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Since the discovery that spherical metallic nanoparticles embedded in SiO₂ can transform to perfectly aligned nanorods after the passage of swift heavy ions, a new alternative among the nanofabrication processes was introduced in order to create nanostructures with such shapes which were difficult to be made with the most conventional techniques (colloidal chemistry, electron beam lithography, ion implantation). In this study, a new methodology was applied by using thin Si₃N₄ TEM windows grid as substrate in order to be able to trace the same nanoparticle before and after the irradiation. Since the elongation of the nanoparticles is expected to be sensitive to the matrix material properties due to the matrix underdensification, analytical comparison of gold nanoparticles elongation in SiO₂ deposited by PECVD and ALD was performed.

The results showed that the nanoparticle elongation depends strongly on the deposition process of SiO₂ and SiO₂ quality in addition to the initial size of the nanoparticles. Consequently, ALD SiO₂ offers greater elongation than PECVD SiO₂. In addition, the irradiation of spherical nanoparticles embedded in other materials, such as Al₂O₃ and TiO₂, was done. While TiO₂ deposited by ALD offers significantly smaller elongation for the gold nanoparticles compared to SiO₂, nanoparticles embedded in Al₂O₃ deposited by ALD elongated similarly as in ALD SiO₂. Apart from spherical nanoparticles, gold nanorods embedded in SiO₂ were irradiated as well. Depending on the nanorod initial size and irradiation fluence, different nanostructure morphologies were created. The most important cases were the re-orientation of nanorods along the ion beam direction and the creation of spikes on top of them. Molecular Dymanics simulations performed by collaborators at University of Helsinki showed that the nanorod re-orientation was a result of small incremental shape changes from nanorod to spheroid and back to a nanorod aligned with the ion beam direction. Finally, the scattering spectra from the elongated nanoparticles using dark field optical spectroscopy confirmed the existence of two discrete plasmon modes, one longitudinal and one transverse. Consequently, the fabricated samples were proved to be possible candidates for photonic applications.

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M.Sc. Spyridon Korkos defends his doctoral dissertation ”Ion beam shaping of embedded metallic nanoparticles for photonic applications” on 31 March 2023 at 12 noon. The opponent is Professor Daniel Primetzhofer (Uppsala University, Sweden) and custos is Professor Timo Sajavaara (Ģ��ֱ��). The language of the dissertation is English.