krishnan - energetic condensation growth of nb films for srf accelerators

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.


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

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


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


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


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!


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


Coating Facilities available at AASC


Three different Coaters at AASC

Coaxial Energetic Deposition (CEDTM)

Cathodic Arc Deposition (CAD)

Filtered Cathodic Arc Deposition (FCAD)


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


CEDTM: Grows a monolayer (≈4Å) of Nb in ≈2ms


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


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


We aim to demonstrate single-step growth of Nb3Sn superconducting films

CAD Coater for compound films


Recent results from Nb thin-films

coated using the CEDTM coater


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


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)


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


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)


Why is our RRR so high relative to other sources?

RRR increases with substrate temperature, thickness and ion energy; dep. rate effect?


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


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


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)


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


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


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


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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)


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


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


Tc vs. substrate heating conditions: MgO

krishnan - energetic condensation growth of nb films for srf accelerators

Technology

doe aasc

sciences corporation

future srf applications

cathodic arc deposition

bulk nb

energetic condensation

cu cavities

films rrr