Germanene on band gap materials – GERMANENE

The project aims at growing germanene, the germanium equivalent of graphene, and study the physics of Dirac fermions in this two-dimensional (2D) material. Indeed, germanene departs from conventional 2D electrons systems and graphene by a buckled atomic structure and a significant spin orbit coupling. It should thus form a rich playground for fundamental studies in low-dimensional physics. Based on the expertise recently gained with the growth of germanene on Al(111) by partners of this project, we want to explore the growth of van der Waals heterostructures, consisting of germanene and 2D layered materials, that allow to minimize the interaction between germanene and these supporting materials. For that purpose, our consortium will rely on state of the art in depth characterization tools at the nanoscale: synchrotron radiation, scanning probe microscopy at low temperature with multiple tips and time-resolved spectroscopy capability. Our analysis based on versatile multi-physical characterization will be compared with calculations performed in the framework of the density functional theory, highlighting the impact of the atomic arrangement on the band structure of germanene and how the nature of the substrate might perturb the structural and electronic properties of this remarkable sheet of Ge atoms. Relevant to this project will be the measurement of the Dirac cone hallmark, the band gap, the carrier mobility and the charge transfer from the underlying layer. Also, we will strive to demonstrate the existence of the quantum spin Hall effect, that is expected due to the substantial spin-orbit coupling in germanene. Of particular interest is the study of defects and lattice deformations, that opens the door to topological transitions, like the Kekulé distortion, causing the attachment of mass to Dirac Fermions. Because of the anticipated poor resistance of germanene to ambient conditions, what would severely limit a deeper characterization and prevent its use in spin/opto-electronic applications, efforts will also be devoted to encapsulate germanene. We want to achieve the growth of germanene on Al(111) ultra-thin films on silicon, followed by the removal of the Si parent substrate and the oxidation of the Al layer, and, to protect the top face of germanene with 2D layered materials transferred in ultra-high vacuum. These schemes will take place along with innovations in instrumentations, in particular Raman spectroscopy in ultra-high vacuum that is the tool of choice for fingerprinting 2D materials. French companies that are involved in the Equipex and Labex investment awards of two of the partners will benefit from transfers of know-how in advanced instrumentations. Progress in the field of the synthesis of germanene, in the understanding of the physics of this material and in the design of dedicated tools will be key to turn germanene into practical technologies at the end of the project.