In a scanning electron microscope (SEM), a backscatter electron detector is a specific type of detector that identifies electrons traveling directly back from the sample after being struck by the electron beam.

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A scanning electron microscope (SEM) is an instrument that forms highly detailed images of the surfaces of specimens. It operates by directing a beam of electrons at the specimen, which knocks off electrons from its surface. These emitted electrons are detected and displayed on a monitor, producing images with a distinct three-dimensional appearance. Scanning electron microscopy is utilized to view the external surfaces of both very small samples and larger objects, such as pollen grains. Some electron microscopes can achieve magnifications up to $${}2,000,000	imes$$.

Scanning Electron Microscope (SEM)

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Microbiology covers the scope and sequence requirements for a single-semester microbiology course for non-majors. The book presents the core concepts of microbiology with a focus on applications for careers in allied health. The pedagogical features of the text make the material interesting and accessible while maintaining the career-application focus and scientific rigor inherent in the subject matter. Microbiology’s art program enhances students’ understanding of concepts through clear and effective illustrations, diagrams, and photographs.

Microbiology is produced through a collaborative publishing agreement between OpenStax and the American Society for Microbiology Press. The book aligns with the curriculum guidelines of the American Society for Microbiology.

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To prepare a specimen for scanning electron microscopy (SEM), it must typically be dried and treated with fixatives. Fixatives are used to reduce artifacts, such as the shriveling that can be caused by the drying process. After fixation and drying, the specimen is sputter-coated with a thin layer of metal, such as gold, before observation.

SEM Specimen Preparation

Backscatter Electron Detector

In a scanning electron microscope (SEM), secondary electron detectors are utilized to capture electrons that travel to the sides after the sample is hit by the electron beam.

Secondary Electron Detector

Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) serve different observational purposes in microbiology. TEM requires extremely thin sections of a specimen and is utilized to visualize internal structures, such as organelles and the interior of membranes. In contrast, SEM is used to view the detailed, three-dimensional surfaces of specimens, ranging from very small samples to larger objects like pollen grains.

TEM vs. SEM

When samples are prepared for viewing using a scanning electron microscope (SEM), they must be dehydrated using an ethanol series and be even drier than necessary for a transmission electron microscope (TEM). Critical point drying achieves this by using inert liquid carbon dioxide under pressure to displace the water from the specimen.

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