Alvaro Gil

Copper-catalyzed Huisgen 1,3-dipolar cycloaddition under oxidative conditions: polymer-assisted assembly of 4-acyl-1-substituted-1,2,3-triazoles.

We herein document the first example of a reliable copper-catalyzed Huisgen 1,3-dipolar cycloaddition under oxidative conditions. The combined use of two polymer-supported reagents (polystyrene-1,5,7-triazabicyclo[4,4,0]dec-5-ene/Cu and polystyrene-2-iodoxybenzamide) overcomes the thermodynamic instability of copper(I) species toward oxidation, enabling the reliable Cu-catalyzed Huisgen 1,3-dipolar cycloadditions in the presence of an oxidant agent. This polymer-assisted pathway, not feasible under conventional homogeneous conditions, provides a direct assembly of 4-acyl-1-substituted-1,2,3-triazoles, contributing to expand the reliability and scope of Cu(I)-catalyzed alkyne-azide cycloaddition.

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.

Stress-free production and effective medium model of colloidal crystals

Colloidal crystals of silica spheres functionalized with N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride have been formed by the Langmuir–Blodgett methodology (LB). Monolayers at the air/water interface of functionalized silica spheres have been characterized by surface pressure–area and surface potential–area isotherms and by Brewster angle microscopy (BAM). In order to control and optimize the production of such a colloidal crystal we have measured the diameter and order of spheres in the films, their defects and the density of spheres in each film. Morphologies of the Langmuir–Blodgett films were analyzed by scanning probe ellipsometric microscopy (SPEM) and by scanning electron microscopy (SEM). The results of SPEM are in agreement with the SEM results. The density distribution of colloidal crystals was evaluated using the ellipsometric data by means of the three-layer Brueggemann effective medium approach. The Langmuir–Blodgett methodology was successful for the synthesis of colloidal crystals without cracks.

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.

Time-domain terahertz spectrometer for angular reflection measurements

We describe a terahertz time-domain spectrometer developed to perform measurements by reflection under a wide range of angles. The different parts of the device are described as well as the process of frequency-scale calibration and signal linearity evaluation. Also the main parameters that characterize the system and account their performance are measured. Finally an example of application to the measurement of the bandgap of a photonic crystal designed for the terahertz band is presented.