Material Removal Mechanisms in Focused Ion Beam Nanopore Drilling

该项目的目的是更好地理解聚焦离子束（FIB）仪器从表面去除材料的方法。FIB仪器在半导体工业中已经很常见，它使用极窄的离子束，小到几纳米宽，来磨或蚀刻表面。随着FIB处理在纳米技术的其他领域得到更广泛的应用，例如在DNA测序的纳米孔钻孔中，这是数十亿美元的分子医学诊断行业的一项使能技术，因此需要更好地了解最精细尺度上的FIB处理。该项目将通过开发材料对离子束响应的预测模型，导致更有效地使用FIB仪器。该项目将包括与欧洲领先的研究小组合作，致力于提高FIB纳米孔制造的分辨率，并定期与美国领先的FIB仪器生产商进行磋商。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，并将制定针对K-12学生的外展计划。推动该项目的假设是，FIB加工中材料去除的基本模式在最小尺度上强烈依赖于通量，从低通量时的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，将在一系列条件下研究FIB纳米孔钻孔，特别强调离子束通量的影响。将进行大规模平行分子动力学模拟，模拟FIB纳米孔在独立薄膜靶上的钻孔过程。模拟将涉及多达1000万个原子，数百万个时间步长，这将是有史以来第一次完整的FIB钻井分子动力学模拟。材料去除和重排机制，特别是爆炸沸腾和热毛细质量运输，将充分表征和解释。将建立一个多尺度统计模型，以扩展分子动力学模拟，以研究低通量FIB处理等长时间尺度过程。最后，有针对性的FIB纳米孔钻探实验将指导基于计算的模型的开发和验证。将使用高分辨率双光束FIB仪器制备直径小于10nm的FIB纳米孔，并对其进行表征，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.