Help with Lab Practical Questions | Solutions & Explanations

In summary: Gaussian probe diameter, which is related to the cathode parameters. XI) The three aberrations that reduce resolution in low voltage operation of an SEM are spherical, chromatic, and astigmatic. The accelerating voltage determines the maximum beam diameter, and there is an optimum divergence angle for maximum resolution because increasing the angle too much will cause the probe to spread too thin. XII) At 20,000 volts, electron microscopes have a much higher resolution than light microscopes due to the diffraction aberration, which is lower for electrons than for light. XIII) The K absorption edge on an EDS pattern will cause a decrease in the intensity of the Kα peak. The Si escape peak can be found at a lower energy
  • #1
djfoolio35
1
0
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! :smile:
 
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  • #2
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
 
  • #3


Hi there,

I am happy to help you with these practice questions for your lab practical. I understand that you have a lot of questions and I will do my best to provide solutions and explanations for each one.

I) When deciding on the magnification to use for examining a sample via optical microscopy, the following factors should be taken into account: the size of the sample, the level of detail needed, the resolution of the microscope, and the type of objective lens being used.

II) The parameters that can be adjusted on the SEM to improve the depth of field are the working distance, the aperture, and the condenser lens. The best parameter to alter would be the working distance because it controls the distance between the sample and the objective lens, thus affecting the depth of field.

III) It might be useful to perform a magnification calibration on the SEM when you need to accurately measure the size or dimensions of the sample being viewed.

IV) The step that may not be a part of the polishing process for optical microscopy and SEM is d) Jet-polishing.

V) The major use of electro-polishing is to remove surface imperfections and enhance the surface finish of a sample. The major limitations are that it can only be used on conductive materials and it may introduce artifacts on the sample surface.

VI) The techniques that can be used for phase analysis include X-ray diffraction, electron diffraction, and Raman spectroscopy.

VII) The aperture angle is different between SEM and TEM. In SEM, the aperture angle controls the convergence of the electron beam, while in TEM, it controls the divergence of the electron beam.

VIII) Numerical aperture is a measure of the light-gathering ability of a microscope objective. It tells us about the resolution and light-gathering power of the microscope.

IX) Depth of field refers to the range of distances from the objective lens where the sample remains in focus. Depth of focus refers to the range of distances from the objective lens where the image remains in focus. Operating an SEM to produce a large depth of field can be in conflict with achieving high resolution because a large depth of field requires a larger aperture, which decreases the resolution.

X) Actual brightness at the first crossover refers to the brightness of the electron beam at the first crossover point. Maximum possible brightness refers to the theoretical maximum brightness that can be achieved by the electron beam. These two relationships combine to provide the maximum Gaussian probe diameter, dg, in relation to cathode
 

1. How can I prepare for a lab practical exam?

To prepare for a lab practical exam, it is important to review all of the material covered in your lab class. This includes lecture notes, lab manuals, and any other study materials provided by your instructor. It may also be helpful to practice any lab techniques or procedures that you will be tested on.

2. What should I expect on a lab practical exam?

A lab practical exam typically consists of a series of questions or tasks that assess your knowledge and understanding of lab techniques and concepts. This may include identifying equipment, performing calculations, or completing lab procedures. Your instructor will provide specific instructions and expectations for the exam.

3. Can I use notes or a textbook during a lab practical exam?

This will depend on your instructor's policies. Some may allow the use of notes or textbooks, while others may require you to complete the exam without any outside resources. It is important to clarify with your instructor beforehand to avoid any potential issues.

4. How can I improve my performance on a lab practical exam?

To improve your performance on a lab practical exam, it is important to actively participate in lab classes and ask questions when you are unsure of something. Additionally, practicing lab techniques and procedures outside of class can also help improve your understanding and confidence in performing them during the exam.

5. How are lab practical exams graded?

Grading for lab practical exams will vary depending on the instructor and the specific exam. Some may be graded solely on the accuracy of your answers, while others may also take into account the cleanliness and efficiency of your lab work. Be sure to review your instructor's grading criteria beforehand to know what to expect.

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