Control of Intrinsic Stresses in Ceramic Thin Films and Coatings Produced by Chemical Vapor Deposition

这项研究项目的主要动机是需要控制陶瓷薄膜和涂层中的残余应力，这包括用于电子和结构应用的各种材料。残余应力产生于薄膜和衬底之间的热膨胀失配，以及薄膜生长过程中的各种内在机制。陶瓷薄膜和涂层的可行性通常是通过计算热应力来评估的，然而，这种计算通常是不准确的，因为它忽略了本征应力。布朗以前的工作表明，薄膜生长过程中岛屿合并引起的拉应力往往盖过了热应力。这项工作还表明，在岛屿合并过程中，这些本征应力可以通过改变工艺来控制。这些努力集中在CVD钻石上，这是这些研究的一个很好的系统，因为钻石具有很大的内在应力，这在一些应用中是有问题的，而且关于CVD钻石的大量文献为理解生长应力提供了坚实的基础。在CVD钻石已取得成功的基础上，将在该项目期间开展以下活动：1)在各种陶瓷薄膜和涂层的颗粒结合过程中，通过改变工艺来控制固有拉应力；2)开发更好的模型来描述固有应力的演变；3)研究残余应力与薄膜性能(断裂等)之间的关系，这将基于Brown开发的加工方法，该方法提供了一种独特的方法来改变应力，而不改变衬底、颗粒尺寸或薄膜成分；4)控制固有应力，以新的方式修改总残余应力；5)调查拉曼光谱与其他用于测量CVD钻石残余应力的方法之间的差异；6)为橡树岭国家实验室正在进行的氧化物涂层工作提供直接意见；以及8)继续开展各种教育工作，包括布朗大学的ExSEL项目(共同参与Pi Rankin教授)，以及由PI为当地初中和高中教师举办的经认可的材料科学研讨会。布朗大学和三一学院(一家本科教学机构)的本科生将继续参与研究活动。陶瓷和金刚石薄膜用于各种重要的技术应用，如计算机和电信。在加工过程中，这些薄膜会产生应力，限制了它们在应用中的有效性。这项研究项目将由布朗大学的两名研究人员和三一学院(一所本科院校)的一名研究人员进行，将调查控制这种压力的方法。这项工作的结果将有助于更好地理解和改进对各种薄膜和涂层中的应力的控制，从而加强它们在应用中的使用。

The primary motivation for this research project is the need to control residual stresses in ceramic thin films and coatings, which encompasses a wide range of materials used for both electronic and structural applications. Residual stresses arise from the thermal expansion mismatch between film and substrate, and from various intrinsic mechanisms during film growth. The viability of ceramic films and coatings are typically evaluated by calculating thermal stresses, however, this calculation is often inaccurate because it ignores intrinsic stresses. Previous work at Brown demonstrates that tensile stresses caused by island coalescence during film growth often overshadow thermal stresses. This work also shows that these intrinsic stresses can be controlled by altering processing during island coalescence. These efforts are focused on CVD diamond, which is an excellent system for these studies since diamond has large intrinsic stresses that are problematic for a number of applications and because the extensive literature on CVD diamond provides a strong basis for understanding growth stresses. Building on the previous success with CVD diamond, the following activities will be carried out during the project: 1) Establish that intrinsic tensile stresses can be controlled by altering processing during grain coalescence in a wide range of ceramic thin films and coatings; 2) Develop better models for describing the evolution of intrinsic stresses; 3) Investigate relationships between residual stress and film properties (fracture, etc.), which will be based on the processing methods developed at Brown that provide a unique approach for varying stress without changing the substrate, grain size, or film composition; 4) Control intrinsic stresses to modify the total residual stress in novel ways; 5) Investigate discrepancies between Raman spectroscopy and other methods that are used to measure residual stress in CVD diamond; 6) Provide direct input to ongoing work on oxide coatings at Oak Ridge National Laboratory; and 8) Continue a variety of educational efforts, including the ExSEL program at Brown (co-PI Prof. Rankin), and an accredited Materials Science workshop for local middle and high school teachers that was developed by the PI. Research activities will continue to involve undergraduates from both Brown and Trinity (an undergraduate teaching institution). %%%Ceramic and diamond thin films are used in a variety of technologically important applications such as computers and telecommunications. During processing these thin films are develop stress that limit their effectiveness in the application. This research project, which will be carried out by two investigators at Brown University and one from Trinity College (an undergraduate institution), will investigated methods of controlling the stress that form. The results from this work will lead to better understanding and improved control of stresses in a variety of thin films and coatings, thus enhancing their usage in the application.***