Ultrafast Structural Dynamics in Solids and Nanoparticles

Florida State University, Tallahassee FL

Investigators

Abstract

******NON-TECHNICAL ABSTRACT****** At the atomic and molecular scale, the ultrafast motions of atoms drive all structural changes, such as the melting of a solid. A thorough understanding of such dynamic behavior on the time and length scales of atomic motions provides the guiding principles to control these structural evolutions, which will have important scientific applications in solid-state physics, chemistry, biology and materials science. The goal of this project is to understand the mechanisms that regulate structural changes in solid materials by directly observing the associated atomic and molecular motion in real time. The project will use a recently developed technique to study several condensed matter physics problems with both fundamental importance and technological implications. They include laser-induced ultrafast structural transformations in metals and metal nanoparticles, and the measurement of the thermal expansion properties of magnetic materials induced by heating their conduction electrons. Graduate students and postdoctoral scholars involved in the project will acquire training and knowledge in the forefronts of contemporary condensed matter physics and ultrafast science, which will prepare trainees for careers in academe, industry, and national laboratories. ****** TECHNICAL ABSTRACT****** This individual investigator award supports a project that will investigate the structural dynamics in metals and metal nanoparticles on the atomic time and length scales. The dynamical processes will be initiated by impulsive excitation using a femtosecond pulse laser. Their temporal evolutions will be probed by directly monitoring atomic motions on the timescale of a single atomic vibrational period using the novel femtosecond electron diffraction, together with femtosecond time-resolved optical spectroscopy measurements of the relevant degrees of freedom. The ultimate goal of this project is to gain a microscopic understanding of structural dynamics beyond the current time-averaged thermodynamic point of view. Issues and questions to be addressed in this project include: (1) the mechanism of laser-induced ultrafast melting in solids, in particular the role of coherent lattice vibration in the order-disorder transformations; (2) size-dependent dynamics of electron-phonon coupling and melting in metal nanoparticles, and the re-crystallization processes; (3) measurement of electronic Gruneisen constants in magnetic materials with low Curie temperature, using the novel approach of transient heating which circumvents the limitation of traditional low-temperature approaches. This project integrates research and education to train graduate students and postdoctoral researchers for cutting-edge techniques and modern methods in the forefront areas of contemporary condensed matter physics and ultrafast science.