sputtering for radiopharmaceutical application
TRANSCRIPT
Padua University, 16 September 2013
Sputtered thin films for corrosion
protection of targets for
radiopharmaceutical production
Anna Skliarova
Radioisotope=radionuclide is an
atom with an unstable nucleus.
Can undergo radioactive decay, resulting in the
emission of γ-ray(s) and/or α- or β-particles.
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PET- positron
emission tomography
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Radionuclides have wide medical applications:
SPECT- single photon emission computed tomography
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Radionuclides have wide medical applications:
Diagnostic
imaging
Therapeutic
applications
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SPECT/PET-CT
Amount of radionuclides produced by
cyclotrons increases year by year
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Monthly [18F]FDG activities from January 2003 to August 2011;there is a >5 fold increase in produced activities over this period.
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Cyclotron
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The most used radionuclide in PET [18F]F¯
is produced almost exclusively via
proton irradiation of [18O]H2O
18Op
18F
n
g
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Proton irradiation cause water radiolysis
H2O H2, O2, H2O2, ∙OH, H, e-aq,
HO2∙, O2-, HO2
-, OH-, H+, …
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Proton irradiated water
is extremely corrosive!
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Liquid target structure
Havar®
(Co, Cr, Fe, Ni, W, Mo, Mn, C)
Nb bulk
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Need of corrosion resistant top-coating
onto the Havar® beam window
Havar® foil corroded on beam spot
Problem 1:
Proton irradiated Water corrosion
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Problem 2:
Liquid metal embrittlement
in liquid metal cooling systems
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Liquid metal embrittlement
Problem 1:
Proton irradiated Water corrosion
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Problem 2:
Liquid metal embrittlement
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Can be solved by appropriate
protective coatings
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Refractory metals Nb, Ta, Pt, Zr
have extreme chemical resistance
Chemical inertness is mandatory,
but not enough
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Microstructure has a great influence
on corrosion process
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Which film deposition techniques
do you know?
Which one can provide the
microstructure control?
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SPUTTERING
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Experimental
technique
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Sputtering system
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Control panel
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Sputtering chamber
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Distance from target to sample – 6 cm
• grounded
• No temperature control
• No heating
• No bias
• No plasma cleaning
• liquid nitrogen-cooled
• Cooling by liquid N2
• Possible temperature control
• Possible bias
• Possible plasma cleaning
• No heating
• heated
• Heated
• Temperature control
• No bias
• No plasma cleaning
• water-cooled
• Cooling by water
• Stated temperature
• No bias
• No plasma cleaning
• No heating
Substrate holders
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Requirement for corrosion protective coatings:
Uniform thickness
Absence of pin-holes
Low porosity
Low diffusion across grain boundaries
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Analyzing technique
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Acid porosity test:
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Acid porosity test: 10% HCl , 30°C, 10 min
1 2 3 4 5
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Liquid Gallium test: 200 °C, 30 h
a) corrosion b) resistance
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X-ray diffractometry
2dsinθ=nλ
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X-ray diffractometry
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Scanning Electron Microscopie
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Scanning Electron Microscopie
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FIB SEM
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SEM, FIB SEM
SEM SEM
FIB SEM FIB SEM
Approach to corrosion
resistance
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Coating must be dense with minimal distance between grain boundaries
The best possible Diffusion Barriers are Amorphous!
Microstructure requirements:
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Amorphous films have no typical
structural defects of the crystalline state
(dislocations and grain boundaries)
Literature search for corrosion resistance
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Diffusion through the amorphous layers is very
difficult due to the irregularity of the atomic
structure
crystalline amorphous
long-range order structure lack of long-range order characteristic
How to obtain an
amorphous film?
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Approaches to obtain an amorphous metal film
Substrate Cooling
Alloying with other elements
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Experimental results
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Coating systems investigated:
Nb
Nb2O5
Nb/Nb2O5 multilayers
Nb-Ta, Nb-Zr, Ta-Zr
Nb
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Parameters investigated for Nb coatings:
substrate temperature
• -100°C ÷ 500°C
applied bias
• -150 V ÷ +80 V
sputtering gas pressure
• 310-3 mbar ÷ 310-2 mbar
deposition rate
• 0.5 nm/sec ÷ 5 nm/sec
Temperature influence
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Thornton’s Structure Zone Model
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3
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Temperature influence: acid test
Floating (~250°C)
400°C
500°C
0°C
-100°C
-50°C
300°C
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4 0.5 %
-100 °C
4 0.4 %
0 °C
4 1 %
Floating
3 0.04 %
500 °C
- 0 %
800 °C
Temperature influence: SEM
Acid test (1÷5)
Optical profilometry
(%)
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4 0.5 %
-100 °C
4 0.4 %
0 °C
4 1 %
Floating
3 0.04 %
500 °C
- 0 %
800 °C
Temperature influence: FIB SEM
Substrate bias influence
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What happens if substrate is at
negative potential?
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-80 V DC
-400 V DC
grounded
DC bias -80 V -50 V -80 V -80 V -150 V
Arpressure,
mbar310-2 510-3 510-2 310-3 310-3
Porosity acid test 3 2 1 1 2
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DC-biased MS
DC-biased MS of Nb:
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SEM SEM
FIB SEM
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All Nb coatings are columnar!
Nb2O5
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Reactive sputtering of Nb2O5 :
Sputtering gas pressure
• 810-3 mbar ÷ 710-2 mbar
Stoichiometry: Ar/O2
• Ar/O2
Applied bias
• -80 V ÷ 0 V
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Right Stoichiometry:
25 sccm Ar : 19 sccm O2
Nb2O5 stoichiometry
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Liquid Ga test
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1 2
6 7
1
3
2
4
The less porous
6 7
Acid test
▬ stoichiometric
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XRD of amorphous Nb2O5:
Amorphous Nb2O5 deposition recipe:
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Ar flux:
3 sccm
O2 flux:
7 sccm
Sputtering pressure:
110-2
mbar
IDC:
0.5 A
Amorphous Nb2O5:
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SEM FIB SEM
Nb2O5 has superior corrosion protection
but..
oxides are used to be brittle
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Multilayer Nb/Nb2O5 coatings
combine:
high ductility & thermal conductivity of Nb with
excellent barrier properties of Nb2O5
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Nb/Nb2O5 multilayers
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thin thick thermal layers layers oxidation
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M 10
M 10
M 9
M 9
M 8
M 8
M 9M 10M 8
Multilayered Nb/Nb2O5
(60 nm double-layer) coatings
showed high corrosion resistance
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Best Nb/Nb2O5 multilayer recipe:
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Ar flux:
3 sccm
O2 flux:
0/7 sccm
Sputtering pressure:
310-3/ 110-2
mbar
Layer thickness:
40/20 nm
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FIB SEM FIB SEM
SEM
Thin Nb/Nb2O5 multilayer:
Nb-Ta, Nb-Zr, Ta-Zr
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Nb-Ta, Nb-Zr and Ta-Zr
were co-deposited in different ratios in
order to find amorphous metallic coating
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Sample holder
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Sample-holder for co-deposition
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Stress in thin film
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Nb Ta
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Nb Ta
After deposition ~1 μm film
3E-03 mbar
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Nb Ta
Compressive stress High compressive stress
3E-03 mbar
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Nb Ta
7E-03 mbar
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Nb Ta
Tensile stress Compressive stress
Nb Ta
7E-03 mbar
Most suitable sputtering pressure:
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Nb-Ta
• 7E-03 mbar
Nb-Zr
• 5E-03 mbar
Ta-Zr
• 8E-03 mbar
Nb-Ta
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17% Ta
84% Ta
93% Ta
0% Ta
97% Ta
100% TaSingle target sputtering
Single target sputtering
Co-sputtering
9% Ta
11% Ta
26% Ta
44% Ta
64% Ta
91% Ta
Amorphous-like
110 211200
Nb-Ta
10-85 % atomic Ta in Nb-Ta alloy
coating lead to amorphous-like structures
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Acid test
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1 2 3 4 5 6 7 8 9 10Nb↑ Ta↑Nb Ta
1 2 3
4
7
5
8 9
6
Nb-Ta
Films with higher Ta content
are less porous
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Nb-Ta
Nb-Zr
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XRD analysis
Acid test
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Sample position 1 2 3 4 5 6 7 8 9 10
Nb content, % 93 89 85 79 65 46 29 - 16 7
Acid test (1÷5) 4 1 4 4 3 2 2 2 2 2
1 2 3 4 5 6 7 8 9 10Nb↑ Zr↑
1 2
6
3
7 8
4 5
9 10
Nb-Zr 5E-03 mbar
Porosity is decreasing with
decrease of Nb content
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Ta-Zr
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XRD Ta-Zr:
Acid test
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Sample position 1 2 3 4 5 6 7 8 9 10
Ta content, weight % 99 98 97 95 90 74 58 32 40 25
Acid test (1 ÷5) 1 2 1 2 2 1 1 2 1 5
1 2
6
3
7
4 5
8 9 10
All samples besides Ta-Zr 10, behave quiet good in acid test!
1 2 3 4 5 6 7 8 9 10Ta↑ Zr↑
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SEM of cross-section amorphous Ta-Zr:
Ta50Zr50
107Not sputtered Havar® substrate Havar® sputtered with Ta-Zr
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The best recipes for corrosion protection:
DC-biased or heated sputtering of Nb
Reactive sputtering of amorphous Nb2O5
Nb/Nb2O5 thin multilayers
Amorphous Ta-Zr
Thank you
for your attention!
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