A scanning electron microscope ( SEM ) image of a normal red blood cell, a platelet, and a white blood cell.

Unlike the TEM, where electrons of the high voltage beam carry the image of the specimen, the electron beam of the scanning electron microscope ( SEM ) does not at any time carry a complete image of the specimen.

The image displayed by an SEM maps the varying intensity of any of these signals into the image in a position corresponding to the position of the beam on the specimen when the signal was generated.

Generally, the image resolution of an SEM is about an order of magnitude poorer than that of a TEM.

However, because the SEM image relies on surface processes rather than transmission, it is able to image bulk samples up to many centimetres in size and ( depending on instrument design and settings ) has a great depth of field, and so can produce images that are good representations of the three-dimensional shape of the sample.

False-color scanning electron microscope | SEM image of the filter setae of an Antarctic krill.

The first SEM image was obtained by Max Knoll, who in 1935 obtained an image of silicon steel showing electron channeling contrast.

Unlike optical and transmission electron microscopes, image magnification in the SEM is not a function of the power of the objective lens.

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 emitted by the specimen in real colour.

The spot size and the interaction volume are both 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 properties of the specimen.

Image: Soybean cyst nematode and egg SEM. jpg | Coloured SEM image of soybean cyst nematode and egg.

Image: FLY EYE. jpg | SEM image of a house fly compound eye surface at 450 × magnification.

Arthropod eyes are a common subject in SEM micrographs due to the depth of focus that an SEM image can capture.

Image: SEM blood cells. jpg | SEM image of normal circulating human blood.

An ant as imaged using a scanning electron microscope ( SEM )

The figure raising Noah's outer and inner garment to expose his nakedness is labelled SEM ( Shem ), rather than CHAM ( Ham ), who is shown looking away toward IAPHET ( Japeth ) who has his hands over his eyes.

The low-voltage electron microscope ( LVEM ) is a combination of SEM, TEM and STEM in one instrument, which operates at relatively low electron accelerating voltage of 5 kV.

* Scanning electron microscope ( SEM ): looks at the surface of bulk objects by scanning the surface with a fine electron beam.

For conventional imaging in the SEM, specimens must be electrically conductive, at least at the surface, and electrically grounded to prevent the accumulation of electrostatic charge at the surface.

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.

Low-voltage SEM is typically conducted in an FEG-SEM because the FEG is capable of producing high primary electron brightness even at low accelerating potentials.

For SEM, a specimen is normally required to be completely dry, since the specimen chamber is at high vacuum.

The secondary electrons are first collected by attracting them towards an electrically biased grid at about + 400 V, and then further accelerated towards a phosphor or scintillator positively biased to about + 2, 000 V. The accelerated secondary electrons are now sufficiently energetic to cause the scintillator to emit flashes of light ( cathodoluminescence ), which are conducted to a photomultiplier outside the SEM column via a light pipe and a window in the wall of the specimen chamber.

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.

By 2009, The world's highest SEM resolution at high-beam energies ( 0. 4 nm at 30 kV ) is obtained with the Hitachi S-5500.

* Pollen micrographs at SEM and confocal microscope

Photomicrograph made with a Scanning Electron Microscope ( SEM ): Fly ash particles at 2, 000x magnification.

Traditionally, an AFM cannot scan images as fast as a SEM, requiring several minutes for a typical scan, while a SEM is capable of scanning at near real-time, although at relatively low quality.

However, several fast-acting designs were suggested to increase microscope scanning productivity including what is being termed videoAFM ( reasonable quality images are being obtained with videoAFM at video rate: faster than the average SEM ).

An SEM may typically operate at an accelerating potential of 10, 000 volts ( 10 kV ) giving an electron velocity approximately 20 % of the speed of light, while a typical TEM can operate at 200 kV raising the electron velocity to 70 % the speed of light.

For example, an electron at an energy of 10 keV has a wavelength of 0. 01 nm, allowing the electron microscope ( SEM or TEM ) to achieve high resolution images.

The best resolution for SEM in 2011 was 0. 4 nanometer.

Further pioneering work on the physical principles of the SEM and beam specimen interactions was performed by Manfred von Ardenne in 1937, who produced a British patent but never made a practical instrument.

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 Scientific Instrument Company as the " Stereoscan ".

Founded in 1984, SEM was the first economics and management school in China.

The initial analysis of ALH 84001 was unusual in that an undergraduate student, Anne Taunton of the University of Arkansas, performed much of the SEM work used to correlate the suspected nanobacterial fossils with known terrestrial nanobacterial fossils.

NASA's David McKay hired Anne Taunton for a 10-week student internship to perform the SEM analysis, but did not inform her about the nature of what she was investigating.

One of the first commercially available polyphonic synthesizers, Oberheim's Two-voice TVS-1, Four-voice FVS-1 in 1975, and Eight-voice in 1977, which was the four voice frame with an external 4 SEM module, configurations were based on the SEM.

After the issurance of ICD106 Strategic Enterprise Management ( IC SEM ), the Intelligence Community budget was more closely aligned to strategic goals and objectives, requirements, and performance criteria.

Another inclusion was a Space Experiment Module ( SEM ).

The lack of competition in the Northern Ireland market is also undoubtedly a factor, although the introduction of the Single Electricity Market ( SEM ) in Ireland in late 2007 was designed to address this.

SEM was founded in August 1997, when L. P. Tiwari and T. M.

A spinoff league called Pro Wrestling SEM was recently launched.

The position of Secretary for Education and Manpower was set up in 1983 when the old Education Department was restructured into the Education and Manpower Branch and Education Department, and the old position of Director of Education was split into SEM and Director of Education accordingly, with the latter reporting to the former.

Since the Principal Officials Accountability System ( POAS ) was introduced in 2002, the SEM, as all other secretary positions, is an ex-officio member of the Executive Council ( ExCo ).

Before the introduction of the POAS in July 2002, the SEM, as well as all other secretary-level positions, was a civil service position.

The position of SEM was renamed Secretary for Education.

Early work utilised a single crystal of known orientation being inserted into the SEM chamber and a particular feature of the EBSP was known to correspond to the pattern centre.

Garry Stewart, who was another of Professor Oatley ’ s students, then moved to the Cambridge Instrument Company where he oversaw the design and building of the world ’ s first commercial SEM, the Stereoscan.