EM 70 FINALS STUDY GUIDE

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2 key things for a good image

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1

2 key things for a good image

contrast brightness

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2

18% gray

mid - point between black and white

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3

SEM has high or low contrast?

low contrast

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4

How many shades of gray are there?

256 shades of gray

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5

What happens if a sample is not mounted properly?

Charging of the sample and knock it off the stub

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6

SE gives what kind of details?

Surface topography

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7

BSE gives what kind of details?

Surface topography, but electrons go deeper into the sample

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8

SE is easier to charge T or F

T It has less energy

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9

BSE is harder to charge T or F

T more energy

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10

What are the 3 aberrations

Spherical Chromatic Astigmatism

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11

Spherical aberration

blurriness at the edge of an image

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12

Chromatic aberration

color distortion

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13

What is the hardest aberration to correct?

Spherical aberration

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14

What does kV influence?

Wavelength

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15

What happens to the wavelength at higher kV and lower kV?

higher kV: shorter wavelength (blue) lower kV: longer wavelength (red)

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16

What happens if the 3 aberrations are not corrected?

Resolution is decreased

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17

What is the most important part of an electron and light microscope?

Objective Lens

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18

Parfocal

lens changed to another lens, stays in focus

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19

What magnification do you have to be at to correct for astigmatism?

Above 1,000x (SEM)

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20

SEM Scanning = ?

Magnification

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21

(SEM) larger area scan

lower mag

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22

(SEM) smaller area scan

higher mag

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23

Does focal point change in the SEM?

No

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24

How do you focus on the Hitachi SEM?

2-3x desired mag, focus, back to desired mag

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25

What becomes difficult to correct for when going higher in mag w/ the SEM?

Astigmatism

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26

How is TEM similar to the SEM?

Identical top columns

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27

Order of SEM column?

  1. Filament

  2. Cathode Cap

  3. Anode Cap

  4. Condenser 1

  5. Condenser 2

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28

What lens does a Cathode Cap use?

Electro static lens

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29

What is Cathode Cap also known as?

Wehnelt Cylinder

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30

Does Cathode Cap have more negative charge than the filament?

Yes

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31

What do you need to turn on filament?

saturation

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32

What happens to the filament if there is too much saturation?

Melts the filament

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33

(TEM) Condenser 1 controls?

Spot Size

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34

What charge does Anode have?

Positive charge

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35

Electrons from the Cathode Cap is attracted to?

Anode and comes down at 1/2 speed of light

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36

(TEM) C1 and C2 controls?

illumination

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37

(TEM) Objective, Intermediate, and Projector controls?

Magnification

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38

Electron microscope use what lens?

Electromagnetic lens

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39

What is found in Electromagnetic lens?

pole piece

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40

What does a pole piece do?

concentrates the magnetic field

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41

What is the BSE energy level

High energy

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42

What is the SE energy level

Low energy

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43

BSE interacts with?

Nucleus and electrons bounce back

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44

SE interacts with?

Electrons of an atom

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45

What is hysteresis?

Residual mag in the lens

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46

FORMULAS

2160 lines/mm x mm/lines = True Mag

|Calculated Mag - Display Mag/Calculated Mag| = Percent Error

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47

SE detector location

SIDE

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48

BSE detector location

TOP

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49

BSE advantages

helps identify if it is high atomic number or low atomic number

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50

High Atomic number looks

bright

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51

Low atomic number looks

dark

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52

Problems w/ SE

can get charging

but more mag, better resolution

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53

Problems w/ BSE

less energy less mag, less resolution

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54

Why choose lower kV?

to see small surface details (5kV), less damage to the sample

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55

If we choose higher kV (15kV)

less details, more damage to sample

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56

Resolution 5kV 15kV

5kV: less resolution (lower kV) 15kV: more resolution (higher kV)

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57

Different W.D will give us different results

Different size of aperture = different results

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58

Low atomic number

electron goes deeper into the sample

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59

Higher kV shoots

through the sample higher energy

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60

Need low kV for what

to see surface

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61

Smaller spot size = ?

better resolution more noise (looks like snow) less signal (electrons)

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62

Spot size affects?

Resolution Noise Signal

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63

Long W.D =

more depth of field

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64

Less W.D =

more/better resolution

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65

Position is dependent on detectors

farther away = more noise (W.D concept)

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66

Bigger spot size

less resolution less noise more signal (electrons)

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67

Can see noise with Electron microscopes T or F

T

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68

Condenser Aperture

Screens out the beam (electrons)

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69

Condenser 2 (TEM)

Crossover

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70

3 types of filament

Tungsten (wire) Field emission (gives great resolution) LaB6 Crystal (Lanthanum hexabond, brighter and lasts longer)

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71

Formula

MAG = Image Size/ Object size (of the sample)

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72

Cathode Cap is reflected by what

Electron mirror

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73

Anode has a larger hole

electrons gets pulled

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74

Aperture

small holes

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75

SLOW SCAN

More electrons = less noise

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76

FAST SCAN

Less electrons = more noise

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77

Why not a longer scan rate?

Probability of charging/ moving the sample

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78

Higher kV decreases?

aberrations

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79

Long WD

worse resolution and less control of the beam

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80

Another reason for charging?

Too many electrons, too negative

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81

To not have charging make sure the sample is?

Conductive and grounded

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82

What is the difference between the SEM and TEM?

SEM has scan coils and detectors

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83

Electromagnetic lens gives us?

Magnification

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84

Spot size is used for what

to get more or less electrons

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85

Focus is the beam getting condensed by

Condenser 2

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86

What are the apertures of TEM

Condenser Aperture Objective aperture Intermediate aperture

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87

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

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88

SEM principles

parameters are based on what sample you use

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89

VENMO

@Chester-Hilario

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