Microscopy and Microanalysis
The Scanning Electron Microscope (SEM) is used in many fields of science. A biologist might use it to study the tiniest structures of an insect, the geologist might use it to learn what chemicals are present in a rock, and the automobile engineer might use it to find tiny defects in a car part. SEM images are created using electrons instead of the photons of light we use to see the world around us. Electrons have a shorter wavelength than photons allowing much greater magnifications and resolution than with conventional light microscopy.
In the SEM, the most common images are made by bombarding a specimen with a narrow beam of electrons and scanning that beam back and forth across the surface of the specimen.
A Transmission Electron Microscope (TEM) is used if even higher magnifications are needed. A biologist might use it to study the membrane of an organelle. The chemist might use it to identify a crystalline substance. A crystalline structure can be determined by studying the patterns of electron diffraction made when the electron beam goes through an ultra-thin crystal.
The most common imaging process begins by passing a beam of electrons through the ultra-thin section to a detector below the specimen. A TEM image of a purified viral DNA is shown here. The theoretical limit of magnification with the TEM is greater than 1,500,000X!
Photons help us view the microscopic world, as for example, in the familiar light microscope and the Confocal Scanning Light Microscope. The confocal microscope captures images at different depths in a thick material, so it does not need to be prepared by a destructive process.
This allows us to trace fluorescently labeled compounds in an organism over time or locate labeled structures in the material and generate three dimensional images.