What is scanning electron microscopy?
In scanning electron microscopy, an electron beam scans the surface of a sample. The interaction between the electrons and the object produces an image. In contrast to light microscopic images, SEM images have a far greater depth of field and allow higher magnifications: while light microscopy can achieve magnifications of around 2,000 times, SEMs can magnify up to a million times.
The electron beam must be generated in a high vacuum. Therefore, the analysed sample must normally be vacuum-stable, i.e. it must not contain any water. This is achieved by critical-point drying. Another problem is electrical charges that arise when non-conductive materials are analysed. To avoid this, the samples are first coated with a wafer-thin layer of precious metal (usually gold) (sputter coating).
What equipment is available at the LIB?
The LIB is equipped with a Zeiss Gemini Sigma 300 VP electron microscope. This is a so-called environmental scanning electron microscope (ESEM), in which only the area in which the electron beam is generated is in a high vacuum, while the sample chamber and the detector are in a low vacuum. This means that non-vacuum-stable or non-gilded samples (museum material) can also be analysed.
A Leica EM CPD300 critical point dryer and a Cressington 108Auto sputter coater are available for preparing the samples.
What is the scanning electron microscope used for at the LIB?
It is used for documentation and description. In contrast to light microscopy, much higher magnifications can be achieved, which allows the ultrastructure to be analysed, for example.
