Spin-echo Small-angle Neutron Research Articles

Spin echo small-angle neutron scattering using superconducting magnetic Wollaston prisms.

We show the implementation of superconducting magnetic Wollaston prisms for spin echo small-angle neutron scattering. Two calibration methods for the spin echo length are presented: one utilizing spin echo modulated small-angle neutron scattering and the other based on the neutron refraction by quartz wedge crystals. Our experimental results with polystyrene nano-particle colloids showcase the system's efficacy in measuring both dilute and concentrated colloidal systems. Additionally, investigations into the pore diameter and pitch of a nano-porous alumina membrane demonstrate its capability in analyzing nano-porous materials. Furthermore, we discuss potential optimizations to further extend the accessible spin echo length.

Simulation of spin-echo SANS (SESANS) using McStas on monochromatic and time of flight instruments

We conduct simulations of Spin Echo Small Angle Neutron Scattering (SESANS) by employing Monte Carlo methods to a setup using four magnetic Wollaston prisms. Our primary focus involves the validation of these models, encompassing monochromatic scenarios across various neutron wavelengths to ascertain the reliability of the simulations. Subsequently, we extend this validation to encompass simulations in time-of-flight mode. Our model consistently and precisely predicts the scattering patterns emanating from dilute spheres in both monochromatic and time-of-flight modes. Notably, it also accurately reproduces the intricate encoding associated with scattering occurring between the third and fourth magnetic Wollaston prism, which provides us with another approach to increase the solid angle coverage of a SESANS instrument. This validation process conclusively demonstrates the efficacy of our simulation methods. Importantly, it paves the way for simulating more intricate and realistic instrumental configurations, broadening the horizons for future research endeavours.

Revealing microscale bulk structures in polymer-carbon nanocomposites using spin-echo SANS.

We have used spin-echo small-angle neutron scattering (SESANS) to probe the hierarchy of structures present in polymer-carbon nanocomposites, with length scales spanning over three orders of magnitude, from 10 nm to 16 μm. The data processing and reduction show a unified approach across two SESANS instruments (TU Delft and Larmor at the ISIS neutron source) and yield consistent data that are able to be modelled using well-established hierarchical models in freely available software such as SasView. Using this approach, we are able to extend the measured length scales by over an order of magnitude compared to traditional scattering methods. This yields information about the structure in the bulk that is inaccessible with conventional scattering techniques (SANS/SAXS) and points to a way for interrogating and investigating polymer nanocomposites routinely across multiple length scales.

Time-of-flight spin-echo small-angle neutron scattering applied to biological cell nuclei

The organization of chromatin in the nuclei of rat lymphocyte was studied by time-of-flight spin-echo small-angle neutron scattering (ToF-SESANS). The procedures of the measurements in ToF and monochromatic SESANS modes were compared. It is shown that the sensitivity of the ToF method is significantly higher than that of the monochromatic mode. As a result, the SESANS correlation function can always be extracted from the ToF measurement of polarization, while this is not always the case with the monochromatic mode. The applicability of SESANS to fractal objects at the micrometre scale is demonstrated. The SESANS correlation function is well fitted by the exponential decay G(z) = exp(−z/ξ) with the correlation length ξ = 3.7 ± 0.1 µm. The exponential decay of the SESANS correlation function can be connected to the logarithmic correlation function γ(r) = ln(r/ξ) and the cubic law of the scattering intensity I(Q) = Q −3, which is in agreement with the concept of scattering from fractal objects. This finding is interpreted as evidence of a very specific logarithmic fractal structure of the large-scale organization of chromatin. The model of the logarithmic fractal is visualized as a hierarchical object obeying the volume-conservation principle at different scales.

Simulations and concepts for a 2-D spin-echo modulated SANS (SEMSANS) instrument

The spin-echo small-angle neutron scattering (SESANS) technique utilises a series of inclined magnetic fields before and after the sample to encode the scattering angle into the polarisation to obtain a much higher resolution than in conventional SANS. The analogous technique (spin echo modulated SANS (SEMSANS)) implements spin manipulations before the sample only to encode the scattering into an intensity modulation. The technique can be combined with SANS to expand the length scale range probed from 1 nm to microns.Using McStas we show that using a series of four magnetic Wollaston prisms in two orthogonal pairs with a 90° rotation can be utilised to create SEMSANS modulations in 2-D. These modulations can also be of different periods in each encoding direction. This method can be applied to anisotropic scattering samples. Also this allows for the simultaneous measurement at two orthogonal independent spin-echo lengths. This technique yields directly information about the structure of oriented structures.

Effect of Cr interlayers on texture and magnetic properties of FeSi films with micrometer thickness

Magnetised soft ferromagnetic films with micrometer thicknesses can be used as π-flippers in spin-echo small-angle neutron scattering instruments. An FeSi film with a total thickness of 2000 nm separated by Cr interlayers (each 10 nm thick) was fabricated using direct-current magnetron sputtering. The thickness of each FeSi layer was 100 nm between adjacent Cr interlayers. Hysteresis loop measurements were performed to characterise the magnetic properties of the FeSi films. X-ray diffraction measurements, high-resolution transmission electron microscopy, and selected-area electron diffraction were used to characterise the texture. Results demonstrated that the saturation magnetisation of the FeSi film separated by Cr interlayers was higher and its coercivity was lower than those of the FeSi film separated by Ta interlayers because of different texture of FeSi layer. The FeSi film separated by Cr interlayers featured FeSi (210) and FeSi (221), and the Cr interlayers presented Cr (110). The FeSi layer between the Cr interlayers demonstrated structural coherency with the upper FeSi layer, and continuity of the lattice fringes from the Cr grains to the FeSi layers was observed. Therefore, degradation in the soft magnetic properties of FeSi films can be prevented by the insertion of Cr interlayers.

Magnetized FeSi film with micrometer thickness inserted with Cr layers as [formula omitted]-flippers for neutron spin-echo spectrometry

Magnetized soft ferromagnetic films with micrometer thickness can be used as π-flippers for a spin echo small-angle neutron scattering (SESANS) instrument. Two FeSi monolayers and two FeSi/Cr multilayers were fabricated using a direct-current magnetron sputtering technique. The thicknesses of the two FeSi monolayers were 114 nm and 1140 nm, respectively. The two FeSi/Cr multilayers with 2 and 20 periods, respectively, were composed of FeSi layers having thicknesses of 1000 nm and 100 nm, respectively, and 10 nm-thick Cr layers. Hysteresis loop measurements and X-ray diffraction measurements were used to characterize their magnetic properties and texture, respectively. Polarized neutron flipping efficiency measurements were conducted using the TPNR (Time-of-flight and Polarized Neutron Reflectometer) to determine the flipping efficiency of the FeSi/Cr multilayer with [100 nm FeSi/10 nm Cr]20. The experimental results show that the saturation magnetization of the FeSi-monolayers decreased and the coercivity increased as their thickness increased. The FeSi/Cr multilayer with [100 nm FeSi/10 nm Cr]20 had higher saturation magnetization (1300 emu/cm 3) and lower coercivity than those of [1000 nm FeSi/10 nm Cr]2, although the total thickness of the FeSi layers was almost the same, and its maximum flipping efficiency was up to 98% for polarized neutrons.

Radial spin echo small-angle neutron scattering method: concept and performance.

A novel spin echo small-angle neutron scattering (SESANS) concept based on a rotationally symmetric magnetic field geometry is introduced. The proposed method is similar to the conventional linear SESANS technique but uses longitudinal precession fields and field gradients in a radial direction, as typically found in neutron spin echo (NSE) spectrometers. Radial SESANS could thus be implemented as an add-on to NSE setups. The neutron trajectory through the instrument is encoded with the help of radial gradients generated by radial shifters, which are coils placed in the beam area similar to Fresnel coils. The present work introduces the setup of the instrument and explores its performance and the relationship between the encoded momentum transfer and the precession angle. The results indicate that radial SESANS is only sensitive to scattering along the radial direction and thus measures the projected correlation function along this direction as a function of the spin echo length, defined similarly to linear SESANS. For an evaluation of the performance of the setup, the case of scattering from solid spheres is considered and the results calculated for the radial and linear SESANS cases are compared. Also discussed is the implementation of the radial magnetic field geometry in spin echo modulated small-angle neutron scattering.

Design and simulations of spin-echo small angle neutron scattering spectrometer at CMRR

Current work presents the design and simulations of the spin-echo small-angle neutron scattering (SESANS) spectrometer at the 20 MW China Mianyang research reactor (CMRR)-based neutron center. Firstly, the components of the SESANS are introduced. Secondly, the Monte Carlo simulations of the key components for determining the technical parameters are presented. The bending radius of the focusing monochromator is set to 2.5 m. The length and radius of curvature of the S-Bender is set to 300 mm and 2.0 m, respectively. Accordingly, simulation results of the virtual spectrometer indicate that the neutron beam transmission is about 0.09 at wavelength of 0.4 nm. Thirdly, the finite element simulation and the testing of the magnetic field suggest that the optimized ampere-turns are 8400 and 8289.9, respectively. Accordingly, the simulation results indicate that the field integral homogeneity of main coil, V-coil, and field stepper are better than 2.91 × 10−6 T m, 2.3 × 10−6 T m, and 3.14 × 10−6 T m, respectively. Last, a multilayer flipper-permalloy with 100 nm FeSi and 10 nm Cr (or Ta) alternately sputtered on a Si wafer was designed and tested. Neutron experiments demonstrate that the maximum flipper efficiency reaches 0.98 and remains stable with increasing the strength of the main fields from 50 Gs to 200 Gs, when the corresponding wavelength is 0.31 nm. Based on the optimized parameters, the SESANS is under construction, and it will be completed at the end of 2021.

Spin-echo small-angle neutron scattering for multiscale structure analysis of food materials

Spin-echo small-angle neutron scattering (SESANS) yields structural information on length scales from 30 nanometres up till 20 micrometres. These length scales match nicely those of colloids, protein networks and fat droplets, which are present in many food materials. This makes SESANS an excellent probe to study food materials. An interesting feature of SESANS is the real space character of the raw data. Several examples of quantitative neutron scattering studies on food materials are shortly reviewed.

Probing magnetic correlations with spin-echo modulated small angle neutron scattering (SEMSANS)

The first measurements of magnetic correlation functions are presented using time-of-flight Spin-echo modulated small angle neutron scattering (SEMSANS) on the Larmor instrument at the ISIS pulsed neutron source. The accessible length scale is beyond that of the conventional SANS. A simplified model is presented to calculate the expected correlation functions for various magnetisation fields applied to the sample. As an example, we present the experimental data of a soft iron sample at various configurations of magnetisation field.

The microscopic distribution of hydrophilic polymers in interpenetrating polymer networks (IPNs) of medical grade silicone

By introducing hydrophilic polymers into silicone medical devices, highly beneficial biomedical properties can be realized. An established solution to introduce hydrophilic polymers is to form an interpenetrating polymer network (IPN) by performing the hydrogel synthesis in the presence of silicone swollen in supercritical carbon dioxide. The precise distribution of the two polymers is not known, and determining this is the goal of this study. Neutron scattering and microscopy were used to determine the distribution of the hydrophilic guest polymer. Atomic force microscopy revealed that the important length scale on the surface of these materials is 10–100 nm, and spin-echo small-angle neutron scattering (SESANS) on IPNs submerged in D2O revealed structures of the same scale within the interior and enabled quantification of their size. SESANS with hydration by D2O proved to be the only scattering technique that could determine the structure of the bulk of these types of materials, and it should be used as an important tool for characterizing polymer medical devices.

Simulations of foil-based spin-echo (modulated) small-angle neutron scattering with a sample using McStas.

For the further development of spin-echo techniques to label elastic scattering it is necessary to perform simulations of the Larmor precession of neutron spins in a magnetic field. The details of some of these techniques as implemented at the reactor in Delft are simulated. First, the workings of the magnetized foil flipper are simulated. A full virtual spin-echo small-angle neutron scattering instrument is built and tested without and with a realistic scattering sample. It is essential for these simulations to have a simulated sample that also describes the transmitted beam of unscattered neutrons, which usually is not implemented for the simulation of conventional small-angle neutron scattering (SANS) instruments. Finally, the workings of a spin-echo modulated small-angle neutron scattering (SEMSANS) instrument are simulated. The simulations are in good agreement with theory and experiments. This setup can be extended to include realistic magnetic field distributions to fully predict the features of future Larmor labelling elastic-scattering instruments. Configurations can now be simulated for more complicated combinations of SANS with SEMSANS.

Revisiting neutron scattering data from deuterated milk

Deuterated milk (dried milk powder that has been dissolved in deuterated water, 2H2O or D2O) is a valuable material for determining the structure of dairy products by neutron scattering. This has primarily been used in the past to study the internal structure of casein micelles, and when longer length scales have been studied, interparticle interactions have been neglected. This will impact fits to the data over all length scales, which will hamper quantitative data analysis. Previously measured large length scale neutron scattering data from the literature, both ultra-small-angle neutron scattering (USANS) and spin-echo small-angle neutron scattering (SESANS) data, have been reanalyzed and improved fits have been obtained using a recently proposed model describing casein micelles as sticky spheres, rather than as hard spheres. This shows that these interactions will also be necessary for modeling neutron scattering data on deuterated milk.

Structural characterization of spray-dried microgranules by spin-echo small-angle neutron scattering

Spray-drying is a widely used industrial technique and has shown an immense potential in the fields of nanoscience and technology. This is due to its ability to synthesize microgranules consisting of correlated nanostructures using evaporation induced assembly through bottom-up approach. Although the nature of correlation among the constituent nanoparticles and their size distribution could earlier be obtained by conventional Small-angle Scattering (SAS) technique, a statistically averaged quantitative measure of the shell thickness and hollowness of the formed granules remained a challenge. In this work, we have used Spin-echo Small-angle Neutron Scattering (SESANS) technique to characterize spray-dried nanostructured microgranules having different hollowness. It is shown that this non-destructive technique provided precise quantification of the granular sizes and hollowness by utilizing polarization property of neutrons in real space directly.

Neutron Larmor diffraction on powder samples.

A hitherto unrecognized resolution effect in neutron Larmor diffraction (LD) is reported, resulting from small-angle neutron scattering (SANS) in the sample. Small distortions of the neutron trajectories by SANS give rise to a blurring of the Bragg angles of the order of a few hundredths of a degree, leading to a degradation of the momentum resolution. This effect is negligible for single crystals but may be significant for polycrystalline or powder samples. A procedure is presented to correct the LD data for the parasitic SANS. The latter is accurately determined by the SESANS technique (spin-echo small-angle neutron scattering), which is readily available on Larmor diffractometers. The analysis technique is demonstrated on LD and SESANS data from α-Fe2O3 powder samples. The resulting d-spacing range agrees with experimental data from high-resolution synchrotron radiation powder diffraction on the same sample.

Spin-echo Small Angle Neutron Scattering for a Compact Neutron Source Daria

Spin-echo small-angle neutron scattering (SESANS) technique is a method to measure the correlation function of the structural organization of materials from nano- to micrometer length scales. As this method does not require neither highly collimated beams nor high incident intensity it can be easily and effectively used at the low flux sources, such as compact accelerator-driven neutron sources. Here we describe an important science case for SESANS setup designed at the compact neutron source DARIA. It was shown that SESANS method is a sensitive tool to study the packaging of DNA in the nuclei of biological cells. The sensitivity of the SESANS signal crucially depends on the neutron wavelength. The pulse character of the compact neutron source suits ideally to these investigations as it implies changeable neutron wavelength in the range from 0.2 to 1.0 nm. Such option allows one to study in great detail the internal structure of the biological cell in the length scale from 10 nm to 100 μm.

Systematically quantifying oil–water microemulsion structures using (spin-echo) small angle neutron scattering

Microemulsion systems consisting of D2O, an alkane, an anionic internal olefin sulfonate surfactant, salt and secondary butyl alcohol (SBA) as co-solvent are studied in a systematic way. In four different sample sets, either the salt content, SBA content or alkane carbon number was varied in order to study the effects of the individual compounds on the structure sizes making up the microemulsion. Using complementary small-angle neutron scattering techniques SANS and Spin-Echo SANS, it was found that the microemulsion systems exhibit the largest structures in the optimum state (domain size of d/2 =144 nm in the model by Teubner and Strey), where the structure is considered bicontinuous. In comparison, at under- and over-optimum states where the structures consist of emulsified spherical droplets, the smallest measured diameter was 2R = 44 nm. Furthermore, the structure sizes in bicontinuous microemulsions decrease exponentially (down to d/2 =15 nm for pentadecane and 5 wt% SBA) as function of both SBA content and alkane carbon number. The observed trends in structure sizes combined with the trends observed in the area per surfactant molecule, are qualitatively explained with the extended Winsor R-ratio, the HLD-NAC model and surfactant film flexibility arguments.

Evolution of dispersion in the melt compounding of a model polymer nanocomposite system: A multi-scale study

We investigate the morphological development of polystyrene (PS)-C60 nanocomposites along the length of a prototype co-rotating twin-screw extruder with sampling capabilities. The effects of C60 concentration and output on the morphological evolution along the extruder are studied employing a suite of characterization techniques covering a wide range of length-scales, thereby shedding new light on the dispersion mechanism in this model system. We show that the relatively new spin-echo small-angle neutron scattering (SESANS) technique is well suited to probe both the distribution and the dispersion of C60. SESANS complements optical microscopy (OM) data as it covers sampling areas several orders of magnitude larger than OM. The multi-scale morphological information conveyed by OM, SESANS, SANS and rheological data shows that for larger outputs, C60 agglomerates are eroded as they travel along the extruder, resulting in C60 dispersion and distribution at both molecular and micrometric levels. The picture is more complex when smaller feed rates are used, as the evolution of C60 dispersion depends on the C60 loading. For larger C60 contents, agglomeration develops along the extruder, whereas dispersion is improved for smaller C60 contents. Overall, it is concluded that an over-high feed rate in extrusion does not necessarily result in a bigger size of the nanoparticle agglomerates because of the complex interplay between stresses and residence time.

Spin-echo small-angle neutron scattering (SESANS) studies of diblock copolymer nanoparticles.

Poly(glycerol monomethacrylate)-poly(benzyl methacrylate) (PGMA-PBzMA) diblock copolymer nanoparticles were synthesized via polymerization-induced self-assembly (PISA) using reversible addition-fragmentation chain-transfer (RAFT) aqueous emulsion polymerization in D2O. Such PISA syntheses produce sterically-stabilized nanoparticles in situ and can be performed at relatively high copolymer concentrations (up to 50 wt%). This PGMA-PBzMA formulation is known to form only spherical nanoparticles in water using aqueous emulsion polymerization (Macromolecules, 2014, 47, 5613-5623), which makes it an ideal model system for exploring new characterization methods. The polymer micelles were characterized using small-angle X-ray scattering (SAXS) and a recently developed form of neutron scattering, spin-echo small-angle neutron scattering (SESANS). As far as we are aware, this is the first report of a study of polymer micelles by SESANS, and the data agree well with reciprocal-space scattering. Using this technique enables characterization of the concentrated, as synthesized dispersions directly without dilution, and this will provide a method to study self-assembled polymer systems that have concentration dependent morphologies, while still maintaining the advantages of scattering techniques.