MENA 3100: - PowerPoint Presentation

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MENA 3100: - PPT Presentation

Diff Analytical Transmissions Electron Microscopy TEM Part I The microscope Sample preparation Imaging Part II Diffraction Defects Part III Spectroscopy Repetision Electron Diffraction ID: 268568

3100 spectroscopy eels mena spectroscopy 3100 mena eels loss energy eds shell electron band electrons peak imaging sample eftem ray diffraction dispersive

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Slide1

MENA 3100:

Diff

Analytical

Transmissions Electron Microscopy (TEM)

Part I:

The microscope

Sample preparationImagingPart II:DiffractionDefectsPart IIISpectroscopy Slide2

Repetision

Electron Diffraction:Powder X-ray diffraction:Small wave lengthLarge Ewald

sphere -- Perfect crystals planeVery sensitive to changes in the crystal structureSmall diffractionStrong intensity – short exposure timeDirectly

observed on the viewing screenObtained from very small crystals

Larger wave lengthSmall Ewald sphere Ring patternLarger driffrationangle

Lower intensityEasier to interpretSlide3

Coherent

incident

high

-kV beamSecond electronsFrom within the specimen (SEM)Incoherent elasticbackscattered electrons (SEM)Direct beam(imaging, diffraction, EELS)Coherent elasticscattered electrons (STEM, Diffraction, EELS)

Incoherent elasticforward scattered

Electrons (STEM, diffraction,EELS)

Incoherent

inelastic

scattered

electrons

(EELS)

Auger

electrons

(XPS)

Characteristic

X-rays

(EDS)

Visible

light

Bremsstrahlung

X-rays

(EDS)

sample

Sample

Electron matter interactionsSlide4

MENA 3100: Spectroscopy

The characteristic energy transitions

Observable with EELS and EDSSlide5

MENA 3100: Spectroscopy

K shell

L shell

M shell

Valence electrons

Empty statesSlide6

MENA 3100: Spectroscopy

Empty states

K shell

shell

2,3

α1

EDS

EELS

α1Slide7

MENA 3100: Spectroscopy

Energy dispersive X-ray spectroscopy

MSlide8

K-

edge

(Si) – 1s orbital

Conduction

band

Filled

bands

L-

edge

(Si)

– 2s and 2p orbital

(K)=

-E(

cond.band

-K)

(L)=

-E

(

cond.band

-L)EELSSlide9

MENA 3100: Spectroscopy

Energy Dispersive

X-ray

Spectroscopy(EDS) Slide10

MENA 3100: Spectroscopy

EDS spectrumSlide11

MENA 3100: Spectroscopy

X-ray Spectroscopy

EDS: Energy Dispersive

Spectroscopy EDXS: Energy Dispersive X-ray SpectroscopyX-EDS: X-ray Energy Dispersive Spectroscopy EDX: Energy Dispersive X-ray analysisSlide12

MENA 3100: Spectroscopy

QuantificationPeak

intensities are proportional to concentration and specimen thickness. They removed the effects of variable specimen thickness by taking ratios of intensities for elemental peaks and introduced a “k-factor” to relate the intensity ratio to concentration ratio:

Each pair of elements requires a different k-factor, which depends on detector efficiency, ionization cross-section and fluorescence yield of the two elements concerned. Slide13

MENA 3100: Spectroscopy

The DetectorSlide14

MENA 3100: Spectroscopy

Detection MechanismSlide15

Oxford

MENA 3100: Spectroscopy

MENA 3100: SpectroscopySlide16

MENA 3100: Spectroscopy

EDS SEM

TEMSlide17

MENA 3100: Spectroscopy

EDS mappingSlide18

MENA 3100: Spectroscopy

Recent advancesSlide19

MENA 3100: Spectroscopy

Comparison Low Z elementSlide20

MENA 3100: Spectroscopy

Comparison on resolutionSlide21

MENA 3100: Spectroscopy

Artefacts in EDS

Si escape peak:A small fraction of the energy is lost and not transformed into electronhole pairs2. Sum peak:

Two photons will enter the detector at exactly the same time. The analyzer then registers an energy corresponding to the sum of the two photons. Likely to occur if:- The input count rate is high.

- The dead times are > 60%.- There are major characteristic peaks in the spectrum.Slide22

MENA 3100: Spectroscopy

3. Fluorescence: This is a characteristic peak from the Si (or Ge) in the detector dead layer.

Sample preparation artefacts (ion milling , grids, reaction to solvent)Cu/Ni slotThickness variations due to millingContaminants and reaction productsSlide23

MENA 3100: Spectroscopy

Electron Energy Loss Spectroscopy

(EELS)Slide24

MENA 3100: Spectroscopy

Omega filterSlide25

MENA 3100: Spectroscopy

Gatan Imaging Filter (GIF)

Post column energy filterSlide26

Electron

gun

Condenser aperture

Sample holder

Objective

aperture

Objective lensDiffraction lensIntermediate apertureIntermediate lensProjector lensesFluorescent screen

Gatan Imaging FilterFor EELS

Microscope outlineSlide27

MENA 3100: Spectroscopy

MENA 3100: SpectroscopySlide28

magnetic prism

Beam

trap

apertureSlitMultipole lenses

Detector

Projector

crossover

Viewing

screenSlide29

MENA 3100: Spectroscopy

Energy Losses

Zero Loss (includes quasi-elastic scattering)Intra-/Inter-band transitions (band gap)

Cherenkov lossesBremsstrahlung

Plasmon lossesCore lossesSlide30

MENA 3100: Spectroscopy

EEL Spectral backgroundSlide31

Low

-Loss EELS

Core

-Loss EELSSlide32

Low

-Loss EELSSlide33

Elastic

scattering

Coulomb

attraction

nucleus

Inelastic

scattering

Coulomb

repulsion

(

outer

shell

electrons

)

Zero Loss Peak

Single electron outer shell

excitationSlide34

MENA 3100: Spectroscopy

The Zero Loss Peak (ZLP)Slide35

Low

-Loss EELS: Bulk

plasmons

Plasmon

peakh: Planck constantN: n/V : Valence electron densitye: Elementary chargeme: Electron massεO: Permittivity of free

spaceOuter-shell inelastic scattering involving many atoms of the solid.

Collective effect is known as a plasma resonance

oscillation

of the valence electron densitySlide36

Low

-Loss EELS:

Surface plasmonsZLP

Surface plasmon (Es):Vacuum

/metal interface:

Dielectric/metal boundary:

Interface between two metals:

Thøgersen,et

al.

Journal

Applied

Physics

109, 084329 (2011).

Slide37

Low

-Loss EELS: Energy

filtering

Kundmann

M.,

Introduction to EELS in TEM, EELS course 2005 San FranciscoSlide38

Low

-Loss EELS: Energy

filtering

Kundmann

M.,

Introduction to EELS in TEM, EELS course 2005 San FranciscoSlide39

Low

-Loss EELS: Energy

filtering

TEM image

ITO

EFTEM imaging of Si/aSi/ITO (Indium Tin Oxide) stack sample for RECSlide40

Low

-Loss EELS: Energy

filtering

EFTEM (16 eV) EFTEM (23 eV)

TEM image

EFTEM imaging of Si/

aSi

/ITO (Indium Tin Oxide) stack sample for RECSlide41

Low

-Loss EELS:

Thickness

t =

thickness

λp = plasmon mean free pathIp = Intensity of the plasmon peakIo = Intensity of the zero loss peak Slide42

Core

-Loss

EELS (Energy-Loss Near-Edge

Structure)Slide43

K-

edge

(Si) – 1s orbital

Conduction

band

Filled

bands

L-

edge

(Si)

– 2s and 2p orbital

(K)=

-E(

cond.band

-K)

(L)=

-E

(

cond.band

-L)Slide44

Core

-Loss EELS: Peak

shapeShape of the edge is a signature of the transition: K-edges: 1s states -- typical sawtooth

profileL2,3-edges -- have a delayed maximum but can contain intense narrow peaks at the onset, known as “white lines”, corresponding to transitions to narrow d bands.Slide45

MENA 3100: Spectroscopy

MENA 3100: SpectroscopySlide46

MENA 3100: Spectroscopy

MicroanalysisSlide47

MENA 3100: Spectroscopy

EFTEM:Slide48

MENA 3100: Spectroscopy

MENA 3100: SpectroscopySlide49

MENA 3100: Spectroscopy

STEM-SIEFTEM-SI

Spectral Imaging (SI)

B.Chaffer