Exfoliation of Alpha‐Germanium: A Covalent Diamond‐Like Structure. Issue 10 (4th February 2021) - Gibaja, Carlos
Abstract: 2D materials have opened a new field in materials science with outstanding scientific and technological impact. A largely explored route for the preparation of 2D materials is the exfoliation of layered crystals with weak forces between their layers. However, its application to covalent crystals remains elusive. Herein, a further step is taken by introducing the exfoliation of germanium, a narrow‐bandgap semiconductor presenting a 3D diamond‐like structure with strong covalent bonds. Pure α‐germanium is exfoliated following a simple one‐step procedure assisted by wet ball‐milling, allowing gram‐scale fabrication of high‐quality layers with large lateral dimensions and nanometer thicknesses. The generated flakes are thoroughly characterized by different techniques, giving evidence that the new 2D material exhibits bandgaps that depend on both the crystallographic direction and the number of layers. Besides potential technological applications, this work is also of interest for the search of 2D materials with new properties. Abstract : α‐Germanium crystals are exfoliated using a wet ball‐milling technique to produce α‐germanium nanolayers (α‐Ge NLs) in a process that is upscaled to gram production. The α‐Ge NLs can be redispersed using a shear‐mixer, yielding very stable suspensions. Theoretical calculations predict a thickness‐dependent bandgap of these NLs that is confirmed by electron energy‐loss spectroscopy of α‐Ge NLs with different orientations.