Environmental SEM and Related Applications

The key to the imaging technology in the ESEM is the ionization of gas molecules by the secondary electrons from the sample and the collection of this amplified signal. Secondary electrons that are generated by the interaction of the primary electron beam with the sample are the signal of choice for high resolution imaging. The primary beam strikes a sample generating both secondary and backscattered electrons. In the ESEM, the secondary electrons are specifically collected by a confined electrostatic field that is generated by gaseous secondary electron detector above the sample. Within this field, the secondary electrons strike gas molecules generating an additional electron; a process termed cascade amplification. The image formed by collection of these electrons is very similar to the image formed by the conventional Everhart-Thornley detector, even though the signal amplification process is different. Scattering of the primary beam electrons also results in the formation of amplified electrons, but contains no relevant image information.