Electron transport in edge-disordered graphene nanoribbons

Ab initio methods are used to study the spin-resolved transport properties of graphene nanoribbons (GNRs) that have both chemical and structural edge disorder. Oxygen edge adsorbates on ideal and protruded ribbons are chosen as representative examples, with the protrusions forming the smallest possible structural disorder consistent with the edge geometry. The impact of the oxygen adsorbate dominates the transport properties of armchair nanoribbons. For zigzag nanoribbons, the transmission properties are markedly affected by the protrusion alone, leading to spin-polarized transport and a smaller perturbation from the oxygen adsorbate. Armchair nanoribbons also exhibit, as a function of their width and the threefold family structure, a repeating pattern related to the existence of the spin polarization and to the variation in the width of the band gap.

Figure 1

Schematics of the representative two-probe transport systems under study. (From left to right) An ideal 5-AGNR, a 5-AGNR with a protrusion, an ideal 4-ZGNR, and a 4-ZGNR with a protrusion. Each system contains one adsorbed oxygen atom. The (green) background-shaded areas show the first principal layers of the semi-infinite leads. Gray, dark (red), and white circles indicate carbon, oxygen, and hydrogen atoms, respectively.

Figure 2

Transmission functions for a 5-AGNR. Black and gray (cyan) curves denote the transmissions for systems with an oxygen atom and with hydrogen termination only, respectively. The bottom panel gives the oxygen PDOS.

Figure 3

Transmission functions for 6-, 7-, and 8-AGNRs with one adsorbed oxygen atom. The solid curve denotes spin up transmission, and the dashed curve denotes spin down transmission. The inset shows spin up minus spin down Mulliken charges for the 6-AGNR with positive and negative values indicated by dark (red) and gray (cyan) solid circles, respectively.

Figure 4

Transmission functions for a 5-AGNR with a protrusion. Black and gray (cyan) curves denote the transmissions for systems with an adsorbed oxygen atom and with hydrogen termination only, respectively. The solid curve denotes spin up transmission and the dashed curve denotes spin down transmission. The inset shows spin up minus spin down Mulliken charges with positive and negative values indicated by dark (red) and gray (cyan) solid circles, respectively.

Figure 5

Transmission functions for protruded 6-, 7-, and 8-AGNRs with an adsorbed oxygen atom. The solid curve denotes spin up transmission and the dashed curve denotes spin down transmission.

Figure 6

Transmission functions for a 5-ZGNR. Black and gray (cyan) curves denote the transmissions for systems with an adsorbed oxygen atom and with hydrogen termination only, respectively. The solid curve denotes spin up transmission, and the dashed curve denotes spin down transmission. The inset shows the spin up minus spin down Mulliken charges with positive and negative values indicated by dark (red) and gray (cyan) solid circles, respectively. The bottom panel gives the oxygen PDOS.

Figure 7

Transmission functions for a protruded 5-ZGNR. Black and gray (cyan) curves denote the transmissions for systems with an adsorbed oxygen atom and with hydrogen termination only, respectively. The solid curve denotes spin up transmission, and the dashed curve denotes spin down transmission. The inset shows the spin up minus spin down Mulliken charges with positive and negative values indicated by dark (red) and gray (cyan) solid circles, respectively. The bottom panel gives the oxygen PDOS.

Figure 8

Transmission functions for 6- and 8-ZGNRs with and without protrusions and with an adsorbed oxygen atom. The solid curve denotes spin up transmission and the dashed curve denotes spin down transmission.