Crystalline Copper Nanowires Research Articles

Beyond linearity: bent crystalline copper nanowires in the small-to-moderate regime.

Several models can describe the nonlinear response of 1D objects to bending under a concentrated load. Successive stages consisting of geometrical and, additionally, mechanical non-linearity can be identified in moderately large extensions. We provide an explicit bending moment function with terms accounting for the linearity (Euler–Bernoulli), quasi-linearity, geometrical and finally, mechanical non-linearity as global features of a moderately large elastic deformation. We apply our method, also suitable for other metals, to the experimental data of Cu nanowires (NWs) with an aspect ratio of about 16 under different concentrated loadings. The spatial distribution of strain-hardening/softening along the wire or through the cross-section is also demonstrated. As a constitutive parameter, the strain-dependent stretch modulus represents, undoubtedly, changes in the material properties as the deformation progresses. At the highest load, the Green–Lagrange strain reaches a 12.5% extension with a corresponding ultra-high strength of about 7.45 GPa at the most strained volume still in the elastic regime. The determined stretch modulus indicates a significantly lower elastic response with an approximated Young's modulus (E ≅ 65 GPa) and a third-order elastic constant, C111 ≅ −350 GPa. Surprisingly, these constants suggest a 25–35% of that of the bulk counterparts. Ultimately, the method not only provides a quantitative description of the bent Cu NWs, but also indicates the robustness of the theory of nonlinear elasticity.

Bio-based synthesis of oxidation resistant copper nanowires using an aqueous plant extract

Copper nanowires have recently emerged as promising nanomaterials for transparent conducting electrodes applications, however, their production commonly involves the use of harmful reagents. In this study, we describe for the first time a simple and cost-effective bio-based synthesis of copper nanowires using an aqueous plant extract (Eucalyptus globulus) as the reducing/stabilizing agent and oleic acid and oleylamine as surfactants. Well-dispersed crystalline copper nanowires (λmáx = 584–613 nm) were obtained with average diameters in the nanometric range (44 and 145 nm) and lengths in the micrometric range (from 5 to dozens of micrometres) using extract concentrations between 10 and 50 mg mL−1. Moreover, the aspect ratio of these nanowires can be adjusted (from around 14–20 to 160–400) by changing the experimental conditions, namely the use of oleic acid. Phenolic compounds were found to have a key role in this bioreduction process allowing to obtain practically only nanowires (without other morphologies). Nevertheless, the use of oleic acid/oleylamine is essential to manipulate their size and aspect ratio. Most importantly, these bio-based copper nanowires were found to be resistant under storage in ethanol and when submitted to air exposure, both for 2 weeks, certainly due to the adsorption of antioxidant biomolecules (phenolic) at their surface, thus avoiding the use of other polymeric protective layers. The conductivity of the CuNWs was found to be 0.009 S cm−1. As a result, this study opens a new standpoint in this field, “closing the door” to the use of hazardous reagents and synthetic polymeric protective layers, on the production of stable copper nanowires with potential application as conductive materials.

Synthesis, Spray Deposition, and Hot-Press Transfer of Copper Nanowires for Flexible Transparent Electrodes.

We report a solution-phase approach to the synthesis of crystalline copper nanowires (Cu NWs) with an aspect ratio >1000 via a new catalytic mechanism comprising copper ions. The synthesis involves the reaction between copper(II) chloride and copper(II) acetylacetonate in a mixture of oleylamine and octadecene. Reaction parameters such as the molar ratio of precursors as well as the volume ratio of solvents offer the possibility to tune the morphology of the final product. A simple low-cost spray deposition method was used to fabricate Cu NW films on a glass substrate. Post-treatment under reducing gas (5% H2 + 95% N2) atmosphere resulted in Cu NW films with a low sheet resistance of 24.5 Ω/sq, a transmittance of T = 71% at 550 nm (including the glass substrate), and a high oxidation resistance. Moreover, the conducting Cu NW networks on a glass substrate can easily be transferred onto a polycarbonate substrate using a simple hot-press transfer method without compromising on the electrical performance. The resulting flexible transparent electrodes show excellent flexibility ( R/ Ro < 1.28) upon bending to curvatures of 1 mm radius.

The Electrochemical Response of Single Crystalline Copper Nanowires to Atmospheric Air and Aqueous Solution.

In this paper, single crystalline copper nanowires (CuNWs) have been electrochemically grown through anodic aluminum oxide template. The environmental stability of the as-obtained CuNWs in both 40% relative humidity (RH) atmosphere and 0.1 m NaOH aqueous solution has been subsequently studied. In 40% RH atmosphere, a uniform compact Cu2 O layer is formed as a function of exposure time following the logarithmic law and epitaxially covers the CuNW surfaces. It is also found that the oxide layers on CuNWs are sequentially grown when subjected to the cyclic voltammetry measurement in 0.1 m NaOH solution. An epitaxially homogeneous Cu2 O layer is initially formed over the surface of the CuNW substrates by solid-state reaction (SSR). Subsequently, the conversion of Cu2 O into epitaxial CuO based on the SSR takes place with the increase of applied potential. This CuO layer is partially dissolved in the solution forming Cu(OH)2 , which then redeposited on the CuNW surfaces (i.e., dissolution-redeposition (DR) process) giving rise to a mixed polycrystalline CuO/Cu(OH)2 layer. The further increase of applied potential allows the complete oxidation of Cu2 O into CuO to form a dual-layer structure (i.e., CuO inner layer and Cu(OH)2 outer layer) with random orientations through an enhanced DR process.

Highly Thermal Conductive Copper Nanowire Composites with Ultralow Loading: Toward Applications as Thermal Interface Materials

Thermal interface materials (TIMs) are of ever-rising importance with the development of modern microelectronic devices. However, traditional TIMs exhibit low thermal conductivity even at high loading fractions. The use of high-aspect-ratio material is beneficial to achieve low percolation threshold for nanocomposites. In this work, single crystalline copper nanowires with large aspect ratio were used as filling materials for the first time. A thermal conductivity of 2.46 W/mK was obtained at an ultralow loading fraction, ∼0.9 vol %, which was enhanced by 1350% compared with plain matrix. Such an excellent performance makes copper nanowires attractive fillers for high-performance TIMs.

Crystalline Liquid and Rubber-Like Behavior in Cu Nanowires

Via in situ TEM tensile tests on single crystalline copper nanowires with an advanced tensile device, we report here a crystalline-liquid-rubber-like (CRYS-LIQUE-R) behavior in fracturing crystalline metallic nanowires. A retractable strain of the fractured crystalline Cu nanowires can approach over 35%. This astonishing CRYS-LIQUE-R behavior of the fracturing highly strained single crystalline Cu nanowires originates from an instant release of the stored ultralarge elastic energy in the crystalline nanowires. The release of the ultralarge elastic energy was estimated to generate a huge reverse stress as high as ~10 GPa. The effective diffusion coefficient (D(eff)) increased sharply due to the consequent pressure gradient. In addition, due to the release of ultrahigh elastic energy, the estimated concomitant temperature increase was estimated as high as 0.6 Tm (Tm is the melting point of nanocrystalline Cu) on the fractured tip of the nanowires. These factors greatly enhanced the atomic diffusion process. Molecular dynamic simulations revealed that the very high reverse stress triggered dislocation nucleation and exhaustion.

Fabrication and characterization of crystalline copper nanowires by electrochemical deposition inside anodic alumina template

Copper nanowires were fabricated by electrochemical deposition inside anodic alumina template anodized on aluminum substrate. The morphology, composition and structure of the copper nanowires were characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive (EDS) and X-ray diffraction spectroscopy (XRD). The results revealed that copper nanowires were dense, continuous, highly-crystalline and uniform with diameters. The electrical properties of copper nanowires wrer characterized with two-terminal electrical measurements. Different current-voltage (I-V) characteristics of single copper nanowire were observed and possible conductive mechanisms were discussed. The crystalline copper nanowires are promising in application of future nanoelectronic devices and circuits.

Rapid and large-scale synthesis of Cu nanowires via a continuous flow solvothermal process and its application in dye-sensitized solar cells (DSSCs)

Single crystalline copper nanowires with pentagonal cross sections and large aspect ratios have been successfully prepared in high yield via a continuous flow solvothermal reduction process at a low temperature. The highly crystalline filaments exhibit the face-centered cubic structure, growing mainly along the [110] direction. Both PVP and the solvent environment play an important role for the growth of nanowires. The growth mechanism has been properly discussed. We also report the flexible transparent Cu nanowire membrane electrode fabricated by coating a polymer layer as a potential replacement for the conventional FTO electrode in dye-sensitized solar cells (DSSCs). Fabricated CuNW membranes exhibit high optical transmittance and electrical conductance, which can be controlled via the synthesis process, conveniently. The efficiency of a DSSC with CuNWs increases upto 5%. The DSSC performs as well as with a FTO electrode, which indicates that the super-high aspect ratio of the Cu nanowires offers a range of electrical transport routes to connect dye loaded photo-anodes, and such an electrode has the potential to replace conventional FTO electrodes for low-cost DSSCs applications.

Formation of CuPd and CuPt Bimetallic Nanotubes by Galvanic Replacement Reaction

A galvanic replacement reaction has been successfully applied to prepare CuPd and CuPt bimetallic nanotubes. The nanotubes were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) techniques. Ultralong, single crystalline copper nanowires (NWs) with a diameter of ∼64 nm and a length of several micrometers were used as template material. By controlling the amount of noble metal salt added, nanotubes with different compositions were obtained. After the replacement of Cu with Pt, nanotubes composed of a PtCu alloy were formed. EDS analysis revealed that the Pt content increased until about 66%. No further increase in the molar ratio resulted in any additional Pt incorporation into the alloy. As for the replacement of Cu with Pd, the thickening of the nanotubes was observed indicating that nanotubes composed of Pd nanoparticles were formed. Backscattered electron imaging and SEM-EDS re...

Tunable Synthesis of Cuprous and Cupric Oxide Nanotubes from Electrodeposited Copper Nanowires

Polycrystalline copper oxide nanostructures with different valence/oxidation states (i.e., Cu2O and CuO) were readily synthesized by thermal oxidation of single crystalline copper nanowires at relative low operating temperature (200 to 300 degrees C). Operating temperature of 200 to 250 degrees C in air oxidized copper to Cu2O and further increased temperature (i.e., 300 degrees C) led to form CuO nanostructures. The morphology of nanostructures significantly altered from nanowires to nanotubes which might be attributed to Kirkendall effect. The electrical resistivity of single copper nanowire, Cu2O and CuO nanotube were determined to be 3.4 x 10(-4), 33, and 211 omega cm, respectively.

Loading path effect on the mechanical behaviour and fivefold twinning of copper nanowires

The effect of loading path on the mechanical behaviour of single crystalline copper nanowires is investigated with molecular dynamics simulations. Different loading conditions including pre-tensile torsion and pre-torsional tension at different temperatures are taken into consideration. It is found that elastic pre-loading conditions can induce a distinct weakening on the resistance against plastic deformation under later applied loads. Meanwhile, coupled thermal and pre-loading effect can also facilitate the transformation from elasticity to plasticity. Formations of fivefold twins are observed in copper nanowires subjected to the loading path with tension after pre-torsion. These fivefold twins all form at the necking stage before fracture, and are found to be pre-torsion- and size-dependent but insensitive to the change in temperature and cross-sectional shape. The results reported here indicate that the loading path effect on the mechanical behaviour plays an important role in the formation of some special microstructures such as multiple twins in metallic nanowires.