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Characterisation of porous materials using Electron Microscopy. Dr. Patricia J. Kooyman DelftChemTech / National Centre for HREM Delft University of Technology [email protected]. Bulk (structural) information. Transmission Electron Microscopy (TEM). Surface information. - PowerPoint PPT Presentation
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Characterisation ofporous materials using
Electron Microscopy
Dr. Patricia J. KooymanDelftChemTech / National Centre for HREMDelft University of [email protected]
Surface information
Scanning probe microscopy: STM, AFM
Scanning Electron Microscopy (SEM)
Scanning techniques
Bulk (structural) informationTransmission Electron Microscopy (TEM)
Electron Microscopy Techniques
+ Direct+ Morphology+ Elemental Analysis
0 Individual Particles
- Small volumes studied- Possible Damage due to Electron Beam- Only Solids
What is TEM?
A technique using high-energy electrons to obtain a 2D projection of a 3D structure.
The highest possible resolution is currently about 0.1 nm.
Electron-solid interactions
Incident electrons
Backscattered electrons
Direct beam
Elasticallyscattered electrons
Inelasticallyscattered electrons
Element specific X-rays
Secondaryelectrons
Visible light
Auger electrons
SpecimenTEM
SEM
EDX
ED / HREM
EELS
The SEM
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SEM TEM
particle morphology (particle
morphology)
surface morphology 2D projection - internal
structure
elemental analysis elemental
analysis
5 nm - 500 micron 1 nm - 5 micron
electr backscatter diffr electron diffraction
EELS
General features of SEM
• Electrons interact with specimen
• High vacuum necessary
• Specimen should be conducting (sputter with
Au)
• Particle morphology
• Surface imaging
• Elemental analysis
• Resolution ~ 1 nm
General features of TEM
• Electrons interact with specimen
• High vacuum necessary (~ 10-7 Torr for HREM)
• Specimen should be very thin (< 10 nm for
HREM)
• 2D projection of 3D structure
• Structural analysis
• Elemental analysis
• Resolution ~0.1 nm
Optical systems
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http://www.vcbio.sci.kun.nl/fesem/info/
Optical system of a TEM
image cross-section TEM
final imageimaging diffraction
intermediate 2
intermediate 1
specimen
focus planefor
image
focus planefor
diffraction
Electron diffraction (TEM)
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MFIHR bright-field image
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ED pattern
Fouriertransform
Electron backscatter diffraction(EBSD - SEM)
High quality EBSD pattern
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Electron backscatter diffraction
(EBSD - SEM)MFISEM image
EBSD patterns spots A and D
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Indexed EBSD patterns spots A and D
Stavinski et al.Angew. Chem.120 (2008) 5719
TEM imaging
bright field dark field centereddark field
HREM
Ru/aluminaSoede, DUT
Bright fieldimage
Ru/aluminaSoede, DUT
Electron DiffractionPattern
d-spacing
Bright fieldimage
Dark fieldimage withRu-diffractedbeam
Ru/aluminaSoedeDUT
TEM - information obtained
Method Information* bright-field * microstructural imaging nb: 2D info of 3D* high resolution structure!imaging
* electron diffraction * crystallographicpattern (cf XRD)
* generated X-rays *elemental analysis (EDX)
Sample preparationpowders / suspensions /
solsSEM Conducting sample holder Powder directly on sample holder Via suspension Sputter insulating samples with eg C, Au Use conducting glue
Sample preparationpowders / suspensions /
solsTEM Sample holder grid with (perforated) carbonfilm Powder directly on sample holder Via suspension Sputter large particles of insulating sampleswith C
Sample preparation: crushing
crush
suspension ineg ethanol
deposit on grid withcarbon film
3 mm
Microgrid carbon film
Quantifoil
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MOF on microgrid carbon film
Gascon, TUD
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TEM Fe-MFI
Taboada, TUD
SEM of same sample
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Sample preparationone-piece samples
SEM
Surface analysis: insert whole specimen Sputter insulating samples with eg C, Au
Internal analysis: cutting, microtomy Use conducting glue
Sample preparationone-piece samples
TEM
Plane view Mechanical polishing + ion milling Electropolishing (+ ion milling) Problem for insulating samples
Cross section Cutting, microtomy + ion milling Ultramicrotomy Connect insulating sample to conductingsubstrate
Sample preparation: ion milling
polishing5-10 micron thick
Ar ion beams
polishing holder
specimen
Sample preparation: ultramicrotomy
water bath
catalyst core
glue mantle
slices on grid
diamond knife
also possible at liquid nitrogen temperature
slices < 50 nm
Ultramicrotomy
ultramicrotomedspecimen
powderspecimen
MCM-41
mesoporous zeotype material pore size > 3 nmpossibility to convert larger moleculesdifferent phases are found
MCM-41
Ordered DisorderedVerhoef, TUD
HPA/MCM-41 fresh
HPA/MCM-41 used
HPA/MCM-41 XRD patterns
0
2000
4000
6000
8000
10000
12000
14000
0 5 10 15 20 25 30 35 40
2 theta
a.u.
pure HPAstarting MCM-41freshly loaded HPA/MCM-41used HPA/MCM-41
Fe-Si-SBA-15: TEM
J. Phys. Chem. B 110 (2006) 26114 -26121
Li, Hensen, TU/e
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Fe-Si-SBA-15: EDX
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Particle size distribution?Alloying?
Use TEM/HREM in combination with EDX
Pt-Rh/alumina (Grisel, UL)
overview
cluster
Pt-Rh/alumina (Grisel, UL)
Pt-Rh/alumina (Grisel, UL)
full scale
enlarged scale
Pt/zeolite
optimal imagingzeolite 5 degree tilt zeolite amorphised
TiO2 in TUD-1
Peeters, TUE
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Hamdy-Saad, TUD
3D TEM
Reconstruct 3D structure from tilt series at different anglesof the same area of material
“Electron Tomography”
3D TEM
Procedure:Acquire tilt series of a particle from +70
to -70 degrees at 1 or 2 degrees stepsRecombine these images to 3D
reconstructionDepict as slices through the particle or as
volume rendering
2D TEM - loss of information
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3D TEM - cycle
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3D TEM - result
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Single image from series Slice of reconstruction
Jansen et al., Utrecht University
New mesoporous mat: SEM
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New mesoporous mat: TEM
MSU-3
Prouzet et al.,
J.Mater.Chem.
12 (2002) 1553
New mesoporous mat: TEM
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New mesoporous mat: 3D-TEM
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Single images from series
New mesoporous mat: 3D-TEM
Single slices from reconstruction
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Energy loss E depends on for exampleelectron excitations, like • plasmons, phonons• secondary electrons (ionisation)• electron transitions to unoccupied states
E, energy of 200 kV electron
E-E
Electron Energy Loss Spectroscopy
EELS spectrum
•Zero loss and peak broadening due toenergy resolution ~ 1 eV.+ phonon scattering 0-0.1 eV
•Low loss: plasmons 0-50 eVPlural scattering in thick specimens
Ionisation edges,K,L,M,… For element characterisation
Graphite
EELS for elemental analysis
• especially useful for low Z elements
C, diamond
Effect of energy resolution - Exciton in diamond
0.2 eV
0.8 eV
EFTEM
• higher spatial resolution than EDS elemental mapping• much better sensitivity for low Z elements than EDS • much shorter acquisition times than EDS
Example: Si-L2,3 EFTEM in MOSFET structureM. Worch et al, Thin Solid Films 405 (2002) 198.
50 nm
BF Si
Si3N4SiO2
O N
Air-sensitive materials - SEM
Normally, samples prepared in air
Problem for air-sensitive samples
Quasi in situ: prevent exposure to air
Real in situ: insert gas in microscopeprevents charging
ESEM
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http://www.egr.msu.edu/cmsc/esem/gallery/index.html
ESEM
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Lee et al.,Journal of the European Ceramic Society 27 (2007) 561-564
Air-sensitive materials - TEM
Normally, samples prepared in air
Problem for air-sensitive samples
Quasi in situ: prevent exposure to air
Real in situ: perform reactions in microscope
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Quasi in situ: transfer holder
The 'slab' structure
Mo, W
S Co, Ni
Nanoparticles
calc 823 Ksulph 613 K
Tungsten sulphide
calc 823 Ksulph 673 K
calc 673 Ksulph 823 K
Real in situ: commercially available
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E-TEM
Max 50 mbar
Resolution lost > 5 mbar
Complete sample holder is heated and can react
Now sold by FEIHaldor TopsoeASU
Real in situ: commercially available
E-TEM
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ASUFEITecnai
Real in situ: commercially available
New FEI Titan E-TEM
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http://www.fei.com/
Towards higher pressure
A few mbar is NOT close to realistic conditions!
NCHREM / Kavli Institute of NS / TUD
develop new concept - nanoreactor
Fredrik Creemer, Henny Zandbergen
Towards higher pressure
Closed nanoreactor
Towards higher pressure
MEMS nanoreactor
Towards higher pressure
Qu
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.TEM holder tip
Towards higher pressure
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.J.F. Creemer et al.
Atomic-scale electron microscopy at ambient pressure
Ultramicroscopy 2008
1.2 bar H2500 oC
Main problems
representativity of specimen areapreparation damageelectron beam damagevery small particle imaging (< 1 nm)visibility of monolayerseffect of support on image of supported
phase