HOŠKOVÁ, M. Vliv tepelných fluktuací na stabilitu samouspořádaných Casimirových mikrodutin [online]. Brno: Vysoké učení technické v Brně. Fakulta strojního inženýrství. 2024.

Posudek vedoucího

Shegai, Timur

The thesis work by M. Hoskova is a good example of symbiosis between theory and experiment. The work includes high-quality experiments using gold nanoflakes in aqueous solution at room temperature. The results are interpreted in terms of Casimir-Lifshitz theory and Debye-Hückel screened electrostatic interaction. Furthermore, thermal fluctuations and potential energy surface reconstruction based on Boltzmann distribution are used to assess the accuracy of the proposed model. The experimental observations are found to be in good agreement with the theory. Most importantly, the reconstructed potential accurately predicts both the equilibrium separation between the flakes and the shape of the potential. This suggests that the unified Casimir-electrostatic potential adequately describes the physical system under study in a wide range of experimental parameters. Finally, the model predicts the limit of stability of self-assembled Casimir microcavities. M. Hoskova has significantly contributed to both the experimental and theoretical aspects of this work, for which reason I rate her performance in this project as excellent. This work sets firm ground for future development of Casimir self-assembly platforms for nanophotonic and polaritonic applications.   

Posudek oponenta

Antosiewicz, Tomasz

The thesis presented by Ms. Michaela Hoskova presents an experimental quantification of the forces involved in the self-assembly of Fabry-Perot cavities composed of think gold films/flakes. She studies how the impact of flake size together with the ionic concentration impacts the relative balance between the two relevant forces: Casimir attraction and screened electrostatic repulsion. The main objective of this thesis is to prove that the above combination of forces is the proper one which governs the self-assembly. Ms. Hoskova in her interdisciplinary work combines the following skills/tools: (i) chemical synthesis of thin, flat gold nanoparticles, (ii) time-resolved optical characterization using a microscope/spectrometer setup, (iii) TMM calculations to fit the measured spectra to obtain the self-assembled Fabry-Perot cavities’ thicknesses, (iv) analysis of the forces based on the stochastic properties of the cavitites movements; (v) obtaining the interaction potential. The ultimate result of her work is a detailed characterization of the Casimir-electrostatic potential as function of the ionic concentration and flake size. Based on these results, she obtains the upper and lower bounds for which the self-assembled cavity is stable, meta-stable, or does not form. These results are very impressive, novel, and rank very high in the current state-of-the-art. The thesis is written in a very good way. A comprehensive three-chapter extensive introduction/theory/methods part presents the motivation and current state-of-the-art, the theoretical background necessary to understand the forces at play and their mutual interaction, and finally the approaches taken in conduction of the work. The results are presented in a concise and clear way, while their discussion is presented in an excellent way and it is used to show/propose further research avenues. The form, structure, and contents of the thesis proves without a shadow of a doubt that Ms. Hoskova has mastered the topic of her thesis, understands it very well, and has all the hallmarks of an excellent scientist. Despite the excellent work put into preparing the thesis, there are several inconsistencies in the thesis. These do not take away anything in the way of novelty and excellence, but rather highlight the great task undertaken by Ms. Hoskova in preparing such a broad thesis. In fact, I would not have been surprised to find similar lapses in a PhD thesis. Overall, I find the thesis to be an excellent, way-above-average one, being easily in the top 5% of MSc theses. I fully endorse awarding Ms. Michaela Hoskova the degree of Master of Science.

eVSKP id 157317