PhD Defence by Yi-Chieh Yang
Title: thesis ‘Establishment of controlled thermal conditions in in-situ TEM heating experiments: Calibration and Application’.
Principal supervisor
Professor Jörg Ralf Jinschek, DTU
Examiners
Associate Professor Søren Bredmose Simonsen, DTU
Prof. Dr. rer. nat. Leopoldo Molina-Luna, TU Darmstadt
Senior lecturer Miryam Arredondo-Arechavala, Queen’s University Belfast
Chairperson at defence
Senior Researcher Alice Bastos da Silva Fanta, DTU
Abstract
Real-time heating experiments in transmission electron microscopy (TEM) allow the investigation of the microstructure in materials at elevated temperatures with high spatial resolution. Thereby it is very important to control and measure the applied thermal conditions in such experiments to reveal temperature-correlated structure-property relationships in materials.
The aim of this work is to provide a solid framework on how well we can control such heating experiments. Several challenges and limitations were identified when determining the local temperature in the material using simulations as well as in-situ and ex-situ experimental methods.
The in-situ method for real-time temperature measurements applied here was systematically investigated to determine its precision and accuracy. For example, the study highlights one of the limitations by showing a strong dependence on the geometry and thickness of the TEM sample. It was further investigated whether such a method can be applied when the sample temperature varies significantly, e.g. when a large thermal gradient is applied. While there was a high agreement between the simulation predictions and the ex-situ experimental methods, the opposite results of the real-time (in-situ) measurements revealed limitations that require further investigation.
In view of the current state of development in equipment and techniques, this study also aimed to understand how to improve the implementation of calibration methods to set the heating conditions in such heating experiments in TEM. The work provides a robust workflow and a critical discussion on the role of temperature measurement and control in such realtime heating analysis to investigate temperature-related phenomena in materials during fabrication or in application.