Grazing-incidence Small-angle X-ray Research Articles

Enhanced magnetic anisotropy and its thermal stability in obliquely deposited Co-Film on the nanopatterned substrate

The deliberate manipulation of magnetic anisotropy through controlled adjustments to surface and interface morphology has become important due to its potential applications in spintronics and magnetic memory devices. In the present work, oblique angle deposition (OAD) at 65° to the surface normal on a rippled substrate, keeping nanopatterns on the SiO2 substrate perpendicular to the OAD projection, has been used to induce in-plane uniaxial magnetic anisotropy (UMA) and its thermal stability in cobalt (Co) thin film. Prior to film preparation, the patterned substrate of wavelength 68 ± 4 nm and amplitude 3.4 ± 0.2 nm was prepared separately using a low-energy ion beam erosion (IBE) process. Grazing incidence small-angle X-ray scattering (GISAXS) and magneto-optical Kerr effect (MOKE) techniques have been used for film characterization. While GISAXS provided information about film structure and morphology, MOKE provided information about magnetic properties, thus making it possible to correlate the temperature-dependent evolution of morphology with that of UMA in the film. A clear anisotropy in the growth of Co film is found to result in strong UMA. Unlike previous studies, which typically observe a reduction in UMA strength with thermal annealing, the present work demonstrates a 31 % increase in UMA strength after annealing up to 200 °C, underscoring the importance of oblique angle deposition on nano-rippled substrates for achieving high UMA and ensuring its thermal stability up to moderate temperatures. The appearance of large UMA and its unusual temperature dependence is understood in terms of the shadowing effects and column coalescence, resulting in more robust shape anisotropy. This work provides insights into morphological anisotropy, elucidating the interplay of shadowing effects, shape anisotropy, and dipolar interactions within interacting column and ripple structures. This method gives rise to morphology-induced anisotropy, which can also be applied to other ferromagnetic films to enhance the magnetic anisotropy and ensure thermal stability.

Equilibrium structure and shape of Ag and Pt nanoparticles grown on silica surfaces: From experimental investigations to the determination of a metal-silica potential.

A combination of experimental and numerical investigations on metallic silver and platinum nanoparticles deposited on silica substrates is presented, with a focus on metal-substrate interactions. Experimentally, the nanoparticles, obtained by ultra-high vacuum atom deposition, are characterized by grazing-incidence small-angle x-ray scattering and high resolution transmission electronic microscopy to determine their structure and morphology and, in particular, their aspect ratio (height/diameter), which quantifies the metal-substrate interaction, from the as-grown to equilibrium state. Numerically, the interactions between the metal and the silica species are modeled with the Lennard-Jones (12, 6) potential, with two parameters for each metal and silica species. The geometric parameters were found in the literature, while the energetic parameters were determined from our experimental measurements of the aspect ratio. The parameters are as follows: σAg-O = 0.278nm, σAg-Si = 0.329nm, ɛAg-O = 75meV, and ɛAg-Si = 13meV for Ag-silica and σPt-O = 0.273nm, σPt-Si = 0.324nm, ɛPt-O = 110meV, and ɛPt-Si = 18 meV for Pt-silica. The proposed Ag-silica potential reproduces quantitatively the unexpected experimental observation of the variation of the aspect ratio for Ag nanoparticles larger than 5nm, which has been interpreted as a consequence of the silica roughness. The nanoparticle orientation, structure, and disorder are also considered. This metal-silica potential for Ag and Pt should be helpful for further studies on pure metals as well as their alloys.

Morphology of Buried Interfaces in Ion-Assisted Magnetron Sputter-Deposited 11B4C-Containing Ni/Ti Multilayer Neutron Optics Investigated by Grazing-Incidence Small-Angle Scattering.

Multilayer neutron optics require precise control of interface morphology for optimal performance. In this work, we investigate the effects of different growth conditions on the interface morphology of Ni/Ti-based multilayers, with a focus on incorporating low-neutron-absorbing 11B4C and using different ion assistance schemes. Grazing-incidence small-angle X-ray scattering was used to probe the structural and morphological details of buried interfaces, revealing that the layers become more strongly correlated and the interfaces form mounds with increasing amounts of 11B4C. Applying high flux ion assistance during growth can reduce mound formation but lead to interface mixing, while a high flux modulated ion assistance scheme with an initial buffer layer grown at low ion energy and the top layer at higher ion energy prevents intermixing. The optimal condition was found to be adding 26.0 atom % 11B4C combined with high flux modulated ion assistance. A multilayer with a period of 48.2 Å and 100 periods was grown under these conditions, and coupled fitting to neutron and X-ray reflectivity data revealed an average interface width of only 2.7 Å, a significant improvement over the current state-of-the-art commercial Ni/Ti multilayers. Overall, our study demonstrates that the addition of 11B4C and the use of high flux modulated ion assistance during growth can significantly improve the interface morphology of Ni/Ti multilayers, leading to improved neutron optics performance.

Effect of Annealing on Stress, Microstructure, and Interfaces of NiV/B4C Multilayers

The functionality and reliability of nanoscale multilayer devices and components are influenced by changes in stress and microstructure throughout fabrication, processing, and operation. NiV/B4C multilayers with a d-spacing of 3 nm were prepared by magnetron sputtering, and two groups of annealing experiments were performed. The stress, microstructure, and interface changes in NiV/B4C after annealing were investigated by grazing-incidence X-ray reflectometry (GIXR), grazing-incidence X-ray diffraction (GIXRD), X-ray diffuse scattering, and grazing-incidence small-angle X-ray scattering (GISAXS). The temperature dependence experiments revealed a gradual shift in the multilayer stress from compression to tension during annealing from 70 °C to 340 °C, with the stress approaching near-zero levels between 70 °C and 140 °C. The time-dependent experiments indicated that most of the stress changes occurred within the initial 10 min, which showed that prolonged annealing was unnecessary. Combining the X-ray diffraction and X-ray scattering measurements, it was found that the changes in the thickness, interface roughness, and lateral correlation length, primarily due to crystallization, drove the changes in stress and microstructure.

An approach to surface electron density-sensing property correlation in non-stoichiometric boron carbide

The key to most surface phenomena lies in the surface electron density. Particularly, it is the electron density distribution over the surface that primarily controls the overall interaction of the material with the external environment, say in processes like heterogeneous catalysis. Hence, a precise understanding of surface electron density is essential to understand and design improved surface active materials for catalysis and sensing. Surface structure has been determined primarily using surface sensitive techniques like high-energy surface x-ray diffraction (XRD), the crystal truncation rod scattering method, low-energy electron diffraction, scanning transmission electron microscopy, and grazing incidence small angle x-ray scattering. In this work, using aspherical electron density models of crystal structures in different molecular and extended solids, we show a convenient and complementary way of determining high-resolution experimental surface electron density distribution from conventional bulk x-ray diffraction data. The usefulness of our method has been validated by the surface functionality of boron carbide. While certain surfaces in boron carbide show the presence of substantial electron deficient centers, they are absent in others. Based on that, a new surface property of boron carbide has been inferred and has also been validated by chemiresistive gas sensing experiments.

Mesoscale self-organization of polydisperse magnetic nanoparticles at the water surface.

In this study, we investigated the self-ordering process in Langmuir films of polydisperse iron oxide nanoparticles on a water surface, employing in situ x-ray scattering, surface pressure-area isotherm analysis, and Brewster angle microscopy. X-ray reflectometry confirmed the formation of a monolayer, while grazing incidence small-angle x-ray scattering revealed short-range lateral correlations with a characteristic length equal to the mean particle size. Remarkably, our findings indicated that at zero surface pressure, the particles organized into submicrometer clusters, merging upon compression to form a homogeneous layer. These layers were subsequently transferred to a solid substrate using the Langmuir-Schaefer technique and further characterized via scanning electron microscopy and polarized neutron reflectometry. Notably, our measurements revealed a second characteristic length in the lateral correlations, orders of magnitude longer than the mean particle diameter, with polydisperse particles forming circular clusters densely packed in a hexagonal lattice. Furthermore, our evidence suggests that the lattice constant of this mesocrystal depends on the characteristics of the particle size distribution, specifically the mean particle size and the width of the size distribution. In addition, we observed internal size separation within these clusters, where larger particles were positioned closer to the center of the cluster. Finally, polarized neutron reflectometry measurements provided valuable insights into the magnetization profile across the layer.

Thermally evaporated vanadium-based phthalocyanine for low moisture detection in humidity sensors

Aluminium / vanadyl 3,10,17,24-tetra-tert-butyl-1,8,15,22-tetrakis(dimethylamino)− 29 H,31 H-phthalocyanine (VTP) / Aluminium, (Al/VTP/Al) has been successfully studied for capacitive humidity sensing. The metal-containing vanadium central atom in the metal phthalocyanine has contributed towards excellent capacitance response at low humidity conditions as low as 10%RH. In addition, high surface roughness revealed by atomic force microscopy (AFM) images has also given insight into the low hysteresis lag. The film's large surface area helped prevent the water molecules from accumulating in the VTP pores and capillaries. Grazing-incidence wide and small-angle X-ray scattering (GIWAXS-GISAXS) indicates some face-on crystallite orientation produced by the partially ordered film, impacting the transient performance of the sensor.

Highly Ordered Monolayers of μm-Sized Polystyrene Spheres Studied by Grazing-Incidence Small-Angle X-ray Scattering, Simulations, and Geometrical Calculations.

Unraveling the two-dimensional (2D) structural ordering of colloidal particles assembled at a flat surface is essential for understanding and optimizing their physical properties. So far, grazing-incidence small-angle X-ray scattering (GISAXS) has been widely used to determine crystallographic information on 2D self-assembled structures of nanosize objects. However, solving the structure of 2D lattices consisting of micrometer (μm)-sized objects still remains a challenge using scattering methods. Here, a model 2D SCALMS (supported catalytically active liquid metal solution) template is fabricated from μm-sized polystyrene (PS) spheres that form a monolayer on top of the flat solid support. GISAXS patterns of the sample were collected for rotation angles around its surface normal in steps of 3°. For every rotation angle, different Bragg-type interference maxima along the out-of-plane (qz) direction were observed. On the basis of simulations of GISXAS patterns of single domains of ordered particle arrangements using the distorted wave Born approximation (DWBA) and validation against a simple geometrical scattering model, the interference maxima could nicely be interpreted to originate from a monolayer of the μm-sized spherical particles which are arranged in domains of hexagonal 2D paracrystalline order. This novel GISAXS evaluation technique serves as a proof of principle for determining the μm-size periodicity of 2D crystalline domains and demonstrates its potential to spatially resolve the relative orientations of such domains with respect to a reference direction.

Controlling Pt nanoparticle sintering by sub-monolayer MgO ALD thin films.

Metal nanoparticle (NP) sintering is a major cause of catalyst deactivation, as NP growth reduces the surface area available for reaction. A promising route to halt sintering is to deposit a protective overcoat on the catalyst surface, followed by annealing to generate overlayer porosity for gas transport to the NPs. Yet, such a combined deposition-annealing approach lacks structural control over the cracked protection layer and the number of NP surface atoms available for reaction. Herein, we exploit the tailoring capabilities of atomic layer deposition (ALD) to deposit MgO overcoats on archetypal Pt NP catalysts with thicknesses ranging from sub-monolayers to nm-range thin films. Two different ALD processes are studied for the growth of MgO overcoats on Pt NPs anchored on a SiO2 support, using Mg(EtCp)2 and H2O, and Mg(TMHD)2 and O3, respectively. Spectroscopic ellipsometry and X-ray photoelectron spectroscopy measurements reveal significant growth on both SiO2 and Pt for the former process, while the latter exhibits a drastically lower growth per cycle with an initial chemical selectivity towards Pt. These differences in MgO growth characteristics have implications for the availability of uncoated Pt surface atoms at different stages of the ALD process, as probed by low energy ion scattering, and for the sintering behavior during O2 annealing, as monitored in situ with grazing incidence small angle X-ray scattering (in situ GISAXS). The Mg(TMHD)2-O3 ALD process enables exquisite coverage control allowing a balance between physically blocking the Pt surface to prevent sintering and keeping Pt surface atoms free for reaction. This approach avoids the need for post-annealing, hence also safeguarding the structural integrity of the as-deposited overcoat.

Film before aggregates: an operando GISAXS study on electrochemically assisted surfactant assembly.

The process of electrochemically assisted surfactant assembly was followed in real time by grazing incidence small angle X-ray scattering with the aim to deconvolute the formation of mesoporous silica film and unwanted porous particles. The X-ray technique proved to be useful for the characterisation of this process, as it takes place at a very dynamic, solid/liquid interface. This paper shows the electrochemically driven onset and evolution of silica/surfactant structures. Additional control experiments indicate the formation of vertically aligned structures without the use of an electric field, although it seems to be beneficial for increased pore ordering.

Molecular-weight effects of a homopolymer on the AB- and ABC-stacks of perforations in block copolymer/homopolymer films.

We have demonstrated the molecular-weight effects of adding homopolystyrene (hPS) on the evolution of perforated layers and double gyroids in polystyrene-block-poly(methyl methacrylate)-based films during isothermal annealing. Two homopolystyrenes of 2.8 and 17 kg mol-1 were used. To prepare blend films, PS-b-PMMA and hPSx (x: 2.8 or 17) were mixed at a weight-fraction ratio of 75/25 in toluene and then spin-coated at SiOx/Si. Spin coating inevitably produced films with thick edges at the periphery of the substrate. The structural evolution of the spun films was in situ characterized by grazing incidence small-angle X-ray scattering (GISAXS). The annealed films were then characterized using a scanning electron microscope (SEM). We found that thin middle regions behaved differently from thick beads for the films. The middle of the blend films mainly formed perforated layers with different spatial orders and orientations, depending on the molecular weight of added hPS chains. Hexagonally perforated layers quickly formed at 205 °C for PS-b-PMMA/hPS2.8 films. However, when hPS17 was used instead of hPS2.8, perforated layers formed with defects in PS-b-PMMA/hPS17 films annealed at 205 °C. Annealing at 240 °C improved the spatial order and orientation of perforated layers for a PS-b-PMMA/hPS17 film. Nevertheless, annealing at 240 °C inversely depressed the in-plane spatial order of perforated layers for a PS-b-PMMA/hPS2.8 film. The depression in the in-plane spatial order is ascribed to a dilution effect of added short chains. Compared to the middle regions, the thick beads went through several metastable phases, such as perpendicularly oriented perforated layers and double gyroids.

Nanoisland Formation on the Low Index Planes of Pt By Repeated Electro-Oxidation and-Reduction

Pt-based electro-catalysts are the most common cathode material in proton exchange membrane fuel cells given their high oxygen reduction reaction activity and stability. However, practical applications are limited by catalyst performance loss and degeneration. A main cause for this is nanoscale Pt surface restructuring, which occurs upon formation and reduction of a Pt surface oxide. During oxidation, a fraction of the Pt surface atoms are extracted in a process known as “place-exchange” from the electrode and are bound at specific sites in an oxide about 1 – 4 Å above the surface [1]. Upon subsequent oxide reduction, these atoms as well as the vacancies from which they originate can agglomerate, leading to the nucleation of adatom and vacancy islands. If this process is repeated, nanoislands with a well-defined lateral size of about 20 – 60 Å are grown [2-6]. Detailed studies of this growth process have been performed on the Pt(111) electrode [2-6], revealing two distinct growth regions which are characterized by different vertical scaling exponents [3].For the development of catalysts with superior long-term stability, a more detailed knowledge of the restructuring of the other low index planes of Pt is required. In our recent study of the Pt oxides on Pt(111) and Pt(100) we already showed a strong dependence of the structural stability of the surface on differences in the atomic-scale oxide structure formed on those two surface orientations [1]. However, the influence of surface structure on the nanoisland growth after repeated oxidation and reduction is largely unclear.We present a comparative operando grazing incidence small angle X-ray scattering (GISAXS) study of the nanoisland formation on Pt(111), Pt(100) and Pt(110) in acidic electrolyte. The GISAXS measurements of the nanoisland growth were performed at a high photon energy of >70 keV, which lowered background scattering from the electrolyte, enabling us to resolve the islands after the very first ox./red. cycle. Differences in island shape and growth behaviour on the low index planes will be discussed.We gratefully acknowledge financial support by the Deutsche Forschungsgemeinschaft via project no. 418603497, MA 1618/23-1 and the BMBF via 05K19FK3.References Fuchs et al., Nat. Catal. 3, 754–761 (2020)Sugawara and K. Itaya, J. Chem. Soc., Faraday Trans. 185, 1351-1356 (1989)Jacobse et al., Nat. Mater. 17 (3), 277-282 (2018)J. Rost, et al., Nat. Commun. 10, 5233 (2019)Ruge et al., J. Am. Chem. Soc. 139, 4532 (2017)Jacobse, et al. ACS Cent. Sci. 5 (12), 1920–1928 (2019)

Error investigation for SI traceable pitch calibration of one-dimensional grating by grazing-incidence small-angle X-ray scattering

Grazing-incidence small-angle X-ray scattering (GI-SAXS) is a promising technique for investigating nanostructured surfaces, particularly for the fine pitch calibration of one-dimensional gratings. However, only a few studies validated this technique from a metrological perspective. In this study, we developed a GI-SAXS system traceable to length and angle standards and used it to analyze the uncertainty of pitch calibrations in detail. Consequently, we found statistically significant systematic errors which have not been reported so far. We also found that the systematic error varied depending on the signal width of the diffracted X-rays. Through theoretical modeling and quantitative experiments, we successfully explained that the source of the systematic error is intensity modulation along the grating truncation rod. Since the systematic error decreases with smaller signal width, optimizing the optical system may efficiently reduce the uncertainty.

Mixed Nanosphere Assemblies at a Liquid-Liquid Interface.

The in-plane packing of gold (Au), polystyrene (PS), and silica (SiO2) spherical nanoparticle (NP) mixtures at a water-oil interface is investigated in situ by UV-vis reflection spectroscopy. All NPs are functionalized with carboxylic acid such that they strongly interact with amine-functionalized ligands dissolved in an immiscible oil phase at the fluid interface. This interaction markedly increases the binding energy of these nanoparticle surfactants (NPSs). The separation distance between the Au NPSs and Au surface coverage are measured by the maximum plasmonic wavelength (λmax) and integrated intensities as the assemblies saturate for different concentrations of non-plasmonic (PS/SiO2) NPs. As the PS/SiO2 content increases, the time to reach intimate Au NP contact also increases, resulting from their hindered mobility. λmax changes within the first few minutes of adsorption due to weak attractive inter-NP forces. Additionally, a sharper peak in the reflection spectrum at NP saturation reveals tighter Au NP packing for assemblies with intermediate non-plasmonic NP content. Grazing incidence small angle X-ray scattering (GISAXS) and scanning electron microscopy (SEM) measurements confirm a decrease in Au NP domain size for mixtures with larger non-plasmonic NP content. The results demonstrate a simple means to probe interfacial phase separation behavior using in situ spectroscopy as interfacial structures densify into jammed, phase-separated NP films.

Modulation of electronic and ionic conduction in mixed polymer conductors via additive engineering: Towards targeted applications under varying humidity

Polymer solids with mixed ion and electron transport hold great promise for next-generation organic electronics, and rational regulation of ionic/electronic contribution within these materials can enable a broadened spectrum of practical applications. However, a fundamental understanding of the conduction mechanisms and their correlations with morphological characteristics remains limited, especially under varying environmental humidity conditions. In the present work, simple additive engineering enables the effective regulation of electronic and ionic contribution in poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) based conductors, giving rising to ion- and/or electron-dominant conductions. As a demonstration, PEDOT:PSS films with different electrical characteristics are successfully applied for thermal energy harvesting, healthcare monitoring and human motion detection upon humidity exposure. Combining operando alternating current (AC) impedance spectroscopy and grazing incidence small-angle X-ray scattering at low and high humidity levels, additive-dependent charge transport mechanisms are elucidated, and correlations between morphological alterations and conductivity evolutions are revealed. This work achieves highly tailorable PEDOT:PSS conduction utilizing Zonyl, dimethyl sulfoxide (DMSO) and carbon nanotubes (CNTs) as additives with distinct humidity responses and gains an in-depth comprehension of underlying mechanisms, which are expected to pave the way for next-generation organic electronics.

Promoting X-ray scattering data analysis with two-dimensional correlation spectroscopy

In situ X-ray scattering (XrS) experiments provide an impressive level of detail about microstructures and their evolution following a change in environment in soft matter; however, a major obstacle is examining the huge amount of data. In this work, the applications of two-dimensional correlation spectroscopy (2DCS) in the XrS data analysis are demonstrated with three exemplary studies. The responses of three typical soft-matter systems (thin film, solution and solid) to a change in environment (i.e. concentration, temperature) were chosen as the subjects of this study. In situ grazing-incidence small-angle X-ray scattering, small-angle X-ray scattering and wide-angle X-ray scattering results were analyzed with the 2DCS method. On the basis of Noda's rule, it is demonstrated that the 2DCS-XrS results could not only disclose the weak scattering signal common to organic-based materials but also determine the sequential order of the structures of interest by referring to their strong response to a change in environment. It is expected that the 2DCS method could promote XrS data analysis in a simple, fast and reliable way, which might interest users without extensive X-ray scattering knowledge. These features could help to convert XrS data into knowledge that can be implemented in advanced materials preparation.

Fostering the Dense Packing of Halide Perovskite Quantum Dots through Binary-Disperse Mixing.

Due to their versatile applications, perovskite quantum dot (PQD)-based optoelectrical devices have garnered significant research attention. However, the fundamental packing behavior of PQDs in thin films and its impact on the device performance remain relatively unexplored. Drawing inspiration from theoretical models concerning packing density with size mixtures, this study presents an effective strategy, namely, binary-disperse mixing, aimed at enhancing the packing density of PQD films. Comprehensive grazing-incidence small-angle X-ray characterization suggested that the PQD film consists of three phases: two monosize phases and one binary mixing phase. The volume fraction and population of the binary-size phase can be tuned by mixing an appropriate amount of large and small PQDs. Furthermore, we performed multi-length-scale all-atom and coarse-grained molecular dynamics simulations to elucidate the distribution and conformation of organic surface ligands, highlighting their influence on PQD packing. Notably, the mixing of two PQDs of different sizes promotes closer face-to-face contact. The densely packed binary-disperse film exhibited largely suppressed trap-assisted recombination, much longer carrier lifetime, and thereby improved power conversion efficiency. Hence, this study provides fundamental understanding of the packing mechanism of perovskite quantum dots and highlights the significance of packing density for PQD-based solar cells.

Monitoring of Pore Orientation by in Operando Grazing Incidence Small-Angle X-ray Scattering during Templated Electrodeposition of Mesoporous Pt Films.

We have used in operando grazing incidence small-angle X-ray scattering (GISAXS) to monitor structural changes during templated electrodeposition of mesoporous platinum films on gold electrodes from a ternary lyotropic liquid crystalline mixture of aqueous hexachloroplatinic acid and the diblock copolymer surfactant Brij56. While the cylindrical micelles of the lyotropic liquid crystal (LLC) in the hexagonal phase have a center-to-center distance of 7.5 nm with a preferential alignment parallel to the electrode surface, the electrodeposited platinum films contain highly ordered mesopores arranged in a 2D hexagonal structure, with a center-to-center distance of about 8.5 nm and a preferential orientation perpendicular to the electrode surface. The progression of structural changes of the LLC template and the deposited mesoporous Pt could be monitored for the first time in operando by GISAXS: within the first 14 s of deposition, a nucleation burst of Pt coincides with a loss of preferential alignment of the LLC. Initially, the morphology of the 2-dimensionally nucleated Pt replicates the Au substrate. During the following 5 to 7 min, the growth morphology of the Pt film changes, and vertically aligned mesopores form. Our results indicate mutual interaction between the species involved in the electrodeposition and the LLC template, leading to a partial loss of horizontal orientation of the LLC during Pt nucleation before vertical rearrangement of the micelles to the electrode surface. The vertically aligned mesopores in the Pt and the possibility to produce freestanding films make these materials interesting in fields such as electrocatalysis, energy harvesting, and nanofluidics.

High magnetic and super-structural uniformity in fcc supercrystalline films of Co nanoparticles evidenced by MOKE

In this paper, we report the first local magnetic study, performed by magneto-optical Kerr effect (MOKE), of supercrystals made of magnetic nanoparticles. The supercrystals are characterized by a film morphology and contain several hundred layers of 7.7 nm-Co NPs, ordered in a face-centered cubic (fcc) superstructure. Conversely to the standard superconducting quantum interference device (SQUID) technique, which provides only a global measurement over an entire sample, the utilization of MOKE enables magnetic measurements of individual localized areas of c.a. 30 µm x 30 µm, from which we can draw conclusions regarding the uniformity of the magnetic properties of the sample, and therefore on the high uniformity of its structure. The latter conclusion is supported by Monte Carlo simulation performed on a model system composed of spherical particles interacting through the dipole-dipole interactions (DDI) and exhibiting a uniaxial magneto-crystalline anisotropy energy (MAE). In addition, by combining these results, with those obtained by SQUID and by grazing incidence small-angle X-ray scattering (GISAXS), we show that magnetic and super-structural properties of supercrystals can be accurately determined.

Ionic Liquid-Induced Inversion of the Humidity-Dependent Conductivity of Thin PEDOT:PSS Films.

The humidity influence on the electronic and ionic resistance properties of thin post-treated poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films is investigated. In particular, the resistance of these PEDOT:PSS films post-treated with three different concentrations (0, 0.05, and 0.35 M) of ethyl-3-methylimidazolium dicyanamide (EMIM DCA) is measured while being exposed to a defined humidity protocol. A resistance increase upon elevated humidity is observed for the 0 M reference sample, while the EMIM DCA post-treated samples demonstrate a reverse behavior. Simultaneously performed in situ grazing-incidence small-angle X-ray scattering (GISAXS) measurements evidence changes in the film morphology upon varying the humidity, namely, an increase in the PEDOT domain distances. This leads to a detriment in the interdomain hole transport, which causes a rise in the resistance, as observed for the 0 M reference sample. Finally, electrochemical impedance spectroscopy (EIS) measurements at different humidities reveal additional contributions of ionic charge carriers in the EMIM DCA post-treated PEDOT:PSS films. Therefrom, a model is proposed, which describes the hole and cation transport in different post-treated PEDOT:PSS films dependent on the ambient humidity.