Perovskite-type superlattices from lead halide perovskite nanocubes.

Atomically defined assemblies of dye molecules (such as H and J aggregates) have been of interest for more than 80 years because of the emergence of collective phenomena in their optical spectra1-3, their coherent long-range energy transport, their conceptual similarity to natural light-harvesting complexes4,5, and their potential use as light sources and in photovoltaics. Another way of creating versatile and controlled aggregates that exhibit collective phenomena involves the organization of colloidal semiconductor nanocrystals into long-range-ordered superlattices6. Caesium lead halide perovskite nanocrystals7-9 are promising building blocks for such superlattices, owing to the high oscillator strength of bright triplet excitons10, slow dephasing (coherence times of up to 80 picoseconds) and minimal inhomogeneous broadening of emission lines11,12. So far, only single-component superlattices with simple cubic packing have been devised from these nanocrystals13. Here we present perovskite-type (ABO3) binary and ternary nanocrystal superlattices, created via the shape-directed co-assembly of steric-stabilized, highly luminescent cubic CsPbBr3 nanocrystals (which occupy the B and/or O lattice sites), spherical Fe3O4 or NaGdF4 nanocrystals (A sites) and truncated-cuboid PbS nanocrystals (B sites). These ABO3 superlattices, as well as the binary NaCl and AlB2 superlattice structures that we demonstrate, exhibit a high degree of orientational ordering of the CsPbBr3 nanocubes. They also exhibit superfluorescence-a collective emission that results in a burst of photons with ultrafast radiative decay (22 picoseconds) that could be tailored for use in ultrabright (quantum) light sources. Our work paves the way for further exploration of complex, ordered and functionally useful perovskite mesostructures.

Spatial arrangement of functional domains in OxyS stress response sRNA.

Small noncoding RNAs are an important class of regulatory RNAs in bacteria, often regulating responses to changes in environmental conditions. OxyS is a 110 nt, stable, trans-encoded small RNA found in Escherichia coli and is induced by an increased concentration of hydrogen peroxide. OxyS has an important regulatory role in cell stress response, affecting the expression of multiple genes. In this work, we investigated the structure of OxyS and the interaction with fhlA mRNA using nuclear magnetic resonance spectroscopy, small-angle X-ray scattering, and unbiased molecular dynamics simulations. We determined the secondary structures of isolated stem-loops and confirmed their structural integrity in OxyS. Unexpectedly, stem-loop SL4 was identified in the region that was predicted to be unstructured. Three-dimensional models of OxyS demonstrate that OxyS adopts an extended structure with four solvent-exposed stem-loops, which are available for interaction with other RNAs and proteins. Furthermore, we provide evidence of base-pairing between OxyS and fhlA mRNA.

In situ small-angle X-ray scattering reveals solution phase discharge of Li-O2 batteries with weakly solvating electrolytes.

Electrodepositing insulating lithium peroxide (Li2O2) is the key process during discharge of aprotic Li-O2 batteries and determines rate, capacity, and reversibility. Current understanding states that the partition between surface adsorbed and dissolved lithium superoxide governs whether Li2O2 grows as a conformal surface film or larger particles, leading to low or high capacities, respectively. However, better understanding governing factors for Li2O2 packing density and capacity requires structural sensitive in situ metrologies. Here, we establish in situ small- and wide-angle X-ray scattering (SAXS/WAXS) as a suitable method to record the Li2O2 phase evolution with atomic to submicrometer resolution during cycling a custom-built in situ Li-O2 cell. Combined with sophisticated data analysis, SAXS allows retrieving rich quantitative structural information from complex multiphase systems. Surprisingly, we find that features are absent that would point at a Li2O2 surface film formed via two consecutive electron transfers, even in poorly solvating electrolytes thought to be prototypical for surface growth. All scattering data can be modeled by stacks of thin Li2O2 platelets potentially forming large toroidal particles. Li2O2 solution growth is further justified by rotating ring-disk electrode measurements and electron microscopy. Higher discharge overpotentials lead to smaller Li2O2 particles, but there is no transition to an electronically passivating, conformal Li2O2 coating. Hence, mass transport of reactive species rather than electronic transport through a Li2O2 film limits the discharge capacity. Provided that species mobilities and carbon surface areas are high, this allows for high discharge capacities even in weakly solvating electrolytes. The currently accepted Li-O2 reaction mechanism ought to be reconsidered.

EIGER2 hybrid-photon-counting X-ray detectors for advanced synchrotron diffraction experiments.

The ability to utilize a hybrid-photon-counting detector to its full potential can significantly influence data quality, data collection speed, as well as development of elaborate data acquisition schemes. This paper facilitates the optimal use of EIGER2 detectors by providing theory and practical advice on (i) the relation between detector design, technical specifications and operating modes, (ii) the use of corrections and calibrations, and (iii) new acquisition features: a double-gating mode, 8-bit readout mode for increasing temporal resolution, and lines region-of-interest readout mode for frame rates up to 98 kHz. Examples of the implementation and application of EIGER2 at several synchrotron sources (ESRF, PETRA III/DESY, ELETTRA, AS/ANSTO) are presented: high accuracy of high-throughput data in serial crystallography using hard X-rays; suppressing higher harmonics of undulator radiation, improving peak shapes, increasing data collection speed in powder X-ray diffraction; faster ptychography scans; and cleaner and faster pump-and-probe experiments.

Silicon- and Germanium-Functionalized Perylene Diimides: Synthesis, Optoelectronic Properties, and Their Application as Non-fullerene Acceptors in Organic Solar Cells.

Organic solar cells have been continuously studied and developed through the last decades. A major step in their development was the introduction of fused-ring non-fullerene electron acceptors. Yet, beside their high efficiency, they suffer from complex synthesis and stability issues. Perylene-based non-fullerene acceptors, in contrast, can be prepared in only a few steps and display good photochemical and thermal stability. Herein, we introduce four monomeric perylene diimide acceptors obtained in a three-step synthesis. In these molecules, the semimetals silicon and germanium were added in the bay position, on one or both sides of the molecules, resulting in asymmetric and symmetric compounds with a red-shifted absorption compared to unsubstituted perylene diimide. Introducing two germanium atoms improved the crystallinity and charge carrier mobility in the blend with the conjugated polymer PM6. In addition, charge carrier separation is significantly influenced by the high crystallinity of this blend, as shown by transient absorption spectroscopy. As a result, the solar cells reached a power conversion efficiency of 5.38 %, which is one of the highest efficiencies of monomeric perylene diimide-based solar cells recorded to date.

Investigating the mechanism of action of DNA-loaded PEGylated lipid nanoparticles.

PEGylated lipid nanoparticles (LNPs) are commonly used to deliver bioactive molecules, but the role of PEGylation in DNA-loaded LNP interactions at the cellular and subcellular levels remains poorly understood. In this study, we investigated the mechanism of action of DNA-loaded PEGylated LNPs using gene reporter technologies, dynamic light scattering (DLS), synchrotron small angle X-ray scattering (SAXS), and fluorescence confocal microscopy (FCS). We found that PEG has no significant impact on the size or nanostructure of DNA LNPs but reduces their zeta potential and interaction with anionic cell membranes. PEGylation increases the structural stability of LNPs and results in lower DNA unloading. FCS experiments revealed that PEGylated LNPs are internalized intact inside cells and largely shuttled to lysosomes, while unPEGylated LNPs undergo massive destabilization on the plasma membrane. These findings can inform the design, optimization, and validation of DNA-loaded LNPs for gene delivery and vaccine development.

Human Antimicrobial Peptide Triggered Colloidal Transformations in Bacteria Membrane Lipopolysaccharides.

Growing concerns of bacterial resistance against conventional antibiotics shifts the research focus toward antimicrobial peptide (AMP)-based materials. Most AMPs kill gram-negative bacteria by destroying their inner membrane, but have to first pass the outer membrane covered with lipopolysaccharides (LPS). Their interplay with the LPS is crucial for bactericidal activity, but is yet to be elucidated in detail. In this study, self-assemblies of Escherichia coli LPS with the human cathelicidin AMP LL-37, free and encapsulated into glyceryl monooleate (GMO) lipid nanoparticles, are analyzed using synchrotron small angle X-ray scattering, dynamic light scattering, and cryogenic transmission electron microscopy. Circular dichroism spectroscopy is used to study modifications in LL-37's secondary structure. LPS is found to form elongated micelles and the addition of LL-37 induces their transformation to multilamellar structures. LPS' addition to GMO cubosomes triggers the swelling of the internal cubic structure, while in multilamellar GMO/LL-37 nanocarriers it causes transitions into unstructured particles. The insights on the interactions among LPS and LL-37, in its free form or encapsulated in GMO dispersions, may guide the design of LPS-responsive antimicrobial nanocarriers. The findings may further assist the formulation of antimicrobial nanomaterials with enhanced penetration of LPS layers for improved destruction of bacterial membranes.

Block-Copolymers Enable Direct Reduction and Structuration of Noble Metal-Based Films.

Noble metal nanostructured films are of great interest for various applications including electronics, photonics, catalysis, and photocatalysis. Yet, structuring and patterning noble metals, especially those of the platinum group, is challenging by conventional nanofabrication. Herein, an approach based on solution processing to obtain metal-based films (rhodium, ruthenium (Ru) or iridium in the presence of residual organic species) with nanostructuration at the 20 nm-scale is introduced. Compared to existing approaches, the dual functionality of block-copolymers acting both as structuring and as reducing agent under inert atmosphere is exploited. A set of in situ techniques has allowed for the capturing of the carbothermal reduction mechanism occurring at the hybrid organic/inorganic interface. Differently from previous literature, a two-step reduction mechanism is unveiled with the formation of a carbonyl intermediate. From a technological point of view, the materials can be solution-processed on a large scale by dip-coating as polymers and simultaneously structured and reduced into metals without requiring expensive equipment or treatments in reducing atmosphere. Importantly, the metal-based films can be patterned directly by block-copolymer lithography or by soft-nanoimprint lithography on various substrates. As proof-of-concept of application, the authors demonstrate that nanostructured Ru films can be used as efficient catalysts for H2 generation into microfluidic reactors.

Direct X-ray and electron-beam lithography of halogenated zeolitic imidazolate frameworks.

Metal-organic frameworks (MOFs) offer disruptive potential in micro- and optoelectronics because of the unique properties of these microporous materials. Nanoscale patterning is a fundamental step in the implementation of MOFs in miniaturized solid-state devices. Conventional MOF patterning methods suffer from low resolution and poorly defined pattern edges. Here, we demonstrate the resist-free, direct X-ray and electron-beam lithography of MOFs. This process avoids etching damage and contamination and leaves the porosity and crystallinity of the patterned MOFs intact. The resulting high-quality patterns have excellent sub-50-nm resolution, and approach the mesopore regime. The compatibility of X-ray and electron-beam lithography with existing micro- and nanofabrication processes will facilitate the integration of MOFs in miniaturized devices.

Phenylene-Bridged Perylene Monoimides as Acceptors for Organic Solar Cells: A Study on the Structure-Property Relationship.

A series of non-fullerene acceptors based on perylene monoimides coupled in the peri position through phenylene linkers were synthesized via Suzuki-coupling reactions. Various substitution patterns were investigated using density functional theory (DFT) calculations in combination with experimental data to elucidate the geometry and their optical and electrochemical properties. Further investigations of the bulk properties with grazing incidence wide angle X-ray scattering (GIWAXS) gave insight into the stacking behavior of the acceptor thin films. Electrochemical and morphological properties correlate with the photovoltaic performance of devices with the polymeric donor PBDB-T and a maximum efficiency of 3.17 % was reached. The study gives detailed information about structure-property relationships of perylene-linker-perylene compounds.

Investigation of the Mechanism of SiO2 Particle and Capsule Formation at the Oil-Water Interface of Dye-Stabilized Emulsions.

In a previous contribution we described the formation of silica nanostructures in dye-stabilized nanoemulsions from tetraethyl orthosilicate droplets in water. Depending on the type of dye, either capsules (crystal violet, CV) or nanoparticles (congo red, CR) are formed. The thorough study of the sol-gel process uses a combination of time- and/or temperature-resolved small-angle X-ray scattering, transmission electron microscopy, and 1H NMR spectroscopy to elucidate the detailed kinetics and mechanism of structure formation. In both cases, small nuclei of 1.5-2 nm are formed, followed by either a fast cluster-cluster (CV) or a much slower monomer-cluster aggregation (CR). The former leads to a cross-linked network and finally to patchy capsules, while the latter leads to individual nanoparticles (SNPs). From an Avrami plot it can be deduced that the SNPs are formed by an interface-controlled one-dimensional growth process. The mechanisms are based on the different local environments at the oil-water interface, which is either slightly acidic (CV) or fairly basic (CR). The kinetics differ by a factor between 3 and 20 and are presumably caused by the different mobility of the catalyzing species H+ or OH-.

Humidity Response of Cellulose Thin Films.

Cellulose-water interactions are crucial to understand biological processes as well as to develop tailor made cellulose-based products. However, the main challenge to study these interactions is the diversity of natural cellulose fibers and alterations in their supramolecular structure. Here, we study the humidity response of different, well-defined, ultrathin cellulose films as a function of industrially relevant treatments using different techniques. As treatments, drying at elevated temperature, swelling, and swelling followed by drying at elevated temperatures were chosen. The cellulose films were prepared by spin coating a soluble cellulose derivative, trimethylsilyl cellulose, onto solid substrates followed by conversion to cellulose by HCl vapor. For the highest investigated humidity levels (97%), the layer thickness increased by ca. 40% corresponding to the incorporation of 3.6 molecules of water per anhydroglucose unit (AGU), independent of the cellulose source used. The aforementioned treatments affected this ratio significantly with drying being the most notable procedure (2.0 and 2.6 molecules per AGU). The alterations were investigated in real time with X-ray reflectivity and quartz crystal microbalance with dissipation, equipped with a humidity module to obtain information about changes in the thickness, roughness, and electron density of the films and qualitatively confirmed using grazing incidence small angle X-ray scattering measurements using synchrotron irradiation.

Supramolecular Chalcogen-Bonded Semiconducting Nanoribbons at Work in Lighting Devices.

This work describes the design and synthesis of a π-conjugated telluro[3,2-ß][1]-tellurophene-based synthon that, embodying pyridyl and haloaryl chalcogen-bonding acceptors, self-assembles into nanoribbons through chalcogen bonds. The ribbons π-stack in a multi-layered architecture both in single crystals and thin films. Theoretical studies of the electronic states of chalcogen-bonded material showed the presence of a local charge density between Te and N atoms. OTFT-based charge transport measurements showed hole-transport properties for this material. Its integration as a p-type semiconductor in multi-layered CuI -based light-emitting electrochemical cells (LECs) led to a 10-fold increase in stability (38 h vs. 3 h) compared to single-layered devices. Finally, using the reference tellurotellurophene congener bearing a C-H group instead of the pyridyl N atom, a herringbone solid-state assembly is formed without charge transport features, resulting in LECs with poor stabilities (<1 h).

Novel Core-Shell Polyamine Phosphate Nanoparticles Self-Assembled from PEGylated Poly(allylamine hydrochloride) with Low Toxicity and Increased In Vivo Circulation Time.

An approach for reducing toxicity and enhancing therapeutic potential of supramolecular polyamine phosphate nanoparticles (PANs) through PEGylation of polyamines before their assembly into nanoparticles is presented here. It is shown that the number of polyethylene glycol (PEG) chains for polyamine largely influence physico-chemical properties of PANs and their biological endpoints. Poly(allylamine hydrochloride) (PAH) are functionalized through carbodiimide chemistry with three ratios of PEG molecules per PAH chain: 0.1, 1, and 10. PEGylated PAH is then assembled into PANs by exposing the polymer to phosphate buffer solution. PANs decrease size and surface charge with increasing PEG ratios as evidenced by dynamic light scattering and zeta potential measurements, with the ten PEG/PAH ratio PANs having practically zero charge. Small angle X-ray scattering (SAXS) proves that PEG chains form a shell around a polyamine core, which is responsible for the screening of positive charges. MTT experiments show that the screening of amine groups decreases nanoparticle toxicity, with the lowest toxicity for the 10 PEG/PAH ratio. Fluorescence correlation spectroscopy (FCS) proves less interaction with proteins for PEGylated PANs. Positron emission tomography (PET) imaging of 18 F labelled PANs shows longer circulation time in healthy mice for PEGylated PANs than non-PEGylated ones.

Template-Mediated Control over Polymorphism in the Vapor-Assisted Formation of Zeolitic Imidazolate Framework Powders and Films.

The landscape of possible polymorphs for some metal-organic frameworks (MOFs) can pose a challenge for controlling the outcome of their syntheses. Demonstrated here is the use of a template to control in the vapor-assisted formation of zeolitic imidazolate framework (ZIF) powders and thin films. Introducing a small amount of either ethanol or dimethylformamide vapor during the reaction between ZnO and 4,5-dichloroimidazole vapor results in the formation of the porous ZIF-71 phase, whereas other conditions lead to the formation of the dense ZIF-72 phase or amorphous materials. Time-resolved in situ small-angle X-ray scattering reveals that the porous phase is metastable and can be transformed into its dense polymorph. This transformation is avoided through the introduction of template vapor. The porosity of the resulting ZIF powders and films was studied by N2 and Kr physisorption, as well as positron annihilation lifetime spectroscopy. The templating principle was demonstrated for other members of the ZIF family as well, including the ZIF-7 series, ZIF-8_Cl, and ZIF-8_Br.

Picosecond pump-probe X-ray scattering at the Elettra SAXS beamline.

A new setup for picosecond pump-probe X-ray scattering at the Austrian SAXS beamline at Elettra-Sincrotrone Trieste is presented. A high-power/high-repetion-rate laser has been installed on-site, delivering UV/VIS/IR femtosecond-pulses in-sync with the storage ring. Data acquisition is achieved by gating a multi-panel detector, capable of discriminating the single X-ray pulse in the dark-gap of the Elettra hybrid filling mode. Specific aspects of laser- and detection-synchronization, on-line beam steering as well protocols for spatial and temporal overlap of laser and X-ray beam are also described. The capabilities of the setup are demonstrated by studying transient heat-transfer in an In/Al/GaAs superlattice structure and results are confirmed by theoretical calculations.

Gelling without Structuring: A SAXS Study of the Interactions among DNA Nanostars.

We evaluate, by means of synchrotron small-angle X-ray scattering, the shape and mutual interactions of DNA tetravalent nanostars as a function of temperature in both the gas-like state and across the gel transition. To this end, we calculate the form factor from coarse-grained molecular dynamics simulations with a novel method that includes hydration effects; we approximate the radial interaction of DNA nanostars as a hard-sphere potential complemented by a repulsive and an attractive Yukawa term; and we predict the structure factors by exploiting the perturbative random phase approximation of the Percus-Yevick equation. Our approach enables us to fit all the data by selecting the particle radius and the width and amplitude of the attractive potential as free parameters. We determine the evolution of the structure factor across gelation and detect subtle changes of the effective interparticle interactions, that we associate to the temperature and concentration dependence of the particle size. Despite the approximations, the approach here adopted offers new detailed insights into the structure and interparticle interactions of this fascinating system.

Peering into the Formation of Cerium Oxide Colloidal Particles in Solution by In Situ Small-Angle X-ray Scattering.

The formation of CeO2 colloidal particles upon heating an aqueous solution of (NH4)2Ce(NO3)6 to 100 °C was investigated by time-resolved in situ SAXS analysis using synchrotron radiation, providing absolute intensity data. In particular, the experiments were performed by applying different temperatures between room temperature and 100 °C as well as under variation of the ionic strength and concentration. Using validated SAXS evaluation tools (SASfit and McSAS software), the analyses revealed the presence of two types of particle populations possessing average dimensions of ca. 2 nm and 5-15 nm, with the latter being agglomerates of the 2 nm particles rather than single crystallites. The analysis revealed not only the changes in the size, but also the relative volume fractions of these two CeO2 particle populations as a function of the aforementioned parameters. Increasing the temperature increases the number of the 5-15 nm agglomerates on one hand by the enhanced nucleation rate of the primary particles. On the other hand, especially at high temperatures (90 and 100 °C) the larger agglomerate particles precipitate, resulting in interesting trends in the fractions of the two populations as a function of time, temperature, ionic strength, and precursor concentration. The experimental studies are complemented by calculating colloidal interaction energies based on classical DLVO theory. Thereby, this study provides detailed insight into the nucleation, growth, and agglomeration of CeO2 nanoparticles. The primary objective of this study is to provide a better understanding of the nucleation and growth of particles by the hydrolysis of the tetravalent cerium ion in aqueous solutions.

Continuous-Flow Synthesis of ZIF-8 Biocomposites with Tunable Particle Size.

Zeolitic imidazolate framework (ZIF) biocomposites show the capacity to protect and deliver biotherapeutics. To date, the progress in this research area is based on laboratory batch methods. Now, the first continuous flow synthetic method is presented for the encapsulation of a model protein (bovine serum albumin, BSA) and a clinical therapeutic (α1-antitrypsin, AAT) in ZIF-8. The in situ kinetics of nucleation, growth, and crystallization of BSA@ZIF-8 were studied by small-angle X-ray scattering. By controlling the injection time of ethanol, the particle growth could be quenched by ethanol-induced crystallization from amorphous particles to ZIF-8 crystals. The particle size of the biocomposite was tuned in the 40-100 nm range by varying residence time prior to introduction of ethanol. As a proof-of-concept, this procedure was used for the encapsulation of AAT in ZIF-8. Upon release of the biotherapeutic from the composite, the trypsin inhibitor function of AAT was preserved.

Stable Ultraconcentrated and Ultradilute Colloids of CsPbX3 (X = Cl, Br) Nanocrystals Using Natural Lecithin as a Capping Ligand.

Attaining thermodynamic stability of colloids in a broad range of concentrations has long been a major thrust in the field of colloidal ligand-capped semiconductor nanocrystals (NCs). This challenge is particularly pressing for the novel NCs of cesium lead halide perovskites (CsPbX3; X = Cl, Br) owing to their highly dynamic and labile surfaces. Herein, we demonstrate that soy lecithin, a mass-produced natural phospholipid, serves as a tightly binding surface-capping ligand suited for a high-reaction yield synthesis of CsPbX3 NCs (6-10 nm) and allowing for long-term retention of the colloidal and structural integrity of CsPbX3 NCs in a broad range of concentrations-from a few ng/mL to >400 mg/mL (inorganic core mass). The high colloidal stability achieved with this long-chain zwitterionic ligand can be rationalized with the Alexander-De Gennes model that considers the increased particle-particle repulsion due to branched chains and ligand polydispersity. The versatility and immense practical utility of such colloids is showcased by the single NC spectroscopy on ultradilute samples and, conversely, by obtaining micrometer-thick, optically homogeneous dense NC films in a single spin-coating step from ultraconcentrated colloids.