The spontaneous assembly of chiral structures from building blocks that lack chirality is fundamentally important for colloidal chemistry and has implications for the formation of advanced optical materials. Here, we find that purified achiral gold tetrahedron-shaped nanoparticles assemble into two-dimensional superlattices that exhibit planar chirality under a balance of repulsive electrostatic and attractive van der Waals and depletion forces. A model accounting for these interactions shows that the growth of planar structures is kinetically preferred over similar three-dimensional products, explaining their selective formation. Exploration and mapping of different packing symmetries demonstrates that the hexagonal chiral phase forms exclusively because of geometric constraints imposed by the presence of constituent tetrahedra with sharp tips. A formation mechanism is proposed in which the chiral phase nucleates from within a related 2D achiral phase by clockwise or counterclockwise rotation of tetrahedra about their central axis. These results lay the scientific foundation for the high-throughput assembly of planar chiral metamaterials.

从缺乏手性的构件中自发组装手性结构对于胶体化学具有根本意义，并且对先进光学材料的形成具有重要意义。在这里，我们发现纯化的非手性金四面体形纳米粒子组装成二维超晶格，在排斥静电和吸引范德华力和耗尽力的平衡下表现出平面手性。解释这些相互作用的模型表明，平面结构的生长在动力学上优于类似的三维产品，这解释了它们的选择性形成。对不同堆积对称性的探索和映射表明，六角手性相的形成完全是由于具有尖锐尖端的组成四面体的存在所施加的几何约束。提出了一种形成机制，其中手性相通过四面体围绕其中心轴的顺时针或逆时针旋转从相关的 2D 非手性相内成核。这些结果为平面手性超材料的高通量组装奠定了科学基础。