Since the scanning electron microscope (SEM) was first commercialized about 40 years ago the SEM has shown remarkable progress. Now many types of SEMs are being used and their performance and functions differ greatly from each other. To utilize these SEMs it is essential to recognize their features, as well as understand the reasons for the contrast of SEM images. Jeol has produced a document aimed at helping SEM users and future SEM users to understand the basics of the SEM, including the instrument principles, specimen preparation and elemental analysis.
The SEM is used for observation of specimen surfaces. When the specimen is irradiated with a fine electron beam (called an electron probe) secondary electrons are emitted from the specimen surface. Topography of the surface can be observed by two-dimensional scanning of the electron probe over the surface and acquisition of an image from the detected secondary electrons.
Construction of SEM
The SEM requires an electron optical system to produce an optical probe, a specimen stage to place the specimen, a secondary electron-detector to collect secondary electrons, an image display unit and an operation system to perform various operations (see Figure 1). The electron optical system consists of an optical gun, a condenser lens and an objective lens to produce an electron probe, a scanning coil to scan the electron probe, and other components. The electron optical system (inside of the microscope column) and a space surrounding the specimen are kept at vacuum.
To improve your knowledge further about the basics of SEM, download the full document, which covers topics such as:-
- Magnification of SEM
- Depth of focus of SEM
- Why images are visible
- Improving image resolution
- Types of electron guns
- Types and capabilities of objective lenses
- Actual resolution of SEM
- Charging and its influence
- Basics of specimen preparation
- Low vacuum SEM
- Basics of Elemental Analysis
- History of SEM