Probing the Electronic Structure and Chemical Bonding of Cryogenically-Cooled Boron and Metal-Boride Nanoclusters

With support from the Chemical Structure, Dynamics, and Mechanisms A (CSDM-A) program in the Division of Chemistry, Professor Lai-Sheng Wang and his research group at Brown University will investigate size-selected boron and metal-boride nanoclusters using high-resolution photoelectron imaging and photoelectron spectroscopy. Boron has only three valence electrons compared to four in carbon and is thus considered to be electron deficient. The electron deficiency of boron results in complicated structures and unique chemical bonds in boron-containing molecules, which are challenging to investigate. Professor Wang and his students will generate boron and metal-boride nanoclusters using a home-built laser-vaporization cluster source and utilize photoelectron spectroscopy and imaging in conjunction with theoretical calculations to provide insights into their stabilities, structures, and chemical bonding. Their studies could lead to the discovery of novel boron- and boride-based nanostructures, as well as provide fundamental knowledge about boron chemistry and chemical bonding. The research in this project will be integrated into the teaching of physical chemistry, and will provide training opportunities for undergraduate and graduate students in the design and construction of advanced experimental instrumentation and computational chemistry. This project focuses on the structure and bonding of boron clusters to provide insight into the nature of the metal-boron bonds and structural evolution of large boron clusters to lay the foundation for new boron-based nanomaterials. To achieve these research goals, Professor Lai-Sheng Wang and his students have built two different types of apparatus for photoelectron spectroscopy. One apparatus involves a magnetic-bottle photoelectron analyzer and is aimed at providing photoelectron spectra with a wide range of photon energies. Well-resolved photoelectron spectra provide electronic fingerprints, which are crucial for comparison with theoretical calculations to elucidate the structures and bonding of size-selected boron nanoclusters. The second apparatus involves high-resolution photoelectron imaging, which is aimed at obtaining vibrational information. A cryogenically cooled ion trap is being developed to create cold boron clusters from the laser-vaporization source; this is needed to obtain vibrationally resolved photoelectron spectra for boron and metal-boride clusters. The broader impact of this project includes the discovery of novel boron-based nanomaterials with potential as new platforms for nanotechnology. 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.