bluuebunny/crossref_metadata_2025 huggingface dataset:
InAs/InP quantum dots (QD): from fundamental understanding to coupled QD 1.55 µm laser applications
Authors: Cornet C. , Hayne M. , Schliwa A. , Doré F. , Even J. , Bimberg D. , Moshchalkov V. V. , Loualiche S.
Published: February 2007

We report a brief overview of recent research developments on InAs/InP quantum dots (QDs). Eight‐band k·p calculations are performed on single InAs/InP QDs, and the impact of substrate orientation ((311)B or (100)) on electronic and optical properties is studied. The quaternary alloy InGaAsP capping is studied by magneto‐photoluminescence. It is found to induce a better electronic confinement than InP. It is then demonstrated that high QDs density can be reached on such a system, leading to lateral coupling between dots. Calculations and (magnetophoto‐) (photo‐) (electro‐) luminescence experiments are used to demonstrate that the lateral coupling leads to miniband effects, and to a better charge carrier redistribution between QDs for laser applications. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Exciton binding energy in type II quantum dots
Authors: Gomes P. F. , Godoy M. P. F. , Veloso A. B. , Nakaema M. K. K. , Iikawa F. , Brasil M. J. S. P. , Bortoleto J. R. R. , Cotta M. A. , Madureira J. R.
Published: February 2007

We investigated the optical properties of self‐assembled InP/GaAs quantum dots using continuous‐wave and time‐resolved photoluminescence spectroscopy. The thermal activation energy, which is directly related to the exciton binding energy in this system, was obtained by photoluminescence measurements as a function of temperature. We obtained thermal activation energies of 6–9 meV for undoped quantum dots and 13 meV for the modulation‐doped sample. Those values are in good agreement with calculated results. The dots presented a recombination time of ∼ 0.8–1.1 ns, which is surprisingly small for a type‐II system. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dilute magnetic bulk GaN semiconductor and nanostructures
Authors: Ferguson I. T.
Published: February 2007

Ga1–xMnxN and Ga1–xFexN thin films and nanostructures were grown by metalorganic chemical vapor deposition. High resolution X‐ray diffraction studies demonstrate that the material is high quality single phase similar in quality and lattice parameter to unalloyed GaN. The as‐grown epitaxial films exhibit ferromagnetic hysteresis at room temperature as measured by SQUID magnetometry; the strength of the observed volume magnetization is almost an order stronger in similarly grown Mn‐doped samples relative to Fe‐doped samples. Raman spectroscopy revealed no significant strain introduced by the transition metal incorporation and a low free carrier concentration, and the most prominent additional mode in Mn‐doped GaN is attributed to vacancy‐related local vibrational modes of the GaN host lattice. A novel growth method has been developed to produce GaN‐based nanostructures using a two‐step process (GaN deposition followed by an activation step) at low growth temperatures (<850 °C) and V‐III ratios (<30). GaMnN nanostructures were grown by introducing Mn to GaN flows under optimal conditions for the formation of nanostructure without the need of an activation step. Manganese icorporation has the tangential benefit that Mn acts as an anti‐surfactant, and promotes the low‐temperature nucleation of these nanostructures. In addition, experiments have been conducted in which Fe was incorporated into GaN nanostructures at 800 °C, and room temperature ferromagnetic behavior of GaFeN nanostructures was observed. Atomic force microscopy measurements revealed that Fe, like Mn, affected the surface morphology of the nanostructures by reducing the nanostructure size. These nanostructures showed a systematic variation in coercive field and saturation magnetization with Fe incorporation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic electrodes in the onion state for spin injection into semiconductors
Authors: Gallo P. , Lombez L. , Bournel A. , Amand T. , Camps T. , Marie X. , Havard E. , Fontaine C. , Arnoult A.
Published: February 2007

We present electrodes in the onion state for spin injection into semiconductors. The electrodes are in the so called “onion state” which allows them to be self‐aligned, and not to generate any stray‐field. The application discussed here is the spin Field Effect Transistor. It is demonstrated that in order to match the in‐plane polarization of the injected carriers, one has to use a quantum wire grown on a (110) surface as a channel. The channel length for the spins to fully switch is calculated to be the order of 150 nm for a gate electric field of 150 kV/cm to 300 kV/cm. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Excitonic polaron in InAs/GaAs self‐assembled quantum dot molecules
Authors: Adames M. , Bedoya M. , Camacho B. A. S.
Published: February 2007

We study the excitonic polaron formation in two InAs/GaAs coupled quantum dots. We calculate the coupling between the exciton and the LO‐phonon states by using the Fröhlich Hamiltonian, from which we determine the excitonic polaron states varying the quantum dot separation. We study the dependence on the excitonic polaron formation with the coupling between the dots. Polaron formation strongly modifies the energy spectra due to the appearance of several anticrossings in the excited states. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Monte Carlo calculation of electron transport properties of GaxIn1–xN
Authors: Akarsu M. , Aydoğu S. , Özbaş Ö.
Published: February 2007

The Monte Carlo method is used to simulate electron transport for electric field strength up to 500 kV/cm in GaxIn1–xN for composition x range from 0.0 to 1.0. Calculations of the electron steady‐state drift velocity, average energy and valley occupancy are examined at a temperature of 300 K. Scattering mechanisms considered in the simulations are ionized impurity, polar optical phonon, acoustic phonon, non‐polar optical phonon, intervalley, dislocation and alloy scatterings. Effects of the alloy scatterings on the drift velocity are examined. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effect of substrate temperature on some of the optical parameters of CuInS2 films
Authors: Aksay S. , Altıokka B.
Published: February 2007

Polycrystalline CuInS2 films have been grown by spray pyrolysis method at different substrate temperatures, a simple method which can produce low cost and highly absorbing samples. Optical characteristics of the CuInS2 films have been analyzed using spectrophotometer in the wavelength range of 400–900 nm. The absorption spectra of the films showed that this compound is a direct band gap material and gap values varied between 1.51–1.80 eV, depending on the substrate temperatures. The refractive index n, extinction coefficient k and dielectric constants ε1 and ε2 were also discussed and calculated as a function of wavelength λ. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Raman analysis of the quantum dot morphology
Authors: Marques G. E. , Alcalde A. M. , Ribeiro A. A. , Dantas N. O. , Trallero Giner C.
Published: February 2007

A theoretical and experimental study of the spatial con.nement of phonons in ternary CdSx Se1–x nanocrystals embedded in a glass matrix is reported. We discuss the morphological characteristics of the nanocrystals by analyzing the dependence of surface phonon modes on the geometrical parameters. The calculated frequencies are compared with experimental Raman spectra. A good theoretical and experimental correlation for CdS‐like and CdSe‐like surface optical modes is observed. Raman selection rules and their connection with the nature of the surface optical phonons is discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Linear excitonic absorption under an external electric field in quantum dot molecules
Authors: Bedoya M. , Camacho A. S.
Published: February 2007

A study of the excitonic states in artificial molecules set up of two vertically coupled double quantum dots is presented. The electron and hole eigenstates are calculated for the quantum dot molecule. In particular, the coupling effect of the barrier and the consequent tunneling is analyzed following the evolution of the absorption spectra as function of the distance between the two dots. On the other hand, the role of the Coulomb correlation between the confined particles is also studied. We present results of relevant interactions in these systems and discuss how the optical properties of double quantum dots are affected by the interdot coupling, by the geometry of the dots and by an applied electric field. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Coherent effects in coupled resonator optical waveguides
Authors: Yannopapas Vassilios , Kanaki Aggeliki , Boviatsis John , Paspalakis Emmanuel
Published: February 2007

We analyze the spontaneous emission and the probe absorption‐dispersion spectra of Γ‐type atomic systems embedded in a coupled resonator optical waveguide (CROW), where one of the atomic transitions decays spontaneously in a CROW and the other decays spontaneously in free space vacuum. We first show that double dark lines can appear in this system. We also show that the atoms become transparent at two different frequencies of a probe laser field coupled to the free space transition. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structural, elastic and electronic properties of AlN: A first principles study
Authors: Çiftci Y. Ö. , Çolakoğlu K. , Deligöz E.
Published: February 2007

The brief results of the first‐principles ground‐state total energy calculations for aliminium nitrat (AlN) in zincblende and rocksalt structures are presented. Structural, elastic, and electronic calculations are performed using the SIESTA method with norm‐conserving pseudopotentials. The obtained results are compared with the available experimental and other theoretical data, and the agreement is, generally, quite good. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Raman scattering and SEM study of bio‐conjugated core‐shell CdSe/ZnS quantum dots
Authors: Torchynska T. V. , Diaz Cano A. , Dybiec M. , Ostapenko S. , Morales Rodrigez M. , Jiménez‐Sandoval S. , Vorobiev Y. , Phelan C. , Zajac A. , Zhukov T. , Sellers T.
Published: February 2007

Core‐shell CdSe/ZnS quantum dots are promising as bio‐luminescent markers: being conjugated to bio molecules (proteins), they serve as luminescence tags in antigen‐antibody biochemical reaction. This presents a possibility to detect, for example, the variation of the protein biomarkers to promote the early cancer diagnosis. We studied the effect of bio molecules conjugated to QDs using Raman scattering spectra, and found that in some cases the conjugation leads to noticeable variation of these spectra, so that the detection of bio molecules could be done more accurately. An explanation of the effect is proposed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Surface photovoltage spectroscopy of interdiffused InAs/InGaAlAs quantum dashes‐in‐well structure
Authors: Donchev V. , Ivanov Ts. , Wang Y. , Djie H. S. , Ooi B. S.
Published: February 2007

We report room temperature surface photovoltage (SPV) spectroscopy studies of both as‐grown and interdiffused InAs quantum dash (QD)–in–InAlGaAs quantum well (QW) structures grown by molecular beam epitaxy on (100) InP substrates. The interdiffusion is achieved by means of rapid thermal annealing at 800 ºC for 30 s. The SPV spectra reveal step‐like structures related to the optical absorption in the QDs, QWs, InGaAlAs separate carrier confinement layer, InAlAs lower cladding layer and InP substrate. The annealing results in a high‐energy shift of these spectral structures. The shift is attributed to the group‐III atoms intermixing from the thermal induced interdiffusion across the heterointerfaces. The effect of interdiffusion is larger for the elements with larger surface‐to‐volume ratio (QDs and QWs). The blue shift of the QD transition is observed also in the photoluminescence spectra. The results contribute to the optimization of the technological procedure for QD bandgap tuning via the interdiffusion technique. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Quantum qubit measurement by a quantum point contact with a quantum Langevin equation approach
Authors: Dong Bing , Horing N. J. M. , Lei X. L. , Cui H. L.
Published: February 2007

We employ a microscopic quantum Heisenberg‐Langevin equation approach to establish a set of quantum Bloch equations for a two‐level system (coupled quantum dots) capacitively coupled to a quantum point contact (QPC). The resulting Bloch equations facilitate our analysis of qubit relaxation and decoherence in coupled quantum dots induced by measurement processes at arbitrary bias‐voltage and temperature. We also examine the noise spectrum of the meter output current for a symmetric qubit. These results help resolve a recent debate about a quantum oscillation peak in the noise spectrum. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hole subband structure in single and double p‐type δ ‐doped diamond quantum wells
Authors: Rodríguez‐Vargas I. , Duque C. A. , Mora‐Ramos M. E. , Velasco V. R.
Published: February 2007

Heavy, light, and split‐off hole states in single and double p‐δ ‐doped diamond quantum wells are studied with the use of a 6 × 6 k·p model. The effective mass Hamiltonian is solved using a local density Thomas‐Fermi‐Dirac approximation for the description of the band bending pro.le. The features of the valence band spectrum are brie.y discussed in both cases. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Acceptor and donor impurity‐related optical absorption spectra in double quantum wells: electric field and hydrostatic pressure effects
Authors: Morales A. L. , Raigoza N. , Duque C. A.
Published: February 2007

The hydrostatic pressure and applied electric field dependencies on the shallow‐impurity related optical absorption spectra in GaAs‐Ga1–x Alx As double quantum wells are calculated. Results are obtained for different well and barrier widths. A pressure dependent blue‐shift and electric field dependent read‐shift in the absorption spectra have been described for two different cases of symmetrical double quantum well systems. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparative study of the hydrostatic pressure and temperature effects on the impurity‐related optical properties in single and double GaAs–Ga1–xAlxAs quantum wells
Authors: Odhiambo Oyoko H. , Porras‐Montenegro N. , López S. Y. , Duque C. A.
Published: February 2007

Using a variational technique within the effective mass approximation we have carried out a comparative study of the effect of hydrostatic pressure and temperature on the shallow‐impurity related optical absorption spectra in GaAs‐Ga1–x Alx As single and double quantum wells. The results show a pressure dependent read‐shift and a temperature dependent blue‐shift in the optical absorption spectra. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effects of humidity and acetone on the optical and electrical properties of porous silicon nanostructures
Authors: Erdamar O. , Bilen B. , Skarlatos Y. , Aktas G. , Inci M. N.
Published: February 2007

Porous silicon (P‐Si) is a suitable material for applications in gas sensors, biomedical sensors and optical sensors. In this work, the effects of humidity and acetone on the optical and electrical properties of porous silicon nanostructures, produced by two different methods, are studied. The first method is stain etching of silicon wafers by evaporation of hydrogen fluoride (HF) based etchant. The second method is the electrochemical anodization of silicon wafers at low current densities in HF‐based solutions under white light. Electrical conduction mechanism of P‐Si samples is examined through AC and DC measurements. It is observed that the I‐V response of the samples shows a rectifying behaviour that is dependent on the ambient relative humidity (rh). AC measurements show that such samples are quite capacitive and this behaviour shows a very little dependence on the relative humidity. Photoluminescence (PL) spectroscopy measurements are performed with pumping the samples with laser wavelengths of 313.8 nm and 365.6 nm. The PL peak position is observed between 600‐650 nm, depending on the sample preparation conditions. The intensity of the luminescence decreases by time and the peak wavelength makes a red‐shift due to oxidation. Photoluminescence spectroscopy measurements are also repeated after exposing the samples to water and acetone. It is observed that water decreases the luminescence intensity very little and causes a slight red‐shift while acetone decreases the intensity more and causes no important shift in the peak wavelength. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical simulation of spin‐qubit operation in coupled quantum dots
Authors: Goto Daisuke , Eto Mikio
Published: February 2007

Electronic states and spin operation in coupled quantum dots are numerically studied, considering realistic shape of quantum dots and electron‐electron interaction. (i) We evaluate the spin coupling J between two electron spins, as a function of magnetic field perpendicular to the quantum dots. We observe a transition from antiferromagnetic coupling (J > 0) to ferromagnetic coupling (J < 0) at magnetic field of a few Tesla. The spin coupling is hardly influenced by the size difference between the quantum dots if the energy levels are matched. (ii) We simulate SWAP gate operations by calculating the time development of two electron spins. We show that a sudden change of tunnel barrier may result in the gate errors. The spin exchange is incomplete in the presence of strong spin‐orbit interaction in InGaAs. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cluster expansion failings when applied to semiconductor superlattices
Authors: Ferreira L. G. , Marques M. , Teles L. K.
Published: February 2007

Cluster expansions (CE), by dealing only with short‐range interactions, become inadequate when the interaction in the alloy is of long range. The classical example is the Madelung interaction (electrostatic energy) which, by decaying slowly with distance (1/r) cannot be described with any precision by CEs. Fortunately, in the case of semiconductors, charge neutrality is attained after a few atoms so that no 1/r term propagates far into the lattice. There are other long‐range interactions, the strain energy due to alloying with different atomic sizes (1/r3), for instance, but this not a more important difficulty to CE than other interactions (the screened Coulomb, the exclusion principle, etc), as it will be shortly seen. In the case of semiconductors, an important test for CEs is how well they can perform with superlattices. This problem was studied before, at a time when the CE techniques were not so well developed. In what follows we show the results of several different CE applications to the wurtzite‐based Ga1–x Alx N alloy system and to a model of strain energy, paying special attention to the superlattices and the special quasirandom structures SQS (A. Zunger, S.‐H. Wei, L.G. Ferreira and J.E. Bernard, Phys. Rev. Lett 65, 353 (1990)). (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electron tunneling/scattering through a QPC saddle potential in crossed electric and magnetic fields
Authors: Fessatidis V. , Horing N. J. M. , Sabeeh K. , Yar A. , Glasser M. L.
Published: February 2007

Electron transmission through a quantum point contact (QPC) in the presence of both electric and magnetic fields is examined. The QPC is modeled as a saddle potential. To start, we derive the relevant Green's function including the effects of arbitrarily time‐dependent electric and constant magnetic fields using Schwinger's operator equation of motion approach. We then apply it to determine transmission of the electron guiding center through the QPC in constant electric and magnetic fields. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of carriers on magnetization relaxation in (Cd,Mn)Te quantum wells
Authors: Goryca M. , Ferrand D. , Kossacki P. , Nawrocki M. , Pacuski W. , Maslana W. , Tatarenko S. , Wojtowicz T. , Karczewski G. , Cibert J.
Published: February 2007

The relaxation of the magnetization after a short pulse of magnetic field in n‐doped and p‐doped (Cd,Mn)Te quantum wells is determined from the giant Zeeman shift of the photoluminescence and transmission lines. This technique allows us to investigate the magnetization dynamics in zero field. In n‐doped samples the magnetization relaxation is found to be faster than 20 ns. In case of p‐doped samples two components of relaxation are observed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magneto‐quantum transport in AlxGa1–xAsySb1–y/InAs quantum wells
Authors: Ishida S. , Fujimoto A. , Tamiya S. , Oto K. , Okamoto A. , Shibasaki I.
Published: February 2007

Magneto‐quantum transport properties in AlxGa1–xAsySb1–y/InAs deep quantum wells (QWs) with different well width (Lw = 15 and 50 nm) have been studied both in low and high magnetic fields. The low‐field magnetoconductance has been explained in the light of the two‐dimensional weak‐localization theory taking account of the effect of Zeeman splitting on spin‐orbit scattering of electrons. Analysis of Quantum Hall effect (QHE) in high‐field region for Lw = 50 nm indicates the existence of a small number of holes only partially participating with the QHE, suggesting that our QW is a type‐II hetero‐structure. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Examination of the optical transmission through metallic nano‐apertures
Authors: Kim Y. C. , Choi S. S. , Joo M. , Shresta S. , Suwal O. , Park M. J. , Kim D. W.
Published: February 2007

There have been tremendous interests about the near‐field optical effect through a sub‐wavelength size metallic aperture. In this report, the computational experiments using the finite‐difference time‐domain (FDTD) method has been performed to examine the optical transmission intensity through the small apertures. In the case that the aperture size is very large compared with the wavelength of the light, the diffracted angle is small and the perpendicular component of the propagation vector is greater than the parallel component of the propagation vector. With decreasing the aperture diameter, the diffraction angle becomes greater and the parallel component of the propagation vector becomes greater. For the aperture diameter smaller than the wavelength of the incident light, the conventional diffraction formula no longer becomes valid. The FDTD simulations are performed to obtain the light intensity distribution transmitted through the various diameters of the apertures. In addition, the FDTD simulation is also carried out to examine the characteristics of the apertures on double layer metallic plate structure. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A theoretical investigation of carrier and optical mode confinement in GaInNAs QWs on GaAs and InP substrates
Authors: Gönül B. , Köksal K. , Bakır E.
Published: February 2007

Both carrier and optical mode confinements are the basic ingredients while designing the semiconductor quantum well lasers. The former strongly depends on the band offsets of the heterostructure and the latter is mainly associated with the difference in the refractive index between the wave guiding core and the cladding layers. It is known that refractive index strongly depends on the direct band gap of the semiconductor material and the band gap of the III‐N‐V semiconductor layer can be engineered by means of adding nitrogen into InGaAs. We investigate, in this work, the refractive indices and the corresponding optical confinement factors of the proposed III‐N‐V laser material systems on GaAs and InP substrates. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Exciton spin dynamics in ZnO epilayers
Authors: Lagarde D. , Lombez L. , Balocchi A. , Renucci P. , Carrère H. , Amand T. , Marie X. , Mei Z. X. , Du X. L. , Xue Q. K.
Published: February 2007

We used time‐resolved optical orientation experiments to study the low temperature spin dynamics of a ZnO epilayer. The sample shows a circular polarisation of the donor‐bound exciton of 11% with a decay time of 275 ps. A very narrow spectral dependence of the initial polarisation and a rapid decrease of the polarisation decay time with temperature are also observed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical properties of nanoporous Al2O3 obtained by aluminium anodization
Authors: Green S. , Badán J. A. , Gilles M. , Cortes A. , Riveros G. , Ramírez D. , Gómez H. , Quagliata E. , Dalchiele E. A. , Marotti R. E.
Published: February 2007

The optical properties of nanoporous alumina (Al2O3) prepared by electrochemical anodization of aluminum foils are studied. The samples show an ordered array of nanometric sized pores. Their reflectance spectra show an absorption edge in the UV that shifts into the visible with anodization temperature. A strong photoluminescence (PL) in the blue‐green spectral range is also shown. The PL spectra shift in the same direction as the reflectance. The PL spectra were also measured at low temperatures. The results are best interpreted assigning the PL to oxygen vacancies. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electroless nickel deposition onto silicon surfaces for micro and nanoelectronics applications and microtechnology processes
Authors: Marques A. E. B. , Santos Filho S. G. , Martini S.
Published: February 2007

We studied and characterized the processes of electroless nickel deposition in order to use it in microelectronics and microtechnology. We perform electroless nickel deposition on silicon surfaces with acid solution on palladium preactivated surfaces as well as alkaline solution without palladium preactivation. Electroless deposition was also performed on aluminum surfaces, deposited by evaporation onto silicon oxide. MOS capacitors were also fabricated to perform electrical characterizations of the structure (nickel‐aluminium‐oxide‐silicon) using capacitance‐voltage plots (C‐V curves). In addition, we also presented the use of electroless nickel deposition for chemical sensors which were fabricated using conventional microelectronics techniques. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mesoscopic Fano effect in an Aharonov‐Bohm interferometer Coulomb‐coupled to a nearby quantum dot
Authors: Ţolea M. , Moldoveanu V. , Tanatar B.
Published: February 2007

Motivated by the pionieering experiments of Buks et al. [Nature 391, 871 (1998)] we investigate the visibility of the Fano effect in a single‐dot Aharonov‐Bohm interferometer which is Coulomb‐coupled to a nearby quantum dot. The latter acts as a ‘Which Path Detector’ and is coupled to two leads on which a finite bias is applied. Using the non‐equilibrium Keldysh‐Green function formalism we compute the currents through the detector and the interferometer. We take into account the first two contributions to the interaction selfenergy and emphasize the correction to the Landauer formula which appears beyond the single‐particle approximation. Particular attention is given to the coherence properties of the interferometer in the presence of the electron‐electron interaction between the embedded dot and the detector. We show that when the detector is subjected to a finite bias the amplitude of Aharonov‐Bohm oscillations of the current through the interferometer decreases. The Fano line is in turn rather stable under interaction. Our results generalize an earlier work of Silva and Levit [Phys. Rev. B 63, 201309 (2001)] and complement the existing description of the controlled dephasing. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical properties of cylindrical interfaces
Authors: Nobre Eloneid F. , Vilela Rivelino C. , Farias Gil A. , Almeida Nilson N.
Published: February 2007

We are interested in the study of the optical properties of cylindrical interfaces by the analysis of the propagation of energy and power in coaxial cylinders. The numerical results are obtained for the surface polaritons propagating in semiconductors coaxial cylinders made of GaN and AlN. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Conductance fluctuations in a MOSFET
Authors: Jimenez‐Montecinos J. , Martínez‐Mares M. , Pereyra P.
Published: February 2007

We study the transport properties in a narrow MOSFET device, which consists of a two dimensional electronic waveguide, with an electric field applied in the transverse direction. Based on recent solutions of the Schrödinger equation for this system, we analyze the conductance fluctuations as a function of the electric field (the gate voltage), and of the Fermi energy. The statistical analysis of these fluctuations shows that the multichannel Poisson kernel description is valid also for this non‐chaotic system. Besides the technological interest on MOSFET devices, it allows us to understand more fundamental quantities like the scattering properties of integrable systems. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Excited states and spontaneous transition lifetimes of donor impurities in quantum dots
Authors: Murillo G. , Arce Julio C. , Duque C. A. , Porras‐Montenegro N.
Published: February 2007

We calculate the 2p→1s‐like transition energy and the spontaneous lifetime of an on‐center shallow donor impurity in a spherical parabolic GaAs‐(Ga,Al)As quantum dot (PQD) as a function of the radius of the structure and the strength of an applied electric field. In our calculations we use a variational method, within the effective mass and dipolar approximations. We find that the spontaneous lifetimes increase with the radius of the PQD and the applied electric field. In this direction our results revel that the electric field can be used to suppress the electron‐phonon interaction driving to the increasing of the 2p‐1s spontaneous life‐time, showing the feasibility of using impurity states to be used in quantum computing developments. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electrical spin injection in InAs/GaAs p‐doped quantum dots through Co/Al2O3/GaAs tunnel barrier
Authors: Lombez L. , Braun P. F. , Renucci P. , Gallo P. , Carrère H. , Binh P. H. , Marie X. , Amand T. , Gauffier J. L. , Urbaszek B. , Arnoult A. , Fontaine C. , Deranlot C. , Mattana R. , Jaffrès H.
Published: February 2007

We have demonstrated by CW electroluminescence the ability to inject spin polarized electrons through Co/Al2O3/GaAs structures into p‐doped InAs/GaAs quantum dots embedded in a PIN GaAs light emitting diode. The spin relaxation processes in the p‐doped quantum dots are characterized independently by optical measurements (time and polarization–resolved photoluminescence). The measured electroluminescence circular polarization is about 15% at 1.7 K in a 2 T magnetic field, leading to an estimation of the electrical spin injection yield of about 35%. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electron‐hole complexes localized on the quantum well interface roughnesses
Authors: Semina M. A. , Sergeev R. A. , Suris R. A.
Published: February 2007

The localization of two‐dimensional electron‐hole complexes on the attractive potential of an arbitrary shape is studied theoretically. General method of a simple and vivid trial function construction for calculation of the ground state binding energy for such complexes is suggested. The limiting cases corresponding to different relations between characteristic parameters are analyzed. The developed method is illustrated by the particular calculations for the case of exciton in two‐dimensional quantum well with an additional lateral con.nement potential. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Self‐organized quantum dot superlattice inside silica mesoporous material
Authors: Sugimoto N. , Funabashi H. , Mitsushima Y.
Published: February 2007

Three‐dimensional quantum dot superlattices were synthesized by self‐assemble process method with silica mesoporous thin films. The diameter (3.8 nm) and position of metal quantum dots can be designed by the crystal morphology of silica mesoporous film which have Pm3n cubic symmetry. The diameter and arrangement of dots were strictly controlled by host materials. The I‐V characteristics and time‐dependent current oscillation were measured with sub‐micron contacts to metal superlattices. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Performance study of SQW GaInNAs Fabry‐Perot lasers
Authors: Tiras E. , Hepburn C. J. , Balkan N. , Saarinen M. , Pessa M. , Jouhti T.
Published: February 2007

The work presented here is concerned with studies of the operational characteristics of single‐quantum‐well GaInNAs/GaAs Fabry‐Perot lasers, where identical layer structures with differing cavity lengths are evaluated both experimentally and theoretically. Standard techniques are used to determine the temperature dependence, in the pulsed mode, of I‐V, L‐I and spectral electroluminescence. Important parameters, such as the threshold current and T0, are determined and tabulated for all the structures. The differential and internal quantum efficiency and hence the internal losses for each of the lasers are obtained from the experimental data. The latter is compared with the gain spectra measured using the Hakki‐Paoli method and calculated from a simple theory. From the spectral measurements above the lasing threshold, we obtain the temperature dependence of the GaInNAs quantum well effective gap as 0.3 meV/K, which is in good agreement with results published by other groups. However, a better fit is obtained using the Varshni temperature dependence using values of E0 = 1.058 eV, α = 4.8 × 10–4 eVK‐2, β = 284 ± 167 K. To put our results in perspective, we also present an up‐to‐date review of similar SQW lasers and suggest improvements to the current structure for enhanced threshold and power characteristics. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effect of electric field on recombination of self‐trapped excitons in silicon nanocrystals
Authors: Vandyshev E. N. , Zhuravlev K. S.
Published: February 2007

Study of the effect of an external electric field on photoluminescence (PL) of silicon nanocrystals formed in SiO2 has been carried out. It was found that the electric field results in a red shift of PL band and a decrease of the PL intensity at any temperature in the range of 5‐290 K. A decay time of PL intensity after pulse excitation does not depend on the electric field strength. The experimental data are explained in framework of the model of recombination of self‐trapped excitons formed at nanocrystal‐matrix boundary. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Control of a double quantum dot structure by stimulated Raman adiabatic passage
Authors: Voutsinas Evangelos , Boviatsis John , Fountoulakis Antonios
Published: February 2007

In this work we study the potential for coherent manipulation of an asymmetric double quantum dot structure by the use of adiabatic methods. These methods are the Stimulated Raman Adiabatic Passage (STIRAP) and its modification the fractional STIRAP. We show that such a method can be used for complete electron transfer between the two lower states of the quantum dots. In addition, with fractional STIRAP a coherent superposition of the two lower states of the quantum dots can be created. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Advanced modelling of GaN/AlGaN HEMT devices with field plate
Authors: Brannick A. , Zakhleniuk N. , Ridley B. K. , Eastman L. F. , Schaff W. J. , Shealy J. R.
Published: February 2007

In this paper we carry out detailed study and numerical modelling of the operation of the GaN/AlGaN High Electron Mobility Transistor (HEMT) with Field Plate (FP) optimisation. The FP has the effect of smoothing the potential gradient along the HEMT channel near the gate edge on the drain side, resulting in the enhancement of the breakdown voltage. We show that the main effect of the FP is a substantial decrease in the longitudinal component of the field EL, along with little variation of the normal component ET. In addition to the main peak of the EL field at the gate edge, there is a secondary peak under the FP edge which grows rapidly with drain bias and eventually surpasses the first. The appearance of the second peak should be taken into account in optimising of the HEMT design. The I‐V characteristics of the FP‐gated device remain practically the same as those of a device without a FP. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Negative long wavelength dielectric constant in semiconductor QWs
Authors: Hessami Pilehrood S. , Gao Feng , Ma Zhongshui , Xu Wen , Zhang Chao
Published: February 2007

In this work we present an analytical and numerical result of the dielectric function of electronic systems with Rashba spin‐orbit interaction. By solving the quantum equation of motion for the electron density matrix, we obtained the dielectric function in the mean‐field approximation. It is shown that when the momentum transfer q for an electronic transition is smaller than a critical value characterized by the spin‐orbit interaction, the static dielectric function increases with q, indicating on‐set of a new collective state. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spin Josephson effect in spintronic nanostructures
Authors: Ma Zhongshui , Xu Wen , Zhang Chao
Published: February 2007

The problem of spin current across a ferromagnetic/normal metal/ferromagnetic junction is formulated. It is shown that the spin current is controlled by the phase difference across the junction. Under zero bias, Jz is time‐independent and Jz is sinusoidal function, where Jz is the Sz current along z ‐direction. Under a dc bias, Jz and |Jz + iJz | are sinusoidal and the phase of the latter is in front by π. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Quantum interference through parallel‐coupled Double Quantum Dots
Authors: Lu Haizhou , Chen Zuo‐zi , Lü Rong , Zhu Bang‐fen
Published: February 2007

The electronic transport is theoretically studied through a double quantum dot (DQD) system. With focus on the effects of the on‐dot Coulomb repulsion U or the electron‐phonon interaction (EPI) on the quantum interference in the parallel DQD, we find that if U is comparable with level separation in the parallel‐coupled DQD, a new type of Fano interference between U ‐hybridized channels in the conductance spectra may appear and show new features; and if the EPI is significant only in one channel, as a prober of “which path” in quantum mechanics, the phonon channel won't interfere with the no‐EPI channel. A closely related transport experiment is proposed to verify the prediction. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
State‐feedback stabilization for high‐order stochastic nonlinear systems with stochastic inverse dynamics
Authors: Xie Xue‐Jun , Tian Jie
Published: February 2007

For a class of high‐order stochastic nonlinear systems with stochastic inverse dynamics which are neither necessarily feedback linearizable nor affine in the control input, this paper investigates the problem of state‐feedback stabilization for the first time. Under some weaker assumptions, a smooth state‐feedback controller is designed, which ensures that the closed‐loop system has an almost surely unique solution on [0, ∞), the equilibrium at the origin of the closed‐loop system is globally asymptotically stable in probability, and the states can be regulated to the origin almost surely. A simulation example demonstrates the control scheme. Copyright © 2007 John Wiley & Sons, Ltd.
Counting connected graphs and hypergraphs via the probabilistic method
Authors: Coja‐Oghlan Amin , Moore Cristopher , Sanwalani Vishal
Published: February 2007

While it is exponentially unlikely that a sparse random graph or hypergraph is connected, with probability 1 − o(1) such a graph has a “giant component” that, given its numbers of edges and vertices, is a uniformly distributed connected graph. This simple observation allows us to estimate the number of connected graphs, and more generally the number of connected d‐uniform hypergraphs, on n vertices with ((d − 1)−1 + ε)n ≤ m = o(nlnn) edges, where ε > 0 is arbitrarily small but independent of n. We also estimate the probability that a binomial random hypergraph Hd(n,p) is connected, and determine the expected number of edges of Hd(n,p) given that it is connected. This extends prior work of Bender et al. (Random Struct Algorithm 1 (1990), 127–169) on the number of connected graphs. While Bender et al. (1990) is based on a recursion relation satisfied by the number of connected graphs, so that the argument is to some extent enumerative, we present a purely probabilistic approach. © 2007 Wiley Periodicals, Inc. Random Struct., 2007
Der Ersatzneubau des Schwebeträgers Hochdonn – Konzepte und Realisierung
Authors: Roßmeier Peter , Heiland Uwe , Pfeiffer Michael
Published: February 2007

Der Aufsatz behandelt die Ausführung des Ersatzneubaus des Schwebeträgers der Eisenbahnhochbrücke Hochdonn über den Nord‐Ostsee‐Kanal bei Hochdonn. Für die Planung, Konstruktion, Fertigung und Montage einer 121 m langen Fachwerkbrücke, die unter komplizierten Randbedingungen in ca. 40 m über einer Wasserstraße aus‐ und einzubauen war, standen weniger als 11 Monate Ausführungszeit zur Verfügung. Die Aufgabe war bestimmt durch die kurzen Zeitfenster der Sperrungen des Nord‐Ostsee‐Kanals und der Eisenbahnstrecke Elmshorn–Westerland für die Demontage‐ und Montagevorgänge. Darüber hinaus wurde der planerische, logistische und sonstige Aufwand dadurch erhöht, daß die Demontage und Montage nicht wie geplant und beauftragt mittels Schwimmkran durchgeführt werden konnte, da der für den Einsatz vorgesehene Schwimmkran zum Zeitpunkt der Sperrungen des Kanals nicht zur Verfügung stand.
Ganzheitliche Wirtschaftlichkeitsbetrachtungen bei Verbundbrücken unter Berücksichtigung des Bauverfahrens und der Nutzungsdauer
Authors: Kuhlmann Ulrike , Pelke Eberhard , Hauf Gunter , Herrmann Torsten , Steiner Josef , Aul Michael
Published: February 2007

Für ausgewählte Brückentypen werden verschiedene Möglichkeiten der ganzheitlichen Wirtschaftlichkeitsuntersuchung durchgeführt. Hierbei werden nicht nur die Herstellkosten, sondern ebenso die Kosten für den Betrieb, Unterhalt und die Sanierung berücksichtigt. Im Vergleich werden besonders auch verschiedene Varianten von Bauverfahren bewertet und die Kosten über die gesamte Nutzungsdauer ermittelt.

Durch die Untersuchung sollen Entwurfs‐ und Entscheidungshilfen geschaffen werden, Kostenangebote zu werten und die Kriterien für die Bewertung eines Bauwerks über die reinen Herstellungskosten zu erweitern. Dieser Beitrag beruht auf einem Gutachten, das für die Hessische Straßen‐ und Verkehrsverwaltung im Rahmen des hessischen Großprojektes “Staufreies Hessen 2015” erarbeitet wurde.
Short‐term hydropower planning coordinated with wind power in areas with congestion problems
Authors: Matevosyan Julija , Söder Lennart
Published: February 2007

In this paper, a day‐ahead planning algorithm for a multi‐reservoir hydropower system coordinated with wind power is developed. Coordination applies to real situations, where wind power and hydropower are owned by different utilities, sharing the same transmission lines, although hydropower has priority for transmission capacity. Coordination is thus necessary to minimize wind energy curtailments during congestion situations. The planning algorithm accounts for the uncertainty of wind power forecast. Only planning for the spot market is considered. Once the production bid is placed on the market, it cannot be changed. The solution of the stochastic optimization problem should, therefore, fulfill the transmission constraints for all wind power production scenarios. An evaluation algorithm is also developed to quantify the impact from the coordinated planning in the long run. The developed planning algorithm and the evaluation algorithm are applied in a case study. The results are compared with uncoordinated operation. The results of the case study show that coordination with wind power brings additional income to the hydropower utility and leads to significant reduction of wind energy curtailments. Copyright © 2007 John Wiley & Sons, Ltd.
Separation of instrumental and chemical errors in the analysis of oils by gas chromatography—A collaborative evaluation
Authors: Craske John D.
Published: February 2007

Thirty‐five analysts studied the concept that, in the gas chromatographic (GC) analysis of fatty acid composition, errors can be separated into those caused by poor chromatograph optimization and those related to inefficient conversion of triacylglycerols (TAG) to fatty acid methyl esters (FAME). A primary standard mixture of FAME was used to determine how well the participants had optimized their chromatographs. A primary standard of the equivalent TAG was used to determine total error of analysis. “Chemistry error” was calculated as the difference between the absolute errors found for the FAME and the TAG standards. Grades of analysis were computed for the FAME and TAG results and for the chemistry errors calculated from these analyses.

Only four analysts achieved grades of analysis for the FAME standard that can be considered excellent or good. These four analysts used different injector/column configurations, indicating that, when properly optimized, a GC with a flame ionization detector is an extremely accurate instrument. Conversely, it is evident that there is the potential for most analysts to improve their instrumental optimization. In agreement with published information, AOCS method Ce 2‐66 and AOAC method 969.33 gave low chemistry grades, but a number of analysts used modifications of these methods, and some achieved much better grades. It would appear that many of the standard methods that are in common use are capable of producing improved results, but that critical parameters need to be better specified to ensure minimization of error. The concept of separating errors into those of instrument origin and those caused by the chemical component of the total method would appear to be a useful concept for the validation of analytical methods.
High‐performance liquid chromatography of selected phenolic compounds in olive oils
Authors: Akasbi M. , Shoeman D. W. , Csallany A. Saari
Published: February 2007

A reverse‐phase high‐performance liquid chromatographic technique with isocratic elution has been developed to separate and quantitate the major phenolic compounds of the hydroalcoholic extracts of olive oils. Hydroxytyrosol, tyrosol, caffeic acid,p‐hydroxyphenylacetic acid and homovanillic acid were analyzed on a μBonapak C18 column with an acetonitrile/water/acetic acid (20:90:0.18, vol/vol/vol) mixture as a mobile phase. Electrochemical detection provided selectivity as well as sensitivity. The method was applied to the analysis of the most important phenolic compounds in olive oils.
Quantitation of cholesterol oxidation products in unirradiated and irradiated meats
Authors: Hwang K. T. , Maerker G.
Published: February 2007

A method to detect 7‐ketocholesterol, cholesterol‐5β,6β‐epoxide, cholesterol‐5α,6α‐epoxide, 4‐cholesten‐3‐one, 4,6‐cholestadien‐3‐one and 4‐cholestene‐3,6‐dione in unirradiated and irradiated beef, pork and veal was developed by use of chloroform‐methanol‐water extraction, solid‐phase extraction, column separation, thin‐layer chromatography and gas chromatography. This method recovered 78–88% of the cholesterol oxidation products and detected the cholesterol oxidation products at 10 ppb or higher. Irradiation of the meats to a dose of 10 kGy increased these compounds, except 4,6‐cholestadien‐3‐one for all three types of meat, over unirradiated, and except cholesterol‐5α,6α‐epoxide and 4‐cholesten‐3‐one for the pork. All the cholesterol oxidation products in the unirradiated meats increased during storage at 0–4°C for 2 wk with some exceptions for the pork. The increases of cholesterol oxidation products in stored irradiated meats were greater than those in the unirradiated.