Influence of polarization direction, incidence angle, and geometry on near-field enhancement in two-layered gold nanowires

The influences of polarization direction, incidence angle, and geometry on near-field enhancements in two-layered gold nanowires （TGNWs） have been investigated by using the vector wave function method. When the polarization direction is perpendicular to the incidence plane, the local field factor （LFF） in TGNW decreases first and then increases with the increase in the incidence angle. The minimum LFF is observed at an incidence angle of 41°. It is found that the increase in the dielectric constant of the inner core leads to a decrease in the LFF. With the increase in the inner core radius, the LFF in TGNW increases first and then decreases, and the maximum LFF is observed at an inner core radius of 27 nm. On the other hand, when the polarization direction is parallel to the incidence plane, the collective motions of the induced electrons are enhanced gradually with the decrease in the incidence angle, and hence the near-field enhancement is increased.

Integration of microfluidic injection analysis with carbon nanomaterials/gold nanowire arrays-based biosensors for glucose detection

Carbon nanotubes(CNTs) and reduced graphene oxide(r GO) nanosheets were utilized to construct glucose biosensors in combination with gold nanowire arrays(Au NWAs), and microfluidic injection analysis driven by gravity force was used to investigate the performances of as-prepared glucose biosensors. The results demonstrated glucose biosensors based on carbon nanomaterials/Au NWAs presented excellent performance at low working potential of-0.2 V versus Ag/Ag Cl(3 mol/L KCl), such as high sensitivity, good anti-interference ability and high throughput(45 h^(-1)). The glucose biosensor based on glucose oxidase(GOx)–CNT–Au NWAs showed a wide linear range from 100 to 3,000 lmol/L with a sensitivity of 4.12 l A/cm^2 mmol/L. Furthermore, the linear range and sensitivity of GOx–r GO–Au NWAs-based glucose biosensor were 50–4,000 lmol/L and 8.59 l A/(cm^2 mmol/L), respectively, which were better than those of glucose biosensor based on GOx–CNT–Au NWAs,suggesting r GO nanosheets in combination with Au NWAs being a good platform for the construction of glucose biosensors.

Investigation of mechanical properties of twin gold crystal nanowires under uniaxial load by molecular dynamics method

Twin gold crystal nanowires, whose loading direction is parallel to the twin boundary orientation, are simulated.We calculate the nanowires under tensile or compressive loads, different length nanowires, and different twin boundary nanowires respectively. The Young modulus of nanowires under compressive load is about twice that under tensile load.The compressive properties of twin gold nanowires are superior to their tensile properties. For different length nanowires,there is a critical value of length with respect to the mechanical properties. When the length of nanowire is greater than the critical value, its mechanical properties are sensitive to length. The twin boundary spacing hardly affects the mechanical properties.

In situ atomic-scale analysis of Rayleigh instability in ultrathin gold nanowires

Comprehensive understanding of the structural/morphology stability of ultrathin （diameter 〈 10 nm） gold nanowires under real service conditions （such as under Joule heating） is a prerequisite for the reliable implementation of these emerging building blocks into functional nanoelectronics and mechatronics systems. Here, by using the in situ transmission electron microscopy （TEM） technique, we discovered that the Rayleigh instability phenomenon exists in ultrathin gold nanowires upon moderate heating. Through the controlled electron beam irradiation-induced heating mechanism （with 〈 100 ~C temperature rise）, we further quantified the effect of electron beam intensity and its dependence on Rayleigh instability in altering the geometry and morphology of the ultrathin gold nanowires. Moreover, in situ high-resolution TEM （HRTEM） observations revealed surface atomic diffusion process to be the dominating mechanism for the morphology evolution processes. Our results, with unprecedented details on the atomic-scale picture of Rayleigh instability and its underlying physics, provide critical insights on the thermal/structural stability of gold nanostructures down to a sub-10 nm level which may pave the way for their interconnect applications in future ultra- large-scale integrated ciroaits.

Efficient DNA-assisted synthesis of trans-membrane gold nanowires

Whereas electric circuits and surface-based(bio)chemical sensors are mostly constructed in-plane due to ease of manufacturing,3D microscale and nanoscale structures allow denser integration of electronic components and improved mass transport of the analyte to(bio)chemical sensor surfaces.This work reports the first out-of-plane metallic nanowire formation based on stretching of DNA through a porous membrane.We use rolling circle amplification(RCA)to generate long single-stranded DNA concatemers with one end anchored to the surface.The DNA strands are stretched through the pores in the membrane during liquid removal by forced convection.Because the liquid–air interface movement across the membrane occurs in every pore,DNA stretching across the membrane is highly efficient.The stretched DNA molecules are transformed into trans-membrane gold nanowires through gold nanoparticle hybridization and gold enhancement chemistry.A 50 fM oligonucleotide concentration,a value two orders of magnitude lower than previously reported for flat surface-based nanowire formation,was sufficient for nanowire formation.We observed nanowires in up to 2.7% of the membrane pores,leading to an across-membrane electrical conductivity reduction from open circuit to <20Ω.The simple electrical read-out offers a high signal-to-noise ratio and can also be extended for use as a biosensor due to the high specificity and scope for multiplexing offered by RCA.

Modulating the alloying mode in the doping-induced synthesis of Au-Pd nanowires

Heterogeneous doping is one effective strategy for synthesizing metal alloy nanowires.Herein,the heterogeneous doping processes of Pd on the ultrathin Au nanowires were systematically modulated and investigated.Au-Pd alloy nanowires with various morphologies and lattice structures can be obtained by adjusting the morphology of the precursor Au nanowires and the kinetics of the heterogeneous doping processes.The effects of the rate of Pd reduction and the concentration of the ligand oleylamine(OAm)on the Pd deposition and alloying mode were articulated.Generally,as the Pd deposition rate decreases,the Pd deposition and alloying mode switches from the island-forming Stransky–Krastanov(SK)mode to the epitaxial Frank-van der Merwe(FM)mode,and eventually to an unconventional twisting alloying mode,where the interdiffusion of Pd and Au causes drastic rearrangement of the lattice structure and formation of helical structures.The kinetics-related variation of alloying mode could also be observed in the Au-Ag nanowires,demonstrating a general design principle for the synthesis of alloy nanostructures.In addition,the electrocatalytic performance of various Au-Pd nanowires was evaluated,and the alloy nanowire formed via the SK mode was found to be an excellent electrocatalyst for oxygen reduction and ethanol oxidation.

Vanadium oxide assisted synthesis of networked silicon oxide nanowires and their growth dependence

Networked silicon oxide nanowires have been synthesized by VO2-assisted chemical vapor deposition at 1000 ~C on silicon substrate without supplying any gaseous or liquid Si source. Systematic study on the nanowire growth has indicated that morphology and composition of the final products are sensitive to the catalyst components, reaction atmosphere and temperature. Compared to Au and V02 as catalysts individually, co-catalysts of Au and V02 play a critical role in the formation of networked Si02 nanowires. Transmission electron microscopy （TEM） and scanning electron microscopy （SEM） observations indicate that the silicon oxide nanowires have smooth surfaces with uniform diameters of 30-100 rim, and their lengths reach several hundred micrometers. X-ray photoelectron spectroscopy （XPS） results reveal the atomic ratio of silicon to oxygen is about 1：2. Growth dependence of the networked nanowires on hydrogen and temperature is also discussed. Vapor-liquid-solid （VLS） process is proposed for the growth mechanism of the networked nanowires. It is also found that the growth mechanism of SiO2 nanowires by increasing the temperature up to 1200 ℃ changes to vapor-solid （VS） processes since wire-like structures can be formed without any catalyst or H2 gas introduced into the system.