Top 10 Scanning Electron Microscope Brand & Manufacturers

What is a Scanning Electron Microscope

A scanning electron microscope (SEM) is a powerful microscope that uses a focused beam of electrons to scan the surface of a specimen. It provides detailed, high - resolution images of the specimen's surface topography and composition. The electrons interact with the atoms on the sample's surface, producing various signals such as secondary electrons, back - scattered electrons, and characteristic X - rays. These signals are detected and used to create an image that reveals the surface features of the sample at a much higher magnification than optical microscopes.

History of Scanning Electron Microscope

The development of the SEM dates back to the 1930s. The first concepts of electron microscopy were being explored, and early electron microscopes were based on transmission electron microscopy (TEM), which focused on looking through thin samples. The idea of scanning the sample with an electron beam to study its surface emerged later. In the 1940s and 1950s, significant progress was made in the development of SEM technology. The first commercial SEMs became available in the 1960s. Since then, continuous improvements in electron - optical systems, detectors, and vacuum technology have led to the highly sophisticated SEMs we have today, with ever - increasing resolution and analytical capabilities.

Purpose of Scanning Electron Microscope

• Materials Science: SEMs are used to study the microstructure of materials. For example, in metallurgy, it can analyze the grain structure of metals, the distribution of alloying elements, and the presence of defects such as cracks and inclusions. In ceramics and polymers, it can investigate the surface morphology and phase distribution.
• Biology: In biological research, SEMs are used to study the surface of cells, tissues, and microorganisms. It can provide detailed images of cell membranes, organelles, and the external structures of bacteria and viruses. For example, it can help in understanding the attachment mechanisms of bacteria to surfaces or the structure of biological membranes.
• Semiconductor Industry: SEMs play a crucial role in the semiconductor manufacturing process. They are used to inspect the quality of wafers, the patterns of integrated circuits, and the presence of any contaminants or defects. This is essential for ensuring the performance and reliability of semiconductor devices.
• Forensic Science: In forensic investigations, SEMs can be used to analyze trace evidence such as fibers, gunshot residue, and paint chips. The high - resolution images can help in identifying the source of the evidence and providing valuable information for criminal investigations.

Principle of Scanning Electron Microscope

Electron Beam Generation and Scanning: The SEM uses an electron gun to generate a beam of electrons. The electrons are accelerated to high energies and then focused into a fine beam using electromagnetic lenses. This beam is then scanned across the sample's surface in a raster pattern (similar to the way a TV screen is scanned).
Signal Generation: When the electron beam strikes the sample, several types of signals are produced. Secondary electrons are emitted from the sample's surface due to the interaction with the primary electron beam. These secondary electrons are low - energy electrons and provide information about the sample's topography. Back - scattered electrons are electrons that are scattered back from the sample's atoms and are related to the atomic number of the elements in the sample. Characteristic X - rays are also emitted, which can be used to identify the elements present in the sample.
Signal Detection and Image Formation: The detectors in the SEM collect these signals. For example, a secondary - electron detector is used to capture the secondary - electron signal. The intensity of the detected signal at each point of the scanned area is then used to create a pixel in an image. The more electrons detected at a particular point, the brighter the pixel in the resulting image.

Features of Scanning Electron Microscope

• High - Resolution Imaging: SEMs can achieve resolutions on the order of a few nanometers. This allows for the visualization of very fine details on the sample's surface, such as the nanostructure of materials or the sub - cellular features in biology.
• Large Depth of Field: Compared to optical microscopes, SEMs have a large depth of field. This means that a greater portion of the sample's surface can be in focus at the same time, providing a three - dimensional - like appearance to the images. It's useful for studying rough or uneven surfaces.
• Elemental Analysis Capability: Through the detection of characteristic X - rays, SEMs can provide information about the elemental composition of the sample. This is a valuable analytical feature, allowing for the identification and mapping of different elements within the sample.[!--empirenews.page--]
• Variable Magnification: SEMs offer a wide range of magnification, from a few tens of times up to several hundred thousand times. This flexibility allows users to observe samples at different scales, from the overall morphology to the finest details.

Types of Scanning Electron Microscope

• Conventional SEM: This is the most common type, which provides high - resolution imaging and basic analytical capabilities such as secondary - electron and back - scattered - electron imaging and elemental analysis through X - ray detection.
• Variable - Pressure SEM (VP - SEM): Also known as environmental SEM, it allows for the examination of samples in a non - ideal vacuum or in the presence of a gas. This is useful for studying samples that are sensitive to vacuum conditions, such as biological samples that contain water or volatile components.
• Field - Emission SEM (FE - SEM): FE - SEMs use a different type of electron - gun technology that provides a more highly focused electron beam. They offer higher resolution and better signal - to - noise ratio compared to conventional SEMs and are often used for high - precision applications such as nanotechnology and advanced materials research.

Precautions for using Scanning Electron Microscope

• Sample Preparation: Samples need to be properly prepared to withstand the high - vacuum environment of the SEM and to provide good conductivity. Non - conductive samples may need to be coated with a thin layer of a conductive material such as gold or carbon to prevent charging artifacts in the image. The sample should also be stable and firmly attached to the sample holder.
• Vacuum System: The SEM operates under a high - vacuum condition. The vacuum system should be properly maintained and monitored. Any leaks in the vacuum system can affect the performance of the microscope and the quality of the images. Before using the SEM, it's essential to ensure that the vacuum is at the appropriate level.
• Electron Beam Damage: The high - energy electron beam can cause damage to the sample, especially for sensitive materials such as biological samples or some polymers. The user should be aware of the beam - current settings and the dwell time of the beam on the sample to minimize damage. In some cases, it may be necessary to use lower beam energies or shorter scan times.
• Detector Calibration: The detectors in the SEM need to be calibrated regularly to ensure accurate signal detection and image formation. Follow the manufacturer's instructions for detector calibration to obtain reliable and reproducible results.

Things to consider when purchasing Scanning Electron Microscope

• Resolution Requirements: Consider the level of resolution you need for your applications. If you're working in nanotechnology or studying very fine - scale structures, a high - resolution FE - SEM may be necessary. For more general - purpose materials or biological imaging, a conventional SEM with a suitable resolution might be sufficient.
• Analytical Capabilities: Determine the importance of elemental analysis and other analytical features. If you need to identify and map elements in your samples, look for an SEM with advanced X - ray detection and analysis capabilities. Some SEMs also offer additional analytical techniques such as electron - backscatter diffraction (EBSD) for crystallographic analysis.
• Sample Types and Vacuum Requirements: Think about the types of samples you'll be working with. If you deal with samples that are difficult to prepare for a high - vacuum environment or are sensitive to vacuum, a VP - SEM might be a better choice. Consider the sample - handling and preparation requirements of the SEM to ensure compatibility with your research or analysis.
• Cost and Budget: SEMs vary widely in price, depending on their type, resolution, and analytical capabilities. Set a budget and look for an SEM that offers the best combination of features and performance within your budget. Consider not only the initial purchase cost but also the cost of maintenance, consumables (such as sample - coating materials), and any necessary training for operators.

Terms of Scanning Electron Microscope

• Secondary Electrons: Electrons emitted from the sample's surface due to the interaction with the primary electron beam. They are used to form images that show the topography of the sample.
• Back - scattered Electrons: These are electrons that are scattered back from the sample's atoms and provide information related to the atomic number of the elements in the sample. They can be used to create images that show contrast based on the composition of the sample.
• Characteristic X - rays:[!--empirenews.page--] X - rays emitted from the sample when the electron beam interacts with the atoms. The energy of these X - rays is characteristic of the elements present in the sample and is used for elemental analysis.
• Electron Gun: The component of the SEM that generates the electron beam. Different types of electron guns, such as thermionic and field - emission guns, have different characteristics in terms of beam quality and intensity.