1. Design of Novel Coatings for Neutron Detection
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, Sweden
2 Thin Film Physics Division, IFM Linköping University, Sweden
3 TU Munich, Germany

2. Background Building the ESS 3He crisis
The world’s best source of neutrons for the study of materials
First neutrons in 2019 on 7 instruments
22 instruments by 2025
3He crisis
280 m2 active detector area  Most need alternatives to 3He 
Thin film neutron converters
LiU – ESS – ILL collaboration 2

3. Thin films from Linköping University
Thin 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
Energy materials
Hard and low-friction coatings
Neutron-detecting films
Power electronics & wide-band semiconductors
Gas and chemical sensors
Conducting polymers
State-of-the-art laboratories
Integrating experiments, theory, and modeling
Active in patenting - results reach the market 3

4. Alternative neutron absorbers
Absorbing
material
Thermal neutron absorption
cross section
Natural isotope
abundance
Disadvantages
3He
5 333 barn
at.%
Not available
Expensive
6Li
940 barn
7.6 at.%
Low efficiency
Highly reactive
10B
3837 barn
19.9 at.%
157Gd
barn
15.65 at.%
Poor n-g discrimination
Reaction paths:
3He + n → 3H + 1p + g
6Li + n → 3H + a
10B + n → 7Li + a + g (94 %) Li + a (6 %)
157Gd + n → 158Gd + g + e-
First choice!
Under investigation 4

5. 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
Incident neutron
CF4 gas
10B
7Li a
Substrate
Choose 10B4C due to:
Easy to handle in dc magnetron sputtering
Excellent wear resistance, thermal and chemical stability
Electrically conducting
High quality 10B coatings with good adhesion are a key ingredient! 5

6. DC magnetron sputtering of 10B4C (PVD)
CemeCon CC800/9 deposition machine:
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!
Patent SE C2
C. Höglund et al., J. Appl. Phys (2012) 6

7. 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
Coated with PVD
H. Pedersen, C. Höglund et al., Chem. Vap. Dep. 18, 221 (2012) 7

8. Thermally activated CVD
Growth parameters:
T = °C
Pressure 50 mbar
RF Coil
BxC deposited at 600 °C in Ar
Films with mm adhere well to both Al and Si (100)
Deposition rate mm/h
B/C close to 4 at 600 °C
5 at.% H at 600 °C
Susceptor
Insulation
TEB
Carrier gas (H2 or Ar)
Quartz tube
 Find a way to lower deposition temperature!
H. Pedersen, C. Höglund et al., Chem. Vap. Dep. 18, 221 (2012) 8

9. 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! 9

10. Increasing efficiency compared to flat cathodes
CVD
PVD
Grooved cathodes with 10B are expected to have an efficiency superior to flat plates
Possible with 30% efficiency gain
Very good agreement between GEANT4 predictions and measurements!
I. Stefanescu, C. Höglund, et al., NIM A 727, 109 (2013) 10

11. Theoretical modeling of neutron detecting films
First-principles Density Functional Theory can reveal…
Phase stability
Electrical character
Atomic structure and defects
Mechanical properties
… of existing and potential future neutron detector materials
Crystalline and amorphous B4C
TM1−xGdxN (TM = Ti, Zr, Hf)
First-principles DFT
Ti  Phase separation
Zr, Hf  Readily mix
B. Alling, C. Höglund et al., Appl. Phys. Lett. 98, (2011) 11

12. 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 fully oxidized within 12 h
Possible solution:
Stabilize GdN by alloying with a chemically, mechanically, and/or thermally more stable nitride! 12

13. Collaborations Samples have also been coated for:
ILL  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…
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., submitted
F. 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!  13

14. Conclusions and outlook
Alternatives to 3He detectors are urgently needed
The next generation of neutron detectors will contain 10B thin films
10B4C thin films can be PVD deposited with ~80 at.% of 10B
Elevated temperatures and high deposition rates yield good adhesion
The 10B4C coatings are not damaged by neutrons
The process can easily be up-scaled for large area neutron detectors
Thermal CVD and PACVD for complex structures is under development
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
Up-scale the process
New deposition system (dedicated for 10B4C) is available in ~6 months!
2019  First 7 instruments at ESS need >3000 m2 coatings
2025  15 more instruments at ESS need >5000 m2 coatings 14

15. The collaborating team
Carina Höglund *
Richard Hall-Wilton
Anton Khaplanov **
Kalliopi Kanaki
Scott Kolya …
Jonathan Correa
Francesco Piscitelli
Bruno Guerard
Patrick van Esch
Thierry Bigault
Jean-Claude Buffet
Mathieu Ferraton …
Mewlude Imam***
Jens Birch
Lars Hultman
Henrik Pedersen
Björn Alling
Annop Ektarawong
Jens Jensen
Irina Stefanescu
Karl Zeitelhack
* stationed at Linköping University
** stationed at ILL
*** 50% paid by ESS 15

16. Thank you for your attention!