Probing the Structures and Chemical Bonding of Size-Selected Boron and Metal-Boride Nanoclusters

在这项由化学系化学结构、动力学和机理(CSDM-A)计划资助的项目中，布朗大学的王来生教授和他的学生正在使用先进的光谱技术来研究由硼原子和金属硼化物形成的微小结构(纳米团簇)，这些结构将硼与金属元素结合在一起。在元素周期表上，硼仅次于碳，但其电子比碳少一个，导致硼被描述为一种缺电子元素。硼的电子缺乏导致了含硼分子和材料具有不同的化学和物理性质，而硼和金属硼化物纳米团簇显示出丰富的结构和化学键特征。研究这些簇有重大的实验挑战，这些簇在反应形成更稳定的物种之前只存在很短时间，因此必须仔细准备。王教授和他的学生正在通过开发创新的实验技术来研究硼和金属硼化物纳米团簇的结构和成键，从而克服这些挑战。该研究不仅提供了有关硼-硼和金属-硼化学键的基础知识，而且有可能发现新的具有工业应用价值的硼和金属-硼化物纳米材料。从事这项研究的学生正在获得批判性思维技能和高级物理化学技术方面的宝贵经验。该项目的重点是：1)大的硼团簇的结构演化，为新的硼纳米结构奠定基础；2)金属-硼化物团簇，探索金属-硼化学键的性质。这些团簇是使用激光蒸发团簇光源产生的，并使用两种不同类型的自制光电子能谱设备进行研究。一种装置包括一个磁瓶光电子分析器，目的是提供具有广泛光子能量的光谱。分辨良好的光电子光谱提供了电子指纹，这对于与理论计算进行比较以阐明大小选定的团簇的结构和成键是至关重要的。一种低温冷却的离子陷阱正在开发中，以产生冷的硼团簇，这对于获得大团簇的高分辨率光电子光谱至关重要。第二种设备包括高分辨率光电子成像，目的是获得振动信息。这项工作的更广泛影响包括发现具有潜在技术应用和社会效益的新型硼基纳米材料。该项目与王教授教授的物理化学教学相结合，并为学生和博士后提供设计和建造先进实验仪器和计算化学的培训机会。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

In this project funded by the Chemical Structure, Dynamics and Mechanisms (CSDM-A) program of the Chemistry Division, Professor Lai-Sheng Wang of Brown University and his students are using advanced spectroscopic techniques to study tiny structures (nanoclusters) formed from boron atoms and metal borides, which combine boron with metallic elements. Boron is next to carbon on the periodic table, but having one-fewer electrons than carbon leads to boron being characterized as an electron-deficient element. The electron deficiency of boron results in distinctive chemical and physical properties for boron-containing molecules and materials, and boron and metal boride nanoclusters display a rich range of structural and chemical bonding characteristics. There are significant experimental challenges to study these clusters, which exist only briefly before reacting to form more stable species, and, thus, must be carefully prepared. Professor Wang and his students are overcoming these challenges by developing innovative experimental techniques to investigate the structures and bonding of boron and metal-boride nanoclusters. The research not only provides fundamental knowledge about the boron-boron and metal-boron chemical bonding, but also has the potential to discover new boron and metal-boride nanomaterials valuable for industrial applications. The students engaged in this research are gaining critical thinking skills and valuable experience in advanced physical chemistry techniques. The project focuses on 1) structural evolution of large boron clusters to lay the foundation for new boron nanostructures and 2) metal-boride clusters to probe the nature of the metal-boron chemical bonds. These clusters are produced using a laser-vaporization cluster source and investigated using two different types of home-built photoelectron spectroscopic apparatuses. One apparatus involves a magnetic-bottle photoelectron analyzer and is aimed to provide spectra with a wide range of photon energies. Well-resolved photoelectron spectra provide electronic fingerprints, which are crucial to be used to compare with theoretical calculations to elucidate the structures and bonding of size-selected clusters. A cryogenically-cooled ion trap is being developed to create cold boron clusters, which are essential to obtain well-resolved photoelectron spectra for large clusters. The second apparatus involves high-resolution photoelectron imaging, which is aimed to obtain vibrational information. The broader impact of this work includes the discovery of novel boron-based nanomaterials, which have potential technological applications and societal benefits. This project is integrated with the teaching of physical chemistry by Professor Wang, as well as providing training opportunities for students and postdoctoral associates in the design and construction of advanced experimental instrumentation and computational chemistry.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.