Our research group is focused on the ultrafast properties of materials, with the goal of visualizing, capturing, and directing the atomic-scale processes that underlie how materials and devices function. These processes involve time-scales extending down to 10-15 seconds, and represent fundamental limits to the efficiency, speed, and reliability of devices. Broad applications to information storage technologies, energy-related materials, and nanoscale optoelectronic devices follow from this work. By seeing directly how these processes occur in real time, we seek to go one step further and engineer new functionality by directly manipulating atomic and electronic degrees of freedom, and harnessing the flow of energy between them.
We are working on elucidating how phase transitions at the nanoscale differ from the bulk, the pathways underlying how they transform, and the associated time-scales, in a variety of semiconducting, superionic, phase-change, and ferroelectric nanomaterials with applications to next generation electrochemical and information storage technologies . These measurements make use of x-ray scattering, spectroscopy and nonlinear optical techniques to visualize the first steps in these processes. New projects include the use of optical tweezers to investigate the dynamics of ferroelectric phase transitions at the single nanoparticle level, the use of high pressure shocks to investigate the ultrafast dynamics of pressure-induced structural transformations at the nanoscale, and investigation of the dynamics of semiconductor nanowires and single atomic layer 2D materials in the limits of extreme strains.
We are also interested in the use of light to manipulate and engineer the functionality of materials. Experiments make use of light ranging from x-rays to far infrared terahertz (THz) frequency light pulses, approaching the limit where the electric and magnetic field turn on and then turn off within a single optical cycle, as a means of controlling the atomic-scale pathways materials follow. Current work is focused on investigating mechanisms for all-optical switching in ferroelectric and multiferroic materials, and their ultrafast photovoltaic response using both optical and x-ray probes. We are also looking at terahertz-driven processes in phase-change materials, and the first steps in field-driven switching processes. For these terahertz studies we utilize sources ranging from electron-beam-based to table-top plasma sources. These are also used as a femtosecond resolution ultrafast spectroscopic probe of carrier dynamics in a range of materials for energy conversion applications.