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We report on self-assembling of spherically shaped voids in nanometer size strained Sn precipitates after irradiation with He+ ions in different conditions. It is found that high-temperature irradiation induces vacancies which are collected by compressively strained Sn precipitates enhancing of out-diffusion of Sn atoms from the precipitates. Nano-voids formation takes place simultaneously with a β- to α-phase transformation in the Sn precipitates. Post-irradiation thermal treatment leads to the removal of voids and a backward transformation of the Sn phase to β-phase. Strain-enhanced separation of point defects along with vacancy assisted Sn out-diffusion and precipitate dissolution are discussed. [ABSTRACT FROM AUTHOR]

Self-diffusion in boron-doped germanium has been studied at temperatures between 526 and 749 °C with secondary ion mass spectrometry. Self-diffusion under acceptor doping is retarded compared to intrinsic conditions. This demonstrates the contribution of charged vacancies in self-diffusion. Taking into account the dominance of doubly negatively charged vacancies under donor doping, the doping dependence of self-diffusion is best described with an inverse level ordering for singly and doubly negatively charged vacancies for all doping conditions. The level ordering explains the dominance of doubly charged vacancies under donor doping and their decreasing contribution with increasing acceptor doping until neutral vacancies mediate self-diffusion. [ABSTRACT FROM AUTHOR]

We report measurements of the thermal conductivity of isotopically modulated silicon that consists of alternating layers of highly enriched silicon-28 and silicon-29. A reduced thermal conductivity of the isotopically modulated silicon compared to natural silicon was measured by means of time-resolved x-ray scattering. Comparison of the experimental results to numerical solutions of the corresponding heat diffusion equations reveals a factor of three lower thermal conductivity of the isotope structure compared to natural Si. Our results demonstrate that the thermal conductivity of silicon can be effectively reduced with isotopically modulated structures. This offers a promising approach to optimize silicon for thermoelectric applications. [ABSTRACT FROM AUTHOR]

We report on the synthesis of hollow tin dioxide nanoislands by molecular-beam deposition of Sn on Si/SiO2 substrates followed by thermal oxidation. Their microstructure and phase composition were studied by transmission electron microscopy. The appearance of small (2–5 nm) initial voids and their evolution into large (10–30 nm) holes in the SnO2 nanoislands correlates with the temperature of oxidation and content of oxygen in the atmosphere. This correlation is discussed on the basis of the Kirkendall effect with the additional assumption that absorption of oxygen atoms on the oxide surface creates an electric field that promotes the diffusion of metal ions. [ABSTRACT FROM AUTHOR]

We report on the bimodal distribution and long-range ordering of GeAs nanodots obtained in strain-relaxed epitaxial Si[sub 0.5]Ge[sub 0.5] alloy layers after arsenic implantation and rapid thermal annealing. GeAs dots of two different average sizes around 15 and 55 nm are found after high temperature rapid thermal annealing. The larger dots are of elliptical shape and located at the surface region; they are distributed preferably along <110> directions which correlates well with the observed cross-hatch pattern. The origin of the bimodal precipitate distribution as well as of the long-range ordering effect of the GeAs nanodots is discussed in terms of strain-induced nucleation and diffusion-limited growth. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The surface morphology and bulk structure of both strained (0.01≤x≤0.053) and strain-free Si1-xSnx (x=0.055) layers grown by molecular beam epitaxy on (001) Si and Si1-yGey substrates have been investigated by atomic force and transmission electron microscopy. The surfaces of all Si1-xSnx layers were found to have a mazelike structure composed of rectangular features faceted primarily by {113} planes. Transmission electron microscopy images of the alloys revealed columnar structures originating at the interface between the alloys and the substrates. The formation of the observed surface morphologies and the columnar structure is attributed to the surface-growth processes modified by the Sn atoms as compared to the growth of pure Si. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]