Research On Controllable Self-Assembled Molecular Devices And Charge Transport Mechanism

Molecular electronics studies the charge transport mechanism based on single molecule or molecular layer by constructing an “electrode-molecular-electrode”structure device at a microscale,and explores functional molecular devices to realize integrated circuits at the molecular scale.Although the concept of molecular electronics has been proposed as early as the 1950 s,Aviram and Ratner theoretically explained it in the 1970 s,but is was limited by the difficulty of molecular-scale operation,and it was not until this century that the micro-scale molecular devices were realized.So far,molecular electronics has made great progress in the preparation of molecular devices,the characterization of charge transport mechanism and the functionalization of devices.However,difficulties in device fabrication and functional molecule synthesis,structural instability,and poor interface contact between molecule and electrode are still bottlenecks restricting its development.Focus on these problems,this dissertation designed and fabricated SAM molecular devices and double-SAM molecular devices from the perspective of molecular device configuration,studied the charge transport properties of electroactive molecular systems,and realized the manual control of molecular device transport mechanism.The main research contents and results are as follows:1.Research on SAM molecular devices based on FHT derivatives.We fabricated SAM molecular device based on electroactive molecule of 6-ferrocenyl hexanethiol(FHT)with a redox active center by suspended nanowires electrophoresis technology.The charge transport mechanism of ferrocene derivatives was studied and compared with the non-electroactive molecule 1-undecanethiol(C11).The electrical behavior of ferrocene derivatives was fitted and analyzed by different charge transport models.A tunneling and hopping coexistence two-channel mixed model is proposed which can fit the electrical curve of ferrocene derivatives very well,and the possible reason is analyzed.2.Modulation of molecular-electrode coupling strength and transport mechanism in double-SAM molecular devices.We designed and fabricated an all-solid metal electrode suspended nanowire molecular device with double-SAM configuration based on the suspended nanowire SAM molecular device.Firstly,the key role of molecularelectrode coupling strength in the molecular device transmission mechanism was described,and then the coupling strength between redox active center and metal electrode was adjusted by using simple commercial molecules to change the length and structure of one layer SAM in the double SAM molecular device,and the transition of the charge transport mechanism from direct single level tunneling mechanism to thermal activated hopping mechanism was realized,as well as the temperature dependence of molecular devices was characterized.Then,the single level tunneling model based on Landauer theory and the hopping model based on Marcus theory were used to fit and analyze the electrical curves of molecular devices,verified the transition of charge transport mechanism.