Pedro. L. Grande

(UFRGS-Brazil)

Recent advances of Recent advances of MEIS (mediumMEIS (medium--energy ion scattering) energy ion scattering)

for near surface analysisfor near surface analysis

1. Introduction (MEIS)

2. Recent Advances

• Nanoparticles (NPs) Analysis

• Simple NPs : Au NPs on Polyeletroyides

• Core-shell NPs: CdSe

• Buried NPs: Pb Nanoisland and Fe NPs

• Simple approach for the 2D MEIS spectra for crystal

3. Conclusions

OutlineOutline

Techniques Techniques (Surfaces/Interfaces/Nano)(Surfaces/Interfaces/Nano)

•XPS

•AES

•LEED

•STM

•Electron microscopic

•EXAFS,

•Raman,

•... Ion Beam Techniques

http://lnmsf.irb.hr/techniques.htm

Ion Beam TechniquesIon Beam Techniques

Improved

depth and mass

resolution

Surface sensitivity

H+

(amorphous)

(crystal)

Ion Scattering Ion Scattering -- MEISMEIS

Penetrating (can access buried interfaces!)

Mass specific

Known interaction law (cross sections are known) – quantitative technique – can determine absolute number of atoms in the sample

Excellent depth resolution

Non-destructive

MEIS MEIS -- AdvantagesAdvantages

MEIS data collectionMEIS data collection

Energy SpectrumEnergy Spectrum Angular SpectrumAngular Spectrum

Yield

Energy

Sca

tter

ing

Ang

le

Yie

ld

Deconvolution of ES gives depth

profile (primarily for amorphous

thin films).

MC ion scattering simulation of

angular yield provides surface

structure.

Schulte H. (Private communication)Schulte H. (Private communication)

MEIS SpectrumMEIS Spectrum

Angle

Ener

gy

Summed over 2 degrees around = 60o

93.0 93.5 94.0 94.5 95.0

0.0

0.5

1.0

1.5

2.0

2.5

3.0

= 60o

Co

un

ts (

arb

. u

nit

s)

proton energy

MEIS userMEIS user CommunityCommunity

• Depth profiling (amourphous)

•High-k materials

•Thin films

…

• Structural determination

•Heterogeneous catalysis

•Surface reconstruction

…

Recent Developments (MEIS)Recent Developments (MEIS)

New detectors (MEIS 3D, TOF-MEIS)

Strain measurements

Organic and biological materials analysis

Better understanding of the energy-loss processes

(ab-inito, simple-models)

Nanoparticle/Nanoislands/Quantum dots analysis

Full description of the 2D MEIS spectrum for crystals

MEIS for MEIS for NanoparticlesNanoparticles

MEIS Potentiality MEIS Potentiality

Depth profiling elements

inside a NP

EnergyEnergy--loss asymmetryloss asymmetry

Depth profile oDepth profile or energyr energy--lossloss asymmetry ???asymmetry ???

60 80 100 120

0.0

0.5

1.0

1.5

Bac

ksca

ttred

Ions

Energy

Ab-initio (coupled-channel calculations)

Analytical formula

Simple models (CasP program)

Investigations on Investigations on the asymmetry of energythe asymmetry of energy--loss distributionloss distribution

(Grande and (Grande and SchiwietzSchiwietz))

0 50 100 150 200 250 300 350 400 450 500 550 6000.000

0.005

0.010

0.015

0.020

M-shell H+(100keV) + Al

L-shell

dP

/dE

(eV

-1)

Energy Transfer ( E) (eV)

Exp. decay

Gaussian

Exponentially Modified Gaussian (EMG)

d

f(x) = exp(-(a x + exp(-ax))/2)

Exp. decay

not Gaussian

Moyal

f(x) = exp(-(ln(x)- )2/2

2)/x

Lognormal

d

distributions

distributions

Asymmetric Gaussian

21

P.L. Grande, G. Schiwietz, Ionization and energy loss beyond perturbation theory,

Advances in Quantum Chemistry, Vol 45 (2004) 7-46.

NIMB 256 (2007) 92

Surface Science 601 (2007)5559

PRL 102 (2009) 096103

Where does the asymmetry come from ?

• Single hard collision (b ~ 0)

• Statistical : # of collisions

correlated or uncorrelated

Asymmetry very important Asymmetry very important for ultrafor ultra--thin films !thin films !

Pezzi at al. Surface Science 601 (2007) 5559

NanoparticleNanoparticle analysisanalysis

NanoparticlesNanoparticles

Full Monte-Carlo Simulation

• any geometrical shape (sphere, cylinder,..)

• density distribution

• size distribution

• asymmetrical lineshape

Full 3D MonteFull 3D Monte--Carlo IntegrationCarlo Integration ((PowerMeisPowerMeis program)program)

outiout

in

EEKE

EEE

1

01

)(

E0

E1

Eout

Sample descriptionSample description PowerMeisPowerMeis GUIGUI

Giant 3D matrix (of matrices)Giant 3D matrix (of matrices)

Pair correlation function g(r)

Shape sensitivityShape sensitivity

Influence of the asymmetry:Influence of the asymmetry: backscattering collisionbackscattering collision

Au

false geometrical shape

false size distribution

NanoparticlesNanoparticles (asymmetrical (asymmetrical lineshapelineshape))

Diameter t > 5nm

Diameter t < 5nm

120 140 160 180 200 220 240 260 280 300 320

96.5

97.0

97.5

98.0

98.5

99.0

99.5

80% 1 nm + 20% 4 nm Au spheres - Gaussian lineshape

Angle (deg)

En

erg

y (

ke

V)

0

1.238E5

2.477E5

3.715E5

4.953E5

6.191E5

7.430E5

8.668E5

9.906E5

1.114E6

1.238E6

1.362E6

1.486E6

1.585E6

120 140 160 180 200 220 240 260 280 300 320

96.5

97.0

97.5

98.0

98.5

99.0

99.5

1nm Au spheres - EMG lineshape

Angle (deg)

En

erg

y (

ke

V)

0

1.160E5

2.320E5

3.480E5

4.641E5

5.801E5

6.961E5

8.121E5

9.281E5

1.044E6

1.160E6

1.276E6

1.392E6

1.485E6

For the full 2DFor the full 2D MEIS spectrum !MEIS spectrum !

Gaussian Asymmetric

NanoparticleNanoparticle analysis analysis -- applicationsapplications

I – Au NPs in polyelectrolytes multilayered films

PolyelectrolytePolyelectrolyte (PE)(PE)

charged polymers

films can be tuned with desired composition and thickness

can be deposited onto different substrates

can be easily removed after nanomaterials synthesis

Au NPs adsorbed in polyelectrolyteAu NPs adsorbed in polyelectrolyte

TEMTEM NPs on the surfaceNPs on the surface

MEIS results (100 MEIS results (100 keVkeV HH++))

M.A. Sortica et al. JAP (2009)

Energy spectrum (1D)Energy spectrum (1D)

Geometrical shape

Size distribution

Good agreement with TEM !

M.A. Sortica et al. JAP (2009)

NP NP interactioninteraction withwith PE PE filmfilm Depends on both Au colloid and PE assembling

procedure

MEIS characterization of nanoparticles on the PE surface

Further MEIS results (100 Further MEIS results (100 keVkeV HH++))

G. Machado et al. Nanoscale 3, (2011)1717

NanoparticleNanoparticle analysis analysis –– applications applications

II – Core-shell characterization of CdSe/ZnS quantum dots

Quantum Quantum dotsdots CdSeCdSe//ZnSZnS

Nanocrystals

Absorption and emission depends on composition and size

Higher efficiency in fluorescence process

Thin band gap

CoreCore--shellshell analysisanalysis ofof CdSeCdSe//ZnSZnS quantum quantum dotsdots

Diluted in toluene at 3.82 g/L

Deposited on SiO2/Si(100) substrate

Liquid sample – EviDots (maple red-orange) in toluene solution – 2.2 mg/L

MEIS MEIS analysisanalysis (150 keV He(150 keV He++))

MEIS analysis MEIS analysis –– 3 angles3 angles

100 110 120 130

0

50

100

150

200

250

300

350

400

100 110 120 130 140100 110 120 130 140

S

SeSe

CdCd

= 128 degrees = 120 degrees

C

oun

ts

= 112 degrees

Cd

Se

S

Experimental

Simulated

Energy (keV)

Zn Zn

Zn

MEIS analysisMEIS analysis

Core stoichiometry Cd0.65Se0.35

Core diameter 5.0 nm

Shell stoichiometry Zn0.41S0.59

Shell thickness 0.6 nm

TEM ResultsTEM Results

TEM spatial and size distribution

MEIS core and shell characterization

3 4 5 6 70

10

20

30

40

# N

Ps

nm

Dr. DaeWon Moon

Buried Buried NanoparticlesNanoparticles ??

NanoparticleNanoparticle analysis analysis –– applications applications

III – Burried Pb NPs ion implantation

Pb nanoislands at SiOPb nanoislands at SiO2 2 / Si/ Si

• Produced by ion implantation (300 keV Pb)

• Thermal annealing : 200oC (100 hours) + 1100oC (1 hour)

• Two SiO2 thicknesses (different etching times)

45 and 65 nm

SiO2 Si

2 D array

3.7x1011 NPs/cm2

PbPb nanoislandsnanoislands : TEM : TEM imagesimages

Cross-section Plan view

MEISMEIS results (100 results (100 keVkeV HeHe++))

thinner (45nm) thicker (65nm) SiO2

SimulationsSimulations ((PowerMeisPowerMeis programprogram))

Same amount of Pb

3.3 x1022 Pb/cm2

Pb Film Experiment

2x1011 NPs/cm2 6x1011 NPs/cm2

• Film (thickness = 0.7nm)

• NPs 1. V = 350 nm3 (2x1011 NPs/cm2)

2. V = 100 nm3 (6x1011 NPs/cm2)

Usual dataUsual data analysisanalysis

60 70 800

20

40

60

Experiment

2.1011

NPs cm-2

6.1011

NPs cm-2

S

Energy (keV)

= 130 deg

Advanced dataAdvanced data analysisanalysis

ExperimentalExperimental vs. Simulationsvs. Simulations

66 68 70 72 74 76 78 800

500

1000

C

ou

nts

(a

.u.)

Energy (keV)

Experimental

Film

2.0x1011

NPs/cm2

3.5x1011

NPs/cm2

6.0x1011

NPs/cm2

TEMTEM pplan lan vviewiew

3.7 x 1011 NPs/cm2

MEIS (best fit) (4.5 ± 1.5) x1011 NPs/cm2

66 68 70 72 74 76 78 800

500

1000

Co

un

ts (

a.u

.)

Energy (keV)

Experimental

Simulation

Where do they deviationsWhere do they deviations come from ?come from ?

atomic Pb ?

NP Size Distribution ?

some NPs in SiO2

Multiple Scattering Effects ?

some NPs in Si (bulk)

EnergyEnergy SpectraSpectra

MS important for < 115 deg !

68 70 72 74 76 78 80

Experimental

Film

TEM

Sphere

Counts (a. u.)

6 x1011

NPs/cm2

Experimental

Film

TEM

Sphere

Co

un

ts (

a. u

.)

3.5x1011

NPs/cm2

Experimental

Film

TEM

Sphere

2x1011

NPs/cm2

Shape Sensitivity Shape Sensitivity

D.F. Sanchez et al. Surface Science 605 (2011) 654

NanoparticleNanoparticle analysis analysis –– applications applications

IV – Burried Au NPs sputtering

SiO2

Au (sputtering)

Si (bulk)

56

SiO2 (sputtering)

SiO2

Au (sputtering)

Si (bulk)

3.1 3.1 ×× 10101515 Au atoms/cmAu atoms/cm22

7.4 7.4 ×× 10101515 Au atoms/cmAu atoms/cm22

1.8 1.8 ×× 10101515 Au atoms/cmAu atoms/cm22

~40 n

m~

40 n

m

Porto Alegre,

Brazil

57

58

25s

Au dissolved

into the SiO2

44 %

9.0 × 1011 NP/cm2

NanoparticleNanoparticle analysis analysis –– applications applications

V – Burried Fe NPs Ion implantation

132 136 140 144 132 136 140 144

109º

As implanted

1 minute

109º

120º

Sca

ttere

d I

nte

nsity (

a.

u.)

120º

131º

Energy (keV)

131º

60 J. Kennedy et. al., Nanotechnology, 22, 115602 (2011)

MEIS →

H+ 150 keV

Fe Si

Fe Si

1.0 1.0 x 10x 101616 atoms/cmatoms/cm22

Lower Hutt, New ZealandLower Hutt, New Zealand

Fe Fe surfacesurface

Fe Fe surfacesurface

61

2 2 RRshellshell

2 2 RRcorecore

Statistics and shape from Statistics and shape from TEM as input to obtain TEM as input to obtain shell stoichiometry from shell stoichiometry from MEIS analysisMEIS analysis

131 134 137 140 143

E

Sc

att

ere

d In

ten

sit

y (

a. u

.)

FexSi

33-xO

67

x = 14

x = 20

x = 10

Core@Shell

Fe@FexSi

33-xO

67

131°

120°

109°

62

Fe@FeFe@FexxSiSi3333--xxOO6767 SiOSiO22 density (atoms/cmdensity (atoms/cm33))

Fe

Si

Fe

Si

Fe@FeFe@Fe1414SiSi1919OO6767

XPS + MEIS/TEM

Simple approach for theSimple approach for the full description of the 2D full description of the 2D ––MEIS MEIS

spectrumspectrum-- CrystalsCrystals

Cu(111):[100] InCu(111):[100] In

Blocking curves Blocking curves –– Cu(111)Cu(111) surfacesurface

66

VEGAS Monte VEGAS Monte Carlo SimulationCarlo Simulation

well established in MEIS

just the area of the surface peak

Phit and Pdet

(only the blocking curves !)

ExtendingExtending the VEGAS codethe VEGAS code to include ion scattered energiesto include ion scattered energies

•Bimetallic surfaces

•Thermal vibration correlations

•Dechanneling background

Improve surface determination

68

Energy LossEnergy Loss

0 50 100 150 200 250 300 350 400 450 500 550 600

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

0.016

0.018

0.020

single collision

dP

/dE

(eV

-1)

Energy Transfer ( E) (eV)

Cu (111) single crystalCu (111) single crystal

•single atomic type

•very small relaxation

•previously analyzed by MEIS

A,.Hentz et al. PRL 102, 096103 (2009)

Comparison with Comparison with abab--initio initio energyenergy--loss calculationsloss calculations

Skimming Effect

Coupled-channel calculations are

very time consuming !

A simple model is needed !

Nice but…Nice but…

Simple Model for the impact Simple Model for the impact parameter dependent parameter dependent

energy loss distributionenergy loss distribution

F( E,b) =

Gaussian( E - Q(b), (b)) b > 0

1/ 0

exp(- E) ( E) b =0

Skimming Effect

Simple model

Simple model

Experimental Data

MEIS for NP characterization

1) On the surface : Excellent (using asymmetrical lineshape)

2) Buried NPs : sensitivity for the areal density

no sensitivity for the geometrical shape

MS effects are important

SummarySummary

This opens new perspectives for nanostructure analysis in situ that

can of great interest.

Pitfall : Dissolved atomic species affect MEIS analysis

Summary IISummary II

Simple approach for the full 2D MEIS spectrum (Crystal)

(VEGAS extended)

• Visibility of each layer

• Electronic energy-loss at hard-collision (asymmetric)

• Impact parameter dependent energy-loss

Input parameters : , dE/dx, dW2/dx

Useful to improve surface determination

Summary IIISummary III

80

Jêróme Leveneur, John Kennedy, Jêróme Leveneur, John Kennedy,

NationalNational Isotope Centre, GNS Isotope Centre, GNS ScienceScience

NewNew ZealandZealand

Mauricio, Dario,Agenor, Paulo, AdrianoMauricio, Dario,Agenor, Paulo, Adriano

Giovanna, ClaudioGiovanna, Claudio

UFRGS UFRGS –– Porto AlegrePorto Alegre

GregorGregor SchiwietzSchiwietz

HelmholtzHelmholtz--ZentrumZentrum BerlinBerlin

Phil Phil WoodruffWoodruff

WarwickWarwick DaewonDaewon MoonMoon

KRISSKRISS

Thank you for your attention !

Obrigado !