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

技术：气相沉积金属薄膜和结构通常通过Volmer-Weber(VW)机制在衬底表面成核、生长和合并。通过这种机制形成的薄膜不能稳定地湿润它们的衬底，因此薄膜的形成是动力学约束的结果，这些约束迫使亚稳态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所有层次的结构演变过程，从而决定了沉积结构的最终性质。我们计划对VW生长过程中结构演化的关键方面进行研究：1)聚合前的岛状演化，以及2)聚合后的表面结构演化。在后一种情况下，我们将包括对同质外延薄膜表面演变的研究，以将表面过程的影响与与颗粒结构相关的影响分开。在这两种情况下，我们将使用原位应力测量来探索岛屿尺度和原子尺度的过程，同时具有表征快速原子尺度动力学过程所需的测量灵敏度和时间分辨率，这些过程在工程应用中典型的成膜条件下运行。我们还将使用原位电子衍射来探测表面结构的演变，并使用非原位探针和电子显微镜来表征淬火结构的形貌和结晶学特征。我们计划研究沉积通量和衬底温度的变化对两种情况下的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)。我们还计划研究低水平表面活性剂覆盖和纳米级光刻定义的衬底地形对岛屿和表面特征的大小、形状、间距、取向和有序性的影响，以及对沉积结构的最终性质的影响。非技术性：金属薄膜和纳米结构在微电子、微机电、微磁和微光子设备和系统中起着关键作用，决定了它们的性能和可靠性。新设想的应用还包括金属纳米颗粒阵列在新的计算设备、能量采集和生物传感应用中的应用。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，我们的目标将是发展对工程实践产生影响的基本理解，从而改善对应用中的金属薄膜和纳米结构的控制。两名研究生研究助理将直接得到该计划的支持。此外，PI的研究生和本科生研究小组现在和历史上一直是直接利用NSF研究在应用中的新见解，特别是在微电子和微机械设备和系统方面。这项研究的很大一部分是由行业直接支持的，并向行业报告。这项研究涉及麻省理工学院内外的合作，结果将像历史上一样，在科学和工程场所报告。研究结果和摘要可通过互联网获得，并包括在麻省理工学院为本科生和研究生以及专业工程师开设的课程中，后者以麻省理工学院短期课程和公司现场课程的形式提供。

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.