扫描电化学显微镜电子控制系统的研究

【作者】 伍海龙；

【导师】 张玉林；

【作者基本信息】 山东大学 ， 控制理论与控制工程， 2007， 硕士

【摘要】 扫描电化学显微镜(Scanning ElectroChemical Microscope，简称SECM)是一种新型的扫描探针显微镜，自1986年被提出后便得到了迅速的发展。它基于电化学原理工作，驱动非常小的探针在靠近样品处进行扫描，可测量微区内物质氧化或还原所给出的电化学电流，从而获得对应的微区电化学和相关信息，目前可达到的最高分辨率为100纳米。由于SECM具有化学灵敏性，不但可以研究导体和绝缘体表面的几何形貌，而且可以分辨不均匀电极表面的电化学活性，对材料进行微米级加工等。国外已经有商品化SECM仪器，但价格非常昂贵，而且不提供任何详细线路图，目前国内尚无生产此类仪器。本文主要研究SECM电子控制系统的两个关键部分：微位移驱动工作台和微电流检测仪，为自主研制这一新型仪器提供技术准备。本文选用压电陶瓷微位移器作为驱动SECM探针的微定位工作台，具有纳米级的高定位精度。压电陶瓷驱动电源是压电陶瓷微位移器的关键部件，国内外已有大量研究，多采用分立器件，电路复杂。本文在分析了压电陶瓷驱动电源的要求后，利用高精度高压运算放大器PA69设计了一种新的电压控制型驱动电源，提高了电路集成度，并补偿了输入失调电压。经实验证明该电源能满足SECM探针驱动中微定位的控制需要，具有精度高、电路简单、可靠性强的特点。SECM实验中需要同时控制两个工作电极的电位，且工作电极上产生的微电流信号极其微弱(一般在纳安级甚至更小)很难采集和识别。本文在现有的研究基础上，提出并设计了一种参考电极虚地的双恒电位仪，两个工作电极的电位控制电路完全对称，从而简化了电路设计，提高了电路的抗干扰性。在微电流检测上通过在反馈回路中串一个电阻器采集电流信号，并用仪表放大器AD620差动测量电阻两端的电压，实验证明该电路较好的满足了微电流信号的检测要求，克服了现有一些仪器灵敏度越高稳定性越差的弊端。SECM的仪器控制部分采用32位嵌入式ARM微控制器LPC2138实现，设计了16位的程控电压源来控制压电陶瓷驱动电源和双恒电位仪，16位的AD数据采集电路实现对微电流信号的采集。同时设计了一个基于CP2102的USB通信接口电路以实现和上位机的通信。软件上采用C语言作为编程语言实现了各个功能模块。最后，针对SECM的后续研究工作提出了进一步完善的建议，为今后的深入研究打下了良好的基础。更多还原

【Abstract】 Scanning electrochemical microscope (SECM) is a new scanning probe microscope, which is proposed in 1986 and has a rapid development. According to electrochemical principle, SECM drives little tip close to sample, measures the electrochemical current which is produced by redox, and acquires the information about sample. The resolution of SECM is up to 100 nanometer. For SECM has chemical sensitivity, it is used not only to detect surface of conductor or nonconductor but also to distinguish electrochemical character of non-uniformility surface and to fabricate in micron.Presently commodity of SECM has been produced abroad, and it is very expensive. There isn’t apparatus of SECM in China. The paper mainly designs the electronic control system of SECM, which includes power supply of piezoelectric ceramic and micro-current detection. The paper is to provide technical preparation for the research and design of SECM..SECM chooses piezoelectric ceramic as micro-positioning stage, which has a super-high resolution in nanometers. The power supply is the key components of piezoelectric ceramic actuators. There are a lot of researches about its power supply, most of which has a complex circuit. After analyzing demands of power supply, the paper designed a new power supply based on voltage-controlled with high voltage amplifier PA69. Thus the integration of circuit is improved, and input offset voltage is compensated. Test proves that the power supply can achieve demands of probe positioning of SECM, and power supply has high precision, simply circuit, and high reliability.There are two work electrodes in cell of SECM. The current signal of work electrode is so weak in nanoampere that it is difficult to be distinguished from the noise. The paper proposes a biopotentiostat with reference electrode of virtual ground. The voltage of two work electrode is controlled dependently by a complete symmetry circuit, which makes design simply and improves anti-jamming. On micro-current detecting, the paper collects signals by a feedback resistor, and amplifies the voltage on resistor by an instrument amplifier AD620. Test proves that the circuit can detect micro-current very well, and overcome disadvantages of some instruments.The control part is designed based on the embedded, 32 bit RISC microcontroller ARM LPC2138. Design a D/A circuit to control power supply of piezoelectric ceramic and Biopotentiostat, a A/D circuit to sample micro-current. Also design an USB circuit of CP2102 to communicate with PC. In software programming , the paper selects C as programming language to realize each functions.In the end, some advice is put forward to improve the performance of SECM, which provides favorable foundation for future research.更多还原