Highlight Lecture (Symp. D01)
In situ TEM studies of fundamental processes in thin films using chip-based heating systems
Erdmann Spiecker, Florian Niekiel, Simon M. Kraschewski
Lehrstuhl für Mikro- und Nanostrukturforschung & Center for Nanoanalysis and Electron Microscopy (CENEM), Friedrich-Alexander Universität Erlangen-Nürnberg, Cauerstr. 6, 91058 Erlangen, Germany
Recent advances in in situ instrumentation for transmission electron microscopy (TEM) open up the possibility for a whole new insight into dynamic processes in materials. Fueled by the development of Cs-correction allowing, i.a., a larger pole piece gap for sophisticated in situ setups without compromising resolution , in situ microscopy has become a hot topic in many areas of materials research . One key advance in technology for in situ microscopy is the incorporation of microelectromechanical systems (MEMS) into the sample environment, allowing for direct thermal, electrical or mechanical stimulation, e.g., micro-electrical heating devices [3, 4]. These systems feature high temperature stability, vanishingly low drift rates and the possibility for rapid temperature changes owed to the small heat capacity. Together with the development of fast cameras/detectors, this allows to max out the capabilities of in situ TEM, achieving a performance previously only known from ex situ experiments.
Here we report on in situ TEM studies of fundamental processes in thin films which demonstrate how the unique capabilities of chip-based heating systems can be exploited to obtain quantitative information on the kinetics of these processes and gain insight into the microscopic mechanisms. In a first application, the fundamental process of solid state dewetting is addressed using thin Au films on amorphous silicon nitride membranes as example. In addition to studying the kinetics of the process by in situ STEM , complementary in situ imaging and diffraction techniques are employed to gain insight into the interplay of grain growth and texture evolution with the process of dewetting. As second application the phenomenon of metal-induced crystallization (MIC) of elementary semiconductors Si and Ge are studied in thin film stacks of Al/AlOx/a-Si and Al/AlOx/a-Ge, respectively, deposited on amorphous silicon nitride membranes. Here, in situ STEM and EDXS are employed for revealing long-range material transport associated with the crystallization process. In order to learn more about the mechanism of MIC the in situ studies are complemented by detailed ex situ analytical measurements on quenched samples aiming at determining the supersaturation of Si (Ge) in the metal layer and potential concentration gradients towards the crystalline nuclei.
From a methodological perspective this work demonstrates the capabilities of today's transmission electron microscopy in combination with state-of-the-art in situ instrumentation. In particular the combination of complementary information from different dedicated techniques in one and the same setup is demonstrated to be highly beneficial.
This work has been carried out in the framework of the Research Training School GRK 1896 “In situ Microscopy with Electrons, X-rays and Scanning Probes” funded by the German Research Foundation (DFG). Additional funding was provided by the DFG Cluster of Excellence EXC 315 “Engineering of Advanced Materials”. Technical support by DENSsolutions (Delft) is gratefully acknowledged.
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 F. Niekiel et al., Acta Mater. 90 (2015) 118.
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