Research On The Technique And System Of High Speed Atomic Force Microscope

Over recent years,micro and nano technology develops rapidly.Due to its high resolution and performance unlimited by the conductivity of the sample surface,the atomic force microscope(AFM)has become one of the most important tools of detection and analysis in micro and nano technology studies.At present,the imaging speed of most conventional AFM is slow(e.g.,each image takes 10 minutes or more),thus failing to achieve high-speed imaging of nano-samples(e.g.,more than one image per second to the video-rate).And most of the existing few number of high-speed AFM systems are large,inconvenient for transportation,and complicated for installation and operation.Moreover,they rely on AC power supply and need wired connection with a computer.This limits the application of AFM to a large extent.To this end,this paper proposes a new kind of high-speed AFM system with microcontroller which is light and small without needing AC power supply or low/high-voltage DC power supply.In addition,WiFi-controlled high-speed AFM imaging is realized.Main areas of research in this dissertation are as follows:Theoretical and simulation research on high-speed AFM is carried out,and a new method of high-speed AFM is proposed and developed.Through theoretical derivation of probe-sample dynamic model,modeling and simulation of scanner characteristics,and research and development of control circuit performance,the key factors limiting the imaging speed in AFM systems are analyzed and summarized.The influence pattern of those factors on high-speed AFM imaging is revealed.Based on this,a high-speed AFM system scheme is proposed and further research on AFM microcontroller is carried out.Furthermore,a high-speed AFM method based on AFM microcontroller is established.A new technology of high-speed AFM is studied and developed to solve core technical problems of high-speed AFM probe design,high-speed scanning control,optical path design,photoelectric detection,signal processing,control circuits,and software and hardware development.A technology scheme of high-speed AFM scanning and feedback control is proposed,which could achieve video-rate imaging of nano-samples.Based on theoretical methods and technical research,a new high-speed AFM system is developed,consisting of high-speed AFM probe,high-speed AFM scanning and feedback control system,embedded control system,computer(host),and related software.High-speed AFM probe consists of AFM tip,combined high-speed scanning and feedback controller,samples,a photoelectric detection module,and coarse and fine tuning mechanisms and so on.The combined high-speed scanning and feedback controller is made up of a tripod scanning and feedback controller and a quartering foliated piezoelectric ceramic scanner which could achieve normal speed to video-rate imaging.The photoelectric detection module adopts the folding optical path design,which greatly reduces the occupation of the optical path while ensuring detection accuracy.A high-speed AFM scanning and controlling method and a "weak feedback"control method are proposed,and high-speed scanning and feedback control circuit is developed.An embedded control system consisting of a Raspberry Pi and microscopic high-speed A/D&D/A interface is developed.Powered by the mobile power supply,this embedded control system could be programmed to control the high-speed scanning and feedback control circuit,thereby achieving the imaging of nano-samples.Based on the above work,research on the miniaturization of the high-speed AFM control system is carried out.When the imaging speed and performance of high-speed AFM is ensured,a high-speed AFM microcontroller consisting of the Raspberry Pi,microscopic high-speed A/D&D/A interface,and control circuit is developed.The AFM microcontroller is light and small,without needing AC power supply or low/high-voltage DC power supply.WiFi(hotspot)connection is used for communication between the computer and AFM microcontroller,overcoming the limitations of conventional AFMs that require wired connection between controller and computer.Performance of high-speed AFM is studied and experiments are carried out.The results show that the high-speed AFM system purposed in this dissertation can achieve high speed to video-rate imaging of nano-samples(6-26 frames/s,128×128 pixels)with good stability and repeatability.At the same time,through WiFi(hotspot)connection,the host can control the high-speed AFM microcontroller and AFM probes within 50 meters,which means high-speed imaging of nano-samples(6-20 frames/s,128×128 pixels)is realized through wireless connection for the first time.In conclusion,the new method,technology,and system of high-speed AFM proposed in this dissertation can achieve high-speed to video-rate imaging of nano-samples.Moreover,WiFi-controlled high-speed AFM imaging based on AFM microcontroller is realized.In this way,limitations of conventional AFMs,such as large size,slow imaging speed,and reliance on AC power supply and low/high-voltage DC power supply,and wired connection between controller and computer,are overcame.As a result,the high-speed AFM proposed in this dissertation applies not only to indoor environments where AC power supply is available,but also to isolated environments,outdoor environments,and even field environments where there is no AC power supply.Therefore,it is expected to be more widely applied in nano-technology and other fields.