Charge distribution within supported metal nanoclusters and how it is influenced by the substrate, adsorption and surface defects

加州大学河滨分校的Jory A. Yarmoff教授得到了化学系大分子、超分子和纳米化学项目的支持，研究负载金属纳米团簇内的电荷分布。Yarmoff教授和他的学生使用专门的表征方法来研究金属纳米颗粒的特性是如何受到它们所处的支撑材料的性质的影响，以及支撑材料中的缺陷是如何改变它们的特性的。特别是，他们测量了簇内单个原子的电荷，并观察簇的大小和支持缺陷的数量如何影响分子是否会粘在支持上。纳米粒子是一类独特的材料，因为它们的大小介于分子（几个原子）和固体（数万亿个原子）之间。纳米材料表现出独特的化学和电子特性，这取决于它们的尺寸，导致许多潜在的应用，包括先进的电子技术，电池技术，太阳能发电，环境修复和化学催化。理解并学习如何广泛地控制纳米材料的性质，将影响基础科学知识和实际应用。加州大学河滨分校（University of California-Riverside）是一所西班牙裔服务机构，该校的研究生和本科生组成了一个多元化的群体，他们通过在现代科学前沿领域进行实验室实验，获得了宝贵的经验。此外，研究结果通过多方面的内部和外联倡议传播。这包括参加暑期物理教师学院，这是一个为期一周的研讨会，包括实践实验室经验，以培训当地高中教师，激发学生对STEM职业的兴趣。支撑金属纳米团簇的边缘原子可能是驱动化学反应的活性位点，通过吸附前体分子到直接与底物结合的团簇原子。也有强有力的证据表明，金属纳米团簇的电子环境是决定其电子和化学行为的关键。负载型金属纳米团簇直接沉积，或通过缓冲层辅助生长（BLAG）在氧化物、硫化物、氟化物和冷冻惰性气体衬底上产生。采用一种新型的低能离子散射（LEIS）方法，通过测量分散的低能碱离子的中和作用来研究金属纳米团簇内的电荷分布。该方法先前表明，金纳米团簇内的电荷是不均匀的，边缘原子带正电，而中心原子基本上是中性的。该项目通过探索电荷分布如何依赖于簇和衬底材料，簇/支撑界面上的缺陷数量，电负性和电正性附着原子和小分子的后续吸附，以及衬底中的缺陷如何改变吸附，建立在这些知识的基础上。研究结果有助于对金属纳米团簇的基本理解，从而使其特性的定制能够提高功能和实用价值。该研究提供了对纳米材料的物理和化学性质的理解，同时开发了控制纳米材料的方法，这将促进纳米材料在许多先进制造领域的应用，可能对该领域产生重大而广泛的影响。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Professor Jory A. Yarmoff of the University of California - Riverside is supported by the Macromolecular, Supramolecular, and Nanochemistry Program in the Division of Chemistry to study the charge distribution within supported metal nanoclusters. Professor Yarmoff and his students use specialized characterization methods to investigate how the properties of metal nanoparticles are affected by the nature of the support material on which they reside and how defects in the support alter their properties. In particular, they measure the charge on individual atoms within the clusters and observe how the cluster size and number of support defects affect what molecules will or will not stick to the supports. Nanoparticles are a distinctive class of materials because they have sizes intermediate between molecules (few atoms) and solids (trillions of atoms). Nanoscale materials exhibit unique chemical and electronic properties that depend on their size, leading to many potential applications that include advanced electronics, battery technologies, solar power generation, environmental remediation, and chemical catalysis. Understanding, and then learning how to control the properties of nanoscale materials broadly, impacts knowledge in basic science and practical applications. A diverse group of graduate and undergraduate students at the University of California-Riverside, an Hispanic serving institution, are gaining valuable experience by conducting laboratory experiments in a field at the forefront of modern science. In addition, the research results are disseminated via multifaceted in-house and outreach initiatives. This includes participation in a Summer Physics Teachers Academy, a week-long workshop which includes hands-on laboratory experiences to train local high school teachers and stimulate the interest of their students in STEM careers. The edge atoms of supported metal nanoclusters may be the active sites that drive chemical reactions via adsorption of precursor molecules to the cluster atoms that are directly bonded to the substrate. There is also strong evidence that the electronic environment of metal nanoclusters is critical in determining their electronic and chemical behaviors. Supported metal nanoclusters are directly deposited, or produced by buffer layer assisted growth (BLAG), onto oxide, sulfide, fluoride and frozen noble gas substrates. A novel form of low energy ion scattering (LEIS) is used to investigate the charge distribution within metal nanoclusters by measuring the neutralization of scattered low energy alkali ions. This method previously showed that the charge within a gold nanocluster is inhomogeneous, with the edge atoms being positively charged while the center atoms are essentially neutral. This project builds on this knowledge by exploring how the charge distribution depends on the cluster and substrate materials, the number of defects at the cluster/support interface, the subsequent adsorption of electronegative and electropositive adatoms and small molecules, and how defects in the substrate modify adsorption. The research results wicontribute to a fundamental understanding of metal nanoclusters, thereby enabling the tailoring of their properties to improve functionality and practical utility. The research may have a significant and broad impact on the field by providing an understanding of the physical and chemical properties of nanoscale materials while developing methods to control them, which will facilitate their use in numerous advanced manufacturing applications.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.