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Lab meetings Week of 6 October

Lab meetings Week of 6 October. We will use the FEI Quanta FEG-SEM MEB 1555b Objectives Learn “knobology” of FEI tools Learn new detectors SSBSE. Feedback from lab 3. 4 threads = 1.27 mm What is wrong? “The diameter of the balls is 1.78 μm.” Cite two problems with this statement.

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Lab meetings Week of 6 October

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  1. Lab meetingsWeek of 6 October • We will use the FEI Quanta FEG-SEM • MEB 1555b • Objectives • Learn “knobology” of FEI tools • Learn new detectors • SSBSE

  2. Feedback from lab 3 • 4 threads = 1.27 mm What is wrong? • “The diameter of the balls is 1.78 μm.” • Cite two problems with this statement. • Future grading: • -5% for each use of insignificant digits off by more than one order of magnitude • -25% for missing copy of lab notes • “Affect” is always a verb (to influence); if you use “effect” as a verb, if is probably incorrect. • Depth of field: compare measurements to theory in text. • “Don’t make small changes.” F. Rosenberger

  3. Lab 3 • This class is not an academic exercise: you get to put on your resume that you know how to use an SEM. How will you remember? • Current path: what is function of gold coating? • Report on a systematic variation of parameters. Trend? Optimum?

  4. Charging • What does it mean? • How do you recognize it? • What causes it? • What machine parameters affect it? • How? • Why? • What is the definition of “probe current”?

  5. Electron yield • How do you use this figure to reduce charging? • Where did it appear in your lab writeup? E1 E2

  6. Paper-writing Process • List conclusions • List data to support conclusions • Collect figures to justify conclusions • “Narrative” must lead reader from what is known (intro) to techniques used to generate data to actual data to conclusions • Executive summary must contain conclusions!

  7. Electron Microscopy: Midterm Review • What information can you gain from an electron microscope? Topography Phase variations Chemical composition BSE EDS

  8. What are the advantages of electron microscopy over other characterization techniques? • High magnification • Huge dynamic range • Low magnification • Huge depth of field • Ability to image sub-surface features • How can you image sub-surface features? • Chemical analysis

  9. SEM components • What are the major components of an SEM? • What is the function of each? • Why does it need a vacuum pump?

  10. Mean Free Path in Gases With sufficient accuracy for approximate calculations we may take: λ = 7 x 10-3/p mbar-cm λ = 5 x 10-3/p Torr-cm λ = 5/p μmHg-cm How is this useful in understanding the operation of an SEM?

  11. SEM Midterm Review • What is the definition of magnification? • What are the pitfalls of “magnification”? • What factors limit the sharpness of an image (resolution) in an SEM? • How or why do these factors influence resolution?

  12. SEM Midterm Review • There are four operating modes for an SEM. How would you achieve each and under what circumstances would you use it? • Resolution mode • High current mode • Depth of focus mode • Low voltage mode

  13. SEM Midterm Review • How many types of electron sources are there? • What are the advantages and disadvantages of each? • What factors determine the brightness of an electron source? • What are the functions of the electromagnetic coils in an SEM? • What are the different currents flowing in an SEM?

  14. SEM Midterm Review • What is meant by “astigmatism”? • How does an SEM correct for astigmatism? • What is the effect of working distance on • Resolution • Depth of field • What factors determine depth of field? • What factors determine field of view?

  15. SEM Midterm Review • What parameters determine the Gaussian beam size? • What is the expression for the resolution limitation due to electron diffraction by the final aperture? • What is the expression for the wavelength of an electron as a function of its energy? • How does chromatic aberration affect probe diameter? • What is chromatic aberration?

  16. SEM Midterm Review • What factors determine the extent of spherical aberrations? • How do the various factors combine to determine the final beam size on the sample?

  17. Beam Sample interactions • Define interaction volume • Define sampling volume • Same for SE and BSE? • On what and how does the energy loss of beam electrons depend? dE/ds = (2**e4*N0*Z* *ln(1.166Ei/J))/A*Ei J = (9.76*Z + 58.5*Z-0.19)*10-3 = average energy loss per scattering event

  18. What is the shape of the interaction volume? • Material dependence? • Beam energy dependence? • Where is rate of energy deposition the greatest? • How does the interaction volume depend on tilt? • Define tilt!

  19. What factors determine the range of electrons in solids?What is meant by “the range of electrons in solids”?

  20. RKO = 0.0276 A*E05/3/Z0.89 *ρ • A = Atomic weight • E0 = Beam energy • Z = Atomic number • ρ = Mass density (gm/cm3) • RKO (nm)= Range of electron beam in material • How does the range depend on tilt angle?

  21. How does SE coefficient depend on beam energy? • How does SE coefficient depend on Z? • How does SE coefficient depend on tilt angle? Why?

  22. How does backscatter coefficient depend on Z? • How does backscatter coefficient depend on beam energy? • How does backscatter coefficient depend on tilt? Why? • How is the beam energy distributed between SE and BSE?

  23. Pixels • How do you determine the pixel size on a sample? • How does pixel size relate to: • Probe diameter? • “Sampling area” • Under what conditions can the probe diameter be too small? • What is the ramification of choosing a probe diameter that is too small?

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