Texture and Texture Transformations in Thin Metal Films

技术概述：金属薄膜是许多纳米和微制造技术的关键元素，包括微电子、光学、传感器和催化剂。由于尺寸的限制，这种薄膜经常被发现有织构；即，组成薄膜的单个金属晶体优先取向于平行于薄膜平面的某些类型的晶体平面。由于薄膜的性质在很大程度上取决于存在的方向，因此理解薄膜的结构对于理解包含薄膜的器件的性能和可靠性至关重要。对导致织构形成的驱动力有很好的共识。然而，现有的模型预测只有一种纹理成分应该出现在平衡状态，而混合纹理是常见的。为了理解这一点，必须了解真实薄膜中织构转变的动力学。在这个项目中，Baker小组将研究金属薄膜从沉积到退火织构转变的动力学。初步研究表明，在这种薄膜中出现的非均匀三维应力状态可能会稳定混合结构。为了研究这一点，Baker团队将生产对薄膜结构和化学控制非常好的薄膜，表征薄膜结构，包括测量晶粒尺寸分布作为取向的函数，并将使用原位同步x射线衍射和TEM方法确定不同织构成分的体积分数，以及其中的应力状态。他们将使用一种高通量方法，使他们能够研究每个薄膜沉积的多个参数。详细的有限元模拟将用于研究单个晶体内的应力分布，分析模型将用于将应力状态、动力学模型和热力学模型连接到一个结构中，该结构将有力地增强对薄膜织构和性能的预测和控制。非技术概要：金属薄膜——厚度小于人类头发丝十分之一的金属层——是计算机芯片、光学系统、催化转换器和许多其他高科技设备的基本元素。这些薄膜由许多微小的金属晶体组成，称为“颗粒”。由于薄膜非常薄，颗粒倾向于自我定向，使其晶体结构的某些方向与薄膜的平面对齐。薄膜的性质，以及包含薄膜的器件的性能和可靠性，非常敏感地依赖于这些取向。这个话题已经研究了很多年，但人们还没有能力预测电影或设备的行为。康奈尔大学的贝克小组提出，载荷分布在颗粒上的方式可以稳定不同的方向组合。为了研究这一点，他们将制作薄膜，使用复杂的工具（如康奈尔高能同步加速器源（CHESS））来表征它们的结构和行为，并将生成计算机模型来帮助解释他们的结果。在这个项目中产生的知识将有助于使下一代纳米制造设备的小型化成为可能，并有助于提高所有包含薄金属薄膜的设备的性能和可靠性。这个项目将涉及康奈尔大学和霍顿学院的本科生，霍顿学院是纽约州北部一个小型的不授予博士学位的机构。本科生的参与将提高项目的科学成果和学生的教育经验。本科生将全面参与研究，并将在专业学会会议和同行评议的论文中展示他们的工作。霍顿学院的学生将由布兰登·霍夫曼教授指导，但暑假将与康奈尔大学的贝克小组一起工作。贝克集团的研究生和博士后积极参与地区学校和机构的外展活动。当前项目的一个好处是，颗粒取向分布的图像可以非常引人注目，并且通常可以作为一种艺术，为与非科学家谈论材料科学提供了一个很好的破冰机会。

TECHNICAL SUMMARY: Thin metal films are critical elements in many nano- and micro-fabricated technologies including microelectronics, optics, sensors, and catalysts. Due to dimensional constraints, such films are often found to be textured; that is, the individual metal crystallites comprising the film are preferentially oriented with certain types of crystal planes parallel to the film plane. Since the properties of the film depend strongly on the orientations present, understanding texture is critical to understanding the performance and reliability of devices containing thin films. There is good general agreement on the driving forces leading to texture formation. However existing models predict that only one texture component should occur at equilibrium, while mixed textures are common. To understand this, the kinetics of texture transformations in real films must be understood. In this project, the Baker group will study the kinetics of the transformation from as-deposited to as-annealed texture in thin metal films. Preliminary work suggested that inhomogeneous 3-D stress states that arise in such films may stabilize the mixed texture. To investigate this, the Baker group will produce films with very good control over film structure and chemistry, characterize film structure, including measurements of grain size distributions as a function of orientation, and will determine the volume fractions of the different texture components, and stress states in them, using in-situ synchrotron x-ray diffraction and TEM methods. They will use a high-throughput method that allows them to investigate multiple parameters with every film deposition. Detailed finite element simulations will be conducted to study the stress distributions within individual crystallites, and analytical models will be used to link stress states, kinetic models, and thermodynamic models into a construct that should strongly enhance prediction and control of thin film texture, and therefore properties.NON-TECHNICAL SUMMARY: Thin metal films---metal layers less than one tenth the thickness of a human hair---are essential elements in computer chips, optical systems, catalytic converters, and many other high-tech devices. These films are made up of many tiny metal crystals, called "grains". Because the films are so thin, grains tend to orient themselves so that certain directions in their crystal structure align with the plane of the film. The properties of thin films, and therefore the performance and reliability of devices containing thin films, depend very sensitively on these orientations. This topic has been studied for many years but people do not yet have the ability to predict how a film or a device will behave. The Baker group at Cornell University has proposed that the way that loads are distributed across the grains can stabilize different combinations of orientations. To study this, they will make films, characterize their structure and behavior using sophisticated tools such as the Cornell High Energy Synchrotron Source (CHESS) and will generate computer models to help interpret their results. The knowledge generated in this project will help make it possible to continue to miniaturize the next generation of nanofabricated devices and should help to improve performance and reliability in all devices that contain thin metal films. This project will involve undergraduates at both Cornell and at Houghton College, a small non-PhD-granting institution in upstate New York. Undergraduate participation will enhance both the scientific output of the project and the educational experience of those students. Undergraduates will participate fully in the research, and will present their work in presentations at professional society meetings and in peer-reviewed papers. Houghton students will be advised at Houghton by Prof. Brandon Hoffman, but will spend summers working with the Baker group at Cornell. Baker group graduate students and post-docs are active in outreach activities to area schools and institutions. A benefit of the current project is that images of grain orientation distributions can be quite striking and can often stand on their own as art, making a nice icebreaker for talking about materials science to non-scientists.