1. Photonic Crystal Structures for Transformational Gain in Scintillator Performance B. Singh (P. I.), M. S. J. Marshall, and V. V. Nagarkar, RMD, Inc. S. Li and G. Barbastathis, MIT M. Salomoni and P. Lecoq, CERN Phase III QPR DNDO BAA Contract # HSHQDC-13-C-B0040 DNDO Program Manager: Dr. Alan Janos Period of Performance: 9/30/2013 to 6/29/2016
April 4th, 2016

2. Outline Executive Overview • Conceptual Overview
• Capabilities; Performance targets; Goals
• Development Approach (technical tasks, teams, schedule)
• Key Challenges / Issues to Address
• Risks; Mitigation
• Accomplishments & Highlights
• Milestones: List all and progress towards each
• Remaining Issues
• Schedule: Gantt chart with milestones & deliverables indicated
• Cost (planned, actual, commitments)
Detailed Technical Discussions

3. Executive Overview

4. Conceptual Overview Effect of refractive index mismatch at interface
From Snell’s law
Extracted Light
(θ < θc)
nair = 1
Larger RI mismatch  Smaller c
Smaller RI mismatch  Larger c
Reflected Light
(θ > θc)
nGYGAG = 1.82 θc
Isotropic Light Emission
Critical angle for scintillator with RI=1.82 coupled to RI=1.5: 55
A large fraction of light hits the air/scintillator interface with angle > c
Due to total internal reflection, all light which hits the crystal–air interface with an angle larger than c cannot escape the crystal.

5. Conceptual Overview
Develop adiabatic gradient-index photonic crystal (GRIN) structures which will enable efficient optical coupling of high index scintillators to detectors.
Enable realization of the next-generation of high sensitivity, high performance detectors using existing scintillation materials.

6. Capabilities Strong multi-disciplinary team of collaborators. RMD
Dr. Bipin Singh: Principal Investigator, expertise in scintillators and nanotechnology
Dr. Matthew S. J. Marshall: Senior Scientist, expertise in nanotechnology and characterization
Dr. Vivek V. Nagarkar: Program Manager, expertise in scintillator technology development
Massachusetts Institute of Technology
Prof. George Barbastathis: expertise in optics and nanotechnology
Shuai Li : Doctoral Student with expertise in nanofabrication and nanoimprinting
CERN
Dr. Paul Lecoq, expertise in particle physics detectors, scintillators and medical imaging
Matteo Salomoni, Doctoral student with expertise in modeling and nanoimprinting
aBeam Technologies
Dr. Keiko Munechika
Dr. Carlos Pina-Hernandez

7. Performance targets/Goals
The ultimate goal of this project is to improve energy and timing resolution of current scintillators through the use of super-transmissivity properties of nanostructured photonic crystals.
Quarterly Targets:
Imprint nanostructures on window of can for SrI2 with new 1"×1" mold and CP4 polymer
Demonstrate 20 – 25% gain in Light output for SrI2 (1 inch diameter, 1 inch high)
Imprint on GYGAG with CP4 polymer, and new 1"×1" conical photonic crystal mold
Demonstrate % gain in light output on GYGAG
Demonstrate 20 – 25% gain in energy resolution

8. Review from October 2015 QPR: Light Yield with old mold, aBeam polymer
Extraction for LYSO, with n = 2.0
14% gain
14% gain
Using a COTS mold from TelAztec, a COTS polymer (CP4a from aBeam) we have exceeded the theoretical predictions
Implication: Our manufacturing approach is sound

9. QPR Review: Challenges of Stamp and Repeat
Large Mold
Stamp and repeat is challenging, need larger molds.

10. QPR Review: ALD Simulations
Angle
Diameter of cone base (y-axis), period of cones on x-axis. Max gain of 16% for L =1 and D = 1.
Light Extraction as a function of angle

11. Higher Light extraction efficiences
Where were we (Oct. 2015)?
Developed a state-of-the art nanoimprinting
Measurements from LYSO, CsI, CLYC
Reliably enhance the light yield
Reliably achieve (and exceed) the values predicted by theory
Where are we now (April 2016)?
Measurements from GYGAG, SrI2 as well as LYSO
Large increases in light yield, energy resolution
In progress: new mold design and manufacture
Two new higher refractive index polymers (aBeam)
In progress: high refractive index ALD process development

12. Increasing the Polymer Refractive Index
Transmission measured with UV-vis spectrometer
Refractive index measured with ellipsometry

13. Performance for different scintillators
Conical PhC mold performance for different scintillators
Currently using CP2 (RI = 420 nm) and CP5 (RI = 420 nm)

14. Preliminary results from nanoimprinted GYGAG
Nanoimprinted GYGAG achieved 33.6% increase in light yield with the first attempt
CP2 n = 550 nm
Energy resolution stayed constant

15. Characterization of Nanoimprinted GYGAG
Scintillator
CP2 (n = 1.80)
Mold for
imprinting
Polymer (n=1.50)
Glass slide cover
Schematic of nanoimprinted GYGAG to solve delamination issues.
Replica mold in 1.5 index polymer.
Cones from old mold after peeling off the scintillator.

16. GYGAG imprinted with CP5
Large gain in light output
40.5% gain for polymer CP5 n = 1.88
33.6% gain for polymer CP2 n = 1.82
Experimental Polymer:
Non-uniformity during imprinting. This is a process engineering issue, may be leading to degradation of energy resolution.

17. Imprinting large areas, hygroscopic scintillators
TOP: Photo of a 1 × 1 × 1 cm LYSO scintillator, with the imprinted nanostructured surface displaying optical interference effects.
RIGHT: Photo of a 30 mm diameter quartz window used for packaging hygroscopic scintillators.
Pitch: 400 nm
Diameter nanohole: 200 nm
Height: 180 nm

18. Hygroscopic Scintillators: SrI2 : Eu
SrI2:Eu light output & energy resolution measured through:
a regular window;
a pattern that is not optimized, imprinted in CP4
Critical angle for SrI2 is 46°

19. Hygroscopic Scintillator: SrI2: Eu
Transmission of imprinted film (CP5) + oil, losses compared to specifications, improvement in energy resolution
Emission of SrI2:Eu
Transmission of Imprinted Layer

20. Mold from aBeam : Progress
Hexagonally close-packed array of cones, with an aspect ratio of approx. 1:1.25 (radius:height) would produce an optimal gain
Our new manufacturer is attempting to make our design
For SrI2, rounded cones give 5% gain, pointy cones give 10%
Significant performance reduction: we have not accepted delivery
Manufacturing Attempt:
Rounded Cones
Rounded Cones only 5% gain

21. Optimized Process: Imprinting on LYSO
50% improvement in energy resolution
Nanoimprinted LYSO exhibits large gains in energy resolution
Large gains in light output
This is using the TelAztec mold, not our optimized design, and the CP4 polymer

22. Increasing Refractive Index with ALD
Key Challenge: Developing high refractive index polymer without degrading the optical properties, must still be imprintable (in progress)
Solution: Use atomic layer deposition (ALD) to cover the nanoimprinted structure with very high index of refraction material
Atomic layer deposition (ALD): Widely used in industry, allows conformal coating of nanocrystals, low-T polymer-compatible process.
TiO2 layer n = 2.6
Name
Composition
Refractive Index (n)
Alumina
Al2O3
1.7
Hafnia
HfO2
2.2
Titania
TiO2
2.6
CP4a polymer n = 1.78

23. Increasing the refractive index:
210 nm TiO2 n = 2.6
CP4a polymer n = 1.78
Simulations show the gain as a function of layer thickness for ALD-grown thin films of TiO2, which has a very high RI;
Potential gains of 44% for a 210 nm thick film

24. ALD Coating of Nanocones:
ALD coating of high refractive index TiO2 over the imprinted nanocones;
Process engineering challenges : TiO2 is oxygen deficient, which increases absorption
ALD Strategy:
Dark areas where ALD film have poor transmission
Light areas with less film have better T
TiO2 layer needs more oxygen, requires tweaking the process;
AT-400 from Anric Technologies installation shortly

25. Metrics Publications Presentations Students
1 peer-reviewed paper published in Optics Express
1 manuscript submitted to peer-reviewed IEEE Trans. Nucl. Sci.
1 manuscript under preparation for submission to IEEE Trans. Nucl. Sci.
Presentations
Oral Presentation in Joint Session at the IEEE NSS/MIC, San Diego, Nov 2015 (BS)
Oral Presentation at the SCINT 2015 Conf., LBNL, June 2015 (AK)
Students
3 Ph.D. students graduated from MIT, 1 Ph.D. student currently supported
1 Ph.D. student supported at CERN

26. Capital Equipment
Scanning electron microscopy (SEM) is extensively used to characterize the morphology of fabricated nanostructures.
~$6,000 used to partially pay for an SEM equipment purchased by RMD. This is ~15% of the total cost of the equipment purchased.

27. Summary
Imprinted on windows for hygroscopic SrI2:Eu; nominal gain in energy resolution
Imprinted directly on GYGAG > 40% increase in light yield
Optimized process on LYSO: >25% gain in light yield, >50% gain in energy resolution.
Next steps:
Delivery of new mold with optimized design
Installation of ALD system for the deposition of high-RI layers on top of polymer
Optimization of process for SrI2 and GYGAG
Demonstrate improvements in timing resolution