The Power and Progress of Electron Microscopy

Electron microscope is a powerful tool that enables the study of particles in nanometer range.

The invention of compound microscope in 1590 started to way to a new era of microscopy. The primitive microscope could magnify the object 20 to 30 times its original size. With more development in the field of optical microscopy by the beginning of the 20th century optical microscopes became more powerful and are capable of magnifying objects to 1000x their original size.

In spite of this tremendous improvement as compared to the original microscope further improvement is restricted by the diffraction barrier. According to Rayleigh's criterion the maximum resolution that can be achieved by an optical microscope is 0.2µm. For objects where resolution higher than that

The electron microscope is mainly divided into two types namely Transmission Electron Microscope (TEM) and Scanning Electron Microscope (SEM). The SEM uses reflectred electrons and yields information on surface of the specimen while in TEM electron passes through the sample and gives information on the internal parts.

In SEM an electron beam is focused into a small probe and is rastered across the surface of a specimen. Several emissions occur as a result of the interaction between the sample and electrons produce various signals like secondary electrons, back-scattered electrons (BSE), characteristic X-rays, light (cathodo-luminescence), specimen current and transmitted electrons. These yield information about the sample composition, and topography.

The main advantage of SEM is that it can be used for almost all kinds of samples, conducting and non-conducting. Since the results are based on surface interaction electron transparency of sample is not needed. SEM has a limitation of low resolution and requirement that the sample surface is stain coated with metals for electron