Lattice mismatch in a bimetallic core-shell nanoparticle will cause strain in the epitaxial shell layer, and if it reaches the critical layer thickness misfit dislocations will appear in order to release the increasing strain. These defects are relevant since they will directly impact the atomic and electronic structures thereby changing the physical and chemical properties of the nanoparticles. Here we report the direct observation and evolution through aberration-corrected scanning transmission electron microscopy of dislocations in AuPd core-shell nanoparticles. Our results show that first Shockley partial dislocations (SPD) combined with stacking faults (SF) appear at the last Pd layer; then, as the shell grows the SPDs and SFs appear at the interface and combine with misfit dislocations, which finally diffuse to the free surfaces due to the alloying of Au into the Pd shell. The critical layer thickness was found to be at least 50% greater than in thin films, confirming that shells growth on nanoparticles can sustain more strain due to the tridimensional nature of the nanoparticles.

中文翻译：

---

Cs 校正 STEM 揭示的双金属核壳纳米粒子的应变释放机制

双金属核壳纳米颗粒中的晶格失配会导致外延壳层发生应变，如果达到临界层厚度，就会出现失配位错以释放增加的应变。这些缺陷是相关的，因为它们将直接影响原子和电子结构，从而改变纳米粒子的物理和化学性质。在这里，我们报告了通过像差校正的扫描透射电子显微镜对 AuPd 核壳纳米粒子中位错的直接观察和演变。我们的结果表明，第一个肖克利部分位错 (SPD) 与堆垛层错 (SF) 相结合出现在最后一个 Pd 层；然后，随着壳的生长，SPDs 和 SFs 出现在界面上并与错配位错结合，由于 Au 合金化到 Pd 壳中，最终扩散到自由表面。发现临界层厚度至少比薄膜大 50%，证实由于纳米颗粒的三维特性，纳米颗粒上的壳生长可以承受更大的应变。