Difracción de Electrones: Interesante trabajo con información sobre la tecnica de caracterización de materiales basada en la difracción de electrones en microscopia electronica de transmisión y barrido (TEM y SEM)
Electron microscope follows the same ideas of optical microscope, but uses electrons instead of light;“Lens” here are not the optical materials (like glass), but electrical field.
A Scanning Electron Microscope uses a beam of electrons to scan the surface of an object to create an image detailing the topography and composition of the object’s surface.
A Transmission Electron Microscope is used to magnify objects. It aims a beam of electrons onto the object to form a magnified image called a micrograph.
In SEM an electron beam is focused into a small probe and is rastered across the surface of a specimen.Several interactions with the sample that result in the emission of electrons or photons occur as the electrons penetrate the surface.These emitted particles can be collected with the appropriate detector to yield valuable information about the material.The most immediate result of observation in the scanning electron microscope is that it displays the shape of the sample.The resolution is determined by beam diameter.
In transmission electron microscopy (TEM), a beam of highly focused electrons are directed toward a thinned sample (<200 nm). Normally no scanning required --- helps the high resolution, compared to SEM. These highly energetic incident electrons interact with the atoms in the sample producing characteristic radiation and particles providing information for materials characterization. Information is obtained from both deflected and non-deflected transmitted electrons, backscattered and secondary electrons, and emitted photons.
The resolution of a scanning electron microscope is lower than that of a transmission electron microscope. While TEM can view the images of objects to atomic level (which is less than 1nm), SEM can only be used to view images that require tens of nm at most.
SEM only scans a specimen. This limits the amount of information you can get from the specimen – it can only show the morphology of the specimen. Conversely, TEM can help you see a lot of characteristics of the specimen, such as the stress of the specimen, its crystallization, morphology, and even its holography.
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