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Recently, there has been significant interest in using dielectric nanocavities for the controlled scattering of light, owing to the diverse electromagnetic modes that they support. For plasmonic systems, electron energy-loss spectroscopy (EELS) is now an established method enabling structure–optical property analysis at the scale of the nanostructure. Here, we instead test its potential for the near-field mapping of photonic eigenmodes supported in planar dielectric nanocavities, which are lithographically patterned from amorphous silicon according to standard photonic principles. By correlating results with finite element simulations, we demonstrate how many of the EELS excitations can be directly corresponded to various optical eigenmodes of interest for photonic engineering. The EELS maps present a high spatial definition, displaying intensity features that correlate precisely to the impact parameters giving the highest probability of modal excitation. Further, eigenmode characteristics translate into their EELS signatures, such as the spatially and energetically extended signal of the low Q-factor electric dipole and nodal intensity patterns emerging from excitation of toroidal and second-order magnetic modes within the nanocavity volumes. Overall, the spatial–spectral nature of the data, combined with our experimental–simulation toolbox, enables interpretation of subtle changes in the EELS response across a range of nanocavity dimensions and forms, with certain simulated resonances matching the excitation energies within ±0.01 eV. By connecting results to far-field simulations, perspectives are offered for tailoring the nanophotonic resonances via manipulating nanocavity size and shape.

Thin films of the solid solution Nd 1 − x La x NiO3 are grown in order to study the expected 0 K phase transitions at a specific composition. We experimentally map out the structural, electronic and magnetic properties as a function of x and a discontinuous, possibly first order, insulator–metal transition is observed at low temperature when x = 0.2. Raman spectroscopy and scanning transmission electron microscopy show that this is not associated with a correspondingly discontinuous global structural change. On the other hand, results from density functional theory (DFT) and combined DFT and dynamical mean field theory calculations produce a 0 K first order transition at around this composition. We further estimate the temperature-dependence of the transition from thermodynamic considerations and find that a discontinuous insulator–metal transition can be reproduced theoretically and implies a narrow insulator–metal phase coexistence with x. Finally, muon spin rotation (µSR) measurements suggest that there are non-static magnetic moments in the system that may be understood in the context of the first order nature of the 0 K transition and its associated phase coexistence regime.

A growth of grain triplets is identified in vapor deposited, a-texture polycrystalline zinc oxide thin films, using a combination of transmission electron microscopy-based automated crystal orientation mapping and high-resolution imaging. Each triplet consists of three wurtzite phase grains, coordinated to near tetrahedral relative growth angles by the close-packed planes of a few nanometer diameter core of metastable zinc blende phase ZnO located at their triple junction. The triplets are aligned such that two of the grains have their fast growing [ 2 1 ¯ 1 ¯ 0 ] axes (near-) parallel to the substrate normal, and so coarsen under the principle of competitive grain growth. In contrast, growth of the third grain with a ( 1 0 1 ¯ 3 ) texture is impeded, such that it forms a small wedge between the ends of its two larger neighbors. Remarkably, all three boundaries between the grains adhere to a [ 2 1 ¯ 1 ¯ 0 ] / ( 0 1 1 ¯ 3 ) coherent twin orientation relationship, which corresponds to a grain geometry that is incommensurate with a perfect crystallographic nature. This coherency is primarily achieved via the small grain having an orientation that rotates internally by 10±2° across its volume, when going between the two interfaces formed with the neighboring large grains. The energy associated with this structural distortion is compensated by the formation of the coherent twin boundaries, such that the triplets are a stable or semi-stable growth form that are abundant in the film. The small ( 1 0 1 ¯ 3 ) texture grains may renucleate persistently, taking either of two possible orientations from the underlying tetrahedral coordination. By developing a phenomenological model for the triplet geometry and form, we associate these two orientations to small hexagonal caps and angled wedges seen in the surface morphology of the film. These findings potentially carry relevance for a wide range of vapor deposited compact films and free-standing nanostructures of wurtzite phase octet binary semiconductor compounds. We therefore believe that these insights can stimulate new research, for instance to obtain a more fundamental understanding of the growth mechanisms at the atomistic level.

Crystallographic point defects (PDs) can dramatically decrease the efficiency of optoelectronic semiconductor devices, many of which are based on quantum well (QW) heterostructures. However, spatially resolving individual non-radiative PDs buried in such QWs has so far not been demonstrated. Here, using high-resolution cathodoluminescence (CL) and a specific sample design, we spatially resolve, image, and analyse non-radiative PDs in InGaN/GaN QWs. We identify two different types of PD by their contrasting behaviour with temperature, and measure their densities from $10^{14}$ cm$^{-3}$ to as high as $10^{16}$ cm$^{-3}$. Our CL images clearly illustrate the interplay between PDs and carrier dynamics in the well: increasing PD concentration severely limits carrier diffusion lengths, while a higher carrier density suppresses the non-radiative behaviour of PDs. The results in this study are readily interpreted directly from CL images, and represent a significant advancement in nanoscale PD analysis., Main text: 8 pages, 6 figures. Supplementary: 11 pages, 8 figures

In an era of new developments in nanomaterials analysis enabled by the unprecedented spatial and energy resolutions of electron energy-loss spectroscopy in the scanning transmission electron microscope (STEM-EELS), it remains that the vast majority of works concern collective or single-particle excitations that are well described by the electrostatic approximation, which neglects retardation and magnetic field effects. Here we demonstrate a simple case in which that approximation is fundamentally inadequate. When the beam energy is above the Cherenkov threshold and the geometric dimensions of the nanomaterial sample are on the order of the wavelength of light in the material, spatial variations in low-loss (less than or similar to 5 eV) spectral maps from guided light modes may be observed. We demonstrate such observations for amorphous silicon disks and offer an interpretation of the results based on the waveguide modes of a cylinder. We also demonstrate explicitly that spatial variations from waveguide modes are manifest in analytic models for the especially simple geometry of a STEM beam penetrating a dielectric ribbon. We discuss how these modes relate to those that have been observed more generally in dielectric nanomaterials.

Nanoscale mapping of the distinct electronic phases characterizing the metal-insulator transition displayed by most of the rare-earth nickelate compounds is fundamental for discovering the true nature of this transition and the possible couplings that are established at the interfaces of nickelate-based heterostructures. Here, we demonstrate that this can be accomplished by using scanning transmission electron microscopy in combination with electron energy-loss spectroscopy. By tracking how the O K and Ni L edge fine structures evolve across two different NdNiO3/SmNiO3 superlattices, displaying either one or two metal- insulator transitions depending on the individual layer thickness, we are able to determine the electronic state of each of the individual constituent materials. We further map the spatial configuration associated with their metallic/insulating regions, reaching unit cell spatial resolution. With this, we estimate the width of the metallic/insulating boundaries at the NdNiO3/SmNiO3 interfaces, which is measured to be on the order of four unit cells.

The success story of blue light-emitting diodes over the past decade is underpinned by the high internal quantum efficiency (IQE) of the InGaN/GaN quantum wells (QWs) within the active region. Yet this extraordinary IQE can only be achieved by adding an indium-containing layer before the QWs—the “underlayer” (UL). In this work, we evidence that any indium-containing III-nitride layer acts to incorporate surface defects; the UL hence acts as a getter for surface defects to avoid their incorporation into the QWs as IQE-reducing point defects (PDs). We directly observe the reduction in PD-density caused by increasing the UL thickness.

The nature of the liquid–solid interface determines the characteristics of a variety of physical phenomena, including catalysis, electrochemistry, lubrication, and crystal growth. Most of the established models for crystal growth are based on macroscopic thermodynamics, neglecting the atomistic nature of the liquid–solid interface. Here, experimental observations and molecular dynamics simulations are employed to identify the 3D nature of an atomic‐scale ordering of liquid Ga in contact with solid GaAs in a nanowire growth configuration. An interplay between the liquid ordering and the formation of a new bilayer is revealed, which, contrary to the established theories, suggests that the preference for a certain polarity and polytypism is influenced by the atomic structure of the interface. The conclusions of this work open new avenues for the understanding of crystal growth, as well as other processes and systems involving a liquid–solid interface., M.Z., N.T., and A.F.i.M. were supported by SNF Back‐Up Schemes Consolidator Grant Nos. BSC‐GI0_157705 and NCCR QSIT, G.I. and M.C. were supported by the NCCR MARVEL, funded by the Swiss National Science Foundation. ICN2 acknowledges funding from Generalitat de Catalunya 2017 SGR 327 and the Spanish MINECO project ENE2017‐85087‐C3. ICN2 was supported by the Severo Ochoa program from Spanish MINECO (Grant No. SEV‐2017‐0706) and was funded by the CERCA Programme/Generalitat de Catalunya. Part of the present work was performed in the framework of Universitat Autònoma de Barcelona Materials Science Ph.D. program. S.M.‐S. acknowledges funding from “Programa Internacional de Becas “la Caixa”‐Severo Ochoa.” The authors acknowledge support from CSIC Research Platform on Quantum Technologies PTI‐001. SuperSTEM is the UK National Research Facility for Advanced Electron Microscopy, supported by the Engineering and Physical Sciences Research Council (EPSRC).

The single-layer graphene film, when incorporated with molecular-sized pores, is predicted to be the ultimate membrane. However, the major bottlenecks have been the crack-free transfer of large-area graphene on a porous support, and the incorporation of molecular-sized nanopores. Herein, we report a nanoporous-carbon-assisted transfer technique, yielding a relatively large area (1 mm2), crack-free, suspended graphene film. Gas-sieving (H2/CH4 selectivity up to 25) is observed from the intrinsic defects generated during the chemical-vapor deposition of graphene. Despite the ultralow porosity of 0.025%, an attractive H2 permeance (up to 4.1 × 10−7 mol m−2 s−1 Pa−1) is observed. Finally, we report ozone functionalization-based etching and pore-modification chemistry to etch hydrogen-selective pores, and to shrink the pore-size, improving H2 permeance (up to 300%) and H2/CH4 selectivity (up to 150%). Overall, the scalable transfer, etching, and functionalization methods developed herein are expected to bring nanoporous graphene membranes a step closer to reality., Graphene shows great promise for gas separation applications, but obtaining large membranes that are free of cracks and tears remains highly challenging. Here, the authors realize monolayer, crack-free, millimeter-scale graphene membranes that exhibit selective gas permeation solely thanks to their intrinsic defects

Bimetallic Ru–Ni and Rh–Ni nanocatalysts coated with a phase transfer agent efficiently cleave aryl ether C–O linkages in water in the presence of hydrogen. For dimeric substrates with weaker C–O linkages, i.e. α-O-4 and β-O-4 bonds, low loadings of the precious metal (Rh or Ru) in the nanocatalysts quantitatively afford monomers, whereas for the stronger 4-O-5 linkage higher amounts of the precious metal are required to achieve complete conversion. Under the optimized, relatively mild operating conditions, the C–O bonds in a range of substituted ether compounds are efficiently cleaved, and mechanistic insights into the reaction pathways are provided. This work paves the way to sustainable approaches for the hydrogenolysis of C–O bonds.

A strong coupling of the lattice to functional properties is observed in many transition metal oxide systems, such as the ABO(3) perovskites. In the quest for tailor-made materials, it is essential to be able to control the structural properties of the compound(s) of interest. Here, thin film solid solutions that combine NdNiO3 and LaNiO3, two materials with the perovskite structure but distinct space groups, are analyzed. Raman spectroscopy and scanning transmission electron microscopy are combined in a synergistic approach to fully determine the mechanism of the structural crossover with chemical composition. It is found that the symmetry transition is achieved by phase coexistence in a way that depends on the substrate selected. These results carry implications for analog-tuning of physical properties in future functional materials based on these compounds.

The ability to obtain three-dimensional (3-D) information about morphologies of nanostructures elucidates many interesting properties of materials in both physical and biological sciences. Here we demonstrate a novel method in scanning transmission electron microscopy (STEM) that gives a fast and reliable assessment of the 3-D configuration of curvilinear nanostructures, all without needing to tilt the sample through an arc. Using one-dimensional crystalline defects known as dislocations as a prototypical example of a complex curvilinear object, we demonstrate their 3-D reconstruction two orders of magnitude faster than by standard tilt-arc TEM tomographic techniques, from data recorded by selecting different ray paths of the convergent STEM probe. Due to its speed and immunity to problems associated with a tilt arc, the tilt-less 3-D imaging offers important advantages for investigations of radiation-sensitive, polycrystalline, or magnetic materials. Further, by using a segmented detector, the total electron dose is reduced to a single STEM raster scan acquisition; our tilt-less approach will therefore open new avenues for real-time 3-D electron imaging of dynamic processes., Scientific Reports, 7, ISSN:2045-2322

Herein, the assembly of CsPbBr3 QD/AlOx inorganic nanocomposite, using atomic layer deposition (ALD) for the growth of the amorphous alumina matrix (AlOx), is proven as a novel protection scheme for this new class of QDs. The nucleation and growth process of AlOx on the QD surface was thoroughly investigated by a miscellanea of techniques which highlighed the importance of the interaction between the ALD precursor and the QD surface to uniformely coat the QDs while preserving the optoelectronic properties. These nanocomposites show an exceptional stability against exposure to air (for at least 45 days), irradiation under simulated solar spectrum (for at least 8h), to thermal treatment (at least up to 200oC in air), and finally against immersion in water. The method was extended to assembly CsPbBrxI3-x QD/AlOx and CsPbI3 QD/AlOx nanocomposites which were more stable compared to the pristine QD films.

ZnO is commonly observed and assumed to crystallize fully in a wurtzite structure. Indeed, while polytypism between a wurtzite and a zinc blende phase is often seen in some II-VI compounds, it has only rarely been observed in ZnO. Here, by means of automated crystal orientation mapping and high-resolution imaging in transmission electron microscopy, we identify nanometer-sized regions of zinc blende forming during the growth of compact nanocrystalline metal–organic chemical vapor deposited ZnO films. We analyze a c-fiber-textured wurtzite ZnO film, where the columnar grain growth, typical for polycrystalline films, is interrupted by the formation of these zinc blende regions. These regions in turn provide surfaces for the heteroepitaxial renucleation of newly oriented wurtzite grains. In contrast to the columnar grains, which grow fastest along their c-axis, these new grains are identified to grow fastest along their basal plane. By means of convergent beam electron diffraction, we show that this difference in fast growth direction relates to the polarity of exposed facets. A growth model is proposed, showing how this polytypism affects the microstructure evolution of the film in ways that were not predicted by existing film growth models.

The oxygen evolution reaction (OER) is an essential anode reaction for the generation of solar and electric fuels through water splitting or CO2 electroreduction. Mixed metal oxides containing Co, Fe, or Ni prove to be the most promising OER electrocatalysts in alkaline medium. However, the active sites and reaction mechanisms of these catalysts are difficult to study due to their heterogeneous nature. Here we describe a general synthesis of Co, Fe, and Ni-containing double-atom catalysts from their single-atom precursors via in-situ electrochemical transformation. Atomic-resolution microscopy and operando X-ray absorption spectroscopy (XAS) reveal molecule-like bimetallic active sites for these supported catalysts. Based on electrokinetic and XAS data, we propose a complete catalytic cycle for each catalyst. These mechanisms follow a similar O-O bond forming step and all exhibit bimetallic cooperation. However, the mechanisms diverge in the site and source of OH- for O-O bond formation as well as the order of proton and electron transfer. Our work demonstrates double-atom catalysts as an attractive platform for fundamental studies of heterogeneous OER electrocatalysts.

Single atom catalysts exhibit well-defined active sites and potentially maximum atomic efficiency. However, they are unsuitable for reactions that benefit from bimetallic promotion such as the oxygen evolution reaction (OER) in alkaline medium. Here we show that a single atom Co precatalyst can be in-situ transformed into a Co-Fe double atom catalyst for OER. This catalyst exhibits one of the highest turnover frequencies among metal oxides. Electrochemical, microscopic, and spectroscopic data including those from operando X-ray absorption spectroscopy, reveal a dimeric Co-Fe moiety as the active site of the catalyst. This work demonstrates double-atom catalysis as a promising approach for the developed of defined and highly active OER catalysts.

The relationship between composition and plasmonic properties in noble metal nanoalloys is still largely unexplored. Yet, nanoalloys of noble metals, such as gold, with transition elements, such as iron, have unique properties and a number of potential applications, ranging from nanomedicine to magneto-plasmonics and plasmon-enhanced catalysis. Here, we investigate the localized surface plasmon resonance at the level of the single Au-Fe nanoparticle by applying a strategy that combines experimental measurements using near field electron energy loss spectroscopy with theoretical studies via a full wave numerical analysis and density functional theory calculations of electronic structure. We show that, as the iron fraction increases, the plasmon resonance is blue-shifted and significantly damped, as a consequence of the changes in the electronic band structure of the alloy. This allows the identification of three relevant phenomena to be considered in the design and realization of any plasmonic nanoalloy, specifically: the appearance of new states around the Fermi level; the change in the free electron density of the metal; and the blue shift of interband transitions. Overall, this study provides new opportunities for the control of the optical response in Au-Fe and other plasmonic nanoalloys, which are useful for the realization of magneto-plasmonic devices for molecular sensing, thermo-plasmonics, bioimaging, photocatalysis, and the amplification of spectroscopic signals by local field enhancement.

The grain size evolution of polycrystalline thin films, which form by competitive grain overgrowth as commonly interpreted using the van der Drift model, is understood to follow a power-law scaling of the average grain size d with film thickness h, i.e. d ∝ hα. While simulations have identified a growth exponent α = 0.4 for three-dimensional growth, previous experimental studies did not confirm this value, instead finding α values in the range of ∼0.5–0.7. Here we study competitive grain overgrowth using a system of ZnO thin films grown by low-pressure metal–organic chemical vapor deposition. We present quantitative data on the evolution of grain size and orientation across the thickness of thin films, obtained by automated crystal orientation mapping of “double-wedge” transmission electron microscopy samples. The data from a-textured ZnO films, grown under three different conditions, are compared against van der Drift model predictions of self-similarity of the grain size distribution and the power-law scaling. The results are further interpreted by comparing to simulations of faceted polycrystalline film growth, which we adapt to the ZnO system by including idiomorphic growth shapes with a six-fold symmetry and random or biased nuclei orientations. As well as showing the predicted self-similarity of grain size distributions during growth, for the first time our experimental data confirm a power-law growth exponent of α = 0.4, as also predicted by the simulations using randomly oriented nuclei. Nevertheless, interpretation of this result is contingent on the absence of factors such as textured nucleation and renucleation during film growth. Indeed, only one film, grown at a higher ratio of H2O/DEZ precursor gases, displaying random initial nucleation, and minimal grain renucleation during growth, shows a proper conformance to the model nature and predictions.

Helium is one of the most inert elements in nature and its solubility in most materials is very low. When introduced by implantation, the energetic helium atoms induce the displacement of a large number of atoms from their lattice position creating excess defects (self-interstitials and vacancies) that may agglomerate to form larger clusters and/or may interact with the implanted atoms as well. In particular, the interaction of vacancies with helium leads to the formation of bubbles that may modify the mechanical and physical properties of materials. This leads to a very active research field in the nuclear domain, where bubbles are responsible for the embrittlement of materials. In covalent materials, helium bubbles can be formed following high fluence implantation as well and the idea to transform bubbles from a liability into an asset has emerged twenty years ago. The most known application is probably the formation of helium and hydrogen disc-like bubbles, the platelets, used to produce silicon-on-insulator wafers. But other potential applications have been demonstrated as well such as proximity gettering of metallic impurities for instance. For all these applications, the control of the bubble formation and evolution is essential. This requires an in-depth understanding of the underlying physical mechanisms. In this work, a multiscale picture of the formation mechanisms of helium bubbles in silicon and their evolution under annealing is derived from the combination of numerical simulations and Electron Energy Loss Spectroscopy (EELS) in the Transmission Electron Microscope (TEM). Using molecular dynamics (MD) and rate equation dynamics calculations, we have identified the atomic scale mechanisms involved in the nucleation and early growth steps of the bubbles and followed their dynamics during experimental timescale. For the smallest length scale, the optimal helium filling in small vacancy clusters was determined (Fig. 1a) [1]. Regarding bubble growth, MD simulations (Fig. 1b) suggest that both Ostwald ripening and migration-coalescence mechanisms are jointly activated during bubble growth. We also discover that an original mechanism, based on the splitting of bubbles, could have a significant contribution. Overall, helium atoms are found to delay growth, proportionally to their concentration. This can be clearly observed at the nanosecond timescale. However, for longer timescales, cluster dynamics calculations also reveal periods of accelerated growth for specific helium concentrations [2]. At larger length scales, the physical properties of the bubbles (helium density, pressure, morphology and size) were investigated experimentally using an original approach based on spatially resolved EELS that we have developed [3]. These experiments allow for an accurate determination of size, aspect ratio and helium density for a large number of single bubbles. These bubbles, 6 to 20 nm in diameter, were synthesized by high fluence helium implantation in silicon, followed by annealing. Very high helium densities, from 60 to 180 He/nm3, were measured in the bubbles depending on the conditions, in stark contrast with previous investigations of helium bubbles in metal with similar sizes. These results were confirmed by atomistic calculations performed for helium bubbles in the diameter range 1 to 13 nm [4]. The structural modifications and, simultaneously, the helium emission from individual bubbles were investigated by spectrum imaging during in situ annealing in the transmission electron microscope (Fig. 1c). We show that helium emission surprisingly takes place at temperatures where bubble migration had hardly started. At higher temperatures, the migration (and coalescence) of voids is clearly revealed. For helium density lower than 150 He.nm-3, the Cerofolini's model taking into account the thermodynamical properties of an ultradense fluid reproduces well the helium emission from the bubbles, leading to an activation energy of 1.8 eV. When bubbles exhibit a higher initial helium density, the Cerofolini's model fails to reproduce the helium emission kinetics. We ascribe this to the fact that helium may be in the solid phase and we propose a model to take into account the properties of the solid [5]. [1] L. Pizzagalli, M.-L. David, J. Dérès, Phys. Stat. Solidi A, 1700263 (2017) [2] L. Pizzagalli, J. Dérès, M.-L. David, T. Jourdan, J. Phys. D : Appl. Phys. 52, P. 455106 (2019) [3] K. Alix, M.-L. David, G. Lucas, D.T.L. Alexander, F. Pailloux, C. Hébert, L. Pizzagalli, Micron 77, p.57 (2015) [4] J. Dérès, M.-L. David, K. Alix, D.T.L. Alexander, C. Hébert, L. Pizzagalli, Phys. Rev. B 96, p. 014110 (2017) [5] K. Alix, M.-L. David, J. Dérès, C. Hébert, L. Pizzagalli, Phys. Rev. B 97, p. 104012 (2018) Figure 1

Predetermined and selective placement of nanoparticles onto large-area substrates with nanometre-scale precision is essential to harness the unique properties of nanoparticle assemblies, in particular for functional optical and electro-optical nanodevices. Unfortunately, such high spatial organization is currently beyond the reach of top-down nanofabrication techniques alone. Here, we demonstrate that topographic features comprising lithographed funnelled traps and auxiliary sidewalls on a solid substrate can deterministically direct the capillary assembly of Au nanorods to attain simultaneous control of position, orientation and interparticle distance at the nanometre level. We report up to 100% assembly yield over centimetre-scale substrates. We achieve this by optimizing the three sequential stages of capillary nanoparticle assembly: insertion of nanorods into the traps, resilience against the receding suspension front and drying of the residual solvent. Finally, using electron energy-loss spectroscopy we characterize the spectral response and near-field properties of spatially programmable Au nanorod dimers, highlighting the opportunities for precise tunability of the plasmonic modes in larger assemblies.

Combining the sol-gel method for fiber material production with the granulated silica method for preform assembly results in a robust method that offers a high degree of freedom regarding both the composition and the geometry of the produced fiber. Using this method, two types of Yb-doped silica glass composition, that feature an excess in P concentration with respect to Al, have been prepared. The elemental distributions in a fiber core were analyzed by scanning transmission electron microscopy (STEM). The elemental mapping shows a similar localization of Al, P and Yb through the microstructure. In addition, the influence of the variation in the co-dopant concentration, with respect to Yb, on the fiber properties has been investigated. The results show an increase in the refractive index step and in the fiber&rsquo, s transmission loss as the excess concentration of P increases. A significant contribution to the losses can be assigned to the existence of impurities such as iron, which was detected in our samples by mass spectrometer. Single exponential fluorescence decays with lifetimes of around 0.88 ms were measured for the two compositions. Finally, pumping at 976 nm a laser slope efficiency of 67% at 1031 nm was achieved for one of the fiber compositions.

A long-standing problem in the application of solid-state nanopores is the lack of the precise control over the geometry of artificially formed pores compared to the well- defined geometry in their biological counterpart, i.e. protein nanopores. To date, experimentally investigated solid-state nanopores have been shown to adopt approximately circular shape. A unique property of hexagonal boron nitride (h-BN) few-layers has been revealed by previous transmission electron microscopy (TEM) studies, where triangular defects or nanopores can be created or enlarged while maintaining their intrinsic triangular shape.1, 2 Here, we investigate the geometrical effect of the nanopore shape on ionic blockage induced by DNA translocation using triangular h-BN nanopores and approximately circular molybdenum disulfide (MoS2) nanopores. We observe a geometry-dependent ion scattering effect, which is further corroborated by a modified ionic blockage model. The well-acknowledged ionic blockage model is derived from uniform ion permeability through the 2D nanopore plane and hemisphere like access region in the nanopore vicinity.3, 4 Based on our experimental results, we propose a modified ionic blockage model, which is highly related to the ionic profile caused by geometrical variations. Our findings shed light on the rational design of 2D nanopores and should be applicable to arbitrary nanopore shapes.

We investigate the structural evolution of polycrystalline zinc oxide films grown by low pressure metal-organic chemical vapor deposition. The goal is to achieve larger grains-leading to higher charge carrier mobility from lower grain boundary density-by controlling the grain orientation during growth. The results are 2-fold. First we describe how the combination of deposition temperature and gas flow influences the nucleation and film thickening stages: low temperature and high gas flow favor a high nucleation density and the development of c-textured films, whereas high temperature and low gas flow lead to a lower nucleation density and a-textured films. Second we demonstrate how a fine control of the film preferential orientation at the different growth stages allows the fabrication of films with grains that are 25% larger, hence improving the carrier mobility with respect to the reference film.

Scleractinian corals begin their biomineralization process shortly after larval settlement with the formation of calcium carbonate (CaCO(3)) structures at the interface between the larval tissues and the substrate. The newly settled larvae exert variable degrees of control over this skeleton formation, providing an opportunity to study a range of biocarbonate structures, some of which are transient and not observed in adult coral skeletons. Here we present a morphological, structural, crystallographic, and chemical comparison between two types of aragonite deposits observed during the skeletal development of 2-days old recruits of Pocillopora damicornis: (1) Primary septum and (2) Abundant, dumbbell-like structures, quasi-randomly distributed between initial deposits of the basal plate and not present in adult corals-At the mesoscale level, initial septa structures are formed by superimposed fan-shaped fasciculi consisting of bundles of fibers, as also observed in adult corals. This organization is not observed in the dumbbell-like structures. However, at the ultrastructural level there is great similarity between septa and dumbbell components. Both are composed of

Highly dispersed iron oxide (Fe2O3) nanoparticles (NPs) have been immobilized on structured supports of activated carbon fibers (ACF). Systematic catalyst characterizations suggest that ACF-based catalysts remain ultra-microporous after Fe2O3 NPs (similar to 2 nm) deposition. The structured nano-catalysts show high activity and chemoselectivity in reduction of different functionalized nitroarenes to the corresponding anilines giving yields of the target products close to 100%. The reaction takes place under mild conditions at normal pressure and low temperatures (

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

This article belongs to the Special Issue Magnetic Nanoparticles in Biological Applications., Aqueous synthesis without ligands of iron oxide nanoparticles (IONPs) with exceptional properties still remains an open issue, because of the challenge to control simultaneously numerous properties of the IONPs in these rigorous settings. To solve this, it is necessary to correlate the synthesis process with their properties, but this correlation is until now not well understood. Here, we study and correlate the structure, crystallinity, morphology, as well as magnetic, relaxometric and heating properties of IONPs obtained for different durations of the hydrothermal treatment that correspond to the different growth stages of IONPs upon initial co-precipitation in aqueous environment without ligands. We find that their properties were different for IONPs with comparable diameters. Specifically, by controlling the growth of IONPs from primary to secondary particles firstly by colloidal and then also by magnetic interactions, we control their crystallinity from monocrystalline to polycrystalline IONPs, respectively. Surface energy minimization in the aqueous environment along with low temperature treatment is used to favor nearly defect-free IONPs featuring superior properties, such as high saturation magnetization, magnetic volume, surface crystallinity, the transversal magnetic resonance imaging (MRI) relaxivity (up to r₂ = 1189 mM-1·s-1 and r₂/r₁ = 195) and specific absorption rate, SAR (up to 1225.1 W·gFe-1)., This work was financially supported by the MagnetoTeranostics project that was scientifically evaluated by the Swiss National Science Foundation (SNSF), financed by the Swiss Confederation and funded by Nano-Tera.ch (Magnetotheranostics project Nº 530 627) and by the Nanoneck2 project funded by Eurostars (Project E!9309 Nanoneck2). Financial support from the Spanish Ministry of Science and Innovation research grant MAT2014-54975-R are gratefully acknowledged.

The properties of nanometric-sized helium bubbles in silicon have been investigated using both spatially resolved electron-energy-loss spectroscopy combined with a recently developed method, and molecular-dynamics simulations. The experiments allowed for an accurate determination of size, aspect ratio, and helium density for a large number of single bubbles, whose diameters ranged from 6 to 20 nm. Very high helium densities, from 60 to 180 He ${\mathrm{nm}}^{\ensuremath{-}3}$, have been measured depending on the conditions, in stark contrast with previous investigations of helium bubbles in metal with similar sizes. To supplement experiments on a smaller scale, and to obtain insights into the silicon matrix state, atomistic calculations have been performed for helium bubbles in the diameter range 1--13 nm. Molecular-dynamics simulations revealed that the maximum attainable helium density is critically related to the strength of the silicon matrix, which tends to yield by amorphization at the highest density levels. Calculations give helium density values for isolated single bubbles that are typically lower than measurements. However, excellent agreement is recovered when the interactions between bubbles and the presence of helium interstitials in the matrix are taken into account. Both experiments and numerical simulations suggest that the Laplace-Young law cannot be used to predict helium density in nanometric-sized bubbles in a covalent material such as silicon.

Second harmonic generation (SHG) is an important tool for the study of plasmonic nanostructures and can open up important sensing applications since the second harmonic (SH) signal has an increased sensitivity to nanostructures shape and environment in comparison with the linear scattering [1,2]. SHG from plasmonic centrosymmetric nanostructures is controlled by two main properties. First, SHG is forbidden in the bulk of centrosymmetric structures in the dipolar approximation, meaning that nanostructures made of metals like gold and silver generate a SH signal coming mainly from their surfaces, where the symmetry is effectively broken. Second, because of the same symmetry reason, a dipolar excitation at the fundamental frequency induces SH modes with vanishing dipole moments [3]. In the case of plasmonic dimers, with the large intensity enhancement occurring in the gap, the SH emission is limited due to out-of-phase SH sources with destructive interferences in the far-field region. Consequently, new strategies must be developed to overcome this limitation.

Herein, the assembly of CsPbBr

While plasmonic antennas composed of building blocks made of the same material have been thoroughly studied, recent investigations have highlighted the unique opportunities enabled by making compositionally asymmetric plasmonic systems. So far, mainly heterostructures composed of nanospheres and nanodiscs have been investigated, revealing opportunities for the design of Fano resonant nanostructures, directional scattering, sensing and catalytic applications. In this article, an improved fabrication method is reported that enables precise tuning of the heterodimer geometry, with interparticle distances made down to a few nanometers between Au–Ag and Au–Al nanoparticles. A wide range of mode energy detuning and coupling conditions are observed by near field hyperspectral imaging performed with electron energy loss spectroscopy, supported by full wave analysis numerical simulations. These results provide direct insights into the mode hybridization of plasmonic heterodimers, pointing out the influence of each dimer constituent in the overall electromagnetic response. By relating the coupling of nondipolar modes and plasmon–interband interaction with the dimer geometry, this work facilitates the development of plasmonic heterostructures with tailored responses, beyond the possibilities offered by homodimers.