Crystallization under geometrical confinement is of fundamental importance in condensed matter physics, biophysics and material science. Even the influence of the simplest geometry, a sphere, on crystallization remains far from well understood, thereby making morphology control of the final superstructures challenging. Here, we employ charged colloids encapsulated in an emulsion droplet as a model system to access the crystallization kinetics at the single-particle level. We find rapid formation of ‘skin’ layers with an icosahedral arrangement of defects under the geometrical frustration effect, followed by interior ordering and slow ripening. The final morphologies are determined by dynamical interplay between the system-independent skin layer formation and the system-dependent structural transformation towards the most stable solid far from the surface. We reveal the crucial role of kinetics in morphological selection under a geometrical constraint, besides the thermodynamics, which may shed new light on the structural design of nanoscale crystals.

几何约束下的结晶在凝聚态物理，生物物理和材料科学中至关重要。即使是最简单的几何形状（球体）对结晶的影响，仍然远未得到很好的理解，从而使最终超结构的形态控制具有挑战性。在这里，我们采用包裹在乳液液滴中的带电胶体作为模型系统，以访问单颗粒水平的结晶动力学。我们发现在几何挫折效应下，具有二十面体缺陷排列的“表皮”层迅速形成，然后内部有序排列并缓慢熟化。最终的形态取决于系统无关的表皮层形成与系统相关的结构转换（朝着远离表面的最稳定固体）之间的动力学相互作用。除了热力学以外，我们还揭示了动力学在几何约束下的形态选择中的关键作用，这可能为纳米级晶体的结构设计提供新的思路。