快重离子微观尺度二维分布的模拟研究

在快重离子的辐照中，无论通过束流扫描还是束流散焦，在微观尺度上入射离子依然是随机分布的。最近，这种微观上的离子不均匀性对于快重离子的前沿应用，如高密度微孔膜的制备和航空电子器件的单粒子效应的评估等变得至关重要。本工作利用蒙特卡罗方法模拟了垂直于束流方向的二维平面上随机分布的离子。从统计角度来看，蒙特卡罗方法模拟的潜径迹的分布与相同离子注量下微孔膜的电镜观测结果相一致。根据模拟结果，微孔膜的有效孔隙率可以通过辐照注量和孔径来进行有效预测。另外，也提出了计算有效孔隙率的经验公式。利用此公式可以在一定程度上预测最优化的离子辐照和化学蚀刻参数，从而得到理想的孔隙率。同时，为了评估微孔膜的选择性，计算了形成重孔的概率，这有助于在膜的孔隙率和选择性之间达到平衡，从而获得最好的膜性能。通过蒙特卡罗模拟，还研究了微观尺度下离子辐照的均匀性问题，其结果可以为单粒子效应等应用提供重要参考。

Foreseeing Two Dimensional Distribution of Swift Heavy Ions at Micro-scale

For Swift Heavy Ion(SHI) irradiation, at micro-scale, the incident ions are randomly distributed regardless of beam scanning or defocusing. Recently, this nonuniformity of ion irradiation is becoming critical for the cutting-edge applications of SHIs, i.e., fabrication of high-density microporous membranes, and evaluation of single event effect for the aerospace electronics. In this study, a Monte Carlo(MC) code is developed for simulating the planar distribution of incident ions. Statistically, the predicted distributions of latent tracks and micropores show good coincidence with the direct observations of microporous membranes. According to the simulations, the porosities of membranes are predicted as functions of ion fluences and pore sizes. An empirical formula is proposed for the estimation of effective porosity prior to ion irradiation and chemical etching. Moreover, to evaluate the selectivity of microporous membranes, the probability of multi-pores formation is estimated. A balance between the porosity and selectivity of the membranes is suggested. By employing the MC simulations, uniformity issues of ion irradiation at micro-scale are investigated, whose results may serve as important references for single event effect etc.