Department of Chemistry, University of California, Riverside, California 92521, United States.
Nano Lett. 2010 Nov 10;10(11):4708-14. doi: 10.1021/nl103008v. Epub 2010 Oct 14.
We report the rapid formation of photonic crystal structures by assembly of uniform nonmagnetic colloidal particles in ferrofluids using external magnetic fields. Magnetic manipulation of nonmagnetic particles with size down to a few hundred nanometers, suitable building blocks for producing photonic crystals with band gaps located in the visible regime, has been difficult due to their weak magnetic dipole moment. Increasing the dipole moment of magnetic holes has been limited by the instability of ferrofluids toward aggregation at high concentration or under strong magnetic field. By taking advantage of the superior stability of highly surface-charged magnetite nanocrystal-based ferrofluids, in this paper we have been able to successfully assemble 185 nm nonmagnetic polymer beads into photonic crystal structures, from 1D chains to 3D assemblies as determined by the interplay of magnetic dipole force and packing force. In a strong magnetic field with large field gradient, 3D photonic crystals with high reflectance (83%) in the visible range can be rapidly produced within several minutes, making this general strategy promising for fast creation of large-area photonic crystals using nonmagnetic particles as building blocks.
我们报告了在外磁场作用下通过组装铁磁流体中的均匀非磁性胶体颗粒快速形成光子晶体结构。由于其较弱的磁偶极矩，使用外部磁场操纵尺寸小至几百纳米的非磁性颗粒（用于产生具有可见光波段带隙的光子晶体的合适构建块）一直很困难。增加磁性孔的偶极矩受到铁磁流体在高浓度或强磁场下容易聚集的不稳定性的限制。通过利用高表面电荷的基于磁铁矿纳米晶的铁磁流体的优异稳定性，在本文中，我们成功地将 185nm 的非磁性聚合物珠组装成光子晶体结构，从 1D 链到 3D 组装，这是由磁偶极力和堆积力的相互作用决定的。在具有大的梯度磁场的强磁场中，在可见光范围内具有高反射率（83%）的 3D 光子晶体可以在几分钟内快速生成，这使得使用非磁性颗粒作为构建块快速创建大面积光子晶体的这种通用策略很有前景。
