Different Types of SEM

Posted By Tom Feltham on 07 May 2014

Posted in Used Equipment Buyers Guides

A scanning microscope is a piece of equipment that takes images of a sample right down to the atomic level. They come in various forms and two of the main types are:

Scanning Electron Microscope

One of the most used types of scanning microscope in the medical industry is the scanning electron microscope (SEM). The SEM scans a given sample with a high-energy beam of electrons in what is known as a ‘raster scan’ pattern. When the electrons interact with the atoms of the sample, they send signals with details about its surface properties such as its topography, electrical conductivity, and its composition.

Within the specimen chamber of this type of scanning microscope, there is a vacuum so a specimen being examined needs to be completely dry. This is fine if the specimen is solid such as bone but with any kind of living tissue, chemical fixation is needed to act as a stabiliser for the structure. It is possible to obtain 3-D images from an SEM by using techniques such as photogrammetry or photometric stereo.

Scanning Tunnelling Microscope

Another type of scanning microscope that was developed in 1981 is the scanning tunnelling microscope (STM) that is capable of imaging individual atoms within a specimen. The STM can be used within a vacuum or within various liquid or gas states including air and water. The invention of the STM has led to other advancements in microscopy technology, including:

1.   Photon scanning microscopy (PSTM) – Has an optical tip to tunnel photons.

2.   Scanning tunnelling potentiometric (STP) - Measures electric potential across a surface.

3.   Spin polarised scanning tunnelling microscopy (SPSTM) - Uses a ferromagnetic tip to tunnel spin-polarised electrons into a magnetic sample.

4.   Atomic force microscopy (AFM) - Measures the force caused by interaction between the tip and sample.