Microscopy Laboratory

Electron microscopy has become ubiquitous in material-related analysis in academia, industry, medicine, and forensic. There are two units of scanning electron microscope (SEM) operating at the chemistry department. Tungsten filament SEM from Emcrafts and Schottky field emission SEM from ThermoFisher. Both SEMs are equipped with energy dispersive X-ray analysis (EDX) detector for elemental analysis.

Our two SEMs are able to provide topological and elemental analysis. These topological and elemental information originate mainly from three signals: secondary electrons (SE), back-scattered electrons (BSE) and characteristic X-rays. The proportion of the three signals detected by the electronics in the SEMs depends on the interaction between the primary beam (the stream of electrons coming from the electron gun) and the sample being investigated. This means the type of information generated depends on how energetics the electron beam is and on the texture and elemental composition of the sample.

In general SE signal is sensitive to the sample’s topology, giving information from the sample’s surface. BSE signal is sensitive to the sample’s composition based on Z-contrast. And finally elemental analysis from the characteristic X-ray signals. As a consequence of where the signals coming from (see figure for e-beam and sample interaction volume) the spatial resolution increases from X-ray<BSE<SE signals.