Cabot Andreu, Smith Rachel K, Yin Yadong, Zheng Haimei, Reinhard Björn M, Liu Haitao, Alivisatos A Paul
Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
ACS Nano. 2008 Jul;2(7):1452-8. doi: 10.1021/nn800270m.
We investigate the evolution of structures that result when spherical Cd nanoparticles of a few hundred nanometers in diameter react with dissolved molecular sulfur species in solution to form hollow CdS. Over a wide range of temperatures and concentrations, we find that rapid Cd diffusion through the growing CdS shell localizes the reaction front at the outermost CdS/S interface, leading to hollow particles when all the Cd is consumed. When we examine partially reacted particles, we find that this system differs significantly from others in which the nanoscale Kirkendall effect has been used to create hollow particles. In previously reported systems, partial reaction creates a hollow particle with a spherically symmetric metal core connected to the outer shell by filaments. In contrast, here we obtain a lower symmetry structure, in which the unreacted metal core and the coalesced vacancies separate into two distinct spherical caps, minimizing the metal/void interface. This pattern of void coalescence is likely to occur in situations where the metal/vacancy self-diffusivities in the core are greater than the diffusivity of the cations through the shell.
我们研究了直径几百纳米的球形镉纳米颗粒与溶液中溶解的分子硫物种反应形成中空硫化镉时所产生结构的演变。在很宽的温度和浓度范围内，我们发现镉通过不断生长的硫化镉壳层的快速扩散将反应前沿定位在最外层的硫化镉/硫界面处，当所有镉都被消耗时会导致形成中空颗粒。当我们检查部分反应的颗粒时，发现该体系与其他利用纳米级柯肯达尔效应制造中空颗粒的体系有显著差异。在先前报道的体系中，部分反应会产生一个具有球对称金属核的中空颗粒，该金属核通过细丝与外壳相连。相比之下，在这里我们得到了一种对称性较低的结构，其中未反应的金属核和合并的空位分离成两个不同的球冠，从而使金属/空位界面最小化。这种空位合并模式可能发生在核中金属/空位自扩散率大于阳离子通过壳层扩散率的情况下。
