Chemical Ordering Phase Transitions in Intermetallic Nanoparticles

技术摘要：拟议的研究将探索有关金属间化合物合金纳米颗粒中化学有序相变的基本问题。具体来说，建模和测量的定量程度的化学秩序的个别，亚10纳米纳米粒子作为一个功能的粒度，颗粒组成，温度，工艺和局部环境的变化与一个特定的重点，以探讨动力学和平衡稳定性的作用。该研究将重点关注L10合金，特别是FePt家族的NixFe 1-xPt和CuAu。最终目标是了解纳米颗粒系统中的相变，并优化磁存储应用中的纳米颗粒化学有序性。对金属间纳米颗粒合金中化学有序性的理解是有限的。平衡热力学模型给出了与实验定性匹配，但定量拟合较差。这些缺点导致了一个问题：我们对纳米粒子有序化的理解是受到有序化动力学的限制，还是我们对平衡热力学的不完全理解？通过相变的有序-无序温度和有序参数将被测量为颗粒尺寸和加工条件的函数。原位TEM加热和非原位退火研究将进行比较。单粒子测量和粒子间的变化将是这项工作不可或缺的。用于研究的材料是专门选择的，以提供一系列用于比较的热力学和动力学性质。对这些材料系统的计算建模将与实验紧密结合，以探索与实验的定量比较以及可能的动力学和热力学参数的相对作用。非技术总结：材料的相变被视为结构或性能的显著变化。熔化，固体到液体的变化，就是一个例子。合金的化学有序化/无序化是相变的一个重要技术实例。未来的磁记录介质将由化学有序的金属合金的纳米尺寸的颗粒制成。颗粒尺寸已被证明对熔化相变有很大的影响，同样，该程序将研究尺寸和成分变量对金属合金中化学有序相变的影响。对影响化学有序相变的因素的基本理解最终将有助于高密度磁数据存储的社会效益，并使纳米技术应用更加复杂。本科生和研究生都将得到支持和培训，以使用专门的实验工具。拟议的计划将进一步发展为这一努力开发的单纳米粒子分析技术。

TECHNICAL SUMMARY:The proposed research will explore the fundamental questions concerning the chemical ordering phase transition in nanoparticles of intermetallic metal alloys. Specifically, modeling and measurement of the quantitative extent of chemical order of individual, sub-10nm nanoparticles as a function of particle size, particle composition, temperature, and process and local environment variations with a specific focus to probe the role of kinetics and equilibrium stability. The study will focus on L10 alloys, specifically NixFe1-xPt from the FePt family and CuAu. The ultimate goal is to understand phase transitions in nanoparticle systems and to optimize nanoparticle chemical ordering for magnetic storage applications. The understanding of chemical ordering in intermetallic nanoparticle alloys is limited. Equilibrium thermodynamic models gives a qualitative match to experiment, but the quantitative fits are poor. These shortcomings lead to the question: Is our understanding of nanoparticle ordering limited by the ordering kinetics or our incomplete understanding of the equilibrium thermodynamics? The order-disorder temperature and the order parameter through the phase transition will be measured as a function of particle size and processing conditions. Both in-situ TEM heating and ex-situ annealing studies will be compared. Single particle measurements and particle-to-particle variations will be integral to this work. The materials for study are specifically chosen to give a range of thermodynamic and kinetic properties useful for comparison. Computational modeling on these material systems will be closely coupled with experiment to explore the quantitative comparison to experiment and the relative role of possible kinetic and thermodynamic parameters. NON-TECHNICAL SUMMARY:A phase change in a material is seen as a significant change in structure or properties. Melting, a solid to liquid change, is one example. Chemical ordering/disordering of alloys is one technologically important example of a phase change. Future magnetic recording media will be made with nanometer sized particles of chemically ordered metal alloys. Particle size has been shown to have a big effect on melting phase changes and similarly this program will study the effect of size and composition variables on chemical ordering phase changes in metal alloys. A fundamental understanding of the factors influencing the chemical ordering phase change would eventually contribute to the societal benefit of high density magnetic data storage and enable further sophistication in nanotechnology applications. Both undergraduate and graduate students will be supported and trained to use specialized experimental tools. The proposed program will further develop the single nanoparticle analysis techniques developed for this effort.