Electronic and spectral properties of Ge1-xSnx quantum dots: an atomistic study

In this paper, we study theoretically the electron and spectral properties of Ge1-xSnx systems, including alloys, cubic- and spherical quantum dots. The single-particle electron and hole states are calculated within the sp3d5s* tight-binding approach and used in further modeling of the optical properties. We systematically study the interplay of Sn-driven indirect-direct band-gap transition and the quantum confinement effect in systems of reduced dimensionality. We demonstrate the regime of sizes and composition, where the ground state in Ge1-xSnx quantum dot is optically active. Finally, we calculate absorbance spectra in experimentally-relevant colloidal quantum dots and demonstrate a satisfactory agreement with experimental data

Electron Beam-Induced Reduction of Cuprite

Cu-based materials are used in various industries, such as electronics, power generation, and catalysis. In particular, monolayered cuprous oxide (Cu2O) has potential applications in solar cells owing to its favorable electronic and magnetic properties. Atomically thin Cu2O samples derived from bulk cuprite were characterized by high-resolution transmission electron microscopy (HRTEM). Two voltages, 80 kV and 300 kV, were explored for in situ observations of the samples. The optimum electron beam parameters (300 kV, low-current beam) were used to prevent beam damage. The growth of novel crystal structures, identified as Cu, was observed in the samples exposed to isopropanol (IPA) and high temperatures. It is proposed that the exposure of the copper (I) oxide samples to IPA and temperature causes material nucleation, whereas the consequent exposure via e-beams generated from the electron beam promotes the growth of the nanosized Cu crystals

Investigation of the epitaxial growth of AIIIBV-N heterostructures for solar cell applications

The InGaAsN/GaAs heterostructures proposed in 1996 by Kondow et al. have been successfully used in telecom laser constructions on GaAs substrate. Additionally, the InGaAsN with a bandgap of 1 eV are lattice matched to both GaAs and Ge for the nitrogen and indium contents of around 3 % and 9 %, respectively. These features make this semiconductor an ideal candidate for high-efficiency multijunction solar cells (MJSCs) based on the Ge/InGaAsN/GaAs/InGaP structure. The growth technology of the GaAsN alloy-based diluted nitrides is very difficult because of the large miscibility gap between GaAs and GaN. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2097

High-pressure Raman scattering in bulk HfS2: comparison of density functional theory methods in layered MS2 compounds (M = Hf, Mo) under compression

We report high-pressure Raman-scattering measurements on the transition-metal dichalcogenide (TMDC) compound HfS2. The aim of this work is twofold: (i) to investigate the high-pressure behavior of the zone-center optical phonon modes of HfS2 and experimentally determine the linear pressure coefficients and mode Grüneisen parameters of this material; (ii) to test the validity of different density functional theory (DFT) approaches in order to predict the lattice-dynamical properties of HfS2 under pressure. For this purpose, the experimental results are compared with the results of DFT calculations performed with different functionals, with and without Van der Waals (vdW) interaction. We find that DFT calculations within the generalized gradient approximation (GGA) properly describe the high-pressure lattice dynamics of HfS2 when vdW interactions are taken into account. In contrast, we show that DFT within the local density approximation (LDA), which is widely used to predict structural and vibrational properties at ambient conditions in 2D compounds, fails to reproduce the behavior of HfS2 under compression. Similar conclusions are reached in the case of MoS2. This suggests that large errors may be introduced if the compressibility and Grüneisen parameters of bulk TMDCs are calculated with bare DFT-LDA. Therefore, the validity of different approaches to calculate the structural and vibrational properties of bulk and few-layered vdW materials under compression should be carefully assessed

Optical markers of magnetic phase transition in CrSBr

Here, we investigate the role of the interlayer magnetic ordering of CrSBr in the framework of $\textit{ab initio}$ calculations and by using optical spectroscopy techniques. These combined studies allow us to unambiguously determine the nature of the optical transitions. In particular, photoreflectance measurements, sensitive to the direct transitions, have been carried out for the first time. We have demonstrated that optically induced band-to-band transitions visible in optical measurement are remarkably well assigned to the band structure by the momentum matrix elements and energy differences for the magnetic ground state (A-AFM). In addition, our study reveals significant differences in electronic properties for two different interlayer magnetic phases. When the magnetic ordering of A-AFM to FM is changed, the crucial modification of the band structure reflected in the direct-to-indirect band gap transition and the significant splitting of the conduction bands along the $\Gamma-Z$ direction are obtained. In addition, Raman measurements demonstrate a splitting between the in-plane modes $B^2_{2g}$/$B^2_{3g}$, which is temperature dependent and can be assigned to different interlayer magnetic states, corroborated by the DFT+U study. Moreover, the $B^2_{2g}$ mode has not been experimentally observed before. Finally, our results point out the origin of interlayer magnetism, which can be attributed to electronic rather than structural properties. Our results reveal a new approach for tuning the optical and electronic properties of van der Waals magnets by controlling the interlayer magnetic ordering in adjacent layers.Comment: 33 pages, 15 figure