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Multiple Quantum (multiple + quantum)

Distribution by Scientific Domains
Physics and Astronomy90%

Terms modified by Multiple Quantum

  • multiple quantum coherence
    		•
  • multiple quantum well
    		•

    Selected Abstracts

    Study of order and dynamic processes in tendon by NMR and MRI

    JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 2 2007
    G. Navon PhD
    Abstract Tendons are composed of a parallel arrangement of densely packed collagen fibrils that results in unique biomechanical properties of strength and flexibility. In the present review we discuss several advanced magnetic resonance spectroscopy (MRS) and imaging (MRI) techniques that have allowed us to better understand the biophysical properties of tendons and ligaments. The methods include multiple quantum and T2 filtering combined with NMR and MRI techniques. It is shown in detail how these techniques can be used to extract a number of useful parameters: 1) the 1H- 1H and 1H- 2H dipolar interactions; 2) the proton exchange rates between water and collagen, and between water molecules; 3) the distribution of fibril orientations; and 4) the anisotropy of diffusion. It is shown that relaxation data as a function of angular dependence can be obtained in vivo using mobile NMR sensors. Finally, this article describes how double quantum filtered (DQF) MRI can be used to image and monitor the healing process in injured tendons. J. Magn. Reson. Imaging 2007. © 2007 Wiley-Liss, Inc. [source]

    Device characteristics and metal,dielectric high reflectivity coating analysis of ,,,,1.3,µm InGaAsP/InGaAsP MQW PBH lasers

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2010
    J. W. Leem
    Abstract The cavity length-dependent characteristics of compressively strained InGaAsP/InGaAsP multiple quantum well planar buried heterostructure lasers operating at ,,,,1.3,µm were investigated under continuous-wave mode. The uncoated 600,µm long laser exhibits Pmax,=,33.6,mW and Ith,=,12.9,mA at 25,°C with d,/dT,=,0.35,nm/K and d,/dPe,=,0.044,nm/mW, leading to stable beam characteristics of 19.7° (parallel),×,24.1° (perpendicular). From the inverse slope efficiency versus cavity length plot, the loss parameters of internal differential efficiency (,i) and internal optical loss (,i) were extracted, i.e., ,i,=,78% and ,i,=,10.6,cm,1. The transparent current density of Jtr,=,0.12,kA/cm2 and modal gain of G,=,49.5,cm,1 were also estimated from cavity length-dependent threshold current density measurements. Metal,dielectric Au/Ti/SiO2 layers for high reflectivity (HR) coating were analyzed using theoretical calculations and experimental results. For the HR-coated 600,µm long laser with Au (150,nm)/Ti (5,nm)/SiO2 (250,nm), Pmax increased up to 61,mW at 25,°C with a reduced Ith of 10.6,mA compared to the uncoated laser, providing an HR of about 94%. [source]

    Atom probe reveals the structure of Inx Ga1,xN based quantum wells in three dimensions

    PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2008
    M. J. Galtrey
    Abstract The three-dimensional atom probe has been used to characterize Inx Ga1,xN based multiple quantum well structures emitting from the green to the ultra-violet with sub-nanometre resolution over a 100 nm field of view. The results show gross discontinuities and compositional variations within the UV-emitting quantum well layers on a 20,100 nm length scale. We propose that these may contribute to the high efficiency of this structure. In addition, the analysis shows the presence of indium in the barrier layers of all the samples, whether or not there was an indium precursor present during barrier growth. The distribution of indium within the blue- and green-emitting Inx Ga1,xN quantum wells is also analyzed, and we find no evidence that Inx Ga1,xN with a range of compositions is not a random alloy, and so rule out indium clustering as the cause of the reported carrier localization in these structures. The upper interface of each quantum well layer is shown to be rougher and more diffuse than the lower, and the existence of monolayer steps in the interfaces that could effectively localize carriers at room temperature is revealed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Quantum and conversion efficiency calculation of AlGaAs/GaAs multiple quantum well solar cells

    PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 9 2005
    J. C. Rimada
    Abstract The quantum well solar cell (QWSC) is a novel device that has been proposed by Barnham and co-workers at Imperial College London. In this work, the quantum efficiency for AlGaAs/GaAs QWSC has been calculated and compared with available data from the group at Imperial College London. Quantum efficiency calculations will be presented and compared with experimental data for several AlGaAs/GaAs QWSC, obtaining good agreement. The photocurrent then is calculated from the quantum efficiency calculations and included in the J(V) relation to optimize the efficiency of AlGaAs/GaAs QWSC. It also shows that for a range of quantum well widths and barrier bandgaps the conversion efficiencies of the quantum well solar cell are higher than the corresponding homogeneous p,i,n solar cell. Our results give a broad representation of quantum well solar cell operation, and provide a profitable guide for designing and interpreting the performance characteristics of AlGaAs/GaAs QWSCs. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Wavelength dependence of the modal refractive index in 1.3 ,m InGaAsP, AlGaInAs and GaInNAs lasers using high pressure

    PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003
    S. R. Jin
    Abstract We report the variation of the modal refractive index at threshold with lasing wavelength in 1.3,,m InGaAsP, AlGaInAs and GaInNAs multiple quantum well lasers by measuring mode spectra under pressure up to 15,kbar. It is shown that the decrease of index with lasing wavelength is about 4% on average in the pressure range studied. We also find that the modal refractive index reduces with increasing injection current and is very sensitive to the injection current around laser threshold. [source]

    Characterization of asymmetric GaN/InGaN multiple quantum well

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009
    Z. Z. Chen
    Abstract The microstructure and electronic structure of the asymmetric GaN/InGaN multiple quantum well (MQW) light emitting diodes are characterized by transmission electron microscope (TEM), cathodoluminescence (CL) and capacitance-voltage (C-V) measurements. In TEM images, the asymmetric structure of InGaN/GaN MQW are observed as designed with different width of QWs and barriers, and indium content in QWs as well. In high-resolution TEM images, the InGaN quantum wells and GaN barriers show the same lattice constant, and some degradation can be seen at the bottom of each InGaN QW. There are two emission peaks, 450 and 530 nm in CL spectrum, similar to the ones in electroluminescence spectrum. The double emission peaks are assigned to the irradiative recombination in different InGaN QWs. From the C-V data, the apparent carrier concentration in the asymmetric MQW is calculated. There are five obvious peaks which are well explained by an energy band scheme of InGaN/GaN MQW. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    First InGaN/GaN thin film LED using SiCOI engineered substrate

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006
    J. Dorsaz
    Abstract InGaN / GaN multiple quantum well (MQW) light emitting diodes (LEDs) were deposited by metal-organic chemical vapor deposition (MOCVD) onto SiCOI engineered substrates. SiCOI substrates are composed of SiC thin film transferred on a silicon substrate through silicon oxide layer by the Smart CutÔ technology. LEDs structures grown on SiCOI were characterized, then transferred onto Si substrates via a metallic bonding process and SiCOI substrates were removed. Three different metallic stacks were used for metallic bonding, including mirror and barrier diffusion. Vertical thin film LED obtained were characterized and showed a 2 to 3 times increase of external quantum efficiency. These results demonstrate the potential of SiCOI engineered substrates as an alternative to laser lift off for thin film LED fabrication. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Advanced buffers for AlGaN/GaN HEMT and InGaN/GaN MQW on silicon substrates

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006
    Y. Dikme
    Abstract GaN growth was carried out on silicon (Si) substrates by metalorganic vapor phase epitaxy (MOVPE). A layer structure starting with HT (high-temperature) AlN and containing AlGaN and GaN as interlayers was employed for the subsequent deposition of GaN buffer layers. At first, the influence of the in-situ Al pre-deposition at the process start with different durations was investigated. Each time, the pre-deposition was followed by the same layer sequence and with thin AlGaN and GaN grown on top to form a high electron mobility transistor (HEMT). A significant enhancement could be observed in the properties of the investigated samples by reducing the pre-deposition time from 8 s to 2 s. Based on these results, multiple quantum well structures (MQW) and HEMT were grown on these buffers. For the MQW, the well thickness was increased and a shift to higher wavelengths was observed. The HEMT structures have shown enhanced properties by optimizing the growth temperatures of the top AlGaN layer. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Defect density dependence of carrier dynamics in AlGaN multiple quantum wells grown on GaN substrates and templates

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005
    G. A. Garrett
    Abstract Subpicosecond time-resolved photoluminescence (TRPL) has been used to compare the room temperature carrier dynamics in Al0.1Ga0.9N/Al0.3Ga0.7N multiple quantum well (MQW) structures simultaneously deposited on a high quality free standing HVPE GaN substrate (dislocation density ,1 × 107cm,2) and 1 µm MOCVD GaN template on sapphire. The PL lifetime of ,500 ps in the MQW on GaN substrate is about 5 times longer than that for the MQW on GaN template, with a concomitant increase in CW PL intensity. This behavior is attributed primarily to an increase in nonradiative lifetime associated with a 100 times reduction in dislocation density in the GaN substrate. The observation that the PL lifetime in the MQW falls short of the ,900 ps dominant decay time in the GaN substrate may be indicative of generation of additional defects and dislocations due to substrate surface preparation, strain relaxation, and nonoptimal growth temperature associated with the difference in heating of the thin GaN template on sapphire and the thick GaN substrate. An extended PL rise time of greater than 20 ps for the MQW emission when above barrier pumping is employed implies that both wells and barriers are of high quality. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]