Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf, D-01314 Dresden, Germany.
Nanotechnology. 2020 Jan 17;31(3):035302. doi: 10.1088/1361-6528/ab4847. Epub 2019 Sep 26.
The interpretation of helium ion microscopy (HIM) images of crystalline metal clusters requires microscopic understanding of the effects of He ion irradiation on the system, including energy deposition and associated heating, as well as channeling patterns. While channeling in bulk metals has been studied at length, there is no quantitative data for small clusters. We carry out molecular dynamics simulations to investigate the behavior of gold nanoparticles with diameters of 5-15 nm under 30 keV He ion irradiation. We show that impacts of the ions can give rise to substantial heating of the clusters through deposition of energy into electronic degrees of freedom, but it does not affect channeling, as clusters cool down between consecutive impact of the ions under typical imaging conditions. At the same time, high temperatures and small cluster sizes should give rise to fast annealing of defects so that the system remains crystalline. Our results show that ion-channeling occurs not only in the principal low-index, but also in the intermediate directions. The strengths of different channels are specified, and their correlations with sputtering-yield and damage production is discussed, along with size-dependence of these properties. The effects of planar defects, such as stacking faults on channeling were also investigated. Finally, we discuss the implications of our results for the analysis of HIM images of metal clusters.
氦离子显微镜（HIM）图像的晶体金属团簇的解释需要微观理解氦离子辐照对系统的影响，包括能量沉积和相关加热以及沟道模式。虽然已经对大块金属中的沟道进行了广泛的研究，但对于小团簇没有定量数据。我们进行了分子动力学模拟，以研究直径为 5-15nm 的金纳米粒子在 30keV 氦离子辐照下的行为。我们表明，离子的撞击可以通过将能量沉积到电子自由度中来使团簇产生大量的加热，但它不会影响沟道，因为在典型的成像条件下，离子连续撞击之间，团簇会冷却下来。同时，高温和小团簇尺寸应该会导致缺陷的快速退火，从而使系统保持结晶状态。我们的结果表明，离子沟道不仅发生在主要的低指数方向，也发生在中间方向。指定了不同通道的强度，并讨论了它们与溅射产额和损伤产生的相关性，以及这些性质的尺寸依赖性。还研究了平面缺陷（如层错）对沟道的影响。最后，我们讨论了我们的结果对金属团簇 HIM 图像分析的影响。
