Size- and Composition-Dependent Electronic and Vibrational Properties of Bimetallic Nanoclusters

The University Of Central Florida Board Of Trustees, Orlando FL

Investigators

Abstract

TECHNICAL SUMMARY: This Award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). Metal nanoclusters exhibit intriguing electronic and atomic vibrational phenomena that deviate dramatically from the corresponding bulk properties. The goal of this study is to combine recently developed micelle-based nanocluster synthesis methods with advanced nanoscale physical analysis of both electronic and vibrational properties. Self-assembled size- and shape-selected bimetallic nanoclusters [57FePt, 57FePd, 57FeCu and 57FeAu] will be synthesized. A synergetic combination of experimental tools including X-ray photoelectron spectroscopy, scanning tunneling and transmission electron microscopy, 57Fe Mössbauer spectroscopy, and 57Fe nuclear resonant inelastic X-ray scattering will be used to find correlations between the nanostructure morphology and electronic structure and its size- and composition-dependent vibrational properties. In addition, modeling of the vibrational dynamics of supported clusters will be conducted by molecular dynamics simulations through an international collaboration (Canada). The intellectual merit of this work is based on the improvement of the current understanding on: (i) the formation, the structural and thermal stability of bimetallic alloys in isolated nanoclusters, (ii) their intrinsic electronic and vibrational properties, (iii) how these characteristics change due to cluster size-effects, cluster-support interactions, the presence of ligands on the cluster surface, and the composition of the nanoalloys, and (iv) whether phonon-induced structural phase transitions (known in ferromagnetic bulk Invar alloys) persist and can be tuned in nanoclusters. Since the electron and phonon density of states are key elements in understanding and predicting important materials properties, this project will advance the present knowledge of basic physical phenomena underlying electrical and thermal conductivity, heat capacity, vibrational entropy, electron-phonon coupling, and 1/f noise in electronic devices. In addition, insight will be obtained on whether phonon-assisted surface chemical reactions could play an important role in the comprehension of the catalytic properties of metal nanoclusters. NON-TECHNICAL SUMMARY: Metal nanoclusters exhibit intriguing electronic and atomic vibrational phenomena that deviate dramatically from the corresponding bulk properties. Metal nanoclusters are used in optics (nanophotonics), magnetism (recording media), medicine (targeted drug delivery), and in chemistry (catalytic materials). Many questions remain on the detailed nature of their electronic and vibrational properties, and a more thorough physical understanding is needed to advance the science and technology of these materials. This project will improve the present knowledge on the formation, the structural and thermal stability of bimetallic alloys in nanoclusters, and the parameters that can be used to tune their intrinsic physical properties such as cluster size, support and composition. A deeper insight into important material properties including electrical and thermal conductivity will be obtained. Graduate and undergraduate students will be trained and given the opportunity to conduct state-of-the-art research, not just at the University of Central Florida, but also at national and international user facilities, including the Advanced Photon Source (Chicago) and Spring8 (Japan). K-12 students teamed up with undergraduates will be in charge of the sample preparation. A website entitled ?Why?s of Science? will be setup to disseminate science-related educational activities among primary and middle school students. In order to stimulate the access of minority (Hispanic) parents to science, the website will be available in English and Spanish.