5 Solid State Characterization Flashcards
Optical vs electron microscopy
optical has smaller resolution, can’t see atoms/molecules 300-700nm
electron 1-10nm
SEM
types scattering
-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
SEM instrumentaion
e- source (cathode) hits sample, scattering, anode (pos) gets transmitted e-
types of e- gun in SEM
Tungsten
- LaB6
-Field emission: best resolution
what’s special about field emission guns
- best resolution
-cold - large potential diff needed to eject e
- very pointy tip
why is SEM done in a vacuum
-prolong e- source life
-eliminate interactions b/w e and molecules in atmos
what are the 3 things the can happen when incident e hits sample
- deflect nuc (backscattered)
- knock e- sample (secondary e-)
-eject core sec e-, relax, release x-ray or auger
what is BSE
-backscattered e imaging
- e deflect off nuc
- more scattering with heavier atoms
- gives contrast (heavier=lighter), can’t see contrast if even distribution
what is SE
- secondary e emission
- less E then BSE
- good topographical info
- 2 e deep in sample not enough E to reach detector
what is EDX
- 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
escape depth
not all e have enough E to reach detector
is EDX, SE-SEM, BS-SEM surface tech?
no, bulk tech
how to get cross sectional images in SEM
rotate sample holder
what is TEM
-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)
What property must SEM and TEM samples have?
-conductive
- if not coated thin layer M (Ag or Cr)
-grounded to prevent build up (charging)
Dark vs bright field imaging
bright: lighter=bright, heavier=dark (like TEM)
Dark: opp like BS-SEM
how to prepare sample for TEM
- 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)
What is SAED
-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
HRTEM
-done under dark field
- can see lines xtal orientation and find d-spacing
what is XPS
-x-ray photoelectron spectroscopy
- x- ray hits, core e ejected, kinetic E phoelectron= KE X-ray- binding E
photoelectron escape depth
low
- only 5-10nm analyzed
-XPS surface tech
Survey vs high resolution scan
survey: elemental composition
-high res (in vacuum): ox state
what is depth profiling
etch surface to do XPS deeper
damages sample
how does chemical envir change BE
- BE incrases with more e w/drawing atoms
peak fitting
in xps deconvolute diff atoms to a peak
Auger e
x ray eject core 2 e, other e relaxes to take place, emit auger e
KE independent x-ray
what is AES
-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
what does KE auger e depend on
- type ejected core e
- type auger e emitted (1s 2s 2p ect
Does ASE-SEM or XPS have better resolution?
AES-SEM better lateral resolution cuz e beam smaller
