Abstract: Superstructures with nanoscale building blocks, when coupled with precise control of the constituent units, open opportunities in rationally designing and manufacturing desired functional materials. Yet, synthetic strategies for the large-scale production of superstructures are scarce. We report a scalable and generalized approach to synthesizing superstructures assembled from atomically precise Ce24O28(OH)8 and other rare-earth metal-oxide nanoclusters alongside a detailed description of the self-assembly mechanism. Combining operando small-angle X-ray scattering, ex situ molecular and structural characterizations, and molecular dynamics simulations indicates that a high-temperature ligand-switching mechanism, from oleate to benzoate, governs the formation of the nanocluster assembly. The chemical tuning of surface ligands controls superstructure disassembly and reassembly, and furthermore, enables the synthesis of multicomponent superstructures. This synthetic approach, and the accurate mechanistic understanding, are promising for the preparation of superstructures for use in electronics, plasmonics, magnetics and catalysis. Synthesizing superstructures with precisely controlled nanoscale building blocks is challenging. Here the assembly of superstructures is reported from atomically precise Ce24O28(OH)8 and other rare-earth metal-oxide nanoclusters and their multicomponent combinations. A high-temperature ligand-switching mechanism controls the self-assembly.

Abstract: Superconducting and normal state properties of Niobium nanofilms have been systematically investigated as a function of film thickness, on different substrates. The width of the superconductingto- normal transition for all films is remarkably narrow, confirming their high quality. The superconducting critical current density exhibits a pronounced maximum for thickness around 25 nm, marking the 3D-to-2D crossover. The magnetic penetration depth shows a sizeable enhancement for the thinnest films. Additional amplification effects of the superconducting properties have been obtained with sapphire substrates or squeezing the lateral size of the nanofilms. For thickness close to 20 nm we measured a doubled perpendicular critical magnetic field compared to its large thickness value, indicating shortening of the correlation length and the formation of small Cooper pairs. Our data analysis indicates an exciting interplay between quantum-size and proximity effects together with strong-coupling effects and the importance of disorder in the thinnest films, placing these nanofilms close to the BCS-BEC crossover regime.

Abstract: Controlled transport of water molecules through membranes and capillaries is important in areas as diverse as water purification and healthcare technologies(1-7). Previous attempts to control water permeation through membranes (mainly polymeric ones) have concentrated on modulating the structure of the membrane and the physicochemical properties of its surface by varying the pH, temperature or ionic strength(3,8). Electrical control over water transport is an attractive alternative; however, theory and simulations(9-14) have often yielded conflicting results, from freezing of water molecules to melting of ice(14-16) under an applied electric field. Here we report electrically controlled water permeation through micrometre-thick graphene oxide membranes(17-21). Such membranes have previously been shown to exhibit ultrafast permeation of water(17,22) and molecular sieving properties(18,21), with the potential for industrial-scale production. To achieve electrical control over water permeation, we create conductive filaments in the graphene oxide membranes via controllable electrical breakdown. The electric field that concentrates around these current-carrying filaments ionizes water molecules inside graphene capillaries within the graphene oxide membranes, which impedes water transport. We thus demonstrate precise control of water permeation, from ultrafast permeation to complete blocking. Our work opens up an avenue for developing smart membrane technologies for artificial biological systems, tissue engineering and filtration.

Abstract: Atoms start behaving as waves rather than classical particles if confined in spaces commensurate with their de Broglie wavelength. At room temperature this length is only about one angstrom even for the lightest atom, hydrogen. This restricts quantum-confinement phenomena for atomic species to the realm of very low temperatures(1-5). Here, we show that van der Waals gaps between atomic planes of layered crystals provide angstrom-size channels that make quantum confinement of protons apparent even at room temperature. Our transport measurements show that thermal protons experience a notably higher barrier than deuterons when entering van der Waals gaps in hexagonal boron nitride and molybdenum disulfide. This is attributed to the difference in the de Broglie wavelengths of the isotopes. Once inside the crystals, transport of both isotopes can be described by classical diffusion, albeit with unexpectedly fast rates comparable to that of protons in water. The demonstrated angstrom-size channels can be exploited for further studies of atomistic quantum confinement and, if the technology can be scaled up, for sieving hydrogen isotopes.

Abstract: The Li-rich rocksalt oxides Li2MO3 (M = 3d/4d/5d transition metal) are promising positive-electrode materials for Li-ion batteries, displaying capacities exceeding 300 mAh g(-1) thanks to the participation of the oxygen non-bonding O(2p) orbitals in the redox process. Understanding the oxygen redox limitations and the role of the O/M ratio is therefore crucial for the rational design of materials with improved electrochemical performances. Here we push oxygen redox to its limits with the discovery of a Li3IrO4 compound (O/M = 4) that can reversibly take up and release 3.5 electrons per Ir and possesses the highest capacity ever reported for any positive insertion electrode. By quantitatively monitoring the oxidation process, we demonstrate the material's instability against O-2 release on removal of all Li. Our results show that the O/M parameter delineates the boundary between the material's maximum capacity and its stability, hence providing valuable insights for further development of high-capacity materials.

Abstract: Dislocation mediated plastic deformation decisively influences the friction coefficient and the microstructural changes at many metal sliding interfaces during tribological loading. This work explores the initiation of a tribologically induced microstructure in the vicinity of a copper twin boundary. Two distinct horizontal dislocation traces lines (DTL) are observed in their interaction with the twin boundary beneath the sliding interface. DTL formation seems unaffected by the presence of the twin boundary but the twin boundary acts as an indicator of the occurring deformation mechanisms. Three concurrent elementary processes can be identified: simple shear of the subsurface area in sliding direction, localized shear at the primary DTL and crystal rotation in the layers above and between the DTLs around axes parallel to the transverse direction. Crystal orientation analysis demonstrates a strong compatibility of these proposed processes. Quantitatively separating these different deformation mechanisms is crucial for future predictive modeling of tribological contacts.

Abstract: Near-edge X-ray absorption spectroscopy (NEXAFS)1 is an essential analytical tool in material science. Combining NEXAFS with scanning transmission X-ray microscopy (STXM) adds spatial resolution and the possibility to study individual nanostructures2, 3. Here, we describe a full-field transmission X-ray microscope (TXM) that generates high-resolution, large-area NEXAFS data with a collection rate two orders of magnitude faster than is possible with STXM. The TXM optical design combines a spectral resolution of E/ΔE = 1 × 104 with a spatial resolution of 25 nm in a field of view of 1520 µm and a data acquisition time of ~1 s. As an example, we present image stacks and polarization-dependent NEXAFS spectra from individual anisotropic sodium and protonated titanate nanoribbons. Our NEXAFS-TXM technique has the advantage that one image stack visualizes a large number of nanostructures and therefore already contains statistical information. This new high-resolution NEXAFS-TXM technique opens the way to advanced nanoscale science studies.

Abstract: Asymmetric dye molecules have unusual optical and electronic properties1, 2, 3. For instance, they show a strong second-order nonlinear optical (NLO) response that has attracted great interest for potential applications in electro-optic modulators for optical telecommunications and in wavelength conversion of lasers2, 3. However, the strong Coulombic interaction between the large dipole moments of these molecules favours a pairwise antiparallel alignment that cancels out the NLO response when incorporated into bulk materials. Here, we show that by including an elongated dipolar dye (p,p′-dimethylaminonitrostilbene, DANS, a prototypical asymmetric dye with a strong NLO response4) inside single-walled carbon nanotubes (SWCNTs)5, 6, an ideal head-to-tail alignment in which all electric dipoles point in the same sense is naturally created. We have applied this concept to synthesize solution-processible DANS-filled SWCNTs that show an extremely large total dipole moment and static hyperpolarizability (β0 = 9,800 × 10−30 e.s.u.), resulting from the coherent alignment of arrays of ∼70 DANS molecules.

Abstract: Silicon dominates the electronics industry, but its poor optical properties mean that III-V compound semiconductors are preferred for photonics applications. Photoluminescence at visible wavelengths was observed from porous Si at room temperature in 1990, but the origin of these photons (do they arise from highly localized defect states or quantum confinement effects?) has been the subject of intense debate ever since. Attention has subsequently shifted from porous Si to Si nanocrystals, but the same fundamental question about the origin of the photoluminescence has remained. Here we show, based on measurements in high magnetic fields, that defects are the dominant source of light from Si nanocrystals. Moreover, we show that it is possible to control the origin of the photoluminescence in a single sample: passivation with hydrogen removes the defects, resulting in photoluminescence from quantum-confined states, but subsequent ultraviolet illumination reintroduces the defects, making them the origin of the light again.

Abstract: NiTi is one of the most popular shape-memory alloys, a phenomenon resulting from a martensitic transformation. Commercial NiTi-based alloys are often thermally treated to contain Ni4Ti3 precipitates. The presence of these precipitates can introduce an extra transformation step related to the so-called R-phase. It is believed that the strain field surrounding the precipitates, caused by the matrixprecipitate lattice mismatch, lies at the origin of this intermediate transformation step. Atomic-resolution transmission electron microscopy in combination with geometrical phase analysis is used to measure the elastic strain field surrounding these precipitates. By combining measurements from two different crystallographic directions, the three-dimensional strain matrix is determined from two-dimensional measurements. Comparison of the measured strain matrix to the eigenstrain of the R-phase shows that both are very similar and that the introduction of the R-phase might indeed compensate the elastic strain introduced by the precipitate.

Abstract: Intrinsic ripples in freestanding graphene have been exceedingly difficult to study. Individual ripple geometry was recently imaged using scanning tunnelling microscopy, but these measurements are limited to static configurations. Thermally-activated flexural phonon modes should generate dynamic changes in curvature. Here we show how to track the vertical movement of a one-square-angstrom region of freestanding graphene using scanning tunnelling microscopy, thereby allowing measurement of the out-of-plane time trajectory and fluctuations over long time periods. We also present a model from elasticity theory to explain the very-low-frequency oscillations. Unexpectedly, we sometimes detect a sudden colossal jump, which we interpret as due to mirror buckling. This innovative technique provides a much needed atomic-scale probe for the time-dependent behaviours of intrinsic ripples. The discovery of this novel progenitor represents a fundamental advance in the use of scanning tunnelling microscopy, which together with the application of a thermal load provides a low-frequency nano-resonator.

Abstract: Stimulus-responsive shape-memory materials have attracted tremendous research interests recently, with much effort focused on improving their mechanical actuation. Driven by the needs of nanoelectromechanical devices, materials with large mechanical strain, particularly at nanoscale level, are therefore desired. Here we report on the discovery of a large shape-memory effect in bismuth ferrite at the nanoscale. A maximum strain of up to ~14% and a large volumetric work density of ~600±90 J cm−3 can be achieved in association with a martensitic-like phase transformation. With a single step, control of the phase transformation by thermal activation or electric field has been reversibly achieved without the assistance of external recovery stress. Although aspects such as hysteresis, microcracking and so on have to be taken into consideration for real devices, the large shape-memory effect in this oxide surpasses most alloys and, therefore, demonstrates itself as an extraordinary material for potential use in state-of-art nanosystems.

Abstract: Determining the three-dimensional (3D) arrangement of atoms in crystalline nanoparticles is important for nanometre-scale device engineering and also for applications involving nanoparticles, such as optoelectronics or catalysis. A nanoparticles physical and chemical properties are controlled by its exact 3D morphology, structure and composition1. Electron tomography enables the recovery of the shape of a nanoparticle from a series of projection images2, 3, 4. Although atomic-resolution electron microscopy has been feasible for nearly four decades, neither electron tomography nor any other experimental technique has yet demonstrated atomic resolution in three dimensions. Here we report the 3D reconstruction of a complex crystalline nanoparticle at atomic resolution. To achieve this, we combined aberration-corrected scanning transmission electron microscopy5, 6, 7, statistical parameter estimation theory8, 9 and discrete tomography10, 11. Unlike conventional electron tomography, only two images of the targeta silver nanoparticle embedded in an aluminium matrixare sufficient for the reconstruction when combined with available knowledge about the particles crystallographic structure. Additional projections confirm the reliability of the result. The results we present help close the gap between the atomic resolution achievable in two-dimensional electron micrographs and the coarser resolution that has hitherto been obtained by conventional electron tomography.

Abstract: Lanthanum carbonate is a new phosphate binder that is poorly absorbed from the gastrointestinal tract and eliminated largely by the liver. After oral treatment, we and others had noticed 23 fold higher lanthanum levels in the livers of rats with chronic renal failure compared to rats with normal renal function. Here we studied the kinetics and tissue distribution, absorption, and subcellular localization of lanthanum in the liver using transmission electron microscopy, electron energy loss spectrometry, and X-ray fluoresence. We found that in the liver lanthanum was located in lysosomes and in the biliary canal but not in any other cellular organelles. This suggests that lanthanum is transported and eliminated by the liver via a transcellular, endosomal-lysosomal-biliary canicular transport route. Feeding rats with chronic renal failure orally with lanthanum resulted in a doubling of the liver levels compared to rats with normal renal function, but the serum levels were similar in both animal groups. These levels plateaued after 6 weeks at a concentration below 3 g/g in both groups. When lanthanum was administered intravenously, thereby bypassing the gastrointestinal tract-portal vein pathway, no difference in liver levels was found between rats with and without renal failure. This suggests that there is an increased gastrointestinal permeability or absorption of oral lanthanum in uremia. Lanthanum levels in the brain and heart fluctuated near its detection limit with long-term treatment (20 weeks) having no effect on organ weight, liver enzyme activities, or liver histology. We suggest that the kinetics of lanthanum in the liver are consistent with a transcellular transport pathway, with higher levels in the liver of uremic rats due to higher intestinal absorption.