The Emergence of Metallic Properties in Free Metal Clusters in a Molecular Beam

****非技术摘要****人们对纳米物体的性质越来越感兴趣。然而，对于仅由几个原子组成的最小金属颗粒或簇的性质，人们所知甚少。在真空室中制造这些极小的颗粒并研究它们的性质是可能的。这个个人研究者奖支持一个项目，该项目将产生一束小金属团簇，随后冷却到极低的温度。这些粒子束在电场和磁场中发生偏转。磁性偏转提供了关于团簇磁性的关键信息，可以与块状材料的磁性进行比较。电场的偏转表明这些小金属颗粒是否导电。有一些证据表明，某些金属团簇即使在室温下也具有类似于超导的性质。这些基础研究将提供关于金属是如何形成金属的重要信息。它们还将表明特定的金属团簇是否可能对纳米技术应用（如磁记录）有用。研究生和本科生将学习各种实验技术，为他们将来在学术界或工业界的职位做准备。他们接受的培训将为他们提供成为纳米级电子物体特性前沿研究人员所需的技能。该奖项由材料研究部和物理部资助。****技术摘要****该个人研究者奖支持一个项目，该项目解决了金属性质如何在金属簇中作为尺寸函数发展的基本问题。利用脉冲激光汽化方法在低温簇源中产生一到几百个原子的小金属簇束，并在高真空中研究了它们从源飞到位置敏感质量分析仪的特性，该分析仪可以同时测量簇的质量和位置。温度约为20k的团簇基本上处于电子和振动基态，因此非常适合研究材料的基态性质。在大块中，金属不能容忍电压差，因此大块金属物体不能有电偶极矩。因此，对小团簇的电偶极子测量将提供有关这一重要金属性质出现的信息。顺磁团簇磁矩的分子束电子自旋共振测量将追踪小碱团簇和铌团簇中g值的大小演变。在后一种情况下，这些测量可能为铁电态和超导性之间的可能联系提供见解。研究生和本科生将学习各种实验技术，为他们将来在学术界或工业界的职位做准备。接受的培训将为他们提供成为纳米级电子物体特性前沿研究人员所需的技能。该奖项由材料研究部和物理部资助。

****NON-TECHNICAL ABSTRACT****There is an increasing interest in the properties of nanoscopic objects. Yet little is known about the properties of the very smallest metal particles, or clusters, which consist of only a few atoms. It is possible to produce these extremely small particles and to study their properties in a vacuum chamber. This individual investigator award supports a project that will produce a beam of small metallic clusters, which are subsequently cooled to extremely low temperatures. Beams of these particles are then deflected in electric and magnetic fields. The magnetic deflections provide critical information about the magnetic properties of the clusters, which can be compared with magnetic properties of bulk materials. Deflections in electric fields show whether these small metal particles conduct electricity or not. There is some evidence that certain metal clusters have properties akin to superconductivity even at room temperature. These fundamental studies will provide important information about what makes a metal a metal. They will also indicate whether specific metal clusters may be useful for nanotechnology applications such as magnetic recording. Graduate and undergraduate students will learn a variety of experimental techniques that will prepare them for future positions in academia or industry. The training they receive will provide them with the skills needed to become forefront researchers in the properties of nanoscopic electronic objects. This award receives funding from the Division of Materials Research and the Division of Physics.**** TECHNICAL ABSTRACT****This individual investigator award supports a project that addresses the fundamental question of how metallic properties develop in metallic clusters as a function of size. Beams of small metal clusters with from one to several hundred atoms are produced in a cryogenic cluster source using the pulsed laser vaporization method and their properties are studied in high vacuum as they fly from the source to a position sensitive mass analyzer that can simultaneously measure both the mass and the positions of the clusters. Clusters with temperatures of about 20 K are essentially in their electronic and vibrational ground states and therefore are ideally suited for studying the ground state properties of the material. In the bulk, metals do not tolerate a voltage difference and therefore bulk metal objects cannot have electric dipole moments. Hence electric dipole measurements of small clusters will provide information on the emergence of this important metallic property. Molecular beam electron spin resonance measurements of the magnetic moments of paramagnetic clusters will trace the size evolution of the g-values in small alkali clusters and in niobium clusters. In the latter case these measurements may provide insight into a possible connection between a ferroelectric state and superconductivity. Graduate and undergraduate students will learn a variety of experimental techniques that will prepare them for future positions in academia or industry. The training the receive will provide them with the skills needed to become forefront researchers in the properties of nanoscopic electronic objects. This award receives funding from the Division of Materials Research and the Division of Physics.