Manipulating light with carbon nitride thin films ; towards applications in metamaterials with organic polymeric carbon-nitride-based optical devices ; Lichtmanipulation mit Kohlenstoffnitrid-Dünnschichten ; auf dem Weg zu Anwendungen in Metamaterialien mit organischen, polymeren Kohlenstoffnitrid-basierten optischen Geräten

Polymeric carbon nitride (pCN) has emerged as a material with desirable optical and mechanical properties for optical and photonic devices. In this thesis, the high intrinsic refractive index and transparency through the visible part of the spectrum in pCN thin films were investigated and explored as potential parameters to guide and manipulate light in optical devices. Inserting the thin film properties in the field of artificially micro- and nanoengineered materials has created many possibilities, which has led this work to the fabrication of organic pCN-based waveguides and a proposition for low-loss flexible fishnet metamaterials. In the first part of the thesis, the optical dispersion properties, composition, and structure of pCN thin films were investigated as a function of the key parameters employed in the chemical vapor deposition (CVD) process. Changes in the real and imaginary parts of the refractive index, C/N ratio, and morphology occurred with changing the precursor amount, the polymerization time, and the carrier gas flow rate. Non-zero values of the extinction coefficient in the out-of-plane have revealed a high optical anisotropy of the thin films, which is addressed to changes in composition and molecular orientation. In addition, the results also show possible routes to avoid gas-phase nucleation and increased roughness. On-surface polymerization in situ studies on the polymerization mechanism, from the precursor melamine to pCN thin films, conclude that polymeric carbon nitride is composed of three different coexisting phases with different hydrogen bonding patterns. In the second part of the thesis, polymeric carbon nitride-based photonic devices for telecommunication wavelengths are demonstrated. The high ordinary refractive index of the polymer of around 2, covering the visible and near-infrared wavelength range, enables small footprint devices, strong mode confinement, and efficient coupling through grating couplers. Proof-of-concept experiments with microring resonators show a Q-factor ...