4.2.1 Electron energy loss spectroscopy (EELS). In 1986, Ruska was awarded the Nobel Prize in physics for the development of transmission electron microscopy. The first TEM was demonstrated by Max Knoll and Ernst Ruska in 1931, with this group developing the first TEM with resolution greater than that of light in 1933 and the first commercial TEM in 1939. For this reason TEM is regarded as an essential tool for nanoscience in both biological and materials fields. What this means is that a TEM is capable of returning an extraordinary variety of nanometer- and atomic-resolution information, in ideal cases revealing not only where all the atoms are but what kinds of atoms they are and how they are bonded to each other. Each mechanism tells the user a different kind of information, depending not only on the contrast mechanism but on how the microscope is used-the settings of lenses, apertures, and detectors. Contrast can arise from position-to-position differences in the thickness or density ("mass-thickness contrast"), atomic number ("Z contrast", referring to the common abbreviation Z for atomic number), crystal structure or orientation ("crystallographic contrast" or "diffraction contrast"), the slight quantum-mechanical phase shifts that individual atoms produce in electrons that pass through them ("phase contrast"), the energy lost by electrons on passing through the sample ("spectrum imaging") and more. Even within conventional imaging, there are many fundamentally different ways that contrast is produced, called "image contrast mechanisms". TEM instruments have multiple operating modes including conventional imaging, scanning TEM imaging (STEM), diffraction, spectroscopy, and combinations of these. TEMs find application in cancer research, virology, and materials science as well as pollution, nanotechnology and semiconductor research, but also in other fields such as paleontology and palynology. Transmission electron microscopy is a major analytical method in the physical, chemical and biological sciences. This enables the instrument to capture fine detail-even as small as a single column of atoms, which is thousands of times smaller than a resolvable object seen in a light microscope. Transmission electron microscopes are capable of imaging at a significantly higher resolution than light microscopes, owing to the smaller de Broglie wavelength of electrons. The image is then magnified and focused onto an imaging device, such as a fluorescent screen, a layer of photographic film, or a sensor such as a scintillator attached to a charge-coupled device. 
An image is formed from the interaction of the electrons with the sample as the beam is transmitted through the specimen.
The specimen is most often an ultrathin section less than 100 nm thick or a suspension on a grid. Transmission electron microscopy ( TEM) is a microscopy technique in which a beam of electrons is transmitted through a specimen to form an image. Operating principle of a transmission electron microscope
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