Why should an electron microscope sample be prepared?

Without Sample preparation step With Sample preparation step

Scanning Electron Microscope (SEM) is a powerful tool for information on the structure and other nanoscale characteristics of a specimen. This microscope provides nanoscale images which can be used to study various samples, including ceramics, metals, alloys, semiconductors, biological samples, etc. For some specimens, a sample preparation step is required before imaging. This step involves deposition of a 10 nm layer of conductive material such as gold, silver, platinum, or chromium on the sample. High-energy electrons, which collide with the sample during the microscopic process, transfer part of their energy and thus heat up the sample. If the specimen is sensitive to electron beams, such as biological samples, the collision of these beams will damage all or part of the sample structure. In these cases, the coating created in the sample preparation stage plays the role of a protective layer. The other classes of samples that need to be prepared before the microscopic process are non-conducting materials. The non-conducting structures of these specimens cause the electrons to be trapped at the surface of the material and, as a result, temporarily charge the surface. This phenomenon causes the charged areas to appear in white in the image taken by the electron microscope. The conducting layer on the sample deposited prior to the microscopic process, eliminates the charges generated on the surface of the sample.

SEM coater

Sputter coater

Carbon coater