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Electron-Volt Neutron Spectroscopy: Beyond

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Electron-Volt Neutron Spectroscopy: Beyond This is the author’s final, peer-reviewed manuscript as accepted for publication (AAM). The version presented here may differ from the published version, or version of record, available through the publisher’s website. This version does not track changes, errata, or withdrawals on the publisher’s site. Electron-volt neutron spectroscopy: beyond fundamental systems Carla Andreani, Maciej Krzystyniak, Giovanni Romanelli, Roberto Senesi and Felix Fernandez-Alonso Published version information Citation: C Andreani et al. “Electron-volt neutron spectroscopy: beyond fundamental systems.” Advances in Physics, vol. 66, no. 1 (2017): 1-73. doi: 10.1080/00018732.2017.1317963 This is an Accepted Manuscript of an article published by Taylor & Francis in Advances in Physics on 28/04/2017, available online: http://dx.doi.org/10.1080/00018732.2017.1317963 This version is made available in accordance with publisher policies. Please cite only the published version using the reference above. This item was retrieved from ePubs, the Open Access archive of the Science and Technology Facilities Council, UK. Please contact [email protected] or go to http://epubs.stfc.ac.uk/ for further information and policies. April 1, 2017 11:52 Advances in Physics eVneutronSpectroscopy__AdvPhys__revised__31mar2017__SUBMITTED To appear in Advances in Physics Vol. 00, No. 00, Month 20XX, 1{84 REVIEW ARTICLE Electron-volt neutron spectroscopy: beyond fundamental systems Carla Andreani,a,b Maciej Krzystyniak,c,d Giovanni Romanelli,c Roberto Senesi,a,b and Felix Fernandez-Alonsoc,e∗ aUniversit`adegli Studi di Roma `Tor Vergata,' NAST Centre and Dipartimento di Fisica, Via della Ricerca Scientifica 1, 00133, Roma, Italy; bConsiglio Nazionale delle Ricerche, CNR-IPCF, Sezione di Messina, Italy; cISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, United Kingdom; dSchool of Science and Technology, Nottingham Trent University, Clifton Campus, Nottingham NG11 8NS, United Kingdom; eDepartment of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom. (last revised 31 March 2017) This work provides an up-to-date account of the use of electron-volt neutron spectroscopy in materials research. This is a growing area of neutron science, capitalising upon the unique insights provided by epithermal neutrons on the behaviour and properties of an increasing number of complex materials. As such, the present work builds upon the aims and scope of a previous contribution to this journal back in 2005, whose primary focus was on a detailed description of the theoretical foundations of the technique and their application to funda- mental systems [see Advances in Physics 54 377 (2005)]. A lot has happened since then, and this review intends to capture such progress in the field. With both expert and novice in mind, we start by presenting the general principles underpinning the technique and discuss recent conceptual and methodological developments. We emphasize the increasing use of the technique as a non-invasive spectroscopic probe with intrinsic mass selectivity, as well as the concurrent use of neutron diffraction and first-principles computational materials modelling to guide and interpret experiments. To illustrate the state-of-the-art, we discuss in detail a number of recent exemplars, chosen to highlight the use of electron-volt neutron spectroscopy across physics, chemistry, biology, and materials science. These include: hydrides and pro- ton conductors for energy applications; protons, deuterons, and oxygen atoms in bulk water; aqueous protons confined in nanoporous silicas, carbon nanotubes, and graphene-related ma- terials; hydrated water in proteins and DNA; and the uptake of molecular hydrogen by soft nanostructured media, promising materials for energy-storage applications. For the primary benefit of the novice, this last case study is presented in a pedagogical and question-driven fashion, in the hope that it will stimulate further work into uncharted territory by newcom- ers to the field. All along, we emphasize the increasing (and much-needed) synergy between experiments using electron-volt neutrons and contemporary condensed-matter theory and materials modelling to compute and ultimately understand neutron-scattering observables, as well as their relation to materials properties not amenable to scrutiny using other experi- mental probes. PACS: 61.05.F-; 63.20.dk; 81.05.-t; 81.07.-b; 87.15.-v; 88.30.-k Keywords: electron-volt neutron spectroscopy; deep-inelastic neutron scattering; neutron Compton scattering; mass-selective neutron spectroscopy; nuclear momentum distribution; nuclear quantum effects; neutron diffraction; proton conductors; water and aqueous media; hydrogen storage. ∗Corresponding author. Email: [email protected] April 1, 2017 11:52 Advances in Physics eVneutronSpectroscopy__AdvPhys__revised__31mar2017__SUBMITTED Contents 3 Case studies in materials science 3.1 Water, from the bulk to the nanoscale 3.1.1 Water around the triple point 1 Setting the scene 3.1.2 Water above melting: the supercrit- 2 Theory and practice ical state 2.1 Conceptual and theoretical prelimi- 3.1.3 Competing quantum effects naries 3.1.4 Confinement in nanopores 2.1.1 The impulse approximation and the 3.1.5 Hydrated proteins and DNA neutron Compton profile 3.2 Molecular hydrogen in carbon-based 2.1.2 Momentum distributions and mean nanostructures kinetic energies 3.2.1 Adsorption energetics 2.2 Momentum distributions of light and 3.2.2 Comparison to theoretical predic- heavy nuclei tions 2.2.1 Classical vs. quantum behaviour 3.2.3 Anisotropic response and molecular 2.2.2 Application to crystalline materials alignment 2.2.3 Beyond phonons and crystalline 3.2.4 What DINS has taught us about order hydrogen in the solid state 2.3 The practice of electron-volt neutron 4 Outlook and perspectives spectroscopy Acknowledgments 2.3.1 The VESUVIO spectrometer Funding 2.3.2 From raw neutron counts to mo- List of acronyms in alphabetical order mentum distributions References 2.3.3 Mass-selective neutron spectroscopy 1. Setting the scene The use of electron-Volt (eV) neutrons to study condensed matter systems was reviewed about a decade ago with an emphasis on a detailed description of the underlying the- oretical formalism and the study of the fundamental properties of bulk systems such as helium (He), molecular hydrogen (H2), and their isotopic counterparts [1]. A lot has happened since then, and the present work intends to capture such progress in the field both in terms of technical as well as conceptual and scientific developments. The primary driver behind these efforts has been the increasing need to understand and subsequently exploit the properties of new and increasingly complex functional materials, an intrin- sically interdisciplinary effort across physics, chemistry, biology, materials science, and engineering. Neutron scattering using thermal and cold neutrons is a well-established non-invasive technique, extensively used to provide direct and unique information on the physical and chemical properties of materials at the atomic level [2, 3]. Current efforts at a global level to investigate materials for energy applications constitute a good case in point, given the pressing need to find clean and sustainable alternatives to the environmentally un- friendly combustion of fossil fuels. In this case, neutrons are exceptionally well suited to study in situ or under operando conditions how the transport and binding of energy- and charge-carrying atoms and molecules are related to structure and transport properties, including a detailed understanding of the micro and mesostructure of porous sorbents and adsorbents as well as the underlying mechanism of molecular and macromolecular uptake. In particular, the development of new technologies for energy and sustainable applications often requires a sound understanding of the behaviour of light atomic and + + molecular species such as H , Li ,H2, or hydrocarbons like methane, all of which are particularly well suited to investigation using neutron-scattering techniques. As a con- sequence of the above, neutron-based analysis is nowadays routinely carried out in the characterisation of hydrogen-storage, fuel-cell, catalytic, and battery materials. Similar 2 April 1, 2017 11:52 Advances in Physics eVneutronSpectroscopy__AdvPhys__revised__31mar2017__SUBMITTED research into solar-cell, nuclear remediation, and carbon-dioxide capture/storage materi- als rely on other unique aspects of neutron scattering and, again, serve to illustrate how its use to probe structural and dynamical properties can provide much-needed insights into material stability or the uptake, binding, or mobility of key atomic, molecular, and supramolecular species of technological interest. There are two types of neutron-scattering processes which can be used to investigate the properties of materials, namely, coherent and incoherent scattering. Coherent scat- tering enables the use of the neutron in much the same way as X-ray crystallography is used to determine atomic and molecular structure. In addition, neutrons can probe collective excitations in condensed matter (e.g., phonons) via the use of Inelastic Neu- tron Scattering (INS) techniques. Incoherent scattering is of particular relevance to the study of hydrogen-containing systems due to the very large incoherent scattering cross section of the 1H nucleus. Furthermore, incoherent INS can be used to study both the stochastic (diffusion) and vibrational
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