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We have used Raman spectroscopy, transmission electron microscopy, x-ray diffraction, and x-ray photoemission spectroscopy to investigate strain relaxation mechanism of Si(0.22)Ge(0.78) heteroepitaxial layer deposited on Si substrates in tensile, neutral, and compressive strain conditions. The three regimes have been obtained by interposing between the SiGe layer and the substrate a fully relaxed Ge layer, a partially relaxed Ge layer, or growing directly the alloy on Si. We found that the deposition of a Ge buffer layer prior to the growth of the SiGe is very promising in view of the realization of thin virtual substrates on silicon to be used for the deposition of strain-controlled high Ge content SiGe alloys. We demonstrate that this is mainly due to the strain relaxation mechanism in the Ge layer occurring via insertion of pure edge 90 degrees misfit dislocations (MDs) and to the confinement of threading arms in to the Ge layer due to a second MD network formed at the SiGe/Ge heterointerface

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The structural defects in two-dimensional transition metal dichalcogenides, including point defects, dislocations and grain boundaries, are scarcely considered regarding their potential to manipulate the electrical and optical properties of this class of materials, notwithstanding the significant advances already made. Indeed, impurities and vacancies may influence the exciton population, create disorder-induced localization, as well as modify the electrical behaviour of the material. Here we report on the experimental evidence, confirmed by ab initio calculations, that sulfur vacancies give rise to a novel near-infrared emission peak around 0.75 eV in exfoliated MoS2 flakes. In addition, we demonstrate an excess of sulfur vacancies at the flake's edges by means of cathodoluminescence mapping, aberration-corrected transmission electron microscopy imaging and electron energy loss analyses. Moreover, we show that ripplocations, extended line defects peculiar to this material, broaden and redshift the MoS2 indirect bandgap emission.

A model to compute the strain relaxation rate in InxGa1−xAs/GaAs single layers has been tested on several compositionally graded buffer layers. The existence of a critical elastic energy has been assumed as a criterion for the generation of new misfit dislocations. The surface strain accuracy results are within 2.5×10−4. The influence of different grading laws and growth conditions on residual strain, threading dislocation density, misfit dislocation confinement, and surface morphology has been studied. The probability of dislocation interaction and work hardening has been shown to strongly influence the mobility and the generation rate of the dislocations. Optimization of the growth conditions removes residual strain asymmetries and smoothes the surface roughness.

In the last decade thermophotovoltaic (TPV) generator has gained an increasing attention as cogeneration system for the distributed generation sector. Nevertheless, these systems are not fully developed and studied: several aspects need to be further investigated and completely understood.\ud The aim of this study is to give a complete overview and the status of the art of thermophotovoltaic generation considering both the research developments and the experiences field. More in details, in this study, the characteristics of a TPV generator are analyzed with a particular attention to the physical relationships which govern the behavior of its main components. Moreover, the current technologies regarding the combustor, the emitter, the optical filter and the photovoltaic cells are investigated by taking into account both the role of each component and also their integration in the whole system. Finally, a critical review of the realized prototypes is presented and discussed

Electroreflectance study of effects of indium segregation in molecular-beam-epitaxy-grown InGaAs/GaAsTunneling microscopy and spectroscopy on cross sections of molecularbeamepitaxygrown (Al)GaAs multilayers J. Vac. Sci. Technol. B 9, 779 (1991); 10.1116/1.585510 dc and ac transport in molecularbeamepitaxygrown metal/ZnSe/GaAs heterojunction structures Summary Abstract: Molecularbeam epitaxial growth of (Al,Ga) As/GaAs heterostructures with interruption at interfaces InxGa l _ xAs/GaAs single heterostructures have been grown by molecular-beam epitaxy with different growing rates and In molar fractions. Indium composition, layer thickness, and residual strain have been measured mainly by Rutherford backscattering/ channeling spectrometry and the results on selected samples compared with the results of other techniques like Auger electron spectroscopy and single-and double-crystal x-ray diffraction.Cathodoluminescence, x-ray topography, transmission electron microscopy, and ion dechanneling have been employed to observe dislocations and to characterize their nature and density. While the onset of misfit dislocations has been found to agree with the predictions of the equilibrium theory, the strain release has been found to be much lower than predicted and the results are compared with the available metastability or nucleation models. Present results are in best agreement with nucleation models. Moreover, annealing experiments show that these heterostructures are at (or very dose to) thermodynamic equilibrium. 1975

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