Understanding Nucleation in Glassy Phase Change Materials

技术：这项拟议的工作将在实验上检验成核科学中的许多理论预测，并提供各种条件下玻璃相变材料中纳米级核的演化数据。形核过程在自然界中是普遍存在的，从这项工作中获得的知识基本上将适用于任何涉及相变的材料体系。相变存储技术就是一个例子，因为成核和结晶是控制快速数据写入和长期保持的关键过程。泵浦探测激光技术、原子力显微镜和薄膜电测温将结合在一起，以了解玻璃相变材料如AgInSbTe、Ge2Sb2Te5和GeSb的成核作用。实验结果将与理论模型计算相关联。首先，一般成核理论的一些预测将在实验上得到验证。我们将探讨稳态亚临界核分布的温度依赖性，以及成核速率与预先存在的亚临界核的依赖关系。其次，研究了界面、成分变化和热历史对相变材料中晶核演化的影响。由于原子核的分布是影响相变存储器速度和稳定性的最重要因素之一，因此将傅里叶变换电子显微镜用于实际存储器件中原子核浓度的测定。第三，作为一项相对探索性的工作，电测温将被用来表征在很高升温速率下的玻璃化转变和成核。重要的热参数取决于温度和加热速率，但常规技术只能提供比实际存储器操作中涉及的速率低许多数量级的加热速率。这项研究的数据将为技术提供关键信息，并从根本上说明瞬时成核的例子。拟议工作的主要任务是研究原子核的基础科学。非技术性：该项目解决与技术相关的材料科学专题领域的基础研究问题，并有望为跨学科领域的研究生和本科生提供独特的培训机会。预计这一研究项目还将通过通过出版物广泛传播这项研究的结果，对该研究领域的男女领导人进行培训，从而产生更广泛的影响。一个或两个本科生将完成这项工作的一部分，作为他们的高级论文。值得注意的是，实验结果可以在教科书和讲座中作为很好的例子来说明形核理论，这是材料科学教育的一个重要课题。将特别通过伊利诺伊大学的Surge(对工程学中代表不足的群体的支持)计划来识别和建议符合条件的学生。

Technical: The proposed work will experimentally test many theoretical predictions in nucleation science, and provide data on the evolution of nanoscale nuclei in glassy phase change materials under various conditions. The nucleation process is ubiquitous in nature, and the knowledge obtained from this work will be applicable to essentially any material systems involving phase transformation. One example is phase change memory technology, since nucleation and crystallization are the key processes that govern fast data writing and long-term retention. A pump-probe laser technique, atomic force microscopy, and membrane electrical thermometry will be combined for understanding nucleation in glassy phase change materials such as AgInSbTe, Ge2Sb2Te5, and GeSb. The experimental results will be correlated with theoretical model calculations. First, some predictions of the general nucleation theory will be tested experimentally. The temperature-dependence of steady-state subcritical nuclei distribution and the dependence of nucleation rate on pre-existing subcritical nuclei will be explored. Second, the effects of interfaces, compositional variation, and thermal history on the evolution of nuclei in phase change materials will be investigated. Since the distribution of nuclei is one of the most important factors that influence the speed and stability of a phase change memory, FTEM will be used to determine the concentration of nuclei in actual memory devices. Third, as a relatively exploratory work, electrical thermometry will be employed to characterize the glass transition and nucleation at very high heating rates. Important thermal parameters are dependent on temperature and heating rate, but conventional techniques can only provide heating rates many orders of magnitude lower than the rates involved in actual memory operations. The data from this study will provide crucial information for technology, and serve as fundamentally illustrative examples of transient nucleation. The principal task of the proposed work is the investigation of the fundamental science of nucleation.Non-technical: The project addresses basic research issues in a topical area of materials science with technological relevance, and is expected to provide unique opportunities for graduate and undergraduate training in an interdisciplinary field. This research project is also expected to have broader impacts through the training of women and men leaders in this research field, through the wide dissemination of the findings of this research through publications. One or two undergraduates will carry out portions of this work as their senior theses. Notably, the experimental results can be used in textbooks and lectures as excellent examples to illustrate the nucleation theory, which is an important subject of materials science education. Qualified students will be identified and advised, in particular through the SURGE (Support of Under-represented Groups in Engineering) program at the University of Illinois.