Transmission electron microscopy: multi analysis device!

 | Post date: 2022/06/20 | 
Transmission electron microscopy (TEM) with its various imaging modes and analytical abilities, is now an indispensable tool for chemical and structural characterization at the nanoscale of all types of materials. It is a microscopy technique in which a beam of energetic electrons is transmitted through a sample and the interaction of electrons with the sample forms an image. The image is then magnified and focused onto an imaging device, such as a fluorescent screen, a layer of photographic film, or a sensor like a charge-coupled device. At lower magnifications TEM image contrast is due to differential absorption of electrons by the material due to differences in its composition or thickness. 
X-ray emission consequent to the interaction of the primary electron beam with the sample, can also be detected by an energy-dispersive spectrometer (EDS) within the TEM. As the resulting X-ray energies are characteristic of the atomic structure of the element they originated from, the spectra generated can be used to identify the constituent elements.
It is also possible to measure the loss of energy from the inelastic scattering of electrons in specimen transmission (EELS). This information can be used to infer elemental composition, chemical bonding, valence and conduction band electronic properties.

A scanning transmission electron microscope (STEM) is a type of TEM. While in TEM parallel electron beams are focused perpendicular to the sample plane, in STEM the beam is focused at a large angle and is converged into a focal point. The transmitted signal is collected as a function of the beam location as it is rastered across the sample.
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