internal chamber at higher pressure than the vacuum in the electron optical column. Electric charge is a fundamental conserved property of some Subatomic particles which determines their Electromagnetic interaction. Positively charged ions generated by beam interactions with the gas help to neutralize the negative charge on the specimen surface. The pressure of gas in the chamber can be controlled, and the type of gas used can be varied according to need. Coating is thus unnecessary, and X-ray analysis unhindered.

Detection of secondary electrons

The most common imaging mode collects low energy (<50 eV) secondary electrons. Secondary electrons are electrons generated as ionization products Due to their low energy, these electrons originate within a few nanometers from the sample surface. A nanometre ( American spelling: nanometer, symbol nm) ( Greek: νάνος nanos dwarf; μετρώ metrό count) is a ^[6] The electrons are detected by an Everhart-Thornley detector^[7] which is a type of scintillator-photomultiplier device. The Everhart-Thornley Detector is a secondary electron detector used in Scanning electron microscopes (SEMs A scintillator is a substance that absorbs high-energy (ie Ionizing) electromagnetic or charged Particle radiation then in response fluoresces Photomultiplier tubes ( photomultipliers or PMT s for short members of the class of Vacuum tubes and more specifically Phototubes are extremely The resulting signal is displayed as a two-dimensional intensity distribution that can be viewed and saved as a digital image. In the fields of communications, Signal processing, and in Electrical engineering more generally a signal is any time-varying or spatial-varying quantity A digital image is a representation of a two-dimensional Image using ones and zeros (binary This process relies on a raster-scanned primary beam. The brightness of the signal depends on the number of secondary electrons reaching the detector. A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument If the beam enters the sample perpendicular to the surface, then the activated region is uniform about the axis of the beam and a certain number of electrons "escape" from within the sample. As the angle of incidence increases, the "escape" distance of one side of the beam will decrease, and more secondary electrons will be emitted. Thus steep surfaces and edges tend to be brighter than flat surfaces, which results in images with a well-defined, three-dimensional appearance. Using this technique, image resolution less than 1 nm is possible. Image resolution describes the detail an Image holds The term applies equally to Digital images film images and other types of images

Detection of backscattered electrons

Comparison of SEM techniques:
* backscattered electrons analysis - composition resolution
* secondary electrons analysis - relief

Backscattered electrons consist of high-energy electrons originating in the electron beam, that are reflected or back-scattered out of the specimen interaction volume. Backscattered electrons may be used to detect contrast between areas with different chemical compositions, especially when the average atomic number of the various regions is different, since the brightness of the BSE image tends to increase with the atomic number. ^[6]. Strong topographic contrast also is produced with a directional detector collecting these electrons from one side above the specimen; the contrast appears as illumination of the topography from that side.

Backscattered electrons can also be used to form an electron backscatter diffraction (EBSD) image. Electron backscatter diffraction ( EBSD) also known as backscatter Kikuchi diffraction ( BKD) is a microstructural- crystallographic technique This image can be used to determine the crystallographic structure of the specimen.

The use of an Everhart-Thornley detector for detection of backscattered electrons is deficient because fewer such electrons are emitted in the solid angle subtended by the detector than the number of secondary electrons forced to the detector by its high bias collection grid. The Everhart-Thornley Detector is a secondary electron detector used in Scanning electron microscopes (SEMs The use of a dedicated backscattered electron detector above the sample in a "doughnut" type arrangement, concentric with the electron beam, greatly increases the solid angle of collection and allows for the detection of more backscattered electrons producing atomic number contrast.

Beam-injection analysis of semiconductors

The nature of the SEM's probe, energetic electrons, makes it uniquely suited to examining the optical and electronic properties of semiconductor materials. The high-energy electrons from the SEM beam will inject charge carriers into the semiconductor. In Physics, a charge carrier denotes a free (mobile unbound particle carrying an Electric charge. Thus, beam electrons lose energy by promoting electrons from the valence band into the conduction band, leaving behind holes. In Solids the valence band is the highest range of Electron energies where electrons are normally present at Absolute zero. In the Physics field of Semiconductors and insulators the conduction band is the range of Electron Energy, higher than that of the An electron hole is the conceptual and mathematical Opposite of an Electron, useful in the study of Physics and Chemistry.

In a direct bandgap material, recombination of these electron-hole pairs will result in cathodoluminescence; if the sample contains an internal electric field, such as is present at a p-n junction, the SEM beam injection of carriers will cause electron beam induced current (EBIC) to flow. In Semiconductor Physics, a direct Bandgap means that the minimum energy of the Conduction band lies directly above the maximum energy of the Cathodoluminescence is an optical and electrical Phenomenon whereby a beam of Electrons is generated by an Electron gun (e A p-n junction is a junction formed by combining P-type and N-type Semiconductors together in very close contact Electron beam induced current (EBIC is a semiconductor analysis technique performed in a Scanning electron microscope (SEM or Scanning transmission electron microscope

Cathodoluminescence and EBIC are referred to as "beam-injection" techniques, and are very powerful probes of the optoelectronic behavior of semiconductors, particularly for studying nanoscale features and defects.

Cathodoluminescence

Cathodoluminescence, the emission of light when atoms excited by high-energy electrons return to their ground state, is analogous to UV-induced fluorescence, and some materials such as zinc sulfide and some fluorescent dyes, exhibit both phenomena. Cathodoluminescence is an optical and electrical Phenomenon whereby a beam of Electrons is generated by an Electron gun (e Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays Fluorescence is a Luminescence that is mostly found as an Cathodoluminescence is most commonly experienced in everyday life as the light emission from the inner surface of the cathode ray tube in television sets and computer CRT monitors. The cathode ray tube (CRT is a Vacuum tube containing an Electron gun (a source of electrons and a Fluorescent screen with internal or In the SEM, CL detectors either collect all light emitted by the specimen, or can analyse the wavelengths emitted by the specimen and display an emission spectrum or an image of the distribution of cathodoluminescence the specimen in real colour. A spectrum (plural spectra or spectrums) is a condition that is not limited to a specific set of values but can vary infinitely within a continuum.

X-ray microanalysis

X-rays, which are also produced by the interaction of electrons with the sample, may also be detected in an SEM equipped for energy-dispersive X-ray spectroscopy or wavelength dispersive X-ray spectroscopy. X-radiation (composed of X-rays) is a form of Electromagnetic radiation. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J Energy dispersive X-ray spectroscopy (EDS EDX or EDXRF is an analytical technique used for the elemental analysis or chemical characterization of a sample The Wavelength dispersive X-ray spectroscopy (WDXRF or WDS is a method used to count the number of X-rays of a specific wavelength diffracted by a crystal

Resolution of the SEM

The spatial resolution of the SEM depends on the size of the electron spot, which in turn depends on both the wavelength of the electrons and the magnetic electron-optical system which produces the scanning beam. The resolution is also limited 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 both might be large compared to the distances between atoms, so the resolution of the SEM is not high enough to image individual atoms, as is possible in the shorter wavelength (i. e. higher energy) transmission electron microscope (TEM). The SEM has compensating advantages, though, including the ability to image a comparatively large area of the specimen; the ability to image bulk materials (not just thin films or foils); and the variety of analytical modes available for measuring the composition and nature of the specimen. Depending on the instrument, the resolution can fall somewhere between less than 1 nm and 20 nm. The world's highest SEM resolution is obtained with the Hitachi S-5500. Resolution is 0. 4nm at 30kV and 1. 6nm at 1kV. In general, SEM images are easier to interpret than TEM images.

Environmental SEM

Main article: ESEM

Conventional SEM requires samples to be imaged under vacuum, because a gas atmosphere rapidly spreads and attenuates electron beams. Esem is the stage name of Georgi Hristov Marinov a Bulgarian electronic music artist (born 10 February 1979 This vacuum means "absence of matter" or "an empty area or space" for the cleaning appliance see Vacuum cleaner. In Physics, attenuation (in some context also called extinction) is the gradual loss in intensity of any kind of Flux through a medium Consequently, samples that produce a significant amount of vapour, e. Vapor pressure (also known as equilibrium vapor pressure or saturation vapor pressure) is the Pressure of a Vapor in equilibrium g. wet biological samples or oil-bearing rock need to be either dried or cryogenically frozen. Processes involving phase transitions, such as the drying of adhesives or melting of alloys, liquid transport, chemical reactions, solid-air-gas systems and living organisms in general cannot be observed. In Thermodynamics, phase transition or phase change is the transformation of a thermodynamic system from one phase to another Glue or adhesive is a compound that adheres or bonds two items together An alloy is a Solid solution or Homogeneous mixture of two or more elements, at least one of which is a Metal, which itself has

The first commercial development of the Environmental SEM (ESEM) in the late 1980s ^{[8] [9]} allowed samples to be observed in low-pressure gaseous environments (e. g. 1-50 Torr) and high relative humidity (up to 100%). The torr (symbol Torr) is a non- SI unit of Pressure defined as 1/760 of an atmosphere. Humidity is the amount of water vapor in the air In daily language the term "humidity" is normally taken to mean Relative humidity. This was made possible by the development of a secondary-electron detector ^{[10] [11]} capable of operating in the presence of water vapour and by the use of pressure-limiting apertures with differential pumping in the path of the electron beam to separate the vacuum regions around the gun and lenses from the sample chamber.

The first commercial ESEMs were produced by the ElectroScan Corporation in USA in 1988 ^[12]. ElectroScan were later taken over by Philips (now FEI Company) in 1996 ^[13].

ESEM is especially useful for non-metallic and biological materials because coating with carbon or gold is unnecessary. Uncoated Plastics and Elastomers can be routinely examined, as can uncoated biological samples. Plastic is the general common term for a wide range of synthetic or semisynthetic organic solid materials suitable for the manufacture of industrial products An elastomer is a Polymer with the property of Elasticity. The term which is derived from elastic polymer, is often used interchangeably with the term Coating can be difficult to reverse, may conceal small features on the surface of the sample and may reduce the value of the results obtained. X-ray analysis is difficult with a coating of a heavy metal, so carbon coatings are routinely used in conventional SEMs, but ESEM makes it possible to perform X-ray microanalysis on uncoated non-conductive specimens. ESEM may be the preferred for electron microscopy of unique samples from criminal or civil actions, where forensic analysis may need to be repeated by several different experts.

See also

• List of surface analysis methods
• Forensic science
• Forensic engineering
• Transmission electron microscopy (TEM)

Terminology

DR-SEM

Defect Review - Scanning Electron Microscopy

CD-SEM

Critical Dimension Measurement - Scanning Electron Microscopy

FIB-SEM

Focused Ion Bean - Scanning Electron Microscopy

References

External links

General

• Notes on the SEM Notes covering all aspects of the SEM

History

• Microscopy History links from the University of Alabama Department of Biological Sciences
• The Early History and Development of SEM from Cambridge University Engineering Department
• Milestones in the History of Electron Microscopy from the Swiss Federal Institute of Zürich
• Environmental Scanning Electron Microscope (ESEM) history

Images

See our image gallery on this topic at: Scanning electron microscopic images

• Tescan Image Gallery Some great SEM images of various specimens, as well as analytical results
• Dennis Kunkel Microscopy, Inc. Large collection of SEM images - mostly false colour
• Jeol SEM Images Twelve SEM images of various specimens
• SEM Lab at the Smithsonian National Museum of Natural History; includes a gallery of images
• Rippel Electron Microscope Facility Many dozens of (mostly biological) SEM images from Dartmouth College. Year 1988 ( MCMLXXXVIII) was a Leap year starting on Friday (link displays 1988 Gregorian calendar) Events 655 - Battle of Winwaed: Penda of Mercia is defeated by Oswiu of Northumbria. Wikimedia Commons (or simply Commons) is a repository of Free content images sound and other multimedia files

Gallery of SEM images

The following are examples of images taken using a scanning electron microscope.

False coloured SEM image of soybean cyst nematode and egg. The soybean cyst nematode (SCN Heterodera glycines, is a plant-parasitic Nematode and a devastating pest of the Soybean ( Glycine The false colour makes the image easier for non-specialists to view and understand the structures and surfaces revealed in micrographs.	Compound eye of Antarctic krill Euphausia superba. Antarctic krill ( Euphausia superba) is a Species of Krill found in the Antarctic waters of the Southern Ocean. Arthropod eyes are a common subject in SEM micrographs due to the depth of focus that an SEM image can capture.	Ommatidia of Antarctic krill eye, a higher magnification of the krill's eye. The Compound eye of Insects is composed of units called ommatidia. Antarctic krill ( Euphausia superba) is a Species of Krill found in the Antarctic waters of the Southern Ocean. SEMs cover a range from light microscopy up to the magnifications available with a TEM.	SEM image of normal circulating human blood. This is an older and noisy micrograph of a common subject for SEM micrographs: red blood cells.
SEM image of a hederelloid from the Devonian of Michigan (largest tube diameter is 0. Hederellids are Extinct colonial Animals with calcitic tubular branching Exoskeletons They range from the Silurian to the Permian and The Devonian is a geologic period and system of the Paleozoic era spanning from to  million years ago. 75 mm). The SEM is used extensively for capturing detailed images of micro and macro fossils.	Backscattered Electron (BSE) image of an Antimony rich region in a fragment of ancient glass. Antimony (IPA (Received Pronunciation, /ˈæntɪmoʊni/ (US is a Chemical element with the symbol Sb (stibium meaning "mark" and Museums use SEMs for studying valuable artifacts in a nondestructive manner. Many BSE images are taken at atmospheric rather than destructive high vacuum conditions.	SEM image of the corrosion layer on the surface of an ancient glass fragment, note the laminar structure of the corrosion layer.	SEM image of a photoresist layer used in semiconductor manufacturing taken on a field emission SEM at 1000 volts, a very low accelerating voltage for an SEM, but achievable with field emission SEMs--this one taken with a Schottky field-emission gun. Photoresist is a Light -sensitive material used in several industrial processes such as Photolithography and Photoengraving to form a patterned coating A semiconductor' is a Solid material that has Electrical conductivity in between a conductor and an insulator; it can vary over that Field emission (FE is the emission of electrons from the surface of a condensed phase into another phase due to the presence of high electric fields Field emission (FE is the emission of electrons from the surface of a condensed phase into another phase due to the presence of high electric fields These SEMs are important in the semiconductor industry for their high resolution capabilities.