Scanning electron microscopy (SEM) is a surface imaging technique capable of achieving nm resolution on topographical features.

To generate electron images – called micrographs – a highly focused electron beam is scanned over the surface of a specimen. As it scans, the beam interacts with the sample to produce several detectable signals (different types of photons and electrons) through elastic and inelastic scattering events. The intensities of these signals depend predominantly on the atomic number of the scattering atom, and the adjacent surface topography. Each signal is affected by these factors slightly differently, and the SEM can be calibrated to detect one or two signals at a time. As the electron beam is scanned, the active detector(s) measure the intensity of the selected signal(s) at each pixel, and correlate these to a grayscale value. When the scan is complete, the system outputs an image that captures topographical (and sometimes relative atomic number) information.

In addition to standard SEM detectors, all Covalent instruments are also outfitted with energy dispersive spectroscopy (EDS) detectors to capture quantitative elemental composition measurements, as well as 2D elemental maps, in addition to conventional SEM images.