Development Study On Measurement System For The Size Of Nano-Particle By Dynamic Light Scattering

During the process of traditional polishing, the polishing plate which is made of asphaltum moves on the surface of the work piece for the smooth surface. The polishing powder is used for polishing surface. The size and size distribution of powder is one of the most important factors which affects the efficiency of polishing and the roughness of surface. The smooth surface can be produced stably by using small and well-proportioned polishing powder. To measure the size of nano-particle polishing powder, a practical and small system is developed in this thesis, and the main work is summarized as follows:1,Several typical measurement methods on nano-particle are analyzed according to their application areas and particle size range. Specifically, the method of dynamic light scattering is introduced in detail. It is effective and can be called Photon Correlation Spectroscopy, Quasi-elastic Light Scattering and Intensity Fluctuate Spectroscopy.2,The technique of dynamic light scattering and inversion algorithm is studied systematically, and the experiments are designed according to the theory. The measurement system of PCS has been established to receive the time -fluctuating intensity, which also calculates the autocorrelation function of the light intensity. Based on the experimental curve, exponential fitting is made by the system to obtain the decay time. Further, diffusion coefficient D_T which indicates the characters of the moving particle in the suspending liquid is calculated.The average size of the polishing powder- 20nm- is achieved finally. The result accords with the value tested by scanning electron microscope (SEM), and proves the reliability of the system.3,Based on the curve of the autocorrelation function of the light intensity , a stochastic inverse technique based on gray-code genetic algorithm (GGA) is proposed to invert particle size distribution from dynamic light scattering (DLS) data. Compared with other usual inversion methods, the algorithm optimizes the merit function efficiently. The fitting error is less than 10^-3 at the 100^th iteration. It makes a good foundation for the research of the impact on the polishing quality of the parameters of polishing powder in the process of ultra precise polishing.