Scanning electron microscopy

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Reference no: EM131494

1. Prepare a schematic diagram below of the major parts of the SEM: filament, anode, Wehnelt, condenser lens, objective lens objective aperture, condenser aperture, and scanning coils. Illustrate briefly the function of each part.

2. The SEM we used for demonstrations was equipped with an airlock to introduce the sample. Describe its function and the advantage that it provides.

3. What is the basic purpose of the "saturation" procedure for the filament, and how is it accomplished? Why is it important not to oversaturate the filament?

4. A small meter on the front of the SEM console calculates 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?

5. The first object that we attempted to image in the SEM was a hemispherical plastic LED. Describe why the image was unsatisfactory. What did we do to the object to improve viewing conditions in the SEM?

6. Does the difference between sample current and beam current represent backscatter current? Why or why not?

7. Evaluate the wavelength of a 30 kV electron. Neglecting the relativistic correction, determine its velocity. How does the latter compare in terms of percentage with the speed of light (c = 3 x 108 m/sec)? (e = electronic charge = 1.6 x 10-19 coul, me = electron mass = 9.1 x 10-31 kg)

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, Evaluate the magnification?

9. Recall that for a wave (photon): E (energy) = h < . If I want my beam electrons to adequately excite the K3 x-ray line of selenium which has a wavelength 8 of 0.9922 Δ (1 Δ = 10-10m), what is the minimum accelerating voltage I should use? (< = c/8, h = 6.6 x 10-34 J.sec, e = electronic charge = 1.6 x 10-19 coul)

10. With a sample in focus in an optical microscope using transmitted light with a 10X objective, Decribe how the condenser height and field aperture should be adjusted to achieve Köhler illumination.

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