Transmission Electron Microscope Electrons are produced with an electron gun, similar to the one in a television. The electrons are then accelerated through the Anode plate and focused with the Magnetic Lens. Both crystallographic information and surface topographic information can be viewed. Specimens must be very thin, on the order of 0.1 micrometers. Electron Gun Anode Controller Monitor Viewer Parallel Detector (SEM) S Specimen Stage Diffraction Information Image Information Computer Control
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This assignment has two parts: A and B. Please be sure you answer both questions. A) Transmission Electron Microscopy Samples prepared for transmission electron microscopy are embedded in an epoxy resin and sliced into ultrathin (100 nm) sections. The sections are usually stained with a heavy metal such as lead to enhance contrast. The sections are then examined with a transmission electron microscope. The photographs of these thin sections are put in order according to their position in the living cell and used to determine the shape of the original sample. B) Microscopes The following picture shows images taken on a bright field microscope, phase-contrast biological microscope, and dark field biological microscope. Which one is which? A) B)
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A scanning electron microscope is used to look at cell structure with $10-\mathrm{nm}$ resolution. A beam of electrons from a hot filament is accelerated with a voltage of $12 \mathrm{kV}$ and then focused to a small spot on the specimen. (a) What is the wavelength in nanometers of the beam of incoming electrons? (b) If the size of the focal spot were determined only by diffraction, and if the diameter of the electron lens is $\frac{1}{5}$ the distance from the lens to the specimen, what would be the minimum separation resolvable on the specimen? (In practice, the resolution is limited much more by aberrations in the magnetic lenses and other factors.)
A transmission electron microscope (TEM) operates by focusing electrons to a small spot on the object and then measuring the yield of electrons that pass through the object. Suppose the electrons in a TEM have energies of 5 MeV. a. Find the electron wavelength. b. Do you expect this TEM to have better resolution than the SEM in Problem $34 ?$ Explain why or why not. c. How does your result from part (a) compare with the spacing between atoms in a solid (about $0.3 \mathrm{nm}) ?$ With the size of an atom (about 0.05 $\mathrm{nm}$ )?
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