Ab initio study of the adsorption of antimony and arsenic on the Si(110) surface

We have performed first principles total energy calculations to investigate the adsorption of Sb and As adatoms on the Si(110) surface using a (2 x 3) supercell. The energetics and atomic structures have been investigated in four atomic configurations. One structure is obtained by placing 1/3 of a monolayer (ML) of Sb (As) atoms on the Si(110) surface. The other three geometries are obtained by depositing 1 ML of Sb (As) atoms on the surface. In the first case the structure is formed by four trimers, in the second case the geometry is formed by zigzag atomic chains and in the third case the structure contains "microfacets". The energetics results of the Sb adsorption show that for low coverage the tetrahedrons formed by the adsorption of 1/3 ML is the most stable configuration, while in the monolayer region the zigzag atomic chain is the most stable structure. However, the total energies of the trimer and microfacet structures are slightly higher, indicating that under some conditions, they may be formed. In an experimental report it has been suggested that the adsorption of 1/3 and 1 ML of Sb corresponds to the low and high coverage in the experiments of Zotov et al. [A. V. Zotov, V. G. Lifshifts, and A. N. Demidchik, Surf. Sci. 274, L583 (1992)]. On the other hand, our results of the As adsorption show that for low coverage, the tetrahedrons in the adsorption of 1/3 ML also give the most stable configuration. However, at the 1 ML coverage, a structure formed by microfacets is the most stable structure, in agreement with previous results. (C) 2010 Elsevier B.V. All rights reserved

Solution to the excitonic problem of an electron in a quantum wire and a hole in a perpendicular 2D quantum layer

We calculate the states of an exciton formed by an electron confined in a ID quantum wire (QW) and a hole confined in a 2D quantum layer (QL) perpendicular to the QW. The effective potential can be exactly calculated in the particular case where the confinement thicknesses are the same for the QW and QL. This effective potential can be used to calculate the exciton states for arbitrary confinement thicknesses, but here we show that in the limit of vanishing thickness the solution of our equation is very similar to the 3D bulk exciton equations, and therefore we can use these 3D exciton solutions as a basis for our system in a quantum perturbative approach

Transit times for electromagnetic waves in metallic layered systems

Metallic multilayered arrays are considered, in the local Drude theory, to investigate transit times of electromagnetic waves and the fast response mediated by plasmon polaritons. The transit times are calculated for frequencies corresponding to band gaps in the dispersion relation of periodic layered media. At these frequencies, and depending on the thickness of the structure, a fast response or even a superluminal effect is predicted. This effect is more evident near the plasmon polariton resonances. Moreover, the time delay is also affected by the surface plasmon coupling between the metallic layers. The metallic superlattices are described according to the Drude theory. (C) 2000 Published by Elsevier Science B.V. All rights reserved

Wannier-Mott excitons formed by electrons in a quantum wire and holes in a perpendicular quantum layer

We analyze Wannier-Mott excitons in which the electrons are constrained in one-dimensional quantum wires and the holes in two-dimensional quantum layers perpendicular to the wires. The resulting three-dimensional exciton Schrodinger equation in the laboratory frame of reference is solved in terms of the common 3D exciton states in the center of mass frame. (C) 2002 Elsevier Science B.V. All rights reserved

Electron energy-loss spectroscopy on the surface of conducting superlattices in the presence of plasma waves

We present calculations for the inelastic scattering of electrons by the surface of binary conductor-conductor periodic superlattices described by local and nonlocal models. The conducting layers consist of metals or highly doped semiconductors and we include their spatial dispersion through the presence of longitudinal plasmons described by a hydrodynamic model. These modes manifest themselves as a series of peaks in the electron-energy-loss spectroscopy spectrum superimposed on the main structure due to the excitation of two coupled surface-plasmon bands. These peaks depend upon the nature of the first layer and are sensitive to the first few layers

Optical response of resonator induced plasmon filters: Nanometric diatomic structures

We investigate the optical response of plasmon filters, which are composed of a diatomic chain of metallic nanoclusters along which a resonator, composed of one or two metallic nanoclusters, is coupled vertically. Taking into account the resonator, we show that the transmission amplitude T of the electromagnetic radiation may display dips when the geometrical parameters are chosen properly. The presence of a resonator composed of one metallic nanocluster yields a dip at the cluster resonance frequency. When the resonator is composed of two nanoclusters, then if the nanoclusters are of the same material, two dips emerge as a consequence of the splitting of the dip of the one-nanocluster resonator. If the resonator is of two different materials, then we obtain two dips near the resonance frequencies of the nanoclusters. These dips appear when the separations between nanoclusters are properly adjusted. Such a device may be used to transfer directionally the electromagnetic radiation. In the limit of equal atomic nanoclusters we reproduce the monoatomic chain results (C) 2010 Elsevier Ltd. All rights reserve

Bulk anisotropic excitons in type-II semiconductors built with 1D and 2D low-dimensional structures

We used a simple variational approach to account for the difference in the electron and hole effective masses in Wannier-Mott excitons in type-II semiconducting heterostructures in which the electron is constrained in an one-dimensional quantum wire (1DQW) and the hole is in a two-dimensional quantum layer (2DQL) perpendicular to the wire or viceversa. The resulting Schrodinger equation is similar to that of a 3D bulk exciton because the number of free (nonconfined) variables is thre