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kc Group Title

Describe the details you were able to see when viewing specimens with the scanning electron microscope in the microscope activity. Scanning electron microscopes (SEM) are useful for studying the details of a specimen’s surface. The electron beam scans the specimen’s surface, which is coated with a thin layer of gold metal. The electrons that scatter off of the gold-coated surface are focused onto a screen, forming a detailed image of the specimen surface. The image is three-dimensional and black and white.

  • 2 years ago
  • 2 years ago

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  1. EbnorEqvine Group Title
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    Why not ask this in the biology section?

    • 2 years ago
  2. cshalvey Group Title
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    Hi @kc - it looks like you were supposed to do a lab in order to answer this question? I don't think we can help you if you haven't done the lab... Also, as @EbnorEqvine mentioned, this *should* have been asked in the Biology section.

    • 2 years ago
  3. tanwar Group Title
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    A scanning electron microscope (SEM) is a type of electron microscope that images a sample by scanning it with a beam of electrons in a raster scan pattern. The electrons interact with the atoms that make up the sample producing signals that contain information about the sample's surfacetopography, composition, and other properties such as electrical conductivity. The types of signals produced by a SEM include secondary electrons, back-scattered electrons (BSE), characteristic X-rays, light (cathodoluminescence), specimen current and transmitted electrons. Secondary electron detectors are common in all SEMs, but it is rare that a single machine would have detectors for all possible signals. The signals result from interactions of the electron beam with atoms at or near the surface of the sample. In the most common or standard detection mode, secondary electron imaging or SEI, the SEM can produce very high-resolution images of a sample surface, revealing details less than 1nm in size. Due to the very narrow electron beam, SEM micrographs have a large depth of field yielding a characteristic three-dimensional appearance useful for understanding the surface structure of a sample. This is exemplified by the micrograph of pollen shown above. A wide range of magnifications is possible, from about 10 times (about equivalent to that of a powerful hand-lens) to more than 500,000 times, about 250 times the magnification limit of the best light microscopes. Back-scattered electrons (BSE) are beam electrons that are reflected from the sample by elastic scattering. BSE are often used in analytical SEM along with the spectra made from the characteristic X-rays, because the intensity of the BSE signal is strongly related to the atomic number (Z) of the specimen. BSE images can provide information about the distribution of different elements in the sample. For the same reason, BSE imaging can image colloidal gold immuno-labels of 5 or 10 nm diameter, which would otherwise be difficult or impossible to detect in secondary electron images in biological specimens. Characteristic X-rays are emitted when the electron beam removes an inner shell electron from the sample, causing a higher-energy electron to fill the shell and release energy. These characteristic X-rays are used to identify the composition and measure the abundance of elements in the sample.

    • 2 years ago
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