Carina Höglund 1,2

CERN 14/10/2013 | [email protected]

Carina Höglund1,2

Björn Alling2, Jens Birch2, Lars Hultman2, Mewlude Imam1,2, Jens Jensen2, Henrik Pedersen2,

Irina Stefanescu3, Karl Zeitelhack3, Richard Hall-Wilton1

1 European Spallation Source, Sweden2 Thin Film Physics Division, IFM

Linköping University, Sweden3 TU Munich, Germany

Design of Novel Coatings for Neutron Detection


Background

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Building the ESS• The world’s best source of neutrons

for the study of materials

• First neutrons in 2019 on 7 instruments

• 22 instruments by 2025

3He crisis280 m2 active detector area

Most need alternatives to 3He

Thin film neutron converters

LiU – ESS – ILL collaboration


Thin films from Linköping UniversityThin Film Physics division in Linköping:• ~60 persons (26 PhD students)• Spin-offs include Ion Bond, Thin Film

Electronics, Impact Coatings, n-Works

Materials Research (~250 persons)

Interdisciplinary, involving industry and institutes

• State-of-the-art laboratories

• Integrating experiments, theory, and modeling

• Active in patenting - results reach the market

• Energy materials• Hard and low-friction

coatings• Neutron-detecting films • Power electronics &

wide-band semiconductors

• Gas and chemical sensors

• Conducting polymers 3


Alternative neutron absorbersAbsorbing material

Thermal neutron absorption cross section

Natural isotope abundance

Disadvantages

3He 5 333 barn 0.00014 at.% Not availableExpensive

6Li 940 barn 7.6 at.% Low efficiency Highly reactive

Expensive 10B 3837 barn 19.9 at.% Low efficiency

157Gd 254 000 barn 15.65 at.% Poor n-g discrimination

Expensive

Reaction paths:3He + n → 3H + 1p + g6Li + n → 3H + a 10B + n → 7Li + a + g (94 %) 7Li + a (6 %)157Gd + n → 158Gd + g + e-

Under investigation

First choice!

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The 10B detector principle

• 10B has a neutron absorption of 70% compared to 3He at l = 1.8 Å

• natB contains 80 at.% 11B and 20 at.% 10B

• 10B + n → 7Li + a + g (94%)10B + n → 7Li + a (6%)

• Charged products emitted back to back• Anode wire / electric field to amplify• Collect signal from ionization process

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Choose 10B4C due to:• Easy to handle in dc magnetron sputtering• Excellent wear resistance, thermal and

chemical stability• Electrically conducting

Incident neutron

CF4 gas

10B

7Li

aSubstrate

High quality 10B coatings with good adhesion are a

key ingredient!


DC magnetron sputtering of 10B4C (PVD)

10B4C

Si 1 mm

• Almost 80 at.% 10B • Impurities H +N + O only ~1 at.%• Good adhesion onto Al, Si, Al2O3, etc • Thicknesses up to above 4 mm• Very low residual stress (0.09 GPa at 1 mm)• Densities of 2.45 g/cm3 (bulk 2.52 g/cm3)• No damage by neutron radiation• 2-sided substrates• Large area (>5 m2/week) Prototypes!

CemeCon CC800/9 deposition machine:

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Patent SE 535 805 C2C. Höglund et al., J. Appl. Phys. 111 104908 (2012)


Chemical vapor deposition of B4C (CVD)• Not a line of sight technique Complex geometries• Can reduce stress Better adhesion

Demands on a CVD process:• Low temperature, < 600 °C• No corrosive gases• Easy up scaling• 10B-enriched version of the

B-precursor must be available

Organoboranes: Very reactive – low process temperature!

- Trimethyl borane (TMB): B(CH3)3

- Triethyl borane (TEB): B(C2H5)3

- Tributyl borane (TBB): B(C4H9)3

Al-substrates

H. Pedersen, C. Höglund et al., Chem. Vap. Dep. 18, 221 (2012)

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Coated with PVD


Thermally activated CVD

InsulationSusceptor

Quartz tube

RF Coil

Carrier gas (H2 or Ar)

Growth parameters:T = 400-600 °CPressure 50 mbar

TEB

• Films with 0.5-1 mm adhere well to both Al and Si (100)

• Deposition rate 0.4-1 mm/h• B/C close to 4 at 600 °C• 5 at.% H at 600 °C

BxC deposited at 600 °C in Ar

Find a way to lower deposition temperature!

H. Pedersen, C. Höglund et al., Chem. Vap. Dep. 18, 221 (2012)

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Plasma assisted CVD• Usually first choice for low temperature CVD• Decompose source gas with energetic species in

the plasma instead of thermal energy• Allows for a low overall process temperature• Use TMB and TEB

We are up and running now!

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Increasing efficiency compared to flat cathodes

I. Stefanescu, C. Höglund, et al., NIM A 727, 109 (2013)

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Grooved cathodes with 10B are expected to have an efficiency superior to flat plates

CVD PVD

• Possible with 30% efficiency gain• Very good agreement between GEANT4

predictions and measurements!


Theoretical modeling of neutron detecting filmsFirst-principles Density Functional Theory can reveal…• Phase stability• Electrical character• Atomic structure and defects• Mechanical properties… of existing and potential future neutron detector materials

TM1−xGdxN (TM = Ti, Zr, Hf)First-principles DFTTi Phase separationZr, Hf Readily mix

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B. Alling, C. Höglund et al., Appl. Phys. Lett. 98, 241911 (2011)

Crystalline and amorphous B4C


GdN compounds with PVD Problems:Gd is known to oxidize severely Can we find a stable and conducting compound?

A GdN thin film of ~200 nm is fullyoxidized within 12 h

Possible solution:Stabilize GdN by alloying with a chemically, mechanically, and/or thermally more stable nitride!

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CollaborationsILL 4+ prototypes, IN6 demonstrator,

planning for IN5 demonstrator

Samples have also been coated for:Czech Technical University, Sintef / Mid Sweden University,University of Milano Bicocca & INFN, Technical University Munich, etc…

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B. Guerard et al., Neutron News 23:4, 20 (2012)A. Khaplanov et al., Proc. of ICANS XX (2012)

J. Correa et al., IEEE TNS, 60, 871 (2013)B. Guerard et al., NIM A 720, 116 (2013)

I. Stefanescu et al., NIM A 727, 109 (2013)A. Khaplanov et al., NOPD submitted

I. Stefanescu et al., J. Instr., submittedF. Krejci et al., 14th ICAPTT proc, subm.

etc.

Contract for new deposition system dedicated for 10B4C coatings production signed last week! From May we have a huge capacity for 10B4C coatings!

Interested in samples? Come and discuss with me!


Conclusions and outlook

• Up-scale the processNew deposition system (dedicated for 10B4C) is available in ~6 months!2019 First 7 instruments at ESS need >3000 m2 coatings2025 15 more instruments at ESS need >5000 m2 coatings

• Technology demonstration 4 multi-grid prototypes, incl. IN6 segment 50% detection efficiency! Grooved cathodes can raise the efficiency by 30% Several collaborations show promising prototype results

• Alternatives to 3He detectors are urgently needed• The next generation of neutron detectors will contain 10B thin films

• Elevated temperatures and high deposition rates yield good adhesion

• The process can easily be up-scaled for large area neutron detectors

• 10B4C thin films can be PVD deposited with ~80 at.% of 10B

• Thermal CVD and PACVD for complex structures is under development

• The 10B4C coatings are not damaged by neutrons

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Jonathan CorreaFrancesco PiscitelliBruno GuerardPatrick van Esch Thierry Bigault Jean-Claude BuffetMathieu Ferraton …

Mewlude Imam***Jens BirchLars HultmanHenrik PedersenBjörn AllingAnnop EktarawongJens Jensen

* stationed at Linköping University** stationed at ILL*** 50% paid by ESS

Carina Höglund *Richard Hall-WiltonAnton Khaplanov **Kalliopi KanakiScott Kolya …

The collaborating team

Irina StefanescuKarl Zeitelhack

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Thank you for your attention!

Carina Höglund 1,2

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