5 Solid State Characterization

Question 1

Optical vs electron microscopy

Answer 1

optical has smaller resolution, can’t see atoms/molecules 300-700nm

electron 1-10nm

Question 2

SEM

types scattering

Answer 2

-scanning e microscopy
- image from source e- and material

• elastic scattering (hit nuc), large angle diffraction, little to no E loss
  -inelastic scattering (hit e-), small angle diffraction, high E loss

Question 3

SEM instrumentaion

Answer 3

e- source (cathode) hits sample, scattering, anode (pos) gets transmitted e-

Question 4

types of e- gun in SEM

Answer 4

Tungsten
- LaB6
-Field emission: best resolution

Question 4

what’s special about field emission guns

Answer 4

• best resolution
  -cold
• large potential diff needed to eject e
• very pointy tip

Question 5

why is SEM done in a vacuum

Answer 5

-prolong e- source life
-eliminate interactions b/w e and molecules in atmos

Question 6

what are the 3 things the can happen when incident e hits sample

Answer 6

• deflect nuc (backscattered)
• knock e- sample (secondary e-)
  -eject core sec e-, relax, release x-ray or auger

Question 7

what is BSE

Answer 7

-backscattered e imaging
- e deflect off nuc
- more scattering with heavier atoms
- gives contrast (heavier=lighter), can’t see contrast if even distribution

Question 8

what is SE

Answer 8

• secondary e emission
• less E then BSE
• good topographical info
• 2 e deep in sample not enough E to reach detector

Question 9

what is EDX

Answer 9

• energy dispersive x-ray spectroscopy
  -qualitative, not smooth background, peak overlap can obscure
• eject core 2 e-, another relaxes to take its place and release x-ray
• can’t do H, He, Li, cuz Be filter
• x ray immitted characteristic element
• EDX with either SE/BSE can make element map

Question 10

escape depth

Answer 10

not all e have enough E to reach detector

Question 11

is EDX, SE-SEM, BS-SEM surface tech?

Answer 11

no, bulk tech

Question 12

how to get cross sectional images in SEM

Answer 12

rotate sample holder

Question 13

what is TEM

Answer 13

-transmission e microscopy
- e transmitted sample (opp SEM)
- sample must be thin to let e pass
- has to be transparent to e
-contrast from mass elements, sample thickness (thicker=darker (opp SEM)), crystal orientation (can’t assume witch one)

Question 14

What property must SEM and TEM samples have?

Answer 14

-conductive
- if not coated thin layer M (Ag or Cr)

-grounded to prevent build up (charging)

Question 15

Dark vs bright field imaging

Answer 15

bright: lighter=bright, heavier=dark (like TEM)

Dark: opp like BS-SEM

Question 16

how to prepare sample for TEM

Answer 16

• org stained with OsO4, RuO4, UO(CH3COO)22H2O (uranyl acetate), Pb(C6H2O7)23H2O (lead citrate)
• stain to improve contrast (pick heavier metals)
• use Cu/C holder (conductive)

Question 17

What is SAED

Answer 17

-selected area e diffraction
- type TEM
- complementary to X-ray diffraction
- small areas (local) only (xrd bulk)
-high cost/time
- if single spots, crystalline but rings if amorphous/polycrystalline

Question 18

HRTEM

Answer 18

-done under dark field
- can see lines xtal orientation and find d-spacing

Question 19

what is XPS

Answer 19

-x-ray photoelectron spectroscopy
- x- ray hits, core e ejected, kinetic E phoelectron= KE X-ray- binding E

Question 20

photoelectron escape depth

Answer 20

low

• only 5-10nm analyzed
  -XPS surface tech

Question 21

Survey vs high resolution scan

Answer 21

survey: elemental composition
-high res (in vacuum): ox state

Question 22

what is depth profiling

Answer 22

etch surface to do XPS deeper
damages sample

Question 23

how does chemical envir change BE

Answer 23

• BE incrases with more e w/drawing atoms

Question 24

peak fitting

Answer 24

in xps deconvolute diff atoms to a peak

Question 25

Auger e

Answer 25

x ray eject core 2 e, other e relaxes to take place, emit auger e KE independent x-ray

Question 26

what is AES

Answer 26

-Auger e spectroscopy -use e (not x ray) - can be coupled SEM -complementary XPS - surface tech - info make up/chem envir material - auger mapping - quantitative must be done using standards

Question 27

what does KE auger e depend on

Answer 27

- type ejected core e - type auger e emitted (1s 2s 2p ect

Question 28

Does ASE-SEM or XPS have better resolution?

Answer 28

AES-SEM better lateral resolution cuz e beam smaller