Atomic Structure of Au-Pd Bimetallic Alloyed Nanoparticles
Atomic Structure of Au-Pd Bimetallic Alloyed Nanoparticles
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DOI：
10.1021/ja105614q
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发表时间：
2010-09-08
影响因子：
15
通讯作者：
Wang, Zhong Lin
中科院分区：
文献类型：
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作者：
Ding, Yong;Fan, Fengru;Wang, Zhong Lin
采用两步种子介导生长的方法，我们合成了具有金八面体核和钯外延壳的双金属纳米粒子（NPs）。利用高分辨率透射电子显微镜系统地研究了NPs的Au核和Pd壳层之间的失配释放机制。在包覆单原子层Pd的NPs中，表面Pd层与Au核之间的应变通过肖克利部分位错（SPDs）释放，并形成层错。对于包覆较多Pd （bbb2.0 nm）的NPs，仍然存在层错，但未发现spd。这可能是由于Au原子扩散到Pd壳层中以消除spd。同时，在界面区发现了一个长时间有序L1(1) AuPd合金相，支持了Au向Pd扩散以释放界面失配的假设。随着钯壳层数的增加，Au - Pd - NP的形状逐步从截八面体转变为立方体。双金属NPs在523 K下退火10 min后，镀有单原子层Pd的NPs表面的spd由于Au原子扩散到表层而消失，但保留了层错和L1(1) Au - Pd合金结构。当退火温度提高到800 K时，电子衍射图和衍射对比图显示NPs成为均匀的Au - Pd合金，大部分层错因退火而消失。尽管如此，一些线索仍然支持L1(1)相的存在，这表明L1(1)相在Au - Pd双金属NPs中是一个稳定的长程有序结构。
Using a two-step seed-mediated growth method, we synthesized bimetallic nanoparticles (NPs) having a gold octahedron core and a palladium epitaxial shell with controlled Pd-shell thickness. The mismatch-release mechanism between the Au core and Pd shell of the NPs was systematically investigated by high-resolution transmission electron microscopy. In the NPs coated with a single atomic layer of Pd, the strain between the surface Pd layer and the Au core is released by Shockley partial dislocations (SPDs) accompanied by the formation of stacking faults. For NPs coated with more Pd (>2 nm), the stacking faults still exist, but no SPDs are found. This may be due to the diffusion of Au atoms into the Pd shell layers to eliminate the SPDs. At the same time, a long-range ordered L1(1) AuPd alloy phase has been identified in the interface area, supporting the assumption of the diffusion of Au into Pd to release the interface mismatch. With increasing numbers of Pd shell layers, the shape of the Au Pd NP changes, step by step, from truncated-octahedral to cubic. After the bimetallic NPs were annealed at 523 K for 10 min, the SPDs at the surface of the NPs coated with a single atomic layer of Pd disappeared due to diffusion of the Au atoms into the surface layer, while the stacking faults and the L1(1) Au Pd alloyed structure remained. When the annealing temperature was increased to 800 K, electron diffraction patterns and diffraction contrast images revealed that the NPs became a uniform Au Pd alloy, and most of the stacking faults disappeared as a result of the annealing. Even so, some clues still support the existence of the L1(1) phase, which suggests that the L1(1) phase is a stable, long-range ordered structure in Au Pd bimetallic NPs.