About Scanning Electron Microscopy (SEM)

Not far from the birth of TEM, SEM was first developed in 1938 by Manfred von Ardenne (Germany scientists)

. The basic concept of SEM was actually delivered by Max Knoll (inventor TEM) in 1935. SEM worked depending on the principle of electron beam scans on the sample surface, and then the information that was obtained was subsequently changed to the images.

The way to form the image formation on the SEM was different from what happened on the optical microscope and TEM. In SEM, the image was made based on the detection of new electrons (secondary electrons) or the reflected electrons emerging from the sample surface when the sample surface was scanned by an electron beam.

After the secondary electrons or reflected electrons were detected further, the signal was strengthened and then the amplitude was displayed in the dark-light shades on the CRT (cathode ray tube) monitor screen. In the CRT screen, a picture of object structure that had been enlarged could be seen. In the process of operation, the SEM did not require the sample that was thinned, so that it could be used to view objects from the perspective of three dimensions.

Thus, the SEM had high and familiar resolution to observe nano-meter sized objects. Nevertheless, high resolution was obtained for scanning in the horizontal direction, while the vertical scan had low resolution. This was the weakness of SEM that had no solution.

However, since around the 1970s, a new microscope has been developed. This new microscope had a high resolution both horizontally and vertically, which was known as "scanning probe microscopy (SPM)." SPM had a working principle that was different from SEM and TEM. It was a new generation of this type of scanning microscope.

Microscopes that are now known to have this type are scanning tunneling microscope (STM), atomic force microscope (AFM) and scanning near-field optical microscope (SNOM). This type of microscope is widely used in nanotechnology research.

About Scanning Electron Microscopy (SEM)

By: Stewart Johnston

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