The growth of InAs quantum dots (QDs) by organometallic vapor phase epitaxy (OMVPE) for use in GaAs based photovoltaics devices was investigated. Growth of InAs quantum dots was optimized according to their morphology and photoluminescence using growth temperature and V/III ratio. The optimized InAs QDs had sizes near 7×40 nm with a dot density of 5(±0.5)×1010 cm-2. These optimized QDs were incorporated into GaAs based p-i-n solar cell structures. Cells with single and multiple (5x) layers of QDs were embedded in the i-region of the GaAs p-i-n cell structure. An array of 1 cm2 solar cells was fabricated on these wafers, IV curves collected under 1 sun AM0 conditions, and the spectral response measured from 300-1100 nm. The quantum efficiency for each QD cell clearly shows sub-bandgap conversion, indicating a contribution due to the QDs. Unfortunately, the overarching result of the addition of quantum dots to the baseline p-i-n GaAs cells was a decrease in efficiency. However, the addition of thin GaP strain compensating layers between the QD layers, was found to reduce this efficiency degradation and significantly enhance the subgap conversion in comparison to the un-compensated quantum dot cells.

We present numerical calculations of electron spectra of single and multiple coupled quantum dots based on Aluminium Gallium Nitride / Gallium Nitride heterostructures. The effect of spontaneous and piezoelectric polarization on the confinement potential seen by the electrons is taken into account through bound interface sheet charges. We also calculated the spectra without polarization effects for reference. For some quantum dot dimensions, the energy eigenvalues shift by several hundred meVs due to the polarization charges. We calculate the spectra for the two cases of box-shaped and cylindrical quantum dots. The latter case is an approximation to quantum dots with hexagonal-facet shapes recently reported in the literature. The quantum dots in our calculations are surrounded by vacuum in the lateral direction, but the same qualitative conclusions will hold if the dots are embedded in some material, as long as the barrier heights are large. For GaN vertical confinement of less than 30 angstroms, most of the bound states are associated with the lowest eigenvalue of the vertical confinement potential. This is also true for higher vertical confinement dimensions because the triangular potential seen by the electrons is the same for the lowest energy eigenstates. The electric field in the vertical direction is a strong function of the aluminium concentration in the AlGaN layer. As the AlGaN layer composition is varied from very high Al concentration to medium Al concentration, the spectra shift by several hundred meVs, referred to the onset of the continuous spectra. The transition frequencies between bound states and between bound and the lowest continuum states lie in the low to the high infra-red range, and can be varied over a wide range by both the dimensions and the barrier aluminium concentration. For the case of 4 coupled quantum dots formed by repeated AlGaN/GaN heterojunctions, we find that the polarization-induced electric fields lead to excessive band-bending and as a consequence there are fewer bound states compared to the spectrum calculated without polarization effects.

Metallic nanoparticles are commonly used as the active phase of heterogeneous catalysts. Today, a current issue in catalysis research is to determine whether a specific crystallographic plane of the metallic nanoparticle is responsible for activity and selectivity properties in a structure sensible reaction. Following this purpose, metallic nanoparticles with specific morphologies have been studied. In the present work, palladium nanostructured particles are prepared in a surfactant mediated aqueous medium by a seeding growth approach, and present various morphologies : rods, tetrahedra and/or bipyramides, cubes, icosahedra... Synthesis of these nanoparticles and observation of their growth by a detailed Transmission Electron Microscopy study will be presented. We provide evidence that nucleation and growth of these particles are dominated by an aggregative mechanism. Moreover, upon ageing nanostructured particles undergo a ripening process to spherical morphology, attributed to an oxidative etching.

The applicability of Sn(OBu)4 based viscous oligomeric concentrates in fabrication of thin oxide fibers and needles is demonstrated. Influence of several crucial parameters like viscosity of the concentrate, humidity of surrounding atmosphere and pulling speed on formation of the structures is discussed. We show that the method enables to obtain fibers less than a micron in diameter and needles with tip radii down to 15 nm, i.e. in range that is of considerable interest for many nanotechnological applications.

We propose a tight-binding model for the polarization that considers direct and dipole contributions and employs microscopic quantities that can be calculated by first-principles methods, e.g. by employing Density Functional Theory (DFT). Applying our model to InxGa1-xAs alloys allows us to settle discrepancies between the values of e14 as obtained from experiments and from linear interpolations between the values of InAs and GaAs. Our calculated piezoelectric coefficient is in very good agreement with photo current measurements of InAs/GaAs(111) quantum well samples.

A novel synthesis of silica nanowires and silica/carbon heterostructures by electron beam irradiation on porous silicon films was investigated. The method allows us to monitor the growth process in real time at atomic scales. Depending on the electron dose we obtain nanowires with diameters in the range of 15-49nm and lengths up to 500 nm. We found that the adequate electron dose was between 0.01 Acm-2 and 2 Acm-2. Additional electron dose causes plastic and failure deformations in the silica nanowires. A growth model consistent with our findings is presented that involves the flow of mass from the substrate to the nanowire driven by the local electric fields. Heterostructures showing a nanopalm-like shape are obtained after exposing the silica nanowire to poor vacuum conditions in which carbon aggregation from the surrounding gas is promoted by the local electric fields enhanced at the tip of the silica wires.

We fabricated and studied the performance of Schottky-Barrier Si nanowire FETs (SiNW FET) by using Vapor-liquid-solid (VLS) grown Au-catalyzed SiNWs (20 nm). These devices were formed on various gate dielectrics (HfO2 or Al2O3) with different metal Source and Drain (S/D) regions (Pd, Ni). P-type behavior was observed and high Ion/Ioff ratio (~105) was achieved from undoped SiNW FETs. Besides, no ambipolar transportation was observed in our devices performance. This is possibly due to the small schottky barrier height for hole carriers at Source sides formed by high work-function metal. Furthermore, low subthreshold slope as 68mV/decade was obtained from SiNW FETs integrated with Ni S/D and Al2O3 High-¦gate dielectric.