Ultralight and Highly Conductive Silver Nanowire Aerogels for High-Performance Electromagnetic Interference Shielding

Metal-based materials possess superior electromagnetic interference (EMI) shielding performance because of their extraordinary electrical conductivity. Nevertheless, the high density and structural rigidity of metals seriously limit their applicability in portable and wearable electronic equipment. A common method for reducing the density of metal-based materials is to prepare metal nanowire aerogels by freeze-drying, but the weak connection among the nanowires results in poor mechanical and electrical properties. Herein, a facile approach is developed for the one-step synthesis of silver nanowire (AgNW) aerogels with ultralow density, good flexibility, high electrical conductivity, and a robust structure. The gel is directly formed by in situ assembly of AgNWs. The end-to-end nanojoining of AgNWs contributes to constructing an interconnected three-dimensional (3D) network, resulting in improved mechanical and electrical properties. The AgNW aerogel with an ultralow density of 4.87 mg cm^-3 demonstrates a high electrical conductivity of 4584 S m^-1. Moreover, the porous structure of the AgNW aerogel provides numerous interfaces for multiple reflections and scattering of EM waves, allowing them to be continuously absorbed and dissipated within the aerogel. Thus, the AgNW aerogel exhibits a superb EMI shielding effectiveness (SE) of 109.3 dB and a normalized surface specific SE (SSE/t, calculated as the SE divided by the density and thickness) of 353 183 dB cm² g^-1, significantly above that of previously known shielding materials. This work provides a new route for preparing high-performance metal nanowire aerogels and their great potential in EMI shielding.

Room-temperature nanojoining of silver nanowires by graphene oxide for highly conductive flexible transparent electrodes

Flexible transparent electrodes for touch panels, solar cells, and wearable electronics are in great demand in recent years, and the silver nanowire (AgNW) flexible transparent electrode (FTE) is among the top candidates due to its excellent light transmittance and flexibility and the highest conductivity of silver among all metals. However, the conductivity of an AgNWs network has long been limited by the large contact resistance. Here we show a room-temperature solution process to tackle the challenge by nanojoining AgNWs with two-dimensional graphene oxide (GO). The conductivity of the AgNWs network is improved 18 times due to the enhanced junctions between AgNWs by the coated GOs, and the AgNW-GO FTE exhibits a low sheet resistance of 23 Ohm sq^-1and 88% light transmittance. It is stable under high temperature and current and their flexibility is intact after 1000 cycles of bending. Measurements of a bifunctional electrochromic device shows the high performance of the AgNW-GO FTE as a FTE.

Investigation of Shear Strength and Microstructure Formation of Joined Ni Superalloys Using Ni Nanopastes

By using Ni nanoparticles, the bonding of Ni base superalloys can be achieved with shear strengths well above 200 MPa in a joining process at comparatively low temperatures between 675 °C and 975 °C. This is enabled due to the high surface-to-volume ratio of nanoparticles, which leads to distinctly lower melting and sintering temperatures than those of the corresponding bulk material. The nanoparticles in this study are employed in high-metal nanopastes, whereby different chemical compositions of the pastes and different sizes of Ni nanoparticles were investigated. The results for the joining of Ni base superalloys showed that both size and composition had a significant influence on the achievable strengths. In addition, an extensive examination was conducted to reveal the influence of the process parameters joining temperature, holding time and joining pressure on the shear strengths as well as microstructure. It was shown that the temperature exerted the most influence on the strengths and the microstructure. The joining pressure also had a significant influence. The holding time, on the other hand, did not have a major influence on the strengths and in some cases even showed an unexpected behavior, as the values decreased for some combinations with longer holding time.

Synthesis of Free-Standing Silver Foam via Oriented and Additive Nanojoining

Silver foams with high porosity and electrical conductivity have many potential applications in energy storage, catalysis, and fuel cells. However, its application is largely hindered by the low efficiency of complicated synthesis processes. In this work, a facile and rapid bottom-up fabrication of silver foams in an aqueous solution allowing large-scale production through oriented and additive nanojoining of silver nanoplate building blocks is reported. Self-assembling of as-grown silver nanoplates facilitates the oriented nanoscale joining to align the atomic lattice, and the local additive of silver promotes diffusion and interconnection at room temperature to realize a rapid synthesis process. The freeze-dried silver foam exhibits a porosity of 95.45%, an ultralow density of 61 mg·cm^-3, low thermal conductivity of 0.29 W·m^-1·K^-1, and high electrical conductivity of 8086 S·m^-1. This oriented and locally additive nanojoining process presents a new strategy to fabricate silver foams that may also inspire the fabrications of other metal foams.

One-Step Fabrication of 3D Nanohierarchical Nickel Nanomace Array To Sinter with Silver NPs and the Interfacial Analysis

Three-dimensional (3D) nanohierarchical Ni nanomace (Ni NM) array was fabricated on copper substrate by only one step with electroplating method, the unique structure was covered with Au film (Ni/Au NM) without changing its morphology, and in the following step, it was sintered with silver nanoparticle (Ag NP) paste. The structure of the Ni NM array and its surface morphology were characterized by X-ray diffraction, scanning electron microscope (SEM), and atomic force microscope. The sintered interface was investigated by SEM, transmission electron microscopy, and energy-dispersive X-ray spectroscopy to analyze the sintering mechanism. The results showed that a metallurgical bond was successfully achieved at 250 °C without any gas or vacuum shield and extra pressure. The Cu substrate with Ni/Au NM array was able to join with the Ag NP paste without obvious voids. Due to the compatible chemical potential between Ag NPs and Ni/Au NM array, the Au element was able to diffuse into the Ag layer with about 800 nm distance. Based on the excellent 3D nanohierarchical structure, the shear strength of Ni/Au NM array was 6 times stronger than the flat Ni/Au coated substrate. It turned out that the substrate surface played a crucial role in improving the shear strength and sintering efficiency. The 3D Ni NM array had achieved an excellent bonding interface and had great potential application in the microelectronics packaging field.