Study Of Intermolecular Interaction At Single-molecule Scale With Mechanically Controllable Break Junction Method

The recent progress of measuring technique and characterization method at single-molecule scale had promoted molecular electronics greatly.However,the reproducibility of single-molecule conductance measurements across different research groups has to be improved.Previous publications in molecular electronics focus on the absolute conductance of molecular junction,whereas in this thesis,after the fabrication of metal/molecule/metal junction via Mechanically Controllable Break Junction(MCBJ),we devoted ourselves to study the effect of the intramolecular interaction on the characterization of molecular junction.The aim of this thesis is to explain the long-standing discrepancy among the single-molecule conductances that reported by different research groups,which is still a challenging issue in molecular electronics.In this thesis,two model systems of oligo(phenylene ethynylene)s(OPEs)and benzene-1,4-dithiol(BDT)were investigated.We focus on the low conductances of these two systems.Employing Electrochemically-Assisted MCBJ(EC-MCBJ),Notched-Wire-MCBJ,and combined MCBJ-Raman methods,in this thesis we demonstrated that the intramolecular ?-? stacking in OPEs system and S-S coupling in BDT system are responsible for the low conductances.The main contents and conclusions of this thesis are as follows:1.I-V characteristic curves of OPEs molecular junctions were measured by EC-MCBJ method.The anomalous low conductance that observed was ascribed to a stacking configuration of two adjacent OPE molecules.2.With respect to BDT,the distribution of its multiple conductance was studied by Notched-Wire-MCBJ method.After a synergistic analysis,it was proposed that the low conductance of BDT molecular junction was ascribed to the dimeric-BDT configuration,which results from the S-S coupling.3.Spectra of BDT junction were in-situ collected by a combined MCBJ-Raman method.The Raman signal of S-S bond was successfully detected,indicating the existence of dimeric-BDT molecules.Combined with the electrical characterization,we confirmed that the dimeric-BDT configuration is responsible for the low conductance state of BDT molecular junction.