16 research outputs found
Alpha scattering and capture reactions in the A = 7 system at low energies
Differential cross sections for He- scattering were measured in
the energy range up to 3 MeV. These data together with other available
experimental results for He and H scattering were
analyzed in the framework of the optical model using double-folded potentials.
The optical potentials obtained were used to calculate the astrophysical
S-factors of the capture reactions HeBe and
HLi, and the branching ratios for the transitions into
the two final Be and Li bound states, respectively. For
HeBe excellent agreement between calculated and
experimental data is obtained. For HLi a value
has been found which is a factor of about 1.5 larger than the adopted value.
For both capture reactions a similar branching ratio of has been obtained.Comment: submitted to Phys.Rev.C, 34 pages, figures available from one of the
authors, LaTeX with RevTeX, IK-TUW-Preprint 930540
Tight-binding study of the influence of the strain on the electronic properties of InAs/GaAs quantum dots
We present an atomistic investigation of the influence of strain on the
electronic properties of quantum dots (QD's) within the empirical tight-binding (ETB) model with interactions up to 2nd nearest neighbors
and spin-orbit coupling. Results for the model system of capped pyramid-shaped
InAs QD's in GaAs, with supercells containing atoms are presented and
compared with previous empirical pseudopotential results. The good agreement
shows that ETB is a reliable alternative for an atomistic treatment. The strain
is incorporated through the atomistic valence force field model. The ETB
treatment allows for the effects of bond length and bond angle deviations from
the ideal InAs and GaAs zincblende structure to be selectively removed from the
electronic-structure calculation, giving quantitative information on the
importance of strain effects on the bound state energies and on the physical
origin of the spatial elongation of the wave functions. Effects of dot-dot
coupling have also been examined to determine the relative weight of both
strain field and wave function overlap.Comment: 22 pages, 7 figures, submitted to Phys. Rev. B (in press) In the
latest version, added Figs. 3 and 4, modified Fig. 5, Tables I and II,.and
added new reference
Texture evolution during crystallization of thin amorphous films
Stress and energy distributions for crystallization of a thin amorphous film are calculated by means of 3D finite element method. The changes in energy are caused by elastic strain induced by different thermal expansion of the film and the substrate and by different mass densities of the crystal and the surrounding amorphous matrix. The calculations were performed for cubic crystal structure and for disc shaped crystal. Three crystal orientations 001 , 011 and 111 were considered. Based on strain energy considerations the 001 orientation of crystals with respect to the film plane is energetically more favorable than the 011 and 111 orientations. Interfacial and surface energies are certain to play a part in these effects as wel
Elastic strain energy study of directional coarsening of gamma precipitates in single crystal superalloys a 3D finite element analysis
On the microstructure of AlxGa1-xN layers grown on 6H-SiC(0001) substrates
The microstructural as well as the compositional evolution of AlxGa1–xN (x~0.15) layers grown on 6H-SiC(0001) substrates by metalorganic vapor phase epitaxy were analyzed by atomic force microscopy, X-ray diffraction, and transmission electron microscopy in conjunction with energy dispersive X-ray spectroscopy. The epitaxial growth was followed from the early nucleation stage on the substrate to the development of a thick bulk-like film. Phase separation was observed during the early stage of growth; that is, islands of two different shapes formed whose Al mole fractions were about 0.035 and 0.18, respectively. The AlxGa1–xN coalesced at a film thickness of about 100 nm with the domains of varying Al content being fully coherent. Such domains were not only found at the film/substrate interface but also further away from the interface. They were arranged in layers that were shifted laterally against each other; that is, Al-deficient domains formed on top of Al-rich domains and vice versa. Increasing the film thickness to more than 100 nm finally led to a homogeneous Al distribution. Finite-element simulations were performed to calculate the strain distribution in these inhomogeneous systems. They allowed the experimental results to be explained by an interplay of strain minimization in the epitaxial film and growth kinetics