In order to investigate the different role of kinetic and potential projectile energy for secondary ion formation, the authors have measured the ionization probability of indium atoms sputtered from a clean indium surface under irradiation with rare gas (Xeq+) ions of different charge states q at the same kinetic impact energy of 20 keV. In this energy range, the kinetic energy of the projectile is predominantly deposited via nuclear stopping, leading to a collision-dominated sputtering process. The authors find that the ionization probability increases significantly if a highly charged ion is used as a projectile, where the ionization energy becomes comparable to or even exceeds the kinetic energy, indicating that a higher level of electronic substrate excitation induced by the potential energy stored in the projectile can boost the secondary ion formation process. This experimental result is discussed in terms of microscopic model calculations describing the secondary ion formation process. At the same time, the authors observe a significant change of the emission velocity distribution of the sputtered particles, leading to a pronounced low-energy contribution at higher projectile charge states. It is shown that this “potential sputtering” contribution strongly depends on surface chemistry even under conditions where the surface is dynamically cleaned by interleaved 5 keV Ar+ ion bombardment.

中文翻译：

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慢速高电荷离子冲击下溅射铟原子的电离概率

为了研究弹丸动能和势能对二次离子形成的不同作用，作者测量了在不同电荷态 q 的稀有气体 (Xeq+) 离子辐照下从干净的铟表面溅射的铟原子的电离概率。 20 keV 的相同动能冲击能量。在这个能量范围内，弹丸的动能主要通过核停止沉积，导致碰撞主导的溅射过程。作者发现，如果使用高度带电的离子作为射弹，电离概率会显着增加，此时电离能与动能相当甚至超过，这表明由弹丸中存储的势能引起的更高水平的电子基板激发可以促进二次离子形成过程。该实验结果根据描述二次离子形成过程的微观模型计算进行讨论。同时，作者观察到溅射粒子的发射速度分布发生了显着变化，导致在较高的弹丸电荷状态下产生明显的低能量贡献。结果表明，即使在通过交错的 5 keV Ar+ 离子轰击动态清洁表面的条件下，这种“潜在溅射”贡献也强烈依赖于表面化学。同时，作者观察到溅射粒子的发射速度分布发生了显着变化，导致在较高的弹丸电荷状态下产生明显的低能量贡献。结果表明，即使在通过交错的 5 keV Ar+ 离子轰击动态清洁表面的条件下，这种“潜在溅射”贡献也强烈依赖于表面化学。同时，作者观察到溅射粒子的发射速度分布发生了显着变化，导致在较高的弹丸电荷状态下产生明显的低能量贡献。结果表明，即使在通过交错的 5 keV Ar+ 离子轰击动态清洁表面的条件下，这种“潜在溅射”贡献也强烈依赖于表面化学。