1. The Hydrogen Observation Diffractometer Paul Henry European Spallation Source (ESS) AB, PO Box 176, 221 00 Lund, Sweden paul.henry@esss.se www.europeanspallationsource.se September 15 th 2014

2. Paul Henry European Spallation Source (ESS) AB, PO Box 176, 221 00 Lund, Sweden paul.henry@esss.se www.europeanspallationsource.se September 15 th 2014 Towards routine structural data collection (and more?) from 1 H materials using a neutron powder diffractometer

3. Instrument Partners Science Case Mark Weller, Chick Wilson, Paul Raithby, Valeska Ting (Bath University, UK) Sten Eriksson, Chris Knee, Paul Henry (Chalmers University, SE) Holger Kohlmann (University Leipzig, DE) Open to further partners Technical Case Paul Henry (ESS, Chalmers University, SE) Britt Rosendahl Hansen (DTU, DK) 3

4. Monochromatic Instruments at ESS 4 Much higher peak brightness than a reactor-based source Much higher time-average brightness than a conventional spallation source Approaches time-average brightness of a reactor-based source Original Proposal Oct 2013 – MODI as a general purpose powder diffractometer MODI also included mode of operation for hydrogenous materials Can an instrument be optimsed for this role which can support the TOF-based instrument suite? (STAP Dec 2013)

5. Scientific Drivers Hydrogen is probably the most important element on Earth – Energy: e.g. Hydrogen generation and storage – Functional materials: e.g. geochemicals, sensors and smart materials – Environment: e.g. geological processes, rock genesis and planetary materials – Life sciences & health: e.g. pharmaceuticals and agrochemicals Strong alignment with National Research Priorities – Horizon2020 themes include Energy, Climate action, Environment, Resource efficiency, Health, Advanced materials and Transport Where is hydrogen? What is it doing? – Key to understanding materials processes – Ability to investigate real materials under real conditions – Design of next-generation materials

6. Enable Transformative Science Routine determination of materials up to 1500 Å 3 and 50 at% H – In situ experiments into real-world materials – Study weak hydrogen bonding in functional organics – Structure solution using combined methods Sample environment development – Gas pressure, humidity and hydro- / solvo-thermal – Chemistry in the neutron beam Multi-technique development – Diffraction/NMR – Diffraction/IR/Raman New experiments – In situ H/D exchange kinetics on bulk materials Simultaneous structural and dynamic information? ‘Specialist’ instrument but can still serve the wider in-situ diffraction community 6

7. Positive v negative scattering length Low absorption cross sections Good coherent scattering cross section 1 H has a large incoherent scattering cross section (background) 2 H low in abundance (expensive) SrD 2 SrH 2 Scattering properties of 1 H and 2 H 7

8. M.T. Weller, P.F. Henry, M.E. Light. Acta Cryst. B 2007, 63(3), 426. P.F. Henry, M.T. Weller, C.C. Wilson, Chem. Commun. 2008, 1557. J.A. Armstrong et al. Am. Mineral. 2010, 95(4), 519. D.M.S. Martins et al. J. Am. Chem. Soc. 2009, 131(11), 3884. V. P. Ting et al. Phys. Chem. Chem. Phys. 2010, 12(9), 2083. F. Tonus et al. Chem. Commun. 2009, 2556. F. Tonus,et al. J. Mater. Chem. 2010, 20(20), 4103. V.P. Ting et al. Angew. Chemie 2010, 49(49), 9408. What can we do now? P. F. Henry, M. T. Weller, C. C. Wilson. J. Appl. Cryst. 2009, 42(6), 1176-1188 M.T. Weller, P.F. Henry, V.P. Ting, C.C. Wilson. Chem. Commun. 2009, 2973-2989 C.C. Wilson, P.F. Henry, M. Schmidtmann et al. Cryst. Reviews 2014, 20(3), 162-206

9. Current Limitations / Instrument Drivers Crystallographic Complexity – Q-range, Resolution, Intensity, Peakshape, Unit cell size, detection efficiency, solid angle of detection, detector stability Background – QENS, Thermal diffuse scattering, inelastic scattering, incoherent scattering – Effects increase with T Deuteration – Limited use, Isotope effects, expensive, ‘model’ systems X-rays – Inherent limitations such as sample damage, weak scattering, want nuclear positions not electron positions Energy dependence of the incoherent scattering – Strongly varying – Chemical environment contribution Other techniques – TOF separation of scattering components – Dynamic Nuclear Polarisation – Use of Polarised beams

10. HOD: monochromatic powder diffractometer 10 Looks like a conventional reactor-based instrument Instantaneous monochromatic flux 13-15x ILL Lower instrument background Energy dispersive information using TOF detector channel Multi-wavelength Applications to incoherent scattering materials Inelastic possibilities

11. Performance (Single wavelength mode) 11 HOD left, D20 right Upper left: open collimation Lower left: 20’ collimation Full range with 40 cm detector Peak widths using constant solid angle detector Count rate × 2.8* or × 1.7* cf. D20 *Background suppression not included

12. 12 Performance (multi-wavelength mode) Ge(hh0) Count rate × 5.25* cf. best- in-class instrument D20 Larger Q-range *Not including background suppression

13. HOD: Applications to incoherent scattering 13 Use a chopper to tailor monochromatic pulse Use sample-detector distance to separate inelastic incoherent scattering Temperature and wavelength provide additional variables Combine with beam polarisation and/or DNP

14. Hydrogen Observation Diffractometer (HOD) Monochromator based Instrument Thermal moderator Sample size 4 cm × 1cm max (typical 2 cm × 0.5 cm) 53 m total length (49 + 2.8 + 1.2 m) Vertically focussing monochromator (Ge(hhl) – 10’ × 10’) Variable takeoff angle: 90-140° Detector 150°, 0.1° wire pitch, 40 cm height = 1.04 Sr Background suppression in TOF mode Multiple wavelength mode Optional Fermi chopper system Configurable sample area with good access Upgrade paths – polarisation, diamond monochromators, DNP 14