Research On Key Techniques Of Bias Scanning Ion Conductance Microscope

Scanning Ion Conductance Microscopy(SICM),as a member of the Scanning Probe Microscope(SPM),has been developing for thirty years since 1989 and applied to many areas,such as surface topography measurement,nanoscale operation,cell volume measurement,cell mechanical properties research,and cell dynamics research.It has been widely used in life science,medicine,materials science,nanofabrication,and other fields.SICM has edges on in-situ non-contact scanning,real-time observation under physiological conditions and scanning without sample pretreatment,especially on nondestructive testing of soft samples which make it become an important measurement tool for living biological samples in practical applications.With the development of SICM applications,the improvement of performance and the expansion of functions have become an inevitable trend of research.Meanwhile,due to the imperfection of the structure,the measurement accuracy is effected by the vibration.Since the probe is difficult to manufacture,and the probe holder is flimsy,not multi-use,and excessively expensive,SICM cannot be comprehensively used.The hysteresis characteristics of the piezoelectric micro platform affect positioning accuracy.The unselectable scanning mode and control mode limit the application of SICM in the field of high-precision nanometer measurement.Based on the fact that the performance of the SICM system has its unique advantages as well as obvious deficiencies,the Bias Scanning Ion Conductance Microscope(B-SICM)is derived from the research of the key techniques of SICM.Through implementing the innovations and improvements of structure design,scanning mode,system modeling,and control method,B-SICM reduces the cost,expands the functionality,enables high-precision scanning,thus make it promising in the market.The main research contents of this paper are as follows:(1)By analyzing the principle and working mode of SICM,the working principle of Bias Scanning Ion Conductance Microscope is determined,and the system module division and the scheme is designed.After comparing the principles,advantages,disadvantages and applicable conditions of various Scanning Modes,the Bias Modulated Mode is proved to be more suitable for scanning complex samples because of its advantages of stability,anti-interference and long working time which is applied to the optimal design of B-SICM in this paper.According to the resistance model of the probe tip and the equivalent circuit diagram of Bias Modulated mode,it is proved that the ion current flowing through the electrode in the scanning probe and the electrode in the petri dish solution is only related to the distance d between the probe tip and the sample excluding other factors.Therefore,the loop current is used as the feedback signal to control the displacement of the probe where the moving track of the probe is the three-dimensional morphology of the sample.On this basis,the principle scheme design and functional module division of B-SICM system are carried out,which lays the foundation for the design of key components and the construction of B-SICM.(2)Based on the design scheme of B-SICM,the results of theoretical analysis and Finite Element Analysis,the B-SICM system is optimized.The structure of the probe holder bracket is designed using the beam theory and the parameters of the cantilever beam are determined by Finite Element Analysis which reduces the influence of resonance on the measurement safety and accuracy.Based on this design,the natural frequencies under different modes are all higher than 7.52 k Hz according to the results of the Modal Analysis of the cantilever beam,which provides support for the selection of piezoelectric ceramic drivers.The optical lighting system is optimized,and a glass probe clamping and lighting device is designed,which ensures that the glass microprobe can be fixated and the probe tip can be illuminated at the same time.The device overcomes the disadvantages of the traditional probe,such as light blocking,structure loosing,which can introduce disturbance easily(The patent has been granted).By using the damping properties,the Polyurethane Foam damping block is added between M-112.1 and P-753.21,and the damping structure of the system is built.The deformation of M-112.1 is decreased to 0.073nm by 93.87%,which effectively reduces the influence of vibration deformation on the control accuracy of the system.(3)To reduce the influence of hysteresis characteristics of piezoelectric ceramics on the control accuracy,the Adaptive Evolutionary Back Propagation Algorithm is optimized,and the Back Propagation Algorithm based on Whale Optimization Algorithm is proposed,a hysteresis model with a high fitting degree and suitable for B-SICM is established.The selection operator of Genetic Algorithm is improved according to the Key Few Rules and adaptive factors are added in the crossover and mutation stages to improve the convergence speed,which is used to optimize the initial value of BP Algorithm,so that the algorithm has high convergence rate,good global optimality,good robustness,and avoids falling into the local optimal solution.The Back Propagation Algorithm based on the Whale Optimization Algorithm establishes the polynomial hysteresis model based on the meta-heuristic Whale Optimization Algorithm,which is used to expand the input space,and the neural network algorithm is used to realize the one-to-one mapping relationship to obtain the height fitting of the hysteresis nonlinearity of the piezoelectric ceramic driver.The experiment shows that the effectiveness in identification using the Adaptive Evolutionary Back Propagation Algorithm and Back Propagation Algorithm based on Whale Optimization Algorithm is better than any other identification method.The fitting error sum of squares of the Back Propagation Algorithm based on the Whale Optimization Algorithm is only0.399?m~2 and the maximum fitting error is 42.69-77.42%lower than the usual algorithms,so it is used as the direct modeling method of hysteresis inverse model for feedforward control.(4)To improve the positioning accuracy of the probe in sample measurement,the FRAMAC control method is proposed.The hysteresis inverse model of the output displacement and input voltage of the piezoelectric actuator is directly established by using the Back Propagation Algorithm based on the Whale Optimization Algorithm which compensates the hysteresis characteristics of piezoelectric ceramic linearization,eliminates the complex operation and ensures the accuracy of the feedforward model.On this basis,the Moving Average Control is used as feedback where parameters are constantly updated by Self-Tuning Control and robustness is improved in the feedback controller.Feedforward control and RAMAC feedback control are linked together to form FRAMAC composite control.Experiments show that this algorithm reduces the hysteresis from 17.64%to 2.51%and the positioning error is much smaller than the PID algorithm which is widely used today,providing technical support for the accurate description of three-dimensional images by Bias Scanning Ion Conductance Microscope.(5)Experiment verifies that the rationality and reliability of the B-SICM and the high-precision image of the standard sample are obtained by improving the scanning mode and control method.The law of pulling parameters of the probe is summarized using the Partitioning method and the result of the law is used to draw the probe.The B-SICM measuring loop current is used to predict the tip radius of the glass probe and the measured results are compared with SEM and patch-clamp technology,which verifies the effectiveness of the B-SICM experimental platform.The probe-sample approach experiment and repeated experiments are conducted,and the consistency of the measured results verifies the stability of the B-SICM experimental platform.Based on above experiments,3D imaging of the standard sample is conducted with different paths and scanning modes,which verifies the accuracy of the FRAMAC control method in the micro-positioning of the probe and realizes the non-contact high-resolution real-time imaging of the sample by B-SICM.