Most TEMs will also include an X-ray detector that can be inserted between the objective lens pole-pieces (near the sample) to analyze composition. Modern TEMs are equipped with electronic detectors (such as charge coupled device, or CCD, detectors), in addition to a retractable fluorescent viewing screen, to capture TEM images in a digital format. The main user-controlled settings include the sample stage position, magnification, objective lens current, beam current (spot size), and the choice of which apertures and detectors to use when acquiring data. Due to the complexity of the instrumentation, most of the components are automatically computer controlled with only a few key parameters controlled by the microscopist. A vacuum system is used to maintain the required vacuum levels throughout the column. The microscope column consists of a series of electromagnetic lenses and apertures to focus the electron beam onto the sample and magnify the TEM image onto the viewing screen (or detectors). Typical accelerating voltages range from 80 kV up to 300 kV. The most powerful modern day TEMs are equipped with modifications and additional detectors that not only push the performance and stability of the microscope but offer the added capability to collect chemical and electronic information at sub-nanometer length scales from a wide range of materials.Īt the top of the column is the electron gun which couples to a high voltage source used to set the kinetic energy of the electron beam. Since the first demonstration of electron optics in the early 1930s, nearly a century of research and development has culminated, establishing TEM as an indispensable technique for both materials and life science applications. Other variations of TEMs include the AC-S/TEM (where AC stands for “aberration corrected”) and the E-S/TEM (where E stands for “environmental”). The two major types of TEM instruments are the conventional TEM (also referred to simply as TEM) and the STEM (scanning transmission electron microscope). A series of electromagnetic lenses and apertures are placed throughout the microscope’s column to focus the beam on the sample, minimize distortions, and magnify the resulting image onto a phosphor screen or a specialized camera.Ī TEM comes in many different forms, but all share the same fundamental principles and components. TEM is used to support human pathology and to address key biological, physical and chemical scientific questions.To form a TEM image, a high energy electron beam is accelerated through an extremely thin “electron transparent” sample, typically thinner than 100 nm. In each case, electron dense heavy-metal stains provide contrast.Īlthough well established in biological research, specimen preparation often introduces processing artefacts (perturbations to structure), so when possible cryo electron microscopy techniques are preferable. This can involve negative staining of viruses and proteins, chemical fixation, dehydration, embedding and cutting (~70nm) thin sections of tissue. This allows the molecular machinery of cells from atomic details to the cellular context and beyond to be studied and understood. This complements light microscopy where fluorescent tags display proteins confined to compartments in living cells, but give no glimpse of the underlying ultrastructure.Įlectron microscopes operate at vacuum so biological samples must be prepared in a specific way. Transmitting a beam of electrons through a specimen captures very fine details thousands of times smaller than those seen in a light microscope. TEMs can show all the structures of a tissue and compartmentalisation of mutually exclusive regions of cells by membrane-enclosed organelles. Transmission electron microscopes (TEMs) are powerful analytical tools for investigating very small structures.
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