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Development Of Optical Image System And Study Of Laser Post-ionization Technology On TOF-SIMS

Posted on:2017-04-26Degree:DoctorType:Dissertation
Country:ChinaCandidate:P Z WangFull Text:PDF
GTID:1108330482489607Subject:Precision instruments and machinery
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As an important constituent part of TOF-SIMS, the optical imaging system observes the real-time images of samples and analyzes measurement locations and information about the diameter and strength of an ion beam spot. Femtosecond laser post-ionization technique, one kind of Secondary Neutral Mass Spectrometry(SNMS), is the key technology to improve the instrument sensitivity on the basis of SIMS.Because any information about the design of commercialized SIMS remains confidential in worldwide, the independent research and development of TOF-SIMS in China is in demand. So is the essential component of TOF-SIMS, the optical imaging system. Its development and application would fill the vacuum and provide subsequent references in the field of the optical imaging system of SIMS. Recently, with the rapid development of laser technology, the usage of femtosecond laser has heavily facilitated the enhancement of Secondary Neutral mass spectrometry(SNMS). The combination of SNMS and SIMS break through the low-sensitivity bottom neck of SIMS. By adopting femtosecond laser to ionize secondary neutral particles of SIMS, this paper analyses the spatial distribution of secondary neutral particles of SIMS to provide substantial information which would make the highly sensitive SIMS possible.The aim of this paper is to realize the optimal imaging system of TOF-SIMS and do researches with femtosecond laser post-ionization technique. The main contents are as follows:(1) The design of the optical imaging system:Grounded on the index parameters of the optical imaging system provided by the instrument, the paper sets a systematic approach in the beginning. To be specific, the paper adopts catadioptric optical imaging system to establish a system model based on Schwarzschild dual reflection configuration and furthermore optimizes the parameters of the model and conducts analysis on image quality of the system. The simulation result shows that the optimum resolution of the system reaches 1μm, the limiting resolution is 0.4μm, the magnification is adjustable, the radius of RMS is smaller than the diameter of airy disk, the wave aberration satisfies Rayleigh judgment and the image quality is good.(2) Study on the integration of the optical imaging system:In order to fulfill the tolerance requirement of the optical imaging system, an integration of Schwarzschild system of mechanical assembly structure, the ultra-high vacuum sample chamber and three-dimension precise sample stage is devised. The integration accomplishes the assembly and testing of the optical imaging system and is applied in independently developed TOF-SIMS. The result of the experiment and applied research indicates that the magnification of the system reaches 300 x, the spatial resolution is 400lp/mmv(micron level) and the zircon sample image and the bombardment mark of the current of primary ion beam is clearly observable.(3) Study on autofocus algorithm for the sample image:To satisfy the request on the focus accuracy of the autofocus system of TOF-SIMS for zircon sample image, the paper proposes an autofocus algorithm for zircon sample image which can automatically eliminate noise. The algorithm includes the recognition and segmentation of zircon image, a sectional-type focusing algorithm and a focusing control strategy. In the distant-peak focusing area, Roberts function and differential accumulation focusing control strategy is used to conduct rough adjustment. In the near-peak focusing area, the paper captures zircon targets in the image to perform recognition and segmentation and does the fine focus by combining the local coordinate function and the hill climbing method to act as the focusing control strategy. The experiment result shows that the focusing error range of the system is ±0.004 mm, internal focusing accuracy reaches 99%, the suppression of noise interference is effective and the precise autofocus of zircon sample image is achieved.(4) Study on femtosecond laser technique:For the sake of improving the sensibility of SIMS, the femtosecond laser technique has been implemented to ionize the secondary neutral particles which produced by primary ion bombardment. The paper takes sterling silver and pure copper as object samples, uses independently developed time-of-flight mass spectrometry to analyze secondary post-ionized ion and studies the ionization efficiency and spatial distribution of secondary neutral particles. The result indicates that neutral particles takes a major part in the sputtering products of primary ion bombardment, the femtosecond laser technique is able to increase the instrument’s secondary ion yield around by 70 times and acquires precise isotopic ratio and abundance, and the spatial distribution of secondary neutral particles is in accord with Maxwell-Boltzmann model. This result provides substantial information for the design method which would improve the sensibility of SIMS.
Keywords/Search Tags:TOF-SIMS, the optical imaging system, Schwarzschild, auto-focus algorithm, the recognition and segmentation of image, laser post-ionization technique, neutral particles
PDF Full Text Request
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