Electron Microscopes were developed due to the limitations of Light Microscopes. There are two general types of electron microscopes developed – the TEM or the transmission electron microscope, and the SEM or the scanning electron microscope. The Transmission Electron Microscope was the first type of Electron Microscope to be developed in the year of 1931. It was patterned exactly on the Light Transmission Microscope. The only difference was that a focused beam of electrons is used instead of light to see through the specimen. The first Scanning Electron Microscope was made and introduced in 1942. Its late development was due to the electronics involved in scanning the beam of electrons that pass across the sample. The transmission electron makes electrons that bounce off the specimen. The scanning electron uses electrons that are radiated off the specimen.
In an electron microscope, a stream of electrons is formed by the electron source. It is then accelerated toward the specimen using a positive electrical potential. This stream is confined and focused using magnetic lenses and metal apertures into a thin and focused beam. This beam is then focused onto the sample with the use of a magnetic lens. Then, interactions take place inside the irradiated sample, affecting the electron beam.
The electron microscopes are the only type of microscopes that use electrons to provide a three dimensional image up to two million times larger. This type of microscopes run on electricity.
Upon the development of the very first electron microscope, Siemens had patented the electron microscope in 1931. Siemens were doing no research on electron microscopes at that time though. In 1937 however, Siemens began developing the electron microscope, funding Ruska and Bodo von Borries just to develop the said instrument. Siemens also employed Ruska’s brother Helmut to work on applications, particularly with biological materials.
By 1939, Siemens have produced the very first transmission electron microscope or TEM. But the very first practical electron microscope was built at the University of Toronto in the previous year of 1938 by Eli Franklin Burton and his students Cecil Hall, James Hillier and Albert Prebus.
Although the modern electron microscopes can magnify objects up to two million times, they are still based upon Ruska’s microscope design. Modern electron microscopes also still are made based on his theory of correlation between wavelength and resolution.
