CAREER: Revealing the Crystallization Kinetics of Marginal Glass Formers Through In Situ Microscopy and Nanocalorimetry Experiments

职业：通过原位显微镜和纳米量热实验揭示边缘玻璃形成体的结晶动力学

• 批准号: 1945520
• 负责人: Melissa Santala
• 金额: $ 75.56万
• 依托单位: Oregon State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-05-01 至 2025-04-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1945520&HistoricalAwards=false
• 关键词: CAREER; Revealing; Crystallization; Kinetics; Marginal

NON-TECHNICAL DESCRIPTION: Phase change materials (PCMs) are materials, generally consisting of antimony and tellurium alloyed with other elements, that are used in memory devices. Data is stored in amorphous (glassy) and crystalline bits of PCMs, which may be considered “bad” glasses because they can crystallize extremely rapidly. Rapid crystallization is required for PCM-based memory, but it makes it difficult to acquire experimental data on the physical mechanisms of crystallization and on the heat flow during the process. These data are needed to test the models that form the basis of understanding of PCM behavior that enables the development of new technologically-useful materials. This project addresses the gap in experimental data by utilizing recent advances in microscopy and nanocalorimetry. Calorimetry is used to measure the heat absorbed or released during a reaction, and now advanced microscopic methods can be used to directly observe crystal growth while simultaneous nanocalorimetry yields data on heat flow during crystallization. The results are of value to scientific communities researching materials for low-power, non-volatile memory. Graduate and undergraduate students engaged in this research are being prepared for careers in characterization and development of advanced materials in research laboratories or high-tech industries. The project supports participation of high school students from traditionally-underrepresented groups in science and engineering in a summer educational program. It also supports the establishment of An Expanding Your Horizons conference for middle school girls, the first of its kind in Oregon.TECHNICAL DETAILS: Crystallization kinetics are key to understanding glass stability across all classes of materials. The data needed to extract important relationships between viscosity, crystal growth rate, and temperature are incomplete for important materials that are marginal glass formers, such as phase change materials (PCMs). PCMs are (semiconducting) alloys used in optical- and resistivity-based memory owing to their fast switching between amorphous and crystalline states. The relationship between crystal growth and viscosity with changes in temperature is not fully understood because crystallization can be so rapid the measurement of physical and thermodynamic properties during crystallization is frustrated. Multiple recent reports of crystal growth and viscosity behavior extracted from calorimetric measurements do not satisfactorily fit existing models of crystal growth. This discrepancy may be due to changes in crystallization mechanism and flawed assumptions about the relative contribution of nucleation and growth in different temperature regimes. In this project, crystallization is being studied with in situ microscopic methods, enabling direct observation of crystal growth and revealing changes in phase transformation mechanisms. Recent advances in transmission electron microscopy (TEM) techniques have made this endeavor possible even at temperatures where crystal growth is extremely rapid. In situ TEM with simultaneous nanocalorimetry provides a seamless connection between thermodynamic and kinetic data. Knowledge resulting from this research advances the understanding of glass stability in PCMs and is of value to scientific communities researching materials for low-power, non-volatile memory and other marginal glass formers, such as bulk metallic glasses. Graduate students participating in this project gain foundational knowledge of the thermodynamics and kinetics of phase transformations and employ cutting-edge in situ TEM and calorimetric characterization techniques.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

非技术描述：相变材料（PCM）是用于存储器装置中的材料，其通常由与其它元素合金化的锑和碲组成。数据存储在PCM的非晶（玻璃状）和结晶位中，这可能被认为是“坏”玻璃，因为它们可以非常迅速地结晶。基于PCM的存储器需要快速结晶，但这使得难以获得关于结晶的物理机制和在该过程中的热流的实验数据。需要这些数据来测试模型，这些模型构成了对PCM行为的理解的基础，从而能够开发新的技术上有用的材料。本计画利用显微镜与奈米量热计的最新进展，探讨实验资料中的差距。量热法用于测量反应过程中吸收或释放的热量，现在先进的显微镜方法可用于直接观察晶体生长，同时纳米量热法可获得结晶过程中热流的数据。研究结果对科学界研究低功耗非易失性存储器材料具有重要价值。从事这项研究的研究生和本科生正在为研究实验室或高科技行业中先进材料的表征和开发做准备。该项目支持传统上代表性不足的科学和工程群体的高中生参与暑期教育计划。它还支持建立一个扩大你的视野会议，为中学女生，这是第一次在俄勒冈州。技术专长：结晶动力学是关键，了解玻璃稳定性的所有类别的材料。提取粘度、晶体生长速率和温度之间的重要关系所需的数据对于作为边缘玻璃形成体的重要材料（例如相变材料（PCM））是不完整的。PCM是（半导体）合金，由于其在非晶态和晶态之间的快速切换，因此用于基于光学和磁性的存储器。晶体生长和粘度与温度变化之间的关系尚未完全理解，因为结晶可以如此迅速，以致于结晶期间的物理和热力学性质的测量受到阻碍。从量热测量中提取的晶体生长和粘度行为的多个最近的报告不能令人满意地拟合现有的晶体生长模型。这种差异可能是由于结晶机制的变化和错误的假设在不同的温度制度的成核和生长的相对贡献。在该项目中，正在使用原位显微镜方法研究结晶，从而能够直接观察晶体生长并揭示相变机制的变化。透射电子显微镜（TEM）技术的最新进展使这一奋进成为可能，即使在晶体生长非常迅速的温度下。原位TEM与同步纳米量热法提供了热力学和动力学数据之间的无缝连接。从这项研究中获得的知识促进了对PCM中玻璃稳定性的理解，对科学界研究低功耗非易失性存储器和其他边缘玻璃形成材料（如块状金属玻璃）具有价值。参与该项目的研究生获得了相变热力学和动力学的基础知识，并采用了尖端的原位TEM和量热表征技术。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Crystallization kinetics and thermodynamics of an Ag–In–Sb–Te phase change material using complementary in situ microscopic techniques

• DOI: 10.1557/s43578-022-00486-5
• 发表时间: 2022-03
• 期刊: Journal of Materials Research
• 影响因子: 2.7
• 作者: Isak McGieson;Victoriea L. Bird;C. Barr;K. Hattar;B. Reed;J. McKeown;F. Yi;D. Laván;M. Santala