A beam of electrons is sent through an ultrathin sample by an electron source. As electrons penetrate through the sample, they also pass through the lenses below.
Data is utilized to generate images displayed directly on a fluorescent screen or a computer screen using a charge-coupled device CCD camera. TEM users can magnify their samples more than 50 million times, while SEM users can only magnify up to 1—2 million times. This feature means that TEM users can only process a tiny portion of their sample.
The two systems also differ in the way they create and process images. Samples are placed at the bottom of the electron column in SEMs, as electron detectors collect back-scattered and secondary scattered electrons. Photomultipliers are used to transform this signal into a voltage signal and then amplified to produce the image on a computer screen. Transmitted electrons pass through the sample and a series of intermediate and projector lenses below it. The resulting image is displayed on a fluorescent screen or a PC screen via a charged-coupled device CCD camera.
Given that they have operational differences, these high-resolution microscopes also have similarities, starting with their components. Compared to TEMs, SEMs cost less to procure, take less time to generate an image, require less time for specimen preparation, accept thicker samples that are much larger. Compared to SEMs, TEMs generate higher-resolution images, provide atomic and crystallographic data, produce 2D images that are easier to interpret than 3D SEM images, and allow users to examine additional characteristics of a given sample.
How many users will utilize the system? Did they undergo sufficient training? TEM imaging is based on a beam of electrons passing through and interacting with an ultra-thin specimen; the transmitted electrons are then recorded with a camera further down the electron column.
Since the sample must be very thin to allow electron transmission, the number of materials specimens that can be viably imaged is limited adding a difficult and expensive sample preparation step to the imaging workflow. SEM Imaging Basics. SEM imaging is very popular with scientists in the materials and life science research areas as its resolution and depth of field capabilities are a significant improvement on those of traditional optical microscopy.
SEM imaging uses deflector coils which alter the path of the electron beam so it scans a sample in a raster pattern. Typically, three detectors are positioned at angles in the sample chamber, these are an X-ray detector, a back-scattered electron detector, and a secondary electron detector.
In particular, biomedical and pharmaceutical research may benefit from the molecular and cellular details that can be revealed by cryo-EM. In general, if you need to look at a relatively large area and only need surface details, SEM is ideal. If you need internal details of small samples at near-atomic resolution, TEM will be necessary.
To learn more about the foundations of EM, please read our Introduction to Electron Microscopy guide. Subscribe now to receive new Accelerating Microscopy posts straight to your inbox. To learn more about electron microscopy, fill out this form to speak with an expert. Only after reading this article I understand it! Thank you for this information. There are a range of benefits associated with using SEM. However, depending on the information required or the type of sample, there are some disadvantages to this method of imaging as well.
Before deciding on SEM, the sample type and information required should be the top consideration. The power of SEM cannot be underestimated. The process by which the focused beam of electrons creates a magnified image is so advanced that the magnification is anywhere between 10 and 1,, times.
As such, it is a key tool for basic research, as well as quality control and failure analysis. SEM allows for the examination of samples such as metals, alloys and ceramics, as well as polymers and biological materials. In short, if the aim of sample imaging is to examine a relatively large area for surface details and composition, SEM is ideal.
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