Simulation Of Ion Irradiation Uniformity For Large Area Ion Track Membrane

Ion track membrane is a porous membrane that utilizes heavy ions to irradiate the membrane to produce ion tracks,and then produces micropores through etching and other post-processing.Ion track membrane are characterized by well-defined pore shapes,controllable pore diameters,and strictly straight pores.It has good application prospects in the fields such as precision filtration and separation,growth of nanostructures,fabrication of metamaterials.For ion track membrane,the pore size and pore density are the main parameters affecting the performance.For cutting-edge researches,such as precision separation,ultra-high absorbance materials,small pore size,high pore density and large membrane area are necessary prerequisites.Facilities for the rapid production of large-area ion track membranes,such as the TR-6 terminal at the Heavy Ion Accelerator in Lanzhou(HIRFL),and the TR-3terminal under construction,realize high-efficiency continuous irradiation by performing irradiation for membrane under transmission.The uniformity of irradiation determines the uniformity of micropore distribution,which will directly affect the performance of ion track membranes.The scanning method which are widely applied can achieve good uniformity in the traditional research of materials irradiation,i.e.,irradiation on stationary targets.However,for irradiation of wide membranes in motion,which is essential for high-efficiency fabrication for large-area ion track membranes,it is still challenging and requires urgent research to ensure uniformity,especially considering the fluctuations in the transmission speed and the flux of ion beam current.This is one of the fundamental tasks in the research and application of precision ion track membranes.To study the irradiation uniformity of transmission and static targets,this thesis investigates the effects of one-dimensional and two-dimensional scanning on irradiation uniformity based on numerical simulation methods,revealing the relationship between beam spot shape,membrane transmission speed and beam scanning frequency on irradiation uniformity,and the results of the research are of guiding significance for improving the irradiation uniformity.The innovation of this thesis lies in the establishment of a simulation model of the scanning method,and the systematic study of irradiation uniformity under the multi-factors of scanning frequency,scanning amplitude,transmission speed and beam spot size,and it is found that in the case of two-dimensional scanning,the coupling of the transmission speed and the scanning frequency is a prerequisite for obtaining a high uniformity.The research in this thesis has three main aspects.1.Irradiation uniformity study for static targets.Two-dimensional distribution of fluence under the ideal beam spot condition of a stationary target is simulated,and the scanning path is a Lissajous figure composed of parallel lines.The simulation results show that for a large area stationary target,high scanning frequencies should be ensured as much as possible in the actual process.On this basis,the larger the beam spot diameter is,the better the uniformity is.At the same time,this thesis also gives a method of estimating the uniformity by using the correspondence between scanning frequency,scanning amplitude and beam spot size.2.Irradiation uniformity study of dynamic targets.The irradiation of a large-area target with uniform transmission speeds is simulated,which corresponds to irradiation of large-area ion track membrane with high efficiency in the actual process.One-dimensional scanning irradiation,i.e.,scanning only along the direction perpendicular to the target transmission direction,and two-dimensional scanning irradiation,i.e.,scanning along the directions perpendicular and parallel to the target transmission directions,are studied.For two-dimensional scanning,there exists a discrete set of coupling speeds.Deviation from these coupling speeds will result in streaky inhomogeneous regions on the target.This phenomenon is due to the properties of Lissajous figure that the path of two-dimensional scanning can be divided into multiple independent trapezoids.The overlapping of these trapezoids results in high uniformity only at the coupling speeds.The coupling speeds are functions of the scanning frequency difference between the two directions of the two-dimensional scanning.The difference between scanning frequencies can be adjusted so that the coupling speeds can converges to the transmission speeds,ensuring the uniformity and precise control of the fluence.3.Study of the effect of beam current parameter fluctuations on the irradiation uniformity of dynamic targets.Corresponding to the often-unavoidable fluctuations of beam current intensity,membrane transmission speeds,and the randomness of beam spot shape in ion irradiations,this thesis studies the effects of these perturbation factors on the uniformity.According to the simulation results,suggestions are given to improve the uniformity:(1)In the case of large fluctuations in beam flux,two-dimensional scanning should be selected,the scanning frequency difference and coupling speeds are then determined according to the aimed ion fluence;(2)For more stable beam flux and lower ion fluence,one-dimensional scanning is recommended,and the scanning frequency should be as high as possible;(3)For complex condition such as the existence of multiple perturbation factors,the model provided in this thesis can be used for rapid simulation to obtain the solution to optimize the uniformity.Overall,this thesis develops a simulation method based on Lissajous figure scanning for the irradiation uniformity of ion track membranes,investigates the main parameters affecting the irradiation uniformity and their influence laws in the cases of static target,transmission target and under fluctuation of beam current parameters,and eventually gives the guiding principles and schemes for obtaining the uniform irradiation in the respective cases.The research results of this thesis are of great significance for improving the irradiation uniformity of heavy ion microporous membranes.