Probing the Vibrational States of Surface Sites on Catalytic Nanoparticles with Atomic Resolution Electron Energy-Loss Spectroscopy

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With the support of the Chemical Measurement and Imaging (CMI) Program in the Division of Chemistry, and partial co-funding from the Catalysis Program in the Division of Chemistry and the Atomic, Molecular, and Optical Physics Program in the Division of Physics, Professor Peter Crozier of Arizona State University is studying development of a new imaging tool to measure the vibrations of atoms on the surface of small particles, with the latter being targeted as catalysts for important chemical conversion processes. The atoms on the surface of a material are constantly vibrating in a variety of different ways, with those different types of vibrations corresponding to different vibrational pathways, referred to as modes. These vibrational modes of the atoms on the surface of a material can help transfer energy to molecules bound to the surface of the material, which may drive catalytic chemical changes in the molecular structure of the surface-bound molecules. However, there are limited methods for gaining information about vibrational modes across the surface of small particles. Professor Crozier will develop and apply novel microscopy techniques that use electrons for the imaging process so as to detect and study the characteristics of surface vibrational modes on very small particles. The fundamental principles anticipated from this study have the potential for long-term impact not only in catalysis but also in other areas of materials and life science. To engage students, teachers, and the public in this research, an educational module entitled “Good Vibrations” will be developed, which will link the area of atomic-level vibrations to vibrational sound waves found in music. A web-based application will be developed that allows students and the public to decompose music passages into fundamental vibrational (harmonic) modes. By incorporating music from contemporary artists, the team hopes to engage high school students in the excitement of vibrational science and generate enthusiasm for careers in science, technology, engineering, and mathematics. The goal of this project is to probe and develop a fundamental understanding of vibrational states at distinct surface sites on catalytic nanoparticles with atomic resolution. To improve our understanding of the vibrational energy exchange process, it is necessary to have information on the local vibrational modes that exist at surface sites. Vibrational dynamics on nanoparticle surfaces are not well understood, in part because there have been no methods to perform atomic resolution probing of surface vibrational modes. The Krozier team will address this deficiency by developing novel approaches to vibrational electron energy-loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM) using the impact component of inelastic electron scattering. Electron scattering in STEM carries information about vibrational states in a manner similar to inelastic neutron scattering, but it can provide atomic resolution. Moreover, the signal may be associated with short wavelength modes that are most sensitive to atomic defects. Overall, this research has the potential to provide a useful new vibrational description of the surfaces of catalysts.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.