Development of an atomic force microscope operating in DC non-contact mode

目的是研制工作在直流不连续模式下的原子力显微镜。在开始的时候，我做了一个带有跷跷板形状的杠杆的力反馈系统。用光学杠杆法检测杠杆偏转。测力灵敏度为-10^&lt；-10；N。然而，跷跷板操纵杆的复杂结构造成了令人无法忍受的热漂移和低频响应。为了克服这些问题，提出了一种新型的力反馈系统，该系统使用了一种商用的微悬臂梁，由于悬臂梁的挠度是由简单的光纤干涉仪来检测的，因此减少了热漂移。而微悬臂梁的高谐振频率允许对样品进行高速扫描。光纤端部镀金薄膜。光纤端与镀金微悬臂梁之间的静电力与探针尖端与样品之间的原子力是平衡的。利用该力反馈系统…测量了一些力曲线更多。这些曲线与传统的由悬臂梁挠度确定相互作用力的方法有很大不同，没有反馈系统。尤其是靠近时的最大吸引力与返回时的最大吸引力的大小顺序相同。提高了系统的稳定性，使力分辨率达到-10^&lt；-11&gt；N，但由于用于测量的控制系统较差，频率响应仍然较差。然后通过扫描样品表面无法获得AFM图像。讨论了设计具有高频响应的反馈控制系统。在探针尖端处于相互作用力的情况下，建立了一个简单的悬臂梁动力学模型。通过对反馈系统的高频响应进行参数估计，仿真结果表明反馈系统的频率响应有可能高于1 kHz。我将实际制作控制器，并尝试以非接触式直流模式操作AFM。较少

The purpose was development of atomic force microscope operating in DC non-contant mode. In beginning, I have made a force feedback system with a seesaw shape lever. The lever deflection was detected by an optical lever method. The sensitivity of force measurement was -10^<-10>N.However the complex structure of the seesaw lever has caused intolerable thermal drift and a low frequency response. To overcome these problems, a novel force-feedback system using a micro-cantilever commercially available was proposed.Since the cantilever deflection is detected by a simple optical fiber interferometer, the thermal drift is reduced. And the high resonant frequency of the micro-cantilever allows the high-speed scanning of samples. The optical fiber end was coated by gold thin film. The electrostatic force between the fiber end and the gold coated micro-cantilever is balanced with the atomic force between the probe tip and sample.Some force curves were measured by using this force feedback system … More . The curves were quite different from those of conventional method in which the interaction force is determined from cantilever deflection without feedback system. Especially the maximum of the attractive force in approaching was in the same order of the maximum in going back. The stability of the system was improved, so that the force resolution was -10^<-11>N.However the frequency response was still poor because the control system used for the measurement was poor. Then I could not obtain an AFM images by scanning the sample surface.A discussion to design the feedback control system with a high frequency response was made. A simple dynamic model of cantilever was proposed in case that the probe tip was in the field of interaction force. Supposing a PID controller, the control parameters were estimated to realize the high frequency response of the feedback system.A simulation result shows a possibility of frequency response of higher than 1kHz. I will actually make the controller and will attempt to operate the AFM with non-contact DC mode. Less