Institute of Semiconductor and Solid State Physics, University Linz, Altenbergerstrasse 69, 4040 Linz, Austria.
ACS Nano. 2010 Jan 26;4(1):423-31. doi: 10.1021/nn901284f.
Although a large diversity of single-component and binary superlattices from colloidal nanocrystals have been demonstrated, applications of such ordered nanocrystal assemblies are still hampered due to a lack of control over the self-assembly processes over large areas. A reel-to-reel compatible large-area coating technique for solutions is given by doctor blade casting, which is applied here to deposit colloidal nanocrystals onto various substrates. The self-assembly process is demonstrated for magnetic nanocrystals, having a high potential for applications in magnetic memory devices. Shape-controlled (spherical and cubic) and monodisperse nanocrystals with a Wustite core and a cobalt ferrite shell are used in particular. Doctor blade casting of these colloidal nanocrystals results in films exhibiting hexagonally closely packed arrangements, which are formed by a top-down growth, as is evidenced by cross sectional transmission electron microscopy. The ordering in the topmost layer extends over large areas, although some defects and irregularities are found. The degree and quality of self-assembly is quantified by analyzing plan view images of the assemblies by means of the decay of their autocorrelation function. This analysis reveals that the degree of ordering obtained by doctor blade casting outperforms those provided by alternative deposition techniques such as inkjet printing or drop casting. The results for the coherent lengths deduced from the autocorrelation analysis are shown to be consistent with those from grazing-incidence small-angle X-ray scattering, giving coherence length on the order of 1000 nm.
尽管已经证明了胶体纳米晶体的多种单组分和双组分超晶格，但由于缺乏对大面积自组装过程的控制，此类有序纳米晶体组装体的应用仍然受到阻碍。刮刀涂布是一种适用于溶液的卷对卷兼容的大面积涂层技术，本文将其应用于将胶体纳米晶体沉积到各种基底上。这里展示了用于磁性纳米晶体的自组装过程，磁性纳米晶体在磁性存储器件中有很高的应用潜力。特别使用了具有尖晶石核和钴铁氧体壳的形状可控（球形和立方体形）和单分散纳米晶体。这些胶体纳米晶体的刮刀涂布导致了表现出六方紧密堆积排列的薄膜，这是由自上而下的生长形成的，这可以通过横截面透射电子显微镜来证明。虽然存在一些缺陷和不规则性，但最顶层的有序度可以扩展到很大的区域。通过分析组装体的平面视图图像并使用自相关函数的衰减来定量分析自组装的程度和质量。该分析表明，刮刀涂布获得的有序度优于喷墨打印或滴铸等替代沉积技术提供的有序度。从自相关分析推断出的相干长度的结果与掠入射小角 X 射线散射的结果一致，给出了约 1000nm 的相干长度。
