Various theories beyond the Standard Model predict new particles with masses in the sub-eV range with very weak couplings to ordinary matter which can possess spin-dependent couplings to electrons and nucleons. We report null results of a search for possible exotic spin-dependent couplings of the neutron which could be induced by the exchange of light weakly coupled bosons or spin-gravity coupling conducted using a spin-echo neutron spectrometer. We constrain the products gA2 and gAgV of the axial vector coupling of the neutron to the matter of the Earth through the exchange of a weakly coupled vector boson for force ranges between the metre scale and the radius of the Earth. We also constrain the constants in some theories of exotic spin-gravity couplings.

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Nanostructured metal hydrides are able to efficiently detect hydrogen in optical sensors. In the literature, two nanostructured systems based on metal hydrides have been proposed for this purpose each with its own detection principle: continuous sub-100 nm thin films read out via optical reflectance/transmittance changes and nanoparticle arrays for which the detection relies on localized surface plasmon resonance. Despite their apparent similarities, their optical and structural response to hydrogen has
never been directly compared. In response, for the case of Pd1−yAuy (y = 0.15−0.30) alloys, we directly compare these two systems and establish that they are distinctively different. We show that the dissimilar optical response is not caused by the different optical readout principles but results from a fundamentally different structural
response to hydrogen due to the different nanostructurings. The measurements empirically suggest that these differences cannot be fully accounted by surface effects but that the nature of the film−substrate interaction plays an important role and affects both the hydrogen solubility and the metal-to-metal hydride transition. In a broader perspective, our results establish that the specifics of nanoconfinement dictate the structural properties of metal hydrides, which in turn control the properties of nanostructured devices including the sensing characteristics of optical hydrogen sensors and hydride-based active plasmonic systems.@en

The detection of hydrogen in a fast, efficient and accurate way is vital for its safe handling in industrial processes and in its use as an energy carrier. Thin film metal hydrides are able to probe the hydrogen pressure, often relying on a change of the optical properties of a sensing layer comprised of palladium and alloys thereof. Apart from hysteresis, these palladium-based thin films suffer from a limited operating range. Here, we study the optical and structural properties of palladium capped hafnium and tantalum thin films. Both tantalum and hafnium thin films offer a stable and hysteresis-free optical response to hydrogen over a much larger pressure range than palladium-based films. Remarkably, the hydrogen content in both cases proves to be linear with the optical signal. In a wider perspective, these results illustrate that palladium-capped transition metals provide ample opportunities to design optical hydrogen sensors with desired properties.

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RF coils have been routinely used for Larmor labelling on the Offspec instrument at ISIS. These coils encode directional information via the neutron polarization using a series of parallelogram-shaped pole shoes which can be tuned to different angles with an RF gradient flipper in the centre of each magnet. We report on measurements of the magnetic field integral through the coils in reflection geometry for a range of scattering angles and different pole shoe angles. Such information is mapped out by measuring the phase of the neutron polarisation and the measurements are discussed in light of data on patterned silicon gratings with a dewetted polymer and the visibility of in-plane structures to SERGIS.

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Hydrogen detection is essential for its implementation as an energy vector. So far, palladium is considered to be the most effective hydrogen sensing material. Here we show that palladium-capped hafnium thin films show a highly reproducible change in optical transmission in response to a hydrogen exposure ranging over six orders of magnitude in pressure. The optical signal is hysteresis-free within this range, which includes a transition between two structural phases. A temperature change results in a uniform shift of the optical signal. This, to our knowledge unique, feature facilitates the sensor calibration and suggests a constant hydrogenation enthalpy. In addition, it suggests an anomalously steep increase of the entropy with the hydrogen/metal ratio that cannot be explained on the basis of a classical solid solution model. The optical behaviour as a function of its hydrogen content makes hafnium well-suited for use as a hydrogen detection material.

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Nanostructuring is widely applied in both battery and hydrogen materials to improve the performance of these materials as energy carriers. Nanostructuring changes the diffusion length as well as the thermodynamics of materials. We studied the impact of nanostructuring on the hydrogenation in a model system consisting of a thin film of magnesium sandwiched between two titanium layers and capped with palladium. While we verified optically the coexistence of the metallic α-MgDx and the insulating β-MgD2–y phase, neutron reflectometry shows significant deviations from the thermodynamic solubility limits in bulk magnesium during the phase transformation. This suggests that the kinetics of the phase transformation in nanostructured battery and hydrogen storage systems is enhanced not only as a result of the reduced length scale but also due to the increased solubility in the parent phases.@en