Question 1: Draw a schematic diagram below of the major parts of the SEM: filament, Wehnelt, anode, condenser lens, condenser aperture, objective lens objective aperture, and scanning coils. Explain briefly the function of each part.
Question 2: The SEM we used for demonstrations was equipped with an airlock to introduce the sample. Explain its function and the advantage that it provides.
Question 3: What is the purpose of the “saturation” procedure for the filament, and how is it accomplished? Why is it important not to oversaturate the filament?
Question 4: A small meter on the front of the SEM console measures the emission current of the gun. During our demonstration, that current remained around 50-70 µA (1 µA = 10-6 A). The beam current was less than 1 nA (10-9 A). What happened to the rest of the emission current?
Question 5: The first object that we attempted to image in the SEM was a hemispherical plastic LED. Explain why the image was unsatisfactory. What did we do to the object to improve viewing conditions in the SEM?
Question 6: Does the difference between beam current and sample current represent backscatter current? Why or why not?
Question 7: Calculate the wavelength of a 30 kV electron. Neglecting the relativistic correction, calculate its velocity. How does the latter compare in terms of percentage with the speed of light (c = 3 . 108 m/sec)? (e = electronic charge = 1.6.10-19 coul, me = electron mass = 9.1 . 0-31 kg)
Question 8: If a beam in the SEM is scanned over a width of 40 µm (1 µm = 10-6 m) and the corresponding width of the trace on the display CRT is 10 cm, what is the magnification?
Question 9: Recall that for a wave (photon): E (energy) = h<. If I want my beam electrons to adequately excite the KΕ x-ray line of selenium which has a wavelength 8 of 0.9922 Δ (1Δ = 10-10 m), what is the minimum accelerating voltage I should use? (< = c/8, h = 6.6.10-34 J.sec, e = electronic charge = 1.6.10-19 coul)
Question 10: With a sample in focus in an optical microscope using transmitted light with a 10X objective, explain how the condenser height and field aperture should be adjusted to achieve Kohler illumination.