Scanning Electron Microscopy

Abstract

Abstract The scanning electron microscope (SEM) is one of the most widely used instruments in materials research laboratories and is common in various forms in fabrication plants. Scanning electron microscopy is central to microstructural analysis and therefore important to any investigation relating to the processing, properties, and behavior of materials that involves their microstructure. The SEM provides information relating to topographical features, morphology, phase distribution, compositional differences, crystal structure, crystal orientation, and the presence and location of electrical defects. The SEM is also capable of determining elemental composition of micro‐volumes with the addition of an x‐ray or electron spectrometer and phase identification through analysis of electron diffraction patterns. The strength of the SEM lies in its inherent versatility due to the multiple signals generated, simple image formation process, wide magnification range, and excellent depth of field. Lenses in the SEM are not a part of the image formation system but are used to demagnify and focus the electron beam onto the sample surface. This gives rise to two of the major benefits of the SEM: range of magnification and depth of field in the image. Depth of field is that property of SEM images where surfaces at different distances from the lens appear in focus, giving the image three‐dimensional information. The SEM has more than 300 times the depth of field of the light microscope. Another important advantage of the SEM over the optical microscope is its high resolution. Resolution of 1 nm is now achievable from an SEM with a field emission (FE) electron gun. Magnification is a function of the scanning system rather than the lenses, and therefore a surface in focus can be imaged at a wide range of magnifications from 3× up to 150,000×. The higher magnifications of the SEM are rivaled only by the transmission electron microscope (TEM), which requires the electrons to penetrate through the entire thickness of the sample. As a consequence, TEM sample preparation of bulk materials is tedious and time consuming, compared to the ease of SEM sample preparation, and may damage the microstructure. The information content of the SEM and TEM images is different, with the TEM image showing the internal structure of the material. Due to these unique features, SEM images frequently appear not only in the scientific literature but also in the daily newspapers and popular magazines. The SEM is relatively easy to operate and affordable and allows for multiple operation modes, corresponding to the collection of different signals. This article reviews the SEM instrumentation and principles, its capabilities and applications, and recent trends and developments.