EM 70 FINALS STUDY GUIDE

2 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?

1. Filament
2. Cathode Cap
3. Anode Cap
4. Condenser 1
5. 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