Optically Switchable Metal Hydride Films: Properties and Structures

通过电子束蒸发合成的薄膜将用于探索和利用某些最近发现的金属氢化物薄膜的显着的光开关特性，其中一些薄膜（例如，钇）可以通过诱导薄膜中氢含量的相对较小变化而快速可逆地从金属镜子转变为透明绝缘体。该项目的目标包括：1)了解光交换的机制（电子相关、间隙位置占用和其他机制已被提出）；2)实现切换次数的改进；3)了解薄膜的稳定性和应变效应；4)在微镜阵列中提供像素切换的演示。利用气体压力、电化学电荷转移和一种新的电输运技术来控制氢含量将被探索。开关速度和氢的扩散率将通过研究特定的薄膜合金、衬底-薄膜应变效应、覆盖层厚度和组成来探索。第一批带有驱动电极的微镜阵列将采用光刻技术制作图案。各种表征和分析技术，包括核磁共振力显微镜提供的新功能，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，输运性质，光学透射，表面和薄膜形态的系统。学生和博士后研究助理将参与本研究。这项工作将探索和利用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点（“像素”））可以快速地从镜子切换到透明。这种“开-关镜像”的行为是通过改变薄膜允许包含的氢量来控制的。这种材料具有直接的应用潜力，从“智能窗户”和其他节能大型产品，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方案来优化和开发这些材料。目标包括：1)理解光交换发生的原因；2)使切换次数更快，使材料对视频设备有用；3)了解影片的结构；4)在微镜阵列中演示像素切换。这项工作将研究改变氢含量的方法；特别地，我们将研究一种利用电流扫过氢气的新技术。薄膜的结构和氢在材料中运动速度的变化将被研究。第一批带有驱动电极的微镜阵列将被制成图案，以展示这些可切换光学材料用于视频显示的实用性。本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，他们将接受凝聚态物理和材料科学当前前沿领域之一的培训。这将有助于他们在本世纪未来几十年加入科技队伍

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.***