Principle : The scanning electron microscope (sem or sem in english for scanning electron microscopy).
allows you to obtain images of surfaces of practically all solid materials, at scales ranging from the size of the magnifying glass (x10) to that of the transmission electron microscope(x500.000 or more). it uses a fine beam of electrons, emitted by an electron gun. of electromagnetic lenses allow to focus the electron beam on the sample. the interaction between the electrons and the sample causes the formation of secondary electrons of lower energy. they are amplified and then detected and converted into an electrical signal. this process is achieved in each point of the sample by a scanning microscope. the set of signals allows to reconstruct the typography of the specimen and provide an image in relief.
the sem conventional works in a vacuum, ordinary (10-5 to 10-6 mbar); the samples can be massive, ranging in size from a few 1μm (particles) to a dozen cm in diameter, or even more (sampling industrial). they must be able to withstand the vacuum without the pollute and be drivers. the preparation is generally simple.
the sem at controlled pressure (say environmental or low vacuum) allows the observation in a vacuum up to 30 mbar, thus making possible the examination of samples wet or greasy (ech. biological), of insulating materials without metallization prior (ceramics, corroded metals), even in the presence of liquid.
equipped with suitable detectors, the sem allows you to do between other of the microanalysis x, elemental analysis, local.