Rosa M de la Cruz

• PhD in Physics
• Professor at University Carlos III de Madrid

We investigate the effects of the geometrical sizes and surrounding media on the optical properties of a periodic square array of GaAs nanowires (NWs) as candidates for applications on photovoltaic solar cells as well as sensors. As filling media, different insulator materials such as PMMA, Polycarbonate, Polystyrene and PVP are considered in this...

We report the effects of radius-, length- and pitch-sizes on the optical reflectance of a periodic square array of GaAs nanowires embedded in epoxy. The simulated system is a multilayer array constituted by alternating layers of epoxy and an effective medium of GaAs nanowires embedded in epoxy. For both s- and p-polarizations, we observe an oscilla...

We report the optical response of a periodic square array of GaAs nanowires embedded in epoxy as a candidate for photovoltaic solar cells. The simulated system is a multilayer array constituted by alternating layers of epoxy and an effective medium constituted by GaAs nanowires arrays embedded in epoxy. To discuss the optical response, we investiga...

In the present paper we report the optical response of an ordered array of silver (Ag) nanoparticles (NPs) using the uniaxial LiNbO3 as a model case. We investigate the anisotropic effects on the effective dielectric tensor taking into account the charges interaction of particles. The Ag NPs dielectric function is described through a modified Drude...

The silver (Ag)-embedded lithium niobate (LiNbO3) composites are theoretically analyzed under the effective medium Maxwell-Garnett approximation to account on the optimal conditions through which such composites present negative epsilon conditions. The dielectric function of Ag nanoparticles (NPs) is described by Drude theory with an additional Lor...

The composite constituted by lithium niobate (LiNbO3) with silver (Ag) nanoparticles (NPs) is theoretically proposed as a candidate of a metamaterial with plausible photonics applications. We numerically evaluate the effective dielectric function (epsilon(eff)) of this composite by using Maxwell-Garnett (M-G) effective theory. The dielectric functi...

Achieving a negative dielectric constant at a single optical frequency ω, where the loss goes to zero, i.e., with Re (ε) < 0 and Im (ε) = 0, is of fundamental importance in nanophotonics. We address the dielectric function of exciton polaritons in a mixture of spherical II-VI semiconductor core-shell nanocrystals of type I (excitons are confined in...

We have investigated the phonons contribution in the infrared and visible optical properties in II–VI semiconductor nanoshells of type I. For this, we use Mie scattering theory by defining appropriate dielectric functions for the constitutive materials of the nanoshells. Indeed, for the core we have considered dielectric function taking into accoun...

By using Varshni's law, we have determined the temperature effects in the effective dielectric function of II–VI semiconductor nanocrystals distribution of type I. For each temperature, we have also used an extended Maxwell–Garnett theory to determine the effective dielectric function. We have taken into account the confinement of charge carriers b...

Optical properties of typical II-VI semiconductor coreshell nanostructures are investigated in a wide range of visible and near-infrared spectrum of light. Indeed, absorption, scattering and extinction coefficients are calculated in these nanostructures by using the scattering Mie theory in dipole approximation. To implement the calculations, Mie t...

We have obtained the lattice parameter profiles for Ge/Si (11n) and InAs/GaAs (11n) heterostructures using the elasticity continuum theory in the linear approximation. In our model we assume that a small fraction of the substrate participates in the heterostructures relaxation in the non-rigid approximation. Minimization of the free energy by the E...

Within the framework of the dielectric continuum (DC) model, we analyze the axial interface optical phonon modes in a double system of nanoshells. This system is constituted by two identical equidistant nanoshells which are embedded in an insulating medium. To illustrate our results, typical II-VI semiconductors are used as constitutive polar mater...

Within the framework of the elasticity continuum theory in the linear approximation we have obtained the lattice parameter profiles for Ge/Si(001) and InAs/GaAs(001) quantum dots. In our model we assume that a small fraction of the substrate participates in heterostructure relaxation in the non-rigid approximation. Minimization of the free energy b...

Within the dielectric continuum model, we calculate the interface phonons in multilayered spherical nanostructures. The effect of the alloying in the shell material, together with the change in the embedding medium are also analyzed. In all investigated heterostructures, the interface characteristics experiment a constantlike tendency at critical g...

Within the continuum elasticity theory, we investigate the substrate orientation effects on the Stranski–Krastanov (SK) growth mode and the band edges in InAs/GaAs nanostructures. Attending to the first part of the study, we estimate the transition thickness and the accumulated stress for substrate orientations (1 1 3) and (1 1 5) and we compare wi...

Within the framework of the continuum elasticity theory, we have investigated the substrate orientation effects on the Stranski-Krastanov growth mode in Ge/Si heterostructures. To do this, we have estimated the transition thickness and accumulated stress in Ge/Si(111) low-dimensional systems and we have compared these with the values obtained previ...

Within the framework of the continuum elasticity theory, we have characterized the Stranski–Krastanov mode in Ge/Si(0 0 1) self-assembled quantum dots by means of the transition thickness and the accumulated stress. The systems under investigation are pseudomorphic structures with a coherent behavior at the substrate/film interface. For the depende...

Within the framework of the standard dielectric continuum model (DCM), we have performed a theoretical study of interface (IF) phonon modes in III–V semiconductor self-assembled quantum dots (SAQDs). We model the SAQD as a truncated cone whose growth-axis is along the polar axis of the cone. Small and arbitrary polar angle approximations are used t...

An energetic balance between surface and elastic strain energies based in continuum elastic theory is applied to evaluate the transition thickness in InAs/GaAs (0 0 1) self-assembled quantum dots. The growth process follows a Stranski-Krastanov (S-K) pattern, where a two-three-dimensional transition is undertaken at the so-called transition thickne...

Positron lifetime experiments have been performed on as-grown samples which had been isochronally annealed up to 820 K and plastically deformed and these experiments yield a constant lifetime of 282+or-2 ps which is attributed to bulk positron states in InSe. Electron-irradiated samples exhibit a two-component spectrum, revealing the presence of po...

We report the interface and longitudinal-optical phonon modes in cylindrical quantum dots using the dielectric-continuum model. We also investigate the effect of the dot surrounding materials on both the top-surface optical (TSO) and the side-surface optical (SSO) phonon modes. We observe that the symmetric and antisymmetric TSO modes are cylinder-...

Positron lifetime and Doppler broadening measurements have been performed on the layered semiconductors GaS, GaSe and GaTe in the temperature range 8-320 K. The temperature dependences of the annihilation parameters in GaS and GaSe are analysed in terms of the thermal expansion coefficient of the lattice and a volume coefficient of the annihilation...

The enhancement of the electronic effective mass in GaAs/AlxGa1−xAs quantum wells is investigated within the framework of a 14-band k.p theory. In this theory, the bulk conduction band dispersion is expanded to fourth order in the wave vector, k, and the anisotropy and spin splitting effects are also included. The analytical expressions for the non...

The form factors of the electron–phonon interaction for GaAs/Ga1−xAlxAs single heterostructures have been evaluated using a finite height barrier. The calculations are performed within the extreme quantum limit approximation, assuming for the envelope electronic wavefunction a modified Fang–Howard wavefunction. Both types of long-wave phonons, long...

Within the framework of the dielectric continuum model, the interface phonon frequencies for spherical GaAs/AlxGa1-xAs quantum dots are obtained as functions of the alloy composition in the range x=0.2–1.0. By imposing electrostatic boundary conditions, the two interface phonon frequencies are calculated for the first three modes. The frequency beh...

Electron scattering by interface phonon modes in GaAs/AlAs quantum dots is investigated. The emission rates are calculated using an electron-phonon interaction Hamiltonian derived in the framework of the dielectric continuum model. The effect of the embedding material AlAs on the electron relaxation by interface phonons is analyzed by comparing the...

The process of solid-state amorphization induced by high-energy ball milling of binary mixture of crystalline elemental powders is investigated by positron lifetime spectroscopy along with X-ray diffraction and differential scanning calorimetry. The experiments are performed on compacted samples of powders mechanically alloyed over a wide compositi...

The role of interface phonon modes in electron relaxation processes in a GaAs quantum dot which is free standing in vacuum is investigated. For this, the electron scattering rates by interface phonons are calculated using an electron-phonon interaction Hamiltonian derived in the framework of the dielectric continuum model. By comparing the relaxati...

The process of mechanical alloying and amorphization of Ni-Zr powders is investigated by positron lifetime spectroscopy, X-ray diffraction and differential scanning calorimetry. The short-lived component of the lifetime spectra is composition and milling-time dependent. The second lifetime component, found during the initial stages of the milling p...

Positron lifetime and microhardness measurements have been performed on untreated, thermal-aged, neutron-irradiated, and postirradiation-annealed samples of reactor pressure vessel steels with the purpose of investigating the mechanisms of irradiation-induced hardening and recovery of the mechanical properties in these materials. The positron lifet...

A generalization of the three-dimensional Fröhlich hamiltonian for a polar semiconductor is presented which describes the interaction between charge carriers of a zero-dimensional electron gas and longitudinal optical (LO) phonon modes confined in three spatial dimensions. This hamiltonian is used to calculate the scattering rate of electrons by LO...

Positron-lifetime and transport measurements have been performed on neutron-transmutation-doped InSe in order to investigate the nature and recovery characteristics of the recoil-induced damage. The results show that the recovery is accomplished in two stages. The first, in the temperature interval 325

Positron annihilation measurements in neutron-irradiated MgO crystals show that the positron lifetime is shorter than in as-grown crystals, suggesting that most of the defects produced by neutron irradiations are positively charged. The concentration of the neutral anion vacancy (possibly also the neutral anion divacancy) is estimated to be no more...

Positron lifetime measurements have been performed on as-grown and electron-irradiated single crystals of the wide-gap compound semiconductors ZnS and ZnSe. The temperature dependence of the positron lifetime in as-grown samples reveals the presence of certain grown-in defects which act as shallow positron traps. No evidence for positron trapping a...

The electrical properties, optical-absorption characteristics, and positron-annihilation lifetimes have been determined for nominally pure ZnO single crystals that were thermochemically reduced in Zn vapor in the temperature range between 1100 and 1500 K. Electrical-conductivity and Hall-effect measurements indicate that donors are produced as a re...

The positron annihilation characteristics of the layered semiconductor InSe have been investigated. No evidence for low temperature positron trapping is found in as-grown and heavily deformed InSe. The temperature dependence of the S-parameter in these sample exhibits an increase rate in good agreement with the linear expansion coefficient along th...

The sintering process of CuO under isochronal annealing has been investigated by positron lifetime spectroscopy. A long-lived component of 370±20 psec, observed in as-pressed samples and samples annealed atT⩽900 K, has been attributed to continuous channels along three-grain junctions. A short-lived component of about 224 psec is attributed to posi...

Thermochemical reduction of hydrogen-laden MgO single crystals at {ital T}{approx}2400 K results in a large concentration of both hydride (H{sup {minus}}) ions and anion vacancies ({gt}10{sup 24} m{sup {minus}3}). Positron-lifetime experiments of these crystals provide evidence for bound positronium hydride states also referred to as ({ital e}{sup...

The effect of the anodic conversion in silicon single crystals is investigated by positron lifetime measurements. Anodization at constant current induces changes in the positron lifetime spectrum of monocrystalline silicon samples. It is found that theses changes are primarily dependent on the silicon resistivity. The annihilation parameter behavio...

One of the factors which greatly influences the Stranski-Krastanov (S-K) growth mode in low-dimensional strained heterostructures is the substrate orientation. A change in the Miller indices of the substrate allows to control the strain relaxation in the heteroepitaxial systems and consequently induces modifications in the onset of the S-K growth m...

The strain relaxation in typical lattice-mismatched heterostructures such as InAs/GaAs is the classical mechanism advanced to describe the self-organization of quantum dots (QDs) in the Stranski-Krastanov (SK) growth mode. On the other hand, the strain induced in these lattice-mismatched heterostructures modifies their band structures, that determi...