Energy characteristics of excitons in structures based on InGaN alloys

Samples containing ultrathin InGaN layers that emit radiation in the spectral range from the ultraviolet to yellow region are studied. The samples are grown by metal-organic vapor-phase epitaxy. The Urbach energy, the localization energy of excitons, and the activation energy of charge carriers are determined to characterize radiative and nonradiative processes in the quantum dots and barriers of the structures. It is shown that these energy parameters are linearly dependent on the photon energy in the range from 3.05 to 2.12 eV. It is established that temperature variations in the emission intensity are due to the increase in the number of charge carriers thermally activated from the quantum wells into barriers as well as due to the enhancement of scattering of free excitons at defects.     

A study of differential models for hierarchical control systems via their discretization

We consider the general approach to studying differential models of hierarchical control systems. The model is considered over a finite time interval. Our approach is based on passing to the discrete counterpart of the model and, consequently, from functionals to objective functions in the criteria. We introduce the notion of Stakelberg equilibriums accounting for stable evolution requirements. The solution is then constructed with the method of Lagrange multipliers; in the general case, with imitational modeling. As an example, we consider a quality control system for river water and show the results.     

10 MeV Au ion irradiation effects in an MgO-HfO2 ceramic-ceramic (CERCER) composite

Room temperature ion irradiation damage studies were performed on a ceramic composite intended to emulate a dispersion nuclear fuel. The composite is composed of 90-mole% MgO and 10-mole% HfO₂. The as-synthesized composite was found to consist of Mg₂Hf₅O₁₂ (and some residual HfO₂) particles embedded in an MgO matrix. X-ray diffraction revealed that nearly all of the initial HfO₂ reacted with some MgO to form Mg₂Hf₅O₁₂. Ion irradiations were performed using 10 MeV Au³⁺ ions at room temperature over a fluence range of 5 × 10¹⁶-5 × 10²⁰ Au/m². Irradiated samples were characterized using both grazing incidence X-ray diffraction (GIXRD) and transmission electron microscopy (TEM), the latter using both selected-area electron diffraction (SAED) and micro-diffraction (μD) on samples prepared in cross-sectional geometry. Both GIXRD and TEM electron diffraction measurements on a specimen irradiated to a fluence of 5 × 10²⁰ Au/cm², revealed that the initial rhombohedral Mg₂Hf₅O₁₂ phase was transformed into a cubic-Mg₂Hf₅O₁₂ phase. Finally, it is important to note that at the highest ion fluence used in this investigation (5 × 10²⁰ Au/m²), both the MgO matrix and the Mg₂Hf₅O₁₂ second phase remained crystalline.     

Reverse bending effect on the texture, structure, and mechanical properties of sheet copper

The effect of reverse room-temperature bending on the crystallographic texture, metallographic structure, and mechanical properties of preliminarily rolled and annealed sheets of copper has been studied. It has been found that the type of the initial structure and the texture represented by the {001}??100?? recrystallization orientation, remains of the deformation texture {112}??111??, and twin orientations do not change; only the ratio of these orientations changes in the process of the reverse bending, which naturally leads to changes in the mechanical properties.     

Output characteristics of high-power low-voltage broadband traveling-wave tubes with helical and ring-rod slow-wave structures

The output characteristics of high-power low-voltage broadband traveling-wave tubes (TWTs) of the C-D band are presented. The decisive role of a continuous high-perveance electron beam provided by a sectoral electron gun is demonstrated. The main features of the TWT computation procedure are described and the results of comparison between calculated and experimental data are presented.     

Strain Mismatch Induced Tilted Heteroepitaxial (000l) Hexagonal ZnO Films on (001) Cubic Substrates

A novel strain mismatch induced tilted epitaxy method has been demonstrated for producing high quality (000l) hexagonal films on (001) cubic substrates. Highly oriented hexagonal (000l) ZnO films are grown on cubic (001) MgO substrates using Sm_0.28Zr_0.72O_{2? δ} (SZO) as a template. The large lattice mismatch of >13% between the obvious crystallographic matching directions of the template and substrate means that cube‐on‐cube epitaxy is energetically unfavorable, leading to growth instead of two high index, low energy compact planes, close to the {111} orientation. These planes give three different in‐plane orientations resulting from coincidence site lattice matching (12 in‐plane orientations in total) and provide a pseudo‐hexagonal symmetry surface for the ZnO to grow on. The texture of the ensuing (000l) ZnO layer is markedly improved over the template. The work opens up both a new avenue for growing technologically important hexagonal structures on a range of readily available, (001) cubic substrates, as well as showing that there are wide possibilities for heteroepitaxial growth of a range of dissimilar materials.