laboratory measurements of sputtering and modeling of ion-surface interaction processes marcelo fama...
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![Page 1: Laboratory measurements of sputtering and modeling of ion-surface interaction processes Marcelo Fama Laboratory for Atomic and Surface Physics University](https://reader035.vdocuments.mx/reader035/viewer/2022062621/551c5665550346b1458b4fd6/html5/thumbnails/1.jpg)
Laboratory measurements of sputtering and modeling of ion-surface interaction processes
Marcelo Fama
Laboratory for Atomic and Surface PhysicsUniversity of Virginia
R.A. BaragiolaR.E. Johnson
SERENA-HEWG Conference - Santa Fe, NM - May 12-14, 2008
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Outline
•Motivation
•IntroductionSputteringLinear Cascade TheorySputtering of CompoundsSurface Morphology
•Computer modelingMonte CarloMolecular Dynamics
•Laboratory simulations
•Discussion
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MotivationA complex scenario
•Electron stimulated desorption•Photon stimulated desorption•Thermal desorption•Sputtering induced by charged particles bombardment•Chemical sputtering•Meteoritic impact
Exosphere
Mercury
- f (Z, m, E, Q)- Surface Compositionand Morphology
Magnetosphere
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IntroductionSputtering
Ion beam (Z1, m1, E, Q, )
Target (Z2, m2, T)
Y = atoms or molecules ejected
incoming ion
Elastic SputteringLinear Cascade Theory(P. Sigmund 1969)
Electronic SputteringPrimary excitationSecondary electronsExciton/Hole Dynamics
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IntroductionLinear Cascade TheoryMono-Atomic Targets
),,( xEFY D : Target Parameters
FD: Distribution of deposited-energy
0024
3
UC
SY n
Sn: Nuclear-stopping cross section (U)
C0 Differential cross section for elastic scattering (B-M)
U0: Surface binding energy
is an energy-independent function of the ratio between the mass of the target m2 and of the projectile m1
Normal IncidenceP. Sigmund, Phys. Rev. 184 (1969) 383
Differential Yield
SSS
S
S
SS
SS EUE
EUY
E
EY
cos
)(
23
0
02
3Maximum at ES = U0 / 2
ES-2 for ES >> U0
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•Mono-atomic targets
•Amorphous materials
•It works satisfactorily at intermediate and high energies (> 1keV)
•It doesn’t consider local U0
IntroductionLinear Cascade TheoryLimitations
U’0 > U0
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IntroductionLinear Cascade TheoryExample #1: Si
Sigmund’s C0 = 1.8 x 10-16 cm2
C0 = (x0 N)-1
Sublimation Energy ~U0 = 4.7 eV
Ycalc. Yexp.
1 keV H+ 0.11 0.008
4 keV He+ 0.28 0.09
Problem partially solved by M. Vicanek et al., NIM B36 (1989) 124 refine calculation for C0
101 102 103 10410-4
10-3
10-2
10-1
100
Y (
atom
s/io
n)
Energy (eV)
1/
1/
th
thn
EE
EESqY
W. Eckstein & R. Preuss, J. Nucl. Mater. 320 (2003) 209
Empirical Fit
4He Si
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IntroductionLinear Cascade TheoryExample #2: H2O (ice)
Sigmund’s C0 = 1.8 x 10-16 cm2
Water Ice C0 = 1.3 x 10-16 cm2
Sublimation Energy ~U0 = 0.45 eV
M. Famá et al., Surf. Sci. 602 (2008) 156
fkTEa
enOH
eY
Y
SSCU
TZmEY
cos1
4
31),,,,(
/
0
1
2
02
0112
10-3 10-2 10-1 100 101 10210-1
100
101
Sp
utt
eri
ng
Yie
ld (
mo
lecu
les/
ion
)
Energy (keV)
H+
He+
N+
O+
Ar+
MD
Model
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IntroductionSputtering of ice grains and icy satellites in Saturn's inner magnetosphere, Planetary and Space Science, In Press
R.E. Johnson, M. Famá, M. Liu, R.A. Baragiola, E.C. Sittler Jr, H.T. Smith
3 4 5 6 7 8 9 10 110.01
0.1
1
10
100
Figure 1a
De
nsi
ty (
1/c
m3 )
R (Rs)
Y =CASSINICASSINI
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IntroductionSputtering of Compounds
i
iYY
Preferential sputtering
•Different binding energies•Recoil implantation•Radiation induced diffusion (segregation)
Surface composition bulk composition
mAB
mAB
cB
cA UUMMYY 212 )/()/(/
ii
ci cYY /
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IntroductionSurface Morphology
A
P
O
Z = h(x,y)
22 )),(()),((arctancos),(, yxhyxhyxhrFrdY yxD
M.A. Makeev & A.L. Barabási, NIM B222 (2004) 316
•Maximum enhancement in the yield ~200%
T.A. Cassidy & R.E. Johnson, Icarus 176 (2005) 499
•Monte Carlo simulations of sputtering within a regolith
YR c YL(0) with 0.2 < c < 1
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~15 eV Semicond.~25 eV Metals
Displacement Energy
SurfaceBinding Energy
LatticeBinding Energy
Computer ModelingMonte CarloTRIM - Binary Collision Approximation
Heat ofSublimation
~1-3 eV
pT
, T
pEV(r)
Equation of Motion
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Computer ModelingMonte CarloTRIM – He+ (4 keV) Albite
Reliability of a popular simulation code for predicting sputtering yields of solids and ranges of low-energy ionsK. Wittmaack, J. Applied Phys. 96 (2004) 2632
NaAlSi3O8
DisplacementEnergy (eV)
Surface
Binding
Energy (eV)
Lattice
Binding
Energy (eV)
Na 25 1.12 3
Al 25 3.36 3
Si 15 4.7 2
O 28 2 3
10-3 10-2 10-110-3
10-2
10-1
O
Si
Al
YTR
IM (
atom
s/io
n)
YCalc.
(atoms/ion)
Na
1.
iicalc UnY
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Computer ModelingMolecular Dynamics
•No assumptions or approximations other than V(r) and Se
•Complete description of the projectile-surface interaction
•Complete description of energy dissipation
•Local surface binding energy, Sn, Tm are naturally included
•Surface topography can be easily considered
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Experimental MethodsTotal Sputtering Yield for Minerals
CambridgeA.J.T. Jull et al., NIM 168 (1980) 357
- Ion microprobe- Interferometry
R
National Physical LaboratoryM.P. Seah et al., SIA 39 (2006) 69- Mesh replica
VirginiaNot tested in minerals yet
- Microgravimetry f
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Experimental MethodsEnergy Distributions of Sputtered Species
Post-ionization
+
-Electron beams-Low energy plasmas-Penning ionization-Post-ionizing laser
Time of flight
30 )( UE
E
E
b
UE
Eexp
)( 30
Secondary ions+
- Non-radiative deexcitation- Neutralization
Argonne National LaboratoryM. J. Pellin (1998)
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Experimental MethodsComplementary Techniques @ Virginia
X-rays
Ultra High Vacuum
(~10-10 Torr)
Quartz Crystal Microbalance (~0.1 ML)
+
SIMS
XPS
NMSe-
or TOF
Nanosecond laser pulses (micrometeorite impact)
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Some ResultsXPS
1100 1000 900 800 700 600 500 400 300 200 100 0
5.0x104
1.0x105
1.5x105
Ca2s
Ca2p
K2p
NaKLL
O2s
Na2s
Na1s
Al2p
Si2p
Si2s
Al2s
C1s
O1s
Surface
2.2 x 1017 He/cm2
In
tensi
ty (
cps)
Binding Energy (eV)
OKLL
Al x-rays200 eV Pass Energy
Albite (NaAlSi3O
8)
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Some ResultsThermal depletion of Na
0 50 100 150 200 250 300 350 400 4500.20
0.22
0.24
0.26
0.28
0.30
0.32
Na/
Si C
once
ntr
atio
n R
atio
Albite Temperature (0C)
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0 1 2 3 4 52
3
4
5
6
7
8
Dukes & BaragiolaFigure 3
Na
(Ato
mic
%)
4 keV He+ Fluence (1015 ions/cm2)
Na/Olivine
= 1 x 1015 cm2
Some ResultsDepletion of Na due to ion bombardment
0 1 2 3 4 52
3
4
5
6
Dukes & BaragiolaFigure 2
Na
(Ato
mic
%)
Na
(Ato
mic
%)
Na
(Ato
mic
%)
x 10-17 cm2Anorthoclase
4 keV He+ Fluence (1017 ions/cm2)
2
3
4
5
6
7
x 10-17 cm2
Albite
1
2
3
4
x 10-18 cm2
Labradorite
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Some ResultsSecondary ions energy distribution
0.1 1 10 100102
103
104
105
b = 3
b = 1
b = 0
Na Al Si O Ca AlO
Cou
nts
(ar
b.
unit
s)
Energy (eV)
~ E-2
E
b
UE
Eexp
)( 30
Ar+ (4 kev) Albite
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Modeling
Exosphere
Mercury
Magnetosphere
Sn
U0
C0
- Surface Composition- Morphology
f (Z, E)
Yi Sn / (C0 U0)Ei E / (E + U0)3
Yi+
Ei+ exp(-b/E) E / (E + U0)3
+
+
Instrument
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Modeling
LaboratorySimulations
MolecularDynamics
Mercuryboundaryconditions
MagnetosphereExospheresimulators
Theory
Sputtering of Minerals
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Questions & Suggestions