Selective Construction Of Single-Molecule Junction With The Applied Electric And Optical Fields

The construction and properties of the single-molecule junction have been studied throughout the whole development of molecular electronics.As a typical model in molecular electronics,single-molecule junctions play an essential role in the discoveries of the novel physical and chemical phenomena at the single-molecule scale and preparing miniaturized,integrated as well as functional molecular electronic devices.So far,scientists have developed many techniques for constructing singlemolecule junctions,including dynamic break junction techniques,such as Mechanically Controllable Break Junction(MCBJ),Scanning Tunneling Microscopy Break Junction(STM-BJ),and static single-molecule junction techniques,such as the Electromigration and Dash-line Lithography.Meanwhile,the previous works reported that the interaction between the molecular and electrode interface was modified by changing electrode materials,altering molecular anchoring groups,and using the external stimulus.However,the primary purpose of these works is to regulate the electron transport properties of the single-molecule junction,and the construction process of the molecular junction is slightly neglected.The construction of molecular junctions is the key to the realization of molecular devices,and how to selectively construct molecular junctions in integrating different functional molecules into specific sites is still a technical challenge to be solved.In this thesis,we study the molecular junction construction under the external field based on the dynamic break junction technologies,including MCBJ and STM-BJ.Besides,we combined with the single-molecule counting technology to quantitatively analyze the molecular junction construction,reflecting the coupling between the molecule and the electrode and the motion behavior of the molecule in the solution.We hope to develop a controlled method to construct a single molecular junction and further improve the success rate of molecular junction construction through the external field.The main research contents and main conclusions are as follows:1.The construction of molecular junctions under the electric field.A series of conjugated molecular junctions with different anchoring groups were fabricated under an electric field by employing STM-BJ technology.The formation probabilities of different molecular junctions and their responses to the external electric field were compared through the combination of the quantitative analysis of the single-molecule counting method and the single-molecule conductance measurement.We found that within a particular range bias,the formation probabilities of the molecular junctions with-SMe anchoring group increases with the increase of applied biases,while the formation probabilities of-SAc,-NH2,-PY anchored molecular junctions decreases with increasing applied biases.DFT calculation showed that the formation of molecular junctions under the electric field is synergistically influenced by the arrangement and distribution of molecules under the electric field and the adsorption energy on the electrode surface.Finally,the selective construction of molecular junctions in bimolecular mixed solution was realized based on the different responses of different molecules to the electric fields.2.The construction of molecular junction under the light field.The conjugated molecules with a size less than 2 nm were trapped in solution through the combination of optical tweezers technology and MCBJ technology,improving the success rate of molecular junction construction.The optical tweezers-mechanically controlled cracking(OP-MCBJ)device with laser imaging function was designed and constructed based on MCBJ technology.Using OP-MCBJ test platform,three aniline molecules with a length of 1.44 nm,1.01 nm,and 0.57 nm were optical trapped.It was found that under the irradiation of 671 nm laser with a power of 30 mW,the formation probabilities of the tree type molecular junctions increased by 23.88%,9.36%,and 5%,respectively,indicating that the improvement effect decreased with the decrease of molecular length.