| Scanning tunneling microscopy (STM) is an important analytical tool for imaging surfaces at the atomic level. For an STM, good resolution is considered to be0.1nm lateral resolution and0.01nm depth resolution. With this resolution, individual atoms within materials are routinely imaged and manipulated. Therefore, the STM has been widely used for studying material surface since it was invented in1981. And the STM allows high resolution imaging in not only in ultrahigh vacuum but also at the internal interface between two condensed media, such as a conducting solid and liquid. So studying the solid liquid interface of materials at the atomic level can be investigated. The traditional surface characterization techniques can not work on the the solid liquid interface of materials due to its dependence on the condition of ultrahigh vacuum.However, the electrochemical reactions in solid-liquid interfaces is the basis of the electrochemistry and related chemical industry. Therefore, it is urgent for us to develop the electrochemical STM (ECSTM) technique to study the microcosmic mechanism of the solid liquid interface and understand the nature of these chemical processes. And it is very important to improve the present instruments and set. Unfortunately, compared with the traditional STM, some fundamental problems remain to be resolved to develop new ECSTM. First, the interference from the faradic current. When the STM tip was immersed into solution, the faradic current produced by the STM tip would annihilate the tunnel current. Second, the interference from the electrochemical reaction. The surface of the STM tip which serves as a separate electrode would change by the chemical reaction, thus resulting in the instability for the tip.Third, large drift and instability. The introduction of the electrolytic cell and the scanning tip extension both could increase the instability of the system. Moreover, the produced leakage current. The increase of humidity above solution will decreases the insulation resistance. And a leakage current which is proportional to the voltage would be produced, resulting in effecting the quality of the imaging.To circumvent these issues, we devoted ourselves to design a high-performance electrochemical STM. With our teacher’s careful guidance, my main job is divided into the following sections during my PhD’s studies. First, a new and highly stable STM is researched and developed. It uses the brand new lens body structure and combines the triple rail and piezoelectric stack motor of rigid contact by four point, which makes the STM high rigidity, high stability and strong anti-interference ability. Besides, the motor is easy to debug and its starting voltage is only8V. If there is no sound insulation damping, we still can get high-definition atomic resolution figures when the STM was directly put onto our common experiment table on the fifth floor. Second, the tungsten tip for STM is successfully prepared by the method of ac corrosion and Dc liquid film corrosion. By now, we have explored a set of the preparation of tungsten tip through the electrochemical corrosion and get high definition atomic resolution images of high polymer graphite and Au (111) surface. We also try to use the three different kinds of tip coating methods and successfully solved the electrochemical STM tip insulation coating problem. The leakage current of insulation coating tip is less than10pA, which could ensure the smooth progress of the electrochemical STM work. Moreoover, we successfully built a set of Pine Computer-Controlled Bipotentiostat which is suitable for electrochemical STM through combining with20fA Resolution of the home-made pre-amplification electric circuit. Successful preparation of noble metal single crystal electrode (such as Pt and Au eal.) with clean, orderly and large area surface provides the required sample base for the development of electrochemical STM experiment. And we set the electrochemical noise damping device with resonant frequency of less than1.5Hz. The electrochemical STM has high stability and its shift is an order of magnitude smaller than that of reported by recent literatures (2nm min-1). Besides, it also showed the function of high repeatable approximation. Motor repeat approximate in Z direction within the range of2mm and the tip of EC STM deviate in x, y plane in the range of50nanometers. This specific sample area by tracking study provides the foundation for the instrument. We successfully get the atomic resolution images of the surface of Au (111) and the absorbed SO42-on the Au (111) in solution. in addition, we also made a further improvement in the device to solve the problem of the electrochemical STM leakage by using scanning tube seal structure. Three, we design a kind of Quartz electrolytic cell of ECSTM which is suitable for droplet single crystal working electrode. The noble metal of droplet single crystal working electrode is very easy to prepare without the process of positioning, cutting, grinding and polishing, so So there is no mechanical scratches on its single crystal surface. Some single crystal droplets, such as Au etc., are widely used in the study of electrochemical STM. However, some active single crystal droplets, such as Pt etc., rarely used in the electrochemical measurement of STM, because the Pt crystal plane made by the traditional method is very easily contaminated. Here, to solve the problems above, we develop a set of quick installation the method of the samples based on the design of the new electrolytic cell. Excitingly, we obtained Pt (111) with clean, orderly and large area surface, which will promote the Pt droplet of single crystal to be widely used in electrochemical STM measurement. Forth, based on the programming system of Labview, we built a set of control software for electrochemical STM, including electrochemical control, scanning control, fast data acquisition, data storage and data processing, etc. The scanning speed of the control software increased nearly10times and reached to100Line s-1. The improvement of the scan mode of the traditional potentiostat,makes it possible to timely adjust the stretch of the scanning tube and maintain constant height on samples for the tip during when there is a drift between the tip and samples, which would reduces the hysteresis caused by manually adjusting the distance between the tip and sample. And we built a control module for the constant current scanning based on the PID feedback adjustment principle. We also set a processing module for the following image processing. Last but not the least, as another sole work, we successfully prepared large area of single-layer graphene by the method of chemical vapor deposition (CVD) and obtained atomic resolution of STM images. We prepared large area of single-layer graphene oxide based on the oxidation-reduction method of graphene and reduced the graphene oxide at high temperature. The morphology changes before and after reduction was characterized by atomic force microscopy, respectively. At the same time, we put forward the idea to construct a dual structure consist of graphene-metal nanoparticles by manufacturing nano defects on the graphene under the help of electrochemical STM technique and modifying the graphene through electrochemical deposition or electrochemical STM nano building method. And we have preliminary built a platform for setting up metal nanoparticles, which laid the foundation of studying the influence of graphene on the structure, catalytic activity and stability of nanoparticles. |
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