Types of Electron Microscope

The prototype of the first electron microscope was devised in 1931 by the German engineers Max Knoll and Ernst Ruska. It was based on the discoveries and ideas of a French physicist called Louis de Broglie.

The resolving power or magnification of this device is much higher as compared to an ordinary light microscope. Nowadays, electron microscopes can magnify objects up to two million times of the original size of the specimen.

It is one of the most essential components of modern laboratories. It is used by researchers to examine body cells, microorganisms, samples of medical biopsy, various large molecules, crystalline and metal structures, the inherent features of numerous surfaces, etc. 

It is extensively used for various applications in industry such as the analysis of failure, quality assurance, and inspection, especially in the fabrication of semiconductor devices.

In this instrument, a beam of electrons is used to form the image of the specimen, with no light being involved. The specimen's image can be studied on a screen that is phosphor coated, and the electron micrographs are produced on photographic plates.

An extremely sharp metal tip, a single crystal of Lanthanum Hexaboride, or a heated tungsten filament is the source of the beam of electrons. A high voltage is used to accelerate this beam down a vertical column, which is done under vacuum, and electromagnetic lenses are used to focus it.

It is not possible to focus electrons using glass lenses. As a matter of fact, an electron beam can be stopped by even an extremely thin piece of glass. The voltages that are used to accelerate the beam can range from a few thousand up to a million volts. The specimens that are examined by a TEM have to be extremely thin (about 50 nanometers or less).

In this device, electrons are used to excite the specimen so that it gives off secondary electrons, which are collected by detectors and uses to create an image. Most images that are seen in books and articles are of this type. The beam also scatters these electrons, resulting in the formation of an image.

As a matter of fact, there are several beam interactions of the specimen that provide useful information on the monitor. For instance, the beam can also cause X-Rays to be emitted by the specimen.

A separate detector can collect and use them to study the elemental components of the specimen. They can also be used for creating the specimen's elemental map on a video screen.

This was an invention of Heinrich Rohrer and Gerd Binnig at IBM's lab in Zurich, Switzerland. This device is used for obtaining images of surfaces that are conductive at the atomic scale of 0.2 nanometer or 2 x 10-10 m. 

It is also used for altering the material that is observed by the manipulation of individual atoms, which helps to trigger off chemical reactions. It used to create ions by individual electrons being removed from atoms, and then reverting them back to atoms by the replacement of the electrons.

This is just a regular microscope with a scanning system added to it. Rather than using a single electron beam, a small spot is used for scanning the specimen, and the image is by a detector that is placed under the specimen. This instrument is particularly efficacious for the X-Ray microanalyses of tiny parts of thin slices of specimens.