Colloidal nanoplatelets are atomically flat, quasi-two-dimensional sheets of semiconductor that can exhibit efficient, spectrally pure fluorescence. Despite intense interest in their properties, the mechanism behind their highly anisotropic shape and precise atomic-scale thickness remains unclear, and even counter-intuitive for commonly studied nanoplatelets that arise from isotropic crystal structures (such as zincblende CdSe and lead halide perovskites). Here we show that an intrinsic instability in growth kinetics can lead to such highly anisotropic shapes. By combining experimental results on the synthesis of CdSe nanoplatelets with theory predicting enhanced growth on narrow surface facets, we develop a model that explains nanoplatelet formation as well as observed dependencies on time and temperature. Based on standard concepts of volume, surface and edge energies, the resulting growth instability criterion can be directly applied to other crystalline materials. Thus, knowledge of this previously unknown mechanism for controlling shape at the nanoscale can lead to broader libraries of quasi-two-dimensional materials.

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各向同性材料固有的生长不稳定性导致准二维纳米片

胶体纳米片是原子平面的准二维半导体薄片，可以显示有效的，光谱纯净的荧光。尽管对其特性表现出浓厚的兴趣，但其高度各向异性的形状和精确的原子尺度厚度背后的机理仍然不清楚，对于由各向同性晶体结构产生的常规研究的纳米片（例如闪锌矿CdSe和卤化钙钛矿），甚至是违反直觉的。在这里，我们表明，生长动力学的内在不稳定性会导致这种高度各向异性的形状。通过将合成CdSe纳米血小板的实验结果与预测在狭窄表面上增长的理论相结合，我们开发了一个模型，该模型可以解释纳米血小板的形成以及观察到的对时间和温度的依赖性。根据标准的体积概念，表面和边缘能量，所产生的生长不稳定性判据可直接应用于其他晶体材料。因此，对这种以前未知的纳米级形状控制机制的了解会导致准二维材料库的扩大。