Study On The Influencing Factors For Single-molecule Conductance Based On Break-junction Technique

Molecular electronics is an important field for the application of nanotechnologies with an ultimate goal of building functional devices using single molecules or molecular arrays to realize the same functionality as macroscopic devices.In order to achieve this goal,it is necessary to understand,measure and modulate the processes of charge transfer within single molecules.The first task of electrical measurement of a single molecule is to connect the individual molecule into a circuit to form a stable electrode-molecule-electrode molecular junction.Various techniques are developed over the past two decades,promoting the development of molecular electronics.Among them,the scanning tunneling microscope(STM)break-junction technique is one of the most widely used techniques for making junctions and testing.We have mainly studied the single molecular conductance based on above technique.Single molecular junction is usually divided into three intercorrelated components: electrode,target molecule and anchoring group.The change of any element will have a significant effect on the electron transport characteristics of single-molecule junction.As a selection,we studied the relationship between aromaticity and conductance of conjugated molecules.In addition to the internal factors(composition),there are many external environmental factors,such as voltage,temperature,solvent,p H value and so on.In this paper,the effects of solvent,voltage and aromaticity on the conductance of a single molecule were investigated by means of the Single Molecular Recognization Tunneling Microscopy whose working principle is the same as STM.The following conclusions were obtained:(1)Compared with the commonly used 1,2,4-trichlorobenzene solvent,H2N-(CH2)n-NH2 saturated linear molecules in aqueous solution have higher conductance value(decay constant,?TCB =0.989 CH2-1,?H2O =0.853 CH2-1),and shown better electron transport characteristics.(2)The conductance of butanediamine and p-phenylenediamine was studied at different voltages.Two different types of molecules have shown obvious difference on voltage dependence.The work indicated that the conductance of saturate molecule(butanediamine)hardly change along with the change of voltage,and the conductance of conjugated molecule(PDA)have increased obviously with the increase of the voltage.In addition,the increase of voltage will destroy the stability of junctions,especially in conjugated molecules.(3)The conductance of six aromatic molecules(Cyclic five-membered rings: pyrrole,thiophene,furan and Cyclic six-membered rings: benzene,pyridine and pyrrole.)was investigated.The work indicated that the aromaticity of the investigated molecules was positive correlated with their conductance under the Au-? binding mode.