We report the realization of a two‐dimensional analog of the archetypical metal‐organic framework UiO‐66 as a Langmuir monolayer, constructed from preformed metal oxo clusters and amphiphilic terephthalic acid ligands at the air–water interface. Structural changes of the metal oxo clusters in aqueous solution were elucidated to clarify their role in interfacial self‐assembly at the water surface. Langmuir balance studies demonstrated that self‐assembly with specifically designed organic linkers proceeds through a coordination‐driven process. The resulting films were characterized by complementary techniques to determine their morphology, thickness, and composition. Based on these findings, a packing model of the monolayer was proposed. Finally, we extended this coordination‐driven self‐assembly strategy beyond aqueous systems to form, for the first time, monolayers at the air–N, N‐dimethylformamide interface.

HYPOTHESIS:The surface-parallel depth-decaying layering at the room-temperature ionic liquid (RTIL)/air interface should exhibit a thermal behavior different from bulk's locally-layered structure. The absence of an (attractive) upper-half-space of matter above the surface should compress the layer spacing and provide for a larger thermal variation compared to the bulk. At the same time, the flat and sharp liquid surface is expected to align the layers macroscopically, and thus enhance the layering depth beyond the range of the bulk's local layering. EXPERIMENTS:Temperature (T)-dependent X-ray reflectivity (XRR) measurements off the free surfaces of a homologous series of model RTILs [Cnmim][NTf2] (Cn, even n=12-18, where n is the carbon number of the cationic hydrocarbon chain). Such combined (n,T) surface structure evolution is not currently available for any aprotic homologous RTIL series. FINDINGS:The surface layering exhibits an anomalous thermal contraction, as does the bulk, rather than a conventional expansion, with surface layer spacings falling below those of the bulk by 5-25%, and exhibiting larger contraction-increases with increasing T. A 10-35% increase in the spacing-normalized layering range was also found at the surface compared to the bulk for all n. Surprisingly, a hardening of the surface layers against T-variations is found for increasing n, shown by the decrease of the surface spacing's thermal slope |∂ds(T)/∂T| with increasing n, while the bulk softens, with its |∂db(T)/∂T|increasing with n. These bulk/surface differences originate in the effects hypothesized above.

Cholesterol, a key structural component of mammalian cell membranes, is crucial in stabilizing the membrane and regulating its biophysical properties. Herein, the self-assembly of graphene oxide (GO) around differently charged lipid monolayers modulated by cholesterol has been investigated using surface pressure-area isotherms and synchrotron-based X-ray reflectivity. In pristine lipid monolayers, electrostatic interactions control the self-assembly of GO nano-flakes around the lipid molecules. However, upon the addition of cholesterol, the adsorption and penetration kinetics of GO nano-flakes into the lipid monolayers are drastically amplified, irrespective of the ionic nature of lipids. The experimental observations are discussed in terms of interactions occurring among GO nano-flakes, phospholipids, and cholesterol molecules.

Graphene and its derivatives, such as graphene oxide (GO) and reduced graphene oxide (rGO), have propelled advancements in biosensor research owing to their unique physicochemical and electronic characteristics. To ensure their safe and effective utilization in biological environments, it is crucial to understand how these graphene-based nanomaterials (GNMs) interact with a biological milieu. The present study depicts GNM-induced structural changes in a self-assembled phospholipid monolayer formed at an air-water interface that can be considered to represent one of the leaflets of a cellular membrane. Surface pressure-area isotherm and electrostatic surface potential measurements, along with advanced X-ray scattering techniques, have been utilized in this study. Experimental findings demonstrate a strong interaction between negatively charged GO flakes and a positively charged monolayer, primarily dictated by electrostatic forces. These GO flakes assemble horizontally beneath the head groups of the monolayer. In contrast, rGO flakes permeate the zwitterionic lipid layer through dominant hydrophobic interaction. This organization of GNMs alters the in-plane elasticity of the lipid film, exhibiting a drop in the electrostatic potential of the surface according to the extent of oxygen-containing groups. These results provide a solid groundwork for designing devices and sensors aimed at augmenting the biomedical applications of GNMs.

The interfacial liquid metal/electrolyte structure for liquid Hg-In alloy electrodes immersed in aqueous sodium tetraborate solution was probed by in situ X-ray reflectivity. X-ray reflectivity data were collected for three different Hg-In alloys that spanned Hg- and In-rich compositions: Hg0.35In0.65, Hg0.50In0.50, and Hg0.95In0.05. The interfaces of these liquid metals with borate electrolyte were studied under potential control between -1.00 and -1.40 V vs E(Ag/AgCl). For all Hg-In alloy compositions, the data suggest Hg surface enrichment at levels inconsistent with predictions from the Gibbs adsorption theorem for an ideal solution. Instead, the surface concentrations of Hg estimated from the fits of the X-ray reflectivity data indicate a large negative enthalpy of mixing in the Hg-In system at all applied potentials. In addition, the reflectivity data as well as scattering measurements at small incident angles suggest a complex atomic arrangement at the surfaces of alloys with high In content, manifesting in increased spacings and microscopic roughness of the topmost atomic layer.

The laser pump – X-ray probe setup at the LISA liquid interface scattering apparatus at beamline P08 at PETRA III enables investigation of photo-induced structural changes at liquid and solid interfaces with a time resolution of 38 ps. Here we report the latest upgrades on the pump – probe setup including the extension of the accessible pump-probe delay time scale and the implementation of laser beam profile transformers. The new laser optical cage system with magnetic holders allows variable laser beam sizes and flat top beam profile which can be advantageous for matching laser and X-ray beam size and profile on heat sensitive samples. The introduction of an additional delay/pulse generator now enables pump-probe measurements to be performed on all time scales from 100 picoseconds to seconds, allowing to study ultrafast and slow optical excitation and relaxation dynamics with any gap in time resolution.

This study focuses on the kinetics of light-induced mesophase transitions in lyotropic liquid crystals containing a mixture of phospho-lipids and azo-benzene amphiphiles. Lipid membranes organize in a wide range of morphologies, directly influencing their functionality and the efficiency of associated components such as proteins. Transitions between mesophases occur naturally during membrane fusion and can also be triggered by multiple factors, such as pH, salinity, temperature and light. Employing light to isomerize artificial photoswitchable lipids in mixed model membranes containing 1,2-dipalmitoyl-phos-pha-tidylcholine or 1,2-didecanoyl-phosphatidylcholine revealed light-induced structural changes including mesophase transitions from a lamellar to a cubic Pn3m phase. Performing time-resolved small-angle X-ray scattering measurements, the kinetics of the change in membrane repeat distance and the transition from a lamellar to a bicontinuous cubic phase could be captured on the timescale of tens of seconds. The results demonstrate new possibilities for investigating intermediate states during mesophase transitions that are important to understand membrane fusion, and they highlight the potential of photoswitchable lipids for designing bespoke drug delivery systems.

Advancements in synchrotron and X-ray free-electron sources and associated developments in instrumentation and techniques offer many new possibilities for researchers. At the same time there is increasing demand and pressure to implement the FAIR data principles by which data should be made Findable, Accessible, Interoperable and Reusable. The consortium DAPHNE4NFDI (DAta from PHoton and Neutron Experiments for NFDI) addresses this challenge within the German National Research Data Infrastructure (NFDI), and also in relation to European / worldwide initiatives. This article gives an overview of our activities and elaborates on our progress, showcasing developments in some of our use cases, including: (1) X-ray reflectivity (XRR), (2) X-ray photon correlation spectroscopy (XPCS) and (3) X-ray absorption spectroscopy (XAS).

The emerging class of hybrid organic-inorganic perovskites (HOIPs) has exhibited fascinating properties for a wide range of technological applications. With halide ions, HOIPs have provided novel optoelectronic devices including efficient solar cells and with pseudohalide anions-like formate (HCOO-), enigmatic electromagnetic properties have been obtained in HOIPs. Large-scale synthesis of such 2D HOIP films is of immense importance for the advancement of its application as solar materials. We have shown using in-situ X-ray measurements that the Langmuir monolayer of perovskite can be formed at the air-water interface by spreading stearic acid molecules on the water subphase having (C4H9NH3)2PbBr4 molecules. The 2D lead formate perovskite films are formed at the air-water interface through a self-initiated reaction and the in-situ X-ray scattering and ex-situ Raman spectroscopy measurements revealed this reaction process. The spreading of lipid molecules having positive and negative head-group charges as surfactants over the water surface shows that the formation of perovskite nanofilms at the air-water interface specifically requires the presence of HCOO- head-group of stearic acid. In this room temperature interfacial reaction, formate anions come from the stearic acid monolayer present on the water surface and completely replace bromines in the perovskite present in water subphase to form (BA)2Pb(HCOO)4 at the air-water interface. Our results show an easy route for large-scale synthesis of 2D pseudohalide perovskites.

Xanthan gum is a biopolymer used in a wide range of products in the food and cosmetic industries. As ionic liquids (ILs) have emerged as antimicrobial molecules, they can be used as preservatives for this polymer. Hence, it is important to understand the interaction of ionic liquids with Xanthan gum. In this investigation, polymer self-assembly at the air-water interface has been studied in the presence of ionic liquids floating at the air-water interface. From the surface pressure-area isotherm, it is shown that the electrostatic interaction drives the polymer to the interface, resulting in a viscoelastic film. In-plane dilation rheology has determined the storage and loss moduli of the film, which are found to depend on the concentration of the polymer dissolved in the water subphase. Additionally, a synchrotron-based X-ray reflectivity study has produced the electron density profile across the interface, depicting the structure of the film and suggesting that the negatively charged side groups of Xanthan gum attach to the positively charged headgroup of ionic liquids. This assembly drives the polymer to disentangle, which has been further verified in an aqueous solution of the polymer showing a non-newtonian shear-thinning behavior. The storage and loss moduli curves show two crossover frequencies, manifesting an elastic plateau width that decreases in the presence of IL in the solution. This, in turn, is a signature of the disentangling effect of the IL.

The microscopic structure of Fe-based metallic glasses (Fe80Ga20)88B12$\left(\left(\right. \left(\text{Fe}\right)_{80} \left(\text{Ga}\right)_{20} \left.\right)\right)_{88} \left(\text{B}\right)_{12}$ (FeGaB) and (Fe90Co10)78Si12B10$\left(\left(\right. \left(\text{Fe}\right)_{90} \left(\text{Co}\right)_{10} \left.\right)\right)_{78} \left(\text{Si}\right)_{12} \left(\text{B}\right)_{10}$ (FeCoSiB) is investigated during in situ thermal annealing using extended X-ray absorption fine structure spectroscopy (EXAFS) above the Fe-K and Co-K absorption edges. FeGaB exhibits a phase transition above 450 degrees C, changing from amorphous glass to a partially crystalline structure. Its medium-range structure after this transition is modeled from crystalline alpha-Fe and FeGa3$\left(\text{FeGa}\right)_{3}$ reference structures, combined with amorphous nearest-neighbor (NN) contributions of Fe2B$\left(\text{Fe}\right)_{2} \text{B}$. Local order in the glass phase is described with the same model, restricted to NN interactions. Changes in the amorphous structure occur at annealing temperatures which coincide with typical observations of changes in magnetic behavior. Meanwhile, in FeCoSiB, the EXAFS response is highly different between the Fe-K and Co-K absorption edges. EXAFS oscillations on the Fe edge are strongly suppressed, as opposed to the Co edge which shows typical amplitudes. Limited resolution in this data set allows modeling only in the first amorphous shell, based on the NN distances from FeCo. The cause of the two materials' different EXAFS behavior at Fe-K despite similar iron content and identical experimental conditions is currently unknown and subject of further investigation.

The functionality and efficiency of proteins within a biological membrane are highly dependent on both the membrane lipid composition and the physiochemical properties of the solution. Lipid mesophases are directly influenced by changes in temperature, pH, water content or due to individual properties of single lipids such as photoswitchability. In this work, we were able to induce light- and temperature-driven mesophase transitions in a model membrane system containing a mixture of 1,2-dipalmitoyl-phosphatidylcholine phospholipids and azobenzene amphiphiles. We observed reversible and reproducible transitions between the lamellar and Pn3m cubic phase after illuminating the sample for 5 min with light of 365 and 455 nm wavelengths, respectively, to switch between the cis and trans states of the azobenzene N=N double bond. These light-controlled mesophase transitions were found for mixed complexes with up to 20% content of the photosensitive molecule and at temperatures below the gel-to-liquid crystalline phase transition temperature of 33°C. Our results demonstrate the potential to design bespoke model systems to study the response of membrane lipids and proteins upon changes in mesophase without altering the environment and thus provide a possible basis for drug delivery systems.

Understanding and controlling the structure and function of liquid interfaces is a constant challenge in biology, nanoscience and nanotechnology, with applications ranging from molecular electronics to controlled drug release. X-ray reflectivity and grazing incidence diffraction provide invaluable probes for studying the atomic scale structure at liquid-air interfaces. The new timeresolved laser system at the LISA liquid diffractometer situated at beamline P08 at the PETRA III synchrotron radiation source in Hamburg provides a laser pump with X-ray probe. The femtosecond laser combined with the LISA diffractometer allows unique opportunities to investigate photo-induced structural changes at liquid interfaces on the pico- and nanosecond time scales with pump-probe techniques. A time resolution of 38 ps has been achieved and verified with Bi. First experiments include laser-induced effects on salt solutions and liquid mercury surfaces with static and varied time scales measurements showing the proof of concept for investigations at liquid surfaces.

2D organic-inorganic hybrid lead halide perovskite films are fascinating optoelectronic materials for white-light emission and lasing applications. Here, it is demonstrated that nano-meter-thick films of perovskites can be formed at room temperature using Langmuir-Schaefer (LS) deposition technique. In situ X-ray measurements reveal a self-assembly process of the 2D perovskite formation at the air-water interface. This formation process requires the presence of stearic acid monolayer on the water subphase having a solution of lead-perovskite in dimethylformamide. Microscopy and X-ray measurements of these nanofilms transferred onto substrates show crystalline phase formation that deviates from the known orthorhombic structure of the bulk crystals. The nanofilms exhibit novel broad optical emission with sharp band-edge transition in temperature-dependent photoluminescence studies. Also, their band-edge emission is distinctly blue-shifted compared to that of thicker 2D perovskite flakes prepared by the slow-cooling chemical synthesis process. 2D flakes exhibit lasing that cannot be obtained in the LS nanofilms as their thicknesses are lower than the lasing wavelength prohibiting wave-guide formation. The results show that the 2D single-crystalline nature of the LS films and flakes are suitable materials to develop broad-band white light emission across the entire visible range and to obtain lasing without external cavities, respectively. This work demonstrates the process of self-assembly-dictated growth of a few nano-meter-thick films of hybrid organic-inorganic perovskites (HOIPs) from the Langmuir monolayer at the air-water interface which shows the fascinating optical property of broad-band white light emission across the entire visible range as a single-component material. The 2D flakes of these HOIPs exhibit a sharp PL peak with strong lasing action. image

We present a high-pressure/high-temperature cell design suitable for in situ X-ray scattering experiments at pressures up to 100 MPa and temperatures up to 773 K. The high energy X-ray beam is guided through two opposing sapphire windows to enable X-ray reflectivity studies for a wide range of momentum transfer allowing access to atomic length scales. The sample cell is heated by four heating cartridges inserted into the cell body. By measuring the temperature directly in the cell volume, high temperature stability of up to 0.1 K can be achieved. A Bridgman sealing system ensures leak tightness of the sample cell even when corrosive and supercritical fluids are used. Custom-built sample holders accommodate solid substrates of various dimensions up to 12x20 mm2 (W × L). The performance of the cell is demonstrated by visual observation of the supercritical phase transition of H2O and an X-ray reflectivity study of octadecyltrichlorosilane coated silicon wafers in contact with sub- and supercritical carbon dioxide. Here, formation of a liquid CO2 layer in the subcritical regime is observed that vanishes at supercritical conditions.

Hypothesis: Room Temperature Ionic Liquids (RTILs) bulk's molecular layering dominates their structure also at the RTIL/sapphire interface, increasing the layer spacing with the cationic alkyl chain length n. However, the negatively-charged sapphire surface compresses the layers, increases the layering range, and affects the intra-layer structure in yet unknown ways. Experiments: X-ray reflectivity (XR) off the RTIL/sapphire interface, for a broad homologous RTIL series 1-alkyl-3-methylimidazolium bis(trifluoromethansulfonyl)-imide, hitherto unavailable for any RTIL. Findings: RTIL layers against the sapphire, exhibit two spacings: d(a) and d(b).d(a) is n-varying, follows the behavior of the bulk spacing but exhibits a downshift, thus showing significant layer compression, and over twofold polar slab thinning. The latter suggests exclusion of anions from the interfacial region due to the negative sapphire charging by x-ray-released electrons. The layering range is larger than the bulk's. d(b) is short and near n-independent, suggesting polar moieties' layering, the coexistence mode of which with the d(a)-spaced layering is unclear. Comparing the present layering with the bulk's and the RTIL/air interface's provides insight into the Coulomb and dispersion interaction balance dominating the RTIL's structure and the impact thereon of the presence of a charged solid interface.

We report on ongoing discussions and plans of NFDI consortia in physics and reltated natural sciences with respect to (persistent) identifiers.