Study Of Scanning Probe Microscope System Based On ARM

Nanotechnology is one of the rapid development frontier fields in recent years. It has been being applied to all the areas of modern science and technology, and formed many new disciplines associated with nanotechnology. The microscopes working on the nanoscale such as the scanning tunneling microscope(STM) and atomic force microscope(AFM) are the important basis for the development of nanotechnology, and they are essential research tools for researchers in the field. Especially, there is a greater demand for AFMs with more applications. In this thesis, the design of an atomic force microscope(AFM) based on ARM was proposed, and its principle and the method were studied in details. An embedded operating system was applied to the control system of AFM. This approach has not only the important theoretical significance and scientific value, but also the broad prospects for practical applications.This thesis discussed the working principles of AFMs based on the review of the state of the art of nano science and technology and AFM applications. It proposed the design of the AFM control system with the ARM embedded operating system of ARM-μCLinux, combined with the current development of AFM application technologies. The DAC of 18 bit output analog signal was controlled by ARM, and amplified by the high voltage amplifier to control the XYZ direction movements of piezo stages. The system used 16 bit synchronized ADCs to collect feedback signals from the micro-cantilever. The real-time data acquisition was done with the advantage of ARM multi-threading, and the data was exchanged through the PC and the LAN port. The AD9851 was controlled by the Atmega128 L output sine wave with the frequency of 0~500KHz and the adjustable amplitude. Its frequency stability was 0.04 Hz, and the amplitude of the output error was within the range of 0.2m V. In the tapping mode, the micro-cantilever of AFM was in the vicinity of the resonance frequency of the oscillation so that the tapping mode AFM scanning was implemented. Through the three-dimensional step scanning platform the large range scanning of up to 90mm×90mm was realized by image matching technology with the accuracy rate of more than 98%. In the design, the non-contact displacement sensor with nanometer resolution was used as the feedback from the automated probe approaching system, and a three-step probe positioning strategy was employed to control the probe approaching process and effectively avoid the damages of the tip and the sample surface. The performance of the developed AFM was tested in the air and liquid environments, and the clear images of sample patterns were obtained and analyzed. The system has been proved to work reliably in the different environments.The main innovations achieved in this work are:1.In the AFM system, the embedded operating system of ARM-μCLinux is introduced and it enhances the real-time performance of the system. This makes it easier to update the system application software and develop the peripheral device drivers. Compared with other AFM systems, the improvements of the system stability and scanning speed are more than 20%.2.In the automated probe approaching system, a three-step probe positioning strategy is employed to control the probe approaching process and effectively avoid errors in the process. The non-contact displacement sensor with nanometer resolution is used for the feedback with the position accuracy of 15 nm.3.In the experiment of cell imaging with the developed AFM, the histogram of cell image is proposed to find the best point of division and perform the imge thresholding, and the cell edge features are extracted by Log edge detection operator with the accuracy rate of more than 98.5%.