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A class of double-perovskite compounds display fast oxygen ion diffusion and high catalytic activity toward oxygen reduction while maintaining excellent compatibility with the electrolyte. The astoundingly extended stability of NdBa_1−xCa_xCo₂O_5+δ (NBCaCO) under both air and CO₂-containing atmosphere is reported along with excellent electrochemical performance by only Ca doping into the A site of NdBaCo₂O_5+δ (NBCO). The enhanced stability can be ascribed to both the increased electron affinity of mobile oxygen species with Ca, determined through density functional theory calculations and the increased redox stability from the coulometric titration.

Ca doping into the A site of NdBaCo₂O_5+δ (NBCO) leads to NdBa_1−xCa_xCo₂O_5+δ (NBCaCO), a new class of double-perovskite compounds that are highly stable under both air and CO₂-containing atmosphere. They display fast oxygen ion diffusion and high catalytic activity toward oxygen reduction while they maintain excellent compatibility with the electrolyte.

A rapid and universal approach for multifunctional material coatings was developed based on a mussel-inspired dendritic polymer. This new kind of polymer mimics not only the functional groups of mussel foot proteins (mfps) but also their molecular weight and molecular structure. The large number of catechol and amine groups set the basis for heteromultivalent anchoring and crosslinking. The molecular weight reaches 10 kDa, which is similar to the most adhesive mussel foot protein mfp-5. Also, the dendritic structure exposes its functional groups on the surface like the folded proteins. As a result, a very stable coating can be prepared on virtually any type of material surface within 10 min by a simple dip-coating method, which is as fast as the formation of mussel byssal threads in nature.

Rapid and universal coatings were developed by mussel-inspired dendritic polyglycerol that mimics mussel foot proteins with regard to functional groups, molecular weight, and molecular structure. Multiple further modifications can be achieved by either pre- or post-functionalization and control of surface roughness.

Global optimization is used to study the structure of the polar KTaO₃ (001) surface. It is found that cation exchange near the surface leads to the most stable structure. This mechanism is likely to be general to metal oxides containing cations of differing charge.

On page 6036, J. Liu and co-workers discover electric-fieldinduced transformations of liquid metals between different morphologies and configurations. With these materialtransformation capabilities, such materials are attractive for future applications such as liquid-metal recycling, soft machine manufacture, locomotion-assisted devices, movable sensors, microfluidic valves and puzmps, or artificial robots.

CH₃NH₃PbI_3-xCl_x is a commonly used chemical formula to represent the methylammonium lead halide perovskite fabricated from mixed chlorine- and iodine-containing salt precursors. Despite the rapid progress in improving its photovoltaic efficiency, fundamental questions remain regarding the atomic ratio of Cl in the perovskite as well as the reaction mechanism that leads to its formation and crystallization. In this work we investigated these questions through a combination of chemical, morphological, structural and thermal characterizations. The elemental analyses reveal unambiguously the negligible amount of Cl atoms in the CH₃NH₃PbI_3-xCl_x perovskite. By studying the thermal characteristics of methylammonium halides as well as the annealing process in a polymer/perovskite/FTO glass structure, we show that the formation of the CH₃NH₃PbI_3-xCl_x perovskite is likely driven by release of gaseous CH₃NH₃Cl (or other organic chlorides) through an intermediate organometal mixed halide phase. Furthermore, the comparative study on CH₃NH₃I/PbCl₂ and CH₃NH₃I/PbI₂ precursor combinations with different molar ratios suggest that the initial introduction of a CH₃NH₃⁺ rich environment is critical to slow down the perovskite formation process and thus improve the growth of the crystal domains during annealing; accordingly, the function of Cl⁻ is to facilitate the release of excess CH₃NH₃⁺ at a relatively low annealing temperatures.

To understand theformation mechanism of CH₃NH₃PbI_3–xClx perovskite, two testing structures, perovskite (precursor mixture)/FTO and PMMA (polymethyl methacrylate)/perovskite (precursor mixture)/FTO, are designed. The different annealing results of these two structures suggest that the formation of CH₃NH₃PbI_3–xClx perovskite is likely driven by the release of gaseous CH₃NH₃Cl through an intermediate organolead mixed halide phase.

Phosphorus displays fascinating structural diversity and the discovery of new modifications continues to attract attention. In this work, a complete stability range of known and novel crystalline allotropes of phosphorus is described for the first time. This includes recently discovered tubular modifications and the prediction of not-yet-known crystal structures of [P₁₂] nanorods and not-yet-isolated [P₁₄] nanorods. Despite significant structural differences, all P allotropes consist of covalent substructures, which are held together by van der Waals interactions. Their correct reproduction by ab initio calculations is a core issue of current research. While some predictions with the established DFT functionals GGA and LDA differ significantly from experimental data in the description of the P allotropes, consistently excellent agreement with the GGA-D2 approach is used to predict the solid structures of the P nanorods.

Phosphorus shows its shapes and colors: DFT methods with the Grimme correction can be used to predict the structures of P allotropes that have weak interactions. For the first time, the stabilities of energetically closely related allotropes could be comprehensively elucidated and correctly predicted on the basis of van der Waals interactions. Insight into previously unknown solid-state structures of P nanorods was also possible.

The 3d transition metal (M) perovskite oxides exhibit a remarkable array of properties, including novel forms of superconductivity, magnetism and multiferroicity. Strain can have a profound effect on many of these properties. This is due to the localized nature of the M 3d orbitals, where even small changes in the M–O bond lengths and M–O–M bond angles produced by strain can be used to tune the 3d– O 2p hybridization, creating large changes in electronic structure. A new route is presented to strain the M–O bonds in epitaxial two-dimensional perovskite films by tailoring local electrostatic dipolar interactions within every formula unit via atomic layer-by-layer synthesis. The response of the O anions to the resulting dipole electric fields distorts the M–O bonds by more than 10%, without changing substrate strain or chemical composition. This distortion is largest for the apical oxygen atoms (O_ap), and alters the transition metal valence state via self-doping without chemical substitution.

The cations of a well-known layered oxide, LaSrNiO₄, are re-arranged in a “polar” structure using molecular beam epitaxy. X-ray probes reveal that the resulting electrostatic dipoles act on the Ni–O bonds, creating large distortions and changes to hybridization. This “electrostatic bond strain” approach has potential to tailor electronic properties in layered oxides by altering the local bonding without epitaxy or doping.

Zinc oxide (ZnO) is regarded as a promising alternative material for transparent conductive electrodes in optoelectronic devices. However, ZnO suffers from poor chemical stability. ZnO also has a moderate work function (WF), which results in substantial charge injection barriers into common (organic) semiconductors that constitute the active layer in a device. Controlling and tuning the ZnO WF is therefore necessary but challenging. Here, a variety of phosphonic acid based self-assembled monolayers (SAMs) deposited on ZnO surfaces are investigated. It is demonstrated that they allow the tuning the WF over a wide range of more than 1.5 eV, thus enabling the use of ZnO as both the hole-injecting and electron-injecting contact. The modified ZnO surfaces are characterized using a number of complementary techniques, demonstrating that the preparation protocol yields dense, well-defined molecular monolayers.

The tuning of the ZnO work function from 4.1 to 5.7 eV is realized by the application of a variety of phosphonic acid based self-assembled monolayers (SAMs). This enables the use of ZnO as both the electron- and hole-injecting contact. The homogenous dense packing of the SAMs is thoroughly characterized using a range of complementary techniques.

Novel β-NaGdF₄/Na(Gd,Yb)F₄:Er/NaYF₄:Yb/NaNdF₄:Yb core/shell 1/shell 2/shell 3 (C/S1/S2/S3) multi-shell nanocrystals (NCs) have been synthesized and used as probes for in vivo imaging. They can be excited by near-infrared (800 nm) radiation and emit short-wavelength infrared (SWIR, 1525 nm) radiation. Excitation at 800 nm falls into the “biological transparency window”, which features low absorption by water and low heat generation and is considered to be the ideal excitation wavelength with the least impact on biological tissues. After coating with phospholipids, the water-soluble NCs showed good biocompatibility and low toxicity. With efficient SWIR emission at 1525 nm, the probe is detectable in tissues at depths of up to 18 mm with a low detection threshold concentration (5 nM for the stomach of nude mice and 100 nM for the stomach of SD rats). These results highlight the potential of the probe for the in vivo monitoring of areas that are otherwise difficult to analyze.

A multi-shell nanocrystal was synthesized and used as an effective probe for in vivo imaging. With emission in the short-wavelength infrared region at 1525 nm, the probe is detectable in tissues at depths of up to 18 mm with a low detection threshold.

Hybrid organo–metal halide perovskite materials, such as CH₃NH₃PbI₃, have been shown to be some of the most competitive candidates for absorber materials in photovoltaic (PV) applications. However, their potential has not been completely developed, because a photovoltaic effect with an anomalously large voltage can be achieved only in a ferroelectric phase, while these materials are probably ferroelectric only at temperatures below 180 K. A new hexagonal stacking perovskite-type complex (3-pyrrolinium)(CdCl₃) exhibits above-room-temperature ferroelectricity with a Curie temperature T_c=316 K and a spontaneous polarization P_s=5.1 μC cm⁻². The material also exhibits antiparallel 180° domains which are related to the anomalous photovoltaic effect. The open-circuit photovoltage for a 1 mm-thick bulky crystal reaches 32 V. This finding could provide a new approach to develop solar cells based on organo–metal halide perovskites in photovoltaic research.

Changing phases: A hexagonal stacking organo–metal halide perovskite-type complex (3-pyrrolinium)(CdCl₃) was designed. It shows above-room-temperature ferroelectricity with a Curie temperature T_c=316 K, an anomalous photovoltaic effect with an open-circuit voltage of 32 V, and the formation of stripe-like electric domains as a result of spontaneous polarization measured by piezoresponse force microscopy (see picture).

Solvent-annealing is found to be an effective method to increase the grain size and carrier diffusion lengths of trihalide perovskite materials. The carrier diffusion length of MAPbI₃ is increased to over 1 μm. The efficiency remains above 14.5% when the MAPbI₃ thickness changes from 250 nm to 1 μm, with the highest efficiency reaching 15.6%.

Light-emitting semiconductor quantum dots (QDs) combined with magnetic resonance imaging contrast agents within a single nanoparticle platform are considered to perform as multimodal imaging probes in biomedical research and related clinical applications. The principles of their rational design are outlined and contemporary synthetic strategies are reviewed (heterocrystalline growth; co-encapsulation or assembly of preformed QDs and magnetic nanoparticles; conjugation of magnetic chelates onto QDs; and doping of QDs with transition metal ions), identifying the strengths and weaknesses of different approaches. Some of the opportunities and benefits that arise through in vivo imaging using these dual-mode probes are highlighted where tumor location and delineation is demonstrated in both MRI and fluorescence modality. Work on the toxicological assessments of QD/magnetic nanoparticles is also reviewed, along with progress in reducing their toxicological side effects for eventual clinical use. The review concludes with an outlook for future biomedical imaging and the identification of key challenges in reaching clinical applications.

Light-emitting semiconductor quantum dots (QDs) combined with magnetic components offer appealing potential for biomedical applications. This review summarizes recent achievements in contemporary synthesis strategies identifying the strengths and weaknesses of different approaches, describes multimodal imaging of tumors in vivo, examines current understanding of the toxicity of QDs/magnetic nanoparticles, and discusses key challenges in reaching clinical applications with these materials and the perspectives for their future use in biomedical imaging.

A novel sequential layer-by-layer sub-100 °C vacuum-sublimation method to fabricate planar-type organometal halide perovskite solar cells is developed. Very uniform and highly crystalline perovskite thin films with 100% surface coverage are produced. The cells attain maximum and average efficiencies up to 15.4% and 14%, respectively. This low- temperature, all-vacuum process is suitable for a wide variety of rigid and flexible applications.

Omniphobic coatings are designed to repel a wide range of liquids without leaving stains on the surface. A practical coating should exhibit stable repellency, show no interference with color or transparency of the underlying substrate and, ideally, be deposited in a simple process on arbitrarily shaped surfaces. We use layer-by-layer (LbL) deposition of negatively charged silica nanoparticles and positively charged polyelectrolytes to create nanoscale surface structures that are further surface-functionalized with fluorinated silanes and infiltrated with fluorinated oil, forming a smooth, highly repellent coating on surfaces of different materials and shapes. We show that four or more LbL cycles introduce sufficient surface roughness to effectively immobilize the lubricant into the nanoporous coating and provide a stable liquid interface that repels water, low-surface-tension liquids and complex fluids. The absence of hierarchical structures and the small size of the silica nanoparticles enables complete transparency of the coating, with light transmittance exceeding that of normal glass. The coating is mechanically robust, maintains its repellency after exposure to continuous flow for several days and prevents adsorption of streptavidin as a model protein. The LbL process is conceptually simple, of low cost, environmentally benign, scalable, automatable and therefore may present an efficient synthetic route to non-fouling materials.

Lubricant-infused coatings provide efficient repellency of various liquids and prevent the adhesion of liquid-borne contaminants. Here, a simple layer-by-layer deposition process is used to create functional, transparent, mechanically robust and stable lubricant-infused coatings on a variety of different materials with arbitrary shapes.

Multimodal nanostructures can help solve many problems in the biomedical field including sensitive molecular imaging, highly specific therapy, and early cancer detection. However, the synthesis of densely packed, multicomponent nanostructures with multimodal functionality represents a significant challenge. Here, a new type of hybrid magneto-plasmonic nanoparticles is developed using an oil-in-water microemulsion method. The nanostructures are synthetized by self-assembly of primary 6 nm iron oxide core-gold shell particles resulting into densely packed spherical nanoclusters. The dense packing of primary particles does not change their superparamagnetic behavior; however, the close proximity of the constituent particles in the nanocluster leads to strong near-infrared (NIR) plasmon resonances. The synthesis is optimized to eliminate nanocluster cytotoxicity. Immunotargeted nanoclusters are also developed using directional conjugation chemistry through the Fc antibody moiety, leaving the Fab antigen recognizing region available for targeting. Cancer cells labeled with immunotargeted nanoclusters produce a strong photoacoustic signal in the NIR that is optimum for tissue imaging. Furthermore, the labeled cells can be efficiently captured using an external magnetic field. The biocompatible magneto-plasmonic nanoparticles can make a significant impact in development of point-of-care assays for detection of circulating tumor cells, as well as in cell therapy with magnetic cell guidance and imaging monitoring.

A new generation of hybrid magneto-plasmonic nanoparticles is developed by utilizing an oil-in-water microemulsion method. The nanoparticles combine a high density of magnetic and plasmonic functionalities together with biocompatibility and molecular targeting capability that provide a promising tool for sensitive and selective cancer detection and other biomedical applications.

In this work, a new approach for construction of high aspect ratio complex moiré superlattice structure with versatile super-periodicity is developed using the moiré fringe and secondary sputtering lithography. Wide assortments of high aspect ratio complex superstructures having different features on a 10 nm scaled wall are easily fabricated from simple starting components. More important is the finding of a new microscale phenomenon, consisting in trapping fluids in the centres of the moiré hexagonal fringes, as the consequence of the modulation of local hydrophilicty of the pattern. Using this phenomenon, target materials can be selectively and hierarchically confined within the moiré superlattice. Hierarchical nanoparticles (QDs) ordering with tunable super-periodicity into selective area of moiré superlattice are successfully demonstrated by just solution-casting of toluene based QD solution on patterned surfaces. This observation is expected to elucidate the key morphological factors that govern the physics of liquid behavior on a complex patterned substrate. Accordingly, in the near future, this facile approach for complex superlattice structure could be used as optical substrate for imaging applications and open interesting perspectives in the assembly processes and the handling of the nano-microsized particles.

A powerful new method is reported for fabricating complex lateral superlattice structures with 10 nm resolution, using the moiré fringe and secondary sputtering lithography. A large assortment of moiré superstructures can be easily fabricated by a simple rotation of the periodic layer. These superlattice structures widen the range of application of moiré patterns to not only the fields of photonics or optical characterization tools, but also to functional nano materials trapping and ordering.

During the last few years, graphene's unusual friction and wear properties have been demonstrated at nano to micro scales but its industrial tribological potential has not been fully realized. The macroscopic wear resistance of one atom thick graphene coating is reported by subjecting it to pin-on-disc type wear testing against most commonly used steel against steel tribo-pair. It is shown that when tested in hydrogen, a single layer of graphene on steel can last for 6400 sliding cycles, while few-layer graphene (3–4 layers) lasts for 47 000 cycles. Furthermore, these graphene layers are shown to completely cease wear despite the severe sliding conditions including high contact pressures (≈0.5 GPa) observed typically in macroscale wear tests. The computational simulations show that the extraordinary wear performance originates from hydrogen passivation of the dangling bonds in a ruptured graphene, leading to significant stability and longer lifetime of the graphene protection layer. Also, the electronic properties of these graphene sheets are theoretically evaluated and the improved wear resistance is demonstrated to preserve the electronic properties of graphene and to have significant potential for flexible electronics. The findings demonstrate that tuning the atomistic scale chemical interactions holds the promise of realizing extraordinary tribological properties of monolayer graphene coatings.

The mechanism of extraordinary wear resistance of just one atom thick graphene layer on steel is revealed. A single layer of graphene is able to reduce steel wear by 3–4 orders of magnitude. The wear-life of graphene significantly increases when tested in hydrogen environment. Hydrogen plays a crucial role in preventing graphene from wear-induced damage by passivating carbon dangling bonds.