Understanding Nucleation in Glassy Phase Change Materials

技术方面：本研究将对成核科学中的许多理论预测进行实验验证，并提供不同条件下玻璃相变化材料中纳米级原子核演化的数据。成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将基本上适用于任何涉及相变的材料系统。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存储的关键过程。将结合泵浦探针激光技术、原子力显微镜和膜电测温技术来了解AgInSbTe、Ge2Sb2Te5和GeSb等玻璃态相变材料的成核。实验结果将与理论模型计算相关联。首先，将对一般成核理论的一些预测进行实验检验。将探讨稳态亚临界核分布的温度依赖性和成核速率对已存在的亚临界核的依赖性。其次，研究相变材料中界面、成分变化和热历史对原子核演化的影响。由于原子核的分布是影响相变存储器的速度和稳定性的最重要因素之一，因此将使用瞬变电磁法来确定实际存储器中原子核的浓度。第三，作为一项相对探索性的工作，电测温将用于表征在非常高的加热速率下的玻璃化转变和成核。重要的热参数依赖于温度和加热速率，但传统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重要的信息，并作为瞬态成核的基本例证。拟议工作的主要任务是研究成核的基础科学。非技术：该项目涉及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培训提供独特的机会。通过培训这一研究领域的男女领导人，通过出版物广泛传播这一研究结果，预期这一研究项目将产生更广泛的影响。一至两名本科生将把本研究的部分内容作为毕业论文。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成核理论，这是材料科学教育的一个重要课题。合格的学生将被确定并得到建议，特别是通过伊利诺伊大学的SURGE（支持工程中代表性不足的群体）项目。

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.