An investigation of enhanced secondary ion emission under Aun+ (n=1–7) bombardment
An investigation of enhanced secondary ion emission under Aun+ (n=1–7) bombardment
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Aun+ (n=1–7) 轰击下增强二次离子发射的研究
DOI：
10.1016/j.jasms.2005.01.024
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发表时间：
2005
影响因子：
3.2
通讯作者：
Amy V. Walker
中科院分区：
文献类型：
--
作者：
Gabriella Nagy;L. Gelb;Amy V. Walker
研究了Aun+（n = 1，2，3，5，7）一次离子轰击Irganox 1010、DL-苯丙氨酸和聚苯乙烯在Si、Al和Ag衬底上的薄膜时，非线性二次离子产额增加的机理。发现使用Au+、Au 2+和Au 3+初级离子束的二次离子产率的最大差异。使用Au5+和Au 7+初级离子观察到二次离子产率的较小增加。产量的提高被发现是更大的Si比Al上，而离子产量是较小的使用Au+束在Si上比Al上。使用Aun+离子结构从密度泛函理论，我们证明，二次产量的提高是不是简单地由于增加的能量每面积沉积到表面（能量沉积密度）。相反，基于简单的机械参数和分子动力学结果Medvedeva等人，我们提出了一种非线性二次离子产率增强的机制，其中多个协调一致的Au影响的行动导致有效的能量转移到衬底原子在近表面区域和从表面喷射的二次离子的数量增加。这种协同影响涉及一个，两个或三个Au原子，这很好地解释了从Au+到Au 2+到Au 3+初级离子观察到的大的非线性产率增强。该模型也能够解释所观察到的底物效应。对于通过更开放的Si表面的Au+离子，其接触比在更致密的Al表面中更少的衬底原子。较少的能量沉积在Si表面区域的Au+初级离子和二次离子产率将是较低的吸附物在Si上比在Al上。在Aun+的情况下，更大的密度的Al导致较早的分裂的初级离子和随之而来的减少的能量转移到近表面区域时，与Si相比。这导致硅上的二次离子产率和产率提高高于铝衬底。
We investigate the mechanism of the nonlinear secondary ion yield enhancement using Aun+(n = 1, 2, 3, 5, 7) primary ions bombarding thin films of Irganox 1010, DL-phenylalanine and polystyrene on Si, Al, and Ag substrates. The largest differences in secondary ion yields are found using Au+, Au2+, and Au3+primary ion beams. A smaller increase in secondary ion yield is observed using Au5+and Au7+primary ions. The yield enhancement is found to be larger on Si than on Al, while the ion yield is smaller using an Au+beam on Si than on Al. Using Aun+ion structures obtained from Density Functional Theory, we demonstrate that the secondary yield enhancement is not simply due to an increase in energy per area deposited into the surface (energy deposition density). Instead, based on simple mechanical arguments and molecular dynamics results from Medvedeva et al, we suggest a mechanism for nonlinear secondary ion yield enhancement wherein the action of multiple concerted Au impacts leads to efficient energy transfer to substrate atoms in the near surface region and an increase in the number of secondary ions ejected from the surface. Such concerted impacts involve one, two, or three Au atoms, which explains well the large nonlinear yield enhancements observed going from Au+to Au2+to Au3+primary ions. This model is also able to explain the observed substrate effect. For an Au+ion passing through the more open Si surface, it contacts fewer substrate atoms than in the more dense Al surface. Less energy is deposited in the Si surface region by the Au+primary ion and the secondary ion yield will be lower for adsorbates on Si than on Al. In the case of Aun+the greater density of Al leads to earlier break-up of the primary ion and a consequent reduction in energy transfer to the near-surface region when compared with Si. This results in higher secondary ion yields and yield enhancements on silicon than aluminum substrates.