Influence of interfacial stress on the stability of epitaxial films

Fried0706460外延生长的薄合金薄膜是电子和其他工业中使用的许多纳米和微米器件的重要组成部分。不幸的是，平面应变薄膜的生长很容易受到不稳定性的影响。这些不稳定性通常表现为表面波纹、表面尖点和岛状丘陵的形成，如量子点和量子线。对具有精确定制的微纳结构的薄膜的需求导致了大量关于合金薄膜外延过程中的形态不稳定性的文献。到目前为止，人们的注意力主要集中在薄膜和衬底之间的晶格参数不匹配和表面扩散引起的不稳定性上。然而，界面应力几乎没有引起人们的注意，因为它可能强烈地影响表面特征的形成。此外，由于描述三维空间中不断变化的表面存在几何复杂性，迄今为止，对生长-应力相互作用的研究仅限于二维理论，其中界面是一条曲线。此外，还没有理论解释表面应力对外延过程中的相分离和相关图案形成的影响。在这个项目中，研究人员和同事们：1.进行稳定性分析和数值模拟，旨在探索表面应力在外延生长薄膜稳定性中的作用。2.将已有的二维理论推广到三维空间。3.发展了一种描述合金外延过程中生长和相分离相互作用的理论。这位研究人员和他的同事们开发和分析了外延生长薄膜的行为和特征的数学模型，并进行了数值模拟。随着对这些薄膜形态稳定性的了解的增加，可以在各种具有重要战略意义的应用中取得进展和创新。例如，在电子工业中，外延生长的多层膜已被用来增加硬盘驱动器的存储容量，目前正在研究可能的改进措施。进步直接取决于控制生长过程中形成的小尺度特征的能力。外延薄膜重要性的另一个引人注目的例子是最近提出的能够检测空气污染的有机/无机混合器件。这些器件在通过分子束外延生长的半导体换能器上结合了一层单分子传感分子。为了确保传感分子正确地附着在换能器上并可靠地工作，需要一个精确定制的表面结构。外延薄膜在开发用于可变波长激光器等应用的光学半导体方面也具有潜力。该设备具有广泛的潜在应用，包括检测来自汽车尾气、工厂、事故、火灾、自然灾害等的有毒气体。利用可变波长激光，可以将测量时间从1-2分钟缩短到1秒，从而在紧急情况下更快速地控制和疏散。

Fried0706460 Epitaxially-grown thin alloy films are essential componentsin many nano- and microscale devices used in the electronics andother industries. Unfortunately, the growth of planar strainedfilms is susceptible to instabilities. These instabilities areoften manifested by the formation of surface ripples, surfacecusps, and island-like mounds such as quantum dots and quantumwires. The demand for films with precisely tailored micro- andnanostructures has led to an extensive literature concerned withmorphological instabilities during the epitaxy of thin alloyfilms. To date, attention has focused primarily on instabilitiesthat arise from a mismatch in lattice parameters between the filmand the substrate and surface diffusion. However, interfacialstress, which may strongly influence the formation of surfacepatterns, has received almost no attention. Moreover, because ofthe geometric complications associated with the description ofevolving surfaces in three space dimensions, studies ofgrowth-stress interactions have thus far confined attention totwo-dimensional theories, wherein the interface is a curve. Additionally, no theory yet accounts for the influence of surfacestress on phase segregation and related pattern formation,processes that occur during epitaxy. In this project, theinvestigator and colleagues: 1. Perform stability analyses and numerical simulations designed to explore the role of surface stress in the stability of epitaxially growing films. 2. Extend the existing two-dimensional theory to three space dimensions. 3. Develop a theory that describes the interaction of growth and phase segregation during the epitaxy of alloys. The investigator and his colleagues develop and analyzemathematical models, and carry out numerical simulations, of thebehavior and characteristics of epitaxially grown thin films. Anincreased understanding of the morphological stability of thesefilms allows for progress and innovation in a variety ofstrategically important applications. For instance, in theelectronics industry, epitaxially grown multi-layers have beenused to increase the storage capacity of hard drives and are nowbeing studied for possible improvements. Progress rests directlyon the ability to control small-scale features that form duringgrowth. Another compelling example of the importance ofepitaxial films is provided by recently proposed hybridorganic/inorganic devices capable of detecting airbornecontaminants. These devices combine a monolayer of sensingmolecules on a semiconductor transducer grown via molecular beamepitaxy. A precisely tailored surface structure is necessary toensure that the sensing molecules adhere correctly to thetransducer and perform reliably. Epitaxial films also havepotential in the development of optical semiconductors forapplications such as variable wavelength lasers. The deviceshave a wide range of potential applications, including thedetection of toxic gases from vehicle exhaust, factories,accidents, fires, natural disasters, etc. With a variablewavelength laser, it is possible to shorten measurement timesfrom 1-2 minutes to 1 second, allowing for more rapid containmentand evacuation during emergencies.