Tunable band gap and magnetic ordering by adsorption of molecules on graphene

Abstract

We have studied the electronic and magnetic properties of graphene and their modification due to the adsorption of water and other gas molecules. Water and gas molecules adsorbed on nanoscale graphene were found to play the role of defects which facilitate the tunability of the bandgap and allow us to control the magnetic ordering of localized states at the edges. The adsorbed molecules push the wavefunctions corresponding to α-spin (up) and β-spin (down) states of graphene to the opposite (zigzag) edges. This breaks the sublattice and molecular point group symmetry that results in opening of a large bandgap. The efficiency of the wavefunction displacement depends strongly on the type of molecules adsorbed.Monolayer graphene [1] with its high electron mobility, unique magnetic phenomena [2], and unusual relativisticlike properties [3] has generated an upsurge of activities in materials science. Materials exhibiting magnetic properties are in great demand for applications in nanoscale electronics and spintronics. Most magnetic materials are metals, where ferromagnetism (which results from an imbalance between the spin-up and spin-down unpaired electrons) is often destroyed by thermal fluctuations. In carbon systems the magnetic properties are stable even at room temperatures. The nonmetalicity of carbon systems makes them biocompatible and therefore are ideal for a wide range of applications not only in nanoelectronics and spintronics [4,5,6], but also in medicine and biology. In most carbon systems the origin of magnetism is unclear, but in graphene it is expected to be the result of spin ordered states localized at the edges [7,8,9,10,11,12,13].The absence of a bandgap is however a major hindrance for graphene's application in nanoelectronics. Various mechanisms for opening a gap have been developed that involve breaking of certain symmetries in graphene by defects [11], an applied bias [4,5], and interaction with other materials [14]. Noting that the conductivity of the carbon systems [15,16] is extremely sensitive to adsorption of gas molecules due to the charge exchange between them, we assume that a more controllable way to induce interactions that break a symmetry of graphene would be gas adsorption. The charge exchange between the adsorbed molecules and graphite was found to be rather low [17], and donor or acceptor behavior is exhibited depending on the type of molecules adsorbed. However, since gas adsorption changes the electronic properties of graphene due to the charge exchange between them, we suspect that adsorption should affect the localization of electronic states along the edges and can facilitate opening of a gap.Here we study the influence of adsorption of water on the electronic and magnetic properties of graphene by molecular mechanical methods using the spin-polarized density functional theory with semilocal gradient corrected functional (UB3LYP/6-31G [18]) in the Jaguar 6.5 program [19]. The van der Waals interactions, which impact the interaction between graphene and adsorpant, are not c...

Humidity sensor using surface adsorbed channel modulated Graphene nanoribbon: NEGF approach

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“…1 Graphene is a 2D building material for carbon materials of all other dimensionalities. [1] Technically, 7 -graphene is a crystalline allotrope of carbon with 2-dimensional properties. It can be described as a one-atom thick layer of graphite.…”

“…In*recent years, much attention has been focused on nanoelectronic devices [1][2][3] and molecular gas adsorption. Since gas and vapor adsorption by these systems could change their electronic properties, this property can be used as a gas and humidity sensing property.…”

Enhanced half-metallicity in the zigzag graphene nanoribbons by adsorption of the zigzag hydrogen fluoride molecular chains

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