CPM Seminar

Imaging rapid, irreversible phase transformations with nanosecond time resolved transmission electron microscopy

Thomas Lagrange

Lawrence Livermore National Lab

A materials response to external stimuli and macroscopic properties can be described through the observation of its microstructural features and dynamical behavior. Materials models and computer simulations aim to predict materials behavior in different environments, but typically require experimental data for validation or interpretation of simulated quantities. Most materials dynamics are inherently rapid, making it difficult to capture transient, fine-scale features of the material process, especially on the length and time scale relevant for most mesoscale models. In effort to meet the need for studying fast dynamics in irreversible material processes, the dynamic transmission electron microscope (DTEM) was constructed at Lawrence Livermore National Laboratory to improve the temporal resolution of in-situ TEM technique to observe transient materials states with nanosecond time resolution.

The DTEM consists of a modified JEOL 2000FX transmission electron microscope column that provides access for two pulsed laser beams. One laser drives the photocathode (which replaces the standard thermionic cathode) to produce the brief electron pulse and nanosecond exposure times. The other strikes the sample, initiating the process to be studied. A series of pump-probe experiments with varying time delays enable the reconstruction of the on-average sequence of events occurring during rapid phase transformations. This presentation will discuss the core aspects of the DTEM instrument and give brief examples how the DTEM has been used to capture rapid nucleation events and quantify phase transition kinetics. The latter part of the talk will discuss the planned instrumentation changes to increase its spatial-temporal resolution.

Work was performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore National Laboratory and supported by the Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, of the U.S. Department of Energy under contract No. DE-AC52-07NA27344.