bluuebunny/crossref_metadata_2025_split huggingface dataset:
Phonon spectrum of compact ceramics: two‐dimensional ordered model
Authors: Salamatov E. I. 
Published: February 2007

AbstractThe low‐frequency range of the phonon spectrum of an ordered two‐dimensional composite, modeling compact nanoceramics is theoretically investigated by the finite‐difference time‐domain method. The necessary conditions for the complete gap to arise have been determined. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Peculiar band gap structure of graphene nanoribbons
Authors: Ezawa Motohiko 
Published: February 2007

AbstractGraphene nanoribbons are quasi‐one‐dimensional meterials with finite width. Characterizing a wide class of nanoribbons by edge shape and width, we make a systematic analysis of their electronic properties. The band gap structure of nanoribbons is shown to exhibit a valley structure with stream‐like sequences of metallic or almost metallic nanoribbons. Among them, all zigzag nanoribbons are metallic, and armchair nanoribbons are metallic by period of 3. We find that these stream‐like sequences correspond to equi‐width curves, and that the band gap of chiral and armchair nanoribbons oscillate as a function of the width. Furthermore a possible application of nanoribbons to nanoelectronics is discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
GaN ballistic negative‐differential‐conductivity diode for potential THz applications
Authors: Dyson A. , Ridley B. K. , Aslan B. , Cha H. Y. , Chen X. , Schaff W. J. , Spencer M. G. , Eastman L. F. 
Published: February 2007

AbstractWe present details of the development of a GaN ballistic diode designed with THz applications in mind. Parallel theoretical and experimental analysis has shown that negative‐differential‐resistance (NDR) can only be achieved when hot electrons are injected into the drift region, contact and spreading resistances must be minimized in order to maximize the field in the drift layer. NDR remains achievable even in the presence of collision dominated transport or when transport is space‐charge limited. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spin‐dependent tunneling in modulated structures of (Ga,Mn)As
Authors: Sankowski P. , Kacman P. , Majewski J. A. , Dietl T. 
Published: February 2007

AbstractThe spin‐dependent tunneling in layered structures based on (Ga,Mn)As, in particular the dependence of the tunneling current on magnetization direction, is studied theoretically. To capture the complexity of the tunneling effects in these semiconductor devices we combine a multi‐orbital tight‐binding approach with Landauer‐Büttiker formalism. This theory allows us to reproduce the tunneling anisotropic magnetoresistance effects observed in (Ga,Mn)As/GaAs Esaki‐Zener diodes. The model is also used to describe the in‐plane and out‐of‐plane anisotropy of tunneling magnetoresistance in (Ga,Mn)As‐based trilayers. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spin currents in AC‐driven double quantum dots
Authors: Sánchez Rafael , Platero Gloria , Aguado Ramón , Cota Ernesto 
Published: February 2007

AbstractWe analyze spin transport through an AC driven double quantum dot device which acts as a spin pump and spin filter. The AC field brings into resonance electronic states in both quantum dots, producing electron pumping. The AC potential affects not only the inter‐dot tunneling but also the tunneling through the contacts by photon‐assisted tunneling proccesses involving photon absorption and emission through the barrier contacts. These processes produce additional resonances in the current characteristics which flows in opposite direction for each spin polarization contribution to the electronic current. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
N‐N pair effects on GaInNAs semiconductor optical amplifiers
Authors: Alexandropoulos D. , Vogiatzis N. , Qiu Y. N. , Pozo J. , Syvridis D. , Rorison J. M. 
Published: February 2007

AbstractWe explore the effects of N‐N pairs on the amplifying properties of GaInNAs based Semiconductor Optical Amplifiers. The bandstructure of GaInNAs is calculated with the 3 band anti‐crossing model to account for the N‐N pairs for the conduction band and k·p theory for the valence bands. For the calculation of the GaInNAs amplifier properties we adopt a multi‐sectioning approach to the rate equation that accounts for amplified spontaneous emission. Based on these we discuss the merits of N‐N pairs for GaInNAs semiconductor optical amplifiers. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Raman and TEM studies of Ge nanocrystal formation in SiOx:Ge/SiOx multilayers
Authors: Dana A. , Ağan S. , Tokay S. , Aydınlı A. , Finstad T. G. 
Published: February 2007

AbstractAlternating germanosilicate‐siliconoxide layers of 10‐30 nm thickness were grown on Si substrates by plasma enhanced chemically vapor deposition (PECVD). The compositions of the grown films were determined by X‐ray photoelectron spectroscopy measurements. The films were annealed at temperatures varying from 670 to 1000 °C for 5 to 45 minutes under nitrogen atmosphere. High resolution cross section TEM images, electron diffraction and electron energy‐loss spectroscopy as well as energy‐dispersive X‐ray analysis (EDAX) data confirm presence of Ge nanocrystals in each layer. The effect of annealing on the Ge nanocrystal formation in multilayers was investigated by Raman spectroscopy and Transmission Electron Microscopy (TEM). As the annealing temperature is raised to 850 °C, single layer of Ge nanocrystals observed at lower annealing temperatures is transformed into a double layer with the smaller sized nanocrystals closer to the substrate SiO2 interface. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spin dynamics through homogeneous magnetic superlattices
Authors: Cardoso J. L. , Pereyra P. 
Published: February 2007

AbstractWe study the spin dynamics of a 2DEG moving across a magnetic superlattice. We describe the spin transitions induced by sectionally homogeneous tilted magnetic fields and the spatial evolution of spin‐1/2 wave functions: amplitude and phase, in terms of the tilting angle, the Fermi energy and the magnetic field strengths. Clear signatures of coherent spin mixing and coherent spin flipping processes are shown. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structural and optical properties of InP quantum dots grown on GaAs (001)
Authors: de Godoy M. P. F. , Nakaema M. K. K. , Lopes J. M. J. , Morschbacher M. J. , Iikawa F. , Brasil M. J. S. P. , Magalhães‐Paniago R. , Bortoleto J. R. R. , Cotta M. A. 
Published: February 2007

AbstractWe present structural and optical properties of type‐II self‐assembled InP/GaAs quantum dots using different techniques. The results reveal that the uncapped InP dots present an efficient optical emission and are partially relaxed: strain relaxation increases with the amount of InP deposited. The photoluminescence spectra show two optical emission bands associated to the quantum dots, in agreement with the bi‐modal dot‐height distribution observed by atomic force microscopy. We observed distinct photoluminescence results for uncapped and capped samples, which are mainly attributed to surface state and strain relaxation effects. A remarkable result is the large blue shift of the optical emission band from uncapped sample as compared to capped one for increasing excitation intensities. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Coherent control of an asymmetric semiconductor quantum well structure
Authors: Dynes James F. , Paspalakis Emmanuel 
Published: February 2007

AbstractWe study coherent control of an asymmetric semiconductor quantum well by simultaneous application of a laser field and its second harmonic. The relative phase of the applied laser fields is externally altered. The electron population and the small signal absorption and dispersion spectra of a weak probe field propagating through such a quantum well structure are computed and are found to be strongly phase dependent. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Surface acoustic wave mediated effects in a coupled multi quantum well
Authors: Ebbecke J. , Pierz K. 
Published: February 2007

AbstractA coupled multi‐quantum well GaAs/AlGaAs heterostructure has been doped in such a way that the widest quantum well is composed of a conductive layer of a two‐dimensional electron gas whereas the narrower quantum wells are free of mobile charge carriers at low temperatures. Photoluminescence measurements exhibit a broad signal of the coupled quantum wells and a surface acoustic wave has been used to excite the electronic system. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effects of growth conditions on morphologies of the ZnO nanostructures
Authors: Erol A. , Arikan M. C. 
Published: February 2007

AbstractNano‐scaled zinc oxide combs/ribbons, nanorods, nanorods with sharp needle‐like tips and hexagonal‐shaped nanoparticles have been synthesized by using vapor liquid solid (VLS) growth technique under different growth conditions. Morphologies of the obtained nanostructures were examined by using X‐Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy Dispersive Spectroscopy (EDS) techniques. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photoluminescence of nanocrystals embedded in oxide matrices
Authors: Estrada C. , Gonzalez J. A. , Kunold A. , Reyes‐Esqueda J. A. , Pereyra P. 
Published: February 2007

AbstractWe used the theory of finite periodic systems to explain the photoluminescence spectra dependence on the average diameter of nanocrystals embedded in oxide matrices. Because of the broad matrix band gap, the photoluminescence response is basically determined by isolated nanocrystals and sequences of a few of them. With this model we were able to reproduce the shape and displacement of the experimentally observed photoluminescence spectra. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Creation and detection of spin‐polarized current using quantum point contact with spin‐orbit interaction
Authors: Yokouchi Hiroto , Eto Mikio 
Published: February 2007

AbstractWe have proposed that quantum point contacts (QPCs) can be a useful tool for producing spin‐polarized currents in the presence of Rashba spin‐orbit (SO) interaction [J. Phys. Soc. Jpn. 74, 1934 (2005)]. No magnetic field is required. When the conductance through a QPC is quantized in units of 2e2/h, the current is spin‐polarized in the transverse direction. This spin polarization, which can be larger than 50% in InGaAs heterostructures, is elucidated using the S‐matrix formalism. We also examine transport properties of a QPC connected to a ferromagnetic lead and show how to detect the spin‐polarized current from the QPC. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Polarization dependence of intraband transitions in QDIPs
Authors: Gebhard T. , Souza P. L. , Schrey F. F. , Strasser G. , Unterrainer K. , Pires M. P. , Landi S. M. , Villas‐Boas J. M. , Studart N. 
Published: February 2007

AbstractPhotocurrent measurements were carried out on doped and undoped InAs/InGaAs/InP quantum dot structures. A photocurrent peak is observed at 5 μm for the undoped sample, which is identified as a bound to bound transition. Additional peaks are detected for the doped structure, which, with the help of a simple 1D model, are tentatively identified as transitions from a dot bound state to a quantum well state. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electron scattering through a quantum dot
Authors: Castelano L. K. , Hai G.‐Q. , Lee M.‐T. 
Published: February 2007

AbstractWe study the electron scattering through a quantum dot using quantum scattering theory. The elastic, inelastic, and spin‐flip scattering cross‐sections are obtained by solving the Lippmann‐Schwinger equations within the multichannel scattering model. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Broadband staircase quantum well infrared photodetector: working in long wavelength infrared range (LWIR)
Authors: Hostut M. , Kartal D. , Ergun Y. , Sokmen İ. 
Published: February 2007

AbstractWe present a theoretical investigation of a staircase‐like quantum well infrared photodetector (QWIP). It detects wavelength between 7.6 μm and 13.5 μm range at an applied electric field of F = 1.9x104 V/cm at 77 K. The dark current density was found to be around 2x10–7 A/cm2 at operating bias, which is lower than the conventional QWIPs in the literature. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spin‐polarized current in a magnetic barrier structure under microwave radiation
Authors: Seo K. C. , Ihm G. , Lee S. J. 
Published: February 2007

AbstractWe have proposed a magnetic barrier structure with dc and ac electric fields between the barriers. We have found a significant amount of spin polarization and resonant structure in the transmission as a function of energy. Sets of Fano resonance peaks are clearly observed only for spin‐down electrons while the inelastic tunneling processes associated with absorption/emission of photons are observed for both spin electrons. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Persistent photoconductivity effect on weak localization in AlxGa1–xAsySb1–y/InAs quantum wells
Authors: Ishida S. , Fujimoto A. , Takeda K. , Shibasaki I. 
Published: February 2007

AbstractWeak‐field magnetoconductance (MC) caused by the weak localization (WL) in AlxGa1–xAsySb1–y/InAs quantum wells (QWs) has been studied by means of tuning the carrier density n via the positive and negative persistent photoconductivity effects in order to explore the origin of spin‐orbit interaction (SOI). We have found the weak antilocalization (WAL) in extremely weak magnetic fields developing with increasing n. The MC has been fitted by taking account of the spin‐Zeeman effect on the SOI arising from the spin splitting in asymmetric systems. The SO field (Bso) inferred has been found to be almost independent of n, thereby confirming the dominant role of the Rashba field as the cause of SOI in our InAs QWs. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A study on the formation of MnFe2O4 nano‐powder by coprecipitation method
Authors: Azadmanjiri J. , Salehani H. K. 
Published: February 2007

AbstractThe microstructure and magnetic properties of manganese ferrite nano powder obtained from MnCl2·4H2O, (NH4)2Fe(SO4)2·6H2O, FeCl3·6H2O and NaOH by coprecipitation and aging in isothermal static conditions at temperature lower than 370 K, has been investigated by X‐ray diffraction (XRD), Transmission electron micrograph (TEM) and vibrating sample magnetometer (VSM). The results reveal the influence of the temperature on the particle size distribution as well as on the structure and composition of the ferrite phase. The magnetic properties of the ferrite are also presented. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The polarizability and the photoionization cross‐section under the external fields for donor impurities in quantum well‐wire
Authors: Koksal M. , Kasapoglu E. , Sari H. , Sokmen I. 
Published: February 2007

AbstractIn this study, we have calculated the donor impurity binding energy, donor impurity related photoionization cross‐section and polarizability in symmetric GaAs/Ga1–x Alx As quantum well‐wire as a function of the impurity positions, dimensions of the structures and external electric and magnetic field, the calculations were performed within the effective mass approximation, using a variational method. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical properties of copper and silver nanowires grown in a nanoporous alumina template
Authors: Green S. , Cortes A. , Riveros G. , Gómez H. , Dalchiele E. A. , Marotti R. E. 
Published: February 2007

AbstractThe optical properties of metallic nanowires (NW) grown in a dielectric template are investigated. The metallic NW of copper or of silver were grown into the nanoporous structure of commercially available alumina membranes. The optical reflectance of the metallodielectric samples prepared at different conditions are compared to each other and to unfilled alumina membranes. A simple model based on the Bruggeman approximation can be used to understand the results and to compare them to the bulk material. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Surface strain and hexagonal/cubic polymorphism in InGaN epitaxy: first‐principles study
Authors: Nakayama T. , Takei Y. 
Published: February 2007

AbstractThe energetics and the growth dynamics of InGaN layers on strained InN substrates are studied using the first‐principles calculations. It is shown that the diffusion of adsorbed atoms on the surface is suppressed when the grown layers receive the tensile stress from the substrate.and the bonding between adsorbed and surface atoms is weakened. The present results indicate that the surface strain is one of relevant factors to promote InGaN hexagonal/cubic polymorphism in epitaxy. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Microscopic theory for intersubband spontaneous emission
Authors: Pereira M. F. , Wacker A. 
Published: February 2007

AbstractThe amplified spontaneous emission spectra of quantum‐cascade laser structures is computed with a Keldysh Green's functions theory. We show that the emission spectra are sharpened in comparison to gain spectra due to wave guide propagation. In addition the different dependence on level occupation causes moderate differences between gain and emission peak positions. Our fit‐parameter‐free theory is valid in ranges of strong nonequilibrium, where fit‐parameters do not even exist. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Detection of terahertz radiation in a slit‐grating gated field‐effect transistor
Authors: Aizin G. , Popov V. , Polischuk O. 
Published: February 2007

AbstractWe calculate the spectra of the resonant terahertz photoresponse associated with higher‐order plasmon resonances in a grating‐gated field‐effect transistor with two‐dimensional electron channel. The dependence of the photoresponse on both the dc bias current and the grating slit width is studied. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Enhancement of electron drift velocity in a quantum well by confinement of polar optical phonons
Authors: Požela Juras , Požela Karolis , Jucienė Vida 
Published: February 2007

AbstractNew approaches to decrease the electron–polar optical (PO) phonon scattering rate in double heterostructures by using phonon barriers (reflective to PO phonons and transparent for electrons) are proposed. Twofold decrease of the electron–PO phonon scattering rate in the AlGaAs/GaAs/AlGaAs quantum well by inserting the InAs phonon barriers is achieved. The enhancement of high electric field drift velocity in the AlGaAs/GaAs/AlGaAs heterostructure with the inserted one monolayer InAs phonon barriers compared with that heterostructure without barriers is observed experimentally. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic and electronic properties of transition metal nitride strained layers
Authors: Ribeiro M. , Scolfaro L. M. R. , Teles L. K. , Marques M. , Ferreira L. G. 
Published: February 2007

AbstractWe present a theoretical study with ab initio techniques on magnetic and electronic properties of 3d transition metal mononitrides. We perform the calculations in the wurtzite (w) and the zincblende (zb) structures, and find the tendency of all zb mononitrides to become half‐metallic (HM) under hydrostatic strain. MnN, CrN, and VN become HM with integer magnetic moments of 4, 3 and 2μB, respectively. CrN shows ferromagnetism (FM) throughout the range of our lattice constant calculations, while VN is FM beyond the lattice constant of 4.65 Å. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Control of polarization of polariton lasers
Authors: Glazov M. M. , Shelykh I. A. , Malpuech G. , Laussy F. , Kavokin K. V. , Kavokin A. V. 
Published: February 2007

AbstractThe polarization of semiconductor microcavities with embedded quantum wells (QWs) in the regime of polariton lasing is studied theoretically. We expect the emitted light to be linearly polarized, with the degree of polarization as well as its direction determined by the asymmetry of QW interfaces or localization of excitons on the anisotropic islands of QW width fluctuations. The ways to control the direction of polarization using external electric field are analyzed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigation of built‐in electric fields in AlGaN/GaN heterostructures grown on misoriented 4H‐SiC substrate by contactless electroreflectance
Authors: Syperek M. , Motyka M. , Kudrawiec R. , Misiewicz J. , Rudzinski M. , Hageman P. R. , Larsen P. K. 
Published: February 2007

AbstractRoom temperature contactless electroreflectance technique was used to investigate the built‐in electric field in AlGaN/GaN heterostructure grown by metaloorganic chemical vapour deposition on [0001] 4H‐SiC substrate. Two heterostructures have been studied: one grown with a misorientation angle (8 degrees toward [11‐20] crystallographic direction of the substrate) and second without misorientation angle. For both heterostructures strong AlGaN‐related resonance with Franz‐Keldysh oscillation (FKO) has been observed. The built‐in electric field in the AlGaN layer was extracted from the FKO period [0.26 MV/cm and 0.47 MV/cm for samples without and with misorientation, respectively]. It has been concluded that the substrate orientation angle has a great impact on the built‐in electric field and charge distribution across the AlGaN/GaN structure. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photoluminescence temperature dependence of doped parabolic quantum wells
Authors: Tabata A. , Martins M. R. , Oliveira J. B. B. , Lamas T. E. , Duarte C. A. , Quivy A. A. , Gusev G. M. 
Published: February 2007

AbstractParabolic quantum wells (PQWs) have been studied by temperature dependent photoluminescence (PL). Two kind of samples have been studied. Concerning the undoped sample, the dominant luminescences were the bulk GaAs and the fundamental transition of the PQW. The evolution on temperature of the energy position of both PL emissions follows the well known Varshing formula. For the doped samples strong radiative recombination of the electron gas with photogenerated holes was observed. At low temperature strong Fermi level enhancement occurs in the luminescence as a result of the multi‐electron‐hole scattering, which is smear out increasing the temperature. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Theoretical investigations on the energy relaxation in twodimensional GaN systems
Authors: Tas M. , Tanatar B. 
Published: February 2007

AbstractWe theoretically study the energy relaxation of hot electrons via LO‐phonon emission in two‐dimensional GaN systems. We employ a model in which electrons and the lattice are in equilibrium separately, and the effective electron temperature is much larger than the lattice temperature. We include the dynamical screening of electrons, electron‐phonon interactions reduced phonon self‐energy correction, the hot‐phonon, and the.nite‐size effects. The power loss to acoustic phonons is also considered. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ballistic effect and optical properties of Si nanocrystallite structures
Authors: Torchynska T. V. 
Published: February 2007

AbstractThe purpose of this work is to clarify the type of corresponding radiative transitions and the PL mechanism in the big silicon nano‐crystallites with the size from the range of 10‐150 nm, which is higher than an exciton Bohr radius (≤5 nm) in corresponding bulk crystal. Photoluminescence in this type of Si nanocrystals is analyzed from the point of view of new concept based on the hot carrier ballistic transport role in the excitation of oxide‐related defects at the Si/SiOx interface. The role of hot carrier ballistic transport in the modification of photocurrent spectra of Si NC device structures is discussed as well. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)