Su Ding

One-Step Fabrication of Stretchable Copper Nanowire Conductors by a Fast Photonic Sintering Technique and Its Application in Wearable Devices.

Copper nanowire (CuNW) conductors have been considered to have a promising perspective in the area of stretchable electronics due to the low price and high conductivity. However, the fabrication of CuNW conductors suffers from harsh conditions, such as high temperature, reducing atmosphere, and time-consuming transfer step. Here, a simple and rapid one-step photonic sintering technique was developed to fabricate stretchable CuNW conductors on polyurethane (PU) at room temperature in air environment. It was observed that CuNWs were instantaneously deoxidized, welded and simultaneously embedded into the soft surface of PU through the one-step photonic sintering technique, after which highly conductive network and strong adhesion between CuNWs and PU substrates were achieved. The CuNW/PU conductor with sheet resistance of 22.1 Ohm/sq and transmittance of 78% was achieved by the one-step photonic sintering technique within only 20 μs in air. Besides, the CuNW/PU conductor could remain a low sheet resistance even after 1000 cycles of stretching/releasing under 10% strain. Two flexible electronic devices, wearable sensor and glove-shaped heater, were fabricated using the stretchable CuNW/PU conductor, demonstrating that our CuNW/PU conductor could be integrated into various wearable electronic devices for applications in food, clothes, and medical supplies fields.

Molecular dynamics simulation of joining process of Ag-Au nanowires and mechanical properties of the hybrid nanojoint

The nanojoining process of Ag-Au hybrid nanowires at 800K was comprehensively studied by virtue of molecular dynamics (MD) simulation. Three kinds of configurations including end-to-end, T-like and X-like were built in the simulation aiming to understand the nanojoining mechanism. The detailed dynamic evolution of atoms, crystal structure transformation and defects development during the nanojoining processes were performed. The results indicate that there are two stages in the nanojoining process of Ag-Au nanowires which are atom diffusion and new bonds formation. Temperature is a key parameter affecting both stages ascribed to the energy supply and the optimum temperature for Ag-Au nanojoint with diameter of 4.08 nm has been discussed. The mechanical properties of the nanojoint were examined with simulation of tensile test on the end-to-end joint. It was revealed that the nanojoint was strong enough to resist fracture at the joining area.

Facile synthesis of Cu–Ag hybrid nanowires with strong surface-enhanced Raman scattering sensitivity

Cu–Ag hybrid nanowires with well-defined Ag nanoparticles on the surface of Cu NWs were successfully prepared by a mild two-step method. High-resolution transmission electron microscopy (HRTEM) results indicated that the as-prepared silver nanoparticles (Ag NPs) with an average diameter of 8.4 nm were directly grown on the surface of the copper nanowires (Cu NWs) through an in situ substitutional reaction with Cu–Ag metallic bonds formed between Ag NPs and Cu NWs. Growth evolution results showed that the Ag nanoseeds were prone to grow into Ag NPs when the ratio of Cu to Ag was small while they tended to grow into Ag nanowires (NWs) as the ratio of Cu to Ag dramatically increased. Furthermore, the strong surface-enhanced Raman scattering sensitivity (SERS) effect of the as-prepared Cu–Ag hybrid NWs was verified using Rhodamine 6G (R6G) and 4-aminothiophenol (4-ATP) probes.

Sintering mechanism of the Cu–Ag core–shell nanoparticle paste at low temperature in ambient air

Copper (Cu) nanoparticle (NP) paste has emerged as a promising choice for future high power electronics. However, the application of CuNP paste is generally limited because of its easy oxidation and complex processing parameters such as high sintering temperature (∼400 °C) and necessary protection atmosphere. Although capping CuNPs with a stable layer to form core–shell NPs could improve its anti-oxidation ability, current coating methods usually required complex equipment and protection atmosphere, and there have been no reports of fabricating joints with core–shell NPs. In this paper, Cu–silver (Ag) core–shell NPs with a unique structure, i.e., tiny AgNPs with an average diameter of 6.9 nm which almost completely cover the surface of initial smooth CuNPs, after first developing them in ambient air and then using a mild two-step method, are reported. After coating the tiny AgNPs on the surface, not only was the anti-oxidation ability improved during keeping (∼2 months), but also the sintering temperature of NP paste was lowered ∼70 °C. Through in situ observation during sintering, it was found that the tiny AgNPs tended to pre-melt and pre-wet to form active quasi-liquid Ag films, after which the Cu–Ag core–shell NPs were joined by the first to be found pure Ag sintering necks. Furthermore, the application of the Cu–Ag core–shell NP paste was demonstrated by fabricating voidless joints with a shear strength of 26.5 MPa in ambient air at 250 °C, and this showed a good potential for the future applications in high power electronics.

The role of chloride ions in rapid synthesis of ultra-long silver nanowires for flexible electrodes

Ultra-long silver nanowires (AgNWs) could be an ideal material to replace the commercial used indium tin oxide in highly conductive and transparent electrodes field. In this report, AgNWs with mean length of 102 μm and even 268 μm have been synthesized through a rapid and one-step polyol method within only 40 min. The effective synthesis was contributed to the relatively high concentration of Cl− which facilitated the generation of silver five-twined seeds by heterogeneous nucleation during the nucleation process. By varying the ratio of Cl−, AgNWs with various diameters ranging from 60 to 141 nm could be obtained. Moreover, AgNWs based electrodes were prepared on paper and polyethylene terephthalate (PET) substrates and the sheet resistance of the PET based transparent electrode were measured to be 14 Ω sq−1 at optical transmittance of 87%. The mechanical properties of the ultra-long AgNWs based electrodes were also characterized.

Highly conductive and transparent copper nanowire electrodes on surface coated flexible and heat-sensitive substrates

Copper nanowire (CuNW) based flexible transparent electrodes have been extensively investigated due to their outstanding performances and low price. However, commonly used methods for processing CuNW transparent electrodes such as thermal annealing and photonic sintering inevitably damage the flexible substrates leading to low transmittance. Herein, a surface coating layer was demonstrated to protect the heat-sensitive polyethylene terephthalate (PET) polymer from being destroyed by the instantaneous high temperature during the photonic sintering process. The stable ceramic surface coating layer avoided the direct exposure of PET to intense light, further reduced the heat releasing to the bottom part of the PET, protecting the flexible PET base from destruction and ensuring high transparency for the CuNW transparent electrodes. A CuNW transparent electrode on surface coated PET (C-PET) substrates with a sheet resistance of 33 Ohm sq−1 and high transmittance of 82% has been successfully fabricated by the photonic sintering method using light intensity of 557 mJ cm−2 within several seconds in ambient conditions. The surface coating layers open a novel method to optimize the rapid photonic sintering technique for processing metal nanomaterials on heat-sensitive substrates.

Joining of silver nanoparticles by femtosecond laser irradiation method

Femtosecond laser irradiation technique is a fast, effective and convenient method to join nanoparticles which has been applied in nanotechnology. The joining of silver nanoparticles with diameter of 150 nm on silicon slices are achieved with a simple femtosecond laser technique. The rapid laser irradiation generated tiny particles due to electron emission. The joining between adjacent silver nanoparticles has been observed by neck growth due to hot spots effect. The formation of the neck is due to the concentration of electromagnetic field under the femtosecond laser irradiation through the finite difference time domain simulation.