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).

1. Recent advances of
MEIS (medium-energy ion scattering)
(medium-
for near surface analysis
Pedro. L. Grande
(UFRGS-Brazil)

2. Outline
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

3. Techniques
(Surfaces/Interfaces/Nano)
•XPS
•AES
•LEED
•STM
•Electron microscopic
•EXAFS,
•Raman,
•... Ion Beam Techniques

4. Ion Beam Techniques
http://lnmsf.irb.hr/techniques.htm

5. Ion Scattering - MEIS
Improved
H+ depth and mass
resolution
(amorphous)
Surface
sensitivity
(crystal)

6. MEIS - Advantages
 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

7. MEIS data collection Schulte H. (Private communication)
Energy Spectrum Angular Spectrum
Yield
gl g
An ter i n
e
at
Sc
Energy
d
el
Yi
MC ion scattering simulation of
Deconvolution of ES gives depth
angular yield provides surface
profile (primarily for amorphous
structure.
thin films).

8. MEIS Spectrum
3.0
o
2.5 = 60
Counts (arb. units)
2.0
Energy
1.5
1.0
0.5
0.0
Angle 93.0 93.5 94.0 94.5 95.0
proton energy
Summed over 2 degrees around = 60o

9. MEIS user Community
• Depth profiling (amourphous)
•High-k materials
•Thin films
…
• Structural determination
•Heterogeneous catalysis
•Surface reconstruction
…

10. 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

11. MEIS for Nanoparticles

12. MEIS Potentiality
Depth profiling elements
inside a NP

13. Energy-
Energy-loss asymmetry
1.5
Backscattred Ions
1.0
0.5
0.0
60 80 100 120
Energy
Depth profile or energy-loss asymmetry ???
or energy-

14. 0.020 distributions
Investigations on
Exponentially Modified Gaussian (EMG)
Moyal
+
M-shell H (100keV) + Al f(x) = exp(-(a x + exp(-ax))/2)
0.015
Gaussian not Gaussian
Exp. decay Exp. decay
dP/d E(eV )
the asymmetry of energy-loss distribution
energy-
-1
0.010
d d
Asymmetric Gaussian
Lognormal
(Grande and Schiwietz)
Schiwietz)
L-shell 2
f(x) = exp(-(ln(x)- ) /2
2
)/x
0.005
1 2
0.000
0 50 100 150 200 250 300 350 400 450 500 550 600
distributions
Energy Transfer ( E) (eV)
 Ab-initio (coupled-channel calculations)
 Analytical formula NIMB 256 (2007) 92
Surface Science 601 (2007)5559
PRL 102 (2009) 096103
 Simple models (CasP program)
P.L. Grande, G. Schiwietz, Ionization and energy loss beyond perturbation theory,
Advances in Quantum Chemistry, Vol 45 (2004) 7-46.

15. Where does the asymmetry come from ?
• Statistical : # of collisions
correlated or uncorrelated
• Single hard collision (b ~ 0)

16. Asymmetry very important
for ultra-thin films !
ultra-
Pezzi at al. Surface Science 601 (2007) 5559

17. Nanoparticle analysis

18. Nanoparticles
Full Monte-Carlo Simulation
• any geometrical shape (sphere, cylinder,..)
• density distribution
• size distribution
• asymmetrical lineshape

19. Full 3D Monte-Carlo Integration
Monte-
(PowerMeis program)
E0 Eout
E1 E0 E in
E out K i ( ) E1 E out
E1

20. Sample description
PowerMeis GUI

21. Giant 3D matrix (of matrices)
Pair correlation function g(r)

22. Shape sensitivity

23. Influence of the asymmetry:
backscattering collision
Au

24. Nanoparticles
(asymmetrical lineshape)
lineshape)
 Diameter t > 5nm
 Diameter t < 5nm
false geometrical shape
false size distribution

25. For the full 2D MEIS spectrum !
Asymmetric Gaussian
80% 1 nm + 20% 4 nm Au spheres - Gaussian lineshape
1nm Au spheres - EMG lineshape 1.485E6 1.585E6
99.5 99.5
1.392E6 1.486E6
1.276E6 1.362E6
99.0 99.0
1.160E6 1.238E6
1.044E6 1.114E6
98.5 98.5 9.906E5
9.281E5
Energy (keV)
Energy (keV)
8.668E5
8.121E5
98.0 98.0 7.430E5
6.961E5
6.191E5
5.801E5
97.5 97.5 4.953E5
4.641E5
3.715E5
3.480E5
97.0 97.0 2.477E5
2.320E5
1.238E5
1.160E5
96.5 96.5 0
120 140 160 180 200 220 240 260 280 300 320 0 120 140 160 180 200 220 240 260 280 300 320
Angle (deg) Angle (deg)

26. Nanoparticle analysis - applications
I – Au NPs in polyelectrolytes
multilayered films

27. Polyelectrolyte (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

28. Au NPs adsorbed in polyelectrolyte

29. TEM
NPs on the surface

30. MEIS results (100 keV H+)
M.A. Sortica et al. JAP (2009)

31. Energy spectrum (1D)
Geometrical shape
Size distribution
Good agreement with TEM !
M.A. Sortica et al. JAP (2009)

32. NP interaction with PE film
 Depends on both Au colloid and PE assembling
procedure
 MEIS  characterization of nanoparticles on the PE
surface

33. Further MEIS results (100 keV H+)
G. Machado et al. Nanoscale 3, (2011)1717

34. Nanoparticle analysis – applications
II – Core-shell characterization of
CdSe/ZnS quantum dots

35. Quantum dots CdSe/ZnS
CdSe/
 Nanocrystals
 Absorption and emission depends on
composition and size
 Higher efficiency in fluorescence process
 Thin band gap

36. Core-
Core-shell analysis of CdSe/ZnS
CdSe/
quantum dots
 Liquid sample – EviDots
(maple red-orange) in
toluene solution – 2.2
mg/L
 Dilutedin toluene at 3.82 g/L
 Deposited on SiO2/Si(100) substrate

37. MEIS analysis (150 keV He+)

38. MEIS analysis – 3 angles
400
Cd Experimental Cd Cd
350 Simulated
300
= 112 degrees = 120 degrees = 128 degrees
250
Counts
200
150 Se
Se
Se
100
Zn Zn Zn
S S
50
0
100 110 120 130 100 110 120 130 100
140 110 120 130 140
Energy (keV)

39. MEIS analysis
 Core stoichiometry  Cd0.65Se0.35
 Core diameter  5.0 nm
 Shell stoichiometry  Zn0.41S0.59
 Shell thickness  0.6 nm

40. 40
TEM Results
30
# NPs
20
10
0
3 4 5 6 7
nm
TEM  spatial and size distribution
MEIS  core and shell characterization

41. Dr. DaeWon Moon

42. Buried Nanoparticles ?

43. Nanoparticle analysis – applications
III – Burried Pb NPs
ion implantation

44. Pb nanoislands at SiO2 / Si
2 D array
SiO2 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

45. Pb nanoislands : TEM images
Cross-section Plan view
3.7x1011 NPs/cm2

46. MEIS results (100 keV He+)
thinner (45nm) thicker (65nm) SiO2

47. Experiment Pb Film Simulations
(PowerMeis program)
Same amount of Pb
3.3 x1022 Pb/cm2
• Film (thickness = 0.7nm)
2x1011 NPs/cm2 6x1011 NPs/cm2 • NPs
1. V = 350 nm3 (2x1011 NPs/cm2)
2. V = 100 nm3 (6x1011 NPs/cm2)

48. Usual data analysis
60
Experiment
11 -2
2.10 NPs cm
11 -2
6.10 NPs cm
40
= 130 deg
S
20
0
60 70 80
Energy (keV)

49. Advanced data analysis

50. Experimental vs. Simulations
Experimental
1000 Film
11 2
2.0x10 NPs/cm
Counts (a.u.)
11 2
3.5x10 NPs/cm
11 2
6.0x10 NPs/cm
500
0
66 68 70 72 74 76 78 80
Energy (keV)

51. TEM plan view
3.7 x 1011 NPs/cm2
MEIS (best fit) (4.5 ± 1.5) x1011 NPs/cm2

52. Where do they deviations come from ?
Multiple Scattering Effects ?
some NPs in Si (bulk)
atomic Pb ?
NP Size Distribution ?
Experimental
1000 Simulation
some NPs in SiO2
Counts (a.u.)
500
0
66 68 70 72 74 76 78 80
Energy (keV)

53. Energy Spectra
MS important for < 115 deg !

54. Shape Sensitivity
11 2
2x10 NPs/cm
Experimental
Film
TEM
Sphere
11 2
3.5x10 NPs/cm
Experimental
Film
Counts (a. u.)
TEM
Sphere
11 2
6 x10 NPs/cm
Experimental
Film
TEM
Sphere
68 70 72 74 76 78 80
Counts (a. u.)
D.F. Sanchez et al. Surface Science 605 (2011) 654

55. Nanoparticle analysis – applications
Au (sputtering)
IV – Burried Au NPs
SiO2
sputtering
Si (bulk)

56. Porto Alegre,
Brazil
~40 nm
SiO2 (sputtering)
Au (sputtering)
7.4 × 1015 Au atoms/cm2
SiO2
3.1 × 1015 Au atoms/cm2
Si (bulk)
1.8 × 1015 Au atoms/cm2
56

57. 57

58. 44 %
9.0 × 1011 NP/cm2
25s
Au dissolved
into the SiO2
58

59. Nanoparticle analysis – applications
V – Burried Fe NPs
Ion implantation

60. As implanted 1 minute
MEIS → 109º 109º
H+ 150 keV
Scattered Intensity (a. u.)
120º 120º
Lower Hutt, New Zealand
131º
Si 131º
Si Fe
Fe Fe surface
1.0 x 1016 atoms/cm2
132 136 140 144 132 136 140 144
Energy (keV)
Fe
surface
J. Kennedy et. al., Nanotechnology, 22, 115602 (2011) 60

61. Statistics and shape from
TEM as input to obtain
shell stoichiometry from
MEIS analysis
2 Rshell
2 Rcore
61

62. XPS + MEIS/TEM
Fe@FexSi33-xO67
33-
SiO2 density (atoms/cm3)
Fe@Fe14Si19O67
Fe Fe
Si Si
62

63. Simple approach for the
full description of the 2D –MEIS
spectrum-
spectrum- Crystals

64. Cu(111):[100] In

65. Blocking curves – Cu(111) surface

66. VEGAS Monte Carlo Simulation
 well established in MEIS
just the area of the surface peak
Phit and Pdet
(only the blocking curves !)
66

67. Extending the VEGAS code
to include ion scattered energies
Improve surface determination
•Bimetallic surfaces
•Thermal vibration correlations
•Dechanneling background

68. Energy Loss
single collision
0.020
0.018
0.016
0.014
dP/d E(eV )
0.012
-1
0.010
0.008
0.006
0.004
0.002
0.000
0 50 100 150 200 250 300 350 400 450 500 550 600 68
Energy Transfer ( E) (eV)

69. Cu (111) single crystal
•single atomic type
•very small relaxation
•previously analyzed by MEIS
A,.Hentz et al. PRL 102, 096103 (2009)

70. Comparison with ab-initio
ab-
energy-
energy-loss calculations

71. Skimming Effect

72. Nice but…
Coupled-channel calculations are
very time consuming !
A simple model is needed !

73. Simple Model for the impact
parameter dependent
energy loss distribution
Gaussian( E - Q(b), (b)) b>0
F( E,b) =
exp(- E) ( E) b =0
1/ 0

75. Simple model
Skimming Effect

76. Experimental Data
Simple model

77. Summary
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

78. Summary II
This opens new perspectives for nanostructure analysis in situ that
can of great interest.
Pitfall : Dissolved atomic species affect MEIS analysis

79. Summary III
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

80. Gregor Schiwietz
Helmholtz-
Helmholtz-Zentrum Berlin
Phil Woodruff Daewon Moon
Warwick KRISS
Mauricio, Dario,Agenor, Paulo, Adriano
Giovanna, Claudio
UFRGS – Porto Alegre
Jêróme Leveneur, John Kennedy,
National Isotope Centre, GNS Science
New Zealand
80

81. Thank you for your attention !
Obrigado !