Nanotech Scanning electron microscopy
When electrons interact with a solid they create an interaction volume. Which signals are produced in the interaction volume?
(Auger electrons and characteristic X-rays Characteristic X-rays and secondary electrons Secondary electrons and Auger electrons) All of the above
What type of information can be gathered from a sample using a scanning electron microscope?
(Compositional information Topological information Crystallographic information) All of the above
Which one of these samples should not be inserted in an SEM?
(Uncoated organic samples Highly degassing samples Liquids) All of above
The image shown is a secondary electron image of an aluminium surface taken with the JSM 6460LA SEM. The central rectangular region has reduced contrast and lacks image sharpness due to contamination deposited from a higher magnification scan. Which of the following can help prevent contamination?
(a.Use the smallest possible specimen. b.Always handle specimens with a gloved hand or forceps. c.Ensure that all specimens and specimen adhesives are dry. d.Store specimen in a vacuum desiccator overnight prior to an SEM session.) A, B, C & D
Which conditions would be most favourable for the collection of backscattered electron images from an insulating material?
15 keV, carbon coated sample
What is the range of energies for Secondary Electrons?
2-50 eV
A typical SEM can operate up to a maximum of _________kV?
30
While the best resolution possible in a light microscope is about 200 nm, a typical SEM has a resolution close to :_____________
5 nm
What is the correct labeling of this LaB6 electron gun assembly?http://www.ammrf.org.au/myscope//images/questions/sem/22.jpg
A - electron emitter, B - Wehnelt, C - electrode
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 http://www.ammrf.org.au/myscope//images/questions/sem/15.jpg
A = 2, B = 4, C = 3, D = 1
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 normal video camera working in the visible range is placed inside an SEM column what else should be done to check the specimen position inside the sample chamber?
A lamp working in the visible range should be inserted within the sample chamber
As director of a Characterization Laboratory you have to find a location for your brand new High definition Field emission SEM; what is for you the best solution?
A room with air-conditioning in the basement, and if possible located in a quite area
What precautions need to be taken when tilting a specimen for observation?
All of the above
If your sample is biological, soft, and contains water, and you want to image the morphology you should?___?
Any of the above (freeze dry, chemical dry, cryo-SEM)
For which experiments is it usually essential that specimens are flat or finely polished?
Backscattered electron imaging
Why are electrons that are near the sample surface only used to produce Secondary electrons images?
Because secondary electrons have very low energies and only those near the sample surface can be emitted and reach the SE detector
Where is a Backscattered Electron Detector located inside an SEM?
Below the upper objective lens
For thermionic electron sources, what is the correct setting of filament current for a saturated filament (find the letter along the filament temperature axis)?http://www.ammrf.org.au/myscope//images/questions/sem/36.png
C
The interaction volumes for a variety of SEM accelerating voltages is shown. Which schematic drawing represents the highest accelerating voltage? http://www.ammrf.org.au/myscope//images/questions/sem/78.jpg
C
Which electromagnetic lens principally controls the electron probe diameter?
Condenser lens
Where was the first commercially available scanning electron microscope developed?
Department of Engineering, Cambridge University
What would you do in order to image an explosive material using an SEM?
Do not look at explosive material using an SEM because it is likely to explode under the beam
How would you best prepare a dry and non-conductive sample of fine particles (e.g. talcum powder) for routine secondary electron (SE) imaging of the surface of the particles?
Dust/ sprinkle onto an adhesive carbon tab and coat with platinum
Study the vacuum system schematic.? What is the status of the SEM?http://www.ammrf.org.au/myscope//images/questions/sem/34.jpg
Evacuation mode
For which material type would cold mounting in epoxy resin be the preferred method to prepare a specimen for BSE imaging?
For specimens with a low melting point
When a high voltage electron beam strikes a specimen, how is most of the energy dispersed?
Heat
What effect will reducing the electron probe size have on a secondary electron image?
Improve resolution
Why are electron micrographs not coloured?
Micrographs are intensity maps of electrons collected by a detector.
What coating type is preferred for carrying out compositional imaging on a conductive specimen?
No coating
In this backscattered electron image of the polished surface of a fractured Fe2SiO4 olivine, why does the olivine show varying contrast?http://www.ammrf.org.au/myscope//images/questions/sem/107.jpg
Orientation differences of planes within the sample
Which sample preparation approach would you avoid in order to observe an initially wet, conductive particulate sample in the SEM?
Place the wet sample onto a specimen stub and directly insert it into the machine
After the sample is placed and the sample chamber is closed you need to___?
Press the button that turns on the rotary pump to evacuate the sample chamber and then switch on the emission gun
For high resolution secondary electron imaging, which objective lens aperture size is preferred?
Small
In secondary electron imaging which aspect of the sample will be dominant in determining the appearance of the image?
Surface roughness
A ceramic contains a mixture of Al2O3, TiO2 , Al2SiO5 and TiO. In backscattered electron imaging which phase appears lightest? The atomic weight of Ti is 47.8, atomic number is 22; the atomic weight of O is 15.9 and atomic number is 8; the atomic weight of Al is 26.9 and atomic number is 13; the atomic weight of Si is 28.1 and the atomic number is 14.
TiO
Why must scanning electron microscopes operate under vacuum?
To stop the scattering of high energy electrons of the beam
Placing and fixing the sample on the sample holder inside the SEM sample chamber you have to take care to:
Use gloves and avoid touching any of the detectors both with the sample holder and the tools
Which of these parameters need adjusting to obtain the best compositional contrast (BSE)image?
a and b
Backscattered electron (BSE) images can be used to show:
a, b, and c
The SEM filament that uses a single crystal of tungsten, from which electrons are pulled off by a field, is called a ___? filament.
field emission (FE)
What should you do if you urgently need to leave the microscope laboratory for 10 minutes, for example if the fire alarm went off?
follow the protocol set by the laboratory
Backscattered electrons (BSE) are:
high energy electrons scattered back from a large interaction volume (typically > 1um).
The two images are of the same object and clearly the left one (optical microscope) and the right one (SEM secondary electron image) have differences that are due to_______?
illumination source, resolution and depth of field
Using a smaller objective aperture will
increase resolution and increase depth of field.
Using a smaller objective aperture will...
increase resolution and increase depth of field.
What is the correct sequence for preparing the scanning electron microscope for imaging?
insert specimen, turn on accelerating voltage, increase beam current, select image mode
When analysing electron beam sensitive samples, it is advisable to:
lower the accelerating voltage.
An SEM image is built by
rastering the electron beam across the sample using scan coils.
A typical (morphological/ topographical) SEM image is generated by collecting the __________________ electrons that come off the sample surface.
secondary
A scanning electron microscope is configured as follows: short WD distance 7 mm; accelerating voltage 5 keV; small objective aperture; small spot size. Which experiment is likely to be undertaken?
secondary electron imaging for high resolution (at high magnification)
The high resolution secondary electron image above is of a diatom imaged at 50000X at 5mm working distance with the JSM 6400F Field emission SEM. Based on your understanding of the SEM parameters required for such images, what would be the most likely diameter settings for beam spot size (diameter of beam at the sample surface) and objective lens aperture. http://www.ammrf.org.au/myscope//images/questions/sem/96.jpg
small diameter beam spot; small diameter aperture
Which detector/s can be used in low vacuum mode?
the backscattered electron detector and microanalysis detectors
What is a common reason for the specimen chamber pump down time to be excessively long?
the specimen is out-gassing strongly
Which electron source is least expensive to replace?
tungsten filament
What is the correct response if you observe a sample melting in the electron beam?
turn down the electron beam, or turn off the accelerating voltage, and remove the sample
