Third year MSci Practical

Introduction to Scanning Electron Microscopy

Dr Paul May, W214

After you have done the practical, fill in the answers to the following questions. You can alter your choices at any time, and the answers will only be processed once you click on the 'Submit Answers' button at the end. I would strongly suggest you look through the book 'Electron Microscopy and Analysis' by Goodhew and Humphreys, before you proceed to answer these questions...

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1) The maximum resolution of modern Scanning Electron Microscope is in the region of:

0.03 nm
0.3 nm
3 nm
30 nm
300 nm

2) Which of the following defines the DEPTH OF FIELD of an electron microscope?

The maximum distance through which the electron beam can penetrate specimen material
The optimum distance between the electron source and the specimen
The thickness of specimen over which the image is observed to be in focus
The optimum distance between the specimen and the viewing screen
The distance over which the final image is in focus

3) Which one of the following defines the DEPTH OF FOCUS of an electron microscope?

4) Secondary Electron imaging in the Scanning Electron Microscope primarily provides information concerning:

The atomic numbers of elements present in the specimen
The electrical conductivity of the specimen
The surface topography of the specimen
The thickness of the specimen
The nature of atomic bonding in the specimen material

5) The magnification of a Scanning Electron Microscope is essentially controlled by:

The distance between the final (objective) aperture and the specimen
The distance between the electron source and the specimen
The distance between the specimen and the detector
The area of specimen surface scanned by the electron beam
The electron beam current

6) What is the main purpose of gold-coating an SEM sample?

To give better contrast
To give better focusing
To give a better depth of field
To prevent the sample charging up

7) The above diagram shows the various modes of clay particle association. (a) dispersed and deflocculated, (b) aggregated but deflocculated, (c) edge-to-face flocculated but dispersed, (d) edge-to-edge flocculated but dispersed, (e) edge-to-face flocculated and aggregated, (f) edge-to-edge flocculated and aggregated, (g) edge-to-face and edge-to-edge flocculated and aggregated. From your SEM observations of the polystyrene/kaolinite dispersion, which of these modes was associated with:

pH	a	b	c	d	e	f	g
Acidic conditions?
Neutral conditions?
Basic conditions?

8) Explain this in terms of intermolecular forces. What does this tell you about the nature of the charge on the polystyrene?:

When you are happy with all your choices, click on the 'Submit' button.