On 1 October at 14:15 Elyad Damerchi will defend his doctoral thesis „Heat-Induced Morphological and Structural Changes in Nanostructures“ for obtaining the degree of Doctor of Philosophy (Materials Science)
Supervisiors:
Professor Veronika Zadin, University of Tartu
Research Fellow Sven Oras, University of Tartu
Associate Professor Sergei Vlassov †, University of Tartu
Opponent:
Chief Researcher Simas Račkauskas, Kaunas University of Technology, Lithuania
Summary: Metallic nanowires are thousands of times thinner than a human hair and invisible to the human eye. Networks of metallic nanowires can form transparent and flexible conductive paths for touchscreens, sensors, and heaters. Their reliability, however, is limited by heat. Even far below the melting point, atoms on a nanowire’s surface can begin to move, changing the wire’s shape and performance. The wire then becomes unstable and may eventually break into small nanoparticles, interrupting the electrical current.
This doctoral thesis examined how temperature, heating time, wire diameter, contact with a supporting surface, and repeated heating and cooling affect the thermal stability of metallic nanowires. Changes were observed using electron microscopes and interpreted with computer simulations. To analyse large collections of microscopy images, the Nano1D software was developed to automatically measure the lengths of nanowires and the fragments formed during their breakup.
The results showed that thinner silver nanowires deform and fragment faster than thicker ones, while higher temperatures accelerate the same process. Heating duration was also important, and prolonged heating, even at lower temperatures, could significantly affect the shape of nanowires. Contact with a supporting surface could either stabilise a nanowire or promote its fragmentation, depending on the heating conditions. Repeated heating and cooling introduced stress and defects in unsupported wire sections, creating locations where fragmentation could begin.
This work improves our ability to predict how metallic nanowires behave under heat and to select suitable materials, dimensions, and operating conditions. The findings support the development of more reliable transparent electrodes, flexible electronic devices, sensors, and nanoscale heaters.
Defence can be followed in Zoom: Doctoral Defence (meeting ID: 953 058 8152, passcode: kaitsmine)
