Structure Evolution During Volmer-Weber Growth of Metallic Films and Micro- and Nano-Structures

技术：气相沉积的金属薄膜和结构通常通过沃尔默-韦伯（VW）机制在衬底表面形成晶体岛形核、生长和聚结。通过这种机制形成的薄膜不能稳定地润湿它们的衬底，因此薄膜的形成是动力学约束的结果，这些约束迫使亚稳或不稳定的薄膜和颗粒的发展。因此，动力学过程决定了薄膜形成过程中各个层次结构演化的过程，从而确定了沉积结构的最终性质。我们计划研究大众生长过程中结构演化的两个关键方面：1)聚并前岛演化；2)聚并后表面结构演化。在后一种情况下，我们将包括对同外延薄膜表面演变的研究，以将表面过程的影响与与晶粒结构相关的影响分离开来。在这两种情况下，我们将使用地应力测量来探测岛屿尺度和原子尺度过程，同时具有测量灵敏度和时间分辨率，以表征在工程应用中典型的薄膜形成条件下运行的快速原子尺度动力学过程。我们还将使用原位电子衍射来探测表面结构演变，并使用非原位探针显微镜和电子显微镜来表征淬火结构的形貌和晶体学特征。我们计划研究两种情况下沉积通量和衬底温度变化对应力和结构演变的影响。我们将研究生长中断的影响以及生长条件的时间变化（包括岛屿大小聚焦技术）。我们还计划研究低表面活性剂覆盖率和纳米级蚀刻定义的衬底形貌对岛屿和表面特征的大小、形状、间距、方向和顺序以及沉积结构的最终性质的影响。非技术：金属薄膜和纳米结构在微电子、微机电、微磁和微光子器件和系统中起着至关重要的作用，定义了它们的性能和可靠性。新的设想应用还包括金属纳米粒子阵列在新的计算设备，能量收集和生物传感应用。在所有这些应用中，都需要对结构和性能进行严格的工程控制。在所有计划的工作中，我们的目标是发展对工程实践的基本理解，从而改善对金属薄膜和纳米结构的控制。两名研究生研究助理将由该计划直接资助。此外，PI的研究生和本科生研究小组现在和历史上都是直接利用来自NSF应用研究的新见解，特别是在微电子和微机械设备和系统方面。这些研究大多是由工业界直接支持的，并向工业界报告。这项研究涉及麻省理工学院内外的合作，研究结果将像以往一样，在科学和工程领域进行报告。研究结果和总结通过互联网提供，并包含在麻省理工学院本科生和研究生以及专业工程师的课程中，后者以麻省理工学院短期课程和公司现场课程的形式出现。

TECHNiCAL: Vapor-deposited metal films and structures generally evolve through the Volmer-Weber (VW) mechanism of crystal island nucleation, growth, and coalescence on substrate surfaces. Films formed via this mechanism do not stably wet their substrate, so film formation is a consequence of kinetic constraints that force the development of metastable or unstable films and particles. Consequently, kinetic processes dictate the course of all levels of structure evolution during film formation, and therefore define the final properties of the as-deposited structures. We plan to study to key aspects of structure evolution during VW growth: 1) pre-coalescence island evolution, and 2) post-coalescence surface structure evolution. In the latter case, we will include studies of evolution of surfaces of homoepitaxial films, to isolate effects of surface processes from effects associated with grain structures. In both regimes we will use in-situ stress measurements to probe both island-scale and atomic scale processes with both the measurement sensitivity and the temporal resolution required to characterize fast atomic-scale kinetic processes that operate during film formation conditions that are typical for engineering applications. We will also use in-situ electron diffraction to probe surface structure evolution, and ex-situ probe-based and electron-based microscopies to characterize morphology and crystallographic characteristics of quenched structures. We plan to investigate the effects of changes in deposition flux and substrate temperature on stress and structure evolution in both regimes. We will investigate effects of growth interruptions as well the temporal variations in the growth conditions (including island size focusing techniques). We also plan to investigate the effects of low-level surfactant coverage and of nano-scale lithographically defined substrate topography on the size, shape, spacing, orientation and ordering of island and surface features, and on the final properties of deposited structures. NON-TECHNICAL: Metallic thin films and nano-structures play critical roles in microelectronic, microelectromechanical, micromagnetic and microphotonic devices and systems, defining their performance and reliability. New envisioned applications also include metallic nano-particle arrays in new computing devices, energy harvesting, and biosensing applications. In all of these applications, stringent engineering control of the structure and properties is required. In all of the planned work, our goal will be to develop fundamental understandings that will have impact on engineering practices leading to improved control of metal films and nano-structures for applications. Two graduate research assistants will be directly supported by the program. In addition, the PI's research group of graduate and undergraduate students is now, and has historically been structured, to directly exploit new insights derived from NSF research in applications, especially in microelectronic and micromechanical devices and systems. Much of this research is directly supported by industry, and reported to industry. The research involves collaborations both inside and outside MIT, and results will be reported, as they have historically been, in both scientific and engineering venues. Research results and summaries are made available via the internet, and are included in MIT courses for undergraduate and graduate students, as well as professional engineers, the latter in the form of short courses at MIT and on-site in companies.