Abstract: The properties of a capacitive HF discharge with growing nanoparticles are studied with the use of kinetic PIC-MCC simulation. At the initial stage of growth, the nanoparticles are shown to be localized at the interface between the near-electrode layer and quasi-neutral plasma, where the rate of ionization by electron impact has the maximum value. At the beginning of formation of particles, plasma parameters change rapidly and a transition between the capacitive and spatial discharge burning modes is observed for a certain critical size of the particles. If the growth of the dust particles continues, their distribution over the discharge becomes more uniform and the steady-state parameters of the gas-discharge plasma hardly change.

Abstract: The flexoelectric and electronic properties of zig-zag graphene nanoribbons are explored under mechanical bending using state of the art first principles calculations. A linear dependence of the bending induced out of plane polarization on the applied strain gradient is found. The inferior flexoelectric properties of graphene nanoribbons can be improved by more than two orders of magnitude by hydrogen and fluorine functionalization (CH and CF nanoribbons). A large out of plane flexoelectric effect is predicted for CF nanoribbons. The origin of this enhancement lies in the electro-negativity difference between carbon and fluorine atoms, which breaks the out of plane charge symmetry even for a small strain gradient. The flexoelectric effect can be further improved by co-functionalization with hydrogen and fluorine (CHF Janus-type nanoribbon), where a spontaneous out of plane dipole moment is formed even for flat nanoribbons. We also find that bending can control the charge localization of valence band maxima and therefore enables the tuning of the hole effective masses and band gaps. These results present an important advance towards the understanding of flexoelectric and electronic properties of hydrogen and fluorine functionalized graphene nanoribbons, which can have important implications for flexible electronic applications. (C) 2020 Elsevier Ltd. All rights reserved.

Abstract: The energy spectrum and density of states of graphene bilayer superlattices (SLs) are evaluated. We take into account doping and/or gating of the layers as well as tunnel coupling between them. In addition, we evaluate the transmission through such SLs and through single or double barriers. The transmission exhibits a strong dependence on the direction of the incident wave vector.

Abstract: Within the framework of the nonlinear Ginzburg-Landau theory we investigate how the vortex expulsion and penetration fields are influenced by the presence of surface defects in superconducting disks with zero thickness. We studied different types and sizes of defects. (C) 2004 Elsevier B.V. All rights reserved.

Abstract: Multiply connected mesoscopic: superconductors are considered within the framework of the nonlinear Ginzburg-Landau theory. The two coupled nonlinear equations are solved numerically and we investigated the properties of a superconducting ring, two concentric rings, and an asymmetric ring. We find that (i) for a mesoscopic superconducting ring the flux through the hole is not quantized, (ii) two concentric mesoscopic superconducting rings are magnetically coupled and the interaction energy increases with increasing sample thickness, and (iii) in asymmetric rings, a stationary phase slip state is predicted.

Abstract: A far-infrared absorption study of electrons in lightly-doped GaAs/Al0.3Ga0.7As superlattices is presented. Both weakly and strongly coupled superlattices are investigated, and the difference between intersubband transitions and transitions between extended minibands is demonstrated. At low temperatures, the absorption spectra are dominated by donor transitions. The 1s-2p(z) transition, which is intimately related to the intersubband transition, is observed. All experimental data are compared to an envelope function calculation for the miniband structure and a variational calculation for the donor energies. Excellent agreement between experiment and theory is achieved.

Abstract: A variational calculation of the ground state of a neutral exciton and of positively and negatively charged excitons (trions) in a single quantum well is presented. We study the dependence of the correlation energy and of the binding energy on the well width and on the hole mass. Our results are compared with previous theoretical results and with available experimental data.

Abstract: The electronic structure of the conduction and valence bands of a quantum ring containing a layer inside the ring opening is modeled This structure (nanocup) consists of a GaAs nanodisk (the cup s bottom) and a GaAs nanoring (the cup s rim) which encircles the disk The whole system is embedded in an (Al Ga)As matrix and its shape resembles realistic ring structures grown by the droplet epitaxy technique The conduction-band states in the structure are modeled by the single-band effective-mass theory while the 4-band Luttinger-Kohn model is adopted to compute the valence-band states We analyze how the electronic structure of the nanocup evolves from the one of a quantum ring when the size of either the nanodisk or the nanoring is changed For that purpose (1) the width of the ring (2) the disk radius and (3) the disk height are separately varied For dimensions typical for experimentally realized structures we find that the electron wavefunctions are mainly localized inside the ring even when the thickness of the Inner layer is 90% of the ring thickness These calculations indicate that topological phenomena like the excitonic Aharonov-Bohm effect are negligibly affected by the presence of the layer inside the ring (C) 2010 Elsevier Ltd All rights reserved