Optically Switchable Metal Hydride Films: Properties and Structures

电子束蒸发合成的薄膜将被用来探索和开发最近发现的某些金属氢化物薄膜的显著光学开关性能，从而使一些薄膜(例如，Y)通过引起薄膜中氢含量的相对较小的变化，可以快速和可逆地从金属反射镜转变为透明绝缘体。这个项目的目标包括：1)了解光学开关的机制(已经提出了电子关联、间隙位置占用和其他机制)；2)实现开关时间的改善；3)了解薄膜中的稳定性和应变效应；以及4)提供微镜阵列中像素开关的演示。将探索利用气体压力、电化学电荷转移和一种新的电传输技术来控制氢含量。开关速度和氢的扩散率将通过研究特定的薄膜合金、基片-薄膜应变效应以及覆盖层的厚度和成分来探索。第一批带有驱动电极的微镜阵列将通过光刻技术进行图案化。各种表征和分析技术，包括核磁共振力显微镜提供的新能力，以及传统的霍尔效应、X射线衍射和原子力显微镜，将被用来描述扩散系数、传输特性、光学传输以及表面和薄膜形态的系统学。学生和博士后研究助理将参与这项研究。这项工作将探索和开发某些薄膜的显著特性。这些薄膜(通常是窗户和镜子上的金属涂层，或者是视频显示器上的小圆点(像素))可以迅速从镜子转换为透明。这种“开-关镜”的行为是通过改变薄膜所允许的氢气量来控制的。这种材料具有立竿见影的应用潜力，从“智能窗户”和其他节能的大型产品，到平板显示器的可切换微镜。这个项目代表了一个多方面的计划，以优化和开发这种材料。目标包括：1)了解为什么会发生光学开关；2)使开关时间更快，以便使材料对视频设备有用；3)了解薄膜的结构；以及4)演示微镜阵列中的像素开关。这项工作将研究改变氢含量的方法；特别是将研究一种新的技术，即氢与电流一起扫描。将研究薄膜的结构和氢在材料中运动速度的变化。第一批具有驱动电极的微镜阵列将被图案化，以展示这些可切换光学材料在视频显示器中的用途。这项研究将在研究生和本科生以及博士后研究助理的协助下进行。因此，他们将接受当前凝聚态物理和材料科学前沿领域之一的培训。这将有助于他们在本世纪今后几十年内进入科学/技术劳动力大军。

Thin films synthesized by electron-beam evaporation will be used to explore and exploit the remarkable optical switching properties of certain recently-discovered metal-hydride thin films, whereby some thin films (e.g., yttrium) can quickly and reversibly transform from a metallic mirror to a transparent insulator, by inducing a relatively small change in the hydrogen content of the thin film. The objectives of this project include: 1) to gain an understanding of the mechanism responsible for the optical switching (electron correlation, interstitial site occupancy, and other mechanisms have been proposed); 2) to achieve an improvement in switching times; 3) to understand the stability and strain effects in the films; and 4) to provide a demonstration of pixel switching in an array of micro-mirrors. Control of hydrogen content using gas pressure, electrochemical charge-transfer, and a novel electrotransport technique will be explored. Switching speed and the diffusivity of hydrogen will be explored by investigating specific thin film alloys, substrate-film strain effects, and overlayer thickness and composition. The first arrays of micro-mirrors with driving electrodes will be patterned by photo-lithographic techniques. Various characterizational and analytical techniques, including the new capabilities offered by nuclear magnetic resonance force microscopy, as well as conventional Hall effect, x-ray diffraction, and atomic force microscopy, will be employed to delineate systematics in diffusion coefficients, transport properties, optical transmission, and surface and film morphology. Students and post doctoral research associates will participate in this research.%%% This work will explore and exploit the remarkable properties of certain thin films. These films (typically, these would be metallic coatings on windows and mirrors, or would make up the small dots ("pixels") on video displays) can be made to quickly switch from being a mirror to being transparent. This "on-off mirror" behavior is controlled by changing the amount of hydrogen that the film is allowed to contain. Such materials have immediate potential for applications, from "smart windows" and other energy-saving large-scale products, to switchable micro-mirrors for flat-panel displays. This project represents a multifaceted program to optimize and develop such materials. Objectives include: 1) understanding why the optical switching occurs; 2) making the switching times faster, in order to make the materials useful for video devices; 3) understanding the structure of the films; and 4) demonstrating pixel switching in an array of micro-mirrors. The work will study the ways that the hydrogen content can be changed; in particular, a new technique whereby the hydrogen is swept along with an electrical current will be examined. The structure of the films and variations in the speed of hydrogen motion in the material will be investigated. The first arrays of micro-mirrors with driving electrodes will be patterned to demonstrate the utility of these switchable optical materials for video displays. This research will be conducted with the assistance of graduate and undergraduate students as well as postdoctoral research associates. They will thereby receive training in one of the current forefront areas of condensed matter physics and materials science. This will facilitate their entry into the scientific/technological workforce during the coming decades of this century.***