SEM Quiz AY2020/21
When conducting quantitative microanalysis several measurements from the same location
should be made. Why do you do this?
A: To check for electron beam induced compositional changes.
In most cases when X-rays pass through matter their intensity will be
A: Reduced
For routine observations which objective lens aperture size is preferred?
A: Medium
What effect will reducing the electron probe size have on a secondary electron image?
A: Improve resolution
Why are only secondary electrons that are near the sample surface involved in producing
the secondary electrons image?
A: Because secondary electrons have very low energies (<50eV) and only those generated
near the sample surface can escape and reach the SE detector
How would you prepare a finely powdered sample for secondary electron imaging?
A: Embed in conducting carbon tape
X-rays that do not produce unique information on the elements that produce them are
called continuum X-rays or braking radiation, or
A: Bremsstrahlung
Which detectors can be used in low vacuum mode?
A: backscattered electron detector and energy dispersive X-ray detector
What coating type is preferred for carry out energy dispersive X-ray analysis on a conducting
specimen?
A: No coating
When a high voltage electron beam strikes a specimen, how is most of the energy dispersed?
A: Heat
what a focussed image the electron beam must be brought to a fine spot positioned at the
surface of the sample. The device directly responsible for this is:
A: the objective lens
What is the most likely effect that reducing the electron probe size has on a backscattered
electron image?
A: Degrade the signal-to-noise ratio
Why are specimens sometimes coated with gold or platinum before microscopy?
A: To improve the yield of secondary electrons and to prevent charging
If your sample is an insulator and a carbon coating is needed the coating film should be:
A: Few tens of nm thick and homogeneous
If EDS X-ray analysis is performed with a correction procedure but no standards, one of the
names often called is:
A: ?
Both scanning and transmission electron microscopes are often fitted with a device to
analyse the elemental composition of samples. What is the abbreviation (acronym) for this
device
A: XRD and XRF (wrong)
For which material type would cold mounting be the preferred method to prepare a
specimen for SEM?
A: For specimens with low melting points
Magnification is a direct process in an SEM. Increased magnification is the result of the
sample area scanned by the beam being:
A: decreased in size
What is the characteristic of a specimen which has been coated with a gold layer that is too
thick?
A: The secondary electron image appears cracked or is covered by nodules
Approximately how long does an atom remain ionized?
A: For a very short time, in the order of 10-14 seconds
The electron transition below will emit a characteristic X-ray. What type of transition is
shown? (M to L)
A: L
Which conditions would be most favourable for the collection of backscattered electron
images from an insulating sample.
A: 15kV primary beam, carbon coated sample
When electrons interact with a solid they create an interaction volume. Which signals are
produced in the interaction volume?
A: All the above
What is the range of energies for Secondary Electrons?
A: 2-50eV
For high resolution secondary electron imaging which objective lens aperture size is
preferred?
A: small
How would you best prepare a dry and non-conductive sample of fine particles (e.g. talcum
powder) for routine secondary electron imaging of the surface of the particles.
A: ?
If you are able to visualize the periodic table of chemical elements using a BSE detector how
will appear the blacks-greys-whites distributions?
A: Black on the top, grey in the middle, white at the bottom
Which electron source is least expensive to replace?
A: tungsten filament
What is the reason for using slow scan rates to accumulate micrographs?
A: The signal-to-noise ratio is improved
What is the most commonly used name in the sample for the inelastic scattering process
whereby primary beam electrons knock out other electrons from their shells?
A: Inner-shell ionization
Which electron source provides the greatest brightness?
A: Cold field emission, tungsten filament (wrong)
How is working distance defined in the SEM?
A: The distance from the specimen to the objective lens pole piece
Starting from the top how is an SEM column organised?
A: Cathode; b, Whenelt cylinder; c, Anode; d, Condenser lens; e Objective lens; f, Sample;
What condition would result in a higher resolution backscattered electron images?
A: Higher atomic number
What is a common reason for the specimen chamber pump down time to be excessively
long?
A: Specimen degassing
What labeling scheme of the SEM shown in this photograph is correct? 1. Secondary
electron detector 2. X-ray detector 3. Specimen chamber 4. OL aperture
A: A = 2, B = 4, C = 3, D = 1
What is the correct labelling for the above image of an electron gun assembly.
A: a, filament; b, Wehnelt; c, electrode; d, porcelin insulator (wrong)
The image below is of a NaCI salt crystal. What mode of imaging is most likely to have
been used to generate this micrograph?
A: Backscattered electrons (wrong)
For which experiments is it essential that specimens are finely polished?
A: Backscattered electron imaging
What is the range of energies for Secondary Electrons?
A: 2-50eV
Which electron source has the shortest working life?
A: Tungsten