Scanning Electron Microscopy (SEM)

The Basics

  • Scanning Electron Microscopy (SEM) is used to image an object at a very small scale. It uses an electron beam to scan across the surface of a sample.
  • Several interactions within the sample that result in the emission of electrons and photons occur as the electrons penetrate the surface. Which include auger electrons, secondary electrons, backscatter electrons, characteristic x-rays, continuum x-rays and cathodoluminescence.
  • These emitted particles can be collected with the appropriate detector to give valuable information about the material.
  • The most immediate result of this is that it displays the sample topography.

Detectors and Emmissions

  • The available detectors within the PEMC allow for the detection of secondary electrons, backscattered electrons, characteristic x-rays and cathodoluminescence.
  • Near the surface of the sample secondary electrons (SE) are emitted, which have a much lower energy than the incident beam and gives very good topographical information (good visual data).
  • Further into the sample backscattered electrons (BSE) are emmitted, which have a similar energy to the incident beam and can give very good atomic number contrast and is classed as sub-surface.
  • Even further into the sample, x-rays can be generated which enables chemical analysis.
  • Additionally the Zeiss Crossbeam 550 has two column detectors, an InLens SE detector and an energy selective backscatter (EsB) detector. Both of these enable the use of much lower accelerating potentials and much shorter working distances to enable maximum resolution.