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ElectronElectron MicroscopyMicroscopyin Materials Sciencein Materials Science

Prof. Dr. Ulrich Krupp

lecture + seminar, www.mb.uni-siegen.de/LMW

OrganizationOrganization of of thethe EM EM CourseCourse1st day9.00-10.30 1 Introduction/ 2 Specimen Preparation

10.45-12.00 3 Main Components of a SEM/TEM12.30-14.00 lunch break14.00-15.00 4 Interactions Electron-Matter – Electron Contrast SEM15.00-16.30 Practical Course SEM 1

2nd day9.00-12.00 5 Electron Diffraction – Electron Contrast TEM

12.00-13.00 lunch break13.00-15.00 6 SEM Channeling Contrast and Electron

Diffraction Techniques15.00-16.00 Practical Course TEM 1

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OrganizationOrganization of of thethe EM EM CourseCourse

3rd day9.00-11.00 7 Analytical Electron Microscopy11.00-12.00 Practical Course SEM2 12.00-13.00 lunch break13.00-14.30 Practical Course - Analytical Electron Microscopy14.30-16.00 8 Case Studies + Discussion

LiteratureLiterature (SEM)(SEM)P.F. Schmidt (ed):Praxis der Rasterelektronenmikroskopie und MikrobereichsanalyseExpert-Verlag, 1994 (in German)J.I. Goldstein, P. Etchlin, D.E. Newbury: Scanning Electron Microscopy and X-ray MicroanalysisPlenum Publishing Corp., New York 1992L. Reimer: Scanning Electron MicroscopySpringer-Verlag, Berlin 1985V. Randle: Microtexture Determination and its ApplicationsThe Institute of Materials, London 1992 (EBSP)

WWW SEM course (in German)http://www.reclot.de/kapitel/0kurs.htm

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LiteratureLiterature (TEM)(TEM)E. Hornbogen, B. SkrotzkiWerkstoffmikroskopieSpringer-Verlag, 1993 (in German)M. v. Heimendahl: Electron Microscopy of MaterialsAcademic Press, New York 1980 (Engl.) vieweg 1970 (Deutsch)Wiliams, D.B.; Carter, C.B.: Transmission Electron Microscopy – A Textbook for Materials SciencePlenum Press, New York 1996J. W. Edington: Practical Electron Microscopy in Materials ScienceTechBooks, Herndon 1976

1 1 IntroductionIntroduction

sperms

Light Light MicroscopyMicroscopy 16741674Robert HookeAntony van Leeuwenhoek

The light microscope opened the first door to the microcosm,the electron microscope opened the second door,what will we see when we open the third door?E. Ruska 1985

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InventionInvention of of ElectronElectron MicroscopyMicroscopy

Ernst Ruska (1906-1988)TEM 1931, Nobel Price 1986

Manfred von Ardenne (1906-1988)SEM 1937-39

Resolution SEM/TEMResolution SEM/TEM

0,5µm

Ti-oxide on superalloy CMSX-6 after exposure at 1000°C to air

0,2µm

SEM TEM

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High Resolution TEMHigh Resolution TEM

Σ5 grainboundary

0.5nm

DepthDepth of Focus OM/SEMof Focus OM/SEM

optical microscopy(Trochodiscus longispinus, marine organism)

scanning electron microscopy

Goldstein et al.: SEM/X-ray microanalysis, Plenum, New York 1992

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DepthDepth of Focusof Focus

DepthDepth of Focusof Focus

2mm

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ScanningScanning ElectronElectron MicroscopesMicroscopes 11

CamScan Philips XL30 LaB6

ScanningScanning ElectronElectron MicroscopesMicroscopes 22Large chamber SEM MIRA

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ScanningScanning ElectronElectron MicroscopesMicroscopes 22

SEM examination of an ancient terracottawarrior (Xi‘An, China)

ScanningScanning ElectronElectron MicroscopesMicroscopes 22

micro gripperin a SEM

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Transmission Transmission ElectronElectronMicroscopyMicroscopy

Hitachi H8100 LaB6

DirectDirect MicroscopyMicroscopy (LM, TEM)(LM, TEM)

light source

specimen

eye

light source(transmission)

electron source

specimen

screen

eye

light microscopy (LM) TEM

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IndirectIndirect MicroscopyMicroscopy (SEM)(SEM)

eye

electron source

specimen screendetector

scanning coilselectron/specimeninteractions

2 Specimen Preparation

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SpecimenSpecimen PreparationPreparation (SEM)(SEM)

dry / fat free (cleaning in ethanol, drying in vacuum)

conductive (non-conductive specimens: sputtering, C coating)

OIM/channeling contrast (electropolishing / finepolishing)

50µmspecimen holderdouble-faced C adhesives(conductive)

Ar+

Au

SpecimenSpecimen PreparationPreparation (SEM): (SEM): SputteringSputtering

glow discharge

specimen

Ar leak valve

vacuum approx. 10-15Pa (rotary pump)

anode

target (Au,Ag..)

high voltage (-1-3kV, 5-15mA)

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SpecimenSpecimen PreparationPreparation (TEM)(TEM)central requirement:electron transparency – metallic substrates: d= approx. 50...200nm

cutting – grinding and polishing

punching small discs (diameter: 3mm)

thinning

cyclindrical specimen holder

SpecimenSpecimen PreparationPreparation (TEM)(TEM)central requirement:electron transparency by thinning

creating a hole with electron-transparent rimby

electrolythical jet-polishing/thinningor

ion polishing

3mm

80-120µm

electron-transparent rim

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ElectrolythicalElectrolythical PolishingPolishing//ThinningThinning

pump

photo diode

specimen

electrolyte

Ion Ion PolishingPolishing//ThinningThinning

dimple grinding

specimen

dimplegrinder

ion polishing Ar+ Me

vacuum chamber

Ar+ guns

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SpecimenSpecimen PreparationPreparation bybyFocussedFocussed Ion Ion BeamBeam MillingMilling (Ga(Ga++))

FEI dual beam (Ga+/FE-SEM) laser-processed LiNbO3

SpecimenSpecimen PreparationPreparation bybyReplicaReplica TechniqueTechnique

polycrystalline Al2O3

vapor deposition

electron transmission

intensity

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SpecimenSpecimen PreparationPreparation bybyExtractionExtraction ReplicaReplica TechniqueTechnique

Mo2C / M23C6 carbidesin 10 CrMo 9 10 steel

1 differential etching2 film application3 matrix etching

TEM TEM SpecimenSpecimen Holder (Double Holder (Double TiltTilt))

retainer / circlip

tweezers

specimen support

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4 Main 4 Main ComponentsComponents(TEM/SEM)(TEM/SEM)

TEM HV generation(up to 1200kV !!)

window

SEM SEM –– SchematicSchematic RepresentationRepresentation

vacuumchamber

e- gun

column(lenses,apertures)

detectore- beam(focussed/scannedon specimen)

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SEM SEM –– SchematicSchematic RepresentationRepresentationfilament high voltage

(30kV)

anode

IGP

electron beam

column (upper part 10 mbar)-8

Wehnelt cap

apertures

monitorcondenser lenses

objective lens

aperture

specimen

scanning coils

vacuum system rough pump/ODPBSE detectorSE-detector

vacuum chamber (10 mbar)-5

stigmator

vacuum system

filament (cathode)Wehnelt capanode

condenser lenscondenser aperture

specimenobjective lens

obejctive aperture

selector apertureintermediate lens

projective lens

fluorescent phophorous screencamera

diffracted intensities

200 kVTEM TEM –– SchematicSchematicRepresentationRepresentation

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Rotary (Rotary (vanevane) pump ) pump --DrehschieberpumpeDrehschieberpumpe

specimen chamberintake fitting

outlet valve

oil

statorslide (Schieber) with spring

rotor

volume increase

VacuumVacuum System:System:Oil Diffusion Pump Oil Diffusion Pump --ÖÖldiffusionspumpeldiffusionspumpe

chamber10-6 mbar

rotarypump

water

water

evaporating oilheater

deflected oil vapor sweepsgas molecules away

baffle

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MolecularMolecular Drag PumpDrag Pump--TurbomolekularpumpeTurbomolekularpumpe

chamber(10-6mbar)

rotor

magnet bearing

rotary pump

stator

Ion Ion GetterGetter Pump Pump -- IonengetterpumpeIonengetterpumpe

Ti atomsgas atoms

ionselectrons

cathode:-4 - -6 kV

ionisation

2. adsorptionat getter film

1. collisionions with cathode

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LaBLaB66 FilamentFilament

heating current

LaB6 single crystalgraphite ring

ceramic base

heating rod

FEG FEG FieldField Emission Emission GunGun

W single crystal sharp tip (diameter <100nm)

extractionvoltage

HV

(E>107V/cm)

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WehneltWehnelt capcap –– WehneltWehnelt ZylinderZylinder

filament tip

Wehnelt cap

height adjustment

WehneltWehnelt capcap –– WehneltWehnelt ZylinderZylinder

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WorkingWorking PrinciplePrinciple::

ElectromagneticElectromagnetic LensLens

electron

Lorentz forceF=-e(v x B)(electron velocity x magnetic flux density)

WorkingWorking PrinciplePrinciple::

ElectromagneticElectromagnetic LensLens

f

1/f=1/q+1/p

Br: rotational force on e- => rotation

Bz: radial force on e- => focussing

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CondenserCondenser//ObjectiveObjective LensLens

condenser lens

obejective lens

d2 final spot size

f focus

weak excitation strong excitation

electrons that donot pass throughfinal lens aperture

max. probe current min. spot size

InfluenceInfluence of of thethe Spot Spot SizeSize (SEM)(SEM)

spot size:

resolution lowhigh

noise lowhigh

SE signal low high

SE imaging

BSE imaging

EDS microanalysis

1 2 3 4 5 6

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InfluenceInfluence of of thethe ApertureAperture Diameter (SEM)Diameter (SEM)(XL30 (XL30 fixedfixed))

final aperture

focus depth

resolution lowhigh

noise

SE imaging

EDS microanalysis

lowhigh

lowhigh

ObjectiveObjective LensLens withwith AsymmetricalAsymmetricalPole Pole PiecesPieces (SEM)(SEM)

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ScanningScanning(SEM, also(SEM, alsoSTEM)STEM)

objective lens

aperture

final aperture: D

specimen

scanning coils(Ablenkspulen)

stigmator

z

x

y(movement by motor stage)

tilt

electron beam

scanned section/gerasterter Probenausschnitt

Image Generation in Image Generation in thethe SEMSEMinteractions electron beam <=> specimen surfacesecondary electronsback-scattered electronsX-rays

B x B

1000 linesdepthof focus T

b x b

δ

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44 InteractionsInteractions ElectronsElectrons Matter Matter --ElectronElectron Contrast Contrast SEMSEM

55 Electron Diffraction Electron Diffraction --Electron ContrastElectron Contrast TEMTEM

6 SEM 6 SEM Channeling ContrastChanneling Contrast and and Electron Diffraction TechniquesElectron Diffraction Techniques

InteractionsInteractions ElectronsElectrons MatterMatter

KLM

electron beam

stroke out of secondary electron

nucleus

elastically deflected electron=> BSE

=> SE

KL

M

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ElectronElectron Penetration Penetration DepthDepth

ca. 1-10nm

SE1SE2

BSE X rays

penetration depth(dependent on E )R 0

ca. 0,5R

electron beam

Auger-e-

specimen current

specimen

AE

SE BSEN(E)

50 eV (convention)

E02 keV E

ElectronElectron Penetration Penetration DepthDepthfoil on Cu grid

HV: 1kV 3.5kV 20kV

polymer

copper

diameter of the interaction volume: approx. 2µm

polymer

copper

polymer

copper

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SecondarySecondary ElectronsElectrons (SE) (SE) DetectorDetector

SecondarySecondary ElectronsElectrons (SE) (SE) DetectorDetectorEverhart Thornley Detector

specimen light guide photo multiplier(successive acceleration+multiplication at dynodes)

collector+300V

scintillator photo cathodebehind quartz window

electrical signal

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ContrastContrast Formation: Formation: TopographyTopography & & EdgesEdges

primary electron beam (PE)

α

SEPE

I

x

Human Human HairHair

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SecondarySecondary ElectronsElectrons GainGain

σ: leaving electrons/incident electrons

δ: SE gain

η: BSE coefficient

negative charging conductive specimens!

E0

BackBack--ScatteredScattered ElectronsElectrons (BSE) (BSE) DetectorDetector

BSESE

electron beam

+

amplifier

Al coating

goldn silicon-

p silicon+

SE-Detektor

BSE-semiconductordetector

elastic scattering

inelastic collision BSE at detector ⇒generation of electron/hole pairsp/n transition inhibits recombination

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BSE BSE DetectorDetector

SE Detector

Material Material ContrastContrast

light elements (low Z) – darkheavy elements (high Z) - bright

Al-Si alloy (with Si precipitates)SE image BSE image (same position)

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ContrastContrast informationinformation::Material Material and and TopographyTopography

BSE detectorB A

55 Electron Diffraction Electron Diffraction --Electron ContrastElectron Contrast TEMTEM

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ElectronElectron DiffractionDiffraction -- BraggBragg‘‘ss lawlaw

x x

d

Θ

primary electronbeam diffracted intensity

lattice planes

2x = 2d sin Θ = Nλ

transmitted intensity

E0=100kV: λ=0.0037nm, Cu (111) planes => Θ=0,5°

DebyeDebye--ScherrerScherrer Diagrams of Diagrams of PolycrystalsPolycrystals

500nm

selected area diffraction TEM micrograph (TlCl standard)

electron beam

specimen

diffraction rings (DS diagrams)

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ElectronElectron DiffractionDiffractionin in thethe TEMTEM

vacuum system

filament (cathode)Wehnelt capanode

condenser lenscondenser aperture

specimenobjective lens

obejctive aperture

selector apertureintermediate lens

projective lens

fluorescent phophorous screencamera

diffracted intensities

200 kV

diffraction spots

Bragg diffraction at lattice planes

2Θ

x

yz

TheThe ReciprocalReciprocalLatticeLattice

reciprocal lattice

camera length L

real lattice

2d sin Θ = Nλ (Bragg)2d Θ ≈ Nλ

R

Θ2Θ

2Θ = tan R/L (geometry)Θ ≈ R/2L

Θ: very small!beam || zone axis

d R = λ Ldiffraction constant

R = const./d

g

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TheThe ReciprocalReciprocal LatticeLattice

R: phosphorous screeng: reciprocal lattice

000420

R2

R1

Evaluation of Evaluation of DiffractionDiffraction Pattern Pattern R2/R1

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DiffractionDiffractionPatternPatternforfor different different Zone Zone AxisAxis

[101] [111]

[211] [100]

[110] [111]

fcc

bcc

KinematicalKinematical TheoryTheory

αβ

x

y

rk0

k

change of wave direction at the atoms => amplitude/phase differences

primary beam (λ)

secondary waves (λ)

( )∑=n

nn ifA ϕexpresultant amplitude:

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TheThe Ewald Ewald SphereSphere

primary beam

lattice planes

s

ko>>gplane of the

diffraction pattern

k

k0

gΘ 2Θ

TheThe Ewald Ewald SphereSphere

two-beam case(Bragg case)

symmetrical case(Laue case)

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Amplitude Phase DiagramsAmplitude Phase Diagrams

OriginOrigin of of WedgeWedge FringesFringes 11

diffracted intensity 0 max 0 max .....

transmitted intensity I0 min I0 min ......

image bright dark bright dark ......

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OriginOrigin of of WedgeWedge FringesFringes 22

diffractedtransmitted

edge

boundary

StackingStacking FaultsFaults

stacking faults in Al-20Sifrom: Hornbogen/Skrotzki: Werkstoffmikroskopie, Springer 1993

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BendBend ContoursContours

Al + Ge particlesfrom: Hornbogen/Skrotzki: Werkstoffmikroskopie, Springer 1993

+ΔΘ

-ΔΘ

DislocationsDislocations

b

g

image

primary beam

Burgers vector

diffracted beam planar dislocation arrangement (Ti alloy LCB, Δσ/2=600MPa)

500nm

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DislocationsDislocations: : PilePile--UpUp at at GrainGrain BoundaryBoundary

grain boundary

DislocationsDislocations ––HighHigh--Resolution Resolution TEMTEM

Si single crystal(image taken at magnific. 30000000)

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ConvergentConvergentElectronElectronDiffractionDiffraction ––KikuchiKikuchiPatternPattern

convergent electron beam

specimen

Kossel cone

bright line (dark line)

Fe alloy

[110]

[111]

[211]

66 SEM SEM Channeling Contrast Channeling Contrast and and Electron Diffraction TechniquesElectron Diffraction Techniques

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InfluenceInfluence of of thethe TiltTilt Angle on Angle on thetheBSE BSE contrastcontrast

ChannelingChanneling ContrastContrastelectron beam electron beam

crystalline lattice

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ImagingImaging of of DislocationDislocation StructuresStructures

PSB in deformed single-crystalline Cu (R. Richter, TU Dresden)

ElectronElectron ChannelingChanneling PatternPattern

Si single crystalSi single crystal„rocking beam“

incident e- beam

„scanning“

lattice planes lattice planes

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BraggBragg‘‘ss lawlaw

x x

d

Θ

primary electronbeam diffracted intensity

lattice planes

2x = 2d sin Θ = Nλ

TheThe EBSD EBSD TechniqueTechnique((electronelectron backback--scatteredscattered diffractiondiffraction))

striping (streifender)incident electron beam

46

BraggBragg DiffractionDiffraction of of ElectronsElectrons

x x

phosphorous screen:intersection with cone => parallel lines

Kossel cones

Θ

TheThe EBSD EBSD TechniqueTechnique

quartz window

phosphorous screen

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EBSD EBSD CalibrationCalibration

Si single crystal specimen – known orientation

[111]

[011][001]

StereographicStereographic ProjectionProjection

[001]-directions

N

S

standard projection of cubic lattice

[001] [010]

[100]

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1 SEM image2 EBSD pattern

EBSD EBSD measurementsmeasurements

3 indexing

4 pole figure

OrientationOrientation ImagingImaging MicroscopyMicroscopy

Hough transformation:

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OrientationOrientation ImagingImaging MicroscopyMicroscopy

different colors correspondto individual orientations

micro texture analysisgrain boundary engineeringphase analysis...

7 Analytical Electron Microscopy

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XX--Ray EmissionRay Emission

KLM

electron beam

nucleus

electron changesenergy level =>characteristic X-rays

electron deceleration in the Coulomb fieldcontinuous X-rays(Bremsstrahlung)

KL

M

CharacteristicCharacteristic XX--RaysRays

incident electron (PE) emitted electron

K

L I

L IIL III

1s

2s

2p

1. ionisation

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CharacteristicCharacteristic XX--RaysRays2. X-ray emission

K

L I

L IIL III

characteristic X-raysKα1

1s

2s

2p

XX--Ray Ray CharacteristicCharacteristicEnergiesEnergies

Z

Fe

M

K

L

α β

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Intensity

Energy E

Lα

Κα

Lβ

Κβ

characteristic X-rays

Bremsstrahlung

E0

EDS EDS spectrumspectrum((energyenergy dispersivedispersive XX--rayray spectroscopyspectroscopy))

I

E

example: brass (Messing)

[keV]

EDS EDS detectordetector

Cu-rod in vacuum

N (l)2

specimen take-off angle

PE

UTW(ultradünnes Polymerfenster)

Si(Li)

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EDS EDS detectordetector

X-Ray quantum

Au contactSi(Li) crystal

Al layer

FET-preamplifier(field effect trasnitsor)

voltage step: mV/ns

500-700 V

generation of electron/hole pairs

Si inactive layer (Totschicht)

LEDmain amplifier/ADC

multi chanel analyzer

X-ray energy

t

Pulse Pulse PilePile UpUp

X-ray energy

t

peak too high due topulse pile up

within DT -> reject100µs = DT (dead time)

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Pulse Pulse PilePile UpUp

input (cps)

output

no signal anymore:pulse pile up

SumSum PeaksPeaks

2 Al Kα X-rays simultaneous

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EscapeEscape PeakPeak

Cu Kα quantum generates Si Kα quantum

RegionsRegions of of InterestInterest –– Line Line ScanScan

energy

example: brass (Messing)intensity

energy

Background (noise/Bremssstrahlung))improvement by narrow energy window

intensity

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RegionsRegions of of InterestInterest –– Line Line ScanScan

NiCrMo-Schicht

Stahl

NiCrMo scale

steel

Element Element MappingMapping

Al Ti

100µm

57

Monte Carlo SimulationMonte Carlo Simulation

characteristic Ta X-rays

WDS WDS crystalcrystal spectrometerspectrometer((wavelengthwavelength dispersivedispersive XX--rayray spectroscopyspectroscopy))

x x

d

Θ

λ

Bragg: 2x = 2d sin Θ = N λ

characteristic X-rays diffracted X-rays (certain λ)

proportional counter(Proportionlazählrohr)

lattice constantof the crystal

(Monochromatorkristall)

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WDS WDS crystalcrystal spectrometerspectrometer

electronbeam (PE)

Θ

r

r =2rKrist.

crystal (Johannson)on Rowland circle

proportional counter

Gas Gas FlowFlow Proportional Proportional CounterCounter

Ar outlet Ar inlethigh voltage (+1 to +3kV)

signal(to pre amplifier)

isolator

FPC window

X-rays are absorbed by Ar atoms => ejection of photo electrons(up to 50000 counts/s – amplification up to 2000)

thin wire (W)

x-ray photon

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ComparisonComparison EDS/WDSEDS/WDS

EDS

WDS

characteristic X-rays emission line

natural width

Quantitative XQuantitative X--Ray AnalysisRay Analysis=> => backgroundbackground subtractionsubtraction

continuous Bremsstrahlung – absorption (<2keV)background modeling or background filtering

2 4 6 8

energy [keV]

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Quantitative XQuantitative X--Ray AnalysisRay Analysis=> => GeometryGeometry of of thethe DetectorDetector

working distance W (10mm), intersection distance d (10mm),elevation angle E (35°), azimuth angle A (45°), Scale S (50mm)surface tilt M (0°) => TAKE OFF=35°TEM different !!

Quantitative XQuantitative X--Ray AnalysisRay Analysis=> ZAF => ZAF CorrectionsCorrections

atomic number effect (Z)

Fe+Cr

electron beam (PE)

FeCr alloy

Cr

BSE yield(different to pure

substances)

TEM:thin foil!!

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Quantitative XQuantitative X--Ray AnalysisRay Analysis=> ZAF => ZAF CorrectionsCorrections

absorption (A) and fluorescence effects (F)

Fe+Cr

electron beam (PE)

FeCrNi alloy

Cr

Fe

Fe

Feabsorption

Fluorescence

8 Case Studies & Discussion

62

BiologicalBiological SpecimensSpecimens

fly – detail of the wing surface - vacuum dried(alterantive: environmental SEM)

Phase Phase CharacterizationCharacterizationTi nitride in NiCr alloy (deep etched/EDS)

63

Phase Phase CharacterizationCharacterizationTi sulfide in CMSX-6 (polished and Au sputtered)

Phase Phase CharacterizationCharacterization

γ´phase in SRR99 (electropolished - perchloric and acetic acid)

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Phase Phase CharacterizationCharacterization/Analysis/Analysis((γγ´́phasephase in in NiNi--basebase superalloysuperalloy CMSXCMSX--6)6)

200nm

EDS 1

EDS 3

EDS 2

FractureFracture SurfacesSurfaces

striations dimples

65

DamageDamage AnalysisAnalysis

broken implant (=> metal fatigue)

3D Images of 3D Images of FractureFracture SurfacesSurfaces

about 5° tilt

66

DamageDamage AnalysisAnalysiscorrosioncorrosion –– EDS EDS analysisanalysis