Self-assembling colloidal particles in the cubic diamond crystal structure could potentially be used to make materials with a photonic bandgap1-3. Such materials are beneficial because they suppress spontaneous emission of light1 and are valued for their applications as optical waveguides, filters and laser resonators4, for improving light-harvesting technologies5-7 and for other applications4,8. Cubic diamond is preferred for these applications over more easily self-assembled structures, such as face-centred-cubic structures9,10, because diamond has a much wider bandgap and is less sensitive to imperfections11,12. 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 crystals3,13. 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 patches14-16. 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 diamond15,17. 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.

中文翻译：

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胶体金刚石

立方金刚石晶体结构中的自组装胶体颗粒有可能用于制造具有光子带隙 1-3 的材料。这些材料是有益的，因为它们抑制了光的自发发射 1，并且因其作为光波导、滤波器和激光谐振器 4 的应用、改进光收集技术 5-7 和其他应用 4、8 的应用而受到重视。与更容易自组装的结构（例如面心立方结构）9,10 相比，立方金刚石更适用于这些应用，因为金刚石具有更宽的带隙并且对缺陷的敏感度较低 11,12。此外，金刚石晶体中的带隙出现在折射率对比度约为 2 的情况下，这意味着在光频率下使用已知材料可以实现光子带隙；这对于面心立方晶体 3,13 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，因此一种方法是用四面体粘性贴片自组装球形颗粒 14-16。但是这种方法缺乏一种机制来确保不规则球体选择最近邻粒子上四面体键的交错取向，这是立方金刚石所必需的 15,17。在这里，我们表明，通过使用部分压缩的四面体簇和回缩的粘性贴片，胶体立方金刚石可以使用贴片-贴片粘附结合空间互锁机制进行自组装，该机制选择所需的交错键取向。光子能带结构计算表明，由此产生的晶格（正晶格和逆晶格）具有良好的光学特性，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且机械稳定，这使得干燥悬浮液并保留金刚石结构成为可能。这使得这些结构适合用于形成具有立方金刚石对称性的高介电对比度光子晶体的模板。