Dynamics at the Nanoscale
Eric D. Isaacs
Argonne National Laboratory
It is a well-known paradigm for both inorganic and biological materials that structure determines function. There is also an emerging understanding that structure alone is not sufficient to determine function, but that dynamics plays a critical role. In this talk, we will highlight some frontier problems in dynamics at the nanoscale that can be impacted by the next generation of very bright x-ray sources, such as XFEL and ERL sources, which will provide unprecedented spatial and temporal coherence, as well as sub-picosecond to second temporal resolution.
We discuss two recent examples of early progress in measuring dynamics at the nanoscale using present-day third generation sources. In the first, coherent x-ray scattering measurements of the dynamics of spin and charge density wave domains in chromium reveal, surprisingly, that at low temperatures the domains remain dynamic and temperature independent with a time-scale of seconds. These results are consistent with a picture in which mesoscale domains of spins coherently tunnel between two local minima in the complex energy landscape. We will also describe first steps towards measuring the structural dynamics of small macromolecular model systems in solution as they are deformed by the sudden (sub-picosecond) optical excitation of electron-hole pairs and relax back to their ground state on a time-scale of picoseconds. Such charge-induced distortions are common to a broad range of important nanoscience problems including molecular electronics, photovoltaics, and catalysis.
