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Electron Microscopy
Dr Manaf Abdulrahman Guma
University Of Anbar- College Of Applied Sciences-Hit(Heet)
Department Of Applied Chemistry
Electron Microscopy (EM)
- The are two type of Electron Microscopy:
1. Transmission Electron Microscopy
(TEM)
2. Scanning Electron Microscopy (SEM)
What is TEM?
- The transmission electron microscope is a very powerful tool for material science.
- TEM uses a high energy beam of electrons is shone through a very thin sample, and the interactions between the electrons and the atoms to observe features of a specimen.
- High resolution can be used to analyse the quality, shape, size and density of quantum wells, wires and dots of an image taken.
What can TEM reveal?
- TEMs can reveal the finest details of internal structure - in some cases as small as individual atoms.
- Examples: the crystal structure and features in the structure like dislocations. Etc.
Describe the diffraction in the TEM?
1. As the electrons pass through the sample, they are scattered by the
electrostatic potential set up by the constituent elements in the specimen.
2. After passing through the specimen they pass through the electromagnetic
objective lens which focuses all the electrons scattered from one point of the
specimen into one point in the image plane.
3. Also, shown in the figure, a dotted line where the electrons scattered in the
same direction by the sample are collected into a single point.
4. This is the back focal plane of the objective lens and is where the diffraction
pattern is formed.
Imaging and diffraction
Describe the preparation techniques for TEM?
1. Dimpling is a preparation technique that produces a specimen with a thinned central area and an outer rim of sufficient thickness to permit ease of handling.
- Ion milling is traditionally the final form of specimen preparation. In this process, charged argon ions are accelerated to the specimen surface by the application of high voltage. The ion impingement upon the specimen surface removes material as a result of momentum transfer
What is SEM?
- SEM:
- SEM is used for inspecting topographies of specimens at very high magnifications.
- SEM magnifications can go to more than 300,000 X.
What is Cryo-EM?
- Cryogenic electron microscopy ( cryo-EM ) is an electron microscopy (EM) technique applied on
samples cooled to cryogenic temperatures ( means very low degree temperatures) and embedded in an
environment of vitreous water.
- An aqueous sample solution is applied to a grid-mesh and plunge-frozen in liquid ethane.
- While development of the technique began in the 1970 s, recent advances in detector technology and
software algorithms have allowed for the determination of biomolecular structures at near-atomic
resolution.
- This has attracted wide attention to the approach as an alternative to X-ray crystallography or NMR
spectroscopy for macromolecular structure determination without the need for crystallization.
Cryo EM: from sample to structure?
Which technique is the most popular so far?
