Cu-Ag Core-shell Nanoparticles Research Articles

Synthesis of Cu-Ag core-shell nanoparticles and its electrochemical characterization

The Cu-Ag core-shell nanoparticles (Cu@Ag NPs) are prepared by chemical reduction method with polyvinyl pyrrolidone (PVP) was used as a capping agent, ascorbic acid (C6H8O6) and sodium borohydride (NaBH4) was used as a reducing agent. Cu@Ag NPs were synthesized with three variations of (Cu:Ag) 1:3, 1:4, and 1:5.. The uniformity of Cu@Ag NPs samples with three variations was verified by the particle size analyzer test. The sizes of Cu@Ag 1:3, 1:4, and 1:5 was obtained sequentially at the range of 270-280 nm, 300-304 nm, and 690-700 nm respectively. Indications of the successful synthesis of Cu@Ag nanoparticles can be seen from UV-Vis spectra of Cu@Ag 1:3, 1:4, and 1:5 respectively forming AgNP at wavelengths of 434 nm, 450 nm, and 428 nm Furthermore, the stability of Cu@Ag NPs was carried out over a period of 0 days, 4 days, 7 days, 11 days, and 14 days. It can be observed that the variation of 1:5 tends to be more stable as the chart continues to experience significant improvements compared to the variation of 1:3 and 1:4. The electrochemical study was then performed by applying cyclic voltammetry from 0 V to 1.8 V. It is clearly shown that the peak of Cu oxidation is appeared at a potential of 1.2 V while the peak value of Ag oxidation is at a potential of 0.9 V.

Structural and Optical Properties of Starch-Sodium Alginate Embedded with Cu-Ag Core-Shell Nanoparticles

Structural and Optical Properties of Starch-Sodium Alginate Embedded with Cu-Ag Core-Shell Nanoparticles

Cu-Ag Bimetallic Core-shell Nanoparticles in Pores of a Membrane Microreactor for Enhanced Synergistic Catalysis.

A bimetallic catalytic membrane microreactor (CMMR) with bimetallic nanoparticles in membrane pores has been fabricated via flowing synthesis. The bimetallic nanoparticle is successfully immobilized in membrane pores along its thickness direction. Enhanced synergistic catalysis can be expected in this CMMR. As a concept-of-proof, Cu-Ag core-shell nanoparticles have been fabricated and immobilized in membrane pores for p-nitrophenol (p-NP) hydrogenation. Transmission electron microscopy (TEM) for the characterization of the bimetallic core-shell nanostructure and X-ray photoelectron spectroscopy (XPS) for the characterization of the electron transfer behavior between Cu-Ag bimetal have been performed. The Ag shell on the core of Cu can improve the utilization of Ag atoms, and electron transfer between bimetallic components can promote the formation of high electron density active sites as well as active hydrogen with strong reducing properties on the Ag surface. The dispersed membrane pore can prevent nanoparticle aggregation, and the contact between the reaction fluid and catalyst is enhanced. The enhanced mass transfer can be achieved by the plug-flow mode during the process of hydrogenation catalysis. The p-NP conversion rate being over 95% can be obtained under the condition of a membrane flux of 1.59 mL·cm-2·min-1. This Cu-Ag/PES CMMR has good stability and has a potential application in industry.

Room-Temperature Coalescence of Tri-n-Octylphosphine-Oxide-Capped Cu-Ag Core-Shell Nanoparticles: Effect of Sintering Agent and/or Reducing Agent

Abstract Metal nanoparticle pastes are useful for nanoinks to form fine conductive patterns in printed electronics. This study reports a novel method for room-temperature coalescence of Cu-Ag core-shell nanoparticles (Cu@Ag NPs), which are expected to have the properties of both migration and oxidation resistance originating from Cu and Ag, respectively. First, oleylamine/oleic-acid capped Cu@Ag NPs were synthesized by the galvanic replacement method. Second, the ligand exchange reaction to tri-n-octylphosphine oxide (TOPO) was carried out on the surface of Cu@Ag NPs. Finally, TOPO-capped Cu@Ag NPs were dipped into methanol containing a sintering agent and/or a reducing agent. When HCl was added as a sintering agent to methanol, the crystallite size of Cu@Ag NPs significantly increased. Furthermore, the almost complete removal of organic compounds and suppression of significant oxidation of Ag and Cu were observed. In consideration of these results, a Cu/Ag conductive thin film was prepared from TOPO-capped Cu@Ag NPs by dipping into methanol containing HCl at room temperature under air atmosphere. Electrical resistivity of the obtained Cu/Ag thin film was (5.1 ± 1.7) × 10−5 Ω m. Microstructural observations and X-ray diffractions of the Cu/Ag thin film revealed that Cu@Ag NPs effectively coalesced at room temperature with slight oxidation.

Towards understanding the facile synthesis of well-covered Cu-Ag core-shell nanoparticles from a complexing model

In this study, a facile and nontoxic synthetic method of well-covered Cu-Ag core-shell nanoparticles (Cu@Ag NPs) was determined. Through chemical reduction reaction in a modified silver ammonia solution with gelatin additive, the as-synthesized Cu@Ag NPs showed attractive comprehensive characteristics, including small and narrow size distribution, low proportion of Ag, dense and uniform Ag shell, good dispersibility, good sphericity, and desirable oxidation resistance. Based on electrochemical analysis, a complexing model was proposed to explain the effects of gelatin on the deposition of Ag. It revealed that the gelatin acted as not only the steric hindrance but also the complexing agent and diffusivity modifier. The gelatin addition could increase the stability and decrease the decoupling rate of complexed Ag ions, thus leading to significant negative shift of the deposition potential and decrease of the deposition rate, promoting the formation of finer and thinner Ag shell. Our study proposes an applicable approach for the synthesis of Cu@Ag core-shell nanoparticles, and the complexing model can provide a theoretical tool to describe the effects of complexing agent on the synthesis of Cu@Ag and other bimetallic nanoparticles.

Multi-particle molecular dynamics simulation: shell thickness effects on sintering process of Cu-Ag core-shell nanoparticles

As a substitute for pure silver nanoparticles, Cu-Ag core-shell nanoparticles (CS NPs) have received significant attention in the fields of electronic packaging and conductive inks. Shell thickness is one of the important factors affecting the sintering performance of CS NPs. In this work, we conduct a multi-particle molecular dynamics simulation to investigate the shell thickness effects on the sintering process of Cu-Ag CS NPs at different temperatures. The results show that the less the shell thickness, the lower the potential energy decrease during sintering. This study mainly involves two sintering mechanisms, plastic deformation mechanism, and diffusion mechanism. During the sintering process, the contribution of the plastic deformation mechanism decrease with the layer thickness decreases. As for the diffusion mechanism, the self-diffusion coefficient at 500 K is much lower than that at higher temperatures. However, the slow diffusion can increase the densification by filling the pores generated in the initial stage of sintering. The self-diffusion coefficient of surface atoms increases as the shell thickness decreases. The decrease of shell thickness can produce more lattice mismatches at the core-shell interface, which hinders crystallization during the sintering process. And we found more amorphous Ag atoms at the sintering neck. A higher sintering temperature can induce the diffusion of Cu atom near the core-shell interface, especially for the particle with thinner shell thickness. Some diffused Cu atoms were found in the neck area of sintered CS NP of Ag5Cu3.5 and Ag5Cu4 at 700 K. Moreover, the sintered neck partly composed of Cu atoms was observed in sintered Ag5Cu4 CS NPs at 900 K.

An improved pretreatment method for the fabrication of Cu-Ag core-shell nanoparticles

A pretreatment method of nitric acid pickling is applied in the fabrication of Cu-Ag core-shell nanoparticles. By tuning the pH value and the concentration of Cu ions after acid pickling, the cleaning and separation process can be eliminated. This simplified pretreatment process can prevent the oxidation and particle loss. The as-prepared Cu@Ag nanoparticles show promising coating quality, oxidation resistance and quasi-spherical core-shell microstructure. Such a pretreatment method provided by this study could be promising in further rapid fabrication of Cu-Ag core-shell nanoparticles.

Tuning of Optical Parameters of Polyvinyl Alcohol by Cu-Ag Core-Shell Nanoparticles

In this work, Cu-Ag core-shell nanoparticles were synthesized via a chemical reduction method. Subsequently, Cu-Ag core-shell nanoparticles were dispersed into polyvinyl alcohol (PVA) and films were grown by solution casting technique. High resolution transmission electron microscopy (HRTEM) was utilized to confirm the synthesis of Cu-Ag core-shell nanoparticles. Optical properties of fabricated films were investigated using UV-Visible absorption spectroscopy. Analysis of absorption data indicated that the band gap of PVA decreases with increasing Cu-Ag core-shell nanoparticles concentration while urbach’s energy increases. The possible reasons for the observed changes in optical parameters of PVA with the incorporation of Cu-Ag core-shell nanoparticles have been discussed in detail.

Synthesis of ˜10 nm size Cu/Ag core-shell nanoparticles stabilized by an ethoxylated carboxylic acid for conductive ink

Bimetallic Cu-Ag Core-shell nanoparticles were synthesized by the reduction of copper 2-[2-(2-methoxyethoxy)ethoxy]acetate with hydrazine hydrate in benzyl alcohol followed by the reduction of silver ions on the copper surface using a galvanic replacement reaction. The morphology and Core-shell structure of the nanoparticles so prepared were investigated by X-ray phase analysis, high-resolution transmission electron microscopy, X-ray energy dispersive spectrometry and optical spectroscopy. The effect of synthesis conditions such as temperature, synthesis time, silver-to-copper molar ratio, and the rate of addition of silver nitrate to the system on thickness, density, and uniformity of the silver shell was studied. The silver coated copper nanoparticles were shown to exhibit improved stability to oxidation.

Room temperature sintering of Cu-Ag core-shell nanoparticles conductive inks for printed electronics

The monodisperse Cu-Ag core-shell nanoparticles (Cu@Ag NPs) for electric conductive inks were successfully prepared by a simple two-step process consisting of thermal decomposition and galvanic displacement. It was found that 20 mol.% coverage of Ag enabled Cu@Ag NPs oxidation resisting with air. A new approach to achieve coalescence and sintering of Cu@Ag NPs at room temperature was proposed. 1-amino-2-propanol (MIPA), hydrophilic amine with a short C-chain, was first applied to replace the strong stabilizer, the strong stabilizer oleylamine (OAM) adsorbed on particles, thereby obtained preliminary agglomeration and hydrophobic -to- hydrophilic transition to improve the wetting capability of electrolyte solution on the surface of metal film. Then, the reducing electrolyte NaBH4 solution was used as the destabilizing agent to deeply coalesce particles, and also inhibit the electrochemical corrosion. It takes only a few minutes to achieve sintering in air at room temperature. Due to the effective sintering at room temperature, the conductive patterns could be formed on thermo-sensitive substrates. The eventual resistivity was found to be as low as 36.3 μΩ·cm.

A green approach of synthesizing of Cu-Ag core-shell nanoparticles and their sintering behavior for printed electronics

In this article, uniform and anti-oxidative Cu-Ag core-shell nanoparticles with average particle diameter of 50 nm and Ag/Cu atomic ratio of 1/10 were synthesized by an environmental-friendly method. The morphology and core-shell structure of the obtained nanoparticles were observed through scanning electron microscope, transmission electron microscopy, energy-dispersive spectroscopy, and x-ray diffraction. Conductive inks were prepared by mixing the synthesized nanoparticles with the mixture of ethylene glycol and ethanol. The structure evolution and electrical resistivity of the Cu-Ag core-shell nanoparticle deposits were investigated upon heating up to 350 °C in comparison with pure Cu nanoparticles with similar sizes. A sintering mechanism was proposed to understand the sintering behavior of the Cu-Ag core-shell nanoparticles. It showed that dewetting of Ag shell through surface diffusion could effectively improve sintering performance at lower temperature besides its protection of Cu core from oxidation up to 156.3 °C.

Room temperature nanojoining of Cu-Ag core-shell nanoparticles and nanowires

Room temperature (Troom, 300 K) nanojoining of Ag has been widely employed in fabrication of microelectronic applications where the shapes and structures of microelectronic components must be maintained. In this research, the joining processes of pure Ag nanoparticles (NPs), Cu-Ag core-shell NPs, and nanowires (NWs) are studied using molecular dynamics simulations at Troom. The evolution of densification, potential energy, and structural deformation during joining process are analyzed to identify joining mechanisms. Depending on geometry, different joining mechanisms including crystallization-amorphization, reorientation, Shockley partial dislocation are determined. A three-stage joining scenario is observed in both joining process of NPs and NWs. Besides, the Cu core does not participate in all joining processes, however, it enhances the mobility of Ag shell atoms, contributing to a higher densification and bonding strength at Troom, compared with pure Ag nanomaterials. The tensile test shows that the nanojoint bears higher rupture strength than the core-shell NW itself. This study deepens understanding in the underlying joining mechanisms and thus nanojoint with desirable thermal, electrical, and mechanical properties could be potentially achieved.

Photonic nanomanufacturing of high performance energy devices on flexible substrates

The authors have investigated various photonic processing for various energy devices on flexible substrates with nanoinks. For printable electronics, different conducting nanoinks are developed, including silver nanowires, silver nanoplates, Cu-Ag core-shell nanoparticles, graphene oxide, and graphene. The authors showed that these inks are enabling for direct writing of antenna on paper for radio frequency (RF) energy harvesting, potentially for wireless charging application. For curing printed nanoinks and nanopastes, the authors compared four kinds of methods: chemical activated self-sintering, thermal sintering, photonic sintering with flash light, and athermal sintering with ultrafast fiber laser irradiation. The authors also developed an innovative and facile approach to fabricate supercapacitors on flexible substrates with femtosecond laser writing and photonic reduction. Au-reduced graphene oxide nanocomposite is used for electrical electrodes and collectors. Unlike previous studies, collectors are fabricated through conventional photolithography gold electrodes is directly written by femtosecond laser reduction of Au ions. The authors found that gold nanoparticles can be well sintered on the surface of reduced graphene. The reduced graphene also work as glues to bridge the electrical interconnection. The measured conductivity of Au/reduced graphene reaches 10% of that of bulk gold. By optimizing an interdigital structure, the areal capacitor is achieved as 1.5 mF/cm2.

Cu-Ag core–shell nanoparticles with enhanced oxidation stability for printed electronics

In this work, we synthesized uniform Cu–Ag core–shell nanoparticles using a facile two-step process that consists of thermal decomposition and galvanic displacement methods. The core–shell structure of these nanoparticles was confirmed through characterization using transmission electron microscopy, energy-dispersive spectroscopy, and x-ray diffraction. Furthermore, we investigated the oxidation stability of the Cu–Ag core–shell nanoparticles in detail. Both qualitative and quantitative x-ray photoelectron spectroscopy analyses confirm that the Cu–Ag core–shell nanoparticles have considerably higher oxidation stability than Cu nanoparticles. Finally, we formulated a conductive ink using the synthesized nanoparticles and coated it onto glass substrates. Following the sintering process, we compared the resistivity of the Cu–Ag core–shell nanoparticles with that of the Cu nanoparticles. The results of this study clearly show that the Cu–Ag core–shell nanoparticles can potentially be used as an alternative to Ag nanoparticles because of their superior oxidation stability and electrical properties.

Energy-filtered electron microscopy for imaging core–shell nanostructures

CuAg core–shell nanoparticles are synthesized by ultra-high vacuum thermal evaporation. We show on this system how the Energy-Filtered Transmission Electron Microscopy (EFTEM) technique allows one to improve the characterization by precisely pointing out the formation of core–shell arrangements in bimetallic nanoparticle assemblies. A criterion to measure the shell thickness from EFTEM images on unique core–shell nanoparticles is defined, that can be used for core–shell nanoparticles of any sizes, with shell thicknesses over 1 nm. It is based on the intensity variation along a line drawn across a core–shell nanoparticle on a EFTEM image. This criterion has been validated by a close comparison of the shell thickness measurements performed in this work and the ones obtained by acoustic micro-Raman spectroscopy. Using this criterion, we report a strong correlation between the size of the Cu cores and the formation of the core–shell arrangements in the nanoparticle assembly studied in this work. The influence of the Cu core shape is also evidenced. The characterisation of such systems using High Resolution TEM (HRTEM) is also discussed.

Cu-Ag core-shell nanoparticles: A direct correlation between micro-Raman and electron microscopy

Vibration modes of metal core-shell nanoparticles have been measured by confocal micro-Raman spectroscopy. Compared to a standard macroscopic scale, the number of analyzed nanoparticles is reduced to ${10}^{3}--{10}^{4}$. We observed two distinct contributions in the same Raman spectrum originating from Cu-Ag core-shell and pure Ag nanoparticles. The nanoparticle sizes are calculated and successfully compared to the ones obtained by electron microscopy on the same micron-scale area. The bond matching between Cu core and Ag shell is pointed out from a conjugated Raman and transmission electron microscopy study.