When the electron beam interacts with a sample in a scanning electron microscope (SEM), multiple events happen. In general, different detectors are needed to distinguish secondary electrons, backscattered electrons, or characteristic x-rays. Depending upon the accelerating voltage and sample density, the signals come from different penetration depths.
Schematic of electron beam interaction
After Auger electrons, the secondary electrons come from the next most shallow penetration depth. A secondary electron detector, or SED, is used to produce a topographic SEM image. SED images have high resolution that are independent of the material and are acquired from inelastically scattered electrons close to the surface. No material composition information is available. An integrated SED is available for the Phenom SEM for large samples.
A backscattered electron detector (BSD) detects elastically scattered electrons. These electrons are higher in energy from atoms below the sample surface. Using a BSD allows for lower vacuum levels, reducing sample preparation requirements and minimizing beam damage.
Schematic of a backscattered electron detector (BSD) for scanning electron microscopy (SEM)
Elemental analysis is accomplished using an energy dispersive x-ray spectroscopy (EDS) detector. The Phenom ProX includes an integrated EDS detector for elemental identification. An integrated EDS detector is also available for the large stage Phenom SEM.