A New Designed Circuit For Tip Preparation Of Scanning Tunneling Microscope

Scanning tunneling microscope(STM)is a high-resolution surface research instrument.The tip has an important impact on the resolution of the STM.The electrochemical corrosion preparation,due to its easy control of reaction conditions,simple manual operation,and good repeatability,has developed rapidly.Based on the technology development of electrochemical corrosion preparation,the DC-drop method due to its relatively high stability has been proposed.In order to avoid the tip to occur excessive reaction and become blunt,a certain automatic power control system to control the timing of the load circuit is needed to be designed.But the existing circuit design exists obvious shortcomings,such as low success rate and unstable corrosion process.A new circuit for overcoming the shortcomings in current popular devices,such as low success rate and unstable corrosion process is proposed in this paper.Firstly,a mechanical structure used for tip corrosion is designed according to the microscopic chemical process of tip corrosion.Secondly,a new type of circuit is designed,in which reaction current measurement mechanism is changed so that the actual voltage between the cathode and anode remains stable during the experiment,which improve the success rate.Moreover,in order to obtain a sharper tip,the differential circuit is used to monitor the reaction process which could be cut off immediately to avoid overreaction and lead to a blunt apex.In order to study the influences of different corrosion parameters on the tip preparation,a kind of image processing method to indirectly measure the length of the tip was proposed.Based on analysis of the measurement data,compared the results of new and old circuits and detected the effect of voltage,cutoff current,the length of tungsten wire in electrolyte,the sensitivity of the differential circuit,the position of cathode ring,and the electrolyte concentration on the tip quality,and the ideal reaction parameters are suggested.Finally,the whole reaction process are observed,and the tip are applied to scan the sample surface in the scanning tunneling microscope after optimization processes,thus the clear surface images with atomic resolution is obtained.The results show that the new circuit is improved in stability and quality,which also proved by the scanning tunneling microscopy test.