Magnetic Assembly of Nanocubes for Orientation-Dependent Photonic Responses
Magnetic Assembly of Nanocubes for Orientation-Dependent Photonic Responses
复制标题
DOI：
10.1021/acs.nanolett.9b02984
复制
发表时间：
2019-09-01
期刊：
影响因子：
10.8
通讯作者：
Yin, Yadong
中科院分区：
文献类型：
--
作者：
Li, Zhiwei;Wang, Mingsheng;Yin, Yadong
紧密堆积是胶体自组装中最有利的方式，产生具有有限空间构型的超结构。这一挑战可以通过将各向异性相互作用纳入组装过程来克服。使用磁铁矿纳米立方体作为积木，我们表明，它们可以磁组装成一维纳米链的边到边，而不是紧密堆积的面对面的方式。积木的立方体形状起着关键作用：它使三个几何轴中的任何一个都易于磁化，有利于紧密堆积。因此，在磁场下，长程塞曼耦合和短程偶极-偶极耦合之间的诱导竞争决定了纳米立方体沿着[110]方向的组装。边到边构型的光子性质取决于链取向和视角两者。与其中最强衍射平行于链（或场）方向发生的纳米球组件不同，纳米立方体允许人们在薄膜的平面中定义它们的长程周期性，同时将光衍射出平面，使得其特别适用于期望在具有最小厚度的膜中实现足够强度的结构色的应用。例如，可以利用它们独特的光子特性来设计“魔术”图案，其旋转被感知为与膜的实际旋转方向相反。很难通过其他手段再现这种不寻常的光学效果;因此，提供了许多用于设计新颖的安全装置的新方法。这项工作揭示了巨大的潜力的磁性组装策略，当结合使用定义明确的非球形积木，控制胶体组件的空间配置和利用其新颖的物理特性有趣的应用。
Close packing is the most favorable manner in colloidal self-assembly, producing superstructures with a limited variety of spatial configurations. This challenge can be overcome by incorporating anisotropic interactions into the assembly process. Using magnetite nanocubes as the building blocks, we show that they can be magnetically assembled into one-dimensional nanochains in an edge-to-edge rather than close-packed face-to-face manner. The cubic shape of the building blocks plays a key role: it decouples the easy magnetization from any of the three geometric axes favoring close packing. Therefore, under magnetic fields, the induced competition between the long-range Zeeman coupling and the short-range dipole-dipole coupling determines the assembly of nanocubes along the [110] directions. The photonic properties of the edge-to-edge configuration are dependent on both chain orientation and viewing angle. Unlike nanosphere assemblies where the strongest diffraction occurs parallel to the chain (or field) direction, the nanocubes allow one to define their long-range periodicity in the plane of a thin film while diffracting light out of the plane, making it particularly useful for applications that desire the achievement of structural colors of sufficient intensity in a film with a minimum thickness. For example, their unique photonic property can be taken advantage of to design "magic" patterns whose rotation is perceived to be opposite to the actual rotational direction of the film. It is difficult to reproduce such unusual optical effects by other means; thereby, many new ways for designing novel security devices are provided. This work reveals the enormous potential of the magnetic assembly strategy, when combined with the use of well-defined nonspherical building blocks, for controlling the spatial configurations of colloidal assemblies and exploiting their novel physical properties for intriguing applications.