PECASE: Mechanisms of Surfactant Mediated Thin Film Growth

微电子学、光电子学和磁记录技术都依赖于生长低缺陷密度、连续超薄膜的能力。本项目的目的是确定如何通过添加表面活性剂来促进超薄连续膜的生长。利用原位变温扫描隧道显微镜（STM）研究表面活性剂对成核和生长动力学的影响及其机理。观察到的机理和动力学将用于发展表面活性剂介导生长的动力学蒙特卡罗模拟。模拟将用于研究生长模式对不同动力学参数的敏感性，从而揭示成功使用表面活性剂形成稳定的超薄连续薄膜所需的关键特征。对于几乎所有的应用，弗兰克-范德默韦（F-vdM）或逐层生长是首选的生长模式，因为它可以产生最薄、最均匀、连续的薄膜。当衬底表面张力大于界面张力和薄膜表面张力之和时，有利于法兰克-范德默威生长。即使有利于F-vdM生长，动力学限制也会导致新层在前一层完成之前成核。表面活性剂的加入可以通过改变表面和界面张力以及成核和生长动力学来促进F-vdM的生长。最近的研究表明后者更为重要，尽管表面活性剂存在下的成核和生长机制和动力学在很大程度上仍然是一个猜测问题。因此，我们将研究控制表面活性剂介导的成核和生长的关键基本过程的动力学：表面扩散、跨台阶扩散、台阶附着、原子-表面活性剂交换屏障、成核。比较两种截然不同的体系，即V族表面活性剂在Si（100）上生长Ag和Ge，将揭示成功使用表面活性剂促进F-vdM生长所需的所有关键特征，以及膜、底物和表面活性剂之间相互作用的性质如何影响动力学参数。包括微电子、光电子和磁记录在内的广泛应用的持续进步取决于在工业标准Si（100）衬底上形成超薄、低缺陷密度薄膜的能力。具体来说，开发在Si（100）上生长光滑Ge薄膜的方法被视为开发基于Ge-Si合金和超晶格结构的高速集成电路的关键，Ag-Si体系是薄膜磁性结构的基础。

ABSTRACT CTS-9733416 Eric I. Altman/Yale U. Microelectronics, optoelectronics, and magnetic recording technologies all rely on the ability to grow low defect density, continuous, ultra-thin films. The objective of this project is to determine how the growth of ultra-thin continuous films can be promoted by addition of surfactants. The effect of surfactants on nucleation and growth kinetics and mechanisms will be studied using in situ variable-temperature scanning tunneling microscopy (STM). The observed mechanisms and kinetics will be used to develop kinetic Monte Carlo simulations of surfactant mediated growth. The simulations will be used to investigate the sensitivity of the growth mode to the different kinetic parameters and thus will reveal the key features required to successfully use surfactants to form stable, ultra-thin continuous films. For almost all applications Frank-van der Merwe (F-vdM) or layer-by-layer growth is the preferred growth mode because it results in the thinnest, most uniform, continuous films possible. Frank-van der Merwe growth is favored when the surface tension of the substrate is greater than the sum of the interfacial tension and the surface tension of the film. Even when F-vdM growth is favored, kinetic limitations can lead to nucleation of new layers before the previous layers are completed. Addition of a surfactant can promote F-vdM growth by altering both surface and interfacial tensions and nucleation and growth kinetics. Recent studies suggest the latter is more important, although nucleation and growth mechanisms and kinetics in the presence of a surfactant remain largely a matter of speculation. Therefore, we will investigate the kinetics of the key elementary processes that govern surfactant mediated nucleation and growth: surface diffusion, diffusion across steps, attachment to steps, adatom-surfactant exchange barrier, nucleation. Comparison of two very different systems, Ag and Ge growth on Si(100) with group V surfactants, will reve al the key features required to successfully use surfactants to promote F-vdM growth, and how the kinetic parameters are affected by the nature of the interactions between the film, the substrate and the surfactant. Continued advances in a wide range of applications including microelectronics, optoelectronics and magnetic recording depend on the ability to form ultra-thin, low-defect density films on industry standard Si(100) substrates. Specifically, the development of methods to grow smooth Ge films on Si(100) is seen as a key to developing high-speed integrated circuits based on Ge-Si alloy and superlattice structures, and the Ag-Si system is of interest as a base for thin film magnetic structures.