Control Approach And Its Applications At Single Atomic/Molecular Scale In Mechanically Controllable Break Junction (MCBJ) Technique

Control technology is widely used in various fields from massive production in manufactories to biologic process in life science.Automatic control technology facilitated our lives and stimulates the development of scientific research.The fields of the control applications include from the plant's production equipment to the cells in living organisms,macromolecules in life processes.However,it is still difficult to reach into the atomic scale.The atomic scale control requires more stringent conditions,such as vacuum,cryogenic temperature and vibration isolation.If the feedback control technology can be applied to the precise control of measurement process of the atomic scale under ambient environment,it will be a breakthrough not only for the application of the automatic control but also for the single-atom or single-molecule researchIn this thesis,we combined the closed-loop PID control technology with Mechanically Controllable Break Junction(MCBJ)technique,used the real-time feedback of closed-loop control to precisely control the gap of metal nano-electrodes pair,to ensure the single-atom or single-molecule are stably bridged between the metal electrodes for a long time.By this way,more precisely detection of the atom or molecule under ambient environment can be realize.Nowadays,the connections at atomic scale within time level of minutes have not been achieved yet,the control approach proposed in this thesis will be both a breakthrough in the fields of not only control technology but also molecular electronics.On the basis of that,we also discussed the possibility of using feedback control to regulate specific configurations in molecular junctions,and then used a combined spectroscopic and electrical method for junction characterization.The main research contents and conclusions of this thesis are as follows:1.The closed-loop PID controller for real-time control the piezo of MCBJ instrument is upgraded into the system of the original MCBJ instrument.By this way,the gap between the electrodes pair can be accurately adjusted to form metal atomic contact structures.This realize a long-term stable contact of single-atom under ambient environment.2.Through the long-term stable control of the Au single atom contact,it ensures to characterize the electrical transport properties of the Au single atom.Compared to the manual open-loop control,it is demonstrated that the long-term stable connection of the atomic scale under ambient environment can be realized by the closed-loop PID control.For control system of the atomic connection,we have optimized the PID control parameters to successfully realize stable Au single atom connection in over 99%of the testing time.3.We extended the application of feedback control technology to MCBJ technique and made it possible to obtain more accurate single-molecule electrical information.Through the application of the feedback control at single-molecule scale,the OPE2 molecule junction was connected stably in over 99%of time,and the longest existing time during the test was up to the 237.6 seconds.4.Based on the connection time of single atomic contact under the feedback control,the stability of the MCBJ instrument can be evaluated.This provides a performance index for the design and optimization of the vibration isolation system for the instrument.What's more,under the feedback control,the Raman spectroscopic and MCBJ technique can be combined to characterize the electronic and optical properties of single molecule simultaneously.