Fabrication of Y-junction Metal Nanowires by AAO Template-assisted AC Electrodeposition

In this communication,we report a synthetic approach to fabricate Y-junction Co nanowires and Y-junction Cu nanowires by AC electrodeposition using a hierarchically designed anodized aluminum oxide template.Morphology study showe that diameters of the stems and branches of the Y-junction nanowires were about 40 nm and 20 nm respectively.Structural analysis indicates that Co nanowires had a mixture of face-center-cubic and hexagonal-close-packed structures,whereas Cu nanowires had a face-center-cubic structure with a <110> texture.The Y-junction Co nanowires exhibited a longitudinal coercivity of 1300 Oe and remnant magnetization of 56%,which was affected by the growth direction and microstructure.The present method can be extended to other metallic systems and thus provides a simple and efficient way to fabricate Y-junction metal nanowires.

Effects of shape of terminus on excitation of surface plasmon modes on metal nanowires

The effects of the shape of a nanowire terminus on the excited surface plasmon polariton （SPP） modes are investigated. The conical terminus and terminus cut at a certain angle are studied. For the first time, the quantitative mode decompositions are carried out to derive the full information about excited SPP modes. It is demonstrated that tuning the shape of the terminus provides an effective method to control the composition of excited SPP modes on metal nanowires. It is especially found that some important patterns, such as the pure TM0 mode and the superposition of TM0 and HE＋1 or HE-1 modes, can be generated by some specific shapes of the terminus, whereas there is no way to produce these patterns using flat-end nanowires.

Terahertz plasmon and surface-plasmon modes in cylindrical metallic nanowires

We present a theoretical study on collective excitation modes associated with plasmon and surface-plasmon oscilla- tions in cylindrical metallic nanowires. Based on a two-subband model, the dynamical dielectric function matrix is derived under the random-phase approximation. An optic-like branch and an acoustic-like branch, which are free of Landau damp- ing, are observed for both plasmon and surface-plasmon modes. Interestingly, for surface-plasmon modes, we find that two branches of the dispersion relation curves converge at a wavevector qz = qrnax beyond which no surface-plasmon mode exists. Moreover, we examine the dependence of these excitation modes on sample parameters such as the radius of the nanowires. It is found that in metallic nanowires realized by state-of-the-art nanotechnology the intra- and inter-subband plasmon and surface-plasmon frequencies are in the terahertz bandwidth. The frequency of the optic-like modes decreases with increasing radius of the nanowires, whereas that of the acoustic-like modes is not sensitive to the variation of the radius. This study is pertinent to the application of metallic nanowires as frequency-tunable terahertz plasmonic devices.

High-performance wearable bimetallic nanowire-assisted composite foams for efficient electromagnetic interference shielding,infrared stealth,and piezoresistive sensing

With the accelerated development of modern detection and communication technology,the multifunctional wearable materials with excellent electromagnetic interference(EMI)shielding,infrared stealth,and human monitoring for improving military combat capability have received extensive attention.In this work,the lightweight melamine foam(MF)@silver nanowires(AgNWs)-iron nanowires(FeNWs)(AgFe-MF)was fabricated by a vacuum-assisted dip-coating method.Due to the porous structure and synergistic electrical and magnetic losses,this lightweight(0.115 g/cm^(3))composite foam with an ultra-low filler content(0.62 vol.%)exhibited an ideal EMI shielding efficiency of 38.4 dB.On the other hand,the AgFe-MF realized a powerful multifunctional integration.The surface saturation temperature of the AgFe-MF reached 94.2℃under a low applied voltage of 1.8 V and remained extremely fast heating and cooling response and terrific working stability,resulting in excellent infrared stealth and camouflage effects.Furthermore,taking virtues of the elastic porous conductive architecture,the AgFe-MF was utilized as a piezoresistive sensor exhibiting board compressive interval of 0–1.62 kPa(50%strain)with a good sensitivity of 0.57 kPa^(−1).This work will provide new ideas and insights for developing multifunctional wearable devices in the fields of EMI shielding,thermal management,and piezoresistive sensing.

Simultaneous fabrication of porous metals and metallic nanowires via atmospheric pressure plasma-assisted electro-dealloying

Porous metals and metallic nanowires have gained significant attention for their potential applications in catalysis, sensing, and energy storage. Developing a versatile and efficient method for fabricating these functional materials is crucial but remains challenging. Herein, we report a novel and facile electro-dealloying strategy to simultaneously fabricate porous metals and metallic nanowires using atmospheric radio-frequency(RF) capacitively coupled plasmas. The synergistic effect of the heating and plasma sheath’s electric field lead to the nonequilibrium melting of the alloy, resulting continuous ejection of the melted segments to form nanowires and let the unmelted residual parts evolve into a porous structure. This method is applicable to alloys with large melting point differences of their constituent elements, and provides a promising approach to fabricate porous metals and metallic nanowires for a wide range of functional applications.

Refit Silver Nanostructures Using a Convergent Electron Beam

Using a superionic conductor AgI thin film and a direct current electric field, we synthesize silver nanowires in diameter of about lOOnm. In order to refit the prepared nanowires, the samples are irradiated by a convergent electron beam （200 k V） inside a transmission electron microscope to prepare new small silver nanostructures. The new nanostructures are investigated in situ by high-resolution transmission electron microscope. This electron- induced crystal growth method is useful for technical applications in fabrication of nanodevices.

Ultra-dense planar metallic nanowire arrays with extremely large anisotropic optical and magnetic properties

A nanofabrication method for the production of ultra-dense planar metallic nanowire arrays scalable to wafer-size is presented. The method is based on an efficient template deposition process to grow diverse metallic nanowire arrays with extreme regularity in only two steps. First, Ⅲ-Ⅴ semiconductor substrates are irradiated by a low-energy ion beam at an elevated temperature, forming a highly ordered nanogroove pattern by a ＂reverse epitaxy＂ process due to self-assembly of surface vacancies. Second, diverse metallic nanowire arrays （Au, Fe, Ni, Co, FeAl alloy） are fabricated on these Ⅲ-Ⅴ templates by deposition at a glancing incidence angle. This method allows for the fabrication of metallic nanowire arrays with periodicities down to 45 nm scaled up to wafer-size fabrication. As typical noble and magnetic metals, the Au and Fe nanowire arrays produced here exhibited large anisotropic optical and magnetic properties, respectively. The excitation of localized surface plasmon resonances （LSPRs） of the Au nanowire arrays resulted in a high electric field enhancement, which was used to detect phthalocyanine （CoPc） in surface-enhanced Raman scattering （SERS）. Furthermore, the Fe nanowire arrays showed a very high in-plane magnetic anisotropy of approximately 412 mT, which may be the largest in-plane magnetic anisotropy field yet reported that is solely induced via shape anisotropy within the plane of a thin film.

Self-organization and tunable characteristic lengths of twodimensional hexagonal superlattices of nanowires directly grown on substrates

The organization of nano-objects on macroscopic surfaces is a key challenge for the technological improvement and implementation of nanotechnologies.For achieving operational functions,it is required to assemble nano-objects as controllable building blocks in highly ordered superstructures.Herein,we demonstrate the growth and self-organization of metallic nanowires on surfaces into hexagonal superlattices with tunable characteristic lengths depending of the stabilizing surfactants employed.Starting from a reacting mixture containing a Pt(111)substrate,a Co organometallic precursor,an amine,and an acid dissolved in a solvent,we quantify the structural evolution of superlattices of vertical single-crystalline Co nanowires on Pt,using a combined analysis of small angle neutron scattering,transmission,and scanning electron microscopies.We show the concerted steps of a spontaneous growth and self-organization of the nanowires into two-dimensional(2D)hexagonal lattice on Pt,at intervals starting from a few hours of reaction to a highly ordered superlattice at longer times.Furthermore,it is shown that apart from long-chain acid and long-chain aliphatic amine pairs used as stabilizers,the combination of a long-chain aliphatic and a short-chain aromatic ligand in the synthesis can also be employed for the nanowire superlattices development.Interestingly,the possibility to employ different pairs allows quantitative modulation of the nanowire arrays,such as the interwire distance and the packing fraction.

Nanowire-based transparent conductors for flexible electronics and optoelectronics

As the necessary components for various modern electronic and optoelectronic devices, novel transparent electrodes(TEs) with the low cost, abundance features, and comparable performance of indium tin oxide(ITO) are inquired materials. Metal nanowires(NWs) with the excellent photoelectric properties as next-generation TE candidates have widely applications in smart optoelectronic devices such as electronic skins, wearable electronics, robotic skins, flexible and stretchable displays. This review describes the synthetic strategies for the preparation of metal NWs, the assemble process for metal NW films,and the practical aspects of metal NW films with the desired properties in various low-cost, flexible,and solution-based photoelectric devices.

Bottom-up synthesis of ultrathin straight platinum nanowires： Electric field impact

We present a study of the electric field effect on electrochemically grown ultrathin, straight platinum nanowires with minimum diameter of 15 nm and length in the micrometer range, synthesized on a silicon oxide substrate between metal electrodes in H2PtC16 solution. The influence of the concentration of the platinum- containing acid and the frequency of the applied voltage on the diameter of the nanowires is discussed with a corresponding theoretical analysis. We demonstrate for the first time that the electric field profile, provided by the specific geometry of the metal electrodes, dramatically influences the growth and morphology of the nanowires. Finally, we provide guidelines for the controlled fabrication and contacting of straight, ultrathin metal wires, eliminating branching and dendritic growth, which is one of the main shortcomings of the current bottom-up nanotechnology. The proposed concept of self-assembly of thin nanowires, influenced by the electric field, potentially represents a new route for guided nanocontacting via smart design of the electrode geometry. The possible applications reach from nanoelectronics to gas sensors and biosensors.

Synthesis and purification of long copper nanowires. Application to high performance flexible transparent electrodes with and without PEDOT：PSS

We demonstrate the hydrothermal synthesis of long copper nanowires based on a simple protocol. We show that the purification of the nanowires is very important and can be achieved easily by wet treatment with glacial acetic acid. Fabrication of random networks of purified copper nanowires leads to flexible transparent electrodes with excellent optoelectronic performances （e.g., 55 Ω/sq. at 94% transparency）. The process is carried out at room temperature and no post-treatment is necessary. Hybrid materials with the conductive polymer PEDOT：PSS show similar properties （e.g., 46 Ω/sq, at 93% transparency）, with improved mechanical properties. Both electrodes were integrated in capacitive touch sensors.

Ultra-high strength yet superplasticity in a hetero-grain-sized nanocrystalline Au nanowire

Nanocrystalline metals often display a high strength up to the gigapascal level,yet they suffer from poor plasticity.Previous studies have shown that the development of hetero-sized grains can efficiently overcome the strength-ductility trade-off of nanocrystalline metals.However,whether this strategy can lead to the fabrication of nanocrystalline nanowires exhibiting both high strength and superplasticity is unclear,similar to the atomistic deformation mechanism.In this paper,we show that ultra-small nanocrystalline Au nanowires comprising grains in both the Hall–Petch and inverse Hall–Petch grain-size regions can exhibit extremely high uniform elongation(236%)and high strength(2.34 gigapascals)at room temperature.In situ atomic-scale observations revealed that the plastic deformation underwent two stages.In the first stage,the super-elongation ability originated from the intergrain plasticity of small grains via mechanisms such as grain boundary migration and grain rotation.This intergrain plasticity caused the grains in the heterogeneous-structured nanowires to grow very large.In the second stage,the superelongation ability originated from intragrain plasticity accompanied by the diffusion of surface atoms.Our results show that the hetero-grain-sized nanocrystalline nanowires,comprising grains with sizes both in the strongest Hall–Petch effect region and the inverse Hall–Petch effect region,were simultaneously ultrastrong and ductile.They displayed neither a strength-ductility trade-off nor plastic instability.

Research Progress of Nanomaterials-Based Sensors for Food Safety

With the improvement of people’s requirements for food quality,food safety has become the focus of society.More and more researchers continue to develop specific and convenient biochemical sensors for the detection of certain components in food,which also imposes higher requirements for the structure and performance of nanomaterials.Biochemical sensors based on carbon nanotubes,metal nanowires,nanofibers,metal-organic framework(MOF)compounds and other functional composite materials have the advantages of high sensitivity,great detection speed and reliable results,and have been continuously developed and widely used in medical,environmental and food safety fields.This paper reviews the progress of research on the application of the sensors based on the above functional nanomaterials in food detection in recent years,demonstrates the advantages brought by the functional composite materials,and discusses the challenges faced by the functional nanomaterials in the field of food safety testing,to provide an effective reference for developing functional composite material sensors for food safety testing.

Theoretical study of photon emission from single quantum dot emitter coupled to surface plasmons

Motivated by the recent pioneering advances on nanoscale plasmonics and also nanophotonics tech- nology based on the surface plasmons （SPs）, in this work, we give a master equation model in the Lindblad form and investigate the quantum optical properties of single quantum dot （QD） emitter coupled to the SPs of a metallic nanowire. Our main results demonstrate the QD luminescence results of photon emission show three distinctive regimes depending on the distance between QD and metallic nanowire, which elucidates a crossover passing from being metallic dissipative for much smaller emitter-nanowire distances to surface plasmon （SP） emission for larger separations at the vicinity of plasmonic metallic nanowire. Besides, our results also indicate that, for both the resonant case and the detuning case, through measuring QD emitter luminescence spectra and second-order correlation functions, the information about the QD emitter coupling to the SPs of the dissipative metallic nanowire can be extracted. This theoretical study will serve as an introduction to un- derstanding the nanoplasmonic imaging spectroscopy and pave a new way to realize the quantum information devices.