Simon Vigonski will defend his PhD thesis "Atomistic study of surface effects in metals" on 4 January 2019. The defence will take place in Helsinki according to a double doctorate degree agreement between University of Helsinki and University of Tartu.
Dr. Vahur Zadin, Institute of Technology, University of Tartu
Dr. Flyura Djurabekova, Department of Physics, University of Helsinki
Prof. Alvo Aabloo, Institute of Technology, University of Tartu
Prof. Roberto Iglesias, Oviedo University (Spain)
The smallest building blocks of materials affect the behavior of the largest objects. The European Organization for Nuclear Research, famous for its discovery of the Higgs boson, is planning the construction of a new particle accelerator. Next to the current Large Hadron Collider, the Compact Linear Collider should be constructed, with a planned length of 50 kilometers. It will allow a much more precise study of the Higgs boson to better understand the underpinnings of the Universe.
The new collider means new technology, namely extremely high electric fields are used to accelerate the particles. Experiments have shown, however, that the accelerator structure itself is unable to bear such a high electric field. Electrical breakdowns, in other words lightning, are observed inside the copper structure. To prevent this, the behavior of copper under high field conditions needs to be studied, specifically at the smallest atomistic scale. A small protrusion consisting of only a few atoms can grow until massive atom evaporation leads to a breakdown and interrupts the work of the whole machine.
Electrical breakdown is too fast and too extreme to study in a microscope. Therefore, computer simulations are employed, where the motion of atoms can be observed with high precision. In this doctoral work, the modification of material surface and its subsequent relaxation are simulated.
It turns out that the structural defects under the material surface – dislocations – activate sufficiently to move to the surface and create plateaus, which are known to promote breakdowns.
Relaxation works with a different mechanism – the reduction of surface energy – which was studied using nanowires. Given sufficient time, nanowires break up into small droplets, like a water stream from a tap. This breakup is very predictable, and the results can be extended both to the accelerator breakdown problem, and nanotechnology in general.