Carmen R. Tubío

3D printing of Al2O3 photonic crystals for terahertz frequencies

Reported here is the fabrication and characterization of a three-dimensional photonic crystal for terahertz frequencies based on 3D printing of Al2O3. Specific inks containing Al2O3, the material required for the structure, are synthesized with the viscosity and rheological properties necessary to be extruded through nozzles of micrometric section. The process is completed by a thermal sintering to obtain compact structures. SEM measurements are performed to evaluate the quality of the structures and measure the geometrical parameters. Finally, the presence of the band gap is demonstrated by THz time-domain spectroscopy.

Preparation and characterization of Ce-doped and Zr-doped sol–gel inks of titanium alkoxide

Inks of titanium diisopropoxide bisacetylacetonate ([(CH3)2CHO]2Ti(C5H7O2)2) are suitable for the fabrication of photonic bandgap materials by direct ink writing (DIW). Using this method we are able to obtain micro-periodic titania (TiO2) structures with high refractive index by calcining the structures built with those inks. Calcining at high temperatures causes titania grain growth and surface roughness of the structure, which has an influence over its optical properties. In order to inhibit the grain growth of titania nanocrystals when the structures are calcined, we have synthesized using the sol–gel technique titanium diisopropoxide bisacetylacetonate inks doped with Cerium (III) nitrate hexahydrate (Ce(NO3)3·6H2O) and Zirconyl nitrate hydrate (ZrO(NO3)2·xH2O). The grain growth process of titania powders derived from the calcined doped sol–gel inks during various heat-treatment programs has been investigated by the X-ray line-broadening analysis. It was demonstrated how the dopants reduce the grain growth of the rutile phase after heat treatment. The influence of the dopants on the rheological behaviour of doped inks were studied and compared with the undoped. The flow and oscillation curves as a function of time demonstrate that doped inks have the same rheological behaviour than undoped inks. Thermogravimetric analysis also proves that doped inks keep the same mass loss after calcination than undoped inks. These results show how doped inks can be applied for DIW in the same conditions than undoped inks with a significant reduction of titania grain growth.