Functionalization of 2D materials by intercalation

International audienceSince the discovery of graphene many studies focused on its functionalization by different methods. These strategies aim to find new pathways to overcome the main drawback of graphene, a missing band-gap, which strongly reduces its potential applications, particularly in the domain of nanoelectronics, despite its huge and unequaled charge carrier mobility. The necessity to contact this material with a metal has motivated a lot of studies of metal/graphene interactions and has led to the discovery of the intercalation process very early in the history of graphene. Intercalation, where the deposited atoms do not stay at the graphene surface but intercalate between the top layer and the substrate, may happen at room temperature or be induced by annealing, depending of the chemical nature of the metal. This kind of mechanism was already well-known in the earlier Graphite Intercalation Compounds (GICs), particularly famous for one current application, the Lithium-ion Battery, which is simply an application based on the intercalation of Lithium atoms between two sheets of graphene in a graphite anode. Among numerous discoveries the GICs community also found a way to obtain graphite with superconducting properties by using intercalated alkali metals. Graphene is now a playground to “revisit” and understand all these mechanisms and to discover possible new properties of graphene induced by intercalation. For example, the intercalation process may be used to decouple the graphene layer from its substrate, to change its doping level or even, in a more general way, to modify its electronic band structure and the nature of its Dirac fermions. In this paper we will focus on the functionalization of graphene by using intercalation of metal atoms but also of molecules. We will give an overview of the induced modifications of the electronic band structure possibly leading to spin-orbit coupling, superconductivity, …We will see how this concept of functionalization is also now used in the framework of other 2D materials beyond graphene and of van der Waals heterostructures based on these materials

Highly n-doped graphene generated through intercalated terbium atoms

We obtained highly n-type doped graphene by intercalating terbium atoms between graphene and SiC(0001) through appropriate annealing in ultrahigh vacuum. After terbium intercalation angle-resolved-photoelectron spectroscopy (ARPES) showed a drastic change in the band structure around the K points of the Brillouin zone: the well-known conical dispersion band of a graphene monolayer was superposed by a second conical dispersion band of a graphene monolayer with an electron density reaching 10(15) cm(-2). In addition, we demonstrate that atom intercalation proceeds either below the buffer layer or between the buffer layer and the monolayer graphene. The intercalation of terbium below a pure buffer layer led to the formation of a highly n-doped graphene monolayer decoupled from the SiC substrate, as evidenced by ARPES and x-ray photoelectron spectroscopy measurements. The band structure of this highly n-doped monolayer graphene showed a kink (a deviation from the linear dispersion of the Dirac cone), which has been associated with an electron-phonon coupling constant one order of magnitude larger than those usually obtained for graphene with intercalated alkali metals