Date: Friday, Feb 28th
Presenter: Dr. Melissa Santala, University of California, Berkeley
In situ transmission electron microscopy (TEM) permits the visualization of dynamic processes in materials, yet many processes propagate at rates far exceeding the temporal resolution of thermionic- or field emission-based TEMs. The dynamic transmission electron microscope (DTEM) is a photoemission TEM capable of nanosecond-scale time-resolved imaging and diffraction. It has been used to study laser-driven crystallization of chalcogenide-based phase change materials used for optical and resistive memory. Crystallization kinetics of phase change materials are vitally important for memory applications as they directly impact device switching speed, but crystal growth rates are difficult to measure during laser- and current-induced annealing. The DTEM was used to image laser-crystallization of amorphous GeTe and directly measure crystal growth rates. Since temperature measurements during laser-driven in situ TEM experiments are inaccessible, finite element analysis simulations were used to model the spatial and temporal temperature profiles. This allowed the DTEM data to be placed in the context of a kinetic model of crystallization, paving the way for a more robust understanding crystallization of phase change materials over the whole range of technologically-relevant temperatures. This work performed under the auspices of the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Dr. Melissa K. Santala is currently is a staff scientist in the Condensed Matter and Materials Division at Lawrence Livermore National Laboratory. Dr. Santala received her B.S. and M.S. in Materials Science and Engineering from the University of California at Berkeley. She was a recipient of a National Science Foundation Graduate Research Fellowship and earned her Ph.D. in Materials Science and Engineering at UC Berkeley in 2009. Her graduate research focused on fundamental studies of the thermodynamic and kinetic properties of surfaces and interfaces in ceramic and ceramic-metal systems. In 2009, she joined Lawrence Livermore National Laboratory as a post-doctoral researcher, where she has been engaged in experimental studies of the kinetics of highly-driven phase transformations.