Material Removal Mechanisms in Focused Ion Beam Nanopore Drilling

该项目的目标是更好地了解聚焦离子束(FIB)仪器从表面去除材料的方法。FIB仪器在半导体行业中已经是常见的工具，它使用极窄的离子束，小到几纳米宽，来研磨或蚀刻表面。随着FIB处理在纳米技术的其他领域得到更广泛的应用，例如用于DNA测序的纳米孔的钻孔，这是数十亿美元的分子医学诊断行业的一项使能技术，因此出现了在最精细的范围内更好地了解FIB处理的需要。该项目将通过开发材料对离子束的响应的预测模型来更有效地使用FIB仪器。该项目将涉及与一个致力于提高FIB纳米孔制造分辨率的领先欧洲研究小组的合作，以及与领先的美国FIB仪器生产商的定期磋商。研究生和本科生将接受离子与材料相互作用的计算和实验科学方面的培训，并将开发一个针对K-12学生的推广计划。推动该项目的假设是，在FIB处理中，材料去除的基本模式在最小的尺度上是强烈的通量相关的，在低通量时由侵蚀驱动过程转变为高通量时的相变过程。为了验证这一假设，将在一系列条件下对FIB纳米孔钻探进行研究，特别强调离子束通量的影响。将进行大规模的并行分子动力学模拟，以模拟FIB纳米孔在独立的薄膜靶中的钻探。这些模拟将涉及数百万个时间步长的多达1000万个原子，这将是FIB钻探的第一次完整的分子动力学模拟。材料去除和重排机制，特别是爆炸沸腾和热毛细管传质，将被充分描述和解释。将开发一个多尺度统计模型来扩展分子动力学模拟，以研究长时间尺度的过程，如低通量FIB处理。最后，对FIB纳米孔钻探的有针对性的实验将指导基于计算的模型的开发和验证。直径小于10 nm的光纤纳米孔将使用高分辨率的双光束FIB仪器进行制备，并进行表征，以便与模拟结果进行比较。

The objective of this project is to better understand the means by which focused ion beam (FIB) instruments remove material from surfaces. FIB instruments, already common tools in the semiconductor industry, use extremely narrow beams of ions, as small as a few nanometers wide, to mill or etch surfaces. As FIB processing finds broader applications in other areas of nanotechnology, such as in the drilling of nanopores for DNA sequencing, which is an enabling technology in the multi-billion dollar molecular medical diagnostics industry, there is an emerging need for better understanding of FIB processing at the finest scales. This project will lead to more effective use of FIB instruments through the development of predictive models for the material response to the ion beam. The project will involve collaboration with a leading European research group working on improving the resolution of FIB nanopore fabrication, and regular consultation with the leading US producer of FIB instruments. Graduate and undergraduate students will be trained in both the computational and experimental science of ion interactions with materials, and an outreach program aimed at K-12 students will be developed.The hypothesis driving the project is that the fundamental mode of material removal in FIB processing is strongly flux-dependent at the smallest scale, changing from an erosion-driven process at low fluxes to a phase-change process at high fluxes. To test this hypothesis, FIB nanopore drilling will be investigated over a range of conditions, with particular emphasis on the effects of ion beam flux. Large-scale parallel molecular dynamics simulations will be carried out to simulate FIB nanopore drilling in a freestanding thin film target. The simulations will involve up to 10 million atoms over millions of time steps, and will be the first-ever full molecular dynamics simulations of FIB drilling. Material removal and rearrangement mechanisms, in particular explosive boiling and thermocapillary mass transport, will be fully characterized and explained. A multiscale statistical model will be developed to extend the molecular dynamics simulations to study long time-scale processes such as low-flux FIB processing. Finally, targeted experiments on FIB nanopore drilling will guide the development and validation of the computation-based model. FIB nanopores, with diameters of less than 10nm, will be fabricated using a high-resolution dual-beam FIB instrument and characterized for comparison to the simulation results.