Texture and Texture Transformations in Thin Metal Films

技术概述：金属薄膜是微电子、光学、传感器和催化剂等许多纳米和微细加工技术中的关键元素。由于尺寸的限制，这种薄膜经常被发现是织构的；也就是说，组成薄膜的单个金属微晶优先地以某些类型的晶面平行于薄膜平面取向。由于薄膜的性能强烈依赖于存在的取向，因此了解织构对于了解包含薄膜的器件的性能和可靠性至关重要。对于导致织构形成的驱动力有很好的普遍共识。然而，现有的模型预测，在平衡时只有一个纹理分量应该出现，而混合纹理是常见的。要理解这一点，必须了解真实电影中纹理转换的动力学。在这个项目中，Baker小组将研究金属薄膜从沉积到退火态织构的转变动力学。初步工作表明，在这类薄膜中出现的不均匀的三维应力状态可能会稳定混合织构。为了研究这一点，Baker小组将生产对薄膜结构和化学有很好控制的薄膜，表征薄膜结构，包括测量作为取向函数的颗粒尺寸分布，并将使用原位同步X射线衍射和透射电子显微镜方法确定不同织构成分的体积分数和应力状态。他们将使用一种高通量方法，使他们能够调查每一次薄膜沉积的多个参数。详细的有限元模拟将被用来研究单个晶体内的应力分布，分析模型将被用来将应力状态、动力学模型和热力学模型连接到一个结构中，该结构将有力地加强对薄膜织构的预测和控制，从而加强对性能的控制。非技术摘要：金属薄膜--金属薄膜--厚度小于人类头发厚度的十分之一--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件。这些薄膜是由许多微小的金属晶体组成的，这些晶体被称为“颗粒”。由于薄膜很薄，颗粒倾向于自我定向，从而使其晶体结构中的某些方向与薄膜的平面一致。薄膜的性能，以及包含薄膜的器件的性能和可靠性，都非常敏感地取决于这些取向。这个话题已经研究了很多年，但人们还没有能力预测一部电影或一个设备将如何表现。康奈尔大学的贝克小组提出，载荷在颗粒间的分布方式可以稳定不同的取向组合。为了研究这一点，他们将制作电影，使用康奈尔高能同步加速器源(CHESS)等复杂工具表征其结构和行为，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继续使下一代纳米软化设备微型化，并应有助于提高所有包含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的一家小型非授予博士学位的机构。本科生的参与将提高项目的科学产出和这些学生的教育经验。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陈述他们的工作。霍顿的学生将在霍顿接受布兰登·霍夫曼教授的建议，但他们将在夏季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联活动。当前项目的一个好处是，颗粒取向分布的图像可以相当引人注目，而且通常可以作为艺术独立存在，成为向非科学家谈论材料科学的很好的破冰者。

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.