Department of Chemical and Biomolecular Engineering, New York University, Brooklyn, NY, USA.
Department of Physics, Center for Soft Matter Research, New York University, New York, NY, USA.
Nature. 2020 Sep;585(7826):524-529. doi: 10.1038/s41586-020-2718-6. Epub 2020 Sep 23.
Self-assembling colloidal particles in the cubic diamond crystal structure could potentially be used to make materials with a photonic bandgap. Such materials are beneficial because they suppress spontaneous emission of light and are valued for their applications as optical waveguides, filters and laser resonators, for improving light-harvesting technologies. Cubic diamond is preferred for these applications over more easily self-assembled structures, such as face-centred-cubic structures, because diamond has a much wider bandgap and is less sensitive to imperfections. In addition, the bandgap in diamond crystals appears at a refractive index contrast of about 2, which means that a photonic bandgap could be achieved using known materials at optical frequencies; this does not seem to be possible for face-centred-cubic crystals. However, self-assembly of colloidal diamond is challenging. Because particles in a diamond lattice are tetrahedrally coordinated, one approach has been to self-assemble spherical particles with tetrahedral sticky patches. But this approach lacks a mechanism to ensure that the patchy spheres select the staggered orientation of tetrahedral bonds on nearest-neighbour particles, which is required for cubic diamond. Here we show that by using partially compressed tetrahedral clusters with retracted sticky patches, colloidal cubic diamond can be self-assembled using patch-patch adhesion in combination with a steric interlock mechanism that selects the required staggered bond orientation. Photonic bandstructure calculations reveal that the resulting lattices (direct and inverse) have promising optical properties, including a wide and complete photonic bandgap. The colloidal particles in the self-assembled cubic diamond structure are highly constrained and mechanically stable, which makes it possible to dry the suspension and retain the diamond structure. This makes these structures suitable templates for forming high-dielectric-contrast photonic crystals with cubic diamond symmetry.
自组装胶体颗粒在立方金刚石晶体结构中，可能被用于制造具有光子带隙的材料。这种材料是有益的，因为它们抑制光的自发发射，并因其作为光学波导、滤波器和激光谐振器的应用而受到重视，可用于提高光捕获技术。与更容易自组装的结构（如面心立方结构）相比，立方金刚石更适合这些应用，因为金刚石具有更宽的带隙，并且对缺陷的敏感性较低。此外，金刚石晶体中的带隙出现在折射率对比度约为 2 的位置，这意味着可以使用已知材料在光学频率下实现光子带隙；这对于面心立方晶体似乎是不可能的。然而，胶体金刚石的自组装具有挑战性。由于金刚石晶格中的颗粒是四面体配位的，一种方法是自组装具有四面体粘性贴片的球形颗粒。但这种方法缺乏一种机制来确保有粘性贴片的球体选择最近邻颗粒上四面体键的交错取向，这是立方金刚石所必需的。在这里，我们表明，通过使用部分压缩的具有缩回粘性贴片的四面体簇，可以使用贴片-贴片粘附以及选择所需交错键取向的位阻互锁机制来自组装胶体立方金刚石。光子带结构计算表明，所得晶格（直接和反转）具有有前途的光学性质，包括宽且完整的光子带隙。自组装立方金刚石结构中的胶体颗粒受到高度约束和机械稳定，这使得可以干燥悬浮液并保留金刚石结构。这使得这些结构成为具有立方金刚石对称性的高介电对比度光子晶体的合适模板。
