the use of atomic-layer deposition to study how surface ... · the use of atomic-layer deposition...
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D. Bassler, W. Shmayda, and W. U. SchröderUniversity of RochesterLaboratory for Laser Energetics
The Use of Atomic-Layer Deposition to Study How Surface Effects Impact Tritium Uptake
1
Tritium Focus Group MeetingOak Ridge, TN
15–17 May 2018
Hydrogen Triton
180 200 220 240 260 280 300Time (s)
1.0
1.5
2.0
2.5
Pre
ssu
re (
To
rr)
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ALD is a vehicle for exploring surface chemistry effects on tritium uptake
• Surface water layers play an important role in tritium adsorption
• Tungsten and hafnium oxide have different electronic andphysical properties than stainless steel
• ALD is a gas–surface reaction that creates thin films frommetal oxides
• An ALD system is being designed to test tungsten and hafniumoxide films
Summary
ALD: atomic-layer deposition
Isotopic exchange is a first step in tritium adsorption on metal surfaces
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Hydrogen
Hydroxyl layer (chemisorbed)
Triton
Metal lattice
Ice-like layers (chemisorbed)
Liquid-like layers (physisorbed)
Hydrogen isotopesOxygenMetal atomHydrogen bondFull chemical bonds
P. A. Thiel and T. E. Madey, Surf. Sci. Rep. 7, 211 (1987).
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Isotopic exchange is a first step in tritium adsorption on metal surfaces
Hydrogen
Hydroxyl layer (chemisorbed)
Triton
Metal lattice
Ice-like layers (chemisorbed)
Liquid-like layers (physisorbed)
Hydrogen isotopesOxygenMetal atomHydrogen bondFull chemical bonds
There is a potential to accomodate large amounts of tritium in water: /mol H m106 3.
Modifications to the metal surface alter the hydroxide concentration
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H2O
OH1.0SS316
Pure Fe0.8
0.6
0.4
Ph
oto
elec
tro
n in
ten
sity
(arb
itra
ry u
nit
s)
0.2
0.0538 536 534
Binding energy (eV)
532 530 528 526
SS316-CRO
Y. Ozeki et al., Fusion Sci. Technol. 60, 1499 (2011).
Hydroxyl-layer alterations may correlate with different surface tritium inventories.
O1s spectra
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Hafnium and tungsten have differing electronic and lattice structure than iron
Hafnium Tungsten Iron
Electronic configuration [Xe] 4f14 6s2 5d2 [Xe] 4f14 6s2 5d4 [Ar] 4s2 3d6
Ionic radius (pm) 71 60 25
Activation energy (kJ/mol) 119.9 118.0 56.5
Hafnium
[Xe]
Tungsten
[Xe][Ar]
ALD grows complete films through alternating injections of reactive gases
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• Reagents (precursors) areinjected in short pulses
180 200 220 240 260 280 300
Time (s)
1.0
1.5
2.0
2.5
Pre
ssu
re (
To
rr)
One cycle = one monolayer
ALD film growth is a self-terminating gas–surface reaction
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180 200 220 240 260 280 300
Time (s)
1.0
1.5
2.0
2.5
Pre
ssu
re (
To
rr)
OH terminated surface
Substrate Substrate Substrate
Substrate
Nex
t AL
D c
ycle
Substrate
H2O pulseN2 purge
N2 purgeHfCl4 pulse
OH OH OH OH
OH OHOH OH OH OH
OHOH
Cl Cl Cl
Cl
Cln*(HCI)
n*(HCI)
n*
n*
Hf
Hf
Hf Hf Hf Hf
H H
Hf Hf
HfHfHf
ClCl Cl
Cl
Cl
Cl
Cl
Cl Cl
ClCl
Cl
Cl
Cl
Cl
O O O O O
O
OOO O O O O O
O OO
O
OO
O
O
ALD film growth is a self-terminating gas–surface reaction
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180 200 220 240 260 280 300
Time (s)
1.0
1.5
2.0
2.5
Pre
ssu
re (
To
rr)
OH terminated surface
Substrate Substrate Substrate
Substrate
Nex
t AL
D c
ycle
Substrate
H2O pulseN2 purge
N2 purgeHfCl4 pulse
OH OH OH OH
OH OHOH OH OH OH
OHOH
Cl Cl Cl
Cl
Cln*(HCI)
n*(HCI)
n*
n*
Hf
Hf
Hf Hf Hf Hf
H H
Hf Hf
HfHfHf
ClCl Cl
Cl
Cl
Cl
Cl
Cl Cl
ClCl
Cl
Cl
Cl
Cl
O O O O O
O
OOO O O O O O
O OO
O
OO
O
O
ALD film growth is a self-terminating gas–surface reaction
E27352b
10
180 200 220 240 260 280 300
Time (s)
1.0
1.5
2.0
2.5
Pre
ssu
re (
To
rr)
OH terminated surface
Substrate Substrate Substrate
Substrate
Nex
t AL
D c
ycle
Substrate
H2O pulseN2 purge
N2 purgeHfCl4 pulse
OH OH OH OH
OH OHOH OH OH OH
OHOH
Cl Cl Cl
Cl
Cln*(HCI)
n*(HCI)
n*
n*
Hf
Hf
Hf Hf Hf Hf
H H
Hf Hf
HfHfHf
ClCl Cl
Cl
Cl
Cl
Cl
Cl Cl
ClCl
Cl
Cl
Cl
Cl
O O O O O
O
OOO O O O O O
O OO
O
OO
O
O
ALD film growth is a self-terminating gas–surface reaction
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180 200 220 240 260 280 300
Time (s)
1.0
1.5
2.0
2.5
Pre
ssu
re (
To
rr)
OH terminated surface
Substrate Substrate Substrate
Substrate
Nex
t AL
D c
ycle
Substrate
H2O pulseN2 purge
N2 purgeHfCl4 pulse
OH OH OH OH
OH OHOH OH OH OH
OHOH
Cl Cl Cl
Cl
Cln*(HCI)
n*(HCI)
n*
n*
Hf
Hf
Hf Hf Hf Hf
H H
Hf Hf
HfHfHf
ClCl Cl
Cl
Cl
Cl
Cl
Cl Cl
ClCl
Cl
Cl
Cl
Cl
O O O O O
O
OOO O O O O O
O OO
O
OO
O
O
There is a temperature plateau for optimal film growth in ALD
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GPC = growth per cycle
GP
C
TG independent self-saturative growth
Precursor decomposition
Low activity of precursor
Growth temperature (°C)
• Hafnium
– 275 °C
• Tungsten
– 350 °C
An ALD system is being design stages to deposit hafnium and tungsten oxide on stainless steel
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ALD timing valves
Heated line
Nitrogen purge line20 sscm
Hafnium tetrachloride
Tungsten chloroxide
WaterHeated chamber
Nominal pressure: 1 Torr Pressure
gaugePressure
gauge
VacuumExhaustGetter
A getter is needed to remove unreacted precursors and hazardous byproducts
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• Unreacted precursors will coat the vacuum pump
– high surface area stainless steel sponge
• In a 50 cycle process, we can produce 82 nmol of HCl(g) – CaO derivative beds can convert up to 80% efficiency
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ALD is a vehicle for exploring surface chemistry effects on tritium uptake
Summary/Conclusions
• Surface water layers play an important role in tritium adsorption
• Tungsten and hafnium oxide have different electronic andphysical properties than stainless steel
• ALD is a gas–surface reaction that creates thin films frommetal oxides
• An ALD system is being designed to test tungsten and hafniumoxide films