Scanning confocal electron microscopy (SCEM) is an
electron microscopy
An electron microscope is a microscope that uses a beam of electrons as a source of illumination. It uses electron optics that are analogous to the glass lenses of an optical light microscope to control the electron beam, for instance focusing i ...
technique analogous to
scanning confocal optical microscopy (SCOM). In this technique, the studied sample is illuminated by a focussed electron beam, as in other scanning microscopy techniques, such as
scanning transmission electron microscopy
A scanning transmission electron microscope (STEM) is a type of transmission electron microscope (TEM). Pronunciation is tÉ›mor ›sti:i:É›m As with a conventional transmission electron microscope (CTEM), images are formed by electrons p ...
or
scanning electron microscopy
A scanning electron microscope (SEM) is a type of electron microscope that produces images of a sample by scanning the surface with a focused beam of electrons. The electrons interact with atoms in the sample, producing various signals that ...
. However, in SCEM, the collection optics are arranged symmetrically to the illumination optics to gather only the electrons that pass the beam focus. This results in superior depth resolution of the imaging. The technique is relatively new and is being actively developed.
History
The idea of SCEM logically follows from SCOM and thus is rather old. However, practical design and construction of scanning confocal electron microscope is a complex problem first solved by
Nestor J. Zaluzec. His first scanning confocal electron microscope demonstrated the 3D properties of the SCEM, but have not realized the sub-nanometer lateral spatial resolution achievable with high-energy electrons (lateral resolution of only ~80 nm has been demonstrated). Several groups are currently working on construction of atomic resolution SCEM.
In particular, atomically resolved SCEM images have already been obtained
Operation
The sample is illuminated by a focused electron beam, and the beam is re-focused on the detector, thus collecting only electrons passing through the focus. In order to produce an image, the beam should be laterally scanned. In the original design, this was achieved by placing synchronized scanning and descanning deflectors. Such design is complex and only a few custom-built setups exist. Another approach is to use stationary illumination and collection, but perform scan by moving the sample with a high-precision piezo-controlled holder. Such holders are readily available and can fit into most commercial electron microscopes thereby realizing the SCEM mode. As a practical demonstration, atomically resolved SCEM images have been recorded.
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Advantages
High energies of incident particles (200 keV electrons vs. 2 eV photons) result in much higher spatial resolution
In physics and geosciences, the term spatial resolution refers to distance between independent measurements, or the physical dimension that represents a pixel of the image. While in some instruments, like cameras and telescopes, spatial resoluti ...
of SCEM as compared to SCOM (lateral resolution <1 nm vs. >400 nm).
As compared to conventional electron microscopy
An electron microscope is a microscope that uses a beam of electrons as a source of illumination. It uses electron optics that are analogous to the glass lenses of an optical light microscope to control the electron beam, for instance focusing i ...
( TEM, STEM
Stem or STEM most commonly refers to:
* Plant stem, a structural axis of a vascular plant
* Stem group
* Science, technology, engineering, and mathematics
Stem or STEM can also refer to:
Language and writing
* Word stem, part of a word respon ...
, SEM), SCEM offers 3-dimensional imaging. 3D imaging in SCEM was expected from the confocal geometry of SCEM, and it has recently been confirmed by theoretical modeling. In particular, it is predicted that a heavy layer (gold) can be identified in light matrix (aluminum) with ~10 nm precision in depth; this depth resolution is limited by the convergence angle of the electron beam and could be improved to a few nanometers in next-generation electron microscopes equipped with two fifth-order spherical aberration
In optics, spherical aberration (SA) is a type of aberration found in optical systems that have elements with spherical surfaces. This phenomenon commonly affects lenses and curved mirrors, as these components are often shaped in a spherical ...
correctors.
See also
*Confocal microscopy
Confocal microscopy, most frequently confocal laser scanning microscopy (CLSM) or laser scanning confocal microscopy (LSCM), is an optical imaging technique for increasing optical resolution and contrast (vision), contrast of a micrograph by me ...
*Confocal laser scanning microscopy
Confocal microscopy, most frequently confocal laser scanning microscopy (CLSM) or laser scanning confocal microscopy (LSCM), is an optical imaging technique for increasing optical resolution and contrast of a micrograph by means of using a s ...
*Electron microscopy
An electron microscope is a microscope that uses a beam of electrons as a source of illumination. It uses electron optics that are analogous to the glass lenses of an optical light microscope to control the electron beam, for instance focusing i ...
*Scanning electron microscope
A scanning electron microscope (SEM) is a type of electron microscope that produces images of a sample by scanning the surface with a focused beam of electrons. The electrons interact with atoms in the sample, producing various signals that ...
*Scanning transmission electron microscopy
A scanning transmission electron microscope (STEM) is a type of transmission electron microscope (TEM). Pronunciation is tÉ›mor ›sti:i:É›m As with a conventional transmission electron microscope (CTEM), images are formed by electrons p ...
*Transmission electron microscopy
Transmission electron microscopy (TEM) is a microscopy technique in which a beam of electrons is transmitted through a specimen to form an image. The specimen is most often an ultrathin section less than 100 nm thick or a suspension on a g ...
References
{{DEFAULTSORT:Scanning Confocal Electron Microscopy
Electron microscopy
Scientific techniques