Research On Key Technologies Of Scanning Electrochemical Microscopy

SECM is an in-situ electrochemical detection instrument that studies the chemical composition,structure,properties and behavior of the interface micro area.It is an electrochemical control technology by a high time and spatial resolution.Its working principle is based on the electrochemistry.The electrochemical current of material oxidation or reduction was measured by scanning near the sample surface in solution containing electroactive materials using a small probe.Thus the electrochemical information of samples was obtained,who can be a conductor,an insulator or a semiconductor.SECM has high electrochemical sensitivity,can not only study the reaction kinetics of heterogeneous reaction at interface and homogeneous reaction in solution,reflect the electrochemical inhomogeneity at electrode microsurface and the morphologies of conductors,but also can be used for micromachining of materials,studying many important biological processes.The SECM instrument was improved from the demand perspective to study the electrochemical methods,in order to adapt to the development of applications in electrochemistry and electroanalytical chemistry.This thesis is aimed to solve the problems at the liquid / liquid and liquid / solid interface,by in-depth understanding of the working principle of SECM,combining with the characteristics of the SECM technology.The following 5 works were done by deeply studying the key technology of each module of the instrument.The overall structure of the SECM instrument system was designed based on analyzing the structure and working principle of the SECM imaging instrument system.We designed the bipotentiostat circuit of double potentiometer control system,the waveform generator circuit,the filter circuit,the signal acquisition circuit and microprocessor circuit,by understanding the working principle of electrochemical bipotentiostat control system.The PCB design was carried out of digital and simulating circuit of bipotentiostat control system.Finally,the design of control system of electrochemical bipotentiostat was completed.In order to meet the displacement control requirements of SECM probe electrode,three dimensional stepper motor control system and three dimensional piezoelectric crystal control system were designed according to the technical parameters of three dimensional mechanical and piezoelectric displacement platform,respectively.The principle of resistance strain gauge measuring piezoelectric displacement output was analyzed in the design of three-dimensional piezoelectric control system.According to load characteristics and strain gauge signal characteristics of piezoelectric crystal,high voltage driving circuit with error amplifier type and the strain gauge signal detection circuit were designed.We mainly focused on the design and improvement of the PID controller for piezoelectric displacement control and precision positioning platform.The mechanical structure of SECM instrument system was designed including 3D mechanical displacement platform,3D displacement platform,clamping structure of piezoelectric probe,electrolytic cell,microscope,basal level adjusting mechanism,electromagnetic shielding device and bottom damping system.The finite element analysis was used to estimate the mechanical structure of SECM by using UGNX8.0 software.The analysis results show that the designed mechanical structure has high rigidity and good aseismic performance.The upper computer control software of the SECM instrument was designed by a hierarchical modular structure.The software structure includes GUI interface,business logic layer and data transmission layer.Each part was also divided into several modules with their independent functions.Several experiments were carried out on the SECM instrument system using the above PC control software,such as cyclic voltammetry test on ultramicro-electrode,progressive curve of the probe,scanning curves and SECM imaging test.In SECM imaging test,gold interdigitated electrode,gold electrode array,the ITO with fingerprint were all used.Results show that the instrument has good imaging performance,achieving the SECM imaging of large space and high spatial precision.A new SECM image-processing technique was proposed involving constrained least squares filtering algorithm,LoG algorithm and NEDI interpolation algorithm.It was further used to process SECM images.The improved constrained least squares filtering algorithm improves the contrast of the edge region of the image,clears the edge area,and smoothes the noise in the image.Therefore,the clarity of the restored image has been obviously improved.The SECM image-processing technique combining LoG algorithm with NEDI algorithm is helpful for the clarity and resolution of SECM images.Comparison with the constrained least squares filtering algorithm,the image processing technology has a better treatment effect for image edge region.The image edge after processing is clearer ignoring the shape of substrate.It may provide a general method for SECM image test.