Quantum confinement effects in silicon nanowires (SiNWs) are expected when their diameter is less than the size of the free exciton (with a Bohr radius ∼5 nm) in bulk silicon. However, their synthesis represents a considerable technological challenge. The vapor–liquid–solid (VLS) mechanism, mediated by metallic nanoclusters brought to the eutectic liquid state, is most widely used for its simplicity and control on the SiNWs size, shape, orientation, density, and surface smoothness. VLS growth is often performed within high-vacuum physical vapor deposition systems, where the eutectic composition and the pressure conditions define the minimum diameter of the final nanowire usually around 100 nm. In this article, we present and discuss the SiNWs’ growth by the VLS method in a plasma-based chemical vapor deposition system, working in the mTorr pressure range. The purpose is to demonstrate that it is possible to obtain nanostructures with sizes well beyond the observed limit by modulating the deposition parameters, like chamber pressure and plasma power, to find the proper thermodynamic conditions for nucleation. The formation of SiNWs with sub-5 nm diameter is demonstrated.

For the first time, memory devices with optimized high density (2E12#/cm/sup 2/) LPCVD Si nanocrystals have been reproducibly achieved and studied on an extensive statistical basis (from single cell up to 1 Mb test-array) under different programming conditions. An original experimental and theoretical analysis of the threshold voltage shift distribution shows that Si nanocrystals have serious potential to push the scaling of NOR and NAND flash at least to the 35 nm and 65 nm nodes, respectively.

In this work, two natural dyes extracted from henna and mallow plants with a maximum absorbance at 665 nm were studied and used as sensitizers in the fabrication of dye-sensitized solar cells (DSSCs). Fourier transform infrared (FTIR) spectra of the extract revealed the presence of anchoring groups and coloring constituents. Two different structures were prepared by chemical bath deposition (CBD) using zinc oxide (ZnO) layers to obtain ZnO nanowall (NW) or nanorod (NR) layers employed as a thin film at the photoanode side of the DSSC. The ZnO layers were annealed at different temperatures under various gas sources. Indeed, the forming gas (FG) (N₂/H₂ 95:5) was found to enhance the conductivity by a factor of 10³ compared to nitrogen (N₂) or oxygen (O₂) annealing gas. The NR width varied between 40 and 100 nm and the length from 500 to 1000 nm, depending on the growth time. The obtained NWs had a length of 850 nm. The properties of the developed ZnO NW and NR layers with different thicknesses and their effect on the photovoltaic parameters were studied. An internal coverage of the ZnO NWs was also applied by the deposition of a thin TiO₂ layer by reactive sputtering to improve the cell performance. The application of this layer increased the overall short circuit current J_sc by seven times from 2.45 × 10⁻³ mA/cm² to 1.70 × 10⁻² mA /cm².

The formation of Si quantum dots on ${\mathrm{SiO}}_2$ by chemical vapor deposition of ${\mathrm{SiH}}_4$ has been investigated in the range from the submonolayer to the complete coverage with Si. In order to investigate the very early stages of the nucleation process of Si on ${\mathrm{SiO}}_2,$ the energy filtered transmission electron microscopy has been chosen as the main characterization technique, because of the high spatial resolution typical of the transmission electron microscopy analysis, coupled to the compositional information obtained by the electron energy loss spectroscopy. The plan view configuration has been used to measure the dot size distributions down to dimensions of about 1 nm, and in cross section to evaluate the dot wetting angle. For all the several experimental conditions, a wetting angle distribution has been obtained and has shown to be centered at about 90°. Data on the dot size distributions are shown and discussed in the framework of a continuous nucleation model, which has been implemented to take into account the dot coalescence process contribution. Through the comparison with experimental data the relevant thermodynamic parameters of the process have been evaluated: the critical radius, the free energy barrier for nucleation, and the concentration of nucleation sites.