Managed by UT-Battelle for the Department of Energy LTP, June 01/2012
Predrag Krstić
Joint Institute of Computational Sciences, U. of Tennessee Ex: Physics Division, Oak Ridge National Laboratory
Support from: US DOE (OFES), ORNL LDRD program NCCS(DOE) & NICS(NSF) Computing
Tuning Plasma by the Nanoscale Lithium-Dopped
Surfaces
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012 2
Close collaborators:
Our thanks to John Hogan (FED, ORNL)
Jae Park (ORISE)
Jonny Dadras (UTK)
Chris (MTSU)
Eric Yang (Purdue)
Students Steve Stuart Clemson U.
Carlos Reinhold PD, ORNL
Theory:
Paul Kent ORNL
Alain Allouche CNRS, Fr
TBDFT modeling K. Morokuma,
Kyoto U.
J. Jakowski, NICS
H. Witek, Taiwan
PWDFT
Mat.
CMD
Stephan Irle Nagoja U, Japan
CMD
Experiment:
Fred Meyer (PD, ORNL)
Eric Hollmann (UCSD)
beam
plasma
JP Allain (Purdue)
Chase Taylor (Purdue)
beam
beam
Jeff Harris (FED, ORNL)
Rick Goulding (Fed, ORNL)
plasma
plasma
Chris Ehemann (MSTD)
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012
1. Why PLASMA-MATERIAL INTERFACE
is such an important problem?
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012
All energy from D-T fusion reactions passes through first wall
Vac.
Supercon–ducting magnet
Shield Blanket
Turbine generator
Plasma
a
Plasma heating
(rf, microwave, . . .)
Schematic magnetic fusion reactor
4
• Flux of (particles + heat + 14 MeV neutrons) ~10 MW/m2
A FUSION REACTOR IMPLIES MANY INTERFACES BETWEEN THE PLASMA AND MATERIALS
Particles and surfaces
Unlike nuclear fission where energy is volume-distributed
Key role of PMI in fusion research well recognized in US and internationally
Why lithium? Carbon?
Why is PMI important?
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012
Guiding principle:
If Edison had a needle to find in a haystack, he would proceed at
once with the diligence of the bee to examine straw after straw
until he found the object of his search… I was a sorry witness of
such doings, knowing that a little theory and calculation would
have saved him 90% of his labor.
–Nikola Tesla, New York Times, October 19, 1931
The traditional trial-and-error approach to PMI for future fusion devices by successively refitting the walls of toroidal plasma devices with different materials and component designs is becoming prohibitively slow and costly
Need bottom-up approach arising from the fundamental atomistic and nano science
5
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012
How to build an effective
science for PMI?
2.Why bottom-up science?
or
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012 7
Probing the PMI requires integration of many experimental and theoretical
techniques spanning orders of magnitude in time, length, and energy scales
e.g., Rutherford backscattering,
elastic recoil detection
e.g., low energy ion scattering,
x-ray photoelectron spectroscopy
e.g., secondary neutral mass spectrometry
e.g., quartz crystal microbalance
Monte-Carlo techniques
Diffusion; transport
Courtesy of J.P. Allain
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012
What does flux of 1025 particles/m2s mean (ITER) for a typical atomistic (MD) simulation?
At a box of surface of 3 nm lateral dim? a few thousands atoms (carbon) The flux is 0.01 particle/nm2ns 1) 1 particle at the interface surface of the cell each 10 ns. But for deuterium with impact energy less then 100 eV: Penetration is less than 2 nm, typical sputtering process takes up to 50 ps Is each impact independent, uncorrelated?
Each particle will functionalize the material, change the surface for the subsequent impact! Processes essentially discrete Atomistic approach!!!
8
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012
3. Why is PMI so difficult problem?
Interfacial physics, “when the two
worlds meet” : traditionally the most
challenging areas of science
Dynamical surface communicates
between two worlds: Plasma and Material
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012 10
PMI has many fundamental processes & synergies
elastic reflection
implantation
re-emission &
sputtering &
chemistry
trapping/detrapping
retention
Plasma Material
diffusion, permeation
Give rise to synergistic effects
Damage Effects: Vacancies, bubbles, blisters, dislocations, voids, neutrons?
Drivers: Multi -T, -n, -species, plasma irradiation, neutrons sheath acceleration
Erosion
Ablation
Melting (metals)
Re-deposition
Co-deposition
When an ion or neutral arrives at a surface it undergoes a series of elastic and inelastic collisions
with the atoms of the solid.
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012 11
Materials exposed to plasma are modified, resulting in a “dynamical” surface
Methane sputtering requires H loading of the surface
Plasma irradiation results in a different surface
Deuterium impact of carbon
Surface morphology
Chemical sputtering of hydrocarbons Amorphization depends on penetration depth rather
than of deposited energy
Depth (A)
-5 0 5 10
sp3 d
ensi
ty (
1/A
3)
0.000
0.005
0.010
0.015
0.0207.5 eV/D
5 eV/D
15 eV/D
20 eV/D
30 eV/D
surf
ace
impact
Krstic et al, New J. of Phys. 9, 219 (2007).
0 50 100 3500 3600
10
15
20
25
30
35
0 50 100 1900 2000
10
20
30
40
50
60
70
No
rma
lize
d M
ass 2
0 s
ign
al
Time (s)
saturated
signal
wall contribution to
saturated signal: ~ 20 %
Beam ONbackground level
Time (s)
saturated
signal
wall contribution to
saturated signal: ~ 10 %
Beam ON background level
10 eV / D
60 eV / D
depth (A)
num
ber
den
sity
(a.
u.)
0
50
100
150
H density
C density
0 10 20-10
impact
surf
ace
5 15 25-5
Fluence (1020
m-2
)
0
0.07
0.14
0.28
0.43
0.57
0.71
0.85
1.00
Reaching “steady state”
CD2
CD
CD3
Impact energy (eV/D)
5 10 15 20 25 30
Sputt
erin
g Y
ield
/D
2x10-3
4x10-3
6x10-3
8x10-3
1x10-2
sp3
sp2
sp
E (eV/D)
5 10 15 20 25 30
5
10
15
z<5
Co
un
ts o
f R
-CD
x m
oie
ties
, x
=1
,2,3
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012 12
4. How to validate theory with experiments (and vv)?
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012 13
Beam-surface exp’t: precision control of projectiles & targets . . .
. . . enabled development & validation of MD approach
Meyer et al, Physica Scripta T128, 50 (2007).
Remarkable agreement of theory & exp’t
when simulation mimics exp’t. No fitting
parameters! Key: simulation prepares surface by bombardment!
• Fluence (not flux) like that in experiment
• Type, internal state, energy, angle as in exp’t
What have we learned from the “next door”
beam-surface experiments?
Beam-surface experiments: Prepared beam & target
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012
Eje
cti
on
en
erg
y (
eV
)0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Translational
Rovibrational
Rotational
Vibrational
Hydrocarbon ejection
D Impact energy (eV)
0 5 10 15 20 25 300.0
0.5
1.0
1.5
2.0
2.5CD3 ejection
(a)
(b)
New physics from theory
Ejection energy Ejection temperature
Functions of hydrocarbon mass and impacting D energy Approximate thermalization indicated
energy (eV)
0 2 4 6 8 10 12
Co
un
ts
0
100
200
300
400
500
600
700rotational distribution of ejecta
Fit based on Maxwell of 0.34 eV
H2 with D impact (10 eV)D2 with D impact (10 eV)
Krstic et al, J. Appl. Phys. 104, 103308 (2008).
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012 15
5. Is the PMI phenomenology with plasma
Irradiation different than with a beam
irradiation?
Can we derive plasma-irradiated PMI from the
beam-PMI?
Can we model plasma irradiation?
Answer is: Yes, No, Yes…
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012 16
Goal: Study synergy in the evolution of surface irradiated by plasma
H alone Ar+ alone
Hopf & von Keudell, 2003
H and Ar+ Ion flux = 3.5 * 1012 cm-2 s-1
H flux = 1.4 * 1015 cm-2 s-1
physical
Experiments with Ar+ and H:
• Sputtering = (chemical) + (physical) • Surface preparation by H impact for
chemical sputtering
• Impurity atoms in plasma are efficient
precursors for erosion
• PM processes very dependent on
inventory of H in the material
He suppresses H retention in W
• He penetrates deeper than H
• Strong dependence on energy
• He bubbles: barrier to H diffusion?
He: 0.1% He: 0%
T=653 K
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012 17
E (eV)
0 2 4 6 8 10
Co
un
ts
0
100
200
300
400
500
600
T=10,000K
sqrt(E) exp(-E/kT)
VXVY
VZ
-0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 -0.20.0
0.2-0.25
-0.20
-0.15
-0.10
-0.05
0.00
T=10,000KAll VZ>0 changed sign
Simulations of the plasma irradiation (D atoms)
Impact energy of D (eV)
0 5 10 15 20 25 30
Yie
ld
0.0
0.2
0.4
0.6
0.8 D ejected
D2 sputtered
plasma
beam
With plasma irradiation:
Reflection significantly higher than
beam, sputtering suppressed !!!
Krstic et al, 2009
Maxwell
uniform
Impact distributions
HOW?
Krstic et al, AIP Conf. Proc. 1161, 75 (2009).
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012 18
6. What is outreach of the PMI science
at the plasma facilities?
Difficult to study PMI in thoroidal facilities !
Importance of the dedicated PMI facilities
Pisces-B, Magnum, …) = Bridge!!!
or
Do we need dedicated PMI plasma facility?
What do we want to do with it?
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012
Beam-surface experiments: Prepared beam & target
MD and MC
with plasma
synergy
ITER,
DEMO
Molecular Dynamics (MD)
& Monte Carlo (MC)
simulation
PMI
Design &
Qualification
High-flux linear PMI experiment: Well-diagnosed plasma & target
QuickTime™ and a decompressor
are needed to see this picture.
Toroidal confinement experiments
Potential models
Quantum-classical MD
Increases in
computational power
Integration of theory & experiment basis for PMI research
Material
Science
Predictive science!!!
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012
What have we learned from carbonfacing plasma?
• PMI extremely difficult interfacial problem (Material mixing create SURFACE entity; its scale depends on impact energy: for sub-100eV => nm-ns scales
• PMI science can be built from bottom-up recognizing its multiscale character and building from shortest time/spatial scales (fs/Angstrom) up
• Theory&modeling of PMI has to be validated by experiment (and v.v.)
• Irradiation create dynamical surface, changing interface, cumulative bombardment is the key for agreement with experiment
• Surface responds to synergy in plasma irradiation (angles, energies, particles), NOT following linear superposition principle; NEED plasma irradiation modeling and experiments; dedicated plasma devices a must
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012
• We know from in-situ experiments labs, and more than 7 different tokamak machines (TFTR , CDX-U, FTU, DIII-D, TJ-II, EAST , and NSTX ) that work with graphite with thin lithium coatings have a "significant" effect on plasma behavior and more specifically on hydrogen recycling. Controlled experiments demonstrated reduced recycling, improved energy confinement time tE, and a reduction of edge instabilities known as edge localized modes (ELMs) Notice the ration of the diemsnions of the plasma and Li layer!!!
• Initially the experimentalists conjecture was that there was some "functionality" that governed the behavior of the Li-C-O-H system observed indirectly by analyzing the O(1s) and •C(1s) peaks. For "some reason" the Li(1s) peaks didn't show much information.
Lithium wall conditioning improves confinement! Why?
~ 1’s m
~ 1-10’s nm
D+
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012
Lithium dynamics: Problem to study theoretically because Li polarizing features when interacting with other elements
Electronegativity is chemical property of an element defining its tendency to attract electrons: Li has it exceptionally low in comparison to H , C, O, Mo, W.
Consequence: Bonding between Li and other atoms covalent and polar; Long-range nonbonding: Coulomb :1/R Lennard-Jones :1/R6, 1/R12
Electronegativity and size of atoms related!
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012
How to treat the dynamics in quaternary system Li-C-O-H
•Li-C , Li-H, Li-O are of very different electronegativities and therefore these could be considered as ionic solids/liquids
•As a result of partial charge transfer from one element to the other, the dominant long-distance binding force between particles is the Coulombic attraction between opposite charges, including multipole interactions
•Classical MD is not a good answer, cannot self-consistently calculate charges (EEM+Tersoff-Brenner covalent models too expensive) Quantum-Classical MD based on Self-Consistent-Charge Density-Functional Tight-Binding (SCC-DFTB) method (developed by Bremen Center for Computational Mat. Science, Germany) a possible answer for qualitative phenomenology is our choice
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012
Chemistry and sputtering/reflection/retention dynamics in lithiated&oxidized carbon material, bombarded by slow deuterium atoms is studied. The objectives of this research are two-fold:
1) To develop the realistic methods for computational
simulation of the Li-C-O-H, validated by experiments.
2) Experiments from Purdue and NSTX (PPPL) indicate higher retention and lower erosion rate with D whenever Li present in C, however XPS diagnostics show dominating D-O-C chemistry. Why – is the question now?
Simulation Goals:
C.N. Taylor, B. Heim, J.P. Allain, Journal of Applied Physics 109, 053306 (2011)
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy
Simulation of deuterium impact to lithiated and oxidized carbon surface (quantum-classical approach, DFTB)
•Cell of a few hunreds atoms of lithiated and oxidated amorphous carbon •(~20% of Li, and/or ~20% of O), at 300K How? •By random seed of Li and O in amorphous carbon and energy minimization, followed by thermalization •bombarded by 5 eV D atoms, up to 500fs for the full evolution •Perpendicularly to the shell interface
•5004 random trajectories (embarrassingly parallel runs at Jaguar, Kraken); Time step 1 fs; several 10,000 CPU hours per run
LTP, June 01/2012
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26 LTP, June 01, 2012
Only C+H
C-Li-O
Slabs studied: Periodicity in x-y
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012
From experiments: There was correlation between hydrogen irradiation and the behavior change of the O(1s) and C(1s) peaks ONLY IN THE PRESENCE OF LITHIUM. The Li(1s) peak was always invariant????
What do experiments teach us? II
600 500 400 300 200 100 0
290 283 57 52535 530
Li 1sC 1s
Virgin Graphite
Lithiated Graphite
Inte
nsity (
a.u
.)
Binding Energy (eV)
Post D Bombardment
O 1s
O 1s C 1s Li 1s
x0.2
Norm
alize
d
Inte
nsity (
a.u
.)
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012
Co
un
ts
100
101
102
C
Li
D
Partial charge (e)
-1.0 -0.5 0.0 0.5 1.0No
rmal
ized
cu
mu
lati
ve
dis
trib
uti
on
0
20
40
60
80
(a) Distribution of average charges of D, Li and C, with impact of D on a-C:Li surface (~23% Li concentration, Li/(Li+C)). D has a slight preference for interacting with Li rather than with C.
D
(a)
(b)
Does Li bond more D’s?
Krstic et al, FE&D, 2011
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy
29
Large percentage of impact D (40%) prefer closeness of Li to settle down
Not much attention to O (already bonded to Li)
But there is only 20% Li in C, < 5% of O
The first try of the model had a nice story. The electropositive nature of Li gave us a clear picture on its influence on hydrogen retention when we compared "with Li" and "without Li" cases in the graphite matrix. The model remained somewhat unconnected to the XPS data that clearly showed it was the O(1s) that was really active and correlated to hydrogen irradiation. BUT ONLY IN THE PRESENCE OF LITHIUM. What was missing...???
What is model teaching us (I)?
LTP, June 01/2012
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012
Comes very interesting and theoretically anticipated result: C. Taylor shows that the chemistry is incident particle energy independent... as expected. But, again a result came by observing the O(1s); in presence of Li Not even the C(1s) showed much.
Is it the impact energy? QM model used 5 eV and experiment (cannot afford higher energy…)
No problem with impact energy!!!
What do experiments teach us? III
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy
Quantum-mechanical, PWDFT “static”
calculations finger -point in the same direction,
Qualitatively benchmark the DFTB findings:
•graphene bilayer with Li and H on the surface
When a lithium atom is co-adsorbed on surface bonding energy of H grows up to values ranging from -2.2 to -2.5 eV, with decreasing the Li-H distance. (compared with -1.9 eV for pure graphite)
The bonding E enhancement is also observed when Li is sandwiched 1 layer below the surface layer (conf. E)
LTP, June 01/2012
Configuration
A B C D E
Bo
nd
ing
of
H (
eV)
-5.0
-4.5
-4.0
-3.5
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
d=1.73A
1.88A
5.71A
3.53A
PWDFT
DFTB
Configurations
A B C D E
Ch
arg
es (
e)
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
Li
H
Allouche&Krstic, Carbon (2012)
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012
Result: The quantitative amount of lithium deposition in the in-situ Purdue studies correlated DIRECTLY with results by Maingi et al on amounts of Li deposited in NSTX and subsequent changes on plasma behavior. 300-500 nm THIN FILM only OF LITHIUM MADE A SIGNIFICANT CHANGE IN PLASMA BEHAVIOR of spatial scales of meters!! NO ELMS. But this behavior was limited in time and for some reason saturated. Then comes another pioneering result by C. Taylor showing how this saturation is attained in lithiated graphite: Connected with O saturation
What do experiments teach us? IV
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012
Here comes the experiment again (Chase): 1) At most 5% oxygen content on the surface of NON-
LITHIATED graphite... AS EXPECTED.
2) With lithium you get 10% of Oxygen
3) IMPORTANT: with LOW-ENERGY IRRADIATION one gets over 20% oxygen on the surface.
..... B/C LITHIUM BRINGS IT THERE WHEN LITHIATED GRAPHITE IS IRRADIATED.
What do experiments teach us? V
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012
!"#
$"#
100 µm 100 µm
50 µm
0 µm
50 µm
0 µm
1.289 µm
0.644 µm
1 µm
1 µm
0.5 µm 0.5 µm
0 µm
29.115 nm
14.558 nm
0 nm
0 nm
0 µm
• Polished graphite samples have surface height variations of >1 µm (for a 100 x 100 µm domain) in addition to local height variations on smaller domains, as shown in the inset atomic force micrographs (AFM) in (b-c).
• The effective film “thickness” of Li is significantly less than the nominal dose due to the increased effective surface area.
• Li rapidly intercalates into graphite following deposition, causing a modest rise in surface oxygen content (10%).
• But in some samples, D ion bombardment dramatically increases the surface oxygen content to as much as 45%.
And more: Effective surface exposed to Li Large
Courtesy of C. Taylor
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012
Multipeak structure is consequence of the discrete structure of the bonding centers
0% Li
0% O
20% Li
5% O
20% O
5% Li
20% Li
20% O
Cou
nts
0
10
20
30
40
50
60
0
10
20
30
40
50
60
Penetration depth (Angs)
-5 0 5 10 150
10
20
30
40
50
60
10
20
30
40
50
60
70
0
<d> = 3.9100
SD = 3.2528
<d> = 5.5704
SD = 3.2651
<d> = 5.3764
SD = 3.3006
<d> = 5.0761
SD = 3.6662
Depth (A)
-5 0 5 10sp
3 d
ensi
ty (
1/A
3)
0.000
0.005
0.010
0.015
0.0207.5 eV/D
5 eV/D
15 eV/D
20 eV/D
30 eV/D
surf
ace
impact
Classical (2500 atoms)
Quantal (250 atoms)
Interestingly: QM and classical give similar penetrations for a:C (deut.)
What is modeling teaching us?
II
Penetration depth?
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012
Indicate that D has a preference for interacting with O and C-O structures rather than with Li or Li-C structures when there is enough O
(c)
How do Li and O compete?
MODEL
-0.3 0.0 0.3 -0.3 0.0 0.3
0
20
40
60
80
100
-0.3 0.0 0.3 -0.3 0.0 0.3 -0.3 0.0 0.3
d)
c) i)
j)
Inte
gra
ted
dis
trib
ution
a)
Matrix
composition:
Matrix
composition:
Matrix
composition:
B EMatrix
composition: A C D
b)
Partial Charge (e)
No
rmalized
Counts
(a.u
.)
e)
f)
h)
g)
A B C D E0
50
100
Matrix Composition
Ne
are
st
Ne
igh
bo
r O
ccu
rre
nce
(%
)
C
Li
O
H
D
52%
16%
16%
16%
E
80%
20%
C
60%
20%
20%
B
80%
20%
A
100%C
Li
O
H
9%
3%5%
9%
91%100%
67%
27%
9%
16%
71%
30%
70%
Courtesy of C. Taylor
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012
(c)
What do the first neighbors to D say? Again: O preference!
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012
0
10
20
30
40
50
60
70
80
Binding energy (eV)
-10 -5 0 5-10 -5 00
10
20
30
40
50
60
70
<Eb> = -4.2029
SD = 0.9706
0% Li & O
<Eb> = -4.2519
SD = 0.99597
20% O & 5% Li
<Eb> = -4.0141
SD = 1.1195
20% Li & O
<Eb> = -3.7450
SD = 2.1216
20% Li & 5% O (b)
(d)
Distribution of binding energies of D in various mixtures consistent with O dominance
0
20
40
60
80
100
120
140
0
20
40
60
80
100
120
Final kinetic energy of bound D (eV)
0.0 0.2 0.4 0.6 0.8 1.00
20
40
60
80
100
120
Co
un
ts
0
20
40
60
80
100
120
0% Li
0% O
20% Li
5% O
20% O
5% Li
20% Li
20% O
Most of the bound D’s in the ground Vib state – width ~0.2 eV) Widths are signatures of various bonding sites
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012
6x1015
6x1016
0
5
10
15
20
25
30
35
40
D+ Fluence (cm
-2)
Post-O
irradiation
Post-Li
deposition
O 1
s S
urf
ace C
oncentr
ation (
%)
Virgin
Graphite
D+ bombarded O-graphite
D+ bombarded Li-graphite
D+ bombarded virgin graphite
Experiment confirms: Li brings enough oxygen into the surface
D+ bombardment of virgin or oxidized graphite surfaces suppresses O content in time Lithiated graphite increases O-content upon D+ irradiation to 20-40%
0 1 2 3 4 50
10
20
30
40
50
60 C 1s %
F 1s %
Li 1s %
O 1s %
N 1s %
Irradiation Time (hr)
Surf
ace
Conce
ntr
atio
n (
%)
C. Taylor et al, 2012
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012
CONCLUSIONS
Li is an excellent oxygen getter: Lithiation of C brings A LOT OF Oxygen inside C and this the main role of Li. Oxygen and Oxygen-Carbon bond D strongly:
suppressing erosion & increasing D retention. Li mainly ineffective in this process.
10
20
70
80
90
A B C D E0.0
0.5
1.0
1.5
Pro
ba
bili
ty p
er
D
Retention
Reflection
a)
b)
Sp
utt
eri
ng
Yie
ld (
%)
Matrix Composition
Carbon
Total
A B C D E0
50
100
Matrix Composition
Ne
are
st N
eig
hbo
r O
ccu
rre
nce
(%
)
C
Li
O
H
D
52%
16%
16%
16%
E
80%
20%
C
60%
20%
20%
B
80%
20%
A
100%C
Li
O
H
9%
3%5%
9%
91%100%
67%
27%
9%
16%
71%
30%
70%
Simulation:
P. Krstic et al, Nature SR, 2012
OFES Review, ORNL, March 02, 2010 Managed by UT-Battelle for the Department of Energy LTP, June 01/2012
It is not Lithium that suppresses erosion of C, and increases retention of H OXYGEN plays the key role in the binding of hydrogen. Lithium is the oxygen getter If there is a SIGNIFICANT amount of oxygen on surface with lithium present in the graphite matrix, OXYGEN becomes the main player; NOT LITHIUM!!! ... consistent with the XPS data!!
What is model teaching us?
A beautiful music of full harmony of theory and experiments