Using high‐resolution transmission electron microscopy and electron energy‐loss spectroscopy, we show that beryllium oxide crystallizes in the planar hexagonal structure in a graphene liquid cell by a wet‐chemistry approach. These liquid cells can feature van‐der‐Waals pressures up to 1 GPa, producing a miniaturized high‐pressure container for the crystallization in solution. The thickness of as‐received crystals is beyond the thermodynamic ultra‐thin limit above which the wurtzite phase is energetically more favorable according to the theoretical prediction. The crystallization of the planar phase is ascribed to the near‐free‐standing condition afforded by the graphene surface. Our calculations show that the energy barrier of the phase transition is responsible for the observed thickness beyond the previously predicted limit. These findings open a new door for exploring aqueous‐solution approaches of more metal‐oxide semiconductors with exotic phase structures and properties in graphene‐encapsulated confined cells.

中文翻译：

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通过石墨烯液体电池合成蜂窝状氧化铍。

使用高分辨率透射电子显微镜和电子能量损失谱，我们发现氧化铍通过湿化学方法在石墨烯液体电池的平面六边形结构中结晶。这些液体池可具有高达1 GPa的范德华压力，从而产生了用于溶液中结晶的小型高压容器。接收到的晶体厚度超过热力学超薄极限，根据理论预测，在该极限之上，纤锌矿相在能量上更有利。平面相的结晶归因于石墨烯表面提供的近乎自立的条件。我们的计算表明，相变的能垒是观察到的超出先前预测极限的厚度的原因。