A study of sonochemically synthesized ZnS:Mn nanoparticles is presented. The particles prepared at low rf power (about 20 W) and room temperature coalesce to form morphologically amorphous large species (30-100 nm in diameter). As the power is increased in the range from 20 to 70 W, and the solution temperature is raised to 60 to 80 degrees C, finer particles are produced with the size ranging from 2 to 20 nm and improved crystallinity. The results indicate the dispersion of the Mn(2+) ions at near-surface sites in the particles. It is shown that the sonochemically fabricated particles approach the quality of the ones obtained by a standard chemical route and show a reasonable luminescence performance.

Photovoltage (PV) transients are studied in ${\text{C}}_{60}–\text{Pb}$ and ${\text{C}}_{60}–\text{Au}$ thin films. The morphology of the ${\text{C}}_{60}$ layers is characterized by x-ray diffraction and atomic force microscopy, which evidence the formation of a nanocrystalline ${\text{C}}_{60}$ layer on polycrystalline Pb and Au underlayers. In contrast to Au substrate, Pb crystallites with a (111) texture are predominantly formed. The signs of the PV signals developed at the ${\text{C}}_{60}–\text{Pb}$ and ${\text{C}}_{60}–\text{Au}$ interfaces are found to be opposite due to very different workfunction values of the two metals. The evolution of the PV rise and decay curves with increasing light illumination intensity is completely different at the ${\text{C}}_{60}–\text{Pb}$ and ${\text{C}}_{60}–\text{Au}$ interfaces. The rise for the ${\text{C}}_{60}–\text{Pb}$ interface speeds up considerably with the increase in intensity, which is markedly different from the behavior at ${\text{C}}_{60}–\text{Au}$ , which exhibits nearly unchanged curve shapes. The PV decay time for ${\text{C}}_{60}–\text{Au}$ is also only weakly affected by varying light intensity. In contrast, increasing the illumination intensity causes the decay curves for ${\text{C}}_{60}–\text{Pb}$ to become multiexponential profiles, developing fast initial decays. The results are discussed in terms of different charge redistribution properties of ${\text{C}}_{60}$ molecules adsorbed on Pb(111) and Au interfaces. The observed transformation of the PV decay curves is explained by the presence of interface states and a subsequent interplay of the charge redistribution properties of ${\text{C}}_{60}$ molecules adsorbed on Pb(111). The results can be applied to sandwich structures containing organic-metal interfaces to account correctly for the interfacial charge transfer dynamics.

Due to their inherent physical properties, thin-film Si/SiGe heterostructures have specific thermal management applications in advanced integrated circuits and this in turn is essential not only to prevent a high local temperature and overheat inside the circuit, but also generate electricity through the Seebeck effect. Here, we were able to enhance the Seebeck effect in the germanium composite quantum dots (CQDs) embedded in silicon by increasing the number of thin silicon layers inside the dot (multi-fold CQD material). The Seebeck effect in the CQD structures and multi-layer boron atomic layer-doped SiGe epitaxial films was studied experimentally at temperatures in the range from 50 to 300 K and detailed calculations for the Seebeck coefficient employing different scattering mechanisms were made. Our results show that the Seebeck coefficient is enhanced up to ≈40% in a 3-fold CQD material with respect to 2-fold Ge/Si CQDs. This enhancement was precisely modeled by taking into account the scattering of phonons by inner boundaries and the carrier filtering by the CQD inclusions. Our model is also able to reproduce the observed temperature dependence of the Seebeck coefficient in the B atomic layer-doped SiGe fairly well. We expect that the phonon scattering techniques developed here could significantly improve the thermoelectric performance of Ge/Si materials through further optimization of the layer stacks inside the quantum dot and of the dopant concentrations.

A simple and time consuming theoretical model that predicts the thermal conductivity of SiO₂ layers with embedded Ge quantum dots is proposed. It takes into account the structural relaxation in the SiO₂ matrix, deviation in mass density of the dots compared to the surrounding matrix and strains associated with the dots.

We present computational results for strain effects on charge carrier confinement in GexSi1$-${}x quantum dots (QDs) grown on an oxidized Si surface. The strain and free carrier probability density distributions are obtained using the continuum elasticity theory and the effective-mass approximation implemented by a finite-element modeling scheme. Using realistic parameters and conditions for hemisphere and pyramid QDs, it is pointed out that an uncapped hemisphere dot deposited on the Si surface with an intermediate ultrathin oxide layer offers advantageous electron-hole separation distances with respect to a square-based pyramid grown directly on Si. The enhanced separation is associated with a larger electron localization depth in the Si substrate for uncapped hemisphere dots. Thus, for dot diameters smaller than 15\char21{}20 nm and surface density of the dots (nQD) ranging from about 1010 to 1012 cm$-${}2, the localization depth may be enhanced from about 8 nm for a pyramid to 38 nm for a hemisphere dot. We find that the effect in a hemisphere dot is very sensitive to the dot density and size, whereas the localization depth is not significantly affected by the variation of the Ge fraction x in GexSi1$-${}x and the aspect ratio of the dot. We also calculate the effect of the fixed oxide charge (Qox) with densities ranging from 10$-${}9 to 10$-${}7 C/cm2 for 10-$\Omega${}cm p-type Si wafers on the carrier confinement. Although the confinement potential can be strongly perturbed by the charge at nQD less than $\approx${}4\ifmmode\times\else\texttimes\fi{}1011 cm$-${}2, it is not very sensitive to the value of Qox at higher nQD. Since, to our knowledge, there are no data on carrier confinement for Ge QDs deposited on oxidized Si surfaces, these results might be applicable to functional devices utilizing separated electrons and holes such as photovoltaic devices, spin transistors, and quantum computing components. The use of hemisphere QDs placed on oxidized Si rather than pyramid dots grown on bare Si may help to confine charge carriers deeper inside the Ge/Si heterostructure in order to reduce the influence of surfaces and interfaces on transport properties of the structures.