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)