The electron microscope has become one of the most widely utilized instruments for materials characterization. An electron microscope is a scientific instrument that allows us to “see” objects so small that they cannot be seen in any other way. (CITE) Electron microscopes have allowed scientists to see individual molecules and atoms for the first time.
Most microscopes, including those in schools and laboratories today, are optical microscopes. They use glass lenses to enlarge, or magnify, an image. An optical microscope cannot produce an image of an object smaller than the length of the light wave in use. To see anything smaller than 2,000 angstroms (about 1/250,000 of an inch) a wave of shorter length would have to be used. In 1923, a French physicist Louis de Broglie suggested that electrons, like light, travel in a wave. In addition, the wavelength of electrons is much shorter than the wavelength of light.
An electron is an elementary particle carrying a unit of charge of negative electricity.
(CITE) J. J. Thompson discovered the electron in 1897 while showing what cathode rays were composed of. (CITE) The first time that the electron was used for a unit of negative electricity was in the late 19th century by the English physicist G. J. Stoney.
The electron is the lightest particle having a non-zero rest mass. Electrons also have a wavelike property, which made them prime candidates for microscopes and other devices.
Ernst Ruska (1906-1988), a German physicist, used De Broglie’s discovery to design a microscope that used an electron beam instead of light to produce an image. (CITE) By 1931, with the help of partner Dr. Max Knoll Ruska had produced a working model of the first electron microscope.
Several types of electron microscopes have been developed since Ruska’s first model.
Some are so large that they are housed in silos several stories high while others are small enough to fit in the palm of a hand. These instruments have given scientists a new look at the world around us.
Ruska’s working model was a transmission electron microscope (TEM). It sends a beam of electrons, rather than light, through the object being viewed. The object to be viewed must be very thin so the electrons can pass through it. Because air is too dense for electrons to pass through, the object must be placed in a vacuum chamber. A beam of electrons is then focused on the object. Magnetic lenses that act in the same way as glass lenses in an optical microscope spread the part of the beam that passes through the object.
Finally, the beam...