Investigation Of Charge Transport At Single-Molecule Scale With Graphene Electrode Based Cross-Plane Break Junction Technique

Single-molecule electrical characterization shows the advantages in high sensiti'vity and time resolution,making it a significant technique in single-molecule science,and the fabrication of electrode/molecule/electrode junction is the key step for the characterization.In the conventional electrode based molecular junctions,the variety of the molecular adsorption configurations and the migration of the surface metallic atoms on metal electrode decrease the controllability and stability of the molecular junction,which restrict the development of molecular devices.Therefore,the improvement of establishing stable molecule/electrode interface is the key factor to solve this problem.Different from the conventional single-molecule electronics studies which focus on the molecular conductance values based on the gold electrode system,the investigations in this thesis have improved and refitted the conventional mechanically controlled break junction(MGBJ)technique,and proposed a new cross-plane break junction(XPBJ)technique.The aim of this thesis is to construct the graphene electrode based molecular junction,to investigate cross-plane quantum transport of the electrode/molecule/electrode,to study the interface between molecules and graphene electrodes,and to provide new ideas for the study of novel molecular devices and even all-carbon molecular devices.In this thesis,graphene is used as the electrode material for single-molecule junction fabrication.Polycyclic aromatic hydrocarbons,oligo(phenylene ethynylene)s(OPEs)and benzodifurans(BDFs)are selected as target molecules for +the investigations of single-molecule two-dimensional van der Waals heterostructures(2D-vdWhs)system,and the charge transport though these systems were thoroughly studied.Based on the cross-plane break junction technique,including scanning tunneling microscope break junction method,Raman spectroscopy characterization and statistical analysis methods,we have studied the interfacial feasibility of single-molecule two-dimensional van der Waals heterostructure.We have investigated a series of molecular configurations and conductivity dependence of the graphene electrode system and observed the quantum transport of these molecular junctions at room temperature.The main contents and results of this thesis are as follows:1.We further developed conventional MCBJ technique and proposed a new XPBJ technique,and successfully verified its feasibility and stability at room temperature.A new and convenient method for graphene/molecule/graphene junction fabrication was developed.2.Single-molecule two-dimensional van der Waals heterostructures of polycyclic aromatic hydrocarbons was constructed by using graphene electrode XPBJ technique.The quantum transport at room temperature were observed,and the junction configuration of the system was further studied by the combination of various characterizations.3.The graphene/OPEs/graphene junction and the graphene/BDFs/graphene junction was constructed by using graphene electrode XPBJ technique.The cross-plane quantum transport properties of OPEs and BDFs were studied for the first time.Moreover,the charge transport regulation of the molecule was realized by changing the attaching site of anchoring group,the central conjugation backbone and the molecular symmetry.