Preparation Of STM Tip By AC Method

Scanning Tunneling Microscope(STM)is an extremely high resolution instrument for studying the surface.STM can firstly observe the arrangement of individual atoms on the surface of materials and the physicalization related to surface electronic behavior.As the core component of the STM,the probe directly scans the surface of sample.The material,shape and size of the probe tip are related to the accuracy of image and data,which is essential for STM.So the paper explores the preparation technology of scanning tunneling microscope probes.At present,for research of tip preparation techniques,the electrochemical etching technique is widely used to prepare probes.In order to find a simpler and more stable method for preparing STM tip,and increase the yield of the tip,the paper adopts AC method to produce STM tip,instead of the traditional DC drop method.In this paper,the development status of probe technology for electrochemical corrosion method at domestic and abroad are introduced in detail.Based on the chemical mechanism of electrochemical corrosion method,the microscopic process of preparing W tip by DC method and AC method is analyzed in detail.Theoretically,the characteristics of W tip are demonstrated,and the evaluation mechanism of the probe tip quality is pointed out.The preparation system is designed and built based on the AC electrochemical corrosion method.The mechanical device in the system can ensure stability of the experimental process.The stepper motor adjusts tungsten height and three-dimensional displacement stage fine-tunes immersion depth of probe into the electrolyte.Based on the feedback control technology,the feedback circuit can cut off the electrolysis voltage at the instant of probe formation and issue a lifting action signal of the stepping motor.Feedback control technology can cut the corrosion circuit with in 100ns.The efficient combination of the mechanical device and the control system ensures the success rate and stability of the W tip preparation.In order to accurately analysis the quality of the W tip,this paper adopts digital image processing technology to measure the size of W tip.The effects of voltage,immersion depth,frequency,reverse voltage,solution concentration and other parameters on the preparation of W tip by AC method are carefully studied.According to the experimental results,the optimal parameter value was determined.The formation process of the W tip was observed under the microscope,and the W tip was optimized.Finally,the W tip was scanned under the STM for Si(111)-7×7 reconstruction.Atomic resolution images of the surface were obtained.The AC method provides a new idea for the preparation of W tip.