Graphene on clean (0001) α-quartz: Numerical determination of a minimum energy path from metal to semiconductor

Abstract

By means of DFT calculations, we have individuated a minimum-energy path connecting two energy minima of clean graphene on clean and relaxed oxygen-terminated (0001)’SiOinline image substrate in the inline image-quartz configuration: one characterized by mutual graphene–SiOinline image substrate distance of inline image2.8 Å and weak (van der Waals) bonds between them, the other by mutual distance of inline image1.4 Å, and presence of strong covalent C–O bonds. Our calculations show that the pathway connecting the two minima goes through a transition state and that the two minima are separated by a barrier of inline image2.25 eV. The covalent C–O bonds, which characterize the lower-energy configuration, induce significant corrugation of the graphene overlayer with consequent important modification of its electronic band structure and transport properties. In particular, we show that a small gap (inline imageeV) opens in the electronic band structure of the graphene/SiOinline image system, and the conical features around the Dirac points are lost. Correspondingly, at the graphene/SiOinline image interface, the diffuse inline image conjugation of the isolated graphene layer is modified by the appearance of near’inline image carbon atoms bound to the top oxygens of the SiOinline image. This fact also affects conductances and I–V characteristics which become different along different cell directions of the graphene overlayer. Our analysis suggests that the energy barrier between the van der Waals and the covalent minima could be overcome by applying a uniform pressure on the graphene overlayer due to the formation of chemical bonds which are important for the experimental integration of graphene on Si-compatible technology

Tunable Graphene Electronics with Local Ultrahigh Pressure

“…Other authors conclude that strong covalent bonds between the C atoms and the substrate atoms are formed (chemisorption), and, as a consequence, the Dirac cone structure is lost. Finally, both covalent bonding and physisorption of graphene on SiO 2 are suggested in other works . To shed some additional light on the binding mechanism, we carried out DFT‐based simulations of adsorption of graphene on SiO 2 with two main goals: first, to clarify whether or not it is possible to induce the formation of covalent bonds between the graphene atoms and the SiO 2 atoms by applying ultrahigh pressure; and second, to estimate a minimum number of covalent bonds needed to maintain the graphene flake strongly coupled to the surface.…”

A First-Principles Approach to Modeling Interfacial Capacitance in Graphene-Based Electrodes

“…The slab surface is terminated by Si atoms to avoid covalent C−O chemical bonding that may occur in the case of oxygen-terminated quartz, which can substantially distort the planar structure of graphene and lead to the disappearance of the Dirac point degeneracy of graphene. 28,29 The Si dangling bonds in the Si-terminated surface, on the other hand, are chemically passive and preserve the linear graphene band structure near the Fermi level, as well as the Dirac point degeneracy. The adsorption energies per carbon atom in the system are evaluated at −39.8 and −22.5 meV for MLG and BLG on silica, respectively, confirming an exogenic adsorption process consistent with the findings of other studies.…”

Unexpected Electron Transport Suppression in a Heterostructured Graphene–MoS2Multiple Field-Effect Transistor Architecture

“…The considered heterostructure model contains 391 (392) atoms in the unit cell for the simulation with (without) S-vacancy, corresponding to a density of S-vacancies of ρ v ≈ 1.8 × 10 13 cm –2 . We keep the lattice constant of graphene unchanged at a 0 = 2.46 Å , and compressed the lattice constant of MoS 2 by roughly ∼2.4%: from 3.15 Å to 3.075 Å. We considered a supercell with about 18 Å of vacuum along the c -direction between periodic images.…”