Ultrathin Gold Nanowires Research Articles

Preparation of Silica-Coated Ultrathin Gold Nanowires with High Morphological Stability

We demonstrated a preparation method of silica-coated straight ultrathin Au nanowires (NWs). Water-dispersive ultrathin Au NWs capped with a long-chain amidoamine derivative (C18AA) were used for silica coating. The Au NWs were partially covered with 3-mercaptopropanoic acid by the ligand exchange method, and silica coating of the Au NWs was carried out by the hydrolysis of tetraethoxysilane (TEOS) at pH > 6.7 because the shape of the Au NWs was changed under acidic conditions. The thickness of the silica layer depended on the concentration of TEOS, and the layer was able to decrease to 6-10 nm thick. We also demonstrated that the silica-coated Au NWs had high morphological stabilities against external stimuli such as a TEM electron beam, heat, and pH compared with the bare Au NWs.

A wearable and highly sensitive pressure sensor with ultrathin gold nanowires

Ultrathin gold nanowires are mechanically flexible yet robust, which are novel building blocks with potential applications in future wearable optoelectronic devices. Here we report an efficient, low-cost fabrication strategy to construct a highly sensitive, flexible pressure sensor by sandwiching ultrathin gold nanowire-impregnated tissue paper between two thin polydimethylsiloxane sheets. The entire device fabrication process is scalable, enabling facile large-area integration and patterning for mapping spatial pressure distribution. Our gold nanowires-based pressure sensors can be operated at a battery voltage of 1.5 V with low energy consumption (<30 μW), and are able to detect pressing forces as low as 13 Pa with fast response time (<17 ms), high sensitivity (>1.14 kPa(-1)) and high stability (>50,000 loading-unloading cycles). In addition, our sensor can resolve pressing, bending, torsional forces and acoustic vibrations. The superior sensing properties in conjunction with mechanical flexibility and robustness enabled real-time monitoring of blood pulses as well as detection of small vibration forces from music.

Bioelectrochemical systems with oleylamine-stabilized gold nanostructures and horseradish peroxidase for hydrogen peroxide sensor

This paper describes ultrathin gold nanowires (NWs) and nanoparticles (NPs) prepared by oleylamine (OA) synthesis and their assembly with horseradish peroxidase enzyme (HRP) for bioelectrochemical sensing of hydrogen peroxide for the first time. The immobilization of oxidoreductase enzyme HRP on the electrodes modified with OA gold nanostructures (OANSs) is discussed. The HRP-sensor characteristics, namely sensitivity, working concentration range, sensor-to-sensor and measurement-to-measurement reproducibility as well as long-term stability, are improved significantly compared to the planar thin-film sensors by using OANSs. The thin-film gold electrodes modified with OANWs and OANPs exhibit a catalytic activity towards oxidation of hydrogen peroxide with a working concentration range from 20µM to 500µM, a sensitivity of 0.031AM−1cm−2 (RSD 0.046) and 0.027AM−1cm−2 (RSD 0.045), and a detection limit of 5µM and 8µM, respectively (RSD near the detection limits was 9–12%). Our study shows that ultrathin gold nanowires and nanoparticles prepared by oleylamine synthesis are prospective materials to assemble biomolecules into functional nanoarchitectures for enzyme-based bioelectrochemical sensors, metalloprotein bioelectronics, and energy research.

Probing the effect of surface chemistry on the electrical properties of ultrathin gold nanowire sensors

Ultrathin metal nanowires are ultimately analytical tools that can be used to survey the interfacial properties of the functional groups of organic molecules immobilized on nanoelectrodes. The high ratio of surface to bulk atoms makes such ultrathin nanowires extremely electrically sensitive to adsorbates and their charge and/or polarity, although little is known about the nature of surface chemistry interactions on metallic ultrathin nanowires. Here we report the first studies about the effect of functional groups of short-chain alkanethiol molecules on the electrical resistance of ultrathin gold nanowires. We fabricated ultrathin nanowire electrical sensors based on chemiresistors using conventional microfabrication techniques, so that the contact areas were passivated to leave only the surface of the nanowires exposed to the environment. By immobilizing alkanethiol molecules with head groups such as -CH3, -NH2 and -COOH on gold nanowires, we examined how the charge proximity due to protonation/deprotonation of the functional groups affects the resistance of the sensors. Electrical measurements in air and in water only indicate that beyond the gold-sulfur moiety interactions, the interfacial charge due to the acid-base chemistry of the functional groups of the molecules has a significant impact on the electrical resistance of the wires. Our data demonstrate that the degree of dissociation of the corresponding functional groups plays a major role in enhancing the surface-sensitive resistivity of the nanowires. These results stress the importance of recognizing the effect of protonation/deprotonation of the surface chemistry on the resulting electrical sensitivity of ultrathin metal nanowires and the applicability of such sensors for studying interfacial properties using electrodes of comparable size to the electrochemical double layer.

Dendrimer-mediated hydrothermal synthesis of ultrathin gold nanowires.

We report the use of poly(amidoamine) dendrimers as stabilizers to synthesize ultrathin Au nanowires (NWs) with a diameter of 1.3 nm via a hydrothermal approach. The formation of uniform Au NWs was optimized by varying the Au/Ag salt molar ratio, dendrimer stabilizers, and reaction solvent, temperature, and time. A novel growth mechanism involving a synergic facet-dependent deposition/reduction of Ag(I) and oriented migration of Au atoms is proposed based on density functional theory calculations and the experimental results. This work can significantly expand the scope of dendrimers as stabilizers to generate metal NWs in aqueous solution that may be further functionalized for different applications.

Ultrathin Gold Nanowire-Functionalized Carbon Nanotubes for Hybrid Molecular Sensing

Carbon nanotubes (CNTs) have shown great potential as sensing component in the electrochemical field effect transistor and optical sensors, because of their extraordinary one-dimensional electronic structure, thermal conductivity, and tunable and stable near-infrared emission. However, the insolubility of CNTs due to strong van der Waals interactions limits their use in the field of nanotechnology. In this study, we demonstrate that noncovalent ultrathin gold nanowires functionalized multiwalled carbon nanotube (GNW-CNT) hybrid sensing agents show highly efficient and selective immune molecular sensing in electrochemical and near-infrared photoacoustic imaging methods. A detection limit of 0.01 ng/mL for the alpha-fetoprotein (AFP) antigen with high selectivity is shown. The extraordinary optical absorption, thermal, and electric conductivity of hybrid GNW-CNTs presented in this study could be an effective tactic to integrate imaging, sensing, and treatment functionalities.

Oleylamine-Stabilized Gold Nanostructures for Bioelectronic Assembly. Direct Electrochemistry of Cytochrome c

Methods to prepare ultrathin gold nanowires and monodisperse nanoparticles based on the intrinsic property of gold(I) ions to form aurophilic interactions stabilized by oleylamine and long-chain alkylamine have been widely explored. Due to the low thermodynamic stability of the high aspect ratio nanostructures, their conjugation and assembly into functional nanosystems have not been explored so far. One of the reasons for this is that the surface of the nanostructures is insulated by stabilization compounds, which preserve the integrity of the nanostructures but at the same time form an insulating barrier in electronic and electrochemical systems in contact areas and for the charge transfer reactions. Conjugation of a metalloprotein cytochrome c (Cyt c) with oleylamine-stabilized gold ultrathin nanowires and nanoparticles into a bioelectrochemically active nanoarchitecture is presented here for the first time. Methods of preparing and assembling the ultrathin nanowires and nanoparticles on the thin-film g...

Single electron transistors with ultra-thin Au nanowires as a single Coulomb island

Single electron transistors exhibiting transport properties based on a single Coulomb island have been fabricated using ultra-thin gold nanowires (AuNWs), which are synthesized via a chemical reduction process. The AuNWs are bottom-contacted with source and drain electrodes to avoid damaging the AuNWs under fabrication processes. We investigate the transport properties in the fabricated devices as a function of the bias and gate voltages at room and low temperatures. At 0.23 K, the periodical Coulomb oscillations and diamonds are clearly observed indicating that an individual AuNW acts as a single Coulomb island. These transport properties can be explained by the orthodox Coulomb blockade theory.

Tunability of Electronic States in Ultrathin Gold Nanowires

The electronic state in ultrathin gold nanowires is tuned by careful engineering of the device architecture via a chemical methodology. The electrons are localized to an insulating state (showing variable range hopping transport) by simply bringing them close to the substrate, while the insertion of an interlayer leads to a Tomonaga Luttinger liquid state.

Features of Transport in Ultrathin Gold Nanowire Structures

The origin of the interface formation appearing due to the realization of contacts to ultrathin gold nanowire devices is revealed. Such interfaces play an important role in transport mechanisms in nanowire structures and can determine the electrical and operating parameters of a nanodevice. Based on experimental results, the specific electrical properties of bundles of ultrathin gold nanowires fabricated by wet chemical synthesis and subsequently assembled and contacted with gold electrodes are reported. It is demonstrated that these properties are strongly affected by the monolayers of organic molecules inevitably present on the surface of the nanowires due to synthetic conditions. In particular, such layers form a potential barrier to tunneling of the electrons from contacts to the nanowires. The electric transport behavior of the investigated nanowire structures in the temperature range from 500 mK to 300 K obeys the model of thermal fluctuation-induced tunneling conduction through the nanowire-metal electrode molecular junction. Application of this model allows calculation of the parameters of the molecular potential barrier. The formation of such a molecular barrier is verified by scanning tunneling microscope (STM) and transmission electron microscope (TEM) measurements performed using a supporting graphene layer. These findings are important for designing novel nanodevices for molecular electronics on the basis of ultrathin nanowires.

Mechanically Strong, Optically Transparent, Giant Metal Superlattice Nanomembranes From Ultrathin Gold Nanowires

Metallic membranes of about 2.5 nm thick but with macroscopic lateral dimensions have been successfully fabricated from ultrathin gold nanowires. Such metallic nanomembranes are transparent, conductive and mechanically strong, with an optical transmittance of 90-97%, an electrical resistance of ∼1142 kΩ sq(-1) , and a breaking strength of ∼14 N m(-1) with a typical atomic force microscope probe.

Coulomb blockade phenomenon in ultra-thin gold nanowires

Ultra-thin gold nanowires with uniform diameters of 2 nm and lengths of over 100 μm are synthesized via the reduction of gold(III) chloride in an oleylamine matrix. The gold nanowires, dispersed on an oxidized substrate, are top-contacted with metallic electrodes to manufacture back gated transistors. We investigate the transport properties in the fabricated devices as a function of the gate voltage, the bias voltage, and the temperature. The nonlinear current-bias voltage characteristics from 7 K up to 300 K are well described by the Coulomb blockade model in a nearly one-dimensional quantum dot array (which results from the gold nanowires’ thermal fragmentation into a granular material). Our results support a picture in which the electronic transport is governed by sequential tunneling at an applied bias above the global Coulomb blockade threshold, whereas in the Coulomb blockade regime, inelastic cotunneling is dominant up to 70 K, at which point it crosses over to activated behavior. The current dependence on the gate voltage that shows irregular oscillations is well explained by the superimposition of Coulomb oscillation patterns generated by each different dot in the one-dimensional array. We find that the competitive effects of excitation energy and stochastic Coulomb blockade balance the number of current peaks observed.

Pristine, adherent ultrathin gold nanowires on substrates and between pre-defined contacts via a wet chemical route

We demonstrate a simple strategy of obtaining clean, ultrathin single crystal Au nanowires on substrates and interconnecting pre-defined contacts with an insight into the growth mechanism. The pristine nature enables electron transport measurement through such ultrathin wires and opens up possibilities of exploring its properties for a wide range of applications.

Surface dislocation nucleation mediated deformation and ultrahigh strength in sub-10-nm gold nanowires

The plastic deformation and the ultrahigh strength of metals at the nanoscale have been predicted to be controlled by surface dislocation nucleation. In situ quantitative tensile tests on individual 〈111〉 single crystalline ultrathin gold nanowires have been performed and significant load drops observed in stress-strain curves suggest the occurrence of such dislocation nucleation. High-resolution transmission electron microscopy (HRTEM) imaging and molecular dynamics simulations demonstrated that plastic deformation was indeed initiated and dominated by surface dislocation nucleation, mediating ultrahigh yield and fracture strength in sub-10-nm gold nanowires. Open image in new window

Fracture of Sub‐20nm Ultrathin Gold Nanowires

AbstractFracture of metals at the nanoscale and corresponding failure mechanisms have recently attracted considerable interest. However, quantitative in situ fracture experiments of nanoscale metals are rarely reported. Here it is shown that, under uni‐axial tensile loading, single crystalline ultrathin gold nanowires may fracture in two modes, displaying distinctively different fracture morphologies and ductility. In situ high resolution transmission electron microscopy (HRTEM) studies suggest that the unexpected brittle‐like fracture was closely related to the observed twin structures, which is very different from surface dislocation nucleation/propagation mediated mechanism in ductile fracture mode. Molecular dynamics (MD) simulations further reveal the processes of shear‐induced twin formation and damage initiation at the twin structure/free surface interface, confirming the experimentally observed differences in fracture morphology and ductility. Finally, a fracture criterion based on competition between twin formation and surface dislocation nucleation/propagation as a function of misalignment angle is discussed.

Oxidation of benzylic compounds by gold nanowires at 1 atm O2

Ultra-thin gold nanowires (GNWs), with uniform surface crystallinity, appear much more active than gold nanoclusters in benzylic compound oxidation. Ethylbenzene oxidation was used as a model reaction and a radical chain reaction mechanism was revealed by the DFT method.

Size‐ and Shape‐Selective Synthesis of Metal Nanocrystals and Nanowires Using CO as a Reducing Agent

Putting the pedal to the metal: A facile strategy for the synthesis of metal nanocrystals is demonstrated that employs carbon monoxide as a reducing agent. Highly monodisperse platinum nanocubes, spherical palladium nanocrystals, and ultrathin gold nanowires can be produced within 15 minutes. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Cold welding of ultrathin gold nanowires

The welding of metals at the nanoscale is likely to have an important role in the bottom-up fabrication of electrical and mechanical nanodevices. Existing welding techniques use local heating, requiring precise control of the heating mechanism and introducing the possibility of damage. The welding of metals without heating (or cold welding) has been demonstrated, but only at macroscopic length scales and under large applied pressures. Here, we demonstrate that single-crystalline gold nanowires with diameters between 3 and 10 nm can be cold-welded together within seconds by mechanical contact alone, and under relatively low applied pressures. High-resolution transmission electron microscopy and in situ measurements reveal that the welds are nearly perfect, with the same crystal orientation, strength and electrical conductivity as the rest of the nanowire. The high quality of the welds is attributed to the nanoscale sample dimensions, oriented-attachment mechanisms and mechanically assisted fast surface-atom diffusion. Welds are also demonstrated between gold and silver, and silver and silver, indicating that the technique may be generally applicable.

Simple and rapid synthesis of ultrathin gold nanowires, their self-assembly and application in surface-enhanced Raman scattering

A simple and one-step method to rapidly synthesize single crystalline ultrathin gold nanowires at room temperature within a few hours has been developed, and the self-assembled ultrathin gold nanowires demonstrated an intriguing application in surface-enhanced Raman scattering (SERS).

Synthesis of Gold Nanostructures with Controlled Morphologies from AuCl(Oleylamine) Complex

This review article briefly discusses the use of AuCl(oleylamine) complex as a precursor in the facile synthesis of gold nanostructures with controlled morphologies. By controlling the solvent, the added metal nanoparticles, and the reaction temperature, we have successfully prepared spherical gold nanoparticles with an average diameter of 12.7 nm, ultrathin gold nanowires with an average diameter of 1.8 nm, and ultrathin gold nanorods with an average diameter of 2 nm. Gold multipod nanostructures have also been prepared by templating against a self-destructive template of magnetic nanoparticles. In addition to the synthetic protocols, this article also provides a brief account of the mechanism responsible for forming each type of gold nanostructure.