The contact resistances of multilayered Sn/Ag electroplating with a 50 nm-thick Ag-Sn alloy film as Ag 3 Sn nano-flakes in 50-200 nm across on copper alloys were investigated after aging at ambient temperatures of 150, 175, and 200 ℃ for 120 h to 3000 h in air. The microstructures and surface characteristics of the Sn/Ag coatings after aging at different temperatures and periods were elaborated using SEM, FE-SEM, XRD, TEM, GDOES, and AES. The Sn/Ag coatings exhibited low and stable contact resistances equivalent to that of as-plated sample even after aging at 200 ℃ for 3000 h, compared to the ever-increasing contact resistances for conventional reflowed Sn coatings without Ag plating, especially at the low-load side. The excellent stability of the contact resistance of the multilayered Sn/Ag coatings can be ascribed mainly to Ag 3 Sn microparticles that are agglutinated on the coating surfaces, and to their good oxidizing resistance, irrespective of the oxidation of Cu-Sn alloys during aging. Moreover, the oxide films on the Sn/Ag coatings after aging were much thinner than those on the reflowed Sn coatings. In particular, a tiny amount of Ag was included the Cu-Sn intermetallic compounds and agglutinated at the Cu 3 Sn/Cu interface with aging. This phenomenon can be attributed to the inward Ag diffusion countered against the outward Cu diffusion from the base materials, which enhanced the anti-oxidation and adhesion characteristics of the coatings, thus leading to a high reliability under high-temperature circumstance for electrical devices in automotive applications.

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The hydrogen embrittlement of SK85 high-strength steel sheets was evaluated using a three-point bending test. The effects of electroplating each with zinc, zincSiO 2 , zincnickel, and zincnickelSiO 2 on hydrogen embrittlement were examined by baking the electroplated steel specimen. Each electroplating type caused hydrogen embrittlement, which was promoted by hydrogen, owing to the reduction due to hydrogen ions during electroplating. The hydrogen embrittlement of both zinc-electroplated and zincSiO 2 -electroplated SK85 steel continued after baking for 24 hours at 200°C, but that of the zincnickel-electroplated and zincnickelSiO 2 -electroplated SK85 steel ceased. Furthermore, TDA revealed that the diffusible hydrogen at approximately 200°C, which was caused because of hydrogen embrittlement, was desorbed from all the electroplated specimens before the baking. However, after the baking, this diffusible hydrogen for each specimen was not desorbed. These results indicate that the hydrogen embrittlement for zinc-based electroplated high-strength steel was caused by another factor except for diffusible hydrogen. The hydrogen formed due to the electroplating was incorporated in the steel substrate, following which the hydrogen-vacancy cluster was formed in the substrate. It seems that the zinc and zincSiO 2 film provided insufficient permeability required for the formation of the hydrogen-vacancy cluster. However, zincnickel and zincnickelSiO 2 film enabled hydrogen-vacancy cluster diffusion from the substrate.

Plasmonic optical tweezers and thermophoresis are promising tools for nanomaterial manipulation. When a gold nanostructure is irradiated with laser light, an electric field around the nanostructure is enhanced because of the localized surface plasmon resonance, which increases the optical radiation pressure applied to the nanomaterials. In addition, a temperature gradient is also generated by the photothermal conversion, and thermophoretic force is then generated. This study numerically evaluated the electric and temperature fields induced by the localized surface plasmon resonance between two gold nanostructures. Here, we focused on the effect of the gap width between nanostructures on the optical radiation pressure and thermophoretic force. The simulation results show that the electric field is locally enhanced according to the gap width, but the effect on the temperature rise due to the photothermal heating is small. This fact suggests that the gap effect between the nanostructures is particularly dominant in nanomanipulation using optical force, whereas it has little effect in nanomanipulation using thermophoresis.

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