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。 在多晶膜的退火期间，晶界凹槽可以加深以形成孔，孔倾向于生长以使膜破裂。 研究人员的初步理论工作表明，表面能各向异性可以显着降低开槽率。 然而，如果暴露的表面取向不包含刻面取向，则各向异性凹槽是平滑的并且看起来与各向同性凹槽完全相同;仅开槽率降低。 该建议的目的是调查表面能各向异性和晶界开槽之间的这种有趣的关系，使用三种方法：连续分析，实验和原子模拟。 研究人员的初步工作假设双晶体的晶体学取向关于晶界是对称的。 然而，大多数双晶体不太可能是对称的。 因此，自相似连续谱分析将扩展到非对称双晶。 研究人员还将考虑以恒定速度迁移的晶界，并研究晶界槽和晶界轮廓之间的耦合。 由于开槽是自相似的，开槽率是非常大的，在开始的凹槽发展，和原子的方法是非常适合捕捉的凹槽形成。研究人员将对铝和硅双晶体进行分子动力学研究。 热槽的长期演变将通过动力学蒙特卡罗模拟进行研究。将考虑倾斜和扭曲边界。表面和晶界能各向异性及其对刻面和生长速率的影响将被系统地研究。 在实验部分中，将使用两种材料，建立和测量表面能各向异性。具有对称晶体取向的双晶体样品将由市售材料制备。在晶界上的凹槽形状的演变，然后将作为热退火时间-温度循环的函数进行显微镜检查，将其形状与理论预测进行比较。晶界开槽是最常用的测量表面扩散系数的技术。 然而，在测量技术中从未考虑过表面能各向异性的延迟效应。 这项研究将有助于阐明表面能各向异性对切槽加工的影响，提高切槽加工的精度。 更好地理解和控制开槽将允许更小的微电子和光电器件。 这意味着更快和更小的计算机芯片，这将维持信息技术的不断发展。 该项目对材料教育也产生了广泛的影响。 目前，在整个路易斯安那州没有材料学位提供计划。 然而，当地的工业需要材料培训的学生，路易斯安那州立大学（LSU）正在建立一个材料计划，以满足这种需求。 该提案是路易斯安那州立大学两个部门之间的合作努力，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部门的材料研究。 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.