金クラスターの変形機構と力学特性に関する分子動力学シミュレーション

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Inelastic deformation of gold (Au) cluster is investigated by using molecular dynamics (MD) simulations. We performed compression and unloading test by computer simulation, where two silicon (Si) plates approach each other and push single Au cluster of 4 nm, 8 nm or 12 nm diameter in between. The potential function we utilized for Au-Au interaction is an embedded atom method (EAM) type proposed by Cai et al. for intermetallic alloys. On the other hand, the interactions between Si and Au atoms are developed on the Lennard-Jones framework by assessing the interaction force obtained by the AFM experiment. By using common neighbor analysis (CNA) suitably used in crystalline structures, initial f.c.c. structure once decreases in compression, but is then recovered in unloading. From stress-strain curves, it is understood that these nano-sized Au clusters possess tremendously large recovery strain in unloading after compression. The large recovery strain is estimated at 10% in average. Smaller cluster tends to show larger recovery strain depending on temperature. The large recovery strain may lead to the possibility of superelastic response of the Au cluster. The present paper also discusses the cause of large recovery appeared in whole shape and clarifies the mechanism of characteristic rearrangement of atoms. By compression, stacking faults are introduced inside the cluster, and then twin deformation occurs with crystalline rotation. In unloading, large recovery strain is obtained.
日本材料学会の論文

金クラスターの変形機構と力学特性に関する分子動力学シミュレーション

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