Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, Sweden.
Jülich Centre for Neutron Science JCNS and Peter Grünberg Institut PGI, JARA-FIT, Forschungszentrum Jülich, 52425 Jülich, Germany.
Nanoscale. 2016 Aug 25;8(34):15571-80. doi: 10.1039/c6nr03776c.
A precise control over the meso- and microstructure of ordered and aligned nanoparticle assemblies, i.e., mesocrystals, is essential in the quest for exploiting the collective material properties for potential applications. In this work, we produced evaporation-induced self-assembled mesocrystals with different mesostructures and crystal habits based on iron oxide nanocubes by varying the nanocube size and shape and by applying magnetic fields. A full 3D characterization of the mesocrystals was performed using image analysis, high-resolution scanning electron microscopy and Grazing Incidence Small Angle X-ray Scattering (GISAXS). This enabled the structural determination of e.g. multi-domain mesocrystals with complex crystal habits and the quantification of interparticle distances with sub-nm precision. Mesocrystals of small nanocubes (l = 8.6-12.6 nm) are isostructural with a body centred tetragonal (bct) lattice whereas assemblies of the largest nanocubes in this study (l = 13.6 nm) additionally form a simple cubic (sc) lattice. The mesocrystal habit can be tuned from a square, hexagonal to star-like and pillar shapes depending on the particle size and shape and the strength of the applied magnetic field. Finally, we outline a qualitative phase diagram of the evaporation-induced self-assembled superparamagnetic iron oxide nanocube mesocrystals based on nanocube edge length and magnetic field strength.
对有序和定向纳米颗粒组装体（即介晶）的介观和微观结构进行精确控制，对于开发潜在应用中的集体材料性能至关重要。在这项工作中，我们通过改变纳米立方体的尺寸和形状以及施加磁场，制备了具有不同介观结构和晶体形态的蒸发诱导自组装介晶。使用图像分析、高分辨率扫描电子显微镜和掠入射小角 X 射线散射（GISAXS）对介晶进行了全面的 3D 表征。这使得能够确定例如具有复杂晶体形态的多畴介晶的结构，并以亚纳米精度定量颗粒间的距离。小纳米立方体（l = 8.6-12.6nm）的介晶与体心四方（bct）晶格等结构，而在这项研究中最大的纳米立方体的组装体（l = 13.6nm）还形成了简单立方（sc）晶格。介晶形态可以根据颗粒尺寸和形状以及施加磁场的强度，从方形、六边形到星型和柱状形状进行调整。最后，我们基于纳米立方体边长和磁场强度，概述了蒸发诱导自组装超顺磁性氧化铁纳米立方体介晶的定性相图。
