In this work, three-dimensional flower-like and petal-like copper hydroxyphosphate Cu5(OH)4(PO4)2 (CHP) based on the self-assembly of numerous nanosheets has been successfully fabricated on a copper foil by a mild one-pot wet-chemical method without ligand assistance. This research contributes to the development of the method to change the morphology of the CHP active material by varying the degree of substrate oxidation. The two different CHP architectures were used to photocatalytically degrade rhodamine 6G (Rh 6G) under solar light, which can absorb wide-range light wavelength from the UV to the near-infrared region. They all exhibit high photocatalytic activity and good durability, which are potential candidates for high performance and recyclable wide wavelength photocatalysis.

Oxide materials with redox capability have attracted worldwide attentions in many applications. Introducing defects into crystal lattice is an effective method to modify and optimize redox capability of oxides as well as their catalytic performance. However, the relationship between intrinsic characteristics of defects and properties of oxides has been rarely reported. Herein, we report a facile strategy to introduce defects by doping a small amount of Ni atoms (∼1.8 at. %) into ceria lattice at atomic level through the effect of microstructure of crystal on the redox property of ceria. Amazingly, a small amount of single Ni atom-doped ceria has formed a homogeneous solid solution with uniform lotuslike morphology. It performs an outstanding catalytic performance of a reduced T50 of CO oxidation at 230 °C, which is 135 °C lower than that of pure CeO2 (365 °C). This is largely attributed to defects such as lattice distortion, crystal defects and elastic strain induced by Ni dopants. The DFT calculation has revealed that the electron density distribution of oxygen ions near Ni dopant, the reduced formation energy of oxygen vacancy originated from local chemical effect caused by local distortion after Ni doping. These differences have a great effect on increasing the concentration of oxygen vacancies and enhancing the migration of lattice oxygen from bulk to a surface which is closely related to optimized redox properties. As a result, oxygen storage capacity and the associated catalytic reactivity has been largely increased. We have clearly demonstrated the change of crystal lattice and the charge distribution effectively modify its chemical and physical properties at the atomic scale.Keywords: atomic level doping; cerium oxide; CO oxidation; oxygen vacancy; solid solution;

The determination of structural evolution at the atomic level is essential to understanding the intrinsic physics and chemistries of nanomaterials. Mechanochemistry represents a promising method to trace structural evolution, but conventional mechanical tension generates random breaking points, which makes it unavailable for effective analysis. It remains difficult to find an appropriate model to study shear deformations. Here, we synthesize high-modulus carbon nanotubes that can be cut precisely, and the structural evolution is efficiently investigated through a combination of geometry phase analysis and first-principles calculations. The lattice fluctuation depends on the anisotropy, chirality, curvature, and slicing rate. The strain distribution further reveals a plastic breaking mechanism for the conjugated carbon atoms under cutting. The resulting sliced carbon nanotubes with controllable sizes and open ends are promising for various applications, for example, as an anode material for lithium-ion batteries.Keywords: anisotropy; carbon nanotube; shear; structural deformation;

A series of systematic electron microscopy imaging evidence are illustrated to prove that a high-quality interface is vital for enhancing quantum efficiency from 23 to 50% effectively, because improved crystal quality of each layer can suppress the disordered atom arrangement and enhance the carrier lifetime via decreasing the overall residual strain. The distribution width of charge rises and then falls as bias increasing, revealing the existence of an optimum operating voltage, which could be attributed to the proper energy band bending. Our results provide new insights into the understanding of the association between macro-property and microstructure of the superlattice system.Keywords: charge accumulation; interfacial components; quantum efficiency; strain distribution; type II superlattice;

•Ag(Cl,Br)–Au micro-necklaces were obtained via a facile solution immersion method.•Both detection and degradation of food contaminant Sudan I were realized.•Reproducible SERS signals with the limit of detection of 10−10 M were achieved.•Enhanced photocatalytic stability and efficiency than AgBr/AgBr–Au control samples.In this paper, we report an air-exposed and room-temperature immersion reaction for synthesis of novel Au nanoparticles decorated Ag(Cl,Br) [Ag(Cl,Br)–Au] micro-necklaces from the AgBr template for efficient and stable photocatalytic degradation and SERS detection of food contaminant Sudan I (SDI) molecules. Amazingly, as the photocatalyst, the partial substitution of bromine atoms by chlorine in crystalline lattices and decoration of Au nanoparticles on the surface have synergistically ensured these Ag(Cl,Br)–Au micro-necklaces of enhanced degradation efficiency of SDI from 65.1% achieved by AgBr to 100% after 18 min of visible light irradiation, along with significantly promoted efficiency maintenance after 12 cycles of the photocatalytic reaction. Meanwhile, due to the designed decoration of Au nanoparticles on surfaces of semiconducting micro-necklaces, these Ag(Cl,Br)–Au micro-necklaces also exhibited the ability to offer sensitive SERS signals for trace detection of SDI molecules with the limit of detection as low as 10−10 M being achieved. Hence, in consideration of the novel structures, facile preparation as well as attractive applications in both SERS detection and photocatalytic degradation of SDI dye of these Ag(Cl,Br)–Au micro-necklaces, it is believable that such bifunctional substrate materials hold great potential for various environmental and health-related applications.Gold nanoparticles decorated Ag(Cl,Br) micro-necklaces were prepared for bifunctional SERS detection and visible-light-driven photocatalytic degradation of food contaminant Sudan I.Download high-res image (114KB)Download full-size image

A facile chemical method for Co doping Ni-CNTs@α-Ni(OH)2 combining with an in situ phase transformation process is successfully proposed and employed to synthesize three-dimensional (3D) hierarchical Ni-CNTs@β-(Ni, Co) binary hydroxides. This strategy can effectively maintain the coaxial-cable-like structure of Ni-CNTs@α-Ni(OH)2 and meanwhile increase the content of Co as much as possible. Eventually, the specific capacitances and electrical conductivity of the composites are remarkably enhanced. The optimized composite exhibits high specific capacitances of 2861.8 F g−1 at 1 A g−1 (39.48 F cm−2 at 15 mA cm−2), good rate capabilities of 1221.8 F g−1 at 20 A g−1 and cycling stabilities (87.6% of capacitance retention after 5000 cycles at 5 A g−1). The asymmetric supercapacitor (ASC) constructed with the as-synthesized composite and activated carbon as positive and negative electrode delivers a high specific capacitance of 287.7 F g−1 at 1 A g−1. The device demonstrates remarkable energy density (96 W h kg−1) and high power density (15829.4 W kg−1). The retention of capacitance remains 83.5% at the current density of 5 A g−1 after 5000 cycles. The charged and discharged samples are further studied by ex situ electron energy loss spectroscopy (EELS) analysis, XRD and SEM to figure out the reasons of capacitance fading. Overall, it is believable that this facile synthetic strategy can be applied to prepare various nanostructured metal hydroxide/CNT composites for high performance supercapacitor electrode materials.Download high-res image (78KB)Download full-size image

A facile and controllable approach has been devised to synthesize PbSe–PbTe heterogeneous nanostructures (HNSs). The defects could be modulated simply by controlling the addition of Se and Te precursors. High-resolution transmission electron microscopy and electron energy-loss spectroscopy show the defect structures in the interface and the distribution of PbSe and PbTe, respectively. Geometric phase analysis based on HRTEM imaging reveals the strain distribution in the defect-free and defect-containing PbSe–PbTe HNSs. The strain distribution and defects in the interface of the PbSe–PbTe HNSs affect the Seebeck coefficient and the electrical conductivity of the PbSe–PbTe HNSs.

Iron diselenium (FeSe2) with rational design and tailored synthesis is a promising transition metal chalcogenide because of its suitable optical and electronic properties. Despite these prospects, controllable synthesis of FeSe2 with a special hierarchical heterostructure has hardly been paid attention to previously. Here, we report a successful synthesis of FeSe2 microtubes in a system of water glycol mixture using a sacrificial self-template method. This method leads to the formation of a FeSe2 microtube embedded with nanooctahedra in the remaining Se template, which can be regarded as a special hetero-junction morphology. Moreover, a growth mechanism of the FeSe2 microtube was discussed. This unique morphology and facile synthesis might facilitate the study of transition metal chalcogenides.

To meet the demand of electromagnetic interference shielding, cheap and easily available microwave absorbers are urgently required. Recently, most of the related research has been focussed on a number of complicated absorbers comprising multi-components because of their better electromagnetic match. However, it is still a great challenge to develop an absorber that simultaneously possesses the advantages of easy fabrication, low-cost, ultra-wide bandwidth, and strong absorption. Hence, development of a simple and convenient absorber with efficient performance is attracting significant attention because of the urgent requirement of this type of absorbers. Herein, a series of single-component iron-based absorbers with different morphologies and grain sizes was successfully prepared. Strong absorption intensity (∼−43.4 dB) was found in plate-like samples, which could even match those of some multi-component absorbers. Electron holography and Lorentz microscopy analysis were used for the further comprehension of the relationships among the microstructure, electromagnetic property, and microwave absorption performance. The primary grain size of the present iron microplate was found fundamentally important for microwave absorption performance. This cheap and available absorber is believed to be an optimal choice for single-component absorbers and useful in the research of absorption mechanism.

Li-rich Mn-based cathode materials have been considered as promising candidates for next generation Li-ion batteries due to their high-energy density, low cost and non-toxicity. However, the atomic arrangement of such materials and the relationship between the microstructure and electrochemical performance are still not fully understood. In this paper, local heterogeneity in the crystal lattice is directly observed in synthesized Li2MnO3/LiMO2 (M = Ni and Mn) cathode materials. With SAED application, for the first time, we accordingly uncover that the lattice heterogeneity is induced by different Li2MnO3 atomic arrangements coexisting in the same crystal domain. The co-growth of Li2MnO3 with different orientations is proved to be a defective feature, which would induce atomic vacancy concentration in the lattice and increase the risk of layered structure collapse in the cycling process. The electrochemical test results also suggest that the composition with a relatively uniform Li2MnO3 arrangement exhibits better cycling performance (the capacity retention is as high as 95.1% after 50 cycles at 0.1C), oppositely, the coexistence of multiple complex Li2MnO3 arrangements results in poor cycling performance (the capacity retention is below 70% after 50 cycles at 0.1C). The crystal lattice structure comparison between primary and cycled is shown to manifest the effect of Li2MnO3 arrangement on the electrochemical performance and structural stability, providing one possible explanation for the capacity degradation of the Li-rich materials.

Quantum efficiency (QE) is a crucial parameter that determines the final performance of photodetector devices. Herein, by fitting the charge distribution fluctuation under a series of bias voltages, revealed by groups of in situ electron holography experiments, a simple model based on modulus square of wave function (MSWF) is qualitatively built to shed new light on the relationship between QE and wave function overlap (WFO). It is found that there exists a competition of WFO between the potential well regions and the interface regions, and a peak value of the overall WFO can be obtained under an appropriate voltage. On combining such competition with the measured QE results from actual infrared photodetectors, the positive correlation between QE and WFO is manifested, and the QE can be boosted to 51% from 34%. Our results offer a new perspective to the understanding of the carrier transportation within superlattice (SL) structures and the design on photoelectric devices with enhanced performance.

Structurally well-defined assemblies of silver nanoparticles, including the dendritic nano-flowers (NFs), planar nano-spheres (NSs) and nano-dendrites (NDs) were obtained by a surfactant-free and ultrafast (≈15 min) self-assembly process on as-purchased carbon-coated copper TEM grids. The silver nano-assemblies, especially the NFs modified TEM grids, when serving as surface-enhanced Raman spectroscopy (SERS) substrates for detecting melamine molecules, demonstrated a long-lived limit of detection (LOD) of as low as 10−11 M, suggesting the potential of these silver-assemblies modified carbon-coated copper grids as novel potable and cost-effective SERS substrates for trace detection toward various food contaminants like melamine.Silver nano-assemblies with various morphologies were obtained on carbon-coated copper grids and showed sensitive and stable SERS activity toward food contaminant melamine.Download high-res image (342KB)Download full-size image

•A novel plasmonic AgCl array was prepared.•Directional ions exchange shaped a rod-like AgCl microcrystal.•This array exhibited an urtal-stable visible-light-driven photocatalytic activity.•A facial photo-irradiation inspires to fabricate a simply SERS substrate based on photosensitive materials in detecting contaminants of one-millionth concentration.A novel arrayed AgCl micro-rods have in situ grown on an Ag foil successfully for the first time. The preparation process is consisted of two facile steps: (1) immersed oxidation and (2) directional ions exchange. The structure of the as-synthesized arrayed substrate has been characterized comprehensively, and the relevant growth mechanism is proposed. This highly aligned AgCl arrays show a remarkable visible-light-driven photocatalytic activity towards degrading 10−5 mol/L rhodamine 6G (R6G) aqueous solution. The ultra-stable catalytic performance of the plasmonic arrays was revealed by the recycled tests in the neutral and acidic conditions. Moreover, a facile SERS substrate based on the AgCl arrays was obtained with the optimal enhancement factor (EF) of ∼3.25 × 107, by directly putting the substrate under a Xe lamp in 7.5 min. Amazingly, the photo-optimized surface-enhanced Raman scattering (SERS) substrate still shows a stable activity for photodegrading R6G. The photocatalytic and SERS mechanism are proposed in this study.Download high-res image (309KB)Download full-size image

A tunable response frequency is highly desirable for practical applications of microwave absorption materials but remains a great challenge. Here, hollow lightweight polydopamine@α-MnO2 microspindles were facilely synthesized with the tunable absorption frequency governed by the aspect ratio. The size of the hard template is a key factor to achieve the unique shape; the polymer layer with uniform thickness plays an important role in obtaining spindles with homogeneous size. With the aspect ratio increasing, the maximum reflection loss, as well as the absorption bandwidth (<−10 dB), increases and then decreases; meanwhile, the microwave absorption band shifts to the low frequency. The optimized aspect ratio of the cavity about the hollow polydopamine@α-MnO2 microspindles is ∼2.8. With 3 mm thickness at 9.7 GHz, the strongest reflection reaches −21.8 dB, and the width of the absorbing band (<−10 dB) is as wide as 3.3 GHz. Via electron holography, it is confirmed that strong charge accumulates around the interface between the polydopamine and α-MnO2 layers, which mainly contributes to the dielectric polarization absorption. This study proposes a reliable strategy to tune the absorption frequency via different aspect ratio polymer@α-MnO2 microspindles.Keywords: aspect ratio; core−shell structure; dielectric loss; electron holography; manganese dioxide; microwave absorption; tunable frequency;

•Li1·2(Mn0·53Co0.27)O2 was successfully synthesized by microwave sintering method.•The batteries show superior rate capacity and cyclic performance.•Crystal growth during microwave and conventional sintering are compared.•Rapid sintering is studied by in-situ TEM heating to give direct evidences.Li1·2(Mn0·53Co0.27)O2 cathode material was successfully synthesized using a microwave sintering method. The as-prepared material remained in an octahedral shape after sintering at 800 °C with a rapid heating rate of 35 °C min−1. The as-prepared sample was demonstrated to have better electrochemical performance than that synthesized using a conventional method. The enhanced electrochemical performance can be ascribed to the minor change in material morphology and less particle agglomeration in the macroscopic scale, which depends on the rapid-sintering mechanism provided by microwave sintering. The rapid-sintering mechanism was studied in an in-situ transmission electron microscopy (TEM) heating experiment, which directly presented the crystal growth process and the evidence for the morphological damage of Li1·2(Mn0·53Co0.27)O2 materials at approximately 830 °C.

Encapsulation of a Cu core into a ZnO shell has been rarely reported by a one-pot method, which is expected to be a novel combination of a reflection core and a dielectric microwave absorber. Here, a facile one-pot strategy has been developed for assembling Cu/ZnO core/shell nanocomposites with different sizes and aspect ratios. The temperature acts as the switch for starting ZnO encapsulation in this strategy, and the sizes and aspect ratios of the resultant nanocomposites depend sensitively on the heating rate in 220–250 °C. The different morphologies and structures of the nanocomposites have been characterized comprehensively, and the relevant growth mechanism is also discussed in this paper. The microwave absorption performances in both as-synthesized Cu@ZnO products (spherical-like and rod-like shapes) are significantly enhanced by comparing with that of pure ZnO due to the enhanced interfacial scattering and dielectric interface polarization in the ZnO shell. This one-pot method can complement for rational methodology in constructing metal/semiconductor core/shell nanocomposites.

Magnetic skyrmion is a nanosized magnetic whirl with nontrivial topology, which is highly relevant for applications on future memory devices. To enable the applications, theoretical efforts have been made to understand the dynamics of individual skyrmions in magnetic nanostructures. However, directly imaging the evolution of highly geometrically confined individual skyrmions is challenging. Here, we report the magnetic field-driven dynamics of individual skyrmions in FeGe nanodisks with diameters on the order of several skyrmion sizes by using Lorentz transmission electron microscopy. In contrast to the conventional skyrmion lattice in bulk, a series of skyrmion cluster states with different geometrical configurations and the field-driven cascading phase transitions are identified at temperatures far below the magnetic transition temperature. Furthermore, a dynamics, namely the intermittent jumps between the neighboring skyrmion cluster states, is found at elevated temperatures, at which the thermal energy competes with the energy barrier between the skyrmion cluster states.

Rare earth oxides/hydroxides are important emerging materials owing to their unique properties. Shape-controlled synthesis of elongated hexagonal bipyramid shaped La(OH)3 nanorods with different aspect ratios and trigram-shaped LaCO3OH nanosheets was systematically carried out by controlling the reaction conditions. Hydrazine and polyvinylpyrrolidone (PVP) surfactants used in synthesis are assumed to play a key “dual-template” role in determining the aspect ratio and shape of the resulting nanostructures. Elongated hexagonal bipyramid shaped La(OH)3 nanorods were found to grow along the preferred orientation [0001]. Six equivalent crystallographic facets, \((20\bar 20)\), \((02\bar 20)\), \((2\bar 200)\), \((0\bar 220)\), \((\bar 2200)\), and \((\bar 2020)\) lattice planes, were found to be exposed on the side surfaces on each nanorod as confirmed by combined transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED) analyses. A double-polarization phenomenon was found to occur at the nanorod surfaces by employing off-axis electron holography, implying that the material could be used as an effective dielectric microwave absorber. La(OH)3 nanorods with larger aspect ratios exhibit better absorption properties with respect to the maximum reflection loss and effective absorbing bandwidth. Thus, a novel method towards the reasonable design of bipyramid shaped La(OH)3 nanorods exhibiting tunable microwave absorption properties is proposed based on our synthesis strategy.

Electrostatic doping in materials can lead to various exciting electronic properties, such as metal–insulator transition and superconductivity, by altering the Fermi level position or introducing exotic phases. Cd3As2, a three-dimensional (3D) analog of graphene with extraordinary carrier mobility, was predicted to be a 3D Dirac semimetal, a feature confirmed by recent experiments. However, most research so far has been focused on metallic bulk materials that are known to possess ultra-high mobility and giant magneto-resistance but limited carrier transport tunability. Here we report on the first observation of a gate-induced transition from band conduction to hopping conduction in single-crystalline Cd3As2 thin films via electrostatic doping by solid electrolyte gating. The extreme charge doping enables the unexpected observation of p-type conductivity in a ~50-nm-thick Cd3As2 thin film grown by molecular beam epitaxy. More importantly, the gate-tunable Shubnikov–de Haas oscillations and the temperature-dependent resistance reveal a unique band structure and bandgap opening when the dimensionality of Cd3As2 is reduced. This is also confirmed by our first-principle calculations. The present results offer new insights toward nanoelectronic and optoelectronic applications of Dirac semimetals in general and provide new routes in the search for the intriguing quantum spin Hall effect in low-dimension Dirac semimetals, an effect that is theoretically predicted but not yet experimentally realized.

Sulfide semiconductors have attracted considerable attention. The main challenge is to prepare materials with a designable morphology, a controllable band structure and optoelectronic properties. Herein, we report a facile chemical transportation reaction for the synthesis of Ga2S3 microspheres with novel hollow morphologies and partially filled volumes. Even without any extrinsic dopant, photoluminescence (PL) emission wavelength could be facilely tuned from 635 to 665 nm, depending on its intrinsic inhomogeneous strain distribution. Geometric phase analysis (GPA) based on high-resolution transmission electron microscopy (HRTEM) imaging reveals that the strain distribution and the associated PL properties can be accurately controlled by changing the growth temperature gradient, which depends on the distance between the boats used for raw material evaporation and microsphere deposition. The stacking-fault density, lattice distortion degree and strain distribution at the shell interfacial region of the Ga2S3 microspheres could be readily adjusted. Ab initio first-principles calculations confirm that the lowest conductive band (LCB) is dominated by S-3s and Ga-4p states, which shift to the low-energy band as a result of the introduction of tensile strain, well in accordance with the observed PL evolution. Therefore, based on our strain driving strategy, novel guidelines toward the reasonable design of sulfide semiconductors with tunable photoluminescence properties are proposed.

To design and fabricate rational surface architecture of individual particles is one of the key factors that affect their magnetic properties and microwave absorption capability, which is still a great challenge. Herein, a series of Co20Ni80 hierarchical structures with different surface morphologies, including flower-, urchin-, ball-, and chain-like morphologies, were obtained using structure-directing templates via a facile one-step solvothermal treatment. The microwave reflection loss (RL) of urchin-like Co20Ni80 hierarchical structures reaches as high as −33.5 dB at 3 GHz, with almost twice the RL intensity of the ball- and chain-like structures, and the absorption bandwidth (<−10 dB) is about 5.5 GHz for the flower-like morphology, indicating that the surface nanospikes and nanoflakes on the Co20Ni80 microsphere surfaces have great influences on their magnetic microwave absorption properties. Electron holography analysis reveals that the surface nanospikes and nanoflakes could generate a high density of stray magnetic flux lines and contribute a large saturation magnetization (105.62 emu g−1 for urchin-like and 96.41 emu g−1 for flower-like morphology), leading the urchin-like and flower-like Co20Ni80 to possess stronger microwave RL compared with the ball-like and chain-like Co20Ni80 alloys. The eddy-current absorption mechanism μ′′(μ′)−2(f)−1 is dominant in the frequency region above 8 GHz, implying that eddy-current loss is a vital factor for microwave RL in the high frequency range. It can be supposed from our findings that different surface morphologies of magnetic hierarchical structures might become an effective path to achieve high-performance microwave absorption for electromagnetic shielding and stealth camouflage applications.

Crystal defects have been introduced into inherently narrow-band-gap and non-toxic Ag2Se quantum dots (QDs) via a facile and efficient thermal vibration approach during synthesis and studied by using electron holography and geometric phase analysis techniques. These crystal defects consequently demonstrated a solid possibility for tuning the optical band-gaps of Ag2Se QDs, and thereby enhancing the visible-light-driven water splitting and hydrogen evolution performance of Ag2Se QD-sensitized TiO2 photocatalysts.

A confined interface coassembly coating strategy based on three-dimensional (3-D) ordered macroporous silica as the nanoreactor was demonstrated for the designed fabrication of novel 3-D ordered arrays of core–shell microspheres consisting of Fe3O4 cores and ordered mesoporous carbon shells. The obtained 3-D ordered arrays of Fe3O4@mesoporous carbon materials possess two sets of periodic structures at both mesoscale and submicrometer scale, high surface area of 326 m2/g, and large mesopore size of 19 nm. Microwave absorption test reveals that the obtained materials have excellent microwave absorption performances with maximum reflection loss of up to −57 dB at 8 GHz, and large absorption bandwidth (7.3–13.7 GHz, < −10 dB), due to the combination of the large magnetic loss from iron oxides, the strong dielectric loss from carbonaceous shell, and the strong reflection and scattering of electromagnetic waves of the ordered structures of the mesopores and 3-D arrays of core–shell microspheres.Keywords: core−shell structures; interface coassembly; magnetic nanomaterials; mesoporous carbon; microwave absorption

Various metal hydroxides/oxides grown on conductive substrates such as nickel foam have been reported and studied as supercapacitor electrode materials. However, the capacitances of these electrodes are extremely limited because of the low content of active materials grown on the limited surface of nickel foam. To achieve high capacitance, we use nickel-coated carbon nanotubes (Ni-CNTs) as the conductive substrate for the growth of β-Ni(OH)2. By a facile chemical method, ultrathin β-Ni(OH)2 nanoplates are vertically grown on the surface of Ni-CNTs. The density, thickness, and content of β-Ni(OH)2 can be easily controlled by modulating the ratio of NiCl2·6H2O to Ni-CNTs. This hierarchical nanostructure can provide remarkable synergistic effects: facilitate electron and ion transport and accelerate the reversible redox reactions. As-prepared Ni-CNTs@β-Ni(OH)2 composites exhibit high specific capacitances (∼1807 F g–1 at 2 A g–1, based on the mass of β-Ni(OH)2; ∼1283 F g–1 at 2 A g–1, based on the mass of composite), good rate capabilities, and excellent cycling stabilities. This strategy has potential for large-scale production and can be applied to the preparation of other hierarchical nanostructured metal hydroxide/oxide composites.Keywords: hierarchical nanostructure; nickel-coated carbon nanotubes; supercapacitor; three-dimensional conductive substrate; β-nickel hydroxide

In this study, CoNi flower-like hierarchical microstructures with different sizes were obtained via a one-step solvothermal method by simply adjusting the concentration of precursors and surfactant. The obtained CoNi microflowers possess uniform and tunable size, good monodispersity, and remarkable magnetic microwave absorption properties as well as electron holography phase images. Characterization results have demonstrated the dependency of properties of CoNi microflowers on their morphologies and sizes. The microflowers exhibit different stray magnetic fields that might be determined by whether the pristine nanoflakes on the flowers’ surface was parallel or perpendicular to grid plane. And as the size of microflowers increased, the coercive force (Hc) value decreased while saturation magnetization (Ms) value gradually increased, and it can be also observed that the values of Ms and Hc at 5 K are higher than those at 300 K. In addition, the blocking temperature decreased when size increased. Typically, the 2.5 μm CoNi microflowers achieve the maximum reflection loss (RL) value of −28.5 dB at 6.8 GHz with a thickness of 2 mm, while on the other hand, the 0.6 μm flowers achieved a broader absorption bandwidth below −10 dB of 6.5 GHz. Therefore, it is believable that the CoNi flowers with different sizes and hierarchical structures in this work have great potential for high performance magnetic microwave absorption applications.Keywords: CoNi microflowers; electron holography; magnetism; microwave absorption; particle size

We present a novel porous Au–Ag alloy particles inlaid AgCl membrane as plasmonic catalytic interfaces with real-time, in situ surface-enhanced Raman spectroscopy (SERS) monitoring. The Au–Ag alloy particles inlaid AgCl membranes were obtained via a facile two-step, air-exposed, and room-temperature immersion reaction with appropriate annealing process. Owing to the designed integration of semiconductor component AgCl and noble metal Au–Ag particles, both the catalytic reduction and visible-light-driven photocatalytic activities toward organic contaminants were attained. Specifically, the efficiencies of about 94% of 4-nitrophenol (4-NP, 5 × 10–5 M) reduction after 8 min of reaction, and degradation of rhodamine 6G (R6G, 10–5 M) after 12 min of visible light irradiation were demonstrated. Moreover, efficiencies of above 85% of conversion of 4-NP to 4-aminophenol (4-AP) and 90% of R6G degradation were achieved as well after 6 cycles of reactions, by which robust recyclability was confirmed. Further, with distinct SERS signals generated simultaneously from the surfaces of Au–Ag particles under laser excitation, in situ SERS monitoring of the process of catalytic reactions with superior sensitivity and linearity has been realized. Overall, the capability of the Au–Ag particles inlaid AgCl membranes to provide SERS monitored catalytic and visible-light-driven photocatalytic conversion of organic pollutants, along with their mild and cost-effective fabrication method, would make sense for in-depth understanding of the mechanisms of (photo)catalytic reactions, and also future development of potable, multifunctional and integrated catalytic and sensing devices.Keywords: Au−Ag alloy; catalysis; persistent organic pollutants; photocatalysis; SERS monitoring

Iron oxides are very promising anode materials based on conversion reactions for lithium-ion batteries (LIBs). During conversion processes, the crystal structure and composition of the electrode material are drastically changed. Surprisingly, in our study, inheritance of a crystallographic orientation was found during lithiation/delithiation processes of single-crystal α-Fe2O3 nanocubes by ex situ transmission electron microscopy. Single-crystal α-Fe2O3 was first transformed into numerous Fe nanograins embedded in a Li2O matrix, and then the conversion between Fe and FeO nanograins became the main reversible electrochemical reaction for energy storage. Interestingly, these Fe/FeO nanograins had almost the same crystallographic orientation, indicating that the lithiated/delithiated products can inherit the crystallographic orientation of single-crystal α-Fe2O3. This finding is important for understanding the detailed electrochemical conversion processes of iron oxides, and this feature may also exist during lithiation/delithiation processes of other transition-metal oxides.Keywords: conversion mechanism; high-angle annular dark-field imaging; inheritance of a crystallographic orientation; lithium-ion battery; α-iron oxide

Highly-dispersed Fe3O4@ZrO2 yolk–shell structures with a ZrO2 shell of homogeneous shell thickness was successfully prepared via a polymer surfactant (hydroxypropyl cellulose) assisted sol–gel method. By using HPC as a surfactant, highly dispersed particles with Zirconia shells of about 25–30 nm thickness were obtained. The yolk–shell Fe3O4@ZrO2 structure was characterized by several techniques, including transmission electron microscopy (TEM), scanning electron microscopy, (SEM) and X-ray diffraction (XRD), which indicated that the particles had a ZrO2 shell 500 nm in diameter and 25–30 nm in thickness, and a Fe3O4 core of 300 nm in diameter. An in situ TEM heating experiment from 20 °C to 1000 °C demonstrated that the obtained yolk–shell Fe3O4@ZrO2 structure was stable, without any distinguishable structural damage below 700 °C. This material has great potential as a high temperature stable microwave absorber. Even at temperatures of 500 °C, this material still preserved over 90% of its reflection loss (RL) value compared to its room temperature properties. These findings may shed light on the development of novel microwave absorbers for high temperature operation.

To meet the demands of strengthening microwave absorption capability, self-assembly nanoparticles (NP) with flexible morphology and abundant interfaces are important and their synthesis remains great challenge. In this paper, cobalt monoxide (CoO) nanostructures with octahedral and 3-dimensional (3D) nano-flower morphologies were controllably synthesized by decomposition of cobalt acetylacetonate at 280 °C, chelated with dual-surfactants of oleylamine and oleic acid with various volume ratios (10:1–7:4). The basic structural units of both octahedrons and 3D nano-flowers are octahedral CoO NP, which was demonstrated by advanced 3D transmission electron microscopy tomography. Dependency of the tunable microwave absorption properties on the 3D geometric morphologies of CoO NP was well established. The absorption bandwidth with a reflection loss (RL) of less than −10 dB is larger than 6 GHz for both octahedrons and nano-flowers. Compared to the spherical CoO NP, the octahedral nano-flowers have highly enhanced microwave absorption capability. Moreover, the maximum RL peak of the nano-flower CoO NP reached as high as −37 dB at 10.5 GHz, compared to that of −17 dB at 12 GHz for the octahedral CoO NP and −6.3 dB at 7.5 GHz for the spherical CoO NP. These results indicate a remarkable dependency of the dielectric polarization absorption and magnetic coupling absorption on the geometric morphology of CoO nano-architecture. It can be supposed from our findings that various morphologies of self-assembling CoO NP might become an effective path to achieve high-performance microwave absorption for electromagnetic shielding and stealth camouflage applications.

The shape anisotropy of the nanostructured nanorattles is one of the key factors that affect their microwave absorption performance. In the present study, the microwave absorption performance of ellipsoidal Fe3O4@CuSiO3 nanorattles with different aspect ratios was investigated. Results demonstrated that the ellipsoidal nanorattles with the aspect ratio of 3–4 exhibited about 20% enhancement of microwave absorption intensity compared with spherical Fe3O4@CuSiO3. Generally, as the aspect ratio increased from 2.0 to 3.5, the microwave absorption peak was enhanced monotonously from −20 dB to −30 dB. It was found that the ellipsoidal nanorattles with larger aspect ratio exhibited higher coercivity and double resonance peaks of the real part of complex permittivity, resulting in the improvement of microwave absorption performance. Our research gives insights into the understanding of the anisotropic effect of nanorattles on microwave absorption performance.

Enhancement of the electrochemical performances of electrode materials is a great challenge in the electrochemical capacitor field. Herein, a novel paramecium-like α-MnO2 hierarchical hollow structure used as an electrode material has been successfully prepared, which possesses an ultra-high specific surface area (285 m2 g−1), uniform crystal orientation, and high specific capacitance (554.3 F g−1 at 1 A g−1) and exhibits 97.9% capacitance retention after 5000 cycles. The earlier carbonaceous coating transformed from dopamine plays an important role in forming this novel paramecium-like morphology. The shells are constructed of ultra-thin α-MnO2 nanoflakes with highly uniform and preferentially exposed [001] crystal orientation. The high specific surface area increases the electrolyte–electrode contact area and the unique orientated structure effectively facilitates ion transportation. Quasi in situ electron energy-loss spectroscopy (EELS) analysis for both hierarchical hollow structures and commercial products at different charge–discharge stages indicates that Mn in our products can be almost completely restored to its original oxidation valence state due to a complete redox reaction, while there is still a fraction of Mn in the commercial product that cannot be restored, which causes the reduction of specific capacitance and retention. All the results suggest that this novel α-MnO2 hierarchical hollow structure with selective growth orientation might become an attractive type of electrode material.

Li-rich layered cathode materials Li1.2(Mn0.4Co0.4)O2 with excellent crystal structure and enhanced electrochemical performance were synthesized by a facile compound molten salt method with different molar ratios of mineralizer NaOH to transition metals R (0, 2.5, 5 and 10). The effects of the molar ratio of NaOH to R on the morphology, selective orientation growth, and electrochemical properties of the as-prepared material were investigated through X-ray diffraction (XRD), transmission electron microscopy (TEM), cyclic voltammetry (CV), and galvanostatic charge–discharge tests. With the introduction of NaOH into the molten salt reaction system, the crystals grew along the [0001] crystal axis predominantly and the particle morphology changed from hexagonal tablets to columns, which resulted in enhanced electrochemical performance by facilitating Li ion migration. The initial capacity increased from 220 mA h g−1 (R = 0) to 258 mA h g−1 (R = 5), and the capacity retention improved from 70.0% (R = 0) to 89.9% (R = 5) at a current density of 0.1 C after 50 cycles. Furthermore, by using high resolution TEM (HRTEM) and electron energy loss spectroscopy (EELS), the crystal local structure variation and Mn ion valence reduction (Mn4+ to Mn3+) were investigated, which are relevant to the capacity loss after charge–discharge cycling. Our work demonstrated that the prepared particle crystal structure was improved in NaOH flux, and the additional formation of a spinel-like structure was remarkably suppressed during cycling, which contributed to the improved electrochemical properties.

3D flower-like β-Ni(OH)2/GO/CNTs composite was prepared via a facile phase transformation method with a high specific capacitance of ∼1815 F g−1 (nearly 96% of its theoretical pseudocapacitance) at 2 A g−1 and a good cycling performance of ∼97% capacitance retention after 2000 cycles at 10 A g−1. The morphology of β-Ni(OH)2 undergoes successive changes that could be controlled by adjusting the reaction time.

The influences of the Li+/Ni2+ replacement modulated by minor Co dopant on cyclic capacity and rate performance of lithium-rich cathode material Li1.2Ni0.2−z/2Mn0.6−z/2CozO2 (z = 0, 0.02, 0.04, 0.10) were investigated from the microstructural point of view by comprehensive techniques of high-resolution transmission electron microscopy (HRTEM) imaging, atomic-resolution electron energy loss spectroscopy (EELS), selected-area electron diffraction (SAED), and X-ray diffraction (XRD). It is found that Co played a vital role in decreasing the Li+/Ni2+ replacement ratio in the hexagonal layered Li1.2Ni0.2−z/2Mn0.6−z/2CozO2 (Rm), which is closely related to the electrochemical performance. An evident cationic ordering in the transition metal layers and a stacking sequence vertical to the Li+ diffusion orientation were observed in the Li1.2Ni0.2−z/2Mn0.6−z/2CozO2 (z > 0) system rather than in the Li1.2Ni0.2Mn0.6O2 system. Compared with Li1.2Ni0.2Mn0.6O2, Li1.2Ni0.18Mn0.58Co0.04O2 showed excellent electrochemical performance with increase in discharge capacity to 288.3 mA h g−1 from 166.3 mA h g−1, improvement in capacity retention to 98.6% from 73.9% at a current density of 0.1 C after 40 cycles, and enhancement in capacity to 161.4 mA h g−1 from 113 mA h g−1 at a higher rate of 2 C. The largest interlayer spacing (0.218 nm of O–Li–O layer), highest proportion of Mn4+ ion component, and the most remarkable superstructure diffraction spots were found for Li1.2Ni0.18Mn0.58Co0.04O2 among all specimens, as confirmed by XRD refinement, EELS, HRTEM, and SAED. Three superstructure vectors modulated by 1/4, 2/4, 3/4 ( = [01]) were simultaneously observed for Li1.2Ni0.18Mn0.58Co0.04O2, indicating a high degree of ordering. Our findings might shed new insights into the understanding of the Li+/Ni2+ replacement by doping minor amounts of Co for optimizing the electrochemical performance in Li-ion batteries cathode material from the microstructural point of view.

SiO2+x nanowires composed of multi-beads with novel chain morphology fabricated on an Au-coated silicon substrate were prepared via a chemical vapor deposition (CVD) technique. The morphology and microstructure of nanowires were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), selective area electron diffraction (SAED) and Fourier transform infrared spectroscopy (FTIR). The results showed that the morphology of SiO2+x could be well tuned by changing substrate temperature and deposition conditions. The growth process of SiO2+x nanowires was investigated by changing the substrate temperature from 400 °C to 1088 °C and the deposition time from 15 min to 60 min. Hence, a ‘dissolution–saturation–precipitation’ growth model suitable for the SiO2+x nanowires was proposed. Electron diffraction analysis showed that the nanowires had an amorphous phase structure. The SiO2+x nanowires emitted ultraviolet light with wavelengths of 308, 327 and 345 nm, respectively, which could be attributed to oxygen-rich composition of the nanowires.

Supported metal nanoparticle (NP) catalysts have been widely used in many industry processes and catalytic reactions. Catalyst deactivation is mainly caused by the sintering of supported metal NPs. Hence, understanding the metal NPs’ sintering behaviors has great significance in preventing catalyst deactivation. Here we report the metal particle migration inside/between mesochannels by scanning transmission electron microscopy and electron energy loss spectroscopy via an in situ TEM heating technique. A sintering process is proposed that particle migration predominates, driven by the difference of gravitational potential from the height of the uneven internal surface of the mesopores; when the distance of the gold nanoparticles with a size of about 3 and 5 nm becomes short after migration, the coalescence process is completed, which is driven by an “octopus-claw-like” expansion of a conduction electron cloud outside the Au NPs. The supports containing an abundance of micropores help to suppress particle migration and coalescence. Our findings provide the understanding toward the rational design of supported industrial catalysts and other nanocomposites with enhanced activity and stability for applications such as batteries, catalysis, drug delivery, gas sensors, and solar cells.Keywords: gold nanoparticles; in situ TEM; mesoporous materials; particle migration;

Large specific surface area is critical for Li4Ti5O12 to achieve good rate capacity and cycling stability, since it can increase the contact area between electrolyte/electrode and shorten the transport paths for electrons and lithium ions. In this study, hierarchical hollow Li4Ti5O12 urchin-like microspheres with ultra-high specific surface area of over 140 m2·g−1 and diameter more than 500 nm have been successfully synthesized by combining the versatile sol-gel process and a hydrothermal reaction, and exhibit excellent electrochemical performance with a high specific capacity of 120 mA·h·g−1 at 20 C and long cycling stability of < 2% decay after 100 cycles. Ex situ electron energy loss spectroscopy (EELS) analysis of Li4Ti5O12 microspheres at different charge-discharge stages indicates that only a fraction of the Ti4+ ions are reduced to Ti3+ and a phase transformation occurs whereby the spinel phase Li4Ti5O12 is converted into the rock-salt phase Li7Ti5O12. Even after 100 cycles, the oxidation-reduction reaction between Ti3+ and Ti4+ can be carried out much more effectively on the surface of Li4Ti5O12 nanosheets than on commercially available Li4Ti5O12 particles. All the results suggest that these Li4Ti5O12 microspheres may be attractive candidate anode materials for lithium ion batteries.

Core-shell nanostructures have attracted considerable attention in the past decades because of their fundamental scientific significance and many technological applications. Recently, it has been reported that the core-shell nanostructures with advanced compositions and complicated morphologies show great potential as high-performance microwave absorbers due to their unique properties, such as large surface areas, multi-functionalities and synergistic effects between the interior core and outer shell. This review article focuses on the recent progress in synthesis and characterization of hierarchical magnetic core-shell nanostructures for microwave absorption applications based on our own work. In addition, several future trends in this field for next-generation microwave absorbers are discussed.

Monodispersed manganese oxide (Mn1−xCox)3O4 (0 ≤ x ≤ 0.5) nanoparticles, less than 10 nm size, are respectively synthesized via a facile thermolysis method at a rather low temperature, ranging from 90 to 100 °C, without any inertia gas for protection. The influences of the Co dopant content on the critical reaction temperature required for the nanoparticle formation, electronic band structures, magnetic properties, and the microwave absorption capability of (Mn1−xCox)3O4 are comprehensively investigated by means of both experimental and theoretical approaches including powder X-ray diffraction (XRD), electron energy loss spectroscopy (EELS), super conductivity quantum interference device (SQUID) examination, and first-principle simulations. Co is successfully doped into the Mn atomic sites of the (Mn1−xCox)3O4 lattice, which is further confirmed by EELS data acquired from one individual nanoparticle. Therefore, continuous solid solutions of well-crystallized (Mn1−xCox)3O4 products are achieved without any impurity phase or phase separation. With increases in the Co dopant concentration x from 0 to 0.5, the lattice parameters change systemically, where the overall saturation magnetization at 30 K increases due to the more intense coupling of the 3d electrons between Mn and Co, as revealed by simulations. The microwave absorption properties of the (Mn1−xCox)3O4 nanoparticles are examined between 2 and 18 GHz. The maximum absorption peak −11.0 dB of the x = 0 sample is enhanced to −11.5 dB for x = 0.2, −12.7 dB for x = 0.25, −15.6 dB for x = 0.33, and −24.0 dB for x = 0.5 respectively, suggesting the Co doping effects. Our results might provide novel insights into the understanding of the influences of metallic ion doping on the electromagnetic properties of metallic oxide nanomaterials.

Using comprehensive transmission electron microscopy (TEM) techniques, the associations between the Mn dopant content, microstructure and improved rate performance of LiFe(1−x)MnxPO4 (0 ≤ x ≤ 0.5) were well established. Via the synergistic mechanism including both templating and chelating effects contributed by cetyltrimethyl ammonium bromide (CTAB) and citric acid, a series of LiFe(1−x)MnxPO4 (0 ≤ x ≤ 0.5) olivine crystals with adjustable Mn doping content were synthesized. No impurity phase was detected. Accidentally, a novel type of roughness phenomenon at the particle boundaries of LiFe(1−x)MnxPO4 particles was observed, which depended on citric acid chelation. At the atomic level, the Mn ions were confirmed to be homogeneously substituted at the iron sites, which were furthermore examined by the combined analysis of electron energy loss spectroscopy (EELS), high angle annular dark-field (HAADF) imaging, magnetic susceptibility measurements and X-ray diffraction (XRD). Li/Fe antisite defects were found in the doped LiFe(1−x)MnxPO4 rather than in pure LiFePO4 by HAADF-EELS acquired from a single-atom column at high spatial resolution. The rate performance of LiFe0.9Mn0.1PO4 and LiFe0.8Mn0.2PO4 was improved compared to that of LiFePO4. Our findings might provide new insights into the understanding of Li-ion battery cathode materials with Mn dopant from a microstructural point of view.

Yolk–shell microspheres with magnetic Fe3O4 cores and hierarchical copper silicate shells have been successfully synthesized by combining the versatile sol–gel process and hydrothermal reaction. Various yolk–shell microspheres with different core size and shell thickness can be readily synthesized by varying the experimental conditions. Compared to pure Fe3O4, the as-synthesized yolk–shell microspheres exhibit significantly enhanced microwave absorption properties in terms of both the maximum reflection loss value and the absorption bandwidth. The maximum reflection loss value of these yolk–shell microspheres can reach −23.5 dB at 7 GHz with a thickness of 2 mm, and the absorption bandwidths with reflection loss lower than −10 dB are up to 10.4 GHz. Owing to the large specific surface area, high porosity, and synergistic effect of both the magnetic Fe3O4 cores and hierarchical copper silicate shells, these unique yolk–shell microspheres may have the potential as high-efficient absorbers for microwave absorption applications.Keywords: copper silicate; hydrothermal synthesis; magnetite; microwave absorption; yolk−shell;

In this paper, we report the facile synthesis of ultrathin barium titanate (BaTiO3) nanowires with gram-level yield via a simple one-step hydrothermal treatment. Our BaTiO3 nanowires have unique features: single crystalline, uniform size distribution and ultra high aspect ratio. The synergistic effects including both Ostwald ripening and cation exchange reaction are responsible for the growth of the ultrathin BaTiO3 nanowires. The microwave absorption capability of the ultrathin BaTiO3 nanowires is improved compared to that of BaTiO3 nanotorus,1 with a maximum reflection loss as high as −24.6 dB at 9.04 GHz and an absorption bandwidth of 2.4 GHz (<−10 dB). Our method has some novel advantages: simple, facile, low cost and high synthesis yield, which might be developed to prepare other ferroelectric nanostructures. The strong microwave absorption property of the ultrathin BaTiO3 nanowires indicates that these nanowires could be used as promising materials for microwave-absorption and stealth camouflage techniques.Keywords: BaTiO3 nanowires; microwave absorption; transmission electron microscopy; ultrathin;

Highly crystalline manganese diselenide (MnSe2) nanorods were synthesized via a facile solvothermal reaction with polyvinylpyrrolidone as a capping agent. The size, morphology, structure as well as phase purity were characterized by scanning electron microscopy, transmission electron microscopy, electron energy loss spectroscopy, powder X-ray diffraction, and energy-dispersive X-ray spectroscopy. All the results demonstrated that the as-synthesized MnSe2 nanorods grow along [2 0 0] axis and have high crystallization degree. Moreover, the aspect ratio of the MnSe2 nanorods ranging from ∼15 to ∼70 can be tuned by simply changing the amount of polyvinylpyrrolidone. Besides, the volume ratio of N,N-dimethylformamide to deionized water has critical influence on the morphology and composition of the products. Moreover, the microwave absorption properties of the MnSe2 nanorods were investigated. All the studies indicate that the MnSe2 nanorods might have potential applications as promising microwave absorbing materials.Graphical abstractHighlights► High-quality MnSe2 nanorods via facile solvothermal method. ► MnSe2 nanorods with different aspect radio can be prepared with different amount of PVP. ► MnSe2 nanorods have great potential application as microwave absorber.

Double-shelled yolk–shell microspheres with Fe3O4 cores and SnO2 double shells have been successfully synthesized by combining the versatile sol–gel process and hydrothermal shell-by-shell deposition method. The as-synthesized double-shelled Fe3O4@SnO2 yolk–shell microspheres have uniform size, unique morphology, well-defined shells, favorable magnetization, large specific surface area, and high porosity and exhibit significantly enhanced microwave absorption properties in terms of both the maximum reflection loss value and the absorption bandwidth. The excellent microwave absorption properties of these microspheres may be attributed to the unique double-shelled yolk–shell structure and synergistic effect between the magnetic Fe3O4 cores and dielectric SnO2 shells.

A facile “hydrothermal-assisted crystallization” route for the synthesis of hierarchical magnetic yolk–shell microspheres with mixed barium silicate and barium titanium oxide shells has been developed. Various yolk–shell microspheres with different shell thicknesses and core sizes have been successfully synthesized by controlling the synthetic parameters. The as-synthesized yolk–shell microspheres possess high magnetization, tailored shells, large specific surface area and high porosity, and are demonstrated to be attractive candidate materials for microwave absorption enhancement. Moreover, a possible formation mechanism based on the sacrificial-templating crystallization, dissolution–precipitation and in situ transformation processes is proposed.

The controllable synthesis of hollow polyhedral hetero-structures composed of metallic and metallic–semiconductor nanograins has aroused great attention not only for the synthetic challenge, but also for the novel functions offered by their unique micro-/nanostructures. Herein, both Au and Au–CuO hierarchical heterostructured cubic microcages have been prepared using Cu2O cubes as sacrificial templates in aqueous solution. The micro-sized Au cubic cages are composed of Au nanograins about 20 nm in size with abundant pores inside the cage walls. Each individual Au–CuO hetero-structured cubic cage is assembled with both gold nanoparticles and CuO nanoneedles. A growth mechanism for the formation process of these delicate hierarchical cubic architectures is presented. Furthermore, the reflection loss (dB) spectra measured in the frequency range 2–18 GHz showed that the Au–CuO hollow hetero-structured cubic cages have an improved electromagnetic interference (EMI) shielding effectiveness (SE) compared to that of both Au hollow cubic microcages and conventional Au hollow microspheres. Moreover, these Au cages and Au–CuO cubic cages might find novel applications in sensing and catalysis due to their hierarchically assembled structures.

In this work, morphology and interfacial characteristics of aluminum matrix composites reinforced with diamond fiber were studied. Samples were fabricated by pressureless metal infiltration process and its thermal conductivity reach as high as 518 W/m K, while its thermal expansion coefficient exhibited as low as 4.61 × 10−6/K. The obtained composites were investigated by scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and element map techniques. The diamond fiber was homogeneously dispersed and well bonded inside the aluminum matrix. It was found that silicon and magnesium were aggraded around the interface. Moreover, aluminum carbide phases (Al4C3) were randomly formed between aluminum matrix and diamond fiber.

Pnictide oxide superconductor GdFePO has been synthesized by a two-step solid reaction method. Gd–Fe–P ternary alloy is firstly prepared using pre-melting technology. The superconductivity at around 6.1 K in GdFePO is observed. An annealing treatment done after synthesis could effectively reduce the dislocation density and furthermore affect the superconducting transition. Detail evidences based on transmission electron microscopy analysis reveal the relationship between the adjustable superconducting properties and the dislocations along [0 0 1] orientation of GdFePO.Research highlightsNew pnictide oxide GdFePO superconductor has been synthesized. The coexistence of antiferromagnetism order and superconductivity order in GdFePO is observed. An important post-annealing treatment done after the synthesis could effectively reduce the dislocation density and improve the superconductivity.

The physical properties of nanometer scale semiconductors are known to be sensitively influenced by their aspect ratios, but the intrinsic mechanisms still remain unclear. Shape-controlled anisotropic PbSe nanorods were obtained by means of the addition of MnCl2, and the aspect ratio of the nanorods can be continuously tuned from 1 to 10 by simply modulating the amount of chloride ions. It was demonstrated that an optimized concentration of Cl− anions is about 0.04 mmol, which controls the competition between thermodynamics and kinetics mechanisms. The emission peaks of the infrared absorbance and photoluminescence spectra were significantly tuned from 1664 nm to 1840 nm and from 1459 nm to 1938 nm only by the aspect ratios, respectively. A strong electric dipole phenomenon localized onside the surface of PbSe nanorods terminated by Pb2+ charge was found by using high-spatial-resolution off-axis electron holography, which was furthermore evidenced by the quantitative analysis of the mean inner potential and the surfaces charge. The charge intensity depended on the aspect ratio of PbSe nanorods. The results provide clear evidence that the energy gap interval reduces as a result of the increasing of conduction charge amounts. A novel strategy to facilely shift the peak position of absorbance and photoluminescence emission was therefore proposed.Off-axis electron holography was first time utilized to map the charge density distribution of uniform anisotropic PbSe nanorods, which were shape-controlled prepared by modulating the quantity of Cl− ions.

Multifunctional composite microspheres with a Co20Ni80 core and anatase TiO2 shells (Co20Ni80@TiO2) are synthesized by combining a solvothermal reaction and a calcination process, and include a series of microspheres with different core sizes (100 nm, 500 nm and 1 μm). The mechanism of self-assembly of the primary particles has been effective in both the fabrication of the core and the process of coating. The obtained core–shell particles possess superior monodispersity, size uniformity, and tailored core sizes, and are characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Furthermore, the electromagnetic shielding performance of the microspheres is investigated in terms of the theory of transmission lines. The Co20Ni80@TiO2 core–shell particle (CoNi@TiO2) with a well-defined core size of 500 nm demonstrates a remarkable wide-band electromagnetic shielding performance of up to 6.2 GHz (10.0–16.2 GHz, <−10 dB) within 2–18 GHz, which is due to the tunable multi-component hierarchical structure of the particles and contributes to the complex permittivity and permeability and the multiple scattering loss of the microwave. The Co20Ni80@TiO2 particle with a specific core size (500 nm) is a promising candidate for the wide-band electromagnetic shielding materials, gathering increasing interest from researchers.

To meet the demand of electromagnetic interference shielding, cheap and easily available microwave absorbers are urgently required. Recently, most of the related research has been focussed on a number of complicated absorbers comprising multi-components because of their better electromagnetic match. However, it is still a great challenge to develop an absorber that simultaneously possesses the advantages of easy fabrication, low-cost, ultra-wide bandwidth, and strong absorption. Hence, development of a simple and convenient absorber with efficient performance is attracting significant attention because of the urgent requirement of this type of absorbers. Herein, a series of single-component iron-based absorbers with different morphologies and grain sizes was successfully prepared. Strong absorption intensity (∼−43.4 dB) was found in plate-like samples, which could even match those of some multi-component absorbers. Electron holography and Lorentz microscopy analysis were used for the further comprehension of the relationships among the microstructure, electromagnetic property, and microwave absorption performance. The primary grain size of the present iron microplate was found fundamentally important for microwave absorption performance. This cheap and available absorber is believed to be an optimal choice for single-component absorbers and useful in the research of absorption mechanism.

Li-rich Mn-based cathode materials have been considered as promising candidates for next generation Li-ion batteries due to their high-energy density, low cost and non-toxicity. However, the atomic arrangement of such materials and the relationship between the microstructure and electrochemical performance are still not fully understood. In this paper, local heterogeneity in the crystal lattice is directly observed in synthesized Li2MnO3/LiMO2 (M = Ni and Mn) cathode materials. With SAED application, for the first time, we accordingly uncover that the lattice heterogeneity is induced by different Li2MnO3 atomic arrangements coexisting in the same crystal domain. The co-growth of Li2MnO3 with different orientations is proved to be a defective feature, which would induce atomic vacancy concentration in the lattice and increase the risk of layered structure collapse in the cycling process. The electrochemical test results also suggest that the composition with a relatively uniform Li2MnO3 arrangement exhibits better cycling performance (the capacity retention is as high as 95.1% after 50 cycles at 0.1C), oppositely, the coexistence of multiple complex Li2MnO3 arrangements results in poor cycling performance (the capacity retention is below 70% after 50 cycles at 0.1C). The crystal lattice structure comparison between primary and cycled is shown to manifest the effect of Li2MnO3 arrangement on the electrochemical performance and structural stability, providing one possible explanation for the capacity degradation of the Li-rich materials.

Crystal defects have been introduced into inherently narrow-band-gap and non-toxic Ag2Se quantum dots (QDs) via a facile and efficient thermal vibration approach during synthesis and studied by using electron holography and geometric phase analysis techniques. These crystal defects consequently demonstrated a solid possibility for tuning the optical band-gaps of Ag2Se QDs, and thereby enhancing the visible-light-driven water splitting and hydrogen evolution performance of Ag2Se QD-sensitized TiO2 photocatalysts.

Using comprehensive transmission electron microscopy (TEM) techniques, the associations between the Mn dopant content, microstructure and improved rate performance of LiFe(1−x)MnxPO4 (0 ≤ x ≤ 0.5) were well established. Via the synergistic mechanism including both templating and chelating effects contributed by cetyltrimethyl ammonium bromide (CTAB) and citric acid, a series of LiFe(1−x)MnxPO4 (0 ≤ x ≤ 0.5) olivine crystals with adjustable Mn doping content were synthesized. No impurity phase was detected. Accidentally, a novel type of roughness phenomenon at the particle boundaries of LiFe(1−x)MnxPO4 particles was observed, which depended on citric acid chelation. At the atomic level, the Mn ions were confirmed to be homogeneously substituted at the iron sites, which were furthermore examined by the combined analysis of electron energy loss spectroscopy (EELS), high angle annular dark-field (HAADF) imaging, magnetic susceptibility measurements and X-ray diffraction (XRD). Li/Fe antisite defects were found in the doped LiFe(1−x)MnxPO4 rather than in pure LiFePO4 by HAADF-EELS acquired from a single-atom column at high spatial resolution. The rate performance of LiFe0.9Mn0.1PO4 and LiFe0.8Mn0.2PO4 was improved compared to that of LiFePO4. Our findings might provide new insights into the understanding of Li-ion battery cathode materials with Mn dopant from a microstructural point of view.

The controllable synthesis of hollow polyhedral hetero-structures composed of metallic and metallic–semiconductor nanograins has aroused great attention not only for the synthetic challenge, but also for the novel functions offered by their unique micro-/nanostructures. Herein, both Au and Au–CuO hierarchical heterostructured cubic microcages have been prepared using Cu2O cubes as sacrificial templates in aqueous solution. The micro-sized Au cubic cages are composed of Au nanograins about 20 nm in size with abundant pores inside the cage walls. Each individual Au–CuO hetero-structured cubic cage is assembled with both gold nanoparticles and CuO nanoneedles. A growth mechanism for the formation process of these delicate hierarchical cubic architectures is presented. Furthermore, the reflection loss (dB) spectra measured in the frequency range 2–18 GHz showed that the Au–CuO hollow hetero-structured cubic cages have an improved electromagnetic interference (EMI) shielding effectiveness (SE) compared to that of both Au hollow cubic microcages and conventional Au hollow microspheres. Moreover, these Au cages and Au–CuO cubic cages might find novel applications in sensing and catalysis due to their hierarchically assembled structures.

A facile “hydrothermal-assisted crystallization” route for the synthesis of hierarchical magnetic yolk–shell microspheres with mixed barium silicate and barium titanium oxide shells has been developed. Various yolk–shell microspheres with different shell thicknesses and core sizes have been successfully synthesized by controlling the synthetic parameters. The as-synthesized yolk–shell microspheres possess high magnetization, tailored shells, large specific surface area and high porosity, and are demonstrated to be attractive candidate materials for microwave absorption enhancement. Moreover, a possible formation mechanism based on the sacrificial-templating crystallization, dissolution–precipitation and in situ transformation processes is proposed.

Highly-dispersed Fe3O4@ZrO2 yolk–shell structures with a ZrO2 shell of homogeneous shell thickness was successfully prepared via a polymer surfactant (hydroxypropyl cellulose) assisted sol–gel method. By using HPC as a surfactant, highly dispersed particles with Zirconia shells of about 25–30 nm thickness were obtained. The yolk–shell Fe3O4@ZrO2 structure was characterized by several techniques, including transmission electron microscopy (TEM), scanning electron microscopy, (SEM) and X-ray diffraction (XRD), which indicated that the particles had a ZrO2 shell 500 nm in diameter and 25–30 nm in thickness, and a Fe3O4 core of 300 nm in diameter. An in situ TEM heating experiment from 20 °C to 1000 °C demonstrated that the obtained yolk–shell Fe3O4@ZrO2 structure was stable, without any distinguishable structural damage below 700 °C. This material has great potential as a high temperature stable microwave absorber. Even at temperatures of 500 °C, this material still preserved over 90% of its reflection loss (RL) value compared to its room temperature properties. These findings may shed light on the development of novel microwave absorbers for high temperature operation.

To meet the demands of strengthening microwave absorption capability, self-assembly nanoparticles (NP) with flexible morphology and abundant interfaces are important and their synthesis remains great challenge. In this paper, cobalt monoxide (CoO) nanostructures with octahedral and 3-dimensional (3D) nano-flower morphologies were controllably synthesized by decomposition of cobalt acetylacetonate at 280 °C, chelated with dual-surfactants of oleylamine and oleic acid with various volume ratios (10:1–7:4). The basic structural units of both octahedrons and 3D nano-flowers are octahedral CoO NP, which was demonstrated by advanced 3D transmission electron microscopy tomography. Dependency of the tunable microwave absorption properties on the 3D geometric morphologies of CoO NP was well established. The absorption bandwidth with a reflection loss (RL) of less than −10 dB is larger than 6 GHz for both octahedrons and nano-flowers. Compared to the spherical CoO NP, the octahedral nano-flowers have highly enhanced microwave absorption capability. Moreover, the maximum RL peak of the nano-flower CoO NP reached as high as −37 dB at 10.5 GHz, compared to that of −17 dB at 12 GHz for the octahedral CoO NP and −6.3 dB at 7.5 GHz for the spherical CoO NP. These results indicate a remarkable dependency of the dielectric polarization absorption and magnetic coupling absorption on the geometric morphology of CoO nano-architecture. It can be supposed from our findings that various morphologies of self-assembling CoO NP might become an effective path to achieve high-performance microwave absorption for electromagnetic shielding and stealth camouflage applications.

Enhancement of the electrochemical performances of electrode materials is a great challenge in the electrochemical capacitor field. Herein, a novel paramecium-like α-MnO2 hierarchical hollow structure used as an electrode material has been successfully prepared, which possesses an ultra-high specific surface area (285 m2 g−1), uniform crystal orientation, and high specific capacitance (554.3 F g−1 at 1 A g−1) and exhibits 97.9% capacitance retention after 5000 cycles. The earlier carbonaceous coating transformed from dopamine plays an important role in forming this novel paramecium-like morphology. The shells are constructed of ultra-thin α-MnO2 nanoflakes with highly uniform and preferentially exposed [001] crystal orientation. The high specific surface area increases the electrolyte–electrode contact area and the unique orientated structure effectively facilitates ion transportation. Quasi in situ electron energy-loss spectroscopy (EELS) analysis for both hierarchical hollow structures and commercial products at different charge–discharge stages indicates that Mn in our products can be almost completely restored to its original oxidation valence state due to a complete redox reaction, while there is still a fraction of Mn in the commercial product that cannot be restored, which causes the reduction of specific capacitance and retention. All the results suggest that this novel α-MnO2 hierarchical hollow structure with selective growth orientation might become an attractive type of electrode material.

Li-rich layered cathode materials Li1.2(Mn0.4Co0.4)O2 with excellent crystal structure and enhanced electrochemical performance were synthesized by a facile compound molten salt method with different molar ratios of mineralizer NaOH to transition metals R (0, 2.5, 5 and 10). The effects of the molar ratio of NaOH to R on the morphology, selective orientation growth, and electrochemical properties of the as-prepared material were investigated through X-ray diffraction (XRD), transmission electron microscopy (TEM), cyclic voltammetry (CV), and galvanostatic charge–discharge tests. With the introduction of NaOH into the molten salt reaction system, the crystals grew along the [0001] crystal axis predominantly and the particle morphology changed from hexagonal tablets to columns, which resulted in enhanced electrochemical performance by facilitating Li ion migration. The initial capacity increased from 220 mA h g−1 (R = 0) to 258 mA h g−1 (R = 5), and the capacity retention improved from 70.0% (R = 0) to 89.9% (R = 5) at a current density of 0.1 C after 50 cycles. Furthermore, by using high resolution TEM (HRTEM) and electron energy loss spectroscopy (EELS), the crystal local structure variation and Mn ion valence reduction (Mn4+ to Mn3+) were investigated, which are relevant to the capacity loss after charge–discharge cycling. Our work demonstrated that the prepared particle crystal structure was improved in NaOH flux, and the additional formation of a spinel-like structure was remarkably suppressed during cycling, which contributed to the improved electrochemical properties.

3D flower-like β-Ni(OH)2/GO/CNTs composite was prepared via a facile phase transformation method with a high specific capacitance of ∼1815 F g−1 (nearly 96% of its theoretical pseudocapacitance) at 2 A g−1 and a good cycling performance of ∼97% capacitance retention after 2000 cycles at 10 A g−1. The morphology of β-Ni(OH)2 undergoes successive changes that could be controlled by adjusting the reaction time.

The influences of the Li+/Ni2+ replacement modulated by minor Co dopant on cyclic capacity and rate performance of lithium-rich cathode material Li1.2Ni0.2−z/2Mn0.6−z/2CozO2 (z = 0, 0.02, 0.04, 0.10) were investigated from the microstructural point of view by comprehensive techniques of high-resolution transmission electron microscopy (HRTEM) imaging, atomic-resolution electron energy loss spectroscopy (EELS), selected-area electron diffraction (SAED), and X-ray diffraction (XRD). It is found that Co played a vital role in decreasing the Li+/Ni2+ replacement ratio in the hexagonal layered Li1.2Ni0.2−z/2Mn0.6−z/2CozO2 (Rm), which is closely related to the electrochemical performance. An evident cationic ordering in the transition metal layers and a stacking sequence vertical to the Li+ diffusion orientation were observed in the Li1.2Ni0.2−z/2Mn0.6−z/2CozO2 (z > 0) system rather than in the Li1.2Ni0.2Mn0.6O2 system. Compared with Li1.2Ni0.2Mn0.6O2, Li1.2Ni0.18Mn0.58Co0.04O2 showed excellent electrochemical performance with increase in discharge capacity to 288.3 mA h g−1 from 166.3 mA h g−1, improvement in capacity retention to 98.6% from 73.9% at a current density of 0.1 C after 40 cycles, and enhancement in capacity to 161.4 mA h g−1 from 113 mA h g−1 at a higher rate of 2 C. The largest interlayer spacing (0.218 nm of O–Li–O layer), highest proportion of Mn4+ ion component, and the most remarkable superstructure diffraction spots were found for Li1.2Ni0.18Mn0.58Co0.04O2 among all specimens, as confirmed by XRD refinement, EELS, HRTEM, and SAED. Three superstructure vectors modulated by 1/4, 2/4, 3/4 ( = [01]) were simultaneously observed for Li1.2Ni0.18Mn0.58Co0.04O2, indicating a high degree of ordering. Our findings might shed new insights into the understanding of the Li+/Ni2+ replacement by doping minor amounts of Co for optimizing the electrochemical performance in Li-ion batteries cathode material from the microstructural point of view.