April 21, 2016

Scanning & Transmission Electron Microscopy

The scanning electron microscope (SEM) is often used when visualization of a solid material is required. Approximate particle size, shape and topographical information can be obtained.

The sample is typically coated with a thin layer of gold and bombarded with electrons to visualize the surface, which is constantly scanned and reconstructed. The source of electrons is focused into a fine probe that is rastered over the surface of the specimen. A detector collects a part of the emitted electrons and an image is built by signal modulation and amplification.

Whereas SEM analyzes the surface, transmission electron microscopy (TEM) probes the internal structure of solids and gives access to micro-structural detail. This technique has proven to be very useful in analyzing crystalline domains in amorphous matrices, as present in supported metal catalysts and microporous zeolite crystals embedded in a mesoporous matrix.

With the addition of energy dispersive x-ray spectrometry (EDS), SEM and TEM can also be used as an elemental analysis tool at specific locations of the sample under investigation. The techniques are considered to be qualitative measurements.

The information obtained by electron microscopy is often complemented by a more quantitative analysis of e.g. particle size, porosity, surface area, or metal dispersion by chemisorption.