Controlling Single Molecular Junction Conductance Based On Electrochemical STM-BJ Method

Due to the limitations of lithography and quantum mechanical laws,it will be more and more difficult to fabricate smaller components and probably not work properly.Hence,molecular electronics has become a hot research topic in recent years.It not only meets the increasing technical demands of the miniaturization of traditional Si-based electronic devices,but also provides an ideal window for exploring the intrinsic properties of materials at the molecular level.Thus,they have the potential to partly replace traditional solid-state device counterparts in the future.Field effect transistors and molecular switches are common molecular electronic devices,which can be obtained by tuning the energy level of electrode or molecule.With the deepening of the research,a number of new effects,including electron-mechanics,optoelectronics,quantum interference?QI?,were discovered at the single-molecule level.Here,we systematically study the gating effect on the electron transport of the benzene based molecule with dihydrobenzo[b]thiophene?BT?as the anchoring group,ferrocene-based molecular with BT as the anchoring group?ferrocene-BT?,(Co?SHBtPy?₂?PF₆?₂ by electrochemical scanning tunneling microscope-break junction method?ECSTM-BJ?,while Au and BMIPF₆ ionic liquids were used as electrode and solvent,respectively.The main work of this paper is as follow:1.The QI effect of meta-benzene based molecule with BT as the anchoring group?meta-BT?can be controlled by manipulating the electrode potential of the junctions in electrolyte,while the redox state of the molecule does not change.More than two orders of magnitude conductance change is observed for meta-BT ranging from<10^-6.0 G₀ to 10^-3.3G₀ with varying the electrode potential,while conductance value of 10^-3.3 G₀ is even larger than the conductance of para-BT?para-benzene based molecule with anchoring group of BT?.Both theory and experiments show sharp-valley featured destructive QI effect for the meta-BT.The current work demonstrates that the QI effect can be tuned by electrochemical gating without change of molecular redox states,and provides a feasible way to realize an effective molecular switch.2.We studied the conductance of single-molecule junction of the ferrocene-BT contacting to Au electrode by employing ECSTM-BJ in the BMIPF₆ ionic liquids.The experimental results show that the conductance of target molecules can be tuned by electrochemical method,meanwhile the redox state of ferrocene-BT molecule can be changed with varying of electrode potential.The maximum value of conductance value can be found near the redox state3.We studied electron transport of single-molecule junction of Co?SHBtPy?₂?PF₆?₂contacting to Au electrode by employing ECSTM-BJ technique in the BMIPF₆ ionic liquids.According to a series of statistical peaks of conductance measured at different electrode potentials,it is found that the conductance increases first and then decreases(ranging from<10^-4.10 G₀ to 10^-3.6 G₀)with varying the electrode potential,and the maximum conductance(10^-3.6G₀)is near the redox state.