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Quantum Confinement (quantum + confinement)
Terms modified by Quantum Confinement Selected AbstractsQuantum Confinement in Self-Assembled Bioinspired Peptide HydrogelsADVANCED MATERIALS, Issue 21 2010Nadav Amdursky The self-assembly process of peptide fibrils is followed by spectroscopic measurements, which show that a quantum confinement (QC) nanocrystal structure is formed within the peptide fibrils as they assemble into a hydrogel. The optical and electronic properties of this first bioorganic-inspired QC structure (see figure) are demonstrated to be related to the QC effect. [source] Effects of Phonon Confinement on Anomalous Thermalization, Energy Transfer, and Upconversion in Ln3+ -Doped Gd2O3 NanotubesADVANCED FUNCTIONAL MATERIALS, Issue 4 2010Andreia G. Macedo Abstract There is a growing interest in understanding how size-dependent quantum confinement affects the photoluminescence efficiency, excited-state dynamics, energy-transfer and thermalization phenomena in nanophosphors. For lanthanide (Ln3+)-doped nanocrystals, despite the localized 4f states, confinement effects are induced mostly via electron,phonon interactions. In particular, the anomalous thermalization reported so far for a handful of Ln3+ -doped nanocrystals has been rationalized by the absence of low-frequency phonon modes. This nanoconfinement may further impact on the Ln3+ luminescence dynamics, such as phonon-assisted energy transfer or upconversion processes. Here, intriguing and unprecedented anomalous thermalization in Gd2O3:Eu3+ and Gd2O3:Yb3+,Er3+ nanotubes, exhibiting up to one order of magnitude larger than previously reported for similar materials, is reported. This anomalous thermalization induces unexpected energy transfer from Eu3+C2 to S6 crystallographic sites, at 11,K, and 2H11/2,,,4I15/2 Er3+ upconversion emission; it is interpreted on the basis of the discretization of the phonon density of states, easily tuned by varying the annealing temperature (923,1123,K) in the synthesis procedure, and/or the Ln3+ concentration (0.16,6.60%). [source] Highly Non-Linear Quantum Dot Doped Nanocomposites for Functional Three-Dimensional Structures Generated by Two-Photon PolymerizationADVANCED MATERIALS, Issue 22 2010Baohua Jia A nanocomposite consisting of a photosensitive organic,inorganic hybrid polymer functionalized with PbS quantum dots has been developed using a sol,gel process. The uniformly dispersed nanocomposite exhibits ultrahigh third-order non-linearity (,3.2,×,10,12 cm2 W,1) because of the strong quantum confinement of small-sized and narrowly distributed quantum dots. The non-linear nanocomposite has been proven to be suitable for the fabrication of 3D micro/nano photonic devices using two-photon polymerization. The fabricated photonic crystals show stop gaps with more than 60% suppression in transmission at the telecommunications wavelength region. [source] Quantum Confinement in Self-Assembled Bioinspired Peptide HydrogelsADVANCED MATERIALS, Issue 21 2010Nadav Amdursky The self-assembly process of peptide fibrils is followed by spectroscopic measurements, which show that a quantum confinement (QC) nanocrystal structure is formed within the peptide fibrils as they assemble into a hydrogel. The optical and electronic properties of this first bioorganic-inspired QC structure (see figure) are demonstrated to be related to the QC effect. [source] A new approach for numerical simulation of quantum transport in double-gate SOIINTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 6 2007Tarek M. Abdolkader Abstract Numerical simulation of nanoscale double-gate SOI (Silicon-on-Insulator) greatly depends on the accurate representation of quantum mechanical effects. These effects include, mainly, the quantum confinement of carriers by gate-oxides in the direction normal to the interfaces, and the quantum transport of carriers along the channel. In a previous work, the use of transfer matrix method (TMM) was proposed for the simulation of the first effect. In this work, TMM is proposed to be used for the solution of Schrodinger equation with open boundary conditions to simulate the second quantum-mechanical effect. Transport properties such as transmission probability, carrier concentration, and I,V characteristics resulting from quantum transport simulation using TMM are compared with that using the traditional tight-binding model (TBM). Comparison showed that, when the same mesh size is used in both methods, TMM gives more accurate results than TBM. Copyright © 2007 John Wiley & Sons, Ltd. [source] Hydrogen surface passivation of Si and Ge nanowires: A semiempirical approachINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 13 2010A. Miranda Abstract A semiempirical nearest-neighbor tight-binding approach, that reproduces the indirect band gaps of elemental semiconductors, has been applied to study the electronic and optical properties of Si and Ge nanowires (NWs). The calculations show that Si-NWs keep the indirect bandgap whereas Ge-NWs changes into the direct bandgap when the wire cross section becomes smaller. Also, the band gap enhancement of Si-NWs showing to quantum confinement effects is generally larger than that of similar-sized Ge-NWs, confirming the larger quantum confinement effects in Si than in Ge when they are confined in two dimensions. Finally, the dependence of the imaginary part of the dielectric function on the quantum confinement within two different schemes: intra-atomic and interatomic optical matrix elements are applied. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem 110:2448,2454, 2010 [source] Simulation of Thermoelectric Performance of Bulk SrTiO3 with Two-Dimensional Electron Gas Grain BoundariesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2010Rui-zhi Zhang Density functional theory calculations and Boltzmann transport theory are used to simulate the thermoelectric properties of SrTiO3 ceramics with two-dimensional electron gas grain boundaries (GBs). This material can achieve a large thermoelectric figure of merit (ZT>1 at room temperature) by utilizing quantum confinement and energy filtering at GBs. The latter causes the ZT value to reach a maximum before decreasing with an increasing GB barrier height. The optimum barrier height was approximately 0.06 eV higher than the Fermi energy of the grain interior. Our results may aid the design of materials with environmentally benign thermoelectric oxides. [source] Ellipsometry study of ultra thin layers of evaporated goldPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2008Alexei Nabok Abstract Optical properties of ultra thin (from 1 to 40 nm) films of gold evaporated on glass and silicon were studied with the method of spectroscopic ellipsometry in both external and internal reflection configurations as well as with the UV-visible absorption spectroscopy. The results obtained showed a gradual shift of the plasmon peak from 580 nm for 1 nm thick films to more than 1000 nm for thick (40 nm) gold films. Such phenomenon can be interpreted in terms of quantum confinement of surface plasmons in gold islands. The threshold of the metal-dielectric transition was found at the film thickness between 4 and 5 nm. Thiolation of the surface of glass has resulted in a slight decrease in the effective thickness of gold layer and respective smaller blue shift of n (,) and k (,) dispersion curves, however no dramatic changes were observed in the film morphology. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Carrier transport studies of dichromatic InGaN-based LEDs with spacer bandgap dependencePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2007Shih-Wei Feng Abstract Carrier transport of dichromatic InGaN-based LEDs with AlGaN spacer bandgap dependence has been studied. TREL measurements show that carrier dynamics could be well explained by the combined effects of carrier effective mass, carrier mobility, quantum confinement, and device structures. The experimental results provide important information for device designs. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Photoluminescence spectroscopy and transport electrical measurements reveal the quantized features of Si nanocrystals embedded in an ultra thin SiO2 layerPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2007C. Dumas Abstract In this paper, we have investigated the quantized charging features revealed by nanometer scale devices containing a 2D array of Si nanoparticles (nps) embedded into a SiO2 layer. The Si nps were synthesized by ultra low energy ion implantation and annealing under slightly oxidizing ambient. The structural characteristics of the material (oxide thicknesses, nps size and density) have been studied by Transmission Electron Microscopy (TEM) and Energy Filtered TEM (EFTEM). Moreover, photoluminescence (PL) spectroscopy and electrical I(V) measurements using a MOS capacitor addressing only a few nps have been performed at room temperature. It is observed that, as the oxidizing annealing temperature increases, the nps size decreases and the oxide quality is restored. These features appear on the PL spectra as a blue shift of the PL red band linked to quantum confinement into nps and on the I(V) characteristics as an increase of the voltage peak width and a decrease of the main current background. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] 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] | ||||||||||