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In this work, porous-silicon samples were prepared by electrochemical etching on p-type (B-doped) Silicon (Si) wafers. Hydrofluoric acid (HF)-ethanol (C2H5OH) [HF:Et] and Hydrofluoric acid (HF)-dimethylformamide (DMF-C3H7NO) [HF:DMF] solution concentrations were varied between [1:2]—[1:3] and [1:7]—[1:9], respectively. Effects of synthesis parameters, like current density, solution concentrations, reaction time, on morphological properties were studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM) measurements. Pore sizes varying from 20 nm to micrometers were obtained for long reaction times and [HF:Et] [1:2] concentrations; while pore sizes in the same order were observed for [HF:DMF] [1:7], but for shorter reaction time. Greater surface uniformity and pore distribution was obtained for a current density of around 8 mA/cm2 using solutions with DMF. A correlation between reflectance measurements and pore size is presented. The porous-silicon samples were used as substrate for hydroxyapatite growth by sol-gel method. X-ray diffraction (XRD) and SEM were used to characterize the layers grown. It was found that the layer topography obtained on PS samples was characterized by the evidence of Hydroxyapatite in the inter-pore regions and over the surface.

Flexible printed electronics has attracted strong interest during the last two decades and is one of the successful trends in material science, representing the future of printed electronics (PE). This research work evaluates the use of screen-printing technology and materials for producing functional circuits for automotive interior parts, which can be subsequently processed through In-Mould Electronics (IME). Since the selection of the materials to build the printed system is of utmost importance, this study evaluates combinations of commercial polycarbonate substrates (LEXAN 8A13E, DE 1-4 060007 and LM 905 2-4 160009) and silver-based inks (ME603, ME604 and CP 6680), all suitable for IME. Different electrically conductive tracks varying in width and spacing (0.5, 0.3 and 0.2 mm) and two capacitive sensors were printed. Tensile tests and surface energy characterizations of the different polycarbonate substrates were carried out, then morphological, electrical, and thermoforming studies were performed on the printed substrates. Morphological characterization showed successful printing for wider lines (0.5 and 0.3 mm), but problems with screen clogging occurred for smaller line widths (0.2 mm). The electrical conductivity of printed tracks was in accordance to the printed layer thickness and ink solids percentage. The proof-of-concept of the electrical functionality was successful, when integrating the sensors into the PCB with SMD LEDs. Thermoforming showed limited functionality, with the best overall performance observed for specific combinations of substrate and ink. In essence, the results indicate that although all the selected substrates and silver-based inks have great compatibility among themselves and can be considered as materials for the production of functional automotive interior parts, there is no ideal pairing of inks and substrates. Therefore, this study empathizes the importance of defining product specifications for a more suitable material selection.