Speaker:

Steven Lewis

Affiliation:

The University of Georgia / Center for Simulational Physics

Title:

Ceramic Nanoparticles: A Crossroads on the Path from Molecules to Crystal


Transition-metal carbide nanocrystals were first produced in the laboratory in the mid 1990's using pulsed-nozzle laser-vaporization techniques. Even though they contain as few as eight atoms, these particles are found to condense as nanoscopic crystals, as if they were fragments of the corresponding bulk material. Recently, a new spectroscopic technique called IR-REMPI has been able to measure, for the first time, the IR vibrational spectra of this family of nanoparticles. These experiments reveal a wealth of surprising results in the composition- and size- dependentce of the bonding and vibrational properties of these crystallites.
The research I will present focuses on providing theoretical understanding for these new experiments. Using first-principles total-energy methods based on density-functional theory, I have analyzed the structural and dynamical properties of metal-carbide nanocrystals for various particle sized and metal species. Since most (and in some cases all) of the atoms in these crystallites reside at the surface, I have also studied the relevant surfaces of the corresponding bulk materials. This comparison has allowed me, for example, to illuminate the connection between measured IR spectral features and bulk surface phonons and to understand the observed size-independence of these features. In addition, my research has been able to explain the observed absence of carbon atoms at corner sites in the metal-carbide nanocrystals. Finally, I have shown how the emergence of new spectral peaks with increasing particle size tracks the evolution of new structural features in the nanocrystalline morphology. In this talk, I will present my research contributions in this area and will also discuss the implications of this work to such diverse disciplines as materials science and stellar astrophysics.
The Seminar Page The Center for Simulational Physics Dep. of Physics and Astronomy The University of Georgia
©Andreas Voigt Last modified: 02/21/2002