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Help! Lab practical!

  1. May 1, 2006 #1
    Hi, I have a lab practical this Thursday evening, and I'm hoping maybe one of you guys can help me find the answers to these practice questions. These are some compiled questions from past labs that I need help with: (takes a big breath)

    I) What are the factors that need to be taken into account when deciding
    magnification to use for examining a sample via optical microscopy?

    II) There are several parameters on the SEM that may be adjusted to improve the depth of field, if depth of field becomes a problem when viewing a sample. What are these parameters and which one would be the best one to alter? and Why?

    III) Under what circumstances might it be useful to perform a magnification calibration on
    the SEM?

    IV) Polishing a bulk sample for optical microscopy and SEM requires many steps. Which of
    the following may not be a step in this process:
    a) Grinding
    b) Polishing
    c) Electro-polishing
    d) Jet-polishing

    V) What is the major use of Electro-polishing and what is (are) the major limitation in its use?

    VI) What are the techniques that can be used for Phase analysis?

    VII) How is the aperture angle different between SEM and TEM. and What exactly does the aperture angle do?

    VIII) What is numerical aperture and what does it tell us about the performance of the

    IX) What are:Depth of field and depth of focus.
    Why can operating an SEM to produce a large depth of field be in conflict with achieving high resolution?

    X) Define actual brightness at the first cross over and maximum possible brightness. Show how these two brightness relationships combine to provide the maximum Gaussian probe diameter, dg, in relation to cathode parameters.

    XI) Low voltage operation of an SEM reduces resolution due to three aberration effects. What are the three aberrations and what is the relationship of accelerating voltage to maximum beam diameter? Explain why there is an optimum divergence angle for maximum resolution.

    XII) Compare resolution for light microscopes and electron microscopes at 20,000 volts based on diffraction aberration.

    XIII) In analyzing an EDS pattern that is composed of a single element with Kα peak, near
    6.0 KeV
    a) What is the effect of the K absorption edge on the pattern.
    b) Where would you find the Si escape peak and what would be the relative
    intensity compared to the Kα peak.
    c) At what approximate energy would you find the Kβ peak and what would be its
    relative intensity?
    d) How does the SEM accelerating voltage affect the intensity of the Kα peak?

    Thanks to whoever at least takes their time to read this! :smile:
  2. jcsd
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