The Emergence of Metallic Properties in Free Metal Clusters: Ground- and Metastable States

* 技术摘要 * 本项目研究从单个原子到几百个原子的原子团簇中金属性质如何随大小而变化。激光产生的金属蒸气云在低温冷却的氦气中凝结成团簇，产生超冷团簇的分子束，这些分子束在静态和振荡的电场和磁场中偏转。从它们的响应，这些集群的电子特性，在基态和激发态，将被确定，揭示超导性的演变，近藤效应，金属导电性和铁磁性是作为原子精确的大小和组成的函数。了解这些金属在纳米尺度上的性质对于纳米科学和纳米技术是至关重要的。这项研究为本科生和研究生提供了一个极好的机会，让他们在学习各种实验技术的同时，积极参与前沿科学。* 非技术摘要 * 金属的许多性质，为什么和如何有些是磁性的，它们如何导电，以及是什么使一些在低温下成为超导体，在大量样品中得到了合理的理解。但是这些金属的单个原子没有这些性质。该项目将揭示这些大块金属性质如何从金属原子簇中的原子性质演变而来。一种独特的装置已经开发出来，可以在高真空中产生这些金属簇，并一次测量一个，以确定它们对磁场和电场的反应。通过测量这些场施加在团簇上的力，并精确了解它们的大小和组成，可以确定金属性质的演变。这些知识对于基础科学和纳米技术都是至关重要的。 这项研究还为本科生和研究生提供了一个很好的机会，在学习各种实验技术的同时，积极参与前沿科学。

****Technical Abstract****This project studies how metallic properties develop as a function of size in clusters of atoms from a single atom to a few hundred atoms. A laser produced metal vapor cloud condenses into clusters in cryogenically cooled helium, producing a molecular beam of ultra cold clusters that are deflected in static and oscillating electric and magnetic fields. From their response the electronic properties of these clusters, in the ground state and in excited states, will be determined, revealing the evolution of superconductivity, the Kondo effect, metal conductivity and ferromagnetism is as a function of atomically precise size and composition. The understanding of these metallic properties on the nanoscale is vital for nanoscience and nanotechnologhy. The research provides undergraduate and graduate students with an exquisite opportunity to be active in frontier science while learning a wide variety of experimental techniques. ****Non-Technical Abstract****Many properties of metals, why and how some are magnetic, how they conduct electricity, and what makes some become superconductors at low temperatures are reasonably well understood in bulk samples. But single atoms of these metal have none of these properties. This project will reveal how these bulk metal properties evolve from atomic properties in clusters of metal atoms. A unique apparatus has been developed that can produce these metal clusters in high vacuum and measure them one at a time to determine how they respond to magnetic and electric fields. By measuring the forces that these fields exert on the clusters with precise knowledge of their size and composition, the evolution of metal properties can be determined. This knowledge is vital for fundamental science as well as for nanotechnology. The research also provides undergraduate and graduate students with an excellent opportunity to be active in frontier science while learning a wide variety of experimental techniques.