Energy filtered transmission electron microscopy

Energy filtered transmission electron microscopy

Energy-filtered transmission electron microscopy (EFTEM) is a technique used in Transmission electron microscopy, in which only electrons of particular kinetic energies are used to form the image or diffraction pattern. The technique can be used to aid chemical analysis of the sample in conjunction with complementary techniques such as electron crystallography.

Principle

If a very thin sample is illuminated with a beam of high-energy electrons, then a majority of the electrons will pass unhindered through the sample but some will interact with the sample, being scattered elastically or inelastically (phonon scattering, plasmon scattering or inner shell ionisation). Inelastic scattering results in both a loss of energy and a change in momemtum, which in the case of inner shell ionisation is characteristic of the element in the sample.

If the electron beam emerging from the sample is passed through a magnetic prism, then the flight path of the electrons will vary depending on their energy. This technique is used to form spectra in Electron energy loss spectroscopy (EELS), but it is also possible to place an adjustable slit to allow only electrons with a certain range of energies through, and reform an image using these electrons on a detector.

The energy slit can be adjusted so as to only allow electrons which have not lost energy to pass through to form the image. This prevents inelastic scattering from contributing to the image, and hence produces an enhanced contrast image.

Adjusting the slit to only allow electrons which have lost a specific amount of energy can be used to obtain elementally sensitive images. As the ionisation signal is often significantly smaller than the background signal, it is normally necessary to obtain more than one image at varying energies to remove the background effect. The simplest method is known as the "jump ratio" technique, where an image recorded using electrons at the energy of the maximum of the absorption peak caused by a particular inner shell ionisation is divided by an image recorded just before the ionisation energy. It is often necessary to cross-correlate the images to compensate for relative drift of the sample between the two images.

Improved elemental maps can be obtained by taking a series of images, allowing quantitative analysis and improved accuracy of mapping where more than one element is involved. By taking a series of images, it is also possible to extract the EELS profile from particular features.

External links

* [http://www.smt.zeiss.com/c1256e4600305472/Contents-Frame/30b85f74aa66dd75c1256e5c002ad32e EFTEM imaging modes Carl Zeiss]
* [http://www.weels.net A Database of EELS fine structure fingerprints at Cornell]

Further reading

*cite book | author=Williams D.B., Carter C.B | title=Transmission Electron Microscopy: A Textbook for Materials Science | publisher=Kluwer Academic / Plenum Publishers | year=1996 | editor= | id=ISBN 0-306-45324-X

*cite book | author=Channing. C. Ahn (ed.) | title=Transmission Electron Energy Loss Spectrometry in Materials Science and the EELS ATLAS | publisher=Wiley-VHC | year=2004 | id=ISBN 3-527-40565-8

* F. Hofer, P. Warbichler and W. Grogger, "Imaging of nanometer-sized precipitates in solids by electron spectroscopic imaging", [http://www.sciencedirect.com/science/article/B6TW1-3YYTTMD-2/2/b9229a5a9fbc2aab2c1de9dcd91a1a61 Ultramicroscopy, Volume 59, Issues 1-4, July 1995, Pages 15-31.]

ee also

*TEM


Wikimedia Foundation. 2010.

Игры ⚽ Поможем сделать НИР

Look at other dictionaries:

  • Energy Filtered Transmission Electron Microscopy — Energiegefilterte Transmissionselektronenmikroskopie (engl. Energy Filtered Transmission Electron Microscopy; EFTEM) ist eine Variante der Transmissionselektronenmikroskopie. Sie nutzt die unterschiedliche Bewegungsenergie der Elektronen nach dem …   Deutsch Wikipedia

  • Transmission electron microscopy — A TEM image of the polio virus. The polio virus is 30 nm in size.[1] Transmission electron microscopy (TEM) is a microscopy technique whereby a beam of electrons is transmitted through an ultra thin specimen, interacting with the specimen as it… …   Wikipedia

  • High-resolution transmission electron microscopy — (HRTEM) is an imaging mode of the transmission electron microscope (TEM) that allows the imaging of the crystallographic structure of a sample at an atomic scale. [cite book |title=Experimental high resolution electron microscopy |last=Spence… …   Wikipedia

  • Scanning transmission electron microscopy — A scanning transmission electron microscope (STEM) is a type of transmission electron microscope. With it, the electrons pass through the specimen, but, as in scanning electron microscopy, the electron optics focus the beam into a narrow spot… …   Wikipedia

  • Electron microscope — Diagram of a transmission electron microscope A 197 …   Wikipedia

  • Electron energy loss spectroscopy — In electron energy loss spectroscopy (EELS) a material is exposed to a beam of electrons with a known, narrow range of kinetic energies. Some of the electrons will undergo inelastic scattering, which means that they lose energy and have their… …   Wikipedia

  • Electron spectrometer — In an Electron spectrometer, an incoming beam of electrons is bent with electric or magnetic fields. As higher energy electrons will be bent less by the beam, this produces a spatially distributed range of energies. Electron spectrometers are… …   Wikipedia

  • Photoemission electron microscopy — (PEEM, also called photoelectron microscopy, PEM) is a widely used type of emission microscopy. PEEM utilizes local variations in electron emission to generate image contrast. The excitation is usually produced by UV light, synchrotron radiation… …   Wikipedia

  • Reflection high energy electron diffraction — (RHEED) is a technique used to characterize the surface of crystalline materials. RHEED systems gather information only from the surface layer of the sample, which distinguishes RHEED from other materials characterization methods that rely also… …   Wikipedia

  • List of materials analysis methods — List of materials analysis methods: Contents: Top · 0–9 · A B C D E F G H I J K L M N O P Q R S T U V W X Y Z μSR see Muon spin spectroscopy …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”