近日，美国西北大学的Chad A. Mirkin&Koray Aydin及其研究团队取得一项新进展。经过不懈努力，他们实现非线性光学胶体超晶体。相关研究成果已于2024年10月31日在国际知名学术期刊《自然—光子学》上发表。
本文展示了如何利用DNA介导的八面体形等离子体金纳米晶体的组装来设计和有意合成非中心对称和中心对称的胶体晶体。重要的是，虽然中心对称结构不表现出明显的二次谐波产生，但非中心对称晶体却会表现出这一现象，这是由等离子体热点中局域电场的不对称分布所导致的。
此外，这种非中心对称的非线性光学（NLO）超晶格是通过自下而上的方法开发的一种三维NLO超材料，其最大二次谐波产生转换效率为10-9，超过了大多数等离子体二维超表面的效率。最后，通过调整粒子构建单元上的DNA负载密度，可以在中心对称和非中心对称相之间切换。
据悉，自然晶体中原子和分子结构的反演对称性破缺决定了它们的物理性质，包括非线性光学（NLO）效应、压电性或铁电性以及非互易电荷传输行为。由纳米级构造单元（即超原子）组成的超材料，其平面表面上的空间反演对称性破缺促成了自旋控制光子学以及NLO超表面的发展。虽然可以人工合成低对称性的三维超晶格，但迄今为止尚未发现其NLO行为（例如谐波产生）。
附：英文原文
Title: Nonlinear optical colloidal metacrystals
Author: Zhang, Ye, Xu, David D., Tanriover, Ibrahim, Zhou, Wenjie, Li, Yuanwei, Lpez-Arteaga, Rafael, Aydin, Koray, Mirkin, Chad A.
Issue&Volume: 2024-10-31
Abstract: Atomic and molecular structure inversion symmetry breaking in naturally occurring crystals dictate their physical properties including nonlinear optical (NLO) effects, piezo- or ferroelectricity, and non-reciprocal charge transport behaviour. With metamaterials composed of nanoscale building blocks (that is, meta-atoms), the spatial inversion symmetry violation on planar surfaces leads to spin-controlled photonics as well as NLO metasurfaces. Synthetically, low-symmetry 3D metacrystals can be synthesized, but NLO behaviour has not been identified so far (for example, harmonic generations). Herein we show how DNA-mediated assembly of octahedron-shaped plasmonic gold nanocrystals can be used to design and deliberately synthesize non-centrosymmetric and centrosymmetric colloidal crystals. Importantly, while the centrosymmetric structures do not exhibit substantial second-harmonic generation, the non-centrosymmetric crystals do—a consequence of the asymmetric distribution of localized electric fields in plasmonic hotspots. Moreover, this non-centrosymmetric NLO metacrystal represents a 3D NLO metamaterial being developed via a bottom-up approach, exhibiting a maximum second-harmonic generation conversion efficiency of 10-9 to surpass the efficiencies observed in the majority of plasmonic 2D metasurfaces. Finally, the DNA-loading density on the particle building blocks can be used to toggle between the centrosymmetric and non-centrosymmetric phases.
DOI: 10.1038/s41566-024-01558-0
Source: https://www.nature.com/articles/s41566-024-01558-0