Electron microscope
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Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are techniques used to image samples at very high magnifications. SEM works by scanning a sample's surface with a focused beam of electrons, while TEM transmits electrons through an ultra-thin sample. Both techniques use electron detectors and electromagnetic lenses to form images with resolutions better than optical microscopes. Key applications include examining biological structures, materials science, and semiconductor manufacturing.
Electron microscope
- 1. TOPIC- SCANNING ELECTRON MICROSCOPY TRANSMISSION ELECTRON MICROSCOPY
- 2. INTRODUCTION • A scanning electron microscope (SEM) is a type of electron microscope that produces images of a sample by scanning the surface with a focused beam of electrons. • The electrons interact with atoms in the sample, producing various signals that contain information about the sample's surface topography and composition. • The electron beam is scanned in a raster scan pattern, and the beam's position is combined with the detected signal to produce an image. • SEM can achieve resolution better than 1 nanometer.
- 3. Principle The basic principle is that a beam of electrons is generated by a suitable source, typically a tungsten filament or a field emission gun. The electron beam is accelerated through a high voltage (e.g.: 20 kV) and pass through a system of apertures and electromagnetic lenses to produce a thin beam of electrons. Then the beam scans the surface of the specimen. Electrons are emitted from the specimen by the action of the scanning beam and collected by a suitably- positioned detector.
- 4. CONSTRUCTION Scanning Electron Microscope’s basic components are as following… Electron gun Condenser lenses Objective Aperture Specimen Chamber Detectors Computer hardware and software
- 6. ELECTRON GUNS Electron guns are typically one of TWO types. 1) Thermionic guns 2) Field emission guns 1) Thermionic guns: Which are the most common type, apply thermal energy to a filament to coax electrons away from the gun and toward the specimen under examination. Usually made of tungsten, which has a high melting point
- 7. Field emission guns: create a strong electrical field to pull electrons away from the atoms they‘re associated with. Electron guns are located either at the very top or at the very bottom of an SEM and fire a beam of electrons at the object under examination. These electrons don't naturally go where they need to, however, which gets us to the next component of SEMs.
- 8. CONDENSOR LENSES Just like optical microscopes, SEMs use Condenser lenses to produce clear and detailed images. The Condenser lenses in these devices however, work differently. For one thing, they aren't made of glass. Instead, the Condenser lenses are made of magnets capable of bending the path of electrons. By doing so, the Condenser lenses focus and control the electron beam, ensuring that the electrons end up precisely where they need to go.
- 9. SPECIMEN CHAMBER The sample chamber of an SEM is where researchers place the specimen that they are examining. Because the specimen must be kept extremely still for the microscope to produce clear images, the sample chamber must be very sturdy and insulated from vibration. In fact, SEMs are so sensitive to vibrations that they're often installed on the ground floor of a building. The sample chambers of an SEM do more than keep a specimen still. They also manipulate the specimen, placing it at different angles and moving it so that researchers don't have to constantly remount the object to take different images.
- 11. DETECTORS SEM's various types of detectors as the eyes of the microscope. These devices detect the various ways that the electron beam interacts with the sample object.
- 12. VACUUM CHAMBER SEMs require a vacuum to operate. Without a vacuum, the electron beam generated by the electron gun would encounter constant interference from air particles in the atmosphere. Not only would these particles block the path of the electron beam, they would also be knocked out of the air and onto the specimen, which would distort the surface of the specimen.
- 13. APPLICATION SEMs have a variety of applications in a number of scientific and industry-related fields, especially where characterizations of solid materials is beneficial. In addition to topographical, morphological and compositional information, a Scanning Electron Microscope can detect and analyze surface fractures, provide information in microstructures, examine surface contaminations, reveal spatial variations in chemical compositions, provide qualitative chemical analyses and identify crystalline structures. In addition, SEMs have practical industrial and technological applications such as semiconductor inspection, production line of miniscule products and assembly of microchips for computers. SEMs can be as essential research tool in fields such as life science, biology, medical and forensic science, metallurgy.
- 14. ADVANTAGE Advantages of a Scanning Electron Microscope include its wide- array of applications, the detailed and topographical imaging and the versatile information garnered from different detectors. SEMs are also easy to operate with the proper training and advances in computer technology and associated software make operation user-friendly. This instrument works fast, often completing SEI, BSE and EDS analyses in less than five minutes. In addition, the technological advances in modern SEMs allow for the generation of data in digital form. Although all samples must be prepared before placed in the vacuum chamber, most SEM samples require minimal preparation actions.
- 15. DISADVANTAGE The disadvantages of a Scanning Electron Microscope start with the size and cost. SEMs are expensive, large and must be housed in an area free of any possible electric, magnetic or vibration interference. Maintenance involves keeping a steady voltage, currents to electromagnetic coils and circulation of cool water. Special training is required to operate an SEM as well as prepare samples. SEMs are limited to solid, inorganic samples small enough to fit inside the vacuum chamber that can handle moderate vacuum pressure. The sample chamber is designed to prevent any electrical and magnetic interference, which should eliminate the chance of radiation escaping the chamber. Even though the risk is minimal,
- 17. INTRODUCTION • The transmission electron microscope (TEM) was the first type of Electron Microscope to be developed and is patterned exactly on the light transmission microscope except that a focused beam of electrons is used instead of light to "see through" the specimen. It was developed by Max Knoll and Ernst Ruska in Germany in 1931. • TRANSMISSION ELECTRON MICROSCOPY (TEM) Transmission electron microscopy (TEM) is a microscopy technique whereby a beam of electrons is transmitted through an ultra thin specimen, interacting with the specimen as it passes through. • An image is formed from the interaction of the electrons transmitted through the specimen; the image is magnified and focused onto an imaging device, such as a fluorescent screen, on a layer of photographic film, or to be detected by a sensor such as a CCD camera.
- 18. • MICROSCOPE RESOLUTION MAGNIFICATION • OPTICAL- Resolution = 200nm, Magnification=1000x • TEM- Resolution=0.2nm, Magnification=500000x •
- 22. APPLICATION • The technique has mainly been used to examine particulate (purified) specimens - e.g.. ribosomes, enzyme molecules, viruses, bacteriophages, microtubules, actin filaments, etc. at a resolution of 1.5-2.5 nm. • This technique generally allows the shape, size, and the surface structure of the object to be studied as well as provide information about subunit stoichiometries and symmetry in oligomeric complexes. • Any surface of the specimen accessible to water can potentially be stained, and thus, that part of the specimen will be imaged at high contrast.
- 23. REFERENCE • https://cmrf.research.uiowa.edu • “A Textbook of Biophysics” by R. N. Roy, NEW CENTRAL BOOK AGENCY PRIVATE LIMITED, Kolkata, India.
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