Novel characterization techniques developed over the past two decades have revolutionized our ability to visualize the microscopic, atomic-scale processes that determine the functional properties of materials. The overarching challenge here is that the relevant time-scales and length-scales for these processes are typically 10-13 seconds (100 femtoseconds) and 10-10 m (1 Å) such that our view of how a material or device functions is often blurred out in time or in space. In this talk I will discuss three recent experiments using femtosecond x-ray, electron, and optical pulses as a means of probing the optoelectronic and structural properties of materials on ultrafast time-scales, as they transform and in-situ. 1) I will describe studies probing the dynamics of phase-change materials, exploring their operation triggered by electric field pulses that are a thousand times shorter than previously investigated. We find that threshold switching takes place on sub-picosecond timescales, a thousand times faster than what has been known to be possible, and that femtosecond all-optical electrical biases can drive amorphous-to-crystalline transformations, with potential implications for next-generation information storage technologies. (2) I will describe experiments probing dynamical switching processes in quasi-two-dimensional materials, and show that optical and electric field excitation can drive switching processes between topological phases of matter. (3) I will describe measurements probing the first steps following photon absorption in the hybrid perovskites. These measurements show that in the prototypical methyl-ammonium lead iodide, dynamical and large amplitude deformations of the lead-iodide octahedra occur on picosecond time-scales, providing a new understanding of the structural processes that underlie the unique optoelectronic functionality of these materials.
Aaron M. Lindenberg is an Associate Professor at Stanford University with joint appointments in the Department of Materials Science and Engineering and the Department of Photon Science. He received his B.A. from Columbia University in 1996 and his Ph.D. in Physics from the University of California, Berkeley in 2001. He was named a Faculty Fellow at Berkeley from 2001-2003 and then became a staff scientist at the SLAC National Accelerator Laboratory from 2003-2007. He is a winner of the DARPA Young Faculty Award, the Department of Energy Outstanding Mentor Award, the Alfred Moritz Michaelis Prize, and was named a Terman Fellow and a Chambers Faculty Scholar at Stanford and an I.I. Rabi Scholar at Columbia.
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