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.
n 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.