Dell JSM-6060LV manual Background

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Background

The scanning electron microscope (SEM) is one of the most versatile instruments for the examination and analysis of the microstructural characteristics of solids. Although the SEM and optical microscope share the same primary function – making microstructural features and objects visible to the human eye – the scanning electron microscope offers some distinct advantages over the optical microscope. The SEM uses electrons rather than visible light waves (200 – 750 nm wavelength) for imaging, which allows for observation of relatively large sample features at low magnifications or very fine details (high resolution) at high magnifications. The SEM also offers a large depth of field that provides good focus over rough specimen surfaces. The large depth of focus provides a three-dimensional appearance of the specimen in a SEM compared to the nearly planar or two-dimensional imaging found in optical microscopes. In addition, many attachments are available for scanning electron microscopes, including x-ray spectrometers for chemical composition analysis, backscattered electron detectors for atomic number contrast, transmitted electron detectors, hot and cold stages for microscopic observation of high or low temperature phenomena, tensile testing stages for observation of deformation and fracture, and special stages for analysis of semiconductor devices.

Disadvantages of the scanning electron microscope include relatively high initial, operational, and maintenance costs, a high vacuum operating atmosphere that is unsuitable for some specimens, and difficulty in preparing certain types of specimens. Figure 1 schematically illustrates image formation in the optical microscope and the scanning electron microscope.

Figure 1. Basic image formation in an optical microscope and a scanning electron microscope.

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