Fusion of metallic nanowires (NWs) is of increasing interest for fabricating printed devices. Atomistic simulations of inter-NW neck growth during thermal fusion of vertically stacked silver nanowires (NWs) with nonorthogonal axes are performed, a geometric configuration that is commonly seen in applications. High NW rotation during fusion is uncovered surprisingly and found that it accelerates inter-NW neck growth beyond that explainable by conventional geometric arguments. Rotation-regulated surface diffusion and dislocation generation are found to be the culpable mechanisms and are shown to be dominant in distinct regimes of initial NW orientation. Motivated by these atomistic observations, an original analytical model of inter-NW neck growth is formulated and validated. The model accurately predicts the unusual trends in neck growth with six orders of magnitude lesser computational effort than atomistic simulations. Further, it can handle nonisothermal temperature histories over millisecond time scales for NWs up to 100 nm in diameter, a capability that is beyond the reach of typical atomistic simulations. The impact of the revealed spatial disparity of nanoscale neck growth on the properties of random-packed NW assemblies, and the foundational role of the model in rational design and processing of printed multi-NW assemblies for a range of applications are discussed.
Integrating nanoparticle (NP)-based electrically conductive elements inside additive manufactured parts has a high potential for next-generation smart structures. We investigate, a novel technique in which mixed silver nanowires (NW) and nanospheres (NS) are printed as interconnects and sintered using out-of-chamber Intense Pulsed Light (IPL) sintering inside 3D printed thermally sensitive Acrylonitrile Butadiene Styrene (ABS) and Polylactide (PLA) polymer structures. The inclusion of NWs with the typically used NSs is found to realize dual advantages of no thermal damage of the polymers and a that is much lesser resistivity than the state-of-the-art (13.1 μΩ-cm) only 8X higher than bulk silver. Resistivity decreases with a greater percentage of NW content. On the contrary, the NS-only sample didn’t show any conductivity even after IPL sintering because the wavy feature of 3D printed surface didn’t allow NSs to bond. Even though a greater reduction of resistivity is achieved due to IPL, sintering temperature was below 97°C and maximum sintering time reported is 0.75 seconds which cumulatively resulted in damage-free substrates. When dynamic resistivity is analyzed during polymer overprinting on interconnects, four different resistance trends are seen and explained here. Surprisingly, overprinting on the post-IPL interconnect to fully embed the interconnect inside the structure causes a further resistivity reduction to 11.8 μΩ-cm as well.
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