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Defect symmetry influence on electronic transport of zigzag nanoribbons.

Zeng H, Leburton JP, Xu Y, Wei J - Nanoscale Res Lett (2011)

Bottom Line: The wave function of asymmetric SW configuration is very similar to that of the pristine GNR, except for the defective regions.Unexpectedly, calculations predict that the asymmetric SW defects are more favorable to electronic transport than the symmetric defects configuration.These distinct transport behaviors are caused by the different couplings between the conducting subbands influenced by wave function alterations around the charge neutrality point.

View Article: PubMed Central - HTML - PubMed

Affiliation: College of Physical Science and Technology, Yangtze University, Jingzhou, Hubei 434023, China. zenghui@yangtzeu.edu.cn.

ABSTRACT
The electronic transport of zigzag-edged graphene nanoribbon (ZGNR) with local Stone-Wales (SW) defects is systematically investigated by first principles calculations. While both symmetric and asymmetric SW defects give rise to complete electron backscattering region, the well-defined parity of the wave functions in symmetric SW defects configuration is preserved. Its signs are changed for the highest-occupied electronic states, leading to the absence of the first conducting plateau. The wave function of asymmetric SW configuration is very similar to that of the pristine GNR, except for the defective regions. Unexpectedly, calculations predict that the asymmetric SW defects are more favorable to electronic transport than the symmetric defects configuration. These distinct transport behaviors are caused by the different couplings between the conducting subbands influenced by wave function alterations around the charge neutrality point.

No MeSH data available.


Related in: MedlinePlus

(Color online) Electronic band structures of defective ZGNRs. (a) for the pristine, (b) for the symmetric SW defects and (c) for the asymmetric SW defects. The solid red (dotted blue) line denotes the α-spin (β-spin) bands. The dashed black line indicates the CNP, and solid circles indicate defect states.
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Figure 3: (Color online) Electronic band structures of defective ZGNRs. (a) for the pristine, (b) for the symmetric SW defects and (c) for the asymmetric SW defects. The solid red (dotted blue) line denotes the α-spin (β-spin) bands. The dashed black line indicates the CNP, and solid circles indicate defect states.

Mentions: The central issue of this study is to investigate the influence of SW defects in the ZGNRs on their electronic and transport behavior. ZGNRs are known to present very peculiar electronic structure, that is, strong edge effects at low energies originated from the wave functions localized along the GNR edges [44]. Spin-unpolarized calculations reveal that all ZGNRs are metallic with the presence of sharply localized edge states at the CNP [25,43,44], while ab initio calculation with spin effect taken into consideration found that a small band gap opens up [18]. The electronic band structures of defective nanoribbons and the corresponding pristine GNRs are shown for comparison. In the case of pristine GNR, zone-folded effects give rise to nondegenerated bands for α- and β-spin states, and the corresponding spin bands shift upward and downward with respect to the CNP, respectively. It also leads to gapless electronic structure as well as 3G0 conductance in the vicinity of CNP (see Figure 3). Meanwhile, zone-folded effects create more subbands near the CNP, namely, four α-spin subbands around 0.4eV and four β-spin subbands around 0.4eV. The presence of symmetric SW defects substantially split the electronic bands, especially for the β-spin bands above the CNP, resulting from the bands anticrossing at Γ or π point. More importantly, the symmetric defects open a band gap of about 0.12eV for α-spin bands and 0.09eV for β-spin bands, which is attributed to the mismatch coupling between its LUES and HOES wave functions due to the presence of defects. It is interesting to note that a defect state deriving from the α-spin subband is located at about 1.15eV above the CNP producing a localized state, where complete backscattering is obtained (see red dashed line in Figure 3). Thus, these changes in the band structures arising from introducing symmetric SW defects are unfavorable to electronic transport. In contrast to the extensive split produced by the symmetric SW defects, the electronic structure modification due to the asymmetric SW defects is slight. Except for some bands splitting that could be unfavorable to electron transport, the band structure away from the CNP does not experience much change. Similar to the emergence of defect states induced by the symmetric SW configuration, two defect states are observed in the asymmetric SW configurations; one defect state arising from the α-spin subband locates at about 0.62eV above the CNP, and the other one from the β-spin is -1.20eV below the CNP. Both defects give rise to localized states that lead to conductance gaps (see, dotted line in Figure 3). Overall, the band structure results reveal that the SW defect states near the CNP lead to complete electron backscattering region, where the location depends on the spatial symmetry of the defects.


Defect symmetry influence on electronic transport of zigzag nanoribbons.

Zeng H, Leburton JP, Xu Y, Wei J - Nanoscale Res Lett (2011)

(Color online) Electronic band structures of defective ZGNRs. (a) for the pristine, (b) for the symmetric SW defects and (c) for the asymmetric SW defects. The solid red (dotted blue) line denotes the α-spin (β-spin) bands. The dashed black line indicates the CNP, and solid circles indicate defect states.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211316&req=5

Figure 3: (Color online) Electronic band structures of defective ZGNRs. (a) for the pristine, (b) for the symmetric SW defects and (c) for the asymmetric SW defects. The solid red (dotted blue) line denotes the α-spin (β-spin) bands. The dashed black line indicates the CNP, and solid circles indicate defect states.
Mentions: The central issue of this study is to investigate the influence of SW defects in the ZGNRs on their electronic and transport behavior. ZGNRs are known to present very peculiar electronic structure, that is, strong edge effects at low energies originated from the wave functions localized along the GNR edges [44]. Spin-unpolarized calculations reveal that all ZGNRs are metallic with the presence of sharply localized edge states at the CNP [25,43,44], while ab initio calculation with spin effect taken into consideration found that a small band gap opens up [18]. The electronic band structures of defective nanoribbons and the corresponding pristine GNRs are shown for comparison. In the case of pristine GNR, zone-folded effects give rise to nondegenerated bands for α- and β-spin states, and the corresponding spin bands shift upward and downward with respect to the CNP, respectively. It also leads to gapless electronic structure as well as 3G0 conductance in the vicinity of CNP (see Figure 3). Meanwhile, zone-folded effects create more subbands near the CNP, namely, four α-spin subbands around 0.4eV and four β-spin subbands around 0.4eV. The presence of symmetric SW defects substantially split the electronic bands, especially for the β-spin bands above the CNP, resulting from the bands anticrossing at Γ or π point. More importantly, the symmetric defects open a band gap of about 0.12eV for α-spin bands and 0.09eV for β-spin bands, which is attributed to the mismatch coupling between its LUES and HOES wave functions due to the presence of defects. It is interesting to note that a defect state deriving from the α-spin subband is located at about 1.15eV above the CNP producing a localized state, where complete backscattering is obtained (see red dashed line in Figure 3). Thus, these changes in the band structures arising from introducing symmetric SW defects are unfavorable to electronic transport. In contrast to the extensive split produced by the symmetric SW defects, the electronic structure modification due to the asymmetric SW defects is slight. Except for some bands splitting that could be unfavorable to electron transport, the band structure away from the CNP does not experience much change. Similar to the emergence of defect states induced by the symmetric SW configuration, two defect states are observed in the asymmetric SW configurations; one defect state arising from the α-spin subband locates at about 0.62eV above the CNP, and the other one from the β-spin is -1.20eV below the CNP. Both defects give rise to localized states that lead to conductance gaps (see, dotted line in Figure 3). Overall, the band structure results reveal that the SW defect states near the CNP lead to complete electron backscattering region, where the location depends on the spatial symmetry of the defects.

Bottom Line: The wave function of asymmetric SW configuration is very similar to that of the pristine GNR, except for the defective regions.Unexpectedly, calculations predict that the asymmetric SW defects are more favorable to electronic transport than the symmetric defects configuration.These distinct transport behaviors are caused by the different couplings between the conducting subbands influenced by wave function alterations around the charge neutrality point.

View Article: PubMed Central - HTML - PubMed

Affiliation: College of Physical Science and Technology, Yangtze University, Jingzhou, Hubei 434023, China. zenghui@yangtzeu.edu.cn.

ABSTRACT
The electronic transport of zigzag-edged graphene nanoribbon (ZGNR) with local Stone-Wales (SW) defects is systematically investigated by first principles calculations. While both symmetric and asymmetric SW defects give rise to complete electron backscattering region, the well-defined parity of the wave functions in symmetric SW defects configuration is preserved. Its signs are changed for the highest-occupied electronic states, leading to the absence of the first conducting plateau. The wave function of asymmetric SW configuration is very similar to that of the pristine GNR, except for the defective regions. Unexpectedly, calculations predict that the asymmetric SW defects are more favorable to electronic transport than the symmetric defects configuration. These distinct transport behaviors are caused by the different couplings between the conducting subbands influenced by wave function alterations around the charge neutrality point.

No MeSH data available.


Related in: MedlinePlus