Atomic-Scale Structure of Mesoporous Silica-Encapsulated Pt and PtSn Nanoparticles Revealed by Dynamic Nuclear Polarization-Enhanced Si-29 MAS NMR Spectroscopy

Mesoporous silica encapsulated Pt (Pt@mSiO2) and PtSn (PtSn@mSiO2) nanoparticles (NPs) are representatives of a novel class of heterogeneous catalysts with uniform particle size, enhanced catalytic properties, and superior thermal stability. In the ship-in-a-bottle synthesis, PtSn@mSiO2intermetallic NPs are derived from Pt@mSiO2 seeds where the mSiO2 shell is formed by polymerization of tetraethyl orthosilicate around a tetradecyltrimethylammonium bromide template, a surfactant used to template MCM-41. Incorporation of Sn into the Pt@mSiO2 seeds is accommodated by chemical etching of the mSiO2 shell. The effect of this etching on the atomic-scale structure of the mSiO2 has not been previously examined, nor has the extent of the structural similarity to MCM-41. Here, the quaternary Q2, Q3 and Q4 sites corresponding to formulas Si(O1/2)2(OH)2, Si(O1/2)3(OH)1 and Si(O1/2)4, in MCM-41 and the mesoporous silica of Pt@mSiO2 and PtSn@mSiO2 NPs were identified and quantified by conventional and dynamic nuclear polarization enhanced Si-29 Magic Angle Spinning Nuclear Magnetic Resonance (DNP MAS NMR). The connectivity of the -Si-O-Si- network was revealed by DNP enhanced two-dimensional 29Si-29Si correlation spectroscopy

Direct observation of hyperpolarization breaking through the spin diffusion barrier

Dynamic nuclear polarization (DNP) is a widely used tool for overcoming the low intrinsic sensitivity of nuclear magnetic resonance spectroscopy and imaging. Its practical applicability is typically bounded, however, by the so-called 'spin diffusion barrier', which relates to the poor efficiency of polarization transfer from highly polarized nuclei close to paramagnetic centers to bulk nuclei. A quantitative assessment of this barrier has been hindered so far by the lack of general methods for studying nuclear-polarization flow in the vicinity of paramagnetic centers. Here we fill this gap and introduce a general set of experiments based on microwave gating that are readily implemented. We demonstrate the versatility of our approach in experiments conducted between 1.2 – 4.2 K in static mode and at 100 K under magic angle spinning (MAS) — conditions typical for dissolution-DNP and MAS-DNP — and for the first time directly observe the dramatic dependence of polarization flow on temperature.The data are organized in subfolders. A PDF document in the root folder summarizes the list of all experiments in the dataset with precisions on experimental parameters and remarks (README.pdf). For each subfolder, the figures of the paper which were produced using the data is the subfolder is listed. Funding provided by: European Research CouncilCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100000781Award Number: 714519: HP4allFunding provided by: H2020 Marie Skłodowska-Curie ActionsCrossref Funder Registry ID: http://dx.doi.org/10.13039/100010665Award Number: 766402: ZULFFunding provided by: NSF/DMR and the State of Florida*Crossref Funder Registry ID: Award Number: 1644779Funding provided by: NSF/DMR NIH*Crossref Funder Registry ID: Award Number: S10 OD018519Funding provided by: National Institutes of HealthCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000002Award Number: P41 GM122698 01Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: CHE 1229170Funding provided by: NSF/DMR and the State of FloridaCrossref Funder Registry ID: Award Number: 1644779Funding provided by: NSF/DMR NIHCrossref Funder Registry ID: Award Number: S10 OD018519All data consist of NMR spectra. Data were collected using high field NMR instruments by Bruker using the software Topspin 3.5.7 and Topspin 3.6.2. They were exported to CSV files

Controlling spin relaxation with a cavity

Spontaneous emission of radiation is one of the fundamental mechanisms by which an excited quantum system returns to equilibrium. For spins, however, spontaneous emission is generally negligible compared to other non-radiative relaxation processes because of the weak coupling between the magnetic dipole and the electromagnetic field. In 1946, Purcell realized that the spontaneous emission rate can be strongly enhanced by placing the quantum system in a resonant cavity -an effect which has since been used extensively to control the lifetime of atoms and semiconducting heterostructures coupled to microwave or optical cavities, underpinning single-photon sources. Here we report the first application of these ideas to spins in solids. By coupling donor spins in silicon to a superconducting microwave cavity of high quality factor and small mode volume, we reach for the first time the regime where spontaneous emission constitutes the dominant spin relaxation mechanism. The relaxation rate is increased by three orders of magnitude when the spins are tuned to the cavity resonance, showing that energy relaxation can be engineered and controlled on-demand. Our results provide a novel and general way to initialise spin systems into their ground state, with applications in magnetic resonance and quantum information processing. They also demonstrate that, contrary to popular belief, the coupling between the magnetic dipole of a spin and the electromagnetic field can be enhanced up to the point where quantum fluctuations have a dramatic effect on the spin dynamics; as such our work represents an important step towards the coherent magnetic coupling of individual spins to microwave photons.Comment: 8 pages, 6 figures, 1 tabl

Direct 17O Isotopic Labeling of Oxides Using Mechanochemistry

While 17O NMR is increasingly being used for elucidating the structure and reactivity of complex molecular and materials systems, much effort is still required for it to become a routine analytical technique. One of the main difficulties for its development comes from the very low natural abundance of 17O (0.04%), which implies that isotopic labeling is generally needed prior to NMR analyses. However, 17O-enrichment protocols are often unattractive in terms of cost, safety, and/or practicality, even for compounds as simple as metal oxides. Here, we demonstrate how mechanochemistry can be used in a highly efficient way for the direct 17O isotopic labeling of a variety of s-, p-, and d-block oxides, which are of major interest for the preparation of functional ceramics and glasses: Li2O, CaO, Al2O3, SiO2, TiO2, and ZrO2. For each oxide, the enrichment step was performed under ambient conditions in less than 1 h and at low cost, which makes these synthetic approaches highly appealing in comparison to the existing literature. Using high-resolution solid-state 17O NMR and dynamic nuclear polarization, atomic-level insight into the enrichment process is achieved, especially for titania and alumina. Indeed, it was possible to demonstrate that enriched oxygen sites are present not only at the surface but also within the oxide particles. Moreover, information on the actual reactions occurring during the milling step could be obtained by 17O NMR, in terms of both their kinetics and the nature of the reactive species. Finally, it was demonstrated how high-resolution 17O NMR can be used for studying the reactivity at the interfaces between different oxide particles during ball-milling, especially in cases when X-ray diffraction techniques are uninformative. More generally, such investigations will be useful not only for producing 17O-enriched precursors efficiently but also for understanding better mechanisms of mechanochemical processes themselves

Matériau paramagnétique pour l'information quantique : manipulations des spins électroniques et nucléaires dans β − Ga2O3 : Ti

Quantum information processing is a major challenge both on fundamental and technological grounds. In this research field, the spin bus concept relies on the use of both the electronic and nuclear spins in which the electron is used as a reading and writing head over the nuclei system which makes the qubit register. The requested material to build a spin bus must have unpaired electrons delocalized over a great number of nuclear spins having long decoherence time. In this work, we studied a spin system composed of titanium (III) interacting with multiple gallium nuclei in gallium oxide. We synthesized and studied the titanium paramagnetic center in gallium oxide single-crystals by continuous wave EPR and ENDOR spectroscopy and showed that the electron is delocalized over eight neighbouring gallium nuclei. This study also revealed a strong isotopic effect on the nucleus-nucleus interaction mediated by the electron. When the two nearest gallium nuclei surrounding the titanium are identical (same isotopes) this interaction is one order of magnitude higher than in the case of inequivalent nuclei. This effect can be used in order to reduce the computation time. Finally, the dynamical properties of the spin system have been characterized by pulsed EPR and ENDOR spectroscopy. The electron spin decoherence is driven by instantaneous and spectral diffusion. The nuclear dynamical properties have also been studied in order to determine the order of magnitude of nuclear spin relaxation and decoherence time.Le traitement quantique de l'information est un domaine très actif dont les enjeux sont importants tant d'un point de vue du savoir scientifique fondamental que des applications technologiques. Dans ce contexte le concept de bus de spin consiste à employer en tandem des spins électroniques et nucléaires. Les électrons célibataires servent de tête de lecture et d'écriture sur le registre de bits quantiques constitué par les spins nucléaires. Les électrons sont délocalisés sur un ensemble de spins nucléaires dont les temps de décohérences doivent être longs. Dans ce travail nous avons étudié un ion titane (III) dans l'oxyde de gallium dont nous avons synthétisé et étudié des monocristaux. Une étude approfondie par RPE et ENDOR en onde continue a montré que l'électron porté par le titane était en interaction avec huit noyaux de gallium qui constituent le registre de qubits potentiel. L'étude a également révélé un effet isotopique sur les interactions noyau-noyau véhiculées par l'électron. Lorsque les deux noyaux de gallium entourant le titane sont identiques (mêmes isotopes), cette interaction est d'un ordre de grandeur plus grande que dans le cas d'isotopes différents, un effet qui peut être employé afin de réduire la durée des opérations logiques. Enfin, la dynamique de cet ensemble de spin a été caractérisée par RPE et ENDOR en impulsions. Il s'avère que la décohérence électronique est dominée par des phénomènes de diffusion instantanée et de diffusion spectrale. La dynamique des spins nucléaires les expériences menées permettent de déterminer l'ordre de grandeur des temps de relaxation longitudinaux et de décohérence des spins nucléaires

Matériau paramagnétique pour l'information quantique (manipulations des spins électroniques et nucléaires dans b - Ga2O3 : Ti)

Le traitement quantique de l'information est un domaine très actif dont les enjeux sont importants tant d'un point de vue du savoir scientifique fondamental que des applications technologiques. Dans ce contexte le concept de bus de spin consiste à employer en tandem des spins électroniques et nucléaires. Les électrons célibataires servent de tête de lecture et d'écriture sur le registre de bits quantiques constitué par les spins nucléaires. Les électrons sont délocalisés sur un ensemble de spins nucléaires dont les temps de décohérences doivent être longs. Dans ce travail nous avons étudié un ion titane (III) dans l'oxyde de gallium dont nous avons synthétisé et étudié des monocristaux. Une étude approfondie par RPE et ENDOR en onde continue a montré que l'électron porté par le titane était en interaction avec huit noyaux de gallium qui constituent le registre de qubits potentiel. L'étude a également révélé un effet isotopique sur les interactions noyau-noyau véhiculées par l'électron. Lorsque les deux noyaux de gallium entourant le titane sont identiques (mêmes isotopes), cette interaction est d un ordre de grandeur plus grande que dans le cas d'isotopes différents, un effet qui peut être employé afin de réduire la durée des opérations logiques. Enfin, la dynamique de cet ensemble de spin a été caractérisée par RPE et ENDOR en impulsions. Il s'avère que la décohérence électronique est dominée par des phénomènes de diffusion instantanée et de diffusion spectrale. La dynamique des spins nucléaires les expériences menées permettent de déterminer l'ordre de grandeur des temps de relaxation longitudinaux et de décohérence des spins nucléairesPARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

Fast and accurate MAS–DNP simulations of large spin ensembles

International audienceA deeper understanding of parameters affecting Magic Angle Spinning Dynamic Nuclear Polarization (MAS–DNP), an emerging nuclear magnetic resonance hyperpolarization method, is crucial for the development of new polarizing agents and the successful implementation of the technique at higher magnetic fields (>10 T). Such progress is currently impeded by computational limitation which prevents the simulation of large spin ensembles (electron as well as nuclear spins) and to accurately describe the interplay between all the multiple key parameters at play. In this work, we present an alternative approach to existing cross-effect and solid-effect MAS–DNP codes that yields fast and accurate simulations. More specifically we describe the model, the associated Liouville-based formalism (Bloch-type derivation and/or Landau–Zener approximations) and the linear time algorithm that allows computing MAS–DNP mechanisms with unprecedented time savings. As a result, one can easily scan through multiple parameters and disentangle their mutual influences. In addition, the simulation code is able to handle multiple electrons and protons, which allows probing the effect of (hyper)polarizing agents concentration, as well as fully revealing the interplay between the polarizing agent structure and the hyperfine couplings, nuclear dipolar couplings, nuclear relaxation times, both in terms of depolarization effect, but also of polarization gain and buildup times