Atomistic Simulations of Acoustic Activation of Surface Processes

该奖项支持对从强声波到原子尺度表面特征的能量转移的基本机制的计算研究。表面声波是沿固体材料表面传播的弹性波。它们能够以极小的损耗远距离传递能量，在许多实际应用中都得到了积极的应用，从机械性能的无损评估到微流体设备中流体流动的微尺度操纵。然而，表面声波影响原子水平表面过程的能力在很大程度上仍未被探索。这一研究结果将有助于在化学催化、低温薄膜生长和热敏分子的质谱学等领域开发新的应用。在更一般的层面上，这项研究的结果可能为在必须避免温度上升的条件下使用声波作为表面过程的非热激活的替代能源开辟了一系列令人兴奋的机会。学生参与高性能并行计算的方方面面，以及与实验和计算合作者的密切互动，将在迅速扩大的科学计算领域创造一个肥沃的教育环境。通过发展先进的计算方法，对强表面和整体声波的自由非线性传播和耗散，以及它们与表面结构和吸附的相互作用进行原子模拟，将实现揭示表面过程的声激活机制的目标。新的计算方法将被用来系统地研究频率上转换、波型的非线性锐化、激波的形成和声波的快速耗散、表面吸附的声能耦合、亚表面晶体缺陷和纳米尺度的异质。将在模拟中阐明导致基片表面区的扩散增强、脱附或原子级结构重排的条件，并将为几个有实际意义的材料系统确定声辅助表面处理的适用范围。

This award supports computational research into the fundamental mechanisms of the energy transfer from strong acoustic waves to the atomic-scale surface features. Surface acoustic waves are elastic waves that propagate along the surfaces of solid materials. Their ability to transfer energy long distances with little losses are actively used in many practical applications, ranging from nondestructive evaluation of mechanical properties to micro-scale manipulation of fluid flow in microfluidics devices. The ability of surface acoustic waves to influence atomic-level surfaces processes, however, remains largely unexplored. The results of this research will facilitate the development of new applications in the areas of chemical catalysis, low temperature thin film growth, and mass spectrometry of heat sensitive molecules. At a more general level, the results of this study may open up an exciting range of opportunities for using the acoustic waves as an alternative source of energy for non-thermal activation of surface processes under conditions where the temperature increase must be avoided. The involvement of students into all aspects of high-performance parallel computing and close interaction with experimental and computational collaborators will create a fertile educational environment in the quickly expanding area of scientific computing.The goal of revealing the mechanisms responsible for the acoustic activation of surface processes will be achieved through the development of advanced computational methodology for atomistic modeling of free nonlinear propagation and dissipation of strong surface and bulk acoustic waves, as well as their interaction with surface structures and adsorbates. The new computational methods will be applied for a systematic investigation of frequency up-conversion, nonlinear sharpening of the wave profiles, shock formation and the onset of rapid dissipation of acoustic waves, acoustic energy coupling to surfaces adsorbates, sub-surface crystal defects, and nanoscale heterogeneities. The conditions leading to the diffusion enhancement, desorption, or atomic-level structural rearrangements in the surface region of the substrate will be elucidated in the simulations and the domains of applicability of the acoustically-assisted surface processing will be established for several material systems of practical interest.