Computational Study of the Generation of Crystal Defects and Controlled Modification of Surface Microstructure by Short Pulse Laser Irradiation

该奖项支持计算和理论研究，以及旨在研究一系列快速非平衡过程的教育，这些过程负责利用皮秒和飞秒级激光脉冲进行材料改性和表面纳米结构。这项研究涉及大规模的模拟，有可能对超快加热和冷却极端条件下材料响应和微观结构演变的基本理解产生革命性的影响，并为以纳米级分辨率控制激光材料的改性开辟新的方向。这项研究计划的目的是通过大规模的原子模拟，揭示在短脉冲激光照射下，金属靶材表面微结构改变的基本过程。将分子动力学方法与电子热传导和电子-声子耦合的连续描述相结合的计算模型将被用来详细分析激光诱导晶体缺陷的产生机制及其在表面微结构和原子混合演化中的作用。将研究导致纳米晶表面结构形成的条件，以及在靶的强过冷液相区内控制微晶形核和生长的原子级过程，特别是自由表面对新晶体的形核动力学和晶体取向的影响。采用分子动力学和动力学蒙特卡罗相结合的方法对二元合金和多层靶材进行分子动力学和动力学蒙特卡罗模拟，研究在快速熔凝、塑性变形和激光诱导的点缺陷过饱和条件下原子混合的不同扩散和非扩散机制的相对贡献。在短脉冲激光加工中，将研究亚稳态晶相和非晶相的形成/稳定的物理过程，并与辐照条件有关。该奖项支持科学计算和激光-材料相互作用领域的教育举措，包括研究生和本科生积极参与高性能计算的各个方面，开发新的激光-材料相互作用研究生课程，以及将研究成果纳入现有课程原子模拟导论。国际学生联合会将继续与少数群体方案办公室保持密切联系，从传统上代表性不足的群体中招收本科生。与来自德国、法国、俄罗斯和伊拉克的团体的国际合作将包括短期和长期的相互访问，并将丰富参与的研究生和本科生的教育和文化经验。该项目的教育部分还包括一个互动网站的设计？极端条件下的材料。对短脉冲激光辐照引起的超快材料现象的一般概念的非技术描述将由本程序中所获得的研究结果来说明，并以图像、计算机动画和简单的交互模拟的形式呈现。

This award supports computational and theoretical research, and education aimed at investigation of a range of fast non-equilibrium processes responsible for material modification and surface nanostructuring by pico- and femtosecond scale laser pulses. The research involves large-scale simulation and has potential for making a transformative impact on the fundamental understanding of material response and microstructure evolution under extreme conditions of ultrafast heating and cooling, as well as for opening new directions for controlled laser material modification with nanoscale resolution. The goal of this research program is to reveal, through large-scale atomistic simulations, the fundamental processes responsible for the modification of surface microstructure of metal targets irradiated by short laser pulses. A computational model combining the molecular dynamics method with a continuum description of the electron heat conduction and electron-phonon coupling will be used to perform a detailed analysis of the mechanisms of laser-induced generation of crystal defects and their role in the evolution of surface microstructure and atomic mixing. The conditions leading to the formation of a nanocrystalline surface structure and the atomic-level processes controlling the nucleation and growth of crystallites within a strongly undercooled liquid region of the target will be investigated with a particular focus on the effect of the free surface on the nucleation kinetics and crystallographic orientation of the new grains. The relative contribution of different diffusive and non-diffusive mechanisms of atomic mixing occurring under conditions of rapid melting/solidification, plastic deformation and laser-induced supersaturation with point defects will be investigated in combined molecular dynamics and kinetic Monte Carlo simulations performed for binary alloys and multi-layered targets. The physical processes responsible for the formation/stabilization of metastable crystalline and amorphous phases will be investigated and related to the irradiation conditions in short pulse laser processing. This award supports educational initiatives in the areas of scientific computing and laser-materials interactions include the active involvement of graduate and undergraduate students into various aspects of high-performance computing, development of a new graduate course on Laser-Materials Interactions, as well as incorporation of the research results into an existing course, Introduction to Atomistic Simulations. The PI will continue to maintain close contacts with the Office of Minority Programs in recruiting undergraduate students from traditionally under-represented groups. International collaborations with groups from Germany, France, Russia, and Iraq will involve short and long-term mutual visits and will enrich the educational and cultural experience of the participating graduate and undergraduate students. The educational component of this project also includes a design of an interactive web-site ?Materials under Extreme Conditions.? A non-technical description of general concepts of ultrafast materials phenomena induced by short pulse laser irradiation will be illustrated by the research results obtained in this program and presented in the form of images, computer animations, and simple interactive simulations.