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ALAMEDA APPLIED SCIENCES CORPORATION aasc10vp01-1
Energetic Condensation Growth of Nb films for SRF
Accelerators *
M. Krishnan, E. Valderrama, C. James, B. Bures and K. Wilson ElliottAlameda Applied Sciences Corporation (AASC), San Leandro, California 94577
X. Zhao, L. Phillips, B. Xiao and C. ReeceThomas Jefferson National Accelerator Facility (Jefferson Lab), Newport News, Virginia 23606
K. SeoNorfolk State University (NSU), Norfolk, Virginia 23504
presented at
Thin Films and New Ideas for Pushing the Limits of RF Superconductivity
October 4 - 6, 2010
This research is supported at AASC by DOE SBIR Ph II Grant DE-FG02-08ER85162.The JLab effort was provided by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177, including supplemental funding provided by the American Recovery and Reinvestment Act. K. Seo/NSU is a subcontractor to AASC.
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Outline
Alameda Applied Sciences Corporation: an Introduction
Motivation
AASC’s Energetic Condensation Coaters
RRR Measurements
Compare AASC’s coater with others
Film Crystallinity (XRD and EBSD)
Future Plans
ALAMEDA APPLIED SCIENCES CORPORATION aasc10vp01-3
Alameda Applied Sciences Corporation
Founded in 1994, privately held CA Corporation
8 employees, ~$2 million 2009 revenue Develop/license IP via contract R&D Four Pre-commercial areas:
Cathodic arc coatings CEDTM
Fast pulsed x-ray sources for calibrationFast pulsed neutron sources for WMD and
HE detectionSpace micro-propulsion thrusters CED™™ coating inside
of furnace tubes
Anti-coking coating on furnace tube
Benefit: extended interval between
de-cokings
10 cm 10 cm
Uncoated Coated
Cathodic Arc Coatings (CEDTM)
SuperconductingThin Films
RRR ~300, Tc =9.27K
Diamond Radiation Detectors
UV and soft x-ray
≤ 15 keV 20W / 1kg/ 100mN / 2000s
Micro-propulsionPulsed Neutron Source
2.5 and 14 MeV neutrons
DPF-2
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Motivation
NP facilities: The CEBAF facility at TJNAF (undergoing a 12GeV upgrade) Facility for Rare Isotope Beams (FRIB).
NSAC report states that as a result of technical advances, a world-class rare isotope facility can be built at ≈ half the cost of the originally planned Rare Isotope Accelerator (RIA), employing a superconducting linac
Commercial applications: More than 1000 particle accelerators worldwide; most use normal cavities Superconducting RF (SRF) cavities offer a ~10x improvement in energy efficiency over normal
cavities, even accounting for cryogenic costs at 2K Operating at higher temperatures (~10K) would further improve accelerator energy efficiency as
the cryogenic cooling becomes less demanding and moves away from liquid He and towards off the shelf cryo-coolers such as those used in cryo-pumps
Replacing bulk Nb with Nb coated Cu cavities would also reduce costs The ultimate payoff would be from cast Al SRF cavities coated with higher temperature
superconductors (Nb3Sn, MoRe, MgB2, oxypnictides)
Our thin film superconductor development is aimed at these broad goals
ALAMEDA APPLIED SCIENCES CORPORATION aasc10vp01-5
The AASC-JLab/NSU collaboration
JLab has begun a three-year DOE funded project that focuses on thin-film development for future SRF applications
AASC has received a companion, three-year grant from DOE
AASC also has DOE funded SBIR grants to study Nb, Nb3Sn and MoRe
AASC and JLab have established a collaborative research agreement, under which AASC develops thin-films using its energetic condensation tools, while JLab uses its array of sophisticated metrology tools to study the film morphology and electrical properties in depth
Prof. Kang Seo is part of this collaboration via subcontracts from AASC
Together, we aim to advance the technology towards more defect-free SRF coatings
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Why do we collaborate?
Because Enzo demands that we do (he did on Monday and again at the banquet)
A great American Patriot (Thomas Paine) said during the American Revolution:
(this is for Enzo to use in the future)
Men, we must hang together, or assuredly, we will all hang separately
Funding for thin-film R&D hangs by a thin thread; so let’s hang together!
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Approach of the AASC-JLab/NSU collaboration
Use CEDTM and FCAD techniques to coat sapphire and Cu coupons
Use surface analysis techniques at JLab/NSU to characterize morphology
Measure RRR and Tc from Nb coated coupons (on sapphire, MgO, amorphous materials …), to evaluate substrate crystal structure effects
Use SIC facility at JLab to measure impedance of films in cavity
Improve our understanding of the relationships between surface characteristics and superconducting properties
CEDTM
FCAD
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Coating Facilities available at AASC
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Three different Coaters at AASC
Coaxial Energetic Deposition (CEDTM)
Cathodic Arc Deposition (CAD)
Filtered Cathodic Arc Deposition (FCAD)
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B Field
Trigger
MoAnodeMesh
Nb Cathode
CEDTM: Helical arc rotates in a weak B-field
CEDTM may be used to coat full cavities in the future
ALAMEDA APPLIED SCIENCES CORPORATION aasc10vp01-11
CEDTM: Grows a monolayer (≈4Å) of Nb in ≈2ms
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Energetic Deposition is different from sputtering and PVD
Comparison of Stress build-up in low energy deposition, energetic condensation, and energetic condensation plus high voltage bias
Relief of compressive stress by pulsed ion impact [*]
[*] M. M. Bilek, R N. Tarrant, D. R. McKenzie, S H. N. Lim, and D G. McCulloch “Control of Stress and Microstructure in Cathodic Arc Deposited Films” IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 31, NO. 5, OCTOBER 2003
(A. Anders) (A. Bendavid, CSIRO)
(M.M. Bilek)
Nb
ALAMEDA APPLIED SCIENCES CORPORATION aasc10vp01-13
CAD: Allows variation of growth rate from 0.1-3 monolayers/pulse
Cathodic Arc Deposition (CAD)
The new CAD apparatus provides flexibility:
Pulse Forming Network is easily adjusted to vary growth rate from 0.1-3 monolayers/pulse
PFN can drive dual targets to grow compound films
Target may be biased, to vary incident ion spectrum, both DC and pulsed bias possible
ALAMEDA APPLIED SCIENCES CORPORATION aasc10vp01-14
We aim to demonstrate single-step growth of Nb3Sn superconducting films
CAD Coater for compound films
ALAMEDA APPLIED SCIENCES CORPORATION aasc10vp01-15
Recent results from Nb thin-films
coated using the CEDTM coater
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Our CEDTM coater has shown RRR>300 in 1.5µm thick Nb films!
This could be a major breakthrough for thin film SRFSee next talk by Anne-Marie on RRR of 223 in biased ECR films
Residual Resistance Ratio (RRR), defined as R300K/R10K, is a figure of merit for superconductors
RRR is a ‘normal’ state measurement, but is related to the electron mean free path in the superconducting state
bulk Nb cavities in superconducting RF accelerators show RRR~300 for high-Q, high field performance
Over two decades of development, RRR in thin film Nb superconductors has slowly increased from ~10 to ~100
Our recent work has pushed RRR in Nb thin films to >300, matching bulk Nb cavities
ALAMEDA APPLIED SCIENCES CORPORATION aasc10vp01-17
RRR of Nb thin films on a-sapphire
Nb thin films grown on a-sapphire crystals have demonstrated record levels of Residual Resistance Ratio (RRR)
ALAMEDA APPLIED SCIENCES CORPORATION aasc10vp01-18
MgO gives the highest RRR ever measured in Nb thin films
Historically, MgO has not been used for Nb film growth because its fcc structure has a 10.9% lattice mismatch for the bcc Nb [110] direction and 21.6% for the Nb [100] direction. We included MgO because its fcc structure was expected to better match to Cu
An APL is in preparation on these results
Next steps are RRR vs. film thickness and RRR for biased coatings
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RRR as measured is an average over the film thickness
(recall Larry’s talk on Monday?)
RRR of uppermost layer (London depth) is higher than <RRR>
Substrate bias improves RRR further (see Anne-Marie’s talk to follow)
ALAMEDA APPLIED SCIENCES CORPORATION aasc10vp01-20
Why is our RRR so high relative to other sources?
RRR increases with substrate temperature, thickness and ion energy; dep. rate effect?
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XRD and EBSD measurements show hetero-epitaxial
growth of single crystal Nb on a-sapphire and on MgO
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Nb on a-sapphire thin films: crystal structure
Hetero-epitaxial, single crystal growth is correlated with higher RRR
RRR=10, 150/150 RRR=31, 300/300 RRR=155, 700/500
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Al2O3
110 NbAl2O3
110 Nb
Al2O3110 Nb
Polycrystal Polycrystal Monocrystal
XRD Pole figures and Bragg-Brentano spectra show improved crystal structure of Nb (110) on a-sapphire as temperature is increased
ALAMEDA APPLIED SCIENCES CORPORATION aasc10vp01-23
Nb on MgO thin films: crystal structure
XRD Pole figures and Bragg-Brentano spectra show change in crystal structure of Nb from (110) to (100) on MgO as temperature is increased
Nb crystal planes shift from (110) to (100) as temperature (& RRR) increase: An APL is in preparation on this fascinating trend (Kang Seo et al)
RRR=7, 150/150 RRR=181, 500/500 RRR=316, 700/700
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200 Nb110 Nb
200110110
200 MgO
200 MgO110 Nb200 MgO
Polycrystal MonocrystalMonocrystal
ALAMEDA APPLIED SCIENCES CORPORATION aasc10vp01-24
Nb on MgO: temp. driven transition in crystal orientation
EBSD data shows intermixed Nb (110) and Nb (100) for lower RRR samples
High RRR samples show pure Nb (100) for the entire surface
Nb (100)
RRR = 333, 600/500
Nb (110)Nb (100)
RRR = 196, 500/500
100µm
1mm1mm
EBSD shows 110 to 100 transition (Pole figure captures the 200 plane): An APL is in preparation on this (Kang Seo et al)
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Nb on MgO: macro-particles show same orientation as flat surface
High RRR has been achieved despite macroparticles
EBSD demonstrates that macroparticles have the same orientation as the Nb (100) thin film elsewhere
RRR = 316, 700/700
Nb (100)
Macroparticle
35µm
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Nb thin films grown on c-sapphire and on Borosilicate
Nb thin films grown on c-sapphire crystals and on amorphous borosilicate show a similar trend of higher RRR with higher substrate temperature
ALAMEDA APPLIED SCIENCES CORPORATION aasc10vp01-27
Nb thin films on c-sapphire: crystal structure
XRD Pole figures and Bragg-Brentano spectra show change in crystal structure of Nb from textured (with twin symmetry) to hetero-epitaxial, as temperature is increased
Textured structure (twins) disappears at higher temperature (RRR)
RRR=16, 700/150 RRR=43, 700/700
200110
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XRD measurements show polycrystalline Nb with more
coherent texture grown on amorphous borosilicate
This opens the possibility of Nb superconductors on cast
Al cavities of the future
Nb crystals grown on amorphous borosilicate
ALAMEDA APPLIED SCIENCES CORPORATION aasc10vp01-29
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Nb thin films on borosilicate: crystal structure
XRD Pole figures and Bragg-Brentano spectra show improvement in crystal structure of Nb as temperature is increased
Nb crystal growth (low texture) despite amorphous substrate;however, EBSD shows grain size is too small, so need to improve this (biasing?)
RRR=10, 150/150 RRR=31, 700/500
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Phi (rotation)
Psi (tilt)
(110) plane(211) plane
150/150C
Intensity increases
(higher crystallinity)
(110) Nb
(220) Nb(211) Nb
(110) Nb
(220) Nb
ODF project:
Pole figure: 110 RawIntensities:
Psi Phi IntensityMin 20.0 192.5 0.000Max 0.0 162.5 88744.410Dimension: 2.5DScale: RootGrid settings:
Psi PhiFirst 0 0Last 90 360Step 30 90
ODF project:
Pole figure: 110 RawIntensities:
Psi Phi IntensityMin 20.0 192.5 0.000Max 0.0 162.5 88744.410Dimension: 2DProjection: SchmidtScale: RootColour map: DefaultContours: 100
Intensity Colour 1
8.700 26
5880.916 51
22627.606 76
50248.771100
86995.795
Grid settings:Psi Phi
First 0 0Last 90 360Step 10 10
(110)
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SIC measurements at JLab
Rs vs. T for thin film Nb on Cu sample TF-AASC-CED-Nb-Cu-103; EP, annealed at 750 C, then EP again
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The AASC/JLab/NSU team hopes to continue our
methodical investigation of Nb, Nb3Sn, MoRe and
other thin film SRF candidates, culminating in high
field cavity tests after better understanding
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Tc vs. substrate heating conditions: MgO