Designing All-Graphene Nanojunctions by Covalent Functionalization

Abstract

We investigated theoretically the effect of covalent edge functionalization, with organic functional groups, on the electronic properties of graphene nanostructures and nanojunctions. Our analysis shows that functionalization can be designed to tune electron affinities and ionization potentials of graphene flakes, and to control the energy alignment of frontier orbitals in nanometer-wide graphene junctions. The stability of the proposed mechanism is discussed with respect to the functional groups, their number as well as the width of graphene nanostructures. The results of our work indicate that different level alignments can be obtained and engineered in order to realize stable all-graphene nanodevices

Optical Properties and Charge-Transfer Excitations in Edge-Functionalized All-Graphene Nanojunctions

“…These systems are characterized by armchair-shaped edges and width parameter N = 8, where N indicates the number of dimer lines along the zigzag direction, borrowing the standard notation used for quasi-1D armchair graphene nanoribbons (AGNRs). 21 We have already shown 15 (MOs) and to prevent the presence of localized magnetic states. 23 The functionalizations treated here comprise both -NH 2 groups, which induce an upshift of the gap region with respect to the hydrogenated counterpart, and -COCH 3 groups and F atoms, which on the contrary downshift the gap region, according to Figure 1.…”

“…In this direction, we recently demonstrated 15 that edge covalent functionalization represents a viable method to tune the ionization potential (IP) of graphene nanoflakes (GNFs), preserving the overall characteristics of the π-conjugation. Furthermore, as illustrated in Figure 1, a corresponding shift of the electron affinity (EA) moves the energy gap region of the GNF in an almost rigid fashion according to the edge termination.…”

“…N = 3p, N = 3p + 1, and N = 3p + 2, which are known to present different electronic properties also upon functionalization. 15 In the following we consider prototypical junctions obtained by functionalizing one side with amino groups (-NH 2 ) and the other side with atomic fluorine (F).…”

Understanding the effects of packing and chemical terminations on the optical excitations of azobenzene-functionalized self-assembled monolayers

“…With increasing complexity of the SAMs, also the need for a microscopic understanding of the physical mechanisms responsible for the excitation processes in these materials has concomitantly increased. In a recent study based on many-body perturbation theory, we have shown that local-field effects are primarily responsible for enhancing intermolecular interactions and transitiondipole coupling, thereby significantly reducing the spectral intensity of the absorption band triggering photoisomerization [26]. We have further demonstrated that the effects of packing density of the chromophores act * Electronic address: caterina.cocchi@physik.hu-berlin.de also in core excitations, by drastically reducing the binding energies of the electron-hole pairs, owing to the interplay between screening, dipole coupling, and wavefunction overlap [27].…”

On Oxygen‐Containing Groups in Chemically Modified Graphenes

“…Among them, it is especially interesting to investigate the presence of carboxylic groups on graphene surfaces because they can bind covalently to different kinds of molecules for various applications, that is, biosensing, [12,13] polymer composites, [14] and electronic devices. [15,16] There are of course a plethora of other fields for which correct and comprehensive information on compositions, contents, and locations of OCGs in graphenes are of high importance, such as energy storage, [17] and solar cells. [18,19] Given the strong influence of OCGs on the basic material properties of graphenes, it is imperative to obtain a comprehensive and correct knowledge of the amount, types, and locations of the OCG, before devising hypotheses on the properties of graphenes and further applications.…”