Scanning Electron Microscopy (SEM)

The JEOL 7100F FEG-SEM at the Nanoscale and Microscale Research Centre

SEM at a glance

SEM is an imaging technique that uses incident electrons to generate secondary sample irradiance. This can then be detected in a variety of ways to visualise sample surfaces with high depth of field and lateral resolutions of around 1-20nm, as well as analyse the physical and chemical state of the substrate.

FIBSEM couples traditional SEM with a focused ion beam that can be used for materials processing and sample preparation (deposition, ablation, sectioning etc.) or at low beam currents, for imaging in its own right.
ESEM allows for the imaging of poorly conductive ‘uncoated’, or ‘wet’ samples that cannot be imaged in the high vacuum conditions of a traditional SEM.
Cryo-SEM allows for biological samples to be rapidly frozen, prepared and then SEM imaged. This preserves the initial substrate morphology and chemistry of the fully hydrated specimen by preventing water loss to vacuum operation.
FEGSEM uses a field emission gun electron source to generate a smaller diameter electron beam than standard thermal emission sources. This allows better spatial resolution to be achieved and makes the technique more suitable for nanostructural characterisation.

Applications of SEM

Morphological and topographical imaging
Compositional contrast imaging
Chemical analysis via energy or wavelength dispersive X-ray spectroscopy (EDS, WDS)
Dynamic macro-, micro- and nano-structural imaging under temperature, pressure and strain variations
Sample manipulation, sectioning and thinning

Scanning Electron Microscopy with cryo-handling capabilities

How does SEM work?

A fine beam of electrons is used to scan across the specimen surface in synchronism with the spot of a cathode ray tube (CRT). This incident beam leads to elastic and inelastic scattering of electrons, as well as variations of electromagnetic radiation. There are subsequently a host of secondary signals that can be detected, including secondary electrons, backscattered electrons, Auger electrons, cathodoluminescence or X-rays. In general, as the primary electron beam is rastered across a substrate, the intensity of the secondary signal will change depending on the surface morphology, chemistry, physical state etc. The contrast is seen by adjusting the brightness of the CRT spot by the amplified version of this detected signal.

Images courtesy of Vladimir Korolkov Photography and Lubrizol Ltd.