Nickel ferrite (NiFe2O4) nanomaterials with different morphologies, including nano-spheres (10–25 nm in diameter), nano-rods (50–60 nm in diameter and ~1 μm in length), and nano-octahedrons (side length ~150 nm), have been synthesized by a single mild hydrothermal method at 160 °C without any surfactant. The crystal structures have been investigated by TEM, HRTEM, and studied by simulations using the program Materials Studio. The variations in the morphology, as well as the preferential crystal growth directions, depend only on the pH value of the reaction solution. A phase formation mechanism is thus proposed. Magnetization measurements at T = 300 K indicate that the NiFe2O4 nano-spheres of 10–25 nm diameter are superparamagnetic with non-saturating magnetization at H = 7 kOe. The saturation magnetization, MS, of the nanorods is 40 emu g−1, less than the bulk value, MS = 46.7 to 55 emu g−1. The coercivity is HC = 40 Oe, reduced from the bulk value of 100 Oe. On the other hand, the nano-octahedrons have a saturation magnetization of MS = 50 emu g−1, the same as the bulk value. However the coercivity, HC = 50 Oe is also much reduced from the bulk value.

A synthetic route to achieve core/shell nanostructures consisting of noble metal cores and single crystal semiconductor shells with different crystal systems is proposed, which involves a simple phosphorization process from corresponding bimetallic heterostructures. The triphenylphosphine is designed to serve as both a capping agent and a phosphorous source during the formation of Au/Ni12P5 core/shell nanoparticles (NPs) from Au-Ni bimetallic heterodimers. The semiconductor shells of the obtained Au/Ni12P5 nanostructures are controlled to form single crystals with a thickness of ~5 nm. The structure-dependent supercapacitor properties of Au-modified Ni12P5 nanostructures were further investigated. The synergistic effect of the metal/semiconductor nanostructure is observed to be superior to its oligomer-like counterpart when serving as a supercapacitor electrode. The specific capacitance of an electrode fabricated from core/shell NPs is 806.1 F g−1 with a retention of 91.1% after 500 charge–discharge cycles.

NiPt hollow spheres decorated by Pt nanoparticles were synthesized by a facile wet chemical route through galvanic replacement. In situ STEM imaging and 3D reconstruction were performed to evidence the migration of Pt atoms during catalysis of CO oxidation, providing a practical insight into the structural stability of bimetallic catalysts.

Nearly monodispersed hollow nanospheres of bimetallic NiPt have been synthesized by a one-pot wet chemical method at room temperature with a precursor Ni nanocompound as a sacrificial template. The size control is carried out via the sacrificial template, from about 35 nm to nearly 100 nm in diameter. The shell thickness of the NiPt hollow sphere reaches down to as thin as 2–3 nm slightly larger than a single layer of alloyed NiPt nanocrystallites. The product with the citric acid as surfactant exhibits enhanced oxygen reduction activities compared to a commercial Pt/C catalyst and the hollow nanospheres coated with PVP. It has potential applications in fuel cells, biotechnology and environmental chemistry with the facile synthesis, low cost and excellent electrocatalytic activity.

ZnS nanostructures with different dimensions and structure-related properties were reviewed in this paper. The crystallization of nanostructures from 0D, 1D to 3D, as well as the heterogonous counterparts, was summarized in the aspect of zinc blende, wurtzite structure, and their combinations. Furthermore, the structure-related energy bands and the corresponding photoelectric properties of ZnS nanostructures were also focused, in which we made a brief summary of the co-relations between photoluminescence and crystallography, especially the defect-related luminescence properties of ZnS nanocrystal.

•We represent a novel and efficient design of flexible coaxial fiber supercapacitor.•We focus on NiCo2O4 nanosheet employed as the active material for the first time using in a fiber-based supercapacitor.•The excellent performance of the NiCo2O4 nanosheet electrode based device is highlighted.•The fiber supercapacitor into designed patterns for wearable electronics applications is proposed.Fiber electronic devices show advantages for the direct use as wearable and embedded device units or integrated textile modules. We successfully developed a coaxial-type flexible fiber supercapacitor by using NiCo2O4 nanosheets grown on Ni wire as the fiber electrodes. The volume capacitance of the fiber-shaped supercapacitor reached 10.3 F/cm3 at a current of 0.08 mA and outstanding cycling stability. An energy density of 1.44 mWh cm−3 and a power density of up to 17 W cm−3 were also obtained for the fiber supercapacitor, which are almost 48-fold higher than the previous values. Furthermore, the coaxial-type fiber supercapacitor does not show any apparent degradation in the bending test, illustrating the promise for use as electrodes for portable and wearable energy storage.

•Nanoscale core-shell hollow hexagon. Two types of Ni(OH)2@Co(OH)2 hollow hexagons at nanoscale with different growth facets have been synthesized by a mild method.•Electron Microscopy characterization. Detailed Electron Microscopy characterizations reveal that both hexagons with different growth facets have core-shell structure with wall thickness ~30 nm.•Facet-selective growth mechanism. The peculiar structure formation is attributed to a facet-selective growth mechanism considering the content of reducing agent and reaction temperature.•Preferable specific capacitance with extraordinary long-term stability. Preferable areal specific capacitance of Ni(OH)2 is maintained in the hexagons with extraordinary long-term stability.•Excellent charge transfer property. Excellent charge transfer property with extremely small charge transfer resistance is obtained in the hollow hexagons.Hollow nanohexagons with a core–shell structure have been synthesized from a mixture of Ni and Co hydroxide by a mild wet chemical approach. Ni(OH)2@Co(OH)2 nanohexagons with controllable sizes of about 200 nm, morphology and structure are obtained. Comprehensive microstructure analysis reveals that the Ni(OH)2 and Co(OH)2 components are single-crystalline. The surfaces of the nanohexagons are smooth and their inner facets can be controlled to be parallel to the outer facets or rotated by 30°. A growth mechanism depending on the N2H4·H2O content and reaction temperature has been proposed to explain the different structures. The parallel inner facets tend to form with higher amounts of N2H4·H2O while the rotated ones tend to form at higher temperature. The specific capacitance of the hollow nanohexagon is about 369 F/g, which can be remained as high as 96.4% after 2500 cycles at current density of 1 A/g.

The structure evolution behaviors of NiAu nanospindles in oxidizing/vacuum conditions were studied by in situ scanning transmission electron microscopy. The spindle structure transforms into Ni@Au@NiO multi-shell structure in the oxidizing atmosphere following an oxidation-driving multilayer reconstruction mechanism. In the vacuum condition, the NiAu nanospindles evolve along four distinct stages: (i) polyhedron recrystallization of Ni matrix; (ii) facets-selected segregation and recrystallization of Au component; (iii) single crystallization of Ni matrix; (iv) wrapping diffusion of Au component. The investigation here provides a practical insight into the structural stability of NiAu bimetallic catalysts through a thermal processes.

Perovskite rare-earth manganites like TbMnO3 exhibit rich magnetic and electric phases, providing opportunities for next-generation multifunctional devices. Here, we report the nonvolatile bipolar switching of resistance and capacitance in TbMnO3 thin films grown on conducting Nb:SrTiO3 substrates. The device shows an ON/OFF resistance ratio of ∼1 × 104, and the resistive switching is accompanied by a frequency-dependent capacitance switching. Detailed analysis of the conduction mechanisms reveals that the migration of oxygen vacancies and the charge trapping/detrapping at the heterojunction interface play important and complementary roles in the switching behaviors. Our results suggest that both electronic and ionic processes should be considered in order to elucidate the conduction mechanisms and the switching behaviors in such heterostructures made of complex oxides.Keywords: capacitance switching; charge trapping; ionic migration; oxygen vacancies; resistive switching; TbMnO3;

Simple oxide heterostructures have been fabricated by depositing TbMnO3 thin films on Nb:SrTiO3 substrates at different temperatures. Remarkable switching with an on/off resistance ratio of ∼5000 is found in the sample grown at 720 °C, while only tiny resistive hysteresis can be observed in the sample grown at 650 °C. A jump switching in the I–V loop at the lower resistance state with negative bias is initiated by a visible light pulse in the sample grown at 650 °C, whereas a drop switching can be observed in the sample grown at 720 °C. A trapping–detrapping process along the TbMnO3/Nb:SrTiO3 interfaces is proposed to explain the anomalous photoresponse.

The magnetism of undoped ZnS nanotetrapods, synthesized by a solvothermal method, has been investigated by magnetization measurements and first principle numerical calculations. The background magnetic impurity concentrations of Fe, Co and Ni were determined at ppm level by inductively coupled plasma mass spectrometry (ICP-MS). Hysteresis loops of weak ferromagnetism were observed, attributable to the magnetic impurities. However, the total magnetic moments analyzed from the paramagnetism are far beyond the explanations from the presence of these magnetic impurities, by about two orders of magnitude larger. It implies a different origin of the magnetic moments. Electron microscopy analysis reveals that there are defects in the sample. Numerical simulations indicate that the excessive magnetic moments might arise from the local band structure of polarized electrons associated with the defects of cation deficiency. This study elaborates on the understanding of magnetic properties in the non-magnetic II–VI semiconductor nanomaterials.

The synergistic effect between the metallic elements in the core–shell nanostructures has attracted increasing interest. In the system of Au@Ni nanostructure, it is challenging to epitaxially grow Ni atoms on Au nanocrystals due to the large lattice mismatch. In this paper, Au@Ni core–shell nanostructures have been synthesized by a facile one-pot wet chemical method. The Ni shell is epitaxially grown on the (111) planes of the icosahedral Au cores. The diameter of the icosahedral Au core is about 10–20 nm and the thickness of the Ni shell is of only several nanometers, providing an ideal structure for the study of synergistic effect. The Curie temperature of the Ni shells is estimated to be lower than 400 K by the field-cooling/zero field-cooling M(T) measurements. It is suppressed considerably from that of the bulk phase, mainly attributed to the finite size effect. The optical properties of the Au@Ni core–shell nanostructures are studied by absorption spectroscopy. The spectral blue-shift tendency is consistent with the results described by the plasmon hybridization theory.

This paper reports that the high pressure in situ angle dispersive x-ray diffraction and Raman scattering studies on CoPt and NiPt hollow nanospheres are performed by means of a diamond anvil cell for generating external pressure at room temperature. The crystal structures of both the CoPt and NiP hollow nanospheres keep stable up to about 41 GPa. Moreover, it shows that the hollow nanospheres possess higher bulk moduli than their bulk counterparts by using the first-principles density functional theory.

Bimetallic nanomaterials consisting of magnetic metals and noble metals have attracted much interest for their promising potentials in fields such as magnetic sensors, catalysts, optical detection and biomedical applications. Bimetallic nanomaterials synthesized by wet-chemical methods with different architectures including nanoparticles, nanowires or nanotubes and their assemblies are summarized in this review. The particular properties of bimetallic nanomaterials, especially their magnetic, catalytic and optical properties, are presented. The advance in electron microscopy makes it possible to understand the nanostructural materials at much higher level than before, which helps to disclose the relationship between the microstructures and properties qualitatively and quantitatively.

An in situ redox process in microfluidic reactors was developed to synthesize hybrid nanoparticles with amorphous metallic cores and uniform metal oxide shells embedded with nanocrystallites at large scale. For example, the fabricated Fe(B)@iron oxides nanoparticles (NPs) exhibit permanent ferromagnetic properties at room temperature due to the strong magnetic coupling between different parts and the nanocrystalline pinning effect, providing an alternative design of nanostructures to break out the superparamagnetic limit in ultratiny particles. The NPs with amorphous metallic cores and uniform metal oxide shells can be well maintained over 4–5 months. The dictated novel microfluidic process provides a large-scale synthetic strategy for metal@metal oxide core–shell NPs with uniform shells and long-term stability and can be extended to a variety of material systems.

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Double-layered NiPt nanobowls with diameter of ∼200 nm and layer thickness of ∼3 nm have been synthesized through a “one-pot” route in water at room temperature without pre-made templates. The nanobowls are self-assembled with asymmetric double layers and exhibit alignment behavior with different orientation on silicon wafer within different dispersant solutions. The as-prepared nanobowls can serve as fluorescence modifiers of Rhodamine 6G (R6G) molecules, attributed to their bowl-like shape with a hollow cavity between layers. It provides a new facile route for synthesis and manipulation of bowl-like nanostructures through a self-assembly method without pre-made templates.

Synthesis and manipulation of advanced bimetallic nanomaterials via a green and low-cost wet chemical route are of great importance for the industrialization potential. Materials design integrating the synthesis of nanomaterials through an environmentally benign route with a simple manipulation method is a challenge. The CoPt hollow nanochains have been successfully synthesized in aqueous solution with shell thickness of about 5 nm and tunable length from 300 nm to 2 μm. The as-prepared CoPt hollow nanochains can be easily aligned by the external magnetic fields and can be attached onto substrates, such as silicon wafer. The synthesis strategy is characterized by room temperature reaction (300 K), low cost, and utilization of facile reagents (water as solvent). Growth kinetics investigation shows the magnetostatic interactions between Co clusters together with the spontaneous galvanic replacement between Co clusters and Pt ions are indispensable for the formation of aligned hollow nanochains. Magnetic measurements indicate that the shape anisotropy of 1D aligned nanochains plays a dominant role on the good controllable behavior.

ZnS nanomaterials at different dimensions, from nanoparticles, nanobelts to nanotetrapods have been synthesized in the same solvothermal system, which is kinetically controlled by ethylenediamine. Microscopy analysis reveals that the four arms of tetrapod are grown from Zn-terminated surfaces of an octahedral core by alternately stacking zinc blende and wurtzite structures along [111]/[0001] direction, while the ZnS nanobelts are self-assembled along [0001] direction by ultra-small wurtzite nanocrystals. These nanobelts can be transformed into their single-crystal counterparts and ZnO/ZnS heterostructures by thermal treatment. Uv–visible analysis demonstrates that the heterostructure presents a strain-induced staggered Type-II band structure. These investigation results suggest an efficient approach for phase-controlled synthesis of nanostructures in group II–VI semiconductors.

ZnS nanotetrapods were investigated by atom-resolved microscopy characterization and quantitative simulation. The octahedron core enclosed with Zn- and S-terminated surfaces was verified. Four hexaprism-shaped arms were selectively grown from Zn-terminated surfaces of the core by alternately stacking zinc blende and wurtzite structures. The stacking order change at the core/arm interface is significant to activate the arm growth. The anisotropic growth mechanism was proposed and further proved by the synthesis of ZnS nanoparticles and nanobelts.

Active, robust, and low-cost catalysis is a key component for the commercialization of efficient catalysts. The development of effective strategies for the synthesis and processing of bimetallic nanoparticles with controllable size and composition is an important approach to the catalyst preparation. In this paper, a noble metal catalyzed chemical growth process has been developed. Nearly monodispersed bimetallic NiPt hollow spheres with an ultrathin shell (2–3 nm) have been successfully synthesized. Size and composition of the NiPt nanospheres has been conveniently tuned by introducing suitable amounts of precursory molecules. The solid, hollow as well as the jingle bell NiPt nanostructures are sequentially observed as results of the catalytic growth and alloying effect of Pt. Also demonstrated are the pronounced decay-resistant effects of Ni doping on the electrocatalytic properties. The excellent electrocatalytic activity and stability make the bimetallic NiPt hollow spheres promising candidates for catalysts and sensing materials.

A fluorescence-amplifying method based on photonic crystal (PC) has been demonstrated for trace TNT detection. The fluorescence enhancement for TNT detection on the optimized PC can be up to 60.6-fold in comparison to that of the control sample, which combines the slow photon effect of PC and large surface areas of the inverse opal structure. Furthermore, the quenching efficiency of the PC-based sensor achieves 80% after exposure to TNT vapor for 300 s. The results suggest that the fluorescence-amplifying method based on PC has enormous potential for the development of highly efficient fluorescence sensors toward detection of trace TNT or other explosives.

Single-crystal MgB2 hexagonal microprisms of 30 μm have been produced in large scale by a facile hybrid physical-chemical vapor deposition method. These microprisms show perfect single-crystal structure and superconducting properties. The morphological variations corresponding to different growing stages are revealed and the possible growth mechanism is suggested.

In this work, we present a facile approach on the remarkable enhancement of fluorescent signal by heterostructure colloidal photonic crystals (PCs) with dual stopbands. The intensity of fluorescent medium on heterostructure PCs with dual stopbands overlapping the excitation wavelength and the emission wavelength of fluorescent medium can be up to 162-fold enhancement in comparison to that on the control sample. Otherwise, parameters of heterostructure PC films such as film thickness or stacking order have important effects on fluorescent signals. The method will be of great significance for developing the highly sensitive fluorescence-based detection.Graphical abstractA remarkable enhancement of fluorescence signal based on heterostructure photonic crystals with dual stopbands is demonstrated in comparison to that on the control sample.Research highlights► A facile approach on the fluorescent enhancement by heterostructure PCs is presented. ► Dual stopbands of heterostructure PCs overlap the excitation and emission wavelength. ► The parameters of heterostructure PCs have important effects on fluorescence signals. ► The approach provides a promising strategy for the sensitive fluorescence-based detection.

A series of highly uniform one-dimensional Ni nanochains, with diameters ranging from 20 to 200 nm, have been synthesized by a facile, template-free, wet chemical method at diverse temperature and magnetic field. Our results indicate that the crystallite size, diameter and length of the prepared nanochains depend critically on the reaction temperature. The characteristic thermodynamic cohesive energies, ΔED and ΔEL, are obtained for the formation of the Ni nanochains. In addition, the chain length also depends on the applied field because of the Zeeman energy of the magnetic Ni nanoparticles. For the morphology control, an external field is required in order to obtain axially aligned rather than dendritic nanochains. The size-dependent magnetic properties are studied systematically. The saturation magnetization is shown to reduce inversely with the chain diameter, attributable to a core−shell structure. The thickness of the shell which encloses the ferromagnetic Ni core is determined to be about 2.3−3.4 nm.

Surprisingly oxidation resistant icosahedral FePt nanoparticles showing hard-magnetic properties have been fabricated by an inert-gas condensation method with in-flight annealing. High-resolution transmission electron microscopy (HRTEM) images with sub-Angstrom resolution of the nanoparticle have been obtained with focal series reconstruction, revealing noncrystalline nature of the nanoparticle. Digital dark-field method combined with structure reconstruction as well as HRTEM simulations reveal that these nanoparticles have icosahedral structure with shell periodicity. Localized lattice relaxations have been studied by extracting the position of individual atomic columns with a precision of about ±0.002 nm. The lattice spacings of (111) planes from the surface region to the center of the icosahedra are found to decrease exponentially with shell numbers. Computational studies and energy-filtered transmission electron microscopy analyses suggest that a Pt-enriched surface layer is energetically favored and that site-specific vacancies are formed at the edges of facettes, which was experimentally observed. The presence of the Pt-enriched shell around an Fe/Pt core explains the environmental stability of the magnetic icosahedra and strongly reduces the exchange coupling between neighboring particles, thereby possibly providing the highest packing density for future magnetic storage media based on FePt nanoparticles.

The magnetism of undoped ZnS nanotetrapods, synthesized by a solvothermal method, has been investigated by magnetization measurements and first principle numerical calculations. The background magnetic impurity concentrations of Fe, Co and Ni were determined at ppm level by inductively coupled plasma mass spectrometry (ICP-MS). Hysteresis loops of weak ferromagnetism were observed, attributable to the magnetic impurities. However, the total magnetic moments analyzed from the paramagnetism are far beyond the explanations from the presence of these magnetic impurities, by about two orders of magnitude larger. It implies a different origin of the magnetic moments. Electron microscopy analysis reveals that there are defects in the sample. Numerical simulations indicate that the excessive magnetic moments might arise from the local band structure of polarized electrons associated with the defects of cation deficiency. This study elaborates on the understanding of magnetic properties in the non-magnetic II–VI semiconductor nanomaterials.

Simple oxide heterostructures have been fabricated by depositing TbMnO3 thin films on Nb:SrTiO3 substrates at different temperatures. Remarkable switching with an on/off resistance ratio of ∼5000 is found in the sample grown at 720 °C, while only tiny resistive hysteresis can be observed in the sample grown at 650 °C. A jump switching in the I–V loop at the lower resistance state with negative bias is initiated by a visible light pulse in the sample grown at 650 °C, whereas a drop switching can be observed in the sample grown at 720 °C. A trapping–detrapping process along the TbMnO3/Nb:SrTiO3 interfaces is proposed to explain the anomalous photoresponse.

Active, robust, and low-cost catalysis is a key component for the commercialization of efficient catalysts. The development of effective strategies for the synthesis and processing of bimetallic nanoparticles with controllable size and composition is an important approach to the catalyst preparation. In this paper, a noble metal catalyzed chemical growth process has been developed. Nearly monodispersed bimetallic NiPt hollow spheres with an ultrathin shell (2–3 nm) have been successfully synthesized. Size and composition of the NiPt nanospheres has been conveniently tuned by introducing suitable amounts of precursory molecules. The solid, hollow as well as the jingle bell NiPt nanostructures are sequentially observed as results of the catalytic growth and alloying effect of Pt. Also demonstrated are the pronounced decay-resistant effects of Ni doping on the electrocatalytic properties. The excellent electrocatalytic activity and stability make the bimetallic NiPt hollow spheres promising candidates for catalysts and sensing materials.

A fluorescence-amplifying method based on photonic crystal (PC) has been demonstrated for trace TNT detection. The fluorescence enhancement for TNT detection on the optimized PC can be up to 60.6-fold in comparison to that of the control sample, which combines the slow photon effect of PC and large surface areas of the inverse opal structure. Furthermore, the quenching efficiency of the PC-based sensor achieves 80% after exposure to TNT vapor for 300 s. The results suggest that the fluorescence-amplifying method based on PC has enormous potential for the development of highly efficient fluorescence sensors toward detection of trace TNT or other explosives.

NiPt hollow spheres decorated by Pt nanoparticles were synthesized by a facile wet chemical route through galvanic replacement. In situ STEM imaging and 3D reconstruction were performed to evidence the migration of Pt atoms during catalysis of CO oxidation, providing a practical insight into the structural stability of bimetallic catalysts.