Research On The Key Technology Of The Vacuum FM Atomic Force Microscope Measurement Unit

Frequency modulated atomic force microscope(FM-AFM)is a high-precision measuring instrument,which can be used to characterize the physical and chemical properties of material surface.It can measure surface uniform insulators and achieve true atomic resolution,while also measuring atomic force spectra,potential differences,etc.,making it a powerful atomic/molecular scale characterization tool.Widely used in the development and characterization of nano electronic components,surface chemical reactions of analytical materials,high-resolution imaging of biological macromolecules,and other fields.However,commercial AFMs currently operating in atmospheric or liquid environments typically use amplitude modulation(AM)mode for measurement.But in this case,the quality factor Q is usually less than 1000,which greatly limits its high-resolution imaging ability.In order to improve resolution and achieve high Q values in the AFM measurement system,a vacuum AFM measurement environment was used,and the frequency modulation working mode was adopted.This article studied the key technologies of the measurement unit and further optimized the design of the key modules in the measurement unit.The research content is as follows:Firstly,the principle of the optical deflection detection system in the measurement unit has been deeply studied.With the aim of reducing the deflection noise and improving the sensitivity,the key parameters and indicators for the optimization of the optical deflection detection system have been analyzed,and the optimization design of the optical path has been completed,including the collimation and focusing of the laser,the selection of the probe and the determination of the optimal laser power.Secondly,based on the angle of the probe when scanning the sample,the layout of the optical deflection detection system is studied,and the optical deflection system and the key components in the system are redesigned and optimized.The optical deflection detection system is tested.The results show that the optical quality is improved,the experimental efficiency is improved,the noise level is further reduced,and the sensitivity of the optical deflection detection system is improved.Thirdly,A principle model of piezoelectric scanning platform has been established,and a more accurate design model of piezoelectric scanner has been proposed.The structure and parameters of the piezoelectric scanning platform have been designed.Through experimental testing results,the piezoelectric constant of the scanner was measured and calibrated.The results showed that the design error was less than 3%,verifying the accuracy of the model.The inertial displacement platform and piezoelectric scanner were tested.The function of the piezoelectric displacement platform was implemented and verified.Fourthly,a measurement unit platform was designed and built to improve the design and processing accuracy.The system was tested as a whole in a vacuum environment,and the experimental results showed that the key measurement parts of the system had good stabilityFifthly,non-linear calibration of AFM system scanning was carried out by measuring standard samples;The built vacuum atomic force microscope system was used to scan the surface of mica samples,and clear step information was observed.The step height was about 2.5 nm,indicating that the resolution of the system reached the nanometer level.Above all,through the optimization design of this study,the optical quality of the optical deflection detection system of the measuring unit is improved,the deflection noise is reduced,and the sensitivity is improved;The new design model and nonlinear calibration model of piezoelectric scanner are verified.The ideas and methods of the platform optimization of the measurement unit are summarized,which provides a new idea for the design of atomic force microscopy.