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Chem 327 > 5 Solid State Characterization > Flashcards

5 Solid State Characterization Flashcards

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1
Q

Optical vs electron microscopy

A

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

electron 1-10nm

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2
Q

SEM

types scattering

A

-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
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3
Q

SEM instrumentaion

A

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

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4
Q

types of e- gun in SEM

A

Tungsten
- LaB6
-Field emission: best resolution

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4
Q

what’s special about field emission guns

A
  • best resolution
    -cold
  • large potential diff needed to eject e
  • very pointy tip
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5
Q

why is SEM done in a vacuum

A

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

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6
Q

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

A
  • deflect nuc (backscattered)
  • knock e- sample (secondary e-)
    -eject core sec e-, relax, release x-ray or auger
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7
Q

what is BSE

A

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

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8
Q

what is SE

A
  • secondary e emission
  • less E then BSE
  • good topographical info
  • 2 e deep in sample not enough E to reach detector
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9
Q

what is EDX

A
  • 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
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10
Q

escape depth

A

not all e have enough E to reach detector

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11
Q

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

A

no, bulk tech

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12
Q

how to get cross sectional images in SEM

A

rotate sample holder

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13
Q

what is TEM

A

-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)

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14
Q

What property must SEM and TEM samples have?

A

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

-grounded to prevent build up (charging)

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15
Q

Dark vs bright field imaging

A

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

Dark: opp like BS-SEM

16
Q

how to prepare sample for TEM

A
  • 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)
17
Q

What is SAED

A

-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

18
Q

HRTEM

A

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

19
Q

what is XPS

A

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

20
Q

photoelectron escape depth

A

low

  • only 5-10nm analyzed
    -XPS surface tech
21
Q

Survey vs high resolution scan

A

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

22
Q

what is depth profiling

A

etch surface to do XPS deeper
damages sample

23
Q

how does chemical envir change BE

A
  • BE incrases with more e w/drawing atoms
24
Q

peak fitting

A

in xps deconvolute diff atoms to a peak

25
Q

Auger e

A

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

KE independent x-ray

26
Q

what is AES

A

-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

27
Q

what does KE auger e depend on

A
  • type ejected core e
  • type auger e emitted (1s 2s 2p ect
28
Q

Does ASE-SEM or XPS have better resolution?

A

AES-SEM better lateral resolution cuz e beam smaller

Chem 327 (18 decks)

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