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Nanocrystalline copper (Cu) is considered to be one of the best interconnected material in integration circuit (IC) industry, because of its ultra-low resistivity and high mechanical stability. Mechanical properties of nanocrystalline Cu are completely different from those of bulk monocrystalline Cu. These properties are of high importance in the assessment of the thermo-mechanical reliability of the interconnected IC structure. To investigate the effects of the grain sizes and temperature on the mechanical properties of nanocrystalline Cu, molecular dynamics simulations of uniaxial tensile test are performed in this study. The results show that the elastic modulus of nanocrystalline Cu with grain sizes of 4.65–12.41 nm gradually increases with the increase of the mean grain sizes, the corresponding flow stress concurrently increases, and the flow stress is proportional to the square-root of the grain size, which satisfies the inverse-Hall–Petch relation. Furthermore, the elastic modulus linearly decreases with the increase of temperature. The coupled effect of the flow stress, strain rate and temperature were elaborated by the Arrhenius hyperbolic sinusoidal model. Meanwhile, the deformation activation energy of nanocrystalline Cu for various grain sizes were obtained. All of the tensile simulation tests confirmed that the mechanism of plastic deformation for nanocrystalline Cu with 4.65–12.41 nm grain sizes is mainly specific to the grain boundary sliding and grain rotation. The dislocation nucleation and migration, which is usually the deformation mechanism of plasticity for macroscopic materials, is no longer the dominant factor for nanocrystalline Cu.

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The electrical performance evolution of a system combining photovoltaic (PV) and thermoelectric generator (TE) is evaluated using thermal resistance calculations. The hybrid system combines a commercial monocrystalline silicon PV and a commercial bismuth telluride TE that is integrated with heat sinks. Here, photovoltaic modules could be cooled using thermoelectric components, leading to an increase in its output power. Additionally, extra thermal electricity is generated from the temperature difference between the backside of photovoltaic modules and heat sinks. Compared with the PV, the photovoltaic conversion efficiency of the PV/TE integrated system is increased by 3.9 % and the total system efficiency is up to 5.9 %.

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