Help with Lab Practical Questions | Solutions & Explanations

[djfoolio35]

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
microscope.

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!

 

[nbryan5]

I) Factors to consider when deciding magnification for optical microscopy include the size of the sample, the resolution needed, and the working distance required to properly focus the microscope. II) Parameters that may be adjusted to improve the depth of field on an SEM include the working distance, beam current, and aperture size. The best parameter to alter is usually the working distance, as it has the greatest effect on depth of field. III) Magnification calibration should be performed on the SEM when there may be a significant difference between the actual magnification and the indicated magnification. This can be due to changes in the microscope components or wear over time.IV) Electro-polishing is not a step in the process of polishing a bulk sample for optical microscopy and SEM. The steps are grinding, polishing, and jet-polishing. V) The major use of electro-polishing is to prepare samples for electron microscopy by removing surface damage caused by mechanical polishing. The major limitations in its use include the need for conductive samples and the potential for surface contamination. VI) Techniques that can be used for phase analysis include dark field imaging, bright field imaging, differential interference contrast (DIC), and phase contrast. VII) The aperture angle of an SEM is smaller than that of a TEM. The aperture angle determines the angular spread of the electrons emitted from the source, which affects the size and shape of the probe and therefore the resolution of the image. VIII) Numerical aperture is a measure of the light-gathering power of an optical system. It tells us about the performance of the microscope in terms of its resolution, light intensity, and field of view. IX) Depth of field is the distance over which the object is in focus, while depth of focus is the distance over which the image is in focus. Operating an SEM to produce a large depth of field is in conflict with achieving high resolution because the larger depth of field necessitates a larger spot size, which reduces the resolution. X) Actual brightness at the first crossover is the product of the accelerating voltage, beam current, and effective source area. Maximum possible brightness is the product of the accelerating voltage, beam current, and maximum source area. These two brightness relationships combine