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51 Cards in this Set
- Front
- Back
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What is the maximum resolution of TEM and SEM? |
1 A and 1 nm respectively |
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Which method has a longer filament lifetime, thermoionic of cold emission? |
Thermoionic |
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How do we prevent the electron from colliding with the walls of the Wenhnelt Cylinder? |
Negatively bias the walls |
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What is emisison reliant on in thermoionic emission vs cold cathode? |
Thermoionic: Thermal energy exciting electrons Cold Cathode: Quantum tunelling |
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What do TEM and SEM stand for |
Transmission Electron Microscope Scanning Electron Microscope |
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Why do electromagnetic lenses induce spinning? |
Lorenz Force induces a spin when a magnetic and electric field interact. |
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What does PMT stand for? What must we use before we use a PMT? What does the PMT do? |
Photomultiplier tube. We must convert the electron into a photon. The PMT increases the signal of a single electron so it detectable. |
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What gives us better compositional data? Back Scattered Electrons or Secondary Electrons? |
Back scattered electrons |
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What do BSE, SE and EDS stand for |
Back scattered electron, secondary electron, energy dispersive x-ray spectrum |
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How do we reject secondary electrons? |
Negatively bias the Faraday cage |
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Which method in a SEM gives us the highest surface sensitivity. Rate the surface sensitivity of a TEM. |
Secondary Electrons Poor |
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Why do we get topographical contrast? |
Electron has a high chance of escaping normal to the surface. |
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How can we distinguish between compositional contrast and channelling. What type of electrons provide compositional contrast. |
Change the position of the detector. BSE. |
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What are the pros and cons of a large probe current. |
Pro: Low acquisition time Cons: Electron-Electron interaction |
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What are the pros and cons of a small incident angle. |
Lower resolution, but large spherical aberration. |
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What are the pros and cons of a higher voltage? |
Higher resolution but increases electron-electron interaction. |
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What are the downsides of a brighter source? |
A bright source results in faster burnout of the filament.
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Name 2 ways we can isolate vibrations? |
Vibration Isolation Table Place equipment in the basement of the building Isolate the equipment Dampening tables Place the equipment in a box, which is dampened by springs |
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Why do we need to prepare our samples for SEM? Name 2 ways |
Charging effects. Carbon paint or metal coating via sputtering |
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What is astigmatism? |
Astigmatism is an off-axis aberrations. |
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Why do we need a vacuum for TEM and SEM |
The electric field used to accelerate electrons/generate them, will cause contaminants to bombard the filament. |
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How do we prepare biological samples |
We remove the water from the sample, by going around the critical point with another liquid. This allows the other liquid to evaporate without destroying the sample. |
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Why will rapidly drying a cell destroy it? |
High vapour pressure ruptures the cell? |
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Why will slowly drying a cell destroy it |
Capillary forces will collapse it |
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How can we tell that a sample has grease contamination. |
Carbon residues show up on sample. |
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Why does mass contrast form on TEM? |
Different probabilities of electrons transmitting through samples of different masses. |
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Is TEM surface sensitive? |
No |
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Why do we achieve a higher resolution with TEM, when the technique is not surface sensitive? |
Higher energy, Lower wavelength. |
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Why does diffraction contrast form? |
Strong diffraction due to Bragg condition off crystal planes. |
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What does SAD imaging map? |
Selected Area Diffraction allows us to observe the reciprocal space mapping. (Diffraction points) |
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Dark Field Imagine in TEM allows us to observe a single ____________ |
Crystal plane |
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What does HRTEM stand for? |
High Resolution Transmission Electron Microscope |
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What does HRTEM rely on the sample being? |
Periodic |
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Why do we prepare samples on carbon grids in TEM. |
Maximize the penetration of electrons through the stage |
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TEM samples must be _______ (Answer relates to thickness) |
Thin |
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Electrolytic thinning is the opposite of ________ |
Electroplating |
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Ion milling thins a sample by _______________ |
Bombarding the sample with an ionized gas. |
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Which technique is effective at thinning samples with a thickness greater than 100 um. |
Mechnical Pre-Thinning |
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What technique submerges the sample in water when thinning. |
Ultramicotomy. Ultramictomy thins samples with a computer controlled razor. |
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A striper pattern occurs on TEM, what is this the result of? |
Wedge Fringes or Bending Contours or Stacking Faults |
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Kikuchi lines arise from what phenomenon? |
Bragg Diffraction of the electron beam |
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What are the main types of dislocations? |
Edge and Screw |
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Why do we need a large electron mean free path? |
Prevent electron interaction with anything but the sample |
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Which requires a higher vacuum, Thermoionic or cold cathode? |
Cold Cathode |
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Name one failure method of the filament |
High temperature High Current High Field |
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What is the optimal number of lenses in a EM? |
3 |
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Why do SEM images appear 3D |
Electron has a high chance of escaping normal to the surface. |
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A raster scan is ___________ |
a scan of every point on the sample |
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Why do we decelerate the electron before it impacts the sample in SEM? |
Minimize electron volume/Maximize resolution |
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Are there more SE or BSE |
SE |
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If we see a series of striped regions in a known single crystal. What is the likely cause? |
Magnetic Domain |
