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The design of a time-of-flight neutron reflectometer proposed for the new generation of compact neutron sources is presented. The reflectometer offers the possibility to use spin-polarized neutrons. The reflectometer design presented here takes advantage of a cold neutron source and uses neutrons with wavelengths in the range of 2–15 Å for the unpolarized mode. In general, due to tight spatial restrictions and the need to avoid moving parts inside the beam channel, a multi-channel collimator guide and reflective neutron guide are used for the first section of the instrument. This enables definition of the desired wavelength band and easy selection of one out of three different Q-resolutions. A low background for the collimator system and the reflectometer is ensured by employing a tangential beam channel and an in-channel sapphire filter. The second section is the time-of-flight (TOF) system, which uses a double-disk neutron chopper followed by polarization elements, the sample environment and the neutron detector system. Monte Carlo simulations and neutron beamline intensity measurements are presented. The design considerations are adoptable for neutron sources where space is limited and sections of the instrument are in a high-radiation environment. [ABSTRACT FROM AUTHOR]

The full design of a liquid neutron reflectometer for China spallation neutron source is reported. The horizontal sample geometry enables studies on both solid and liquid samples. A neutron beam with a wavelength range from 1 to 10 Å and neutron flux intensity of 4 × 107 n/cm2/s was optimized for the classical specular reflection. A multi-blade detector with high detection efficiency and a high neutron counting rate was used to ensure the performance of neutron detection. Data acquisition and reduction routines were demonstrated to confirm the reliability of the measurements. The design and algorithms developed in this study pave the way for the future construction of liquid reflectometry for high-performance neutron scattering measurements. [ABSTRACT FROM AUTHOR]

The Spatz neutron beam instrument is the second time‐of‐flight neutron reflectometer to be installed at the OPAL research reactor. The instrument was formerly the V18 BioRef reflectometer at the BER‐II reactor in Berlin and was transferred to Australia in 2016. Subsequently the instrument was re‐installed in the neutron guide hall of the OPAL reactor at the end position of the CG2B cold‐neutron guide and recommissioned. The instrument performance has not been compromised by the move, with reflectivity achieved down to 10−7 and good counting statistics within a reasonable time frame using a wavelength range of 2–20 Å. Several different samples at the solid–air interface and the solid–liquid interface have been measured to demonstrate the instrument's capabilities. [ABSTRACT FROM AUTHOR]

With the closure of the BER-II Reactor in Berlin, the Helmholtz Zentrum Berlin (HZB) started to find new homes for their suite of world-class neutron scattering instruments. In September 2015, it was agreed that the Australian Nuclear Science and Technology Organisation (ANSTO) would take ownership of the V18 BioRef Neutron Reflectometer. One year later, there was a joint team from ANSTO and HZB dismantling BioRef and packing the parts into shipping containers for the long journey to Australia. The instrument arrived at ANSTO in February 2017 and was renamed Spatz, which is German for sparrow. The process of installing Spatz in the neutron guide hall of the OPAL Research Reactor began shortly after and was completed in October 2018. The hot commissioning process has demonstrated that BioRef will continue to have a long and successful life down under as Spatz. This article describes the steps that were followed to bring BioRef from Germany to Australia and highlights key considerations needed when taking such an undertaking. [ABSTRACT FROM AUTHOR]

Neutron reflectometry (NR) is a powerful tool for providing insight into the evolution of interfacial structures, for example via operando measurements for electrode–electrolyte interfaces, with a spatial resolution of nanometres. The time resolution of NR, which ranges from seconds to minutes depending on the reflection intensity, unfortunately remains low, particularly for small samples made of state‐of‐the‐art materials even with the latest neutron reflectometers. To overcome this problem, a large‐area focusing supermirror manufactured with ultra‐precision machining has been employed to enhance the neutron flux at the sample, and a gain of approximately 100% in the neutron flux was achieved. Using this mirror, a reflectivity measurement was performed on a thin cathode film on an SrTiO3 substrate in contact with an electrolyte with a small area of 15 × 15 mm. The reflectivity data obtained with the focusing mirror were consistent with those without the mirror, but the acquisition time was shortened to half that of the original, which is an important milestone for rapid measurements with a limited reciprocal space. Furthermore, a method for further upgrades that will reveal the structural evolution with a wide reciprocal space is proposed, by applying this mirror for multi‐incident‐angle neutron reflectometry. [ABSTRACT FROM AUTHOR]

The exact resolution function of the transfer vector for the HERMÈS reflectometer at the Laboratoire Léon Brillouin is calculated as an example of a neutron time‐of‐flight spectrometer with a double‐disk chopper. The calculation accounts for the wavelength distribution of the incident beam, the tilt of the chopper axis, collimation and gravity, without an assumption of Gaussian distributions or the independence of these different contributions. A numerical implementation is provided. It is shown that data fitting using this exact resolution function allows much better results to be reached than with the usual approximation by a Gaussian profile. [ABSTRACT FROM AUTHOR]

In the past decade, several neutron reflectometry methods for determining the modulus and phase of the complex reflection coefficient of an unknown multilayer thin film have been worked out among which the method of variation of surroundings and reference layers are of highest interest. These methods were later modified for measurement of the polarization of the reflected beam instead of the measurement of the intensities. In their new architecture, these methods not only suffered from the necessity of change of experimental setup but also another difficulty was added to their experimental implementations. This deficiency was related to the limitations of the technology of the neutron reflectometers that could only measure the polarization of the reflected neutrons in the same direction as the polarization of the incident beam. As the instruments are limited, the theory has to be optimized so that the experiment could be performed. In a recent work, we developed the method of variation of surroundings for one directional polarization analysis. In this new work, the method of reference layer with polarization analysis has been optimized to determine the phase and modulus of the unknown film with measurement of the polarization of the reflected neutrons in the same direction as the polarization of the incident beam. [ABSTRACT FROM AUTHOR]

Specular neutron reflectometry has become an established probe of the nanometer scale structure of materials in thin film and multilayered form. It has contributed especially to our understanding of soft condensed matter of interest in polymer science, organic chemistry, and biology and of magnetic hard condensed matter systems. In this paper we examine a number of key factors which have emerged that can limit the sensitivity of neutron reflection as such a probe. Among these is loss of phase information, and we discuss how knowledge about material surrounding a film of interest can be applied to help resolve the problem. In this context we also consider what role the quantum phenomenon of interaction-free measurement might play in enhancing the statistical efficiency for obtaining reflectivity or transmission data. [ABSTRACT FROM AUTHOR]

Abstract We describe a new sensitive method for the investigation of weakly magnetic films placed inside a tri-layer planar waveguide. Polarized neutrons tunnel into the waveguide through the surface, channel along the layers and are emitted from the end face as a narrow and slightly divergent microbeam. Polarization analysis permits to detect very small magnetization in the order of a few 10 Gauss. The magnetic film containing the rare-earth element Tb was investigated using both fixed wavelength and time-of-flight polarized neutron reflectometers. The experimental results are presented and discussed. [ABSTRACT FROM AUTHOR]

Neutron bandpass-limiting disk chopper for implementing the time-of-flight (TOF) mode of measurements at reflectometers at steady flux sources is presented. A sufficiently compact multi-disk system cuts off the contaminant slow neutrons, allows to make measurements with different TOF resolutions and/or different TOF bases. A method of analyzing the effect of beam divergence on the disk chopper performance is proposed. The parameters of the disk chopper, which is designed for the neutron reflectometer SONATA (reactor PIK, Gatchina, Russia), are used for the model simulations. [ABSTRACT FROM AUTHOR]

A general virtual experiment for the time-of-flight neutron reflectometer is introduced to simulate the experimental data collection and processing, including instrument simulation, sample modeling, detector simulation, and data reduction. The process mimics the experimental data processing and reduction routines. The reduced data agree well with the theoretical calculation, confirming the reliability of the data reduction algorithms. The methodology and algorithms developed in this study pave the way for the future development of data processing and data reduction software for the time-of-flight neutron reflectometer of China Spallation Neutron Source. [ABSTRACT FROM AUTHOR]

A new time-of-flight neutron reflectometer GRAINS with a horizontal sample plane (vertical scattering plane) has recently been put into operation at the pulsed reactor IBR-2 (JINR, Dubna). The scattering geometry applied makes it possible to carry out complex studies of nanostructured interfaces in solid and liquid states by measuring the specular reflectivity and the intensity of diffuse scattering of thermal neutrons from open surfaces and hidden interlayer boundaries, including solid-liquid interfaces, over a wide momentum transfer range. The classical analysis of specular reflectivity allows one to determine the scattering length density profile in the object under study in a direction perpendicular to the interface for a thickness of ~100 nm with a resolution of 1 nm. The analysis of off-specular (diffuse) neutron scattering makes it possible to characterize lateral correlations on surfaces and interlayer boundaries. The paper summarizes the first experience in the operation of the GRAINS reflectometer. The instrument characteristics are presented together with the possibilities for experiments with solid and liquid samples illustrated with simple systems. Further steps for the development of the reflectometer are discussed. [ABSTRACT FROM AUTHOR]

The suitability of a transportable 3 He-spin filter as temporary broadband polarizer for a Time-of-Flight neutron reflectometer is demonstrated. A simple two-wavelength method for characterisation of a 3 He-spin filter is proposed, which can be applied even if the absolute transmittance of the 3 He-spin filter cannot be accurately determined. We demonstrate the data treatment procedure for extracting the spin-up and spin-down neutron reflectivity from measurements obtained with a time dependent 3 He polarization. The extraction of a very weak magnetic signal from reflectivity data, measured on the in-situ grown magnetic heterostructure Fe 1 nm / Cu 20 nm / Si substrate in an externally applied magnetic field of 30 mT is presented and compared to similar measurements on the growth stage Cu 20 nm / Si substrate of the very same sample, which does not yet contain any magnetic material. [ABSTRACT FROM AUTHOR]

A neutron polarizer using four successive reflections on m = 2.5 supermirrors was built and installed at the GINA neutron reflectometer at the Budapest Neutron Centre. This simple setup exhibits 99.6% polarizing efficiency with 80% transmitted intensity of the selected polarization state. Due to the geometry, the higher harmonics in the incident beam are filtered out, while the optical axis of the beam remains intact for easy mounting and dismounting the device in an existing experimental setup. [ABSTRACT FROM AUTHOR]

Results of experimental investigations of space, angular and wavelength distribution in neutron microbeams obtained for the first time with the help of a resonant planar neutron waveguide at the time-of-flight reflectometer of the IBR-2 pulsed reactor are reported and comparison with theoretical calculations is presented. Possible application of microbeams in physical experiments is discussed. [ABSTRACT FROM AUTHOR]

The article discusses how neutrons can be used to answer questions about the performance of formulations under industrially-relevant conditions. Topics include neutrons as a complementary probe to X-rays in the study of the physical properties of materials, neutron reflectometry experiments using the Institut Laue-Langevin's (ILL's) fluid interfaces grazing angles reflectometer (FIGARO) in Grenoble, France, and potential industrial applications of FIGARO's overflowing cylinder (OFC).

Lipid translocation in membranes is still far from beingunderstoodand well characterized for natural cell membranes as well as for simplerbilayer model systems. Several discrepancies with respect to its occurrenceand its characteristic time scale are present in the literature. Inthe current work, the structural changes induced by lipid rearrangementin a distearoyl-/dimyristoyl-phosphocholine binary lipid system havebeen addressed by means of neutron reflectivity. It has been shownthat a fast, spontaneous compositional reorganization with lipid transferbetween the two leaflets of the bilayer takes place only when thelipid species are both in the fluid phase. This process has been identifiedas the so-called lipid flip-flop. Moreover, the influence of the preparationprotocol on the structural properties of the system has been investigated. [ABSTRACT FROM AUTHOR]

We have investigated the magnetization profiles in superlattices composed of the two ferromagnets La0.7Sr0.3MnO3 and SrRuO3 using spin-polarized neutron reflectometry. In combination with magnetometry, the neutron data indicate a noncollinear spin configuration where orientation of the Ru moments changes from in plane at the interface to out of plane deep inside the SrRuO3 layers. The spin structure originates in a competition between antiferromagnetic exchange interactions of Mn and Ru moments across the interface, and the magnetocrystalline anisotropy of the Ru moments, and it is closely related to the "exchange spring" structures previously observed in multilayers composed of ferromagnetic elements and alloys. [ABSTRACT FROM AUTHOR]

The effect of giant injection magnetoresistance (GIMR) was recently observed in a granular SiO2/(54--75 at. % Co) film on a semiconductor GaAs substrate in a temperature range near T = 300 K. The magnetoresistance coefficient reaches a value of 105% in a magnetic field of 1.9 T and at a voltage of 90 V. A structural model of the film was proposed based on the results of the grazing-incidence small-angle scattering (GISAXS) and x-ray reflectivity, which showed a specific interface layer 70-75 Âthick separating bulk (Co) granular film from the semiconductor substrate. This layer is formed by a monolayer of flattened Co particles which are laterally spaced apart much further than the particles in the bulk film. In the present work, using polarized neutron reflectometry (PNR), we study both the structural and magnetic properties of Si02(Co) film separately in the bulk and in the interface layer, which is possible due to the depth resolution of the method. Temperature-dependent PNR and magnetization measurements performed by Superconducting Quantum Interference Device (SQUID) revealed the occurrence of two types of magnetic nanoparticles with different blocking temperatures and magnetization. The magnetization hysteresis curve demonstrated specific two-loop structure in fields 0.5-2 T. Thus our self-consistent results of PNR, GISAXS, and SQUID measurements emphasize the role of the interface features in the Si02(Co)/GaAs heterostructures and show a direction for further development of the GIMR theory. [ABSTRACT FROM AUTHOR]

Li-ion batteries are made possible by the solid electrolyteinterphase,SEI, a self-forming passivation layer, generated because of electrolyteinstability with respect to the anode chemical potential. Ideallyit offers sufficient electronic resistance to limit electrolyte decompositionto the amount needed for its formation. However, slow continued SEIgrowth leads to capacity fade and increased cell resistance. Despitethe SEI’s critical significance, currently structural characterizationis incomplete because of the reactive and delicate nature of the SEIand the electrolyte system in which it is formed. Here we present,for the first time, in situ neutron reflectometry measurements ofthe SEI layer as function of potential in a working lithium half-cell.The SEI layer after 10 and 20 CV cycles is 4.0 and 4.5 nm, respectively,growing to 8.9 nm after a series of potentiostatic holds that approximatesa charge/discharge cycle. Specified data sets show uniform mixingof SEI components. [ABSTRACT FROM AUTHOR]

Using neutron reflectometry and resonant x-ray techniques we studied the magnetic proximity effect (MPE) in superlattices composed of superconducting YBa2Cu307 and ferromagnetic-metallic Lao.67Cao.33Mn03 or ferromagnetic-insulating LaMn03+&b.delta;. We find that the MPE strongly depends on the electronic state of the manganite layers, being pronounced for the ferromagnetic-metallic Lao.67Cao.33Mn03 and almost absent for ferromagnetic-insulating LaMn03+&b.delta;. We also detail the change of the magnetic depth profile due to the MPE and provide evidence for its intrinsic nature. [ABSTRACT FROM AUTHOR]

The ever increasing need for product advancement and miniaturization keeps thin film assemblies, membranes, magnetic and non-magnetic multilayer and patterned heterostructures in the limelight of materials science and technological development. A number of thin film and surface characterization methods have emerged recently to meet the new challenges. The increased interest in magnetic thin film analytical instruments – mainly triggered by the discovery of the giant magnetoresistance and related phenomena [1] – resulted in a boom of Polarized Neutron Reflectometry studies as well as in construction of a number of new neutron reflectometers with polarization option. This article reports on the design, construction and operation parameters and first example uses of the “Grazing Incidence Neutron Apparatus” (GINA) a recently installed neutron reflectometer at the Budapest Neutron Centre (BNC) in Hungary. [ABSTRACT FROM PUBLISHER]

We demonstrate that delta doping can be used to create a dimensionally confined region of metallic ferromagnetism in an antiferromagnetic (AFM) manganite host, without introducing any explicit disorder due to dopants or frustration of spins. Theoretical consideration of these additional carriers shows that they cause a local enhancement of ferromagnetic double exchange with respect to AFM superexchange, resulting in local canting of the AFM spins. This leads to a highly modulated magnetization, as measured by polarized neutron reflectometry. The spatial modulation of the canting is related to the spreading of charge from the doped layer and establishes a fundamental length scale for charge transfer, transformation of orbital occupancy, and magnetic order in these manganites. Furthermore, we confirm the existence of the canted, AFM state as was predicted by de Gennes [Phys. Rev. 118, 141 (1960)] but had remained elusive. [ABSTRACT FROM AUTHOR]

Neutron reflectometry is a well established technique for the study of nanometre scale layered systems which are of direct relevance to a broad range of disciplines cutting across the physical and life sciences [1,2,3]. The second target station (TS2) at ISIS [4] is optimised to produce a large flux of cold neutrons, which when coupled with the large wavelength bandwidth provided by the 10Hz repetition rate offers the possibility for a step change in capability for the study of nanoscale systems. [ABSTRACT FROM AUTHOR]

We describe an apparatus for measuring scattering length density and structure of molecular layers at planar solid-liquid interfaces under high hydrostatic pressure conditions. The device is designed for in situ characterizations utilizing neutron reflectometry in the pressure range 0.1-100 MPa at temperatures between 5 and 60 °C. The pressure cell is constructed such that stratified molecular layers on crystalline substrates of silicon, quartz, or sapphire with a surface area of 28 cm2 can be investigated against noncorrosive liquid phases. The large substrate surface area enables reflectivity to be measured down to 10-5 (without background correction) and thus facilitates determination of the scattering length density profile across the interface as a function of applied load. Our current interest is on the stability of oligolamellar lipid coatings on silicon surfaces against aqueous phases as a function of applied hydrostatic pressure and temperature but the device can also be employed to probe the structure of any other solid-liquid interface. [ABSTRACT FROM AUTHOR]

The article focuses on the use of neutron reflectometry (NR) to investigate model cell membranes at the liquid-solid interface. The NR characterizes the composition, organization and structure of the model membranes. The measurements of the interactions of the model membranes with an external stimuli, including the adherence of live mouse fibroblast cells are presented.

Neutron reflectometry has been used to determine the interface structure and swelling of thin polymer films, when annealed in contact with a series of 1-alkyl-3-methylimidazolium ionic liquids (ILs). By choosing immiscible polymer/IL combinations, we have established that thin polymer films can be annealed for several hours in contact with ILs at temperatures well above the glass transition temperature and that this nonsolvent annealing environment can be exploited to direct self-assembly in polymer films. The ingress of IL into polymer films was quantified in terms of the swelling up to 10%. The polymer/IL interfacial width generally also increased from 0.9 nm up to ∼3 nm, but there was remarkably little correlation between interfacial width and swelling. For one combination of polymer and IL (deuterated PMMA and Bmim-BF4) the interfacial width decreased slightly with increasing temperature, consistent with LCST behavior for this system. All of the ILs tested had a profound influence the distribution of carboxy-end-functionalized deuterated polystyrene, “dPS-COOH”, in blended films with polystyrene homopolymers. The ILs promoted dPS-COOH adsorption at the film/IL interface and the simultaneous rapid desorption at the film silicon−oxide interface. The rate of desorption was found to correlate with the swelling behavior of the polymer with respect to the IL anion species: PF6−< Br−< Cl−< BF4−, suggesting that the polymer films are plasticized by the IL as it penetrates the film. [ABSTRACT FROM AUTHOR]

In this article, we show how neutron reflectometry (NR) can provide deep insight into the absorption and desorption properties of commercially promising hydrogen storage materials. NR benefits from the large negative scattering length of hydrogen atoms, which changes the reflectivity curve substantially, so that NR can determine not only the total amount of stored hydrogen but also the hydrogen distribution along the film normal, with nanometer resolution. To use NR, the samples must have smooth surfaces, and the film thickness should range between 10 and 200 nm. We performed a systematic study on thin Mg1-xAlx alloy films (x = 0.2, 0.3, 0.4, 0.67) capped with a Pd catalyst layer. Our NR experiments showed that Mg0.7Al0.3 is the optimum alloy composition with the highest amount of stored hydrogen and the lowest desorption temperature. All the thin films expand by about 20% because of hydrogen absorption, and the hydrogen is stored only in the MgAl layer with no hydrogen content in the Pd layer. Nous montrons ici comment la Réflectométrie Neutronique (NR) peut permettre une étude plus approfondie des propriétés d'absorption et de désorption de matériaux de stockage d'hydrogène commercialement prometteurs. NR utilise la grande longueur de diffusion négative des atomes d'hydrogène qui change substantiellement la courbe de réflectivité de telle sorte que NR peut déterminer non seulement la quantité totale d'hydrogène stockée, mais également la distribution de l'hydrogène selon la normale au film, avec une précision du nanomètre. Pour pouvoir utiliser NR, les films doivent avoir une surface lisse et leur épaisseur doit se trouver entre 10 et 200 nm. Nous avons étudié systématiquement des films minces d'alliage Mg1-xAlx (x = 0,2, 0,3, 0,4, 0,67) recouverts d'une couche de Pd comme catalyseur. Nos mesures montrent que Mg0,7Al0,3 est l'alliage optimum qui permet le plus haut stockage d'hydrogène et la plus basse température de désorption. Tous les films minces gonflent d'environ 20 % suivant l'absorption d'hydrogène qui est stocké uniquement dans la couche de MgAl, sans hydrogène dans le Pd. [ABSTRACT FROM AUTHOR]

Neutron guides made of supermirror-coated glass are important components of most neutron scattering instruments, thus their quality and possible deterioration due to various deleterious effects (e.g., surface contamination or defects) deserve careful examination. The modification of the reflectivity of supermirrors and the transmission of neutron guides due to surface contamination with hydrocarbon oil has been investigated using neutron reflectometry together with model calculations. A significant loss in the neutron reflectivity was observed for supermirrors covered with thin hydrocarbon oil films, which were confirmed in model calculations. Simulations carried out for several typical arrangements show drastic decreases in the transmitted neutron flux of neutron guides. These simulations show that determining the distortion of the beam profile (using a slit or a pin hole) enables the detection of oil contamination even in an operating neutron guide. [ABSTRACT FROM AUTHOR]

We have investigated the formation of supported surfactin−phospholipid mixed bilayers using neutron reflectometry. Micellar mixtures of phospholipid (diphosphatidyl choline, DPPC), surfactin, and β-d-dodecyl maltoside were used to make the deposition. When the surfactin concentration is at its critical micelle concentration (CMC = 6 × 10−6M) in the bulk solution, there is no adsorption at all on the silica. When the surfactin concentration is lowered below the CMC, a mixed bilayer of surfactin and DPPC is formed. Since surfactin does not adsorb on silica from solutions of surfactin alone, this shows that there is a strong attraction between surfactin and DPPC. The variation of adsorbed amount, composition, and structure of the adsorbed layer are consistent with the attractive interaction between surfactin and DPPC and with their respective negative and positive affinities for the silica surface. Three phospholipid isotopic contrasts were measured and used to define the composition and structure of the surfactin−phospholipid bilayer. The maximum amount of surfactin in the bilayer reaches a mole fraction of about 0.2 and this is located in the outer leaflet of the bilayer within the headgroup and part of the adjacent chain region. [ABSTRACT FROM AUTHOR]

The optical properties of slow neutrons, which includes refraction, reflection and interference, were recognized in the very early days of neutron physics. Fermi and co-workers [1] reported the total (or critical) reflection of slow neutrons. Goldberger and Seitz showed that the intensity of reflected and transmitted neutrons follow the same laws as electromagnetic radiation. The early applications of those neutron optical phenomena included the determination of neutron scattering lengths, and the production of neutron guides and neutron spin polarizers. The development of graded multi-layer mirrors, “supermirrors” [2] quickly followed. From such developments and the pioneering neutron guide installations at the Institute Laue Langevin, ILL, in Grenoble, sophisticated neutron optical devices are now commonplace on all neutron sources. The potential to use neutron reflectivity to probe surface structure arose out of those early applications. As such neutron reflectometry (NR) has evolved [3-6] over the past quarter century to become an established probe of the structure of thin films and periodic multilayers of both soft and hard condensed matter. From the beginning, specular neutron reflectivity measurements have been used to determine scattering length density depth profiles related to chemical composition and, with polarized beams, the vectorial magnetization depth profile in magnetic thin film systems. The success of NR can be attributed not only to instrumentation advances and the formulation of quantitatively accurate theoretical methods for the analysis of reflectivity data, but to the advances in various thin film deposition techniques required to prepare satisfactory sample systems for study. In this article, a partial history of neutron reflectometry development is briefly outlined in the form of complementary perspectives from the two authors. Length limitations, however, make it impossible to acknowledge here, let alone adequately describe, all of the important work that so many people have contributed to the implementation of neutron reflectometry in many fields of scientific investigation. [ABSTRACT FROM AUTHOR]

Neutron reflectometry was used to examine the interactions of polymer electrolyte fuel cell (PEFC) materials that comprise the triple-phase interface. Smooth, idealized layers of Nafion on glassy carbon (GC) and Pt surfaces were used to experimentally model the PEFC electrode interfaces. Different multilayer structures of Nafion were found in contact with the Pt or GC surfaces. These structures showed separate hydrophobic and hydrophilic domains formed within the Nafion layer when equilibrated with saturated D20 vapor. A hydrophobic Nafion region was formed adjacent to a Pt film. However, when Nafion was in contact with a PtO surface, the Nafion at the Pt interface became hydrophilic. The adsorbed oxide layer caused. a long-range restructuring of the perfluorosulfonic acid polymer chains that comprise Nafion. The thicknesses of the hydrophobic and hydrophilic domains changed to the same magnitude when the oxide layer was present compared to a thin hydrophobic domain in contact with Pt. A three-layer Nafion structure was formed when Nafion was in direct contact with GC. The findings in this research are direct experimental evidence that both the interfacial and long-range structural properties of Nafion are affected by the material with which it is in contact. Evidence of physical changes of aged Nafion films was obtained, and the results showed a permanent increase in the thickness of the Nafion film and a decrease in the scattering length density (SLD), which are attributed to irreversible swelling of the Nafion film. The aging also resulted in a decrease in the SLD of the GC substrate, which is likely due to either an increase in surface oxidation of the carbon or loss of carbon mass at the GC surface. [ABSTRACT FROM AUTHOR]

Determining how analytes are sequestered into thin films is important for solid-state sensors that detect the presence of the analyte by oxidative luminescence quenching. We show that thin (230 ± 30 Å) and thick (750 ± 50 Å) films of a first-generation dendrimer comprised of 2-ethylhexyloxy surface groups, biphenyl-based dendrons, and a 9,9,9′,9′-tetra-n-propyl-2,2′-bifluorene core, can rapidly and reversibly detect p-nitrotoluene by oxidative luminescence quenching. For both the thin and thick films the photoluminescence (PL) is quenched by p-nitrotoluene by ∼90% in 4 s, which is much faster than that reported for luminescent polymer films. Combined PL and neutron reflectometry measurements on pristine and analyte-saturated films gave important insight into the analyte adsorption process. It was found that during the adsorption process the films swelled, being on average 4% thicker for both the thin and thick dendrimer films. At the same time the PL was completely quenched. On removal of the analyte the films returned to their original thickness and scattering length density, and the PL was restored, showing that the sensing process was fully reversible. [ABSTRACT FROM AUTHOR]

We studied the swelling of polyelectrolyte (PE) multilayers (PEM) in water (H2O) vapors. The PEM were made from polyanion poly(styrene sulfonate) (PSS) and polycation poly(diallyldimethylammonium chloride)-N-methyl-N-vinylacetamide (pDADMAC−NMVA). While PSS is a fully charged polyanion, pDADMAC−NMVA is a random copolymer made of charged pDADMAC and uncharged NMVA monomer units. Variation of the relative amount of these two units allows for controlling the charge density of pDADMAC−NMVA. The degree ofswelling was studied as a function of the relative humidity in the experimental chamber (respectively water concentration in the gas phase) for PEM prepared from PSS and pDADMAC−NMVA with their different charge densities - 100%, 89% and 75%. The films were prepared by means of spraying technique and consisted of six PE couples−PSS/pDADMAC−NMVA. Neutron reflectometry was applied as main tool to observe the swelling process. The technique allows to obtain in a single experiment information about film thickness and amount of water in the film. The experiments were complemented with AFM measurements to obtain the thickness of the films. It was found that the film thickness increases when the charge density of the polycation decreases. The swelling of the PEM increases with the relative humidity and it depends on the charge density of pDADMAC−NMVA. The swelling behavior is 2-fold, splitting up in a charge dependent mode with relatively little volume increase, and a second mode with high volume expansion, which is independent from charge density of PEM. The “swelling transition” occurs for all samples at a relative humidity about 60% and a volume increase of ca. 20%. The results were interpreted according to the Flory−Huggins theory which assumes a phase separation in PEM network at higher water contents. [ABSTRACT FROM AUTHOR]

A molecular beam epitaxy (MBE) facility has been built to enable in situ neutron scattering measurements during growth of epitaxial layers. While retaining the full capabilities of a research MBE chamber, this facility has been optimized for polarized neutron reflectometry measurements. Optimization includes a compact lightweight portable design, a neutron window, controllable magnetic field, deposition across a large 76 mm diameter sample with exceptional flux uniformity, and sample temperatures continuously controllable from 38 to 1375 K. A load lock chamber allows for sample insertion, storage of up to 4 samples, and docking with other facilities. The design and performance of this chamber are described here. [ABSTRACT FROM AUTHOR]

Neutron reflectometry was used to probe in situ the structure of supported lipid bilayers at the solid-liquid interface during the early stages of UV-induced oxidative degradation. Single-component supported lipid bilayers composed of gel phase, dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), and fluid phase, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), phospholipids were exposed to low-dose oxidative stress generated by UV light and their structures were examined by neutron reflectometry. An interrupted illumination mode, involving exposures in 15 mm increments with 2 h intervals between subsequent exposures, and a continuous mode involving a single 60 (or 90) mm exposure period were employed. In both cases, pronounced differences in the structure of the lipid bilayer after exposure were observed. Interrupted exposure led to a substantial decrease in membrane coverage but preserved its total thickness at reduced scattering length densities. These results indicate that the initial phase during UV-induced membrane degradation involves the formation of hydrophilic channels within the membrane. This is consistent with the loss of some lipid molecules we observe and attendant reorganization of residual lipids forming hemimicellar edges of the hydrophilic channels. In contrast, continuous illumination produced a graded interface of continuously varied scattering length density (and hence hydrocarbon density) extending 100-150 Å into the liquid phase. Exposure of a DPPC bilayer to UV light in the presence of a reservoir of unfused vesicles showed low net membrane disintegration during oxidative stress, presumably because of surface back-filling from the bulk reservoir. Chemical evidence for membrane degradation was obtained by mass spectrometry and Fourier transform infrared spectroscopy. Further evidence for the formation of hydrophilic channels was furnished by fluorescence microscopy and imaging ellipsometry data. [ABSTRACT FROM AUTHOR]

In this paper, we describe the construction of a new neutron surface force confinement cell (NSFCC). The NSFCC is equipped with hydraulically powered in situ, temporally stable, force control system for simultaneous neutron reflectometry studies of nanoconfined complex fluid systems. Test measurements with deuterated toluene confined between two opposing diblock copolymer (polystyrene+poly 2-vinylpyridine) coated quartz substrates demonstrate the capabilities of the NSFCC. With increasing hydraulically applied force, a series of well-defined decreasing separations were observed from neutron reflectivity measurements. No noticeable changes in the hydraulic pressure used for controlling the surface separation were observed during the measurements, demonstrating the high stability of the apparatus. This newly designed NSFCC introduces a higher level of control for studies of confinement and consequent finite size effects on nanoscale structure in a variety of complex fluid and soft condensed matter systems. [ABSTRACT FROM AUTHOR]

A polarized neutron reflectometer for vertical samples is available at Dhruva reactor guide hall, Trombay. The reflectometer has been designed for horizontal scattering vector. It uses a position-sensitive detector for obtaining the reflectivity pattern. This arrangement allows one to obtain diffuse or off-specular intensity around any specular peak at one go. We have used this instrument for studying the structure of various metal{ metal and metal{semiconductor multilayers by specular reflectometry. We have also been successful in understanding interface morphology of several films through diffuse neutron reflectometry (DNR) on this reflectometer. Some of the recent results are presented in this paper to demonstrate the strength of these two techniques. [ABSTRACT FROM AUTHOR]

A scintillation strip detector designed for precise experiments on the reflectometry of thermal neutrons is described. Test results obtained on the beam of a time-of-flight spectrometer have shown that the detector has a detection efficiency for thermal neutrons close to 100%, a lowered sensitivity to the neutron background, and a low level of intrinsic noise. The coordinate resolution of the detector can be varied in the range 1.5-0.1 mm. The strip is manufactured from a mixture of a ZnS(Ag) scintillator and a 6LiF neutron converter. [ABSTRACT FROM AUTHOR]

An elastic neutron scattering instrument, the advanced neutron diffractometer/reflectometer (AND/R), has recently been commissioned at the National Institute of Standards and Technology Center for Neutron Research. The AND/R is the centerpiece of the Cold Neutrons for Biology and Technology partnership, which is dedicated to the structural characterization of thin films and multilayers of biological interest. The instrument is capable of measuring both specular and nonspecular reflectivity, as well as crystalline or semicrystalline diffraction at wave-vector transfers up to approximately 2.20 Å-1. A detailed description of this flexible instrument and its performance characteristics in various operating modes are given. [ABSTRACT FROM AUTHOR]

A polarized neutron reflectometer for vertical sample geometry has been installed in the guide tube laboratory of Dhruva reactor at Trombay, India. The instrument uses a monochromatic neutron beam of 2.5 Å in a step scan mode with a linear position sensitive detector for data collection. This allows one to collect off-specular or diffuse neutron reflectivity (DNR) data quite easily besides specular reflectivity data. The design aspects of this instrument have been presented. The instrument can easily switch between unpolarized and polarized mode, since the beam to the sample is prepared by reflection from a polarizing supermirror or a non-polarizing supermirror. Specular reflectivity studies in unpolarized and polarized mode, for chemical and magnetic structure of thin film samples have been presented. DNR data has been collected from a Ni film. Interface morphology at the air-film interface has been obtained from this data. [ABSTRACT FROM AUTHOR]

A time-of-flight neutron reflectometer is to be built at the new 20 MW research reactor (OPAL) in Sydney. The instrument will be positioned at the end of a curved supermirror neutron guide that will provide optimal transmission of cold neutrons (2–20 Å) while removing fast neutrons and high-energy γ-rays. The reflectometer will utilise a white neutron beam that will be pulsed using a series of boron coated disc choppers. Typically three angle settings will be required to collect a complete reflectivity profile (from Q z = 0.005–0.5 Å - 1 ). The new instrument will operate with a vertical scattering plane, making it suitable for both solid and “free-liquid” surfaces. The instrument will also be capable of producing a spin-polarized neutron beam making provision for polarized neutron reflectometry studies. Detection of the reflected neutrons will take place using a 2-dimensional 3 He delay-line detector with high-speed data acquisition electronics. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we report the results of our first tests of a novel proof-of-principle instrument developed at the IPNS, Argonne. The experiment was performed on the time of flight POSY1 instrument, the polarized reflectometer at the IPNS, which was modified to accommodate the apparatus. Two sets of RF-flippers were tested together, generating a modulated intensity by zero effort (MIEZE)-type neutron resonant spin echo signal which was observed at the detector using a wide neutron wavelength band. [Copyright &y& Elsevier]

We describe a variable temperature, relative humidity (0%–100% RH), and bulk liquid neutron reflectometry sample cell suitable for the study of polymeric and biomimetic materials (e.g., lipid bilayers). Compared to previous reflectometry cells, one of the advantages of the present sample environment is that it can accommodate ovens capable of handling either vapor or bulk liquid hydration media. Moreover, the design of the sample cell is such that temperature gradients are minimal over a large area (∼80 cm2) allowing for the nontrivial 100% RH condition to be attained. This permits the study, by neutron reflectometry, of samples that are intrinsically unstable in bulk water conditions, and is demonstrated by the lamellar repeat spacing of lipid bilayers at 100% RH being indistinguishable from those same bilayers hydrated in liquid water. [ABSTRACT FROM AUTHOR]

Abstract: The scattering length density profile for a thin film structure can be determined uniquely if both the modulus and phase of the reflection coefficient is known. Here, we describe a method for recovering the phase information which utilize a magnetic substrate and based on polarization analysis of the reflected beam. The method is derived in the formalism of transfer matrix so it is applicable for any unknown real scattering length density of nonmagnetic films (i.e. in the case where there is no effective absorption). [Copyright &y& Elsevier]

A multi-wire proportional counter with delay line readout, a sensitive area of 500×500 mm2 and a spatial resolution of ∼2×2 mm2 is being developed for the reflectometer REFSANS at the new reactor FRM-II in Munich in Germany. The characterization of a prototype of this detector with γ-rays and neutrons is presented. [Copyright &y& Elsevier]

The neutron spin-echo (NSE) method, which is the most powerful tool of high-resolution neutron spectroscopy, is known in two versions: with the long solenoids and short alternating fields. Here we consider an alternative version that makes use of spin flippers consisting of thin magnetic foils (TMF) with an in-plane rotating magnetic field vector. MNCP simulations show the perfect performance of the NSE spectrometer build upon such flippers. The requirements for TMF are estimated. Some possible applications of such technique are discussed. This approach can be considered as an alternative to the present day NSE techniques. [Copyright &y& Elsevier]

Discusses a method to perform neutron reflectometry measurements, the spin-echo small-angle neutron scattering technique. Two different modes of applications, giving successively information about the structure perpendicular to and parallel to the sample plane; Comparison of the simulated results of the perpendicular mode to those obtained by conventional methods.

Discusses the neutron reflectometry research in Australia. Scientific applications of neutron reflectometry by Australian researchers; Influence of planar geometry of an interface on the structure of the bulk in the proximity of the interface; Instrument specifications for the Australian Replacement Research Reactor.

The role of polarized neutrons in specular reflectometry to solve the longstanding phase problem is reviewed. A survey of recently proposed reference layer methods based on polarization measurements is given and the essentials of the reconstruction procedure are summarized. Future developments as well as a dedicated reflectometer set-up for phase determination are discussed. [Copyright &y& Elsevier]