The BSc thesis entitled "Evaluation of Different Dielectrics for Mid-Infrared Waveguides" by Mr. Ales Konecny provides an experimental comparison of different dielectric layers with respect to their integration into plasmonic waveguides for mid-infrared wavelengths. The experimental works cover the fabrication by magnetron sputtering and by plasma-enhanced physical vapor deposition, optical characterization using mid-infrared ellipsometry and lithographic steps to define prototype waveguides. Finally, these results are corroborated by waveguide calculations to estimate the propagation length for sensor chips.

The obtained results provide a solid basis for the future integration and fabrication of mid-infrared sensors at CEITEC. In addition to the commonly used dielectrics SiOx and SiNx, he also started the characterization of TiO2 in the mid-infrared region, which is a risky work package with no guaranteed outcome. The experimental data are therefore immediately useful and will impact future research.

After basic initial training, the student performed the experiments and data analysis fully independently and self-motivated, which needs to be highlighted in particular, since he did the ground-breaking work in a research group that was only recently established at CEITEC. The experimental work was done carefully, ensuring a high reproducibility of the results. The thesis is well-written and clearly summarizes the techniques and advantages or disadvantages of the investigated materials. During this thesis work, Mr. Konecny built up experimental expertise within the CEITEC Nano research infrastructure, which will allow him to tackle more complex research projects in future.

The bachelor thesis of Aleš Konečný deals with the fabrication and characterization of mid-infrared waveguides with potential to be incorporated into devices for sensitive detection of liquid and gas species. The work focuses on the optimization of the dielectric layer on top of the metal, as a way to ensure large propagation distances and increased sensitivity of the waveguides. I was positively impressed by the numerous experimental techniques he employed in the work, including different thin film growth methods, photolithography as well as spectroscopic ellipsometry. The work briefly explores numerical simulations via Lumerical, too. I think that relevant conclusions are obtained in terms of how to minimize the optical absorption of the dielectric layer. While the thesis includes a few minor errors, the manuscript is well structured and it is easy to follow the reasoning utilized, and the English level is satisfactory.

The manuscript slightly misses to point out what is the effect of the different growth temperature on the properties of the dielectric layer (structure, roughness, grain size, presence of defects...) which in turn influence the mid-infrared absorption. It would have been positive to mention such connections between the structural and optical properties in order to better understand the role of the growth temperature. On the other hand, I felt that references were sometimes lacking were due, for example when mentioning the Palik database (page 19), without explicitly including the citation.

Despite these few aspects that could have been further improved, I believe that the work is of very good quality and hence I would like to grant the highest overall mark “A”. Topics for thesis defence:

1. What is the influence of the growth temperature on the dielectric layer physical properties? (structure, etc.) What material properties can be linked in the dielectric layers to a higher or lower absorption (k value)?
2. Could you please explain better why Al is better for the metallic layer than Au? Which material between the two is more absorptive in the mid-infrared? What other materials do you think that can be of potential use for mid-infrared waveguides, for the metallic and dielectric layers?