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Epitaxial growth of Au@Ni core-shell nanocrystals prepared using a two-step reduction method

机译：两步还原法制备Au @ Ni核壳纳米晶的外延生长

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Au@Ni core-shell nanocrystals were prepared using a two-step reduction method. First, mixtures of octahedral, triangular and hexagonal platelike, decahedral, and icosahedral Au core seeds were prepared by reducing HAuCl _4 · 4H_2O in ethylene glycol (EG) using microwave (MW) heating in the presence of polyvinylpyrrolidone (PVP) as a polymer surfactant. Then, Ni shells were overgrown on Au core seeds by reducing Ni(NO_3)_2·6H_2O in EG with NaOH and PVP using oil bath heating. Resultant crystal structures were characterized using transmission electron microscopic (TEM), high-resolution TEM, TEM-energy dispersed X-ray spectroscopic (EDS), selected area electron diffraction (SAED), and X-ray diffraction (XRD) measurements. Because a very large mismatch (13.6%) exists in lattice constants between Au (0.4079 nm) and Ni (0.3524 nm), the epitaxial growth of Ni shells over Au cores was expected to be difficult. Nevertheless, about 40 monolayers of Ni{111} shells were grown epitaxially on flat planes and sharp corners of Au{111} cores after heating reagent solution at 175 °C for 2 h. The SAED patterns showed Ni layers parallel to Au layers. This result is contrasted with our recent result for Au@Cu with a smaller lattice mismatch between Au and Cu (11.4%). In the case of Au@Cu, although the epitaxial growth of Cu{ 111} shells over Au core was observed, the growth rate on sharp corners was slower than that on flat {111} facets. Our results and reported data show that the lattice mismatch is not a significant factor for the crystal growth of Au@Ni on sharp corners.
机译：使用两步还原法制备Au @ Ni核壳纳米晶体。首先，在聚乙烯吡咯烷酮（PVP）作为聚合物表面活性剂的情况下，使用微波（MW）加热，通过在乙二醇（EG）中还原HAuCl _4·4H_2O来制备八面体，三角形和六边形板状，十面体和二十面体Au核心种子的混合物。然后，通过用油浴加热用NaOH和PVP还原EG中的Ni（NO_3）_2·6H_2O来在Ni核种子上长满Ni壳。使用透射电子显微镜（TEM），高分辨率TEM，TEM能量分散X射线光谱仪（EDS），选择区域电子衍射（SAED）和X射线衍射（XRD）测量来表征所得的晶体结构。因为在Au（0.4079 nm）和Ni（0.3524 nm）之间的晶格常数中存在非常大的失配（13.6％），所以预期在Au核上外延生长Ni壳非常困难。然而，将试剂溶液在175°C加热2 h后，约40个单层的Ni {111}壳层在平面和Au {111}核的尖角上外延生长。 SAED图案显示出与Au层平行的Ni层。这个结果与我们最近对Au @ Cu的结果形成了对比，Au @ Cu在Au和Cu之间的晶格失配较小（11.4％）。在Au @ Cu的情况下，尽管观察到Cu {111}壳在Au核上的外延生长，但在尖角上的生长速率比在平坦{111}面上的生长速率慢。我们的结果和报道的数据表明，晶格失配不是在尖角处Au @ Ni晶体生长的重要因素。

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