Molecular Doping Of Graphene Research Articles

Combined molecular and periodic DFT analysis of the adsorption of co macrocycles on graphene.

The molecular doping of graphene with π-stacked conjugated molecules has been widely studied during the last 10 years, both experimentally or using first-principle calculations, mainly with strongly acceptor or donor molecules. Macrocyclic metal complexes have been far less studied and their behavior on graphene is less clear-cut. The present density functional theory study of cobalt porphyrin and phthalocyanine adsorbed on monolayer or bilayer graphene allows to compare the outcomes of two models, either a finite-sized flake of graphene or an infinite 2D material using periodic calculations. The electronic structures yielded by both models are compared, with a focus on the density of states around the Fermi level. Apart from the crucial choice of calculation conditions, this investigation also shows that unlike strongly donating or accepting organic dopants, these macrocycles do not induce a significant doping of the graphene sheet and that a finite size model of graphene flake may be confidently used for most modeling purposes. © 2017 Wiley Periodicals, Inc.

Molecular doping of graphene across ultra‐thin molybdenum disulphide spacers

Molecular doping of graphene is intriguing since the electronic and vibrational properties of graphene are not only determined by the interfacial charge transfer process, but they can also be influenced by adsorbate–graphene hybridization, adsorbate–adsorbate interactions, as well as Fermi‐level pinning of the molecule. In this work, we investigate the change in vibrational properties of graphene induced by an organic electron acceptor molecule in the presence of intervening spacers of ultra‐thin molybdenum disulphide (MoS2) of variable thickness, down to a single layer. Mechanically exfoliated single‐layer graphene and few‐layer MoS2 crystals are combined to form heterostructures, which are then subjected to molecular doping by means of an organic hole‐dopant, 7,7,8,8‐tetracyanoquinodimethane (TCNQ). Variations in Raman G‐peak parameters are discussed in terms of molecular doping of graphen e, when the dopant:graphene separation is controllably increased. We show that dopant‐separation dependent Fermi level variations of graphene cannot be completely accounted within a simple charge transfer model. The additional mechanisms relevant to the complex nature of molecular doping are discussed.

Molecular doping of graphene with ammonium groups

Successful doping of an electronic material entails the existence of stable dopant configurations that cause a shift in the Fermi level without altering significantly the electronic states of the host system. The selection of chemical groups that satisfy these conditions when adsorbed on graphene is still an open challenge. Here we show with first-principles calculations that ammonium groups meet the criteria of stable physisorption and efficient doping of graphene. We also describe processes of deactivation of ammonium dopants through their dissociation over graphene impurities or nanoribbon edges. Finally, we show that carbon nanotubes can be used to spatially confine the dopants and avert their edge-related de-activation.

Molecular Doping of Graphene

Graphene is considered as one of the most promising materials for post silicon electronics, as it combines high electron mobility with atomic thickness [Novoselov et al. Science 2004, 306, 666-669. Novoselov et al. Proc. Natl. Acad. Sci. U.S.A. 2005, 102, 10451-10453]. The possibility of chemical doping and related excellent chemical sensor properties of graphene have been demonstrated experimentally [Schedin et al. Nat. Mater. 2007, 6, 652-655], but a microscopic understanding of these effects has been lacking, so far. In this letter, we present the first joint experimental and theoretical investigation of adsorbate-induced doping of graphene. A general relation between the doping strength and whether adsorbates are open- or closed-shell systems is demonstrated with the NO2 system: The single, open shell NO2 molecule is found to be a strong acceptor, whereas its closed shell dimer N2O4 causes only weak doping. This effect is pronounced by graphene's peculiar density of states (DOS), which provides an ideal situation for model studies of doping effects in semiconductors. We show that this DOS is ideal for "chemical sensor" applications and explain the recently observed [Schedin et al. Nat. Mater. 2007, 6, 652-655] NO2 single molecule detection.