The Influence Of Molecule Structure On Single Molecule Junction

Single-molecule device was proposed in theoretically since 1974.Though the single molecule devices can simply consist of one molecule and two or three electrodes,there are still many issues to be understood and solved,such as energy scales,the influence of the electrodes and the role of various molecular degrees of freedom.In this paper,we use scanning tunneling microscope breaking junction(STM-BJ)method to investigate the influence of molecular structures on the single molecular junction.The main researches of the thesis are as follows:1.The conductance of single-molecule junction with benzo[1,2-b:4,5-b’]dithiophene,2,6-dibromobenzo[1,2-b:4,5-b’]dithiophene and thieno[3,2-b]thiophene binding to Au electrode are systematically studied by using STM-BJ.The result shows that the conductance of benzo[1,2-b:4,5-b’]dithiophene is larger than 2,6-dibromobenzo[1,2-b:4,5-b’]dithiophene.However,there is no peak in the conductance histogram of thieno[3,2-b]thiophene.The reason is that the interaction between anchoring group and electrode is weak,which may have a very small possibility to form molecular junction.And the result shows that the backbone structure can influence the interaction between anchoring group and electrode.2.We measured the conductance of molecules HPB-SMe,HP(OMe)B-SMe,PP(Me)4-SMe and PP-SMe with sulfur methyl(-SCH3)as anchoring group contacting to Au electrode at room temperature.Those molecules have same backbone length and different substituent.The results show that the substituent has effect on the single molecular conductance,and an additional electronic transmission channel may formed through space mechanism as the substituent groups of HP(OMe)B-SMe with four methoxyphenyl.3.Taking BT1,BT2,BT3 and BT4 with different backbone length as target molecules,we have measured their conductance values with Au electrode by scanning tunneling microscope breaking junction,and analysis the relationship between the conductance value and molecule backbone length.Tunneling decay of 2.8nm-1is found for those molecules,which is similar as literature reported.4.We have measured the conductance of pyrazine molecular junction contacting with Cu and Ag electrodes by using an electrochemical jump-to-contact based scanning tunneling microscopy break junction(ECSTM-BJ).The result shows that the conductance of pyrazine with Ag electrode is larger than that with Cu electrode,which can contribute to the different efficiency of electron transport along the molecular junction between Ag and Cu electrodes.And the current work shows the important role of the electrode material in electron transport...