Studied by 16 people2 key things for a good image
contrast brightness
18% gray
mid - point between black and white
SEM has high or low contrast?
low contrast
How many shades of gray are there?
256 shades of gray
What happens if a sample is not mounted properly?
Charging of the sample and knock it off the stub
SE gives what kind of details?
Surface topography
BSE gives what kind of details?
Surface topography, but electrons go deeper into the sample
SE is easier to charge T or F
T It has less energy
BSE is harder to charge T or F
T more energy
What are the 3 aberrations
Spherical Chromatic Astigmatism
Spherical aberration
blurriness at the edge of an image
Chromatic aberration
color distortion
What is the hardest aberration to correct?
Spherical aberration
What does kV influence?
Wavelength
What happens to the wavelength at higher kV and lower kV?
higher kV: shorter wavelength (blue) lower kV: longer wavelength (red)
What happens if the 3 aberrations are not corrected?
Resolution is decreased
What is the most important part of an electron and light microscope?
Objective Lens
Parfocal
lens changed to another lens, stays in focus
What magnification do you have to be at to correct for astigmatism?
Above 1,000x (SEM)
SEM Scanning = ?
Magnification
(SEM) larger area scan
lower mag
(SEM) smaller area scan
higher mag
Does focal point change in the SEM?
No
How do you focus on the Hitachi SEM?
2-3x desired mag, focus, back to desired mag
What becomes difficult to correct for when going higher in mag w/ the SEM?
Astigmatism
How is TEM similar to the SEM?
Identical top columns
Order of SEM column?
Filament
Cathode Cap
Anode Cap
Condenser 1
Condenser 2
What lens does a Cathode Cap use?
Electro static lens
What is Cathode Cap also known as?
Wehnelt Cylinder
Does Cathode Cap have more negative charge than the filament?
Yes
What do you need to turn on filament?
saturation
What happens to the filament if there is too much saturation?
Melts the filament
(TEM) Condenser 1 controls?
Spot Size
What charge does Anode have?
Positive charge
Electrons from the Cathode Cap is attracted to?
Anode and comes down at 1/2 speed of light
(TEM) C1 and C2 controls?
illumination
(TEM) Objective, Intermediate, and Projector controls?
Magnification
Electron microscope use what lens?
Electromagnetic lens
What is found in Electromagnetic lens?
pole piece
What does a pole piece do?
concentrates the magnetic field
What is the BSE energy level
High energy
What is the SE energy level
Low energy
BSE interacts with?
Nucleus and electrons bounce back
SE interacts with?
Electrons of an atom
What is hysteresis?
Residual mag in the lens
FORMULAS
2160 lines/mm x mm/lines = True Mag
|Calculated Mag - Display Mag/Calculated Mag| = Percent Error
SE detector location
SIDE
BSE detector location
TOP
BSE advantages
helps identify if it is high atomic number or low atomic number
High Atomic number looks
bright
Low atomic number looks
dark
Problems w/ SE
can get charging
but more mag, better resolution
Problems w/ BSE
less energy less mag, less resolution
Why choose lower kV?
to see small surface details (5kV), less damage to the sample
If we choose higher kV (15kV)
less details, more damage to sample
Resolution 5kV 15kV
5kV: less resolution (lower kV) 15kV: more resolution (higher kV)
Different W.D will give us different results
Different size of aperture = different results
Low atomic number
electron goes deeper into the sample
Higher kV shoots
through the sample higher energy
Need low kV for what
to see surface
Smaller spot size = ?
better resolution more noise (looks like snow) less signal (electrons)
Spot size affects?
Resolution Noise Signal
Long W.D =
more depth of field
Less W.D =
more/better resolution
Position is dependent on detectors
farther away = more noise (W.D concept)
Bigger spot size
less resolution less noise more signal (electrons)
Can see noise with Electron microscopes T or F
T
Condenser Aperture
Screens out the beam (electrons)
Condenser 2 (TEM)
Crossover
3 types of filament
Tungsten (wire) Field emission (gives great resolution) LaB6 Crystal (Lanthanum hexabond, brighter and lasts longer)
Formula
MAG = Image Size/ Object size (of the sample)
Cathode Cap is reflected by what
Electron mirror
Anode has a larger hole
electrons gets pulled
Aperture
small holes
SLOW SCAN
More electrons = less noise
FAST SCAN
Less electrons = more noise
Why not a longer scan rate?
Probability of charging/ moving the sample
Higher kV decreases?
aberrations
Long WD
worse resolution and less control of the beam
Another reason for charging?
Too many electrons, too negative
To not have charging make sure the sample is?
Conductive and grounded
What is the difference between the SEM and TEM?
SEM has scan coils and detectors
Electromagnetic lens gives us?
Magnification
Spot size is used for what
to get more or less electrons
Focus is the beam getting condensed by
Condenser 2
What are the apertures of TEM
Condenser Aperture Objective aperture Intermediate aperture
Location of astigmatism on TEM
C2: Corrected; round beam/focused Incorrect: Oval shape, not sharp Objective: Corrected; even fringes Incorrect: oval fringe Intermediate: Corrected; even spikes Incorrect: spikes misaligned
SEM principles
parameters are based on what sample you use
VENMO
@Chester-Hilario
Note
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