![]() ![]() These pumps are used for pumping down the column. Examples include turbo pumps or diffusion pumps. One or more types of high vacuum pumps that require “backing” by a rough pump to reach ultra-high vacuum levels (i.e., 10 -5 to 10 -10 mbar).Roughing pumps are also used to “back” certain high vacuum pumps, providing an additional layer of pumping. The roughing pump is often used multiple times during a session to pump out the specimen load lock chamber before it enters the ultra-high vacuum environment of the column. These pumps are very loud because they are mechanically pumping relatively large volumes of air. Roughing pumps pump down from atmospheric pressure down to a “low” vacuum level (around 0.01 mbar).Typical TEMs will employ three types of vacuum pumps: To eliminate electron beam interactions with anything but the specimen, a high vacuum system is connected to the column. Optional electron energy-loss spectrometers located at the end of column are used for electron energy-loss spectroscopy (EELS). 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. To form a TEM image, a high energy electron beam is accelerated through an extremely thin “electron transparent” sample, typically thinner than 100 nm. ![]()
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