Electron Microscope & Uses

Electron microscopes use highly energetic electron beams to produce an electronically magnified image for extremely detailed observation. They have much higher magnification power than a normal light microscope, magnifying up to two million times. They are used widely by researchers all over the world in many industries and are crucial to many continuing scientific developments and discoveries.

Background and Uses

• Electron microscopes can magnify both biological and inorganic materials and are commonly used to examine cells, microorganisms, metals, crystals and biopsy samples. However, samples must be viewed in a vacuum and are usually ultra-thin and stained with dyes for better viewing. This type of microscope can reveal a wide variety of information about a specimen including morphology, crystallographic information, compositional information and topography. It's possible to study the small details of a cell. Electron microscopes are valuable tools in medical and biological fields, as well as for materials research. Nearly any scientific field can utilize electron microscopes. They are most commonly used in biology, medicine, chemistry, and forensics.

Transmission Electron Microscope

• The transmission electron microscope (TEM), the original form of electron microscopes, uses a high voltage beam of electrons to create an image of a specimen. The electrons emitted by an electron gun are accelerated, focused and transmitted through a partially transparent specimen. The beam then emerges from the specimen and carries information to the objective lens where magnification occurs. Photographic recording of the image can also occur by exposing film directly to the beam. TEMs can yield information about the morphology including size, shape and arrangement of particles. They can also relay crystallographic information, such as the arrangement of atoms and their degree of order, as well as compositional information, including the relative ratios of the elements and compounds or defects in areas as small as a few nanometers. A TEM can help determine ductility, strength, reactivity, melting point, hardness, conductivity and electrical properties.

Scanning Electron Microscope

• Unlike the TEM, where the electrons carry the entire image, the scanning electron microscope (SEM) makes an image by using the electron beam that scans the specimen across a rectangular area. Known as raster scanning, the electron beam loses energy as it scans each point on the specimen. This lost energy converts into heat, light and secondary electron emission. The display maps these varying intensities into an image relying on surface process rather than transmission. While an SEM produces an image with a slightly lower resolution, it can bulk samples of much larger specimens, up to several centimeters in size, and can produce great representations of 3-D shapes. Like the TEM, an SEM can relay information about morphology, composition and crystallographic information. However, they are limited to looking at composition in areas of one micrometer and degrees of order on single-crystal particles of greater than 20 micrometers. In addition, an SEM can also yield information about topography, or the surface features and texture, down to a few nanometers.