Generation of a Pristine Sapphire Surface by Oxidation and Solid State Conversion of a Sputtered Al Coating

该项目包括对产生原始蓝宝石表面的新方法背后的机制进行深入研究。该工艺被命名为AGOG，代表了三个加工步骤：在蓝宝石上沉积Al薄膜，生长氧化铝层，生长晶粒以产生单晶表面。AGOG过程中每一步的加工条件都是系统变化的，并与表面结构的变化相关。确定铝膜的微观结构和厚度对氧化行为的影响。使用（0001）、（11-20）和（01-12）取向的蓝宝石来确定界面条件对Al到氧化铝相变的影响。相变行为的研究将与氧化/升温速率实验同时进行。一旦多晶氧化铝层被创造出来，固态转换的处理条件将被检查。最后，将探讨在初始氧化步骤中消除丘状生长的策略。蓝宝石，氧化铝的单晶形式，被用于许多重要的商业应用中，其中最终表面光洁度的质量是至关重要的。一个例子是最近用作高功率蓝光发光二极管（LED）和激光二极管的衬底材料。这些器件是大量应用所需要的，包括全彩电致发光显示器，以及用于磁性和光学介质上高密度信息存储的读写激光源。蓝色LED的成功商业生产也为来自固态器件的明亮白光光源提供了潜力。与传统的白炽灯和荧光灯相比，优点包括更高的能源效率和更高的可靠性。蓝宝石也广泛用于可见光和中波红外（IR）机载窗口和制导系统的天线罩。目前，蓝宝石组件的表面是通过机械和化学抛光的结合来完成的。最后的抛光步骤非常耗时，并且通常占总成本的很大一部分。AGOG工艺是实现蓝宝石高质量表面光洁度的一种潜在的更具成本效益的方法。

This project consists of an in-depth investigation into the mechanisms behind a novel method for generating a pristine sapphire surface. The process is named AGOG, representing the three processing steps: Al thin film deposition on sapphire, Growth of an aluminum Oxide layer, and grain Growth to produce a single crystal surface. Processing conditions at each step in the AGOG process will be varied systematically and correlated to the resulting changes in surface structure. The effect of Al film microstructure and thickness on oxidation behavior will be determined. Sapphire of (0001), (11-20), and (01-12) orientation will be used to identify the effect of interface conditions on the Al to alumina phase transformation. Studies of phase transition behavior will be carried out concurrently with oxidation/heating rate experiments. Once a polycrystalline alumina layer has been created, solid-state conversion processing conditions will be examined. Finally, strategies for eliminating hillock growth during the initial oxidation step will be explored.Sapphire, the single crystal form of alumina, is utilized in many important commercial applications where the quality of the final surface finish is critical. One example is the recent use as a substrate material for high-power blue light emitting diodes (LED's) and laser diodes. These devices are required for a large number of applications including full color electroluminescent displays, and read-write laser sources for high-density information storage on magnetic and optical media. The successful commercial production of blue LED's also offers the potential for bright, white light sources derived from solid state devices. Advantages over conventional incandescent and fluorescent sources include far higher energy efficiency and increased reliability. Sapphire is also widely used for visible and midwave infrared (IR) airborne windows and radomes for guidance systems. Currently, the surfaces of sapphire components are finished by a combination of mechanical and chemical polishing. The final polishing steps are time-consuming, and typically make up a significant fraction of the total cost. The AGOG process is a potentially more cost-effective method for achieving a high quality surface finish in sapphire.