Assembly Of Nanowires Research Articles

Adhesive aero-hydrogel hybrid conductor assembled from silver nanowire architectures

Conductive and adhesive hydrogels are promising materials for designing bioelectronics. To satisfy the high conductivity of bioelectronic devices, metal nanomaterials have been used to fabricate composite hydrogels. However, the fabrication of a conductive-nanomaterial-incorporated hydrogel with high performance is a great challenge because of the easy aggregation nature of conductive nanomaterials making processing difficult. Here, we report a kind of adhesive aero-hydrogel hybrid conductor (AAHC) with stretchable, adhesive and anti-bacteria properties by in situ formation of a hydrogel network in the aerogel-silver nanowires (AgNWs) assembly. The AgNWs with good conductivity are well-integrated on the inner-surface of shape-memory chitosan aerogel, which created a conductive framework to allow hydrogel back-filling. Reinforcement by the aerogel-silver makes the hybrid hydrogel tough and stretchable. Functional groups from the hydrogel allow strong adhesion to wet tissues through molecular stitches. The inherent bacteria-killing ability of silver ions endows the conductive hydrogel with excellent anti-bacteria performance. The proposed facile strategy of aerogel-assisted assembly of metal nanomaterials with hydrogel opens a new route to incorporate functional nanoscale building blocks into hydrogels.

The Effect of Electroosmotic Flow on the Dielectric Assembly of Nanowires

The assembly of nanowires is important to the manufacture of microelectronic components, and dielectrophoresis is a method of assembling nanowires with low cost, good operability, accurate positioning and high assembly efficiency. In this paper, a model of the dielectric assembly of nanowires in the microelectrode system is established, and the dielectrophoretic force and electroosmotic flow of the nanowires are analyzed, and the regulations of the dielectric assembly of nanowires is obtained. Based on the preparation of planar microelectrode pairs, the nanowire dielectric assembly experiment was performed. Through the analysis of the experimental results, the regulations of nanowire dielectric assembly are consistent with the simulation.

Morphology-Controlled Vapor Phase Growth and Characterization of One-Dimensional GaTe Nanowires and Two-Dimensional Nanosheets for Potential Visible-Light Active Photocatalysts.

Gallium telluride (GaTe) one-dimensional (1D) and two-dimensional (2D) materials have drawn much attention for high-performance optoelectronic applications because it possesses a direct bandgap for all thickness. We report the morphology-controlled vapor phase growth of 1D GaTe nanowires and 2D GaTe nanosheets by a simple physical vapor transport (PVT) approach. The surface morphology, crystal structure, phonon vibration modes, and optical property of samples were characterized and studied. The growth temperature is a key synthetic factor to control sample morphology. The 1D GaTe single crystal monoclinic nanowires were synthesized at 550 °C. The strong interlayer interaction and high surface migration of adatoms on c-sapphire enable the assembly of 1D nanowires into 2D nanosheet under 600 °C. Based on the characterization results demonstrated, we propose the van der Waals growth mechanism of 1D nanowires and 2D nanosheets. Moreover, the visible-light photocatalytic activity of 1D nanowires and 2D nanosheets was examined. Both 1D and 2D GaTe nanostructures exhibit visible-light active photocatalytic activity, suggesting that the GaTe nanostructures may be promising materials for visible light photocatalytic applications.

Photogenerated Charge Separation between Polar Crystal Facets Under a Spontaneous Electric Field

AbstractUntil now, the photogenerated charge separation mechanism is not clear in photocatalysis. Based on the structures at the atomic scale of the polar crystal facets with photocatalytic activities, a general separation model of photogenerated charge between polar facets under a spontaneous electric field is presented. This charge separation model is proven by photo‐induced selective redox reactions on polar planes, photovoltaic and rectification effects in the polar direction orientated thin films, and electric field assisted assembly and alignment of semiconductor nanowires grown along the polar direction. This polar structure is similar to a semiconductor p–n junction, which can control the movement of electronic carriers and can be used to fabricate high‐efficiency photocatalysts and electronic and optoelectronic devices based on a new principle.

Kinetics of Guided Growth of Horizontal GaN Nanowires on Flat and Faceted Sapphire Surfaces.

The bottom-up assembly of nanowires facilitates the control of their dimensions, structure, orientation and physical properties. Surface-guided growth of planar nanowires has been shown to enable their assembly and alignment on substrates during growth, thus eliminating the need for additional post-growth processes. However, accurate control and understanding of the growth of the planar nanowires were achieved only recently, and only for ZnSe and ZnS nanowires. Here, we study the growth kinetics of surface-guided planar GaN nanowires on flat and faceted sapphire surfaces, based on the previous growth model. The data are fully consistent with the same model, presenting two limiting regimes—either the Gibbs–Thomson effect controlling the growth of the thinner nanowires or surface diffusion controlling the growth of thicker ones. The results are qualitatively compared with other semiconductors surface-guided planar nanowires materials, demonstrating the generality of the growth mechanism. The rational approach enabled by this general model provides better control of the nanowire (NW) dimensions and expands the range of materials systems and possible application of NW-based devices in nanotechnology.

Solvent-Induced Assembly of Microbial Protein Nanowires into Superstructured Bundles.

Protein-based electronic biomaterials represent an attractive alternative to traditional metallic and semiconductor materials due to their environmentally benign production and purification. However, major challenges hindering further development of these materials include (1) limitations associated with processing proteins in organic solvents and (2) difficulties in forming higher-order structures or scaffolds with multilength scale control. This paper addresses both challenges, resulting in the formation of one-dimensional bundles composed of electrically conductive protein nanowires harvested from the microbes Geobacter sulfurreducens and Escherichia coli. Processing these bionanowires from common organic solvents, such as hexane, cyclohexane, and DMF, enabled the production of multilength scale structures composed of distinctly visible pili. Transmission electron microscopy revealed striking images of bundled protein nanowires up to 10 μm in length and with widths ranging from 50-500 nm (representing assembly of tens to hundreds of nanowires). Conductive atomic force microscopy confirmed the presence of an appreciable nanowire conductivity in their bundled state. These results greatly expand the possibilities for fabricating a diverse array of protein nanowire-based electronic device architectures.

Dielectrophoresis Assembly of Nanowires in a Conductive Island-based Microelectrode System

Dielectrophoresis has attracted much attention in the field of nanowire assembly because of its high precision, high efficiency. However, the research on the mechanism related to the motion trajectory in the process of nanowire assembly is still in development. In this paper, a conductive island-based microelectrode system is reported to optimize the dielectric assembly process of nanowires. The existence of conductive islands can improve the positioning accuracy of nanowires during their assembly process. A simulation model of nanowire dielectric assembly based on the conductive island-based microelectrode system is established to analyze the dielectrophoresis force and motion trajectory of the nanowire during the assembly process. The simulation results show that the final position of the nanowire is mostly located in the gap between the electrode and the conductive island due to the dielectrophoretic force in the near field. Moreover, the nanowire has a tendency to move parallel to the tangent of the electric field line due to the action of the dielectrophoretic force. Therefore, the nanowire connects the electrode and the two ends of the conductive island in parallel.

Thermal conductivity of Mg2Si1−xSnx nanowire assemblies synthesized using solid-state phase transformation of silicon nanowires

Recent studies have indicated that doping, alloying, interface-engineering and nanostructuring are some of the strategies useful for obtaining high power factors and low thermal conductivities in materials that are needed for the fabrication of highly efficient thermoelectrics. With the intent of experimentally demonstrating the use of these strategies for designing highly efficient thermoelectrics, our group has in the past reported a solid-state phase transformation strategy for converting silicon nanowires into Mg2Si nanowires and Mg2Si welded nanowire networks. In this paper, the phase transformation strategy is extended to obtain Mg2Si0.92Sn0.08 nanowires from silicon nanowires. This report discusses not only the synthesis of Mg2Si0.92Sn0.08 nanowires from silicon nanowires, but also demonstrates that it is possible to control their diameters using variations of the silicon nanowire diameters as a parameter. Moreover, thermal conductivities of the nanowire assemblies discussed in detail in this paper indicated that nanostructuring through the formation of Mg2Si0.92Sn0.08 nanowires led to a drastic decrease in their thermal conductivities.

Significant enhancement of the electrochemical performance of hierarchical Co3O4 electrodes for supercapacitors via architecture design and training activation

Binder-free Co3O4 electrodes with hierarchical structures, nanoflowers and nanowire network, were directly grown on nickel foams with a facile hydrothermal strategy and subsequent annealing treatment. The architectures of the electrodes, flowers- or nanowires-dominated, can be selectively synthesized by simply controlling the reaction time of hydrothermal synthesis. It is clarified that the nanoflowers with mesoporous petals were constructed by the assembly of nanowires, resulting in the flowers-dominated Co3O4 electrode exhibiting enhanced electrochemical performance: including high specific capacitance (2.266 and 1.91 F cm−2 at 1 and 10 mA cm−2, respectively), remarkable rate capability and superior cycle stability. A cyclic voltammetry (CV) training technique was proposed to explore the full energy storage potential of Co3O4 electrode material for supercapacitors; after trained over 200 CV cycles at the scan rate of 5 mV s−1, the specific capacitance of the flower-dominated electrode further enhanced from 2.266 to 4.472 F cm−2 at current density of 1 mA cm−2, coupled with excellent electrochemical performance: rate capability (80.3% capacity retention at 10 mA cm−2) and cycle stability (84.6% capacitive retention over 5000 GCD cycles). An asymmetric supercapacitor (ASC) was constructed by employing flower-dominated Co3O4 as positive electrode and activated carbon as negative electrode. The ASC device delivered a high energy density of 0.215 mWh cm−2 at a power density of 1.49 mW cm−2. This encouraging result reveals that the flower architecture is acceptable for electrode material and provides a highly efficient training process to significantly enhance the electrochemical performance for supercapacitors.

Extraordinary Magnetic Hardening in Nanowire Assemblies: the Geometry and Proximity Effects

AbstractBrown's theorem on coercivity of ferromagnetic materials has predicted that the coercivity level is substantially higher than in practice for all the materials studied in experiments in the past seven decades, which is known as the Brown's paradox. In this paper, a system with a coercivity close to the one predicted by Brown's theorem is investigated. Cobalt nanowires are obtained by chemical synthesis that give rise to coercive forces significantly higher than the magnetocrystalline anisotropy field, verifying the Brown's theorem. It is found that the coercivity is strongly dependent on the nanowire diameter, the alignment of the wires in an assembly, and the packing density of the assembly. An analysis based on the current experimental results and related literature reveals a coercivity ceiling in consideration of geometrical dimensions and the effective magnetic anisotropy. Quantitative information is obtained about the proximity effect on the coercivity and the magnetization which shows the correlation between the energy product and the packing density. Furthermore, it is found that by coating the nanowires with Fe, the energy density can be enhanced. These findings provide a guideline for materials design of future high‐performance permanent magnets that take advantage of shape anisotropy at the nanoscale.

In situ assembly of ultrafine AuPd nanowires as efficient electrocatalysts for ethanol electroxidation

Improving the catalytic activity and durability of the ethanol oxidation reaction (EOR) is crucial for realizing the commercialization of direct ethanol fuel cells (DEFCs). Herein, we design a facile route to fabricate AuPd nanowires as highly efficient electrocatalysts toward ethanol oxidation reaction (EOR), where AuPd nanowires were in-situ assembled through the co-reduction of HAuCl4 and PdCl2 in aqueous solution in the presence of Triton X-114 and with potassium borohydride as the reducing reagent. The surface microstructure and composition of AuPd alloyed nanowires with the diameter of 4 nm were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and high resolution-transmission electron microscopy (HR-TEM). Among the AuPd NWs series, Au8Pd3 NWs demonstrated the best electrocatalytic activity (mass activity 10,570 mA mg−1Pd) and enhanced durability for ethanol electroxidation (retained 54% after 300 cycles) among the samples. The enhanced activities in EOR can be ascribed to the synergic electronic and structural effects of AuPd NWs. This work can provide a feasible method to boost Pd-alloy based electrocatalysts for EOR in direct ethanol fuel cells.

Highly Mesoporous Hybrid Transition Metal Oxide Nanowires for Enhanced Adsorption of Rare Earth Elements from Wastewater

Removal of rare earth elements (REEs) from industrial wastewater is a continual challenge. To date, several approaches to the synthesis of nanoadsorbants for this application have been reported, although these are characterized by insufficient adsorption capacity and limitations in cycling stability. The present work reports the fabrication and performance of hierarchical hybrid transition metal oxide (TMO) nanowires deposited on carbon fibers. An ordered assembly of hybrid TMO nanowires exhibits an outstanding adsorbance of 1000 mg·g-1 of REEs with 93% recyclability. This superior performance is attributed to the unique mesoporous architecture of the nanowires, which exhibits a high surface area of 122 cm3·g-1. Further, rapid adsorption/desorption of the REEs reveals minimal morphological alteration and hence high structural stability of these hybrid TMO nanowires after multiple cycles. The ready accessibility of the adsorption sites at crystallite boundaries and the surfaces as well as rapid adsorption of the REEs on the mesoporous nanostructure facilitate considerable adsorption capacity, improved structural stability, and extended cyclability, all of which suggest the potential for this material in REE extraction.

Growth of Homogeneous Luminescent Silicon-Terbium Nanowires by One-Step Electrodeposition in Ionic Liquids.

An electrodeposition method for the growth of homogeneous silicon–terbium nanowires (NWs) with green light emission is described. The method involves template-assisted electrochemical co-deposition of Si/Tb NWs with 90-nm diameter from an electrolyte bath containing Si and Tb precursors in an ionic liquid (IL). This method of deposition is advantageous over other conventional techniques as it is relatively simple and cost-effective and avoids harsh deposition conditions. The deposited NWs are of uniform dimensions with homogeneous composition incorporating 10% of Tb and exhibit intense room temperature (RT) luminescence in the visible range due to Tb emission. These results were confirmed by combining classical characterization such as scanning electron microscopy (SEM) and photoluminescence (PL) performed on an assembly of NWs with spatially resolved experiments such as transmission electron microscopy (TEM) and cathodoluminescence (CL). This electrodeposition method provides an alternative and extremely simple approach for depositing silicon-rare earth nanostructures for optical and sensing applications.

Autocatalytic MNAzyme-integrated surface plasmon resonance biosensor for simultaneous detection of bacteria from nosocomial bloodstream infection specimens

Early accurate profiling of pathogenic bacteria in patients with nosocomial bloodstream infections (nBSIs) is crucial to optimize antibiotic therapy and patient survival. We present a novel autocatalytic Multi-component DNAzyme (MNAzyme)-integrated surface plasmon resonance (SPR) biosensor assay that rapidly and sensitively detects the DNA of three nBSI pathogenic bacteria. This strategy combines autocatalytic MNAzyme cleavage on magnetic beads, as the molecular recognition and signal amplification element, with hybridization chain reaction (HCR)-mediated nanowire assembly on SPR sensing film, as the signal readout and further amplification. Once the MNAzyme complex was activated as a biocatalyst by co-recognizing the bacterial DNA and initial probes, the MNAzyme substrate was catalytically cleaved into two DNA segments. One hybridized with immobilized probes triggering folded hairpin probes to self-assemble into massive nanowire structures via HCR on the sensing interface, and the other co-recognized the initial probes trigging another cycle of multi-turnover cleavage. As a result, the amount of cleaved DNA segments was increasing and greatly enhancing the SPR signal from the analyte. This assay system can provide the fast and quantitative analysis at low concentration (67 cfu/mL of S. aureus, 57 cfu/mL of K. pneumonia and 61 cfu/mL of E. coli, respectively) in a nonenzymatic manner. More importantly, the biosensor was successfully applied to DNA extracted from clinical blood specimens of patients with nBSIs, showing good consistence and practicability. The developed autocatalytic MNAzyme-integrated SPR biosensor provides a sensitive, rapid, reliable and culture-independent approach to efficiently determine multiple pathogenic bacteria for the early diagnosis of nBSIs.

Structural, morphological and magnetic properties of compositionally modulated CoNi nanowires

Ferromagnetic nanowires (NWs) are novel materials that offer unique magnetic properties, as the geometrical dimensions become comparable to key length scales in magnetism, such as the exchange length or the domain wall width. In this work, compositionally modulated Co1−xNix nanowires (diameter 10–15 nm) with high coercivity have been synthesized via a thermal decomposition method. The structural analysis demonstrates that the hexagonal close-packed (hcp) crystal structure and the wire-shape morphology are maintained up to Ni content of x = 0.3. Based on the shape anisotropy and orientation, the aligned Co1−xNix nanowire assemblies show that the coercivity at room temperature decreases from 11.4 to 5.4 kOe with increasing x from 0 to 0.3. The monotonous decrease in coercivity with Ni content is related to the effective magnetic anisotropy and nanowire diameter which are found to be strongly varied with Ni addition. In addition, it is found that the increase of Ni content in the nanowires brings more resistance to oxidation than the pristine Co nanowires. The exchange bias study indicates that the Ni addition leads to lower blocking temperature of the CoNiO grains and consequently the switch-on temperature for the exchange bias field shifts to low temperatures with the increase of Ni content. Further, the exchange bias behavior that is associated with the existence of antiferromagnetic and spin-glass-like states are confirmed by temperature-dependent magnetization measurements.

(Invited) Three-dimensional Free-standing Assemblies of Electrodeposited Nanowires for Photoelectrochemical and Catalytical Applications

The implementation of metal and semiconductor nanostructures in devices for catalysis, sensing, and energy conversion requires an excellent control on geometry, crystallinity and composition of the individual nanostructures, as well as its successful assembly into 2-D and 3-D architectures. In particular, nanowire ensembles offer important advantages compared to planar films including e.g. larger surface area and surface to volume ratio, and better crystalline quality.Ion-track nanotechnology is a powerful technique to create templates for the controlled synthesis of such 3-D nanowire architectures. Etched ion-track membranes are fabricated in two separate process steps: (i) sequential irradiation of polymer foils from one or various directions with swift heavy ions resulting in the creation of tracks; (ii) converting the ion tracks into nanochannels by selective chemical etching. Channel density and orientation, as well as diameter and geometry are adjusted by the irradiation and etching conditions, respectively. Afterwards, by electrodeposition in the nanochannels and subsequent removal of the polymer template 3-D assemblies of nanowires are synthesized. Since the nanowires adopt the exact shape of the host channel, their diameter can be adjusted between ~15 nm and a few µm, and their length between ~1 and several tens of µm.In this talk, we will discuss the electrochemical deposition of Au1-xAgx, Cu, and Cu2O in interconnected nanochannel networks, the characterization of the resulting 3-D nanowire assemblies, and the investigation of their photoelectrochemical and catalytical properties.

In-Plane Oriented Linear Assembly of Te Nanowires in Polydimethylsiloxane-Based Composite Film for the Enhancement of Piezoelectric Property

Flexible piezoelectric materials are attractive as empowering devices in the field of sensors, actuators and energy harvesting. Herein, we fabricate a polymer-based nanocomposite with piezoelectric property by incorporation of tellurium (Te) nanowires. Firstly, large-scale selective synthesis of uniform single crystalline tellurium nanowires with a diameter of 150 nm av. and 10 μm av. in length, can be realized by a hydrothermal process. The Te nanowires with random distribution in pre-polymer of polydimethylsiloxane (PDMS) is relocated forming linearly aligned assembly controlled by application of external AC electric field. The aligned Te-PDMS at 0.5 wt% Te content gives a maximum output voltage of 13.9 V, which is 2.4-fold comparing corresponding film with random distribution. This work provides an effective alignment of nanofillers in a viscous polymer matrix and noble method to fabricate enhance piezoelectric composite film materials.

Bioprocess-inspired preparation of silica with varied morphologies and potential in lithium storage

As one of the most delicate bioprocesses in nature, biosilicification is closely related to biosilica with various morphologies, and has provided abundant inspiration to materials synthesis. In the present study, to explore the biosilica formation process and fabricate silica with an exquisite microstructure for lithium-ion battery (LIB) electrodes, a bacterial phage (M13) is used as a biotemplate to synthesize silica with diverse morphologies: cylinders, hexagonal prisms, assemblies of smaller cylinders and nanowires. A facile ethanol bath method is conducted to coat the nanowires with nitrogen-containing carbon and carbon-coated SiO2 nanowires with mesochannels (C@msSiO2NWs) are first used as anode materials for LIBs. Attributed to the uniform carbon coating and parallel mesochannel structure, the electronic conductivity and capacity to accommodate volume variations were significantly improved. In the electrochemical performance test, the composites calcined at 750 °C (C@msSiO2NWs-750) show an impressive capacity of 653 mA h g−1 at a current density of 500 mA g−1 and stability (1000 cycles). In view of the electrochemical test outcomes, the preparation of a sophisticated structure with an outstanding potential is easily achieved via a biomimetic strategy.

Facile conversion of nickel-containing electroplating sludge into nickel-based multilevel nano-material for high-performance pseudocapacitors

The recovery of heavy metals from electroplating sludge is an important technology, which can not only reduce environmental pollution, but also serve as a secondary source of metals. However, the current techniques are either non-selective or difficult to operate, which limits its applications in recovery technologies. Herein, based on the existence of multiple metal ions in electroplating sludge, Fe and Al co-doped ultrathin α-Ni(OH)2 nanosheets embedded in Ni(HCO3)2 nanowire assembly spheres were prepared by adjusting the ratio of urea under hydrothermal condition. Under the optimum conditions, the recovery of Ni, Fe, and Al are 92.58%, 81.52%, and 61.19% respectively. In addition, at the current density of 1 A g−1, the specific capacitance of the spherical composite electrode is as high as 495.6 C g−1, and the retention rate of the initial capacity is 55.58% after 3500 cycles in 6 M KOH electrolyte, showing good cycling stability. Furthermore, the ASC device (NN-4//AC) achieved a high energy density of 30.27 Wh kg−1 at a power density of 0.37 kW kg−1. A new method for converting electroplating sludge into nickel-based energy storage materials was developed, which provided a new strategy and idea for the harmless and resourceful treatment of electroplating sludge.

FORC signatures and switching-field distributions of dipolar coupled nanowire-based hysterons

Analysis of first-order reversal curves (FORCs) is a powerful tool to probe irreversible switching events in nanomagnet assemblies. As in essence switching events are related to the intrinsic properties of the constituents and their interactions, the resulting FORC diagrams contain much information that can be cross-linked and complex to deconvolute. In order to quantify the relevant parameters that drive the FORC diagrams of arrays of perpendicularly magnetized nanomagnets, we present step-by-step simulations of assemblies of hysterons to determine the specific signatures related to different known inputs. While we explored the consequences of dipolar interactions using either mean field or magnetostatic approaches, we completed by taking the hysteron switching field distribution (SFD) as either normal or lognormal. We demonstrated that the transition between FORC diagrams composed of an isolated interaction field distribution (IFD) and a wishbone shape operates via the SFD deviation, σHsw, in the presence of a weakly dispersed interaction field. In the presence of a magnetostatic interaction field, the IFD profile is peaked and a coercive field distribution (CFD) sums to the IFD as σHsw increases. A transition between IFD + CFD and wishbone shapes is clearly demonstrated as a function of the interaction field deviation σHint. In addition, we demonstrate that whatever the considered cases, σHswcan be quantitatively extracted from the FORC diagrams within an error inferior to 10%. These findings are of interest for dipolar coupled perpendicularly magnetized nanomagnets, as in assemblies of magnetic nanowires and nanopillars, as well as bit patterned media.