Control Of The Charge Transport Through Single-Molecule Junctions By Solvent-Molecule Interaction And Metal-Organic Compounds

Based on the investigation of the single-molecule charge transport properties,molecular electronics provide a scientific concept for the design and development of functional molecular devices.A stable and efficient single-molecule measurement technique is a prerequisite to the investigation of the single-molecule charge transport properties.Up to now,a variety of efficient and reliable electrical measurement techniques have been developed and widely used in studying molecular electronics,such as mechanically controllable break junction(MCBJ)technique and scanning tunneling microscope break junction(STM-BJ)technique.On the other hand,it also provides a way to study physical and chemical phenomena under the molecular scale.With the development of molecular electronics,we focus not only on the internal factors,such as molecular structure,but also on the external factors,such as the environment,which could help us to further understanding of molecular charge transport mechanism and the development of functional molecular devices.Therefore,from the perspective of the solvent gating and metal-organic hybrid system,this study explored the influence of internal and external factors on the molecular charge transport properties.Based on the measurement and analysis method of single-molecule conductance developed in our laboratory,we explored the mechanism of the interaction between solvent and molecules.It provides a new strategy to regulate the single-molecule charge transport,and further the understanding of solvent-molecule interaction.To measure the single-molecule conductance under specific environmental,we developed the STMBJ technique and built a homemade gas-phase environmental controllable scanning tunneling microscope break junction(GEC-STM)technique device.The charge transport properties of metal-organic hybridized molecules,which could be easily oxidized in the air,were measured using GEC-STM.The main research contents and results are summarized as follows:1.The charge transport of oligophenylacetylene molecules in different polar solvents were measured using MCBJ technique,and it was found that the molecular conductance in tetrahydrofuran increased by nearly ten times compared with that of mesitylene.Moreover,we found that the molecular conductance is positively correlated to the ratio of polar solvents in mixed solvents.The control experiments show that the solvent induced gating is not only related to the solvent,but also to the molecular anchors.We use DFT theory to build a reasonable molecular model and analyze the mechanism how the solvent-molecule interaction affects the single-molecule charge transport properties.It was found that,only in the weak coupling of molecules,solvent molecules could shift molecular frontier orbital energy through electrostatic interaction,thus tuning the molecular charge transport properties.It is proved that solvent gating is an effective method to control the molecular conductance.2.To control the influence of the environment on the single-molecule conductance measurement,the homemade GEC-STM technology device was developed by combining the environmental control system with the STM system.The GEC-STM with the extremely precise atmosphere environment control system provided a solution for the measurement of the environment-sensitive molecules.3.The GEC-STM was used to measure the single-molecule charge transport property of a series of metal-organic hybridized molecules.A simplified molecular structure was proposed based on theoretical calculations,and the molecular frontier orbits and their roles in the process of charge transport were simulated.The δ orbital provided by Mo2 center is involved in charge transport and reduces the HOMO-LUMO gap of the molecular junction.