Aurelio Garcia-Valenzuela

The enhancement of microporosity in HMDSO-derived plasma polymer films through sequential cycles of plasma polymerization and etching has been demonstrated using positron spectroscopy techniques. These thin films exhibit a labyrinthine nanoporous architecture, characterized by an interconnected pore network with bottlenecks. The configuration of the plasma reactor significantly influences the final nanoporous structure, governed by the balance between ion-induced densification and chemical oxidation of residual hydrocarbons. By fine-tuning the plasma parameters and reactor design, small nanopores within the Si–O–Si cage structure are optimized to approximately 0.3 nm. These structural units are acting as interconnections of larger nanopores around 0.65 nm, functionalized with Si–OH groups along the pore walls. The high precision of positron annihilation spectroscopy enables clear differentiation between samples, with complementary insights provided by ellipsometry and Rutherford backscattering spectroscopy. Further optimization of the intrinsic microporosity was achieved through near-plasma chemical surface engineering, effectively mitigating ion-induced densification. Given the application potential of superhydrophilic SiOx-like thin films, the thermal stability of the nanoporous network was evaluated at moderate temperatures, revealing excellent structural integrity. These findings support the use of plasma polymer films fabricated via polymerization of hexamethyldisiloxane followed by etching as advanced membrane materials, where well-defined, defect-free microporous structures are essential.

The morphology of numerous nanocolumnar thin films deposited by the magnetron sputtering technique at oblique geometries and at relatively low temperatures has been analyzed for materials as different as Au, Pt, Ti, Cr, TiO₂, Al, HfN, Mo, V, WO₃ and W. Despite similar deposition conditions, two characteristic nanostructures have been identified depending on the material: a first one defined by highly tilted and symmetric nanocolumnar structures with a relatively high film density, and a second one characterized by rather vertical and asymmetric nanocolumns, with a much lower film density. With the help of a model, the two characteristic nanostructures have been linked to different growth dynamics and, specifically, to different surface relaxation mechanisms upon the incorporation of gaseous species with kinetic energies above the surface binding energy. Moreover, in the case of Ti, a smooth structural transition between the two types of growths has been found when varying the value of the power used to maintain the plasma discharge. Based on these results, the existence of different surface relaxation mechanisms is proposed, which quantitatively explains numerous experimental results under the same conceptual framework.

Optical and structural in-air stability of transparent conductive oxide SnO₂:Ta (1.25 at% Ta) up to 800 °C is shown by a 12 hour lab furnace exposure. Raman spectra and DFT calculations reveal partially healing V_Sn- and O_i-type point defects.

We demonstrate the existence of stoichiometric variations at the nanoscale when growing nanocolumnar SiO_x thin films by reactive magnetron sputtering deposition at oblique angles. Results show stoichiometric variations in the range 0.3 < x < 1.3 when growing a SiO_0.5 thin film. This agrees with results from a numerical growth model that obtains a shift of the stoichiometry in all nanocolumns from lower values at the side facing the Si target to higher values at the opposite side. The different momentum distribution of the gaseous reactive and sputtered species results in preferential incorporation of the latter at a particular side of the nanocolumns. The general occurrence of this mechanism during the reactive magnetron sputtering deposition of substoichiometric thin films at oblique angles is discussed.