Force-electrical Characterization Of Single Molecules Based On Atomic Force Microscopy

The development of molecular characterization techniques provides a unique opportunity for the study of novel physicochemical phenomena at a single molecular scale.Therefore,the study of metal-molecule-metal junctions explains physical and chemical properties at the atomic and molecular scale.In this thesis,a complete precision instrument was built to simultaneously measure the mechanical force and electrical conductivity of monomolecular junctions,and to conduct in-depth research on the microscopic properties of single-molecule.The characterization technologies based on single molecular junction include mechanically controlled break junction(MCBJ)technique and scanning tunneling break junction(STM-BJ)technique,both of which obtain the molecular conductivity values through a high-frequency acquisition system while dynamically constructing single molecular junctions.However,these techniques based on conductance signal still have the space to be improved that a single conductance signal cannot effectively explain the behaviors and connections of single molecules in the system.Hence,a technique of force-conductivity co-measurement based on atomic force microscope break junction(AFM-BJ)technique was developed in this thesis,to reveal the interrelated information between molecular structure and function in multiple dimensions at the single molecular level.The main research contents are as follows:1.A system of AFM-BJ based on atom force microscope was designed and built,realizing the measurement of break-junction.2.AFM-BJ was optimized and upgraded from the aspects of framework module,data acquisition module,motion module,electrode module,seismic and shielding module,logarithmic amplifier module,and control module,to improve the stability of the instrument and increase the success rate of the experiment and the amount of effective data.3.Two molecular systems were tested and the data processing program of forceconductivity co-measurement was developed.Through the developed system,we measured the curves of conductivity-time,force-time,conductivity-distance,and force-distance curve measurement,where molecular step lengths and force of molecular junctions could be obtained.This thesis proposes a method to further explain single molecular configuration and dynamic changes.