Berlin 2015 – scientific programme
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O: Fachverband Oberflächenphysik
O 70: Structural Dynamics in Nanoscale Materials Probed by Ultrashort Electron Pulses
O 70.18: Poster
Wednesday, March 18, 2015, 18:15–21:00, Poster A
Structure and Dynamics with Ultrafast Electron Microscopes — •Bradley Siwick1, Mark Stern1, Lily Nikolova2, Federico Rosei2, Jennifer McLeod2, Tom Lagrange3, and Bryan Reed3 — 1McGill University, Center for the Physics of Materials, Montreal, Canada — 2Institut National de la Recherche Scientifique, Centre Énergie, Matériaux, Télécommunications, Varennes, Canada — 3Condensed Matter and Materials Division, Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, USA
This poster will describe a series of recent experiments on explosive crystallization in amorphous germanium, where we have directly "watched" the nano-micro structural evolution in the material using dynamic transmission electron microscopy (DTEM). Direct visualization of the crystallization front allows for time-resolved snapshots of the initiation and roughening of dendrites on sub-microsecond time scales and a rapid transition to a ledge-like growth mechanism at longer times. Direct observations of the speed of the explosive crystallization front as it evolves along a laser-imprinted temperature gradient have been used to experimentally determine the complete interface response function (i.e., the temperature-dependent front propagation speed) for this process, which reaches a peak of 16m/s. These result suggests a modification to the liquid-mediated mechanism commonly used to describe this process that replaces the phase change at the leading amorphous-liquid interface with a change in bonding character (from covalent to metallic) occurring in the hot amorphous material.