Synthesis of Honeycomb‐Structured Beryllium Oxide via Graphene Liquid Cells

• Published in: Angewandte Chemie (International ed.) 2020-09, Vol.59 (36), p.15734-15740
• Main Authors: Wang, Lifen, Liu, Lei, Chen, Ji, Mohsin, Ali, Yum, Jung Hwan, Hudnall, Todd W., Bielawski, Christopher W., Rajh, Tijana, Bai, Xuedong, Gao, Shang‐Peng, Gu, Gong
• Format: Article
• Language: English
• Subjects: aqueous-solution synthesis; Beryllium; Beryllium oxide; Crystallization; Crystals; Electron energy; Electronics industry; Graphene; graphene liquid cells; high-resolution transmission electron microscopy; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Phase transitions; Spectroscopy; structural phase transition; thermodynamic ultra-thin limit; Thickness; Transmission electron microscopy; Wurtzite
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202007244

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. Hexagonal, exceptional: In a graphene liquid cell, beryllium oxide can crystallize in a rare sp2‐coordinated, hexagonal BeO polymorph. The thickness of the crystals produced this way is beyond the thermodynamic ultra‐thin limit above which the wurtzite phase is energetically more favorable. Calculations show that the energy barrier of the phase transition is responsible for the observed occurrence of hexagonal layers.