Study On The Electronic Transport Properties Of Molecular Devices With Graphene Electrodes

With the continuous development of micro-electronics and integrated circuits,it has been a developing trend to use single molecules and atomic clusters to construct various components of electronic circuits for the continuous miniaturization of electronic devices.In recent years,single-molecule devices were designed and measured by using a variety of experimental methods,such as self-assembled monolayers(SAMs)and organic molecular beam epitaxy(OMBE)combined with scanning tunneling microscope(STM)and atomic force microscope(AFM).The novel physical properties of single-molecule devices,including switching,negative differential resistance(NDR),and rectification effect,have attracted more and more attention,which make it possible to realize the elementary functionalization of electronic devices in electronic circuits.However,in a real experimental study,compared with the electrode,the molecule is a very small system in size.Therefore,the change of external factors has a significant influence on the configuration of the molecular device,which will strongly influence the electronic performance of the molecular device.Therefore,it is very important to understand the electronic transport properties of molecular devices by studying the changes in the configuration of molecular devices,including the geometry of molecules and the interface structures between molecule and electrode.In this thesis,using graphene nanoribbons as electrodes,a dipyrimidinyl–diphenyl and dihydroazulene(DHA)/vinylheptafulvene(VHF)with photothermal conversion properties have been investigated by applying first-principles method based on density functional theory combined with non-equilibrium Green's function,and we construct a graphene-molecule-graphene sandwich system to investigate the relationship between the structure and electronic transport properties of the molecular devices.Furthermore,we have focused on the effect of torsion angle and the contact structure between molecule and electrode on the electronic transport properties of the molecular devices.This thesis mainly includes the following five chapters:The first chapter is the summary part.We mainly introduce the background of molecular electronics,the research significance of molecular devices,and the structural characteristics and electronic structure of graphene.Finally,the main research contents of this thesis are given.The second chapter has focused on the method of all the research work in this thesis that is first-principles method based on density functional theory combined with nonequilibrium Green's function.And it briefly introduces the general processing and theoretical methods for solving the electron transport properties in molecular devices.In the third chapter,the effect of torsion angle in the dipyrimidinyl–diphenyl system on the electronic transport properties of the molecular devices with tailoring graphene nanoribbon electrodes has been investigated.The results show that torsion angle in the dipyrimidinyl–diphenyl molecule plays an important role on the electronic transport properties of the molecular devices.When the torsion angle rotates from 0° to 90°,the molecular devices exhibit very different current-voltage characteristics,namely the current value of 0° is obviously larger than that of 90°.There is the result from high conductance to low conductance when torsion angle in the dipyrimidinyl–diphenyl molecule rotates,which means that molecule devices show the unique switching behavior.In the fourth chapter,the effect of different anchoring groups on the electronic transport properties of the molecular devices with zigzag-edged graphene nanoribbon electrodes has been investigated,and carbon atom and amide endgroup are usually used as linkages between a molecule and GNRs.DHA and VHF have the photothermal conversion properties,and the molecule translates between DHA and VHF.The results show that the molecule junction with carbon atom anchoring group can obtain the higher current switching ratios when the molecule translates between DHA and VHF,and it tends to increase with the increase of the voltage.But the switching ratio of the molecule junction with amide endgroup is smaller and oscillating.Furthermore,An NDR behaviour can be observed in VHF with amide anchoring group in a bias range from 0.72 to 0.8 V.The fifth chapter is a comprehensive summary of the study on the electronic transport properties of molecular devices with GNRs electrodes.And we view the development of the molecular devices in the future.