线缺陷石墨烯纳米带的电输运研究

Electron transport in graphene nanoribbons with line defects

石墨烯的能带工程是当前凝聚态物理的热点问题,旨在费米能级处打开能隙.另外实验报道石墨烯存在多种线缺陷,但人们尚未讨论线缺陷与石墨烯能带工程间的关系.本文采用Landauer-Büttiker公式及格林函数方法,研究了三种4-8环线缺陷随机排列方式对石墨烯纳米带电输运的影响.计算结果发现:尽管4-8环线缺陷随机分布的石墨烯纳米带在费米能级处存在电子态,但该电子态为局域态且体系在费米能级处存在透射能隙,这是由线缺陷随机排列诱导产生结构无序进而引起的Anderson局域化现象.当线缺陷无序程度较低或纳米带宽度较窄时,石墨烯纳米带的透射能隙依赖4-8环线缺陷的随机排列方式;随着线缺陷无序程度的增强或纳米带宽度的增加,三种线缺陷石墨烯纳米带的透射能隙趋于一致.总之,4-8环线缺陷随机分布的石墨烯纳米带具有透射能隙,该能隙对线缺陷的排列方式、无序程度及纳米带宽度均表现稳健性.

Bandgap engineering in graphene has been a hot topic in condensed matter physics.Although several line defects have been experimentally reported in graphene,the relationship between the bandgap engineering and the line defects has not yet been discussed.In this work,by combining the Green’s function method with the Landauer-Büttiker formula,we study theoretically the electron transport along disordered ZGNRs through taking into account three types of line defects which arise from random distribution of 4-8 rings.Our results show that although there exist electronic states around the Fermi energy of the disordered ZGNRs with randomly distributed line defects,all these electronic states are localized and a transmission gap appears around the Fermi energy.This localization phenomenon originates from the structural disorder induced by the randomly distributed line defects.To demonstrate the robustness of transmission gaps,we further calculate the conductance values of disordered ZGNR with different insertion probabilities and widths,finding that the size of transmission gap strongly depends upon the types of disorder,disorder degree,and width.When the disorder degree of line defects is low or the width of the nanoribbon is narrow,there is a notable difference in the size of the transmission gaps among the three types of disordered ZGNRs.As the width or disorder degree increases,the transmission gap size tends to be consistent.Like armchair ZGNRs,the transmission gap size decreases with the increase of width or disorder of ZGNR.Nonetheless,the openings of the transmission gaps in three types of disordered ZGNRs remain robust,regardless of variations in degree of disorder or width.These results are helpful in designing line-defect based nanodevices.