Influence of Electromechanical Effects and Wetting Layers on Band Structures of AIN/GaN Quantum Dots and Spin Control

In a series of recent papers we demonstrated that coupled electromechanical effects can lead to pronounced contributions in band structure calculations of low dimensional semiconductor nanostructures LDSNs such as quantum dots QDs , wires, and even wells. Some such effects are essentially nonlinear. Both strain and piezoelectric effects have been used as tuning parameters for the optical response of LDSNs in photonics, band gap engineering, and other applications. However, the influence of spin orbit effects in presence of external magnetic field on single and vertically coupled QD has been largely neglected in the literature. The electron spin splitting terms which are coupled to the magnetic field through the Pauli spin matrix in these QDs become important in the design of optoelectronic devices as well as in tailoring properties of QDs in other applications areas. At the same time, single and vertically stacked QDs are coupled with electromagnetic and mechanical fields which become increasingly important in many applications of LDSN-based systems, in particular, where spin splitting energy is important. These externally applied electric and magnetic fields as well as the separation between the vertically coupled QDs can be used as tuning parameters. Indeed, as electromagnetic and elastic effects are often significant in LDSNs, it is reasonable to expect that the externally applied magnetic fields oriented along a direction perpendicular to the plane of two-dimensional electron gas in the QDs may also be used as a tuning parameter in the application of light emitting diodes, logic devices, for example, OR gates, AND gates and others. In this paper, by using the fully coupled model of electroelasticity, we analyze the influence of these effects on optoelectronic properties of QDs. Results are reported for III–V type semiconductors with a major focus given to AlN/GaN based QD systems

First Principles Molecular Dynamics Study of CdS Nanostructure Temperature-Dependent Phase Stability

First principles molecular dynamics simulations are used to determine the relative stability of wurtzite, graphitic, and rocksalt phases of the CdS nanostructure at various temperatures. Our results indicate that in the temperature range from 300 to 450 K, the phase stability sequence for the CdS nanostructure is rocksalt, wurtzite, and graphitic phases. The same situation holds for bulk CdS crystals under high pressure and 0 K. Our work also demonstrates that although the temperature can affect the total energy of the CdS nanostructure, it cannot change its phase stability sequence in the temperature range studied in this letter

Accounting for the Effect of Internal Viscosity in Dumbbell Models for Polymeric Fluids and Relaxation of DNA

The coarse-graining approach is one of the most important mod- eling methods in research of long-chain polymers such as DNA molecules. The dumbbell model is a simple but e±cient way to describe the behavior of polymers in solutions. In this paper, the dumbbell model with internal viscosity (IV) for concentrated polymeric liquids is analyzed for the steady-state and time-dependent elongational flow and steady-state shear °ow. In the elongational flow case, by analyzing the governing ordinary di®erential equations the contribution of the IV to the stress tensor is discussed for fluids subjected to a sudden elongational jerk. In the shear °ow case, the governing stochastic differential equation of the finitely extensible nonlinear elastic dumbbell model is solved numerically. For this case, the extensions of DNA molecules for different shear rates are analyzed, and the comparison with the experimental data is carried out to estimate the contribution of the e®ect of internal viscosity

Dynamics of Shape Memory Alloys Patches with Mechanically Induced Transformations

A mathematical model is constructed for the modelling of two di- mensional thermo-mechanical behavior of shape memory alloy patches. The model is constructed on the basis of a modified Landau-Ginzburg theory and includes the coupling effect between thermal and mechanical fields. The free energy functional for the model is exemplified for the square to rectangular transformations. The model, based on nonlinear coupled partial differential equations, is reduced to a system of differential-algebraic equations and the backward differentiation methodology is used for its numerical analysis. Computational experiments with representative distributed mechanical loadings are carried out for patches of different sizes to analyze thermo-mechanical waves, coupling effects, and 2D phase transformations