Quantifying transient states in materials with the dynamic transmission electron microscope

Abstract

(250 words)The Dynamic Transmission Electron Microscope (DTEM) offers a means of capturing rapid evolution in a specimen through in-situ microscopy experiments by allowing 15 ns electron micrograph exposure times. The rapid exposure time is enabled by creating a burst of electrons at the emitter by ultraviolet pulsed laser illumination. This burst arrives a specified time after a second laser initiates the specimen reaction. The timing of the two Q-switched lasers is controlled by highspeed pulse generators with a timing error much less than the pulse duration. Both diffraction and imaging experiments can be performed, just as in a conventional TEM. The brightness of the emitter and the total current control the spatial and temporal resolutions. We have demonstrated 7 nm spatial resolution in single 15 ns pulsed images. These single-pulse imaging experiments have been used to study martensitic transformations, nucleation and crystallization of an amorphous metal, and rapid chemical reactions. Measurements have been performed on these systems that are possible by no other experimental approaches currently available.2

Revealing the transient states of rapid solidification in aluminum thin films using ultrafastin situtransmission electron microscopy

“…Under these circumstances, solid Al grows into a superheated liquid throughout the entire solidification process. 1 This result is in good agreement with conventional solidification theory [15,16] of solid growth into a superheated liquid, which predicts stable, texture-less growth by propagation of a planar liquid-solid interface and provides in situ experimental verification for the first time with nm spatial resolution that the morphology of the liquid solid interface during rapid solidification of the metal can be explained by conventional solidification theory [15,16].…”

“…A 50 nm thick SiO 2 layer was used as a laser transparent cap layer. In situ melting experiments were performed in the dynamic transmission electron microscope (DTEM) [1,13,14] at Lawrence Livermore National Laboratory. The DTEM uses a YAG laser with wavelength ¼ 1064 nm to provide a thermal stimulus.…”

“…However, rapid solidification under these extreme conditions can occur in nanoscale systems with planar geometries, such as thin films, rendering them ideal for transmission electron microscopy studies. The unique Dynamic Transmission Electron Microscope (DTEM) at Lawrence Livermore National Laboratory provides both nanosecond temporal and nanometer spatial resolution [1][2][3][4][5][6], allowing us to study rapid solidification in metal and alloy thin films.…”

SHS in Ni/Al Nanofoils: A Review of Experiments and Molecular Dynamics Simulations

“…The exothermic intermixing of Ni and Al in the liquid layer appears as the main mechanism driving the self‐sustaining propagation in the reactive Ni/Al nanofoils. In situ studies, both XRD and DTEM, support this hypothesis . Moreover, by investigating the applicability of the model, Turlo et al demonstrated that the reactive dissolution of Ni into liquid Al may be the only driving mechanism for propagation in the case of equiatomic Ni/Al RMNFs with a bilayer thickness less than 54 nm.…”

“…Diffraction techniques are used to determine the local composition along the front. On the other hand, in situ observations within the dynamic TEM have revealed microstructure changes and local melting events during reaction propagation …”