The metal assisted etching mechanism for Si nanowire fabrication, triggered by doping type and level and coupled with choice of metal catalyst, is still very poorly understood. We explain the different etching rates and porosities of wires we observe based on extensive experimental data, using a new empirical model we have developed. We establish as a key parameter, the tunneling through the space charge region (SCR) which is the result of the reduction of the SCR width by level of the Si wafer doping in the presence of the opposite biases of the p- and n-type wafers. This improved understanding should permit the fabrication of high quality wires with predesigned structural characteristics, which hitherto has not been possible.

The organic/inorganic interface in thin nanosized porous structures has a key role in determining the final properties of the composite materials. By use of the porous silicon/eumelanin hybrids as a case study, the role of this interface was investigated by experimental and computational methods. Our results show that an increased polymer density close to the hybrid interface strongly modifies the diffusion of the chemical species within the polymer molecule, affecting then the oxidation level of the pores’ inner Si surface. We observed a greater stability induced by increased pore diameter, a behavior that with computational and chemical arguments we attributed to a modified diffusion of the hydrogen peroxide toward the Si/eumelanin interface. Our results show that the overall behavior of a polymer when inserted in a tiny nanoscale structure must be taken into account for a correct understanding and control of the hybrids properties and that the formation of the interface alone may not be sufficient.

A multifunctional, semitransparent photovoltaic device is proposed for\ud harvesting sunlight over a tunable spectral range extending from the UV to\ud the IR. Self-assembled monolayers of nanospheres applied to luminescent\ud concentrators provide a photon management architecture, which relies\ud on luminescence and diffraction of light. The light diffraction is tuned by\ud changing the sphere diameter to match the transparency region of the\ud fl uorophores. The importance of each optical mechanism is inferred from\ud a systematic experimental investigation of the external quantum effi ciency\ud of fabricated devices, and from the calculation of the resulting photocurrent\ud under the AM 1.5 solar spectrum. Compared to the conventional\ud luminescent concentrator, relative photocurrent improvements are shown\ud between 50% and 500% depending on the spectral properties of the device\ud components. It has been demonstrated how to tailor the photovoltaic performances,\ud the color and the degree of transparency of the device to provide a\ud versatile photovoltaic unit for sustainable building-integrated applications

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The self-assembly (SA) of diblock copolymers (DBCs) based on phase separation into different morphologies of small and high-density features is widely investigated as a patterning and nanofabrication technique. The integration of conventional top-down approaches with the bottom-up SA of DBCs enables the possibility to address the gap in nanostructured lateral length standards for nanometrology, consequently supporting miniaturization processes in device fabrication. On this topic, we studied the pattern characteristic dimensions (i.e., center-to-center distance L and diameter D) of a cylinder-forming polystyrene-b-poly( methyl methacrylate) PS-b-PMMA (54 kg mol, styrene fraction 70%) DBC when confined within periodic SiO trenches of different widths (W, ranging between 75 and 600 nm) and fixed length (l, 5.7 μm). The characteristic dimensions of the PMMA cylinder structure in the confined configurations were compared with those obtained on a flat surface (L = 27.8 ± 0.5 nm, D = 13.0 ± 1.0 nm). The analysis of D as a function of W evolution indicates that the eccentricity of the PMMA cylinders decreases as a result of the deformation of the cylinder in the direction perpendicular to the trenches. The center-to-center distance in the direction parallel to the long side of the trenches (L) is equal to L measured on the flat surface, whereas the one along the short side (L) is subjected to an appreciable variation (ΔL = 5 nm) depending on W. The possibility of finely tuning L maintaining constant L paves the way to the realization of a DBC-based transfer standard for lateral length calibration with periods in the critical range between 20 and 50 nm wherein no commercial transfer standards are available. A prototype transfer standard with cylindrical holes was used to calibrate the linear correction factor c(Δx') of an atomic force microscope for a scan length of Δx' = 1 μm. The relative standard uncertainty of the correction factor was only 1.3%, and the second-order nonlinear correction was found to be significant.