A Theoretical, Experimental, and Atomistic Investigation of Surface Energy Anisotropy Effects on Grain-boundary Grooving

固体薄膜是大多数微电子和光电子器件的基本结构。在多晶膜的退火过程中，晶界凹槽会加深，形成孔洞，这些孔洞往往会长大，从而使薄膜破裂。研究人员的初步理论工作表明，表面能各向异性可以显著降低刻槽速度。然而，如果暴露的表面方向不包含小平面方向，则各向异性凹槽是光滑的，看起来与各向同性凹槽完全相同；只有凹槽速率降低。这一建议旨在利用三种方法：连续分析、实验和原子模拟来研究表面能各向异性与晶界沟槽之间的有趣关系。研究人员的初步工作假设双晶的晶体取向关于晶界对称。然而，大多数双晶不太可能是对称的。因此，自相似连续谱分析将扩展到非对称双晶。研究人员还将考虑恒速迁移的晶界，并研究晶界凹槽和晶界轮廓之间的耦合。由于沟槽是自相似的，所以在沟槽发展的初期，沟槽的速率非常大，原子法非常适合捕捉沟槽的形成。研究人员将对铝和硅双晶进行分子动力学研究。热槽的长时间演化将通过动力学蒙特卡罗模拟来研究。倾斜和扭曲边界都将被考虑。系统地研究了表面和晶界能量各向异性及其对刻面和生长速率的影响。在实验部分，将使用两种材料，建立并测量其表面能量各向异性。具有对称晶体取向的双晶样品将由商业上可获得的材料制备。晶界沟槽是测量表面扩散系数的最常用的方法，我们将通过微观分析来研究晶界沟槽形状随热退火时间-温度循环的变化规律，并与理论预测进行比较。然而，在测量技术中从来没有考虑到表面能各向异性的迟滞效应。拟议的研究将阐明表面能量各向异性对刻槽的影响，并提高该技术的精度。更好地理解和控制沟槽将使更小的微电子和光电子器件得以制造。这将转化为更快和更小的计算机芯片，从而支持信息技术的不断进步。该项目也对材料教育产生了广泛的影响。目前，路易斯安那州全州还没有材料学位课程。然而，当地工业需要接受材料培训的学生，路易斯安那州立大学(LSU)正在建立一个材料课程来满足这一需求。这项建议是路易斯安那州立大学两个系之间的合作努力，将加强校园内的材料研究活动。它将支持研究生和本科生，并让他们接触到这两个系的材料研究。它还将允许在路易斯安那州立大学提供更多的材料课程。

Thin solid films are the basic structure in most microelectronic and optoelectronic devices. During annealing of a polycrystalline film, grain-boundary grooves can deepen to form holes, which tend to grow to breakup the film. The investigators' preliminary theoretical work has shown that surface energy anisotropy can reduce the grooving rate significantly. However, if the exposed surface orientations do not contain a facet orientation, then the anisotropic groove is smooth and looks exactly the same as an isotropic groove; only the grooving rate is reduced. This proposal aims to investigate this intriguing relationship between surface energy anisotropy and grain-boundary grooving using three methods: continuum analysis, experiment, and atomistic simulations. The investigators' preliminary work assumes that the crystallographic orientations of the bicrystal are symmetric about the grain boundary. However, most bicrystals are unlikely to be symmetric. Thus, the self-similar continuum analysis will be extended to asymmetric bicrystals. The investigators will also consider grain boundaries migrating at constant speed and study the coupling between the grain-boundary groove and the grain-boundary profile. Because grooving is self similar, the grooving rate is very large at the beginning of groove development, and atomistic methods are ideally suited to capture the groove formation. The investigators will perform molecular dynamics on aluminum and silicon bicrystals. The long-time evolution of the thermal groove will be studied by kinetic Monte Carlo simulations. Both tilt and twist boundaries will be considered. Surface and grain boundary energy anisotropy and their effect on faceting and growth rate will be systematically investigated. In the experimental part, two materials will be used for which surface energy anisotropy is established and measured. Bicrystal samples with symmetric crystallographic orientations will be prepared from commercially available material. The evolving groove shape at the grain boundary will then be microscopically examined as a function of thermal annealing time-temperature cycle to compare its shape with theoretical predictions.Grain-boundary grooving is the most commonly used technique for measuring surface diffusion coefficients. However, the retardation effect of surface energy anisotropy has never been considered in the measurement technique. The proposed investigation will clarify the effects of surface energy anisotropy on grooving and improve the accuracy of the technique. Better understanding and control of grooving will allow smaller microelectronic and optoelectronic devices to be made. This translates into faster and smaller computer chips, which will sustain continuous advancement of information technology. This project has also broad impact on materials education. Presently, there is no Materials degree offering program in the whole State of Louisiana. However, local industries need students with materials training, and Louisiana State University (LSU) is building a materials program to meet that demand. This proposal is a collaborative effort between two departments at LSU and will enhance materials research activities on campus. It will support graduate and undergraduate students and expose them to materials research in both departments. It will also allow more materials courses to be offered at LSU.