Electronic Transport Decay Rule In Junction Of Oligophenylene-linked Molecule

It is generally believed that the nonresonant tunneling exponential decay tlhrough a molecular junction is dependent on the properties of molecule and its contact to electrodes.Here we study the dependence of molecular length on the transport of junctions with different graphene nanoribbon(GNR)electrodes,in which the molecule consisting one,two,and three phenyls are considered,re-spectively.By the ab initio calculations,we demonstrate that the current via zigzag-edge GNR(ZGNR)electrode junction reaches to magnitude of ?A with a convex-arc-shaped dependence under low bias,which is different from that via the similar Au-electrode junction(?nA)with a linear relationship over the same bias scope.Interestingly,the current,drops to?PA with a nonlinear dependence when the electrodes are replaced by the same width conducting armchair-edge GNR(AGNR)in connection with molecule at the insulating carbon-dimer chain.However,when the molecule?AGNR connection is moved to a conducting chain,the current increases up to?nA.The currents through the chiral GNR-electrode junctions axe of different orders of magnitude(few to hundreds of nA),but show the similar-I-V characteristics to that for AGNR-electrode junction.Nonetheless,for all types of GNR-electrode junctions the relationship between resistance and molecular length all display a straight line in the semilog coordinate but with dif-ferent slopes.Therefore,although the transport exponential law itself is electrode?independent,importantly,the exponential factor is sensitively dependent not only on electrode materials but also on the morphology of electrode-molecule coupling.Our results here have demonstrated a universal characteristic in transport for molecular junctions.The paper is divided into four chapters,the first chapter mainly introduces the discovery and development of graphene materials.Then the band structure,band dispersion relation,main physical properties,experimental and theoretical research progress of graphene nanoribbons axe introduced in detail.Finally,the research background,main content and significance of this thesis are summarized.The second chapter mainly elaborates the method of charge transport theory base on the ab into method including the first principle,single electron approx-imation method,the adiabatic approximation,density functional theory,green's function method and molecular electronics.At the end of the chapter,a brief introduction is given to the software package.In the third chapter,we study the decay rule of oligomerphenyl molecules in the graphene junctions with the first principle method.In this chapter,changes of decay factor of oligomerphenyl molecules which is connected with ZGNR,AGNR,(1,2)GNR and(4,1)GNR electrodes axe investigated respectively.The ? is related to not only the intrinsic quality of the molecule itself and the configuration inside the molecrule,but also the nature of the electrode material.The charge trans-port properties of a molecular device are dominated by the property of molecule-electrode contact rather than by the molecule itself,the contact topology,quality,and physics/chemistry become very important.The physical mechanism of the change of ? is analyzed emphatically.In the fourth chapter,the research methods,contents and conclusions of this paper are summarized in detail.We illustrate the main innovation points and the scientific significance of this thesis then presented the prospect of follow-up work.