Scanning microscopes, also called scanning electron microscopes or SEM, is one of the different types of electron microscopes that produces magnified images of a sample with the use of electrons as the main source of illumination. A scanning microscope, as implied by the term, scans the image by causing the electrons to interact with the sample. This produces various signals that are then detected and translated into information about the topography of the sample’s surface.
A Brief History
The first model of a scanning microscope was developed in 1937 by Manfred von Ardenne, who created a microscope with high magnification capabilities by scanning a small raster with an electron beam. Ardenne then applied this principle to eliminate the common chromatic aberration that is experienced when a conventional electron microscope is used. His work was continued by several people, including a group from Cambridge back in the 50s and early 60s. All the effort led to the release of the first commercial scanning microscope called the ‘Stereoscan’, which came out in 2965 and was offered by Cambridge Scientific Instrument Company.
What It Can Do
A scanning microscope can achieve resolutions greater than 1 nanometer and can observe specimens in many conditions, such as high vacuum, low vacuum, and wet conditions. It can also produce various types of signals including secondary electrons (SE), back-scattered electrons (BSE), characteristic x-rays, and cathodoluminescence, among others. However, different machines may be required to produce all these signals.
In layman’s terms, scanning microscopes can magnify objects at more than 300,00 times its size, which is called the magnification power. Compared to other electron microscopes, it also boasts of a tremendous depth of field and is capable of providing a 3D image, which is way better than the flat images offered by traditional microscopes. This is found extremely helpful by researchers especially for analytical purposes.
Scanning microscopes are also known for being able to provide information about the composition of an object, something other microscopes are not capable of doing.
A scanning microscope is made up of several key components, which include:
- Electron gun
- Condenser lens
- Sample chamber
- X-ray detector
- Vacuum chamber
- Electron beam
- Objective lens
- Backscatter detector
- Secondary detector
Disadvantages of Scanning Microscopes
Scanning microscopes also have certain disadvantages. First of all, there’s the cost of acquiring one. Secondly, there’s the skill required in operating one. On top of these, scanning microscopes are also heavy and bulky, but need to be handled with care. Due to these, SEMs are often only used in research and industrial applications, making them less accessible.