Electron microscopy

Scanning Electron Microscopy (SEM)

by Dr. David Miller

In the scanning electron microscope (SEM) an electron beam is scanned across the surface of a sample. The interaction of the electron beam with the sample produces a number of secondary signals that can be used to produce images and spectra.
The most commonly used signals for imaging in the electron microscope are secondary electrons and backscattered electrons. The emission of secondary electrons is dependent on the topography of the sample and is used to produce images with topographic contrast. The emission of backscattered electrons is dependent on the atomic number (Z) of the sample and can be used to produce images with compositional contrast.
The different elements in a sample also emit characteristic X-rays when bombarded by electrons. The energy of these X-rays can be measured to generate spectra which can then be quantified and/or used to produce elemental maps and lines cans showing elemental distribution.

Transmission Electron Microscopy (TEM)