What is Scanning Electron Microscopy and How Does it Work?

The origins of the electron microscope (EM) can be traced back to the early years of the 20th century, when scientists were first able to use electrons to magnify objects beyond the limits of the light microscope. In particular, the development of the scanning electron microscope (SEM) in the 1950s brought with it a new wave of analytical potential and paved the way for a whole new era of research.

Overview of SEM

The SEM is a type of electron microscope that produces detailed images of the surface of solid objects, providing high-resolution information at magnifications ranging from about 10x to 200,000x. This is achieved by firing a beam of high-energy electrons onto the surface of a sample, which in turn induces the emission of secondary electrons, backscattered electrons, and other signals that can be detected and analyzed by the microscope's detectors. The resulting data can then be used to construct a three-dimensional image of the sample's surface, revealing the topography, morphology, and other structural features in unprecedented detail.

How SEM works

Unlike traditional optical microscopes, which typically use visible or UV light to produce magnified images, SEMs use electrons. The electron beam is generated by a heated filament, which emits a stream of electrons when heated to high temperatures. The beam is then focused and accelerated by a series of lenses and electromagnetic fields, allowing it to be precisely directed onto the sample surface. As the beam interacts with the sample, a range of signals are generated, including secondary electrons (SEs) and backscattered electrons (BSEs), which are collected by various detectors to create an image.

SEM applications and limitations

The SEM is widely used in materials science, biology, and a variety of other fields for imaging and analysis of samples. It can provide detailed information on the morphology, topography, composition, and three-dimensional structure of materials at high resolution. Some of its key applications include investigating the morphology and structure of cells and tissues, characterizing the composition and behavior of various materials, conducting failure analysis, and studying defects, cracking, and microstructures in materials. However, there are some limitations to SEM imaging techniques, including poor resolution at low magnifications, limitations in sample size and preparation, and the presence of charging effects, particularly in non-conductive materials.

In summary, SEM is an invaluable tool for scientists and researchers interested in exploring the structure and properties of materials at high resolution. By using a beam of high-energy electrons to probe the surface of a sample, SEM can provide detailed information that is difficult (or impossible) to obtain using traditional optical microscopy techniques. With continuing advances in technology, SEM is sure to remain a powerful imaging and analytical tool for decades to come.