Phase Transitions and the Properties of Liquid Nanoclusters

该奖项是根据2009年《美国复苏和再投资法案》(公法111-5)提供资金的。在这个由实验物理化学项目资助的奖项中，马丁·雅罗尔德教授和他的学生将研究具有10-1000个原子的孤立金属纳米团簇中的熔化和冻结转变。像熔化和冻结这样的相变通常与块状物体有关。这项工作将考察当一个物体的尺寸缩小到纳米尺寸时会发生什么，在纳米尺寸范围内，属性取决于存在的原子数量，增加或减少单个原子可以产生很大的不同。将使用热容测量、离子迁移率测量和俘获离子电子衍射来研究熔化和冻结转变。这项工作将解决三个主要问题：在多大小的情况下会发生块状熔化和冻结转变，特定尺寸的纳米团簇是否会发生过热和过冷，以及液体纳米团簇的性质。比方说，100个原子的液态金属团簇预计具有与大块液体非常不同的性质。两个国际合作将为该项目做出贡献。西班牙巴拉多利德大学的安德烈斯·阿瓜多教授将进行对理解实验手段至关重要的理论计算。德国卡尔斯鲁厄大学的Manfred Kappes教授将合作研究中等尺寸金属纳米团簇的熔化过程。这项工作提高了我们对小系统统计热力学的认识，并为实验和计算物理化学方面的研究生和博士后研究人员提供了极好的培训。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). In this award, funded by the Experimental Physical Chemistry program, Professor Martin Jarrold and his students will study melting and freezing transitions in isolated metal nanoclusters with 10-1000 atoms. Phase transitions like melting and freezing are normally associated with bulk objects. This work will examine what happens when the size of an object is reduced into the nanometer size regime, where the properties depend on how many atoms are present, and adding or subtracting a single atom can make a big difference. The melting and freezing transitions will be investigated using heat capacity measurements, ion mobility measurements, and trapped ion electron diffraction. The work will address three main topics: at what size do bulk-like melting and freezing transitions occur, whether superheating and supercooling occurs for specific sizes of nanoclusters, and the properties of the liquid nanoclusters. A liquid metal cluster with say 100 atoms is expected to have properties that are very different from a bulk liquid. Two international collaborations will contribute to the project. Prof. Andres Aguado (Universidad de Valladolid, Spain) will perform theoretical calculations that are critical to understanding the experimental meaurements. Prof. Manfred Kappes (Universität Karlsruhe, Germany) will collaborate on using trapped ion electron diffraction to investigate the melting of medium-sized metal nanoclusters.This work improves our knowledge of the statistical thermodynamics of small systems, and provides excellent training for graduate and postdoctoral researchers in experimental and computational physical chemistry.