recent advances of meis for near surface analysis
DESCRIPTION
Apresentação do professor Pedro Grande, da seção UFRGS do Instituto Nacional de Engenharia de Superfície. Palestra convidada do Simpósio Engenharia de Superfície do X Encontro da SBPMAT. Realizada no dia 26 de setembro de 2011 em Gramado (RS).TRANSCRIPT
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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
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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
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Techniques Techniques (Surfaces/Interfaces/Nano)(Surfaces/Interfaces/Nano)
•XPS
•AES
•LEED
•STM
•Electron microscopic
•EXAFS,
•Raman,
•... Ion Beam Techniques
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http://lnmsf.irb.hr/techniques.htm
Ion Beam TechniquesIon Beam Techniques
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Improved
depth and mass
resolution
Surface sensitivity
H+
(amorphous)
(crystal)
Ion Scattering Ion Scattering -- MEISMEIS
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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
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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)
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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
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MEIS userMEIS user CommunityCommunity
• Depth profiling (amourphous)
•High-k materials
•Thin films
…
• Structural determination
•Heterogeneous catalysis
•Surface reconstruction
…
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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
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MEIS for MEIS for NanoparticlesNanoparticles
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MEIS Potentiality MEIS Potentiality
Depth profiling elements
inside a NP
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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
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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
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Where does the asymmetry come from ?
• Single hard collision (b ~ 0)
• Statistical : # of collisions
correlated or uncorrelated
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Asymmetry very important Asymmetry very important for ultrafor ultra--thin films !thin films !
Pezzi at al. Surface Science 601 (2007) 5559
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NanoparticleNanoparticle analysisanalysis
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NanoparticlesNanoparticles
Full Monte-Carlo Simulation
• any geometrical shape (sphere, cylinder,..)
• density distribution
• size distribution
• asymmetrical lineshape
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Full 3D MonteFull 3D Monte--Carlo IntegrationCarlo Integration ((PowerMeisPowerMeis program)program)
outiout
in
EEKE
EEE
1
01
)(
E0
E1
Eout
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Sample descriptionSample description PowerMeisPowerMeis GUIGUI
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Giant 3D matrix (of matrices)Giant 3D matrix (of matrices)
Pair correlation function g(r)
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Shape sensitivityShape sensitivity
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Influence of the asymmetry:Influence of the asymmetry: backscattering collisionbackscattering collision
Au
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false geometrical shape
false size distribution
NanoparticlesNanoparticles (asymmetrical (asymmetrical lineshapelineshape))
Diameter t > 5nm
Diameter t < 5nm
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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
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NanoparticleNanoparticle analysis analysis -- applicationsapplications
I – Au NPs in polyelectrolytes multilayered films
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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
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Au NPs adsorbed in polyelectrolyteAu NPs adsorbed in polyelectrolyte
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TEMTEM NPs on the surfaceNPs on the surface
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MEIS results (100 MEIS results (100 keVkeV HH++))
M.A. Sortica et al. JAP (2009)
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Energy spectrum (1D)Energy spectrum (1D)
Geometrical shape
Size distribution
Good agreement with TEM !
M.A. Sortica et al. JAP (2009)
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NP NP interactioninteraction withwith PE PE filmfilm Depends on both Au colloid and PE assembling
procedure
MEIS characterization of nanoparticles on the PE surface
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Further MEIS results (100 Further MEIS results (100 keVkeV HH++))
G. Machado et al. Nanoscale 3, (2011)1717
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NanoparticleNanoparticle analysis analysis –– applications applications
II – Core-shell characterization of CdSe/ZnS quantum dots
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Quantum Quantum dotsdots CdSeCdSe//ZnSZnS
Nanocrystals
Absorption and emission depends on composition and size
Higher efficiency in fluorescence process
Thin band gap
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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
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MEIS MEIS analysisanalysis (150 keV He(150 keV He++))
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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
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MEIS analysisMEIS analysis
Core stoichiometry Cd0.65Se0.35
Core diameter 5.0 nm
Shell stoichiometry Zn0.41S0.59
Shell thickness 0.6 nm
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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
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Dr. DaeWon Moon
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Buried Buried NanoparticlesNanoparticles ??
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NanoparticleNanoparticle analysis analysis –– applications applications
III – Burried Pb NPs ion implantation
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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
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3.7x1011 NPs/cm2
PbPb nanoislandsnanoislands : TEM : TEM imagesimages
Cross-section Plan view
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MEISMEIS results (100 results (100 keVkeV HeHe++))
thinner (45nm) thicker (65nm) SiO2
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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)
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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
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Advanced dataAdvanced data analysisanalysis
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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
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TEMTEM pplan lan vviewiew
3.7 x 1011 NPs/cm2
MEIS (best fit) (4.5 ± 1.5) x1011 NPs/cm2
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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)
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EnergyEnergy SpectraSpectra
MS important for < 115 deg !
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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
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NanoparticleNanoparticle analysis analysis –– applications applications
IV – Burried Au NPs sputtering
SiO2
Au (sputtering)
Si (bulk)
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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
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57
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58
25s
Au dissolved
into the SiO2
44 %
9.0 × 1011 NP/cm2
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NanoparticleNanoparticle analysis analysis –– applications applications
V – Burried Fe NPs Ion implantation
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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
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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
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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
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Simple approach for theSimple approach for the full description of the 2D full description of the 2D ––MEIS MEIS
spectrumspectrum-- CrystalsCrystals
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Cu(111):[100] InCu(111):[100] In
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Blocking curves Blocking curves –– Cu(111)Cu(111) surfacesurface
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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 !)
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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
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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)
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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)
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Comparison with Comparison with abab--initio initio energyenergy--loss calculationsloss calculations
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Skimming Effect
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Coupled-channel calculations are
very time consuming !
A simple model is needed !
Nice but…Nice but…
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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
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Skimming Effect
Simple model
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Simple model
Experimental Data
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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
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This opens new perspectives for nanostructure analysis in situ that
can of great interest.
Pitfall : Dissolved atomic species affect MEIS analysis
Summary IISummary II
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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
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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
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Thank you for your attention !
Obrigado !