The convergence and power density of the electron-beam are steered by two condenser objectives before interaction with the copy. The objective objective is contrastforming the objective with a Blendenöffnung in its back fuel level and supplies a fundamental increase linear rendition (20-50). The picture, which is formed by this objective, is increased afterwards by a further row mediator and projector objectives, before the electrons with a phosphor detector of the screen, camera of the CCD (charge-coupled device) or sheet of the film to collide. It is also to the picture the back fuel level of the objective objective possible and in such a way forms an electron diffraction sample. 2,3 sample electron interaction electrons has a large scattering cross section, says we with X-ray is compared and to affect very strongly affair.
For this reason an electron microscope under vacuum must to be maintained and only dry samples be able to be investigated. This has serious consequences for biological materials, which contain usually approx. 85 per cent water. So tremendous effort entered into developing methods for the support of the samples, while they are drained before observation. Therefore the methods, the chemical networking also to include and distort stain finally, the native structure and limit the details, those to be made visible and the reached resolution. Saccharose, glucose, trehalose or gerbstoffartige acid were used, over to stabilize/blocked water at room temperature and in the frozen, hydratisierten condition replace. However water is singular and nothing can it replace, without to introduce possibly important, structural changes. An alternative beginning at Dehydratisierung of Fernandes Moran, in order to regard suggested the samples, which were maintained in a frozen condition within the microscope. At a low sufficient temperature the steam pressure of the water is enough small, so that the sample keeps its water. The Entwicklungsfähigkeit of CryoEM was demonstrated by Chanzy in Europe and in Glaesar and by Taylor in the USA in the seventies, in which electron diffraction experiments showed that freezing could conserve highly soluble structure in hydratisierten polysaccharid and protein crystals. Also in the seventies, ministers developed a Klimazelle, in which the sample at the ambient temperature in a completely hydratisierten condition was maintained and it was, highly soluble structural retaining by electron diffraction to demonstrate. However is a consequence of the strong interaction of the electrons that the strength of the sample, it can be investigated is limited and therefore wet cell, with its connected water vapour, was unpractically for representation
For an explainable picture this is an announcement over suitable maximum copy strength. This increases for more energy electrons at the higher accelerating tensions. Usually like the strength of the sample increases, the resolution, which can be the obtained decreases, which are suitable plural and inelastic scattering. For these highly soluble studies of the reasons by Cryoelektron microscopy to thinner samples were limited. The use of an energy filter to remove you inelastically absent-minded electrons from the picture makes possible to be investigated little stronger samples and is at present important in the tomographischen studies. However stronger samples must, how complete cells are first subdivided or broken, before microscopy, and their treatment is beyond the range of this chapter.
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