Nanoclusters of Boron and Borides

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).TECHNICAL SUMMARYAtomic clusters containing a few to few hundred atoms exhibit dramatic size-dependent chemical and physical properties and form the foundation for nano-science. In this proposal, supported by both the Divisions of Materials Research (DMR) and Chemisty (CHE) at NSF, Dr. Wang and his students plan to investigate nanoclusters of elemental boron and metal borides. Their experiment involves primarily photoelectron spectroscopy studies of size-selected cluster anions, produced by a laser vaporization cluster source. Photoelectron spectra contain electronic structure fingerprints for the clusters, which are combined with theoretical calculations to provide information about the structure, stability, and chemical bonding of the clusters. The objective of the research is to elucidate the structural transitions of boron nanoclusters as a function of size and lay the foundation for new forms of boron nanostructures. In addition, high resolution photoelectron imaging is proposed for boron clusters to obtain vibrational information. The proposed research will systematically elucidate the structures and structural transitions of boron clusters to build the knowledge base for understanding the viability and stability of boron nanotubes and fullerenelike nanostructures. Guided by the cluster studies, exploratory synthesis is also planned. Transition metal diborides have been recently investigated as candidates for superhard materials. However, very little is known about the metal-boron chemical bond at the molecular level. Dr. Wang and his students also plan to study the structures and bonding of small bimetallic boride clusters, MxBy (M = Re, Os, Ir, Ru, and Fe), by combining photoelectron spectroscopy and theoretical calculations. Information about the M-B bond strengths, and the stability and bonding in the MxBy boride clusters, will be valuable to design and understand superhard diboride materials. NON-TECHNICAL SUMMARYFundamental studies of atomic clusters have led to major advances in nanoscience and materials science, such as the fullerenes and carbon nanotubes. The focus of this research program is on clusters of boron and metal borides. The new molecular structures and concepts of chemical bonding discovered in the gas-phase clusters are expected to have broad impact in chemistry, as well as in nanoscience and materials science. The proposed work on boron clusters may lead to discoveries of boron nanotubes and boron fullerenes, which may open up new directions of research. The metal boride cluster work will help the design and discovery of new superhard boride materials, which have wide industrial applications. The research program will involve significant national and international collaborations, providing a dynamic learning environment for students engaged in the research. The research program is also integrated to the teaching of both graduate and undergraduate students and contribute to the development of research infrastructure through new research methodologies.