Enhanced Half-Metallicity in Edge-Oxidized Zigzag Graphene Nanoribbons

Abstract

We present a novel comprehensive first-principles theoretical study of the electronic properties and relative stabilities of edge-oxidized zigzag graphene nanoribbons. The oxidation schemes considered include hydroxyl, carboxyl, ether, and ketone groups. Using screened exchange density functional theory, we show that these oxidized ribbons are more stable than hydrogen-terminated nanoribbons except for the case of the etheric groups. The stable oxidized configurations maintain a spin-polarized ground state with antiferromagnetic ordering localized at the edges, similar to the fully hydrogenated counterparts. More important, edge oxidation is found to lower the onset electric field required to induce half-metallic behavior and extend the overall field range at which the systems remain half-metallic. Once the half-metallic state is reached, further increase of the external electric field intensity produces a rapid decrease in the spin magnetization up to a point where the magnetization is quenched completely. Finally, we find that oxygen containing edge groups have a minor effect on the energy difference between the antiferromagnetic ground state and the above-lying ferromagnetic state.

Half-Metallic Zigzag Carbon Nanotube Dots

“…This conclusion is in striking difference from the case of ZZ-GNRs, where the ground electronic state was found to have an AFM spin ordering regardless of the dimensions of the ribbon. [19][20][21][22][23][24][25][26]28,29,42,[45][46][47][48][49][50][51][52] Interestingly, contradicting results have been reported in the literature, 33 indicating that the ground state of unpassivated zigzag CNTs has a low-spin AFM ordering even for nanotubes that have earlier been considered to present a high-spin ferromagnetically ordered ground state. 32 In light of the considerable progress that has been made in the synthesis and fabrication of ultra-short [60][61][62][63][64] and open ended 65 CNTs and ultra-narrow GNRs, [66][67][68][69] it is desirable to obtain a full understanding of their electronic properties.…”

“…Unlike previous reports on these systems, 32,37 we find that all zigzag CNTs studied present an antiferromagnetically ordered ground state, regardless of their diameter and length. Furthermore, as is the case with infinitely long [45][46][47] and finite 52 GNRs, the application of an external axial electric field results in half-metallic behavior.…”

“…30,40,43 A unique mechanism for spin ordering in graphene based systems is related to the appearance of edge states. [18][19][20][21][22][23][24][25][26][27][28][29]42,[45][46][47][48][49][50][51][52] When cutting a graphene sheet along its zigzag axis to form a narrow and elongated graphene nanoribbon (GNR), distinct electronic states appear, which are localized around the exposed edges. [54][55][56][57][58][59] These states are predicted to carry spin polarization, resulting in a well defined magnetic ordering.…”

“…[54][55][56][57][58][59] These states are predicted to carry spin polarization, resulting in a well defined magnetic ordering. [19][20][21][22][23][24][25][26]28,29,42,[45][46][47][48][49][50][51][52] Due to the bipartite hexagonal structure of graphene, the electronic ground state of such zigzag graphene nanoribbons (ZZ-GNRs) is characterized by an antiferromagnetic (AFM) spin ordering, where the edge states located at the two zigzag edges of the ribbon have opposite spins. Under the influence of an external electric field, these systems have been predicted to become half-metallic with one spin channel being semiconducting and the other metallic, 45,47 thus acting as perfect spin filters with important implications to the field of spintronics.…”

Charge carrier exchange at chemically modified graphene edges: a density functional theory study

“…[16][17][18][19] It is of great importance to develop optimized electrode materials based on graphene which combine both the intrinsic high charge carrier conductivity and chemical stability in aqueous solutions. It is widely reported that functionalized graphene nanoribbons can speed/hinder charge carrier exchange and hence affect the overall performance of electrodes used in diverse electrochemical devices.…”