离子在近电子能损阈值能区诱发云母表面小丘形成

Formation of Hillock on Muscovite Mica Surface Induced by Energetic Ion near Electronic Energy Loss Threshold

利用0.65 MeV的He^+离子轰击白云母膜,并在大气环境下用原子力显微镜(AFM)的轻敲模式分析了辐照后的膜表面。实验结果显示,在不同温度下离子诱导的小丘高度在小于1 nm到几nm之间,且室温条件下能诱发小丘生成的He^+离子电子能损阈值在0.44 keV/nm以下。此外,升高温度至973 K并在其中选取不同温度进行表面辐照来验证观测到的小丘结构。实验发现,相比于室温,小丘直径和高度的统计分布在更高温度下表现出了更大的歧离。分别利用分析热峰模型和双温热峰模型计算了辐照过程中的核能损与电子能损,并选取了用能损在阈值附近的离子辐照所产生的小丘的实验数据与模拟结果相比较,发现实验结果与双温热峰模型吻合较好。

Muscovite mica sheets were bombarded with He^+ ions of 0.65 MeV.The irradiated surfaces were analyzed in the air with atomic force microscopy (AFM) in the tapping mode.It reveals the ion-induced hillocks with height from less than 1 nm to a few nm at various temperatures.The electronic energy loss threshold for the hillock formation is found to be below 0.44 keV/nm by using He^+ ions at the room temperature.The surfaces were also bombarded at various elevated temperatures up to 973 K to confirm the observed hillocks.It is found that the statistical distribution of the diameter and height of the hillocks gets more divergent and spreads with larger values at higher temperatures due to the thermal annealing,compared with that at the room temperature.The mean diameter and height of the hillocks do not show any significant change.The two thermal spike model calculations were compared with the experiment near the threshold.The analytical thermal spike model and the two-temperature thermal spike model were taken into account in both the electronic and nuclear energy loss.The threshold value calculated by analytical thermal spike model is quite beyond the experimental value.It is found that the experimental threshold is little below the calculated value if only the electronic energy loss is considered.Taking into account the small nuclear energy loss,the hillocks can be formed within the framework of the two-temperature thermal spike model.