Investigation On Micro-cantilever Displacement Detection System Of Atomic Force Microscope Based On Fabry-perot Interferometer

Atomic force microscopy（AFM）has been widely used in many fields such as surface detection and nanofabrication with advantages of high resolution,no damage to the sample,etc.In AFM,the surface topography of the samples is obtained by detecting the atomic force between the probe and sample.It needs detecting the displacement of cantilever accurately.The beam deflection method is most commonly used to detect the micro-cantilever displacement due to its high sensitivity and no effect on the micro-cantilever.In order to ensure the effective reception and detection of the reflected light,the beam deflection method requires a high reflectivity of the micro-cantilever and a small spot size of the light source,which limits its application.In order to avoid the defects of the optical beam deflection method,micro-cantilever detection systems based on planar Fabry-Perot（F-P）and spherical F-P interference are designed.The experimental platform is built to verify the feasibility of the design of detection system based on F-P interference.The thesis contents are as follows:（1）Systematically elaborated the working principles of AFM,several methods of detecting micro-cantilever displacement are introduced,and their advantages and disadvantages are analyzed and compared.The principle of the most commonly used beam deflection method is studied and the defects of detection and the artifacts of AFM imaging are analyzed.The scheme of micro-cantilever displacement detection based on F-P interference is established.（2）Micro-cantilever detection models based on planar F-P interference and spherical F-P interference are established.The influence of the deflection angle caused by the micro-cantilever shape changing on the detection of micro-cantilever displacement and the AFM image is simulated and analyzed.According to the simulation results,the structure of the spherical F-P interferometer is designed,it can avoid the influence of the deflection angle of the micro-cantilever by a certain angle between the micro cantilever and the normal of optical axis,The range of the angle between the micro-cantilever and the normal of optical axis is given.（3）The effects of the reflectivity of the mirror and micro-cantilever,the wavelength,stability of and spectral width of light source on the detection of the micro-cantilever and the AFM image are simulated and analyzed.The parameters of detection systems based on the F-P interference and the spherical F-P interference are designed.The designed detection systems are compared and analyzed from the aspects of sensitivity,stability and detection range.The artifacts in AFM images caused by the micro-cantilever detection system based on F-P interference are simulated,the results show that the designed detection systems do not produce interference fringes on the image,but they have a great influence on the sensitivity of AFM detection.（4）According to the existing conditions,the plane mirror is used to replace the micro-cantilever and experimental platform is built.The experimental results verify the feasibility of the micro-cantilever detection system based on F-P interference,The linear fitting correlation of the working area data of the detection system based on the planar F-P interference is 98.8%,the minimum resolution of micro-cantilever displacement detection can be up to 5.8×10^-6nm,limited by the reading accuracy of the experimental instrument,the measured resolution is 0.58nm.In the engineering applications,the high resolution data acquisition card will be used instead of the power meter head,and the designed micro-cantilever detection system based on F-P interferometer can meet the requirements of micro-cantilever displacement detection of AFM.According to the experimental light path,the detector based on F-P interference is developed preliminarily.