Lei Qun-Li, Ni Ran, Ma Yu-Qiang
National Laboratory of Solid State Microstructures and Department of Physics, Collaborative Innovation Center of Advanced Microstructures , Nanjing University , Nanjing 210093 , China.
School of Chemical and Biomedical Engineering , Nanyang Technological University , 62 Nanyang Drive , 637459 , Singapore.
ACS Nano. 2018 Jul 24;12(7):6860-6870. doi: 10.1021/acsnano.8b02116. Epub 2018 Jun 20.
Chiral crystals consisting of microhelices have many optical properties, while presently available fabrication processes limit their large-scale applications in photonic devices. Here, by using a simplified simulation method, we investigate a bottom-up self-assembly route to build up helical crystals from the smectic monolayer of a colloidal helix racemate. With increasing the density, the system undergoes an entropy-driven cocrystallization by forming crystals of various symmetries with different helical shapes. In particular, we identify two crystals of helices arranged in binary honeycomb and square lattices, which are essentially composed of two sets of opposite-handed chiral crystals. Photonic calculations show that these chiral structures can have large complete photonic band gaps. In addition, in the self-assembled chiral square crystal, we also find dual polarization band gaps that selectively forbid the propagation of circularly polarized light of a specific handedness along the helical axis direction. The self-assembly process in our proposed system is robust, suggesting possibilities of using chiral colloids to assemble photonic metamaterials.
由微螺旋组成的手性晶体具有许多光学特性，然而目前可用的制造工艺限制了它们在光子器件中的大规模应用。在此，通过使用一种简化的模拟方法，我们研究了一种自下而上的自组装途径，以从胶体螺旋外消旋体的近晶单分子层构建螺旋晶体。随着密度的增加，系统通过形成具有不同螺旋形状的各种对称性的晶体经历熵驱动的共结晶。特别地，我们识别出两种排列在二元蜂窝晶格和正方形晶格中的螺旋晶体，它们基本上由两组相反手性的手性晶体组成。光子学计算表明，这些手性结构可以具有大的完全光子带隙。此外，在自组装的手性正方形晶体中，我们还发现了双偏振带隙，其选择性地禁止特定手性的圆偏振光沿螺旋轴方向传播。我们所提出系统中的自组装过程是稳健的，这表明使用手性胶体组装光子超材料的可能性。
