Electron Microscopy of Pulsed Laser Induced Rapid Solidification and Transient Solid State Phenomena in Nano-Scale Metal and Alloy Thin Films

技术概要：本项目是研究纯金属和富铝铝（铜）薄膜的快速凝固过程。主要技术是在劳伦斯利弗莫尔国家实验室（LLNL）使用动态TEM（DTEM）进行超快电子衍射（UED）和成像的原位透射电子显微镜（TEM）。目前还没有其他测量技术能够观察快速凝固过程的界面速度范围从约0.1至100米/秒的金属薄膜所需的纳米尺度的空间和时间分辨率的DTEM提供。该研究将揭示与Al和富Al Al（Cu）薄膜以及单次脉冲激光熔化后的FCC，BCC和HCP金属相关的极其快速的液-固转变和其他瞬态现象（例如固-固转变）的定量动态细节。强大的建模软件代码，验证了直接比较与定量测量从原位DTEM纯金属实验，将开发脉冲激光熔化。验尸和原位微观结构表征将被用来研究微观结构的演变和缺陷形成的固态凝固后的纯金属具有不同的晶体结构。富铝Al（Cu）薄膜的研究，预计将有助于确定的条件下的形态不稳定的生长界面的脉冲激光功率的函数，合金成分和热提取参数的Al和Al2Cu之间的亚共晶，共晶和过共晶组合物。确定稳定性或不稳定性的转变前沿的参数所获得的数据将使理论凝固模型的验证。除了在激光诱导快速凝固的极端条件下提供有关金属的基本科学知识外，还将开发最先进的原位TEM实验技术，以在接近计算建模的时间尺度上探测材料体积的行为。非技术摘要：凝固是材料制造中普遍存在的基本过程，特别是对于金属，这对能源生产和传输，运输和信息技术至关重要。在激光加工的极端条件下，生长动力学决定了最终的微观结构，从而决定了工程部件和设备的性能相关特性。理解这些现象在科学上是有趣的，在技术上是重要的。这项研究的结果将通过同行评审的出版物和介绍加以传播。该项目涉及通过宾夕法尼亚州少年科学院向高中生推广，并为新的匹兹堡科学技术学院（6 - 12年级）的学生提供长达一个学期的研究经验。&学生将接受真空和激光科学，物理冶金，薄膜科学，微加工方法，散射和衍射物理，透射和扫描电子显微镜，晶体学，热力学，传输现象和材料建模的数值方法的培训。访问，并与持续互动，LLNL将提供学术环境之外的专业准备，并获得最先进的仪器。

TECHNICAL SUMMARY: This project is an investigation of rapid solidification processes in pure metal and Al-rich Al(Cu) thin films. The main technique is in-situ transmission electron microscopy (TEM) using the dynamic TEM (DTEM) at Lawrence Livermore National Laboratory (LLNL) for ultrafast electron diffraction (UED) and imaging. There are no other measurement techniques currently capable of observing rapid solidification processes with interfacial velocities ranging from about 0.1 to 100 m/s in metal thin films with the required nano-scale spatial and temporal resolution offered by the DTEM. The research will reveal quantitative dynamic details of the extremely rapid liquid-solid transformation and other transient phenomena (e.g. solid-solid transitions) associated with Al and Al-rich Al(Cu) thin films and other FCC, BCC and HCP metals after single-shot pulsed laser melting. Robust modeling software codes, validated by direct comparison with quantitative measurements from in-situ DTEM experiments on pure metals, will be developed for the pulsed-laser melting. Post-mortem and in-situ microstructural characterization will be used to investigate microstructural evolution and defect formation in the solid state following solidification of pure metals with different crystal structures. The study of Al-rich Al(Cu) thin films is expected to help identify the conditions of morphological destabilization of the growth interface as function of pulsed laser power, alloy composition and heat-extraction parameters for hypo-eutectic, eutectic and hypereutectic compositions between Al and Al2Cu. The data obtained on parameters that determine the stability or instability of the transformation front will enable validation of theoretical solidification models. Apart from delivering basic scientific knowledge on metals under the extreme conditions of laser-induced rapid solidification, state-of-the-art experimental techniques for in-situ TEM will be developed for the purpose of probing the behavior of material volumes at time scales close to those accessible by computational modeling.NON-TECHNICAL SUMMARY: Solidification is a ubiquitous and fundamental process in materials fabrication, especially for metals, which are critical to energy generation and transmission, transportation and information technologies. Under extreme conditions of laser processing the growth dynamics determine the final microstructure and consequently performance-related properties in engineered components and devices. Understanding such phenomena is scientifically interesting and technologically important. The results of this research will be disseminated by peer-reviewed publications and presentations. The project involves outreach to high school students, via the Pennsylvania Junior Academy of Science and the development of semester-long research experiences for students enrolled in the new Pittsburgh Science & Technology Academy (grades 6-12). Students will receive training in vacuum and laser science, physical metallurgy, thin film science, micro-fabrication methods, scattering and diffraction physics, transmission and scanning electron microscopy, crystallography, thermodynamics, transport phenomena and numerical methods for materials modeling. Visits to, and continuous interaction with, LLNL will provide professional preparation outside the academic environment and access to state-of-the-art instrumentation.