Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94705, USA.
J Am Chem Soc. 2009 Nov 25;131(46):16851-7. doi: 10.1021/ja906503w.
We show that nanocrystals (NCs) with well-established synthetic protocols for high shape and size monodispersity can be used as templates to independently control the NC composition through successive cation exchange reactions. Chemical transformations like cation exchange reactions overcome a limitation in traditional colloidal synthesis, where the NC shape often reflects the inherent symmetry of the underlying lattice. Specifically we show that full or partial interconversion between wurtzite CdS, chalcocite Cu(2)S, and rock salt PbS NCs can occur while preserving anisotropic shapes unique to the as-synthesized materials. The exchange reactions are driven by disparate solubilites between the two cations by using ligands that preferentially coordinate to either monovalent or divalent transition metals. Starting with CdS, highly anisotropic PbS nanorods are created, which serve as an important material for studying strong two-dimensional quantum confinement, as well as for optoelectronic applications. In NC heterostructures containing segments of different materials, the exchange reaction can be made highly selective for just one of the components of the heterostructure. Thus, through precise control over ion insertion and removal, we can obtain interesting CdS|PbS heterostructure nanorods, where the spatial arrangement of materials is controlled through an intermediate exchange reaction.
我们证明，具有高形状和尺寸单分散性的纳米晶体（NCs）可以用作模板，通过连续的阳离子交换反应独立控制 NC 的组成。像阳离子交换反应这样的化学转化克服了传统胶体合成中的一个限制，在传统胶体合成中，NC 的形状通常反映了基础晶格的固有对称性。具体来说，我们表明，在保留各向异性形状的情况下，纤锌矿 CdS、辉铜矿 Cu2S 和岩盐 PbS NCs 之间可以完全或部分进行互变，而这在合成材料中是固有存在的。通过使用优先与单价或二价过渡金属配位的配体，两种阳离子之间的不同溶解度驱动了交换反应。从 CdS 开始，生成了高度各向异性的 PbS 纳米棒，这是研究二维强量子限制以及光电应用的重要材料。在含有不同材料段的 NC 异质结构中，交换反应可以对异质结构的一个组件进行高度选择性。因此，通过对离子插入和去除的精确控制，我们可以获得有趣的 CdS|PbS 异质结构纳米棒，其中材料的空间排列通过中间交换反应来控制。
