140 research outputs found
ZnSe/GaAs(001) heterostructures with defected interfaces: structural, thermodynamic and electronic properties
We have performed accurate \emph{ab--initio} pseudopotential calculations for
the structural and electronic properties of ZnSe/GaAs(001) heterostructures
with interface configurations accounting for charge neutrality prescriptions.
Beside the simplest configurations with atomic interdiffusion we consider also
some configurations characterized by As depletion and cation vacancies,
motivated by the recent successfull growth of ZnSe/GaAs pseudomorphic
structures with minimum stacking fault density characterized by the presence of
a defected (Zn,Ga)Se alloy in the interface region. We find that--under
particular thermodynamic conditions--some defected configurations are favoured
with respect to undefected ones with simple anion or cation mixing, and that
the calculated band offsets for some defected structures are compatible with
those measured. Although it is not possible to extract indications about the
precise interface composition and vacancy concentration, our results support
the experimental indication of (Zn,Ga)Se defected compounds in high-quality
ZnSe/GaAs(001) heterojunctions with low native stacking fault density. The
range of measured band offset suggests that different atoms at interfaces
rearrange, with possible presence of vacancies, in such a way that not only
local charges but also ionic dipoles are vanishing.Comment: 26 pages. 5 figures, revised version, in press (Physical Review B
Resonant spin-dependent electron coupling in a III-V/II-VI heterovalent double quantum well
We report on design, fabrication, and magnetooptical studies of a III-V/II-VI
hybrid structure containing a GaAs/AlGaAs/ZnSe/ZnCdMnSe double quantum well
(QW). The structure design allows one to tune the QW levels into the resonance,
thus facilitating penetration of the electron wave function from the diluted
magnetic semiconductor ZnCdMnSe QW into the nonmagnetic GaAs QW and vice versa.
Magneto-photoluminescence studies demonstrate level anticrossing and strong
intermixing resulting in a drastic renormalization of the electron effective g
factor, in perfect agreement with the energy level calculations.Comment: 4 pages, 5 Postscript figures, uses revtex
Fire analysis of steel frames with the use of artificial neural networks
The paper presents an alternative approach to the modelling of the mechanical behaviour of steel frame material when exposed to the high temperatures expected in fires. Based on a series of stress-strain curves obtained experimentally for various temperature levels, an artificial neural network (ANN) is employed in the material modelling of steel. Geometrically and materially, a non-linear analysis of plane frame structures subjected to fire is performed by FEM. The numerical results of a simply supported beam are compared with our measurements, and show a good agreement, although the temperature-displacement curves exhibit rather irregular shapes. It can be concluded that ANN is an efficient tool for modelling the material properties of steel frames in fire engineering design studies. (c) 2007 Elsevier Ltd. All rights reserved
Extreme Energy Cosmic Rays (EECR) Observation Capabilities of an "Airwatch from Space'' Mission
The longitudinal development and other characteristics of the EECR induced
atmospheric showers can be studied from space by detecting the fluorescence
light induced in the atmospheric nitrogen. According to the Airwatch concept a
single fast detector can be used for measuring both intensity and time
development of the streak of fluorescence light produced by the atmospheric
shower induced by an EECR. In the present communication the detection
capabilities for the EECR observation from space are discussed.Comment: 3 pages (LaTeX). To appear in the Proceedings of TAUP'9
The influence of LiF layer abd ZnO nanoparticels addings on the performances of flexible photovoltaic cells based on polymer blends
International audienceFlexible organic solar cells were successfully prepared using spin-coating technique on PET substrates covered with a thick layer of ITO. The goal of this study is to identify the effects of the LiF layer and ZnO nanoparticles mixing in PEDOT:PSS solution and to compare the photovoltaic properties of these âcustomizedâ cells PET/ITO/PEDOT:PSS + ZnO nanoparticles/P3HT:PCBM(1:1)/Al, PET/ITO/PEDOT:PSS + ZnO nanoparticles/P3HT:PCBM(1:1)/LiF/Al, with ones of the âconventionalâ structures, PET/ITO/PEDOT:PSS/P3HT:PCBM(1:1)/Al. The thickness of the LiF layer, deposited by thermal vacuum evaporation, was two nanometers. Composite samples were prepared by adding ZnO nanoparticles into PEDOT:PSS solution, followed by ultrasonication. I-V characteristics were measured in dark and under A.M.1.5 conditions for all samples immediately and after one month from the preparation date. The action spectra measurements revealed that the structures which have a nanometric LiF layer are more stable than those without. Photoelectrical measurements indicate that the ZnO nanoparticles have a positive influence on the conversion efficiency and also to reduce the serial resistance of the structure
Conservative treatment followed by chemotherapy with doxorubicin and ifosfamide for cervical sarcoma botryoides in young females
THE INFLUENCE OF LiF LAYER AND ZnO NANOPARTICLES ADDINGS ON THE PERFORMANCES OF FLEXIBLE PHOTOVOLTAIC CELLS BASED ON POLYMER BLENDS
Self-Suspended Nanomesh Scaffold for Ultrafast Flexible Photodetectors Based on Organic Semiconducting Crystals
Selfâstanding nanostructures are of fundamental interest in materials science and nanoscience and are widely used in (optoâ)electronic and photonic devices as well as in microâelectromechanical systems. To date, largeâarea and selfâstanding nanoelectrode arrays assembled on flexible substrates have not been reported. Here the fabrication of a hollow nanomesh scaffold on glass and plastic substrates with a large surface area over 1 mm2 and ultralow leakage current density (â1â10 pA mmâ2 @ 2 V) across the empty scaffold is demonstrated. Thanks to the continuous subâmicrometer space formed in between the nanomesh and the bottom electrode, highly crystalline and dendritic domains of 6,13âbis(triisopropylsilylethinyl)pentacene growing within the hollow cavity can be observed. The high degree of order at the supramolecular level leads to efficient charge and exciton transport; the photovoltaic detector supported on flexible polyethylene terephthalate substrates exhibits an ultrafast photoresponse time as short as 8 ns and a signalâtoânoise ratio approaching 10^5. Such a hollow scaffold holds great potential as a novel device architecture toward flexible (optoâ)electronic applications based on selfâassembled micro/nanocrystals
Fast-Response Photonic Device Based on Organic-Crystal Heterojunctions Assembled into a Vertical-Yet-Open Asymmetric Architecture
Crystalline dioctyl-3,4,9,10-perylenedicarboximide nanowires and 6,13-bis(triisopropylsilylethynyl) pentacene microplates are integrated into a vertical-yet-open asymmetrical heterojunction for the realization of a high-performance organic photovoltaic detector, which shows fast photoresponse, ultrahigh signal-to-noise ratio, and high sensitivity to weak light
A nanomesh scaffold for supramolecular nanowire optoelectronic devices
Supramolecular organic nanowires are ideal nanostructures for optoelectronics because they exhibit both efficient exciton generation as a result of their high absorption coefficient and remarkable light sensitivity due to the low number of grain boundaries and high surface-to-volume ratio. To harvest photocurrent directly from supramolecular nanowires it is necessary to wire them up with nanoelectrodes that possess different work functions. However, devising strategies that can connect multiple nanowires at the same time has been challenging. Here, we report a general approach to simultaneously integrate hundreds of supramolecular nanowires of N,NâČ-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) in a hexagonal nanomesh scaffold with asymmetric nanoelectrodes. Optimized PTCDI-C8 nanowire photovoltaic devices exhibit a signal-to-noise ratio approaching 107, a photoresponse time as fast as 10â
ns and an external quantum efficiency >55%. This nanomesh scaffold can also be used to investigate the fundamental mechanism of photoelectrical conversion in other low-dimensional semiconducting nanostructures
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