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The identification of similarities in the material requirements for applications of interest and those of living organisms provides opportunities to use renewable natural resources to develop better materials and design better devices. In our work, we harness this strategy to build high-capacity silicon (Si) nanopowder—based lithium (Li)—ion batteries with improved performance characteristics. Si offers more than one order of magnitude higher capacity than graphite, but it exhibits dramatic volume changes during electrochemical alloying and de-alloying with Li, which typically leads to rapid anode degradation. We show that mixing Si nanopowder with alginate, a natural polysaccharide extracted from brown algae, yields a stable battery anode possessing reversible capacity eight times higher than that of the state-of-the-art graphitic anodes.

A current limitation in nanoparticle superlattice engineering is that the identities of the particles being assembled often determine the structures that can be synthesized. Therefore, specific crystallographic symmetries or lattice parameters can only be achieved using specific nanoparticles as building blocks (and vice versa). We present six design rules that can be used to deliberately prepare nine distinct colloidal crystal structures, with control over lattice parameters on the 25- to 150-nanometer length scale. These design rules outline a strategy to independently adjust each of the relevant crystallographic parameters, including particle size (5 to 60 nanometers), periodicity, and interparticle distance. As such, this work represents an advance in synthesizing tailorable macroscale architectures comprising nanoscale materials in a predictable fashion.

In this paper, capacitive-type humidity sensors were prepared by sequentially drop-coating the aqueous suspensions of zinc oxide (ZnO) nanopowders and polyvinyl pyrrolidone–reduced graphene oxide (PVP-RGO) nanocomposites onto interdigitated electrodes. Significant improvements in both sensitivity and linearity were achieved for the ZnO/PVP-RGO sensors compared with the PVP-RGO/ZnO, PVP-RGO, and ZnO counterparts. Moreover, the produced ZnO/PVP-RGO sensors exhibited rather small hysteresis, fast response-recovery time, and long-term stability. Based on morphological and structural analyses, it can be inferred that the excellent humidity sensing properties of the ZnO/PVP-RGO sensors may be attributed to the high surface-to-volume ratio of the multilayer structure and the supporting roles of the PVP-RGO nanocomposites. The results in this work hence provide adequate guidelines for designing high-performance humidity sensors that make use of the multilayer structure of semiconductor oxide materials and PVP-RGO nanocomposites.

An electron tomography method is demonstrated that can determine the three-dimensional structure of a gold nanoparticle at 2.4 Å resolution, including the locations of some of the individual atoms within the sample. Atomic-scale grain of truth Electron tomography, an extension of transmission electron microscopy that was developed in the late 1960s, is widely used to obtain three-dimensional images of samples in the biological and materials sciences. Advances in recent years mean that the method can be used to determine the internal structure of nanomaterials at atomic resolutions, as long as certain assumptions are made concerning the sample structure. Scott et al . now demonstrate an electron-tomography method that bypasses the need for such assumptions, enabling the authors to determine the three-dimensional structure of a gold nanoparticle at 2.4-ångström resolution, including the locations of some of the individual atoms in the sample. Transmission electron microscopy is a powerful imaging tool that has found broad application in materials science, nanoscience and biology 1 , 2 , 3 . With the introduction of aberration-corrected electron lenses, both the spatial resolution and the image quality in transmission electron microscopy have been significantly improved 4 , 5 and resolution below 0.5 ångströms has been demonstrated 6 . To reveal the three-dimensional (3D) structure of thin samples, electron tomography is the method of choice 7 , 8 , 9 , 10 , 11 , with cubic-nanometre resolution currently achievable 10 , 11 . Discrete tomography has recently been used to generate a 3D atomic reconstruction of a silver nanoparticle two to three nanometres in diameter 12 , but this statistical method assumes prior knowledge of the particle’s lattice structure and requires that the atoms fit rigidly on that lattice. Here we report the experimental demonstration of a general electron tomography method that achieves atomic-scale resolution without initial assumptions about the sample structure. By combining a novel projection alignment and tomographic reconstruction method with scanning transmission electron microscopy, we have determined the 3D structure of an approximately ten-nanometre gold nanoparticle at 2.4-ångström resolution. Although we cannot definitively locate all of the atoms inside the nanoparticle, individual atoms are observed in some regions of the particle and several grains are identified in three dimensions. The 3D surface morphology and internal lattice structure revealed are consistent with a distorted icosahedral multiply twinned particle. We anticipate that this general method can be applied not only to determine the 3D structure of nanomaterials at atomic-scale resolution 13 , 14 , 15 , but also to improve the spatial resolution and image quality in other tomography fields 7 , 9 , 16 , 17 , 18 , 19 , 20 .

Crystal power now in 3D Many engineering and chemical applications make use of crystalline nanoparticles, harnessing properties that are controlled by their precise three-dimensional morphology, structure and composition. Sandra Van Aert and colleagues demonstrate that it is possible to obtain full three-dimensional structural information for such particles at atomic resolution using a mix of electron tomography and electron microscopy, coupled with separately available knowledge of the crystallographic structure of the target nanoparticle. Such information should ultimately lead to a better understanding of the desirable properties of these systems. This study demonstrates how it is possible to extract full three-dimensional structural information at atomic resolution using a combination of electron tomography and electron microscopy, coupled with separately available knowledge of the crystallographic structure adopted by the target nanoparticle. Such information should ultimately lead to a better understanding of the desirable properties of these systems. 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 nanoparticle’s physical and chemical properties are controlled by its exact 3D morphology, structure and composition 1 . Electron tomography enables the recovery of the shape of a nanoparticle from a series of projection images 2 , 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 microscopy 5 , 6 , 7 , statistical parameter estimation theory 8 , 9 and discrete tomography 10 , 11 . Unlike conventional electron tomography, only two images of the target—a silver nanoparticle embedded in an aluminium matrix—are sufficient for the reconstruction when combined with available knowledge about the particle’s 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.

Localized surface plasmon resonances of an individual silver nanocube are reconstructed in three dimensions using electron energy-loss spectrum imaging, resulting in a better understanding of the optical response of noble-metal nanoparticles. Observing surface excitations for nano-optics Metal nanoparticles exhibit a range of striking and useful optical properties thanks to the excitation of localized surface plasmon resonances (LSPRs). But the precise relationship between the three-dimensional structure of the nanoparticles and the resulting LSPRs can be hard to determine. Paul Midgley and colleagues have developed a spectrally sensitive imaging technique, based on electron energy-loss spectroscopy, that permits three-dimensional visualization of many of the key features associated with these LSPRs. With this technique, the interplay between the LSPRs, nanoparticle structure and substrate–nanoparticle interactions can be directly probed. This study focuses on silver nanocubes, but the method demonstrated is applicable to similar plasmonic phenomena across all metal nanoparticles. The remarkable optical properties of metal nanoparticles are governed by the excitation of localized surface plasmon resonances (LSPRs). The sensitivity of each LSPR mode, whose spatial distribution and resonant energy depend on the nanoparticle structure, composition and environment, has given rise to many potential photonic, optoelectronic, catalytic, photovoltaic, and gas- and bio-sensing applications 1 , 2 , 3 . However, the precise interplay between the three-dimensional (3D) nanoparticle structure and the LSPRs is not always fully understood and a spectrally sensitive 3D imaging technique is needed to visualize the excitation on the nanometre scale. Here we show that 3D images related to LSPRs of an individual silver nanocube can be reconstructed through the application of electron energy-loss spectrum imaging 4 , mapping the excitation across a range of orientations, with a novel combination of non-negative matrix factorization 5 , 6 , compressed sensing 7 , 8 and electron tomography 9 . Our results extend the idea of substrate-mediated hybridization of dipolar and quadrupolar modes predicted by theory, simulations, and electron and optical spectroscopy 10 , 11 , 12 , and provide experimental evidence of higher-energy mode hybridization. This work represents an advance both in the understanding of the optical response of noble-metal nanoparticles and in the probing, analysis and visualization of LSPRs.

Semiconducting polymers are promising materials for photocatalysis, batteries, fuel applications, etc. One of the most useful photocatalysts is polymeric carbon nitride (PCN), which is usually produced during melamine condensation. In this work, a novel method of obtaining a PCN nanocomposite, in which PCN forms an amorphous layer coating on oxide nanoparticles, is presented. Microwave hydrothermal synthesis (MHS) was used to synthesize a homogeneous mixture of nanoparticles consisting of 80 wt.% AlOOH and 20 wt.% of ZrO2. The nanopowders were mechanically milled with melamine, and the mixture was annealed in the temperature range of 400–600 °C with rapid heating and cooling. The above procedure lowers PCN formation to 400 °C. The following nanocomposite properties were investigated: band gap, specific surface area, particle size, morphology, phase composition, chemical composition, and photocatalytic activity. The specific surface of the PCN nanocomposite was as high as 70 m2/g, and the optical band gap was 3 eV. High photocatalytic activity in phenol degradation was observed. The proposed simple method, as well as the low-cost preparation procedure, permits the exploitation of PCN as a polymer semiconductor photocatalytic material.

Heterogeneous catalysts that contain bimetallic nanoparticles may undergo segregation of the metals, driven by oxidizing and reducing environments. The structure and composition of core-shell Rh₀.₅Pd₀.₅ and Pt₀.₅Pd₀.₅ nanoparticle catalysts were studied in situ, during oxidizing, reducing, and catalytic reactions involving NO, O₂, CO, and H₂ by x-ray photoelectron spectroscopy at near-ambient pressure. The Rh₀.₅Pd₀.₅ nanoparticles underwent dramatic and reversible changes in composition and chemical state in response to oxidizing or reducing conditions. In contrast, no substantial segregation of Pd or Pt atoms was found in Pt₀.₅Pd₀.₅ nanoparticles. The different behaviors in restructuring and chemical response of Rh₀.₅Pd₀.₅ and Pt₀.₅Pd₀.₅ nanoparticle catalysts under the same reaction conditions illustrates the flexibility and tunability of the structure of bimetallic nanoparticle catalysts during catalytic reactions.

The perovskite nanopowders of lanthanum strontium cobalt ferrite (LSCF) have been synthesized using the alginate mediated ion-exchange process. This perovskite-based material is a promising cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs) due to its high electrical conductivity, low polarizability, high catalytic activity for oxygen reduction, enhanced chemical stability at an elevated temperature in high oxygen potential environment and high compatibility with the ceria based solid electrolytes. Phase pure LSCF 6428, LSCF 6455, and LSCF 6482 corresponding to La0.6Sr0.4Co0.2Fe0.8O3-δ, La0.6Sr0.4Co0.5Fe0.5O3-δ, and La0.6Sr0.4Co0.8Fe0.2O3-δ, respectively were successfully synthesized. The simultaneous thermal analysis (DSC-TGA) and XRD were used to determine the optimum calcination temperature for the dried ion-exchanged beads. Single phase nanopowders of LSCF (6428, 6455, and 6482) have been successfully prepared at a calcination temperature of 700 °C. The TGA analysis showed that every ton of LSCF-ALG dried beads can potentially yield 360 kg of LSCF nanopowders suggesting a potential for scaling-up of the process of manufacturing nanopowders of LSCF.

Porosity in several zirconia-based pressure compacted nanopowders was studied using the positron lifetime technique combined with the mass-density measurements. Two kinds of pores were identified: (i) the larger pores of ≈ 10 to 19 nm diameter arising likely from a formation of secondary particle aggregates, and (ii) the smaller ones (≈ 1 nm) which are obviously of a more complex origin.