Shi Qianqian, Gómez Daniel E, Dong Dashen, Sikdar Debabrata, Fu Runfang, Liu Yiyi, Zhao Yumeng, Smilgies Detlef-M, Cheng Wenlong
Department of Chemical Engineering, Faculty of Engineering, Monash University, Clayton, 3800, Victoria, Australia.
The Melbourne Centre for Nanofabrication, 151 Wellington Road, Clayton, 3168, Victoria, Australia.
Adv Mater. 2019 Jul;31(28):e1900989. doi: 10.1002/adma.201900989. Epub 2019 May 9.
2D freestanding nanocrystal superlattices represent a new class of advanced metamaterials in that they can integrate mechanical flexibility with novel optical, electrical, plasmonic, and magnetic properties into one multifunctional system. The freestanding 2D superlattices reported to date are typically constructed from symmetrical constituent building blocks, which have identical structural and functional properties on both sides. Here, a general ligand symmetry-breaking strategy is reported to grow 2D Janus gold nanocrystal superlattice sheets with nanocube morphology on one side yet with nanostar on the opposite side. Such asymmetric metallic structures lead to distinct wetting and optical properties as well as surface-enhanced Raman scattering (SERS) effects. In particular, the SERS enhancement of the nanocube side is about 20-fold of that of the nanostar side, likely due to the combined "hot spot + lightening-rod" effects. This is nearly 700-fold of SERS enhancement as compared with the symmetric nanocube superlattices without Janus structures.
二维独立纳米晶体超晶格代表了一类新型的先进超材料，因为它们能够将机械柔韧性与新颖的光学、电学、等离子体和磁学特性整合到一个多功能系统中。迄今为止报道的独立二维超晶格通常由对称的组成构建块构成，其两侧具有相同的结构和功能特性。在此，报道了一种通用的配体对称性破缺策略，以生长二维双面金纳米晶体超晶格薄片，其一侧具有纳米立方体形态，而另一侧具有纳米星形态。这种不对称金属结构导致了不同的润湿性和光学特性以及表面增强拉曼散射（SERS）效应。特别是，纳米立方体一侧的SERS增强约为纳米星一侧的20倍，这可能是由于“热点+避雷针”效应的综合作用。与没有双面结构的对称纳米立方体超晶格相比，这是SERS增强的近700倍。
