Thermally-induced Rayleigh-taylor like instabilities for nanoscale synthesis

kalyanaraman：美国能够继续在技术创新方面成为全球领导者的一种方式是，如果它能为未来制定一个健全的经济计划，那么它就可以在高科技制造业中雇佣大部分人口。一个潜在的未开发但高增长的领域是制造用于太阳能电池、计算机数据存储设备和疾病检测传感器的复杂纳米材料。人们普遍认为大自然已经找到了许多方法以经济的方式制造有用的复杂材料。在自然界中经常发现的一个原理是自组织或自组装，在这种原理中，相互竞争的力量导致有用结构的出现。例如，瑞利-泰勒（RT）效应是在天花板底部形成均匀水滴的核心。在这种情况下，是重力干扰水膜-空气界面导致液滴形成的结果。除了在液体中很明显，RT效应也可以在诸如黑洞和超新星等天文结构的行为以及地球物理现象中找到。如果RT效应可以应用到纳米尺度上，就可以产生一种成本效益高的制造纳米材料的方法。然而，由于重力很少影响纳米尺度，因此需要找到其他方法来产生RT效应。本文提出的研究将探索在液体环境中快速加热材料可以在纳米尺度上产生RT效应的假设。实验部分将包括通过使用激光脉冲加热感兴趣的材料来创建这样一个场景。各种显微镜和计算机建模技术将被用来研究产生的纳米材料。在这项研究的过程中，将实现对K-12、本科和研究生课程中少数民族和代表性不足的学生的培训。他们将接受科学和工程的基本原则和应用原则的培训，目标是使他们成为STEM学科和/或技术相关行业的未来社会领导者。本文提出的研究是对纳米尺度上瑞利-泰勒（RT）不稳定性的一种理解。最近的实验结果表明，在流体环境中激光脉冲熔化的薄膜中可以观察到RT不稳定性。这一发现的初步假设是，由于纳秒激光脉冲的快速加热，在膜/蒸气界面上形成的大热梯度导致了大的压力梯度，这是最终观察到的行为的原因。热模拟的早期结果支持这一假设。然而，流体性质、激光参数和其他薄膜流体动力学不稳定性的作用目前还缺乏，以便明确地建立对这一现象的理解。受此启发，几种基于流体（甘油、水、甲苯）、薄膜（Au、Ag、Si、TiO2）和衬底（玻璃、Si、蓝宝石）性质组合的模型系统已经被确定。将执行以下任务。(1)热输运的理论建模，以理解ns脉冲激光加热各种流体/薄膜/衬底系统。(2)各种流体、薄膜和基材组合的激光熔化实验。(3)利用各种纳米尺度工具表征图案形态、纳米颗粒结构和化学成分。这包括扫描和透射电子显微镜、原子力显微镜、拉曼光谱、电子能量损失光谱和光学光谱。(4)在流体力学理论背景下对实验结果进行建模，以解释观测结果。

CBET-1402962KalyanaramanOne way the United States can continue to be the global leader in technology innovation with a sound economic plan for the future is if it can employ large fractions of the population in high-tech manufacturing jobs. One potentially untapped, but high growth, area, is the manufacturing of sophisticated nanomaterials for use in solar cells, computer data storage devices, and sensors for disease detection. It is widely acknowledged that nature has found many ways to make useful and complex materials in economical fashion. One of the principles often found in nature is that of self-organization or self-assembly, in which competing forces lead to the emergence of a useful structure. For example, the Rayleigh-Taylor (RT) effect is at the heart of the formation of a uniform collection of water droplets on the underside of a ceiling. In this case, it is the result of gravity disturbing the water film-air interface that leads to droplet formation. Besides being evident in liquids, the RT effect can also be found in the behavior of astronomical structures such as black holes and supernova, and in geophysical phenomenon. If the RT effect can be applied to the nanoscale, a cost-effective way to make nanomaterials could result. However, since gravity rarely influences the nanoscale, other ways need to be found to create the RT effect. The research proposed here will explore the hypothesis that rapid heating of a material in liquid ambient can produce RT effects in the nanoscale. The experimental component will involve creating such a scenario by using laser pulses to heat the material of interest. A variety of microscopy and computer modeling techniques will be employed to study the resulting nanomaterials. During the course of this research, training of minority and underrepresented students from K-12, undergraduate, and graduate programs will be achieved. They will be trained in basic and applied principles of science and engineering, with the goal of making them future leaders of the society in STEM disciplines and/or in technologically relevant industries. The research proposed here is an understanding of the Rayleigh-Taylor (RT) instability in the nanoscale. Recent experimental findings show that the RT instability can be observed in thin films melted by laser pulses in a fluid ambient. The preliminary hypothesis underlying the discovery is that the large thermal gradient that develop at the film/vapor interface due to the rapid heating under nanosecond laser pulses lead to large pressure gradients, which are ultimately responsible for the observed behavior. Early results of thermal modeling support this hypothesis. However, the role of fluid properties, laser parameters and other thin film hydrodynamic instabilities is presently lacking in order to unequivocally establish an understanding of this phenomenon. Motivated by this, several model systems based on a combination of fluid (glycerol, water, toluene), film (Au, Ag, Si, TiO2), and substrate (Glass, Si, Sapphire) properties have been identified. The following tasks will be performed. (1) Theoretical modeling of thermal transport to understand ns pulsed laser heating of various fluid/film/substrate systems. (2) Laser melting experiments of various combinations of fluid, film and substrate. (3) Characterization of pattern morphology, nanoparticle structure, and chemical composition by various nanoscale tools. This includes scanning and transmission electron microscopy, atomic force microscopy, Raman spectroscopy, electron energy loss spectroscopy, and optical spectroscopy. (4) Modeling of the experimental results in the context of fluid dynamics theories to explain the observations.