Study Of The Fabrication And Electrical-Spectroscopic Characterizations Of Single-Molecule Electrical Devices

Molecular electronics has been developing for decades since the concept was proposed.Its ultimate goal is to study the electrical properties of atoms and molecules from the most basic units,to realize the design and fabrication of functional molecular devices.The development of single-molecule conductance measurement has promoted the observation of a series of unique phenomena at the quantum scale and provided a method of principle verification for organic molecular electronic devices.In molecular electronics,the practical fabrication of single-molecule junctions(SMJs)is a technical challenge,and understanding the relationship between the electrical properties and the structures of SMJs is a critical scientific topic.This dissertation focuses on the fabrication and characterization of SMJs.The SMJs are fabricated by the break junction(BJ)technique,and the electrical properties are characterized by using a large amount of statistical information in the BJ processes.We developed the Microfabricated-Mechanically Controllable Break Junction(Microfabricated-MCBJ)methodology with higher stability.To avoid the inherent spectroscopic background signals from the traditional polymer insulating layer and improve the chemical stability of the sacrificial layer,an elastic metal substrate with an inorganic oxide insulating/sacrificial layer was introduced into the fabricating process for the first time.The combined electrical-spectroscopic characterization instrument was constructed to realize the two-dimensional characterization of single-molecule junctions.The main conclusions of this dissertation are as follows:1.Single-molecule junctions were fabricated via Scanning Tunneling Microscopy-Break Junction(STMBJ),and the charge transport mechanism of the molecules with the parallel conductance pathways was explored.Additionally,we explained the total conductance of the SMJs by the conductance superposition theory of molecular circuits.2.A single-molecule scale mechanochemical reaction process is studied using the STMBJ,and the unsupervised spectral clustering algorithm was introduced to classify the conductances from junctions with complex components,verifying the ability of single-molecule conductance measurement technology in structure identification.3.The technology of fabricating MCBJ chips based on micro/nanofabrication was developed,and the suspended metallic nano bridges with a linewidth of less than 100 nm were successfully achieved.4.A combined electrical-spectroscopic characterization methodology was successfully developed.Based on Microfabricated-MCBJ,single-molecule junctions with high stability were fabricated.The in-situ SERS signals on SMJs with reaction were collected,allowing the study of the structure-activity relationship in SMJs.