Transport Properties Of Helical Graphene Nanostructures

Since the birth of graphene,people have studied it for decades,and the related applications of graphene emerge in an endless stream.Meanwhile,graphene derivatives have been a hot topic in recent years.Among them,helical graphene is one of them.Because of its unique geometric structure and topological characteristics,it shows many interesting electrical transport properties.Based on the first principles,this paper will study the electrical transport characteristics of helical graphene nanoribbons and helical graphene nanotubes with different sizes,shapes and pitches from the simple helical graphene nanoribbons,reveal the special electrical transport characteristics of these structures,and elaborate the internal physical mechanism of producing the characteristics.Firstly,different kinds of helical graphene nanoribbons were constructed based on the helical graphene which were successfully prepared in the laboratory this year,and their electrical transport properties were calculated.It is found that there is a metal-semiconductor transition with the change of pitch.When the pitch is very small,it is metallic,and when the pitch increases,it is semiconductor.After the analysis,it is found that the reason for this phenomenon is due to its special intralayer and interlayer coupling.Secondly,based on the special transmission of the helical graphene nanoribbons in the ferromagnetic state,a three terminal structure is constructed,and a grid voltage is applied in the central scattering region to achieve the spin polarization effect.It is proved that the spin polarization effect can be obtained by applying either positive bias or negative bias in the system,and arbitrary spin polarizability can be achieved by electrical control.Finally,it is proved that the spin polarization current is due to the p orbit of the carbon atoms which located in the zigzag edge.This kind of electric control system is better than the traditional magnetic control method,which may be applied in the future nano electronic devices.Finally,we studied the electrical transport properties of the helical graphene nanotubes in the ferromagnetic state,and found that there is a phenomenon that the magnetism changes from nothing to some with the increase of the pitch.Later analysis shows that this is due to the magnetic moment generated by the serrated edge of the helical graphene nanotubes,which is similar to the graphene nanoribbons.This pitch dependent magnetic property may be used as a nano pressure and tension sensor in the future.