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Quantum Wires (quantum + wire)
Selected AbstractsSynthesis of Ideal AM-6 and Elucidation of V4+ -to-O Charge Transfer in Vanadate Quantum Wires,ANGEWANDTE CHEMIE, Issue 29 2010Jit Datta, Shuvo Der Vanadosilicat-Zeolith AM-6 mit einer dreidimensionalen Anordnung von Vanadat(VIVO32,)-Quantendrähten (siehe Bild) wurde in Form hochwertiger Kristalle (frei von VV, Titanosilicat-Kristallkeimen und organischen Templatkationen in den Poren) aus preiswertem V2O5 hergestellt. Die lineare Abhängigkeit von ,max und der Bandlückenenergie Eg von der Partialladung der O-Atome zeigt, dass die UV-Bande von AM-6 auf einen Metall-Ligand-Ladungstransfer von VIV zu O zurückgeht. [source] Self-organized InAs quantum dots grown in a V-groove InGaAs quantum wirePHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 9 2007Chang-Sik Son Abstract Self-organized InAs quantum dots (QDs), by the Stranski,Krastanow mode, have been grown by using low-pressure metalorganic chemical vapor deposition on V-groove GaAs substrates. By adjusting the flow rate of AsH3 during the growth of InAs QDs, a one dimensional InAs QD array was successfully formed along the [01] direction only at the bottom of V-grooves. No QDs were observed on the sidewalls and the surface of the mesa top. The InAs QDs took on an oval shape. They were spatially well-isolated along the [01] direction with a line density of 3 × 103 cm,1. These low-density InAs QDs are expected to be used in areas of quantum information and quantum computing. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Excitons in a perfect quasi-1D organic quantum wire, an isolated polydiacetylene chainPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2008Laurent Legrand Abstract The exciton in single luminescent polydiacetylene (PDA) chains dispersed in their single crystal monomer matrix is studied. As reported these quantum wires have the properties of a perfect quasi-1D semiconducting system. The macroscopic spatial coherence of a single exciton state on a chain as a function of temperature is investigated using an interference experiment. The interference pattern contrast decreasing with increasing temperature is non zero up to 30 K. Experiments developed in order to observe the regime of formation of the stationary coherent exciton state are described. Within the time resolution of the experiment, it is concluded that the formation of this state is faster than ,5 picoseconds which confirms the assumption of a transient regime. Finally the first steps of the manipulation of phase locked excitonic wave-packets on a PDA wire are discussed. The experimental results measured in a weak exciton-photon coupling regime are compared to simulations obtained through the Bloch optical equations in the framework of a three-levels model. A direct estimate of the coherence time of the vibronic state photocreated in the present non resonant scheme is derived. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Electron spin and nuclear spin manipulation in semiconductor nanosystemsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 14 2006Yoshiro Hirayama Abstract Manipulations of electron spin and nuclear spin have been studied in AlGaAs/GaAs semiconductor nanosystems. Non-local manipulation of electron spins has been realized by using the correlation effect between localized and mobile electron spins in a quantum dot- quantum wire coupled system. Interaction between electron and nuclear spins was exploited to achieve a coherent control of nuclear spins in a semiconductor point contact device. Using this device, we have demonstrated a fully coherent manipulation of any two states among the four spin levels of Ga and As nuclei. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effect of dielectric screening on the binding energies and diamagnetic susceptibility of a donor in a quantum well wirePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2006M. Latha Abstract The effect of the dielectric screening on donor binding energies in a quantum wire has been estimated. Since the screening function is shown to be significant in a few phenomena like carrier transport, and not so in a few cases like the donor binding energy calculations, five different screening functions have been used in the calculations to see their relative merits. It is observed that the dielectric function obtained by Resta using the Thomas,Fermi approximation not only gives lower estimates of the ionization energies for all well widths (L ), but also is shown to vary very rapidly with L . The other functions used are those of Hermanson and Vinsome & Richardson. Using the results of the variational calculations for the finite barrier problem, the diamagnetic susceptibility of a donor as a function of L has also been estimated. Though experimental results are not available, we have compared our results for Eion with other theoretical estimates available in the literature. The agreement is found to be good. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Evidence of different confinement regimes in site-controlled pyramidal InGaN structuresPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2005V. Pérez-Solórzano Abstract We deposited InGaN on GaN micropyramids, which were grown by selective metal-organic vapor phase epitaxy on sapphire. We expected the formation of a quantum well on the side-walls of the pyramids, a quantum wire on the edges, and a quantum dot on its apex. We studied the emission properties of these structures using low-temperature time-resolved photoluminescence. Our measurements showed three regions of different confinement within the emission in the wavelength range between 2.12 eV and 2.40 eV. By analyzing the decay behavior, the characteristics of the luminescence was determined to originate from localized states. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Transverse Stark effect of electrons in a semiconducting quantum wirePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2003G. J. Vázquez Abstract We investigate the effect of an electric field applied tranversely to the axis of cylindrical symmetry of a cylindrical quantum wire on the ground-state energy of the electrons in the wire using an infinite confining potential well model. For low electric fields, we find a quadratic shift of the energy levels with the electric field; while for strong fields, the Stark shift of the ground-state energy increases almost linearly with the electric field. This increase is greater for wide wires, but for narrow wires, the Stark shift of the ground-state energy does not change much with the electric field. Also, at higher electric fields, the Stark shift of the ground-state energy increases with increasing wire radius. This will lead to the decrease of the effective bandgap of a semiconducting quantum wire with electric field. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Control of electron transport through a quantum wire by side-attached nanowiresPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S1 2004P. A. Orellana Abstract A system of arrays of nanowires side-coupled to a quantum wire is studied. Transport through the quantum wire is investigated by using a noninteracting-electron Anderson tunneling Hamiltonian. An analytical expression of the conductance at zero temperature is given, showing a band with alternating forbidden and allowed minibands due to the discrete structure of the nanowires. The conductance is found to exhibit a forbidden miniband in the center of the band for an odd number of sites in the nanowires, while shows an allowed band for an even number. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Functionalized Self-Assembled InAs/GaAs Quantum-Dot Structures Hybridized with Organic MoleculesADVANCED FUNCTIONAL MATERIALS, Issue 3 2010Miaoxiang Chen Abstract Low-dimensional III,V semiconductors have many advantages over other semiconductors; however, they are not particularly stable under physiological conditions. Hybridizing biocompatible organic molecules with advanced optical and electronic semiconductor devices based on quantum dots (QDs) and quantum wires could provide an efficient solution to realize stress-free and nontoxic interfaces to attach larger functional biomolecules. Monitoring the modifications of the optical properties of the hybrid molecule,QD systems by grafting various types of air-stable diazonium salts onto the QD structures surfaces provides a direct approach to prove the above concepts. The InAs/GaAs QD structures used in this work consist of a layer of surface InAs QDs and a layer of buried InAs QDs embedded in a wider-bandgap GaAs matrix. An enhancement in photoluminescence intensity by a factor of 3.3 from the buried QDs is achieved owing to the efficient elimination of the dangling bonds on the surface of the structures and to the decrease in non-radiative recombination caused by their surface states. Furthermore, a narrow photoluminescence band peaking at 1620,nm with a linewidth of 49 meV corresponding to the eigenstates interband transition of the surface InAs QDs is for the first time clearly observed at room temperature, which is something that has rarely been achieved without the use of such engineered surfaces. The experimental results demonstrate that the hybrid molecule,QD systems possess a high stability, and both the surface and buried QDs are very sensitive to changes in their surficial conditions, indicating that they are excellent candidates as basic sensing elements for novel biosensor applications. [source] A neural network-based approach to determine FDTD eigenfunctions in quantum devicesMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 9 2009Antonio Soriano Abstract This article combines a Neural Network (NN) algorithm with the Finite Difference Time Domain (FDTD) technique to estimate the eigenfunctions in quantum devices. A NN based on the Least Mean Squares (LMS) algorithm is combined with the FDTD technique to provide a first approach to the confined states in quantum wires. The proposed technique is in good agreement with analytical results and is more efficient than FDTD combined with the Fourier Transform. This technique is used to calculate a numerical approximation to the eigenfunctions associated to quantum wire potentials. The performance and convergence of the proposed technique are also presented in this article. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2017,2022, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24562 [source] Excitons in a perfect quasi-1D organic quantum wire, an isolated polydiacetylene chainPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2008Laurent Legrand Abstract The exciton in single luminescent polydiacetylene (PDA) chains dispersed in their single crystal monomer matrix is studied. As reported these quantum wires have the properties of a perfect quasi-1D semiconducting system. The macroscopic spatial coherence of a single exciton state on a chain as a function of temperature is investigated using an interference experiment. The interference pattern contrast decreasing with increasing temperature is non zero up to 30 K. Experiments developed in order to observe the regime of formation of the stationary coherent exciton state are described. Within the time resolution of the experiment, it is concluded that the formation of this state is faster than ,5 picoseconds which confirms the assumption of a transient regime. Finally the first steps of the manipulation of phase locked excitonic wave-packets on a PDA wire are discussed. The experimental results measured in a weak exciton-photon coupling regime are compared to simulations obtained through the Bloch optical equations in the framework of a three-levels model. A direct estimate of the coherence time of the vibronic state photocreated in the present non resonant scheme is derived. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Spin-dependent electron tunnelling and spin relaxation in quantum dots in regime with filling factor of around twoPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2007S. Tarucha Abstract Spin-dependent electron tunnelling and spin relaxation were studied for a quantum dot in the regime with a filling factor between two and four. In this regime, the electronic configuration of a quantum dot undergoes transitions between a spin singlet and triplet states for an even number of electrons, and between two doublet states for an odd number of electrons. These transitions were clearly distinguished by using quantum wires as spin filtering contact leads to the dot. In addition, the temporal behaviour of electron tunnelling was studied for a quantum dot in a similar filling factor regime, using a quantum point contact as a charge sensor. Electron tunnelling through the dot in a spin singlet state could be well distinguished from that in a triplet state using the fact that the tunnelling rate was much larger for the triplet state. The difference in the tunnelling rate was also used to derive a triplet-to-singlet-state relaxation time. The obtained relaxation time agreed fairly well with that predicted by the theory of spin-orbit interaction. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Pressure dependence of photoluminescence of InAs/InP self-assembled quantum wiresPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2007M. Ruiz-Castillo Abstract This paper investigates the electronic structure of self-assembled InAs quantum wires (QWrs), grown under different conditions by molecular beam epitaxy on InP, by means of photoluminescence measurements under pressure. In samples with regularly distributed QWrs, room pressure photoluminescence spectra consist of a broad band centred at about 0.85 eV, which can be easily de-convoluted in a few Gaussian peaks. In samples with isolated QWrs, photoluminescence spectra exhibit up to four clearly resolved bands. Applying hydrostatic pressure, the whole emission band monotonously shifts towards higher photon energies with pressure coefficients ranging from 72 to 98 meV/GPa. In contrast to InAs quantum dots on GaAs, quantum wires photoluminescence is observed up to 10 GPa, indicating that InAs QWrs are metastable well above pressure at which bulk InAs undergoes a phase transition to the rock-salt phase (7 GPa). (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Elastic relaxation of a truncated circular cylinder with uniform dilatational eigenstrain in a half spacePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003Frank Glas Abstract We give a fully analytical solution for the displacement and strain fields generated by the coherent elastic relaxation of a type of misfitting inclusions with uniform dilatational eigenstrain lying in a half space, assuming linear isotropic elasticity. The inclusion considered is an infinitely long circular cylinder having an axis parallel to the free surface and truncated by two arbitrarily positioned planes parallel to this surface. These calculations apply in particular to strained semiconductor quantum wires. The calculations are illustrated by examples showing quantitatively that, depending on the depth of the wire under the free surface, the latter may significantly affect the magnitude and the distribution of the various strain components inside the inclusion as well as in the surrounding matrix. [source] Auger recombination process of biexciton in semiconducting carbon nanotubesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2009Kouta Watanabe Abstract We calculated the T-matrix for the Auger recombination process of the biexciton in semiconducting carbon nanotubes (s-CNTs) within the first Born approximation and clarified the difference between s-CNTs and GaAs quantum wires (QWRs). The wavefunction and the binding energy of the biexciton, EXX, are given by the dynamics controlled truncation (DCT) scheme. We find that the Auger recombination rate is ,/, , 0.1EXX. This means that the Auger recombination process doesn't prevent the biexciton formation. In addition, the Auger recombination rate is much larger than that of the QWR. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Spin densities in parabolic quantum wires with Rashba spin-orbit interactionPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2006Sigurdur I. Erlingsson Abstract Using canonical transformations we diagonalize approximately the Hamiltonian of a gaussian wire with Rashba spin-orbit interaction. This proceedure allows us to obtain the energy dispersion relations and the wavefunctions with good accuracy, even in systems with relatively strong Rashba coupling. With these eigenstates one can calculate the non-equilibrium spin densities induced by applying bias voltages across the sample. We focus on the z -component of the spin density, which is related to the spin Hall effect. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Giant quantum oscillations of the longitudinal magnetothermopower at the electron topological transition induced by stretch of quantum wires of bismuth doped with TePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2004A. A. Nikolaeva Abstract Thermoelectric and magneto-thermoelectric properties of quantum wires of bismuth doped with Te were investigated at electron topological transitions (ETT) induced by stretch in the temperature interval 4.2-300 K and magnetic fields up to 14T. Single Bi, Bi Observation of charged excitons in V-groove quantum wiresPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2004T. Otterburg Abstract We report on the observation of negatively and positively charged excitons in the photoluminescence spectra of V-groove quantum wires. The charged exciton binding energy increases with the strength of the quantum confinement. We demonstrate that the charged excitons are localized by the fluctuations of the confinement potential and estimate a minimal value of the localization length. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Proceedings of the 7th International Workshop on Nonlinear Optics and Excitation Kinetics in Semiconductors (NOEKS 7)PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2003Martin Wegener The 7th International Workshop on Nonlinear Optics and Excitation Kinetics in Semiconductors (NOEKS 7) was held at the Universität Karlsruhe (TH) from 24,28 February 2003. Topics of NOEKS 7 were: Ultrafast dynamics (coherent effects, coherent control, quantum kinetics, THz-experiments), photonic crystals (2D and 3D photonic band gap materials), quantum dot physics (quantum dots, quantum wires), spin effects (spin dephasing, spin transport), disorder-related effects, organic semiconductors, semiconductor quantum optics (luminescence, photon statistics), device physics (quantum cascade lasers, superlattices, interband lasers), and Bose-Einstein condensation of excitons. [source] Piezoelectric effects in sidewall quantum wires grown on patterned (311)A GaAs substratePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2003D. Alderighi Abstract Time-resolved photoluminescence measurements have been performed on sidewall InGaAs/AlGaAs quantum wires and quantum wells. Experimental data show a band filling of quantum wells and quantum wires that is dominant in the first 400 ps after the excitation pulse, then a dynamical screening of the built-in piezoelectric field (Fp) by means of fast injection of photo-generated charges is observed allowing an efficient radiative recombination. At longer time delay, during the regime when the Fp unscreened value is recovered, a strong quantum confined Stark effect is observed. A good agreement is obtained for the energy shift and the overlap integrals of electrons and heavy holes by means of discrete element calculations. [source] The World of Carbon Nanotubes: An Overview of CVD Growth MethodologiesCHEMICAL VAPOR DEPOSITION, Issue 6 2006L. Terranova Abstract Carbon nanotubes are a new form of completely artificial crystalline carbon, which have never been found as a natural form. These fascinating hollow cylinders can be considered as prototypes of one-dimensional quantum wires, exhibit peculiar chemical-physical properties very different from those of other C-based nanostructures, and are envisaged to have potential in a wide range of applications. This review examines some of the most interesting CVD methodologies employed for the synthesis of carbon nanotubes. The results obtained from different methodologies demonstrate that carbon nanotubes can be grown by CVD under a wide range of experimental conditions, permitting flexible, tunable synthesis. Overall, in the last few years, CVD approaches have emerged as the most promising among those proposed for synthesizing carbon nanotubes. [source]
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