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In this paper, we study the metal-catalyzed synthesis of Si nanowires (Si-NWs) in a plasma based chemical vapor deposition system. In these deposition systems due to the high efficiency of precursor molecule dissociation, both uncatalyzed and catalyzed growth mechanisms can take place. The first one gives rise to the formation of the quasi one-dimensional (1D) Si-NWs, while the second one to a continuous two-dimensional (2D) Si layer over the substrate or on the nucleated Si-NWs. The Si-NWs formation is then the result of the competition between these two processes. The control parameters ruling these two contributions are here explored. Samples with different weights of 1D and 2D growth are deposited and characterized by using a plasma based chemical vapor deposition apparatus operating at T < 400 °C. It is found that the main control parameter of these processes is the plasma power through the distribution of the precursor dissociation products. By properly tuning the power, Si-NWs with 1 × 1010 cm−2 of density, up to 1 μm long and without uncatalyzed growth are obtained. The optical functionality of the samples, grown with different 1D/2D contributions, is investigated and it is demonstrated that the uncatalyzed layer produces a total reflectance as high as ∼40%, similar to that found in a planar Si wafer, while the highly dense Si-NWs, without the uncatalyzed deposition, produce a total reflectance of ∼15%.

The ability to form ordered nanostructures at the wafer level with low cost methodologies has represented a challenge in the last decade in many research fields spanning from nanoelectronics to photovoltaics (PVs). For the latter application the nanostructures have demonstrated interesting capabilities for exploiting the quantum effects in terms of efficient visible light absorption. To fabricate ordered nanostructures many solutions have been proposed but they provide feature densities lower than 10 9 cm À2 or present high fabrication costs. We propose a wafer level and low-cost Lithography based on block CoPolymers self-assembling (LCP), which allows the formation of nanofeatures controlled down to 10 nm and density higher than 5 Â 10 10 cm À2. We propose to use this technique to form radial junctions in nanoholes for solar cells. The approach is similar to that of the nanowires, i.e., it decouples the optical path of the visible photons from the electrical path of the carriers, but since the one-dimensional (1D) structures are embedded inside the bulk of the wafer the structure is more robust and allows easier implementation. To form the junction inside the nanoholes a novel strategy based on the deposition of monolayers of dopant-containing molecules is proposed. This technique allows to obtain shallow and controlled junction depths with peak carrier concentrations of about 10 19 cm À3 for both n-and p-type doping.

In this work, the morphological and structural evolution of gold nanodots deposited on Si substrates has been monitored for 2.4×10 3 h. Gold nanodots on Si are of great scientific interest because they can be used in numerous ways, for example as subwavelength antennas in plasmonics, as electrical contacts in nanometric devices, or as catalysts for the formation of quasi-1dimensional nanostructures. Their characteristics have been studied in a very large number of papers in literature, and among the several aspects, it is known that continuous Au films peculiarly interact with Si by interdiffusion even at room temperature. It would be expected that also small nanostructures could undergo to an interdiffusion and consequent modifications of their structure and shape after aging. Despite the cruciality of this topic, no literature papers have been found showing a detailed morphological and structural characterization of aged Au nanodots. Au nanoparticles have been deposited by sputtering on Si and stored in air at temperature between 20 and 23°C and humidity of about 45 %, simulating the standard storage conditions of most of the fabrication labs. The morphological and structural characterizations have been performed by bright field transmission electron microscopy (TEM). A specific procedure has been used in order to avoid any modification of the material during the specimen preparation for the TEM analysis. A digital processing of the TEM images has allowed to get a large statistical analysis on the particles size distribution. Two different types of nanoparticles are found after the deposition: pure gold crystalline nanodots on the Si surface and gold amorphous nanoclusters interdiffused into the Si subsurface regions. While the nanodots preserve both morphology and structure all over the time, the amorphous agglomerates show an evolution during aging in morphology, structure, and chemical phase.