Characterisation of porous materials using Electron Microscopy

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



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





ED pattern

Fouriertransform

Electron backscatter diffraction(EBSD - SEM)

High quality EBSD pattern



Electron backscatter diffraction

(EBSD - SEM)MFISEM image

EBSD patterns spots A and D



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



MOF on microgrid carbon film

Gascon, TUD



TEM Fe-MFI

Taboada, TUD

SEM of same sample



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



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



full scale

enlarged scale

Pt/zeolite

optimal imagingzeolite 5 degree tilt zeolite amorphised

TiO2 in TUD-1

Peeters, TUE



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



Single image from series Slice of reconstruction

Jansen et al., Utrecht University

New mesoporous mat: SEM



New mesoporous mat: TEM

MSU-3

Prouzet et al.,

J.Mater.Chem.

12 (2002) 1553

New mesoporous mat: TEM



New mesoporous mat: 3D-TEM


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Single images from series

New mesoporous mat: 3D-TEM

Single slices from reconstruction





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



http://www.egr.msu.edu/cmsc/esem/gallery/index.html

ESEM



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



Real in situ: commercially available



E-TEM

Max 50 mbar

Resolution lost > 5 mbar

Complete sample holder is heated and can react

Now sold by FEIHaldor TopsoeASU


E-TEM



ASUFEITecnai


New FEI Titan E-TEM



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


Closed nanoreactor


MEMS nanoreactor


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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

Documents

Characterisation of porous materials using Electron Microscopy