Scanning electron microscope

The scanning electron microscope is an electron microscope that views objects in relief.

Technique of the scanning electron microscope

The scanning electron microscope (SEM) uses a thin electron beam emitted by an electron gun. The electron beam is focussed onto the sample by electro-magnetic lenses.

Interaction between the electrons and the sample leads to the formation of secondary, lower energy electrons. These are amplified and then detected and converted into an electric signal. This process is performed at each point in the sample by the microscope scanning the sample. The set of signals are used to reconstruct the shape of the sample and provide a an image in relief.

Sample preparation is complex. The samples must be dehydrated and then processed to become conducting (fixing the tissues and cleaning). The sample is then placed on the sample holder.

Use of the scanning electron microscope

The surface of objects, bacteriaand materials etc. can be seen through the scanning electron microscope. One benefit of this microscope is its depth of field. However its resolution (1 nanometre) is not as good as the transmission electron microscope (0.1 nanometre).