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Optical Characterization (optical + characterization)
Selected AbstractsOptical Characterization and Crystal Structure of the Novel Bronze Type CaxBa1-xNb2O6 (x = 0.28, CBN-28).CHEMINFORM, Issue 38 2003M. Esser Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Synthesis, Structural, and Optical Characterization of a New Europium(II) Tin Selenide, Eu8(Sn4Se14)(Se3)2 with a (Sn4Se14)12- Building Block.CHEMINFORM, Issue 48 2001Carl R. Evenson IV Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Bacteriorhodopsin-Monolayer-Based Planar Metal,Insulator,Metal Junctions via Biomimetic Vesicle Fusion: Preparation, Characterization, and Bio-optoelectronic Characteristics,ADVANCED FUNCTIONAL MATERIALS, Issue 8 2007D. Jin Abstract A reliable and reproducible method for preparing bacteriorhodopsin (bR)-containing metal,biomolecule,monolayer-metal planar junctions via vesicle fusion tactics and soft deposition of Au top electrodes is reported. Optimum monolayer and junction preparations, including contact effects, are discussed. The electron-transport characteristics of bR-containing membranes are studied systematically by incorporating native bR or artificial bR pigments derived from synthetic retinal analogues, into single solid-supported lipid bilayers. Current,voltage (I,V) measurements at ambient conditions show that a single layer of such bR-containing artificial lipid bilayers pass current in solid electrode/bilayer/solid electrode structures. The current is passed only if retinal or its analogue is present in the protein. Furthermore, the preparations show photoconductivity as long as the retinal can isomerize following light absorption. Optical characterization suggests that the junction photocurrents might be associated with a photochemically induced M-like intermediate of bR. I,V measurements along with theoretical estimates reveal that electron transfer through the protein is over four orders of magnitude more efficient than what would be estimated for direct tunneling through 5,nm of water-free peptides. Our results furthermore suggest that the light-driven proton-pumping activity of the sandwiched solid-state bR monolayer contributes negligibly to the steady-state light currents that are observed, and that the orientation of bR does not significantly affect the observed I,V characteristics. [source] Optical characterization of Zn0.97Mn0.03Se/ZnSe0.92Te0.08 type II multiple-quantum-well structuresPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2007D. Y. Lin Abstract The optical characterization of type II Zn0.97Mn0.03Se/ZnSe0.92Te0.08 multiple-quantum-well structures have been studied using photoluminescence (PL), temperature-dependent PL, polarized PL, power-dependent PL, and photoreflectance (PR) in this study. The PL data reveal that the band alignment of the ZnMnSe/ZnSeTe system is type II. Comparing with the theoretical calculation based on the Schrodinger equation, the valence band offset is estimated to be 0.6 eV. From the power-dependent PL spectra, it is observed that the peak position of PL spectra shows a blueshift under different excitation power. The blueshift can be interpreted in terms of the band-bending effect due to spatially photoexcited carriers in a type II alignment. The thermal activation energy (EA) for quenching the PL intensity was determined from tem- perature-dependent PL spectra. The thermal activation energy was found to decrease as the thickness of ZnMnSe and ZnSeTe layers decreased. The polarized PL spectra exhibit a large in-plane polarization with the polarization degree up to 50%. The polarization does not depend on the excitation intensity as well as temperature. The large polarization is an inherent orientation of the interface chemical bonds. The higher transition features observed in PR spectra show a blueshift with the similar trend observed in the PL spectra as decreasing the thickness of ZnSeTe layer. This result provides a consistent evidence for the assumption that square-like well shapes were built in the ZnSeTe layers. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Optical characterization of bulk GaN substrates with c -, a -, and m -plane surfacesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009P. P. Paskov Abstract Thick free-standing GaN grown by hydride vapour phase epitaxy and epi-ready substrates with c -, a -, m -plane surfaces are examined by variable-temperature photoluminescence (PL), polarized PL and spatially resolved micro-PL. Both as-grown samples and polished substrates exhibit linewidth of the donor-bound exciton emission below 0.7 meV at 2 K indicative of a high structural quality of the material. For as-grown samples the relative intensity of green (2.4 eV) and red (1.8 eV) deep-level-defect emissions are found to decrease with increasing sample thickness. Based on plentiful two-electron-transition spectra measured in the samples the electronic fine structure of the donors and their bound-exciton complexes was examined and discussed. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Optical characterization of GaN microcavity fabricated by wet etchingPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006C.-Y. Lu Abstract We report a novel technique to fabricate gallium nitride (GaN) microcavities by combining the methods of photo-enhanced wet chemical oxidation and crystallographic etching. Such GaN microcavities exhibit mirror-like vertical facets composing of {1100}GaN and various gemoetry of hexagonal, trigonal and cylindrical shapes. The emission spectra of the GaN micro-cavities are found in resonance with the whispering gallery (WG) modes when pumped with a 266 nm Nd:YAG laser. The signatures of GaN microcavities were further characterized by an increase of the WG mode spacing with the reduced device size and suppression of the side mode emission intensity with pump intensity. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Optical characterization of concentrated dispersions: applications to laboratory analyses and on-line process monitoring and control,POLYMER INTERNATIONAL, Issue 9 2004H Buron Abstract Light scattering methods are often used to study the stability of suspensions or emulsions and to estimate the dispersed phase properties such as particle size and volume fraction. However, such optical methods often require a previous dilution of the dispersion because of a limited measurement range, and are then unable to give information about the real physical state of dense heterogeneous media. A new technology based on multiple light scattering analysis and called Turbiscan has been recently developed by a French company, Formulaction, to fill this gap and to characterize both diluted and concentrated dispersions. In the first part, we review the physical concepts of multiple light scattering by dispersions. In relation to the optical analyser Turbiscan, we present physical and statistical models for the radiative transfer in dense suspensions. In the second part, we investigate the influence of particle volume fraction and particle size (polystyrene latex bead suspensions) on the backscattered and transmitted light fluxes measured by Turbiscan. The experimental data are compared with results from the physical models. In the last section, we use the optical analyser Turbiscan Lab to detect and characterize various concentrated dispersions destabilization (coalescence, flocculation, creaming and sedimentation), and then the Turbiscan On Line to monitor and characterize an emulsification process under ultrasonic agitation. Copyright © 2004 Society of Chemical Industry [source] 4241: Optical characterization of PCOACTA OPHTHALMOLOGICA, Issue 2010TJTP VAN DEN BERG Purpose Opacification of the posterior capsule (PCO) is known to degrade visual function on both counts: small angle resolution (visual acuity and contrast sensitivity) as well as large angle light scatter (straylight). No studies have been performed to delineate the optical characteristics of PCO as a basis for explanation of these visual function defects. Methods Preparations of IOL-capsule combinations were harvested from donor eyes after removal of the cornea. They were mounted submersed in saline in an optical set-up, used earlier to characterize the optics of the crystalline lens (van den Berg et al. VR 1999). Illuminated by monochromatic beams of light, the light spreading originating from different areas of the preparation was measured as function of wavelength for different angles. Based on physical optics theory, the optical characteristics of PCO was derived. The data will be presented translated into the straylight parameter, directly comparable to the figures obtained in vivo using the clinical straylight meter (C-Quant from Oculus). Results Twenty successful preparations were harvested with at least some PCO areas. PCO grades varied from severe to slight. Two physically different types of light spreading could be discriminated. One type corresponding to pearl-like appearance, characterized by little wavelenght dependence and smal angle dominance. The other type corresponding to diffuse scatter, characterized by strong wavelength dependence and large angle dominance. The scatter values measured corresponded to clinical measures of straylight in PCO patients using the C-Quant. Conclusion The light scattering characteristics of PCO show two types of optical disturbance: a refractile type, probably dominated by pearl-like structures, and a diffuse type of scattering of yet unclear origin. [source] Growth and optical characterization of cerium and lead-doped Bi12TiO20 sillenite single crystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 9 2005J. F. Carvalho Abstract Bi12TiO20 (BTO) single crystals doped with PbO and CeO2 were grown by the Top Seeded Solution Growth (TSSG) technique from the liquid phase with nominal compositions of 10Bi2O3 : (1,x)TiO2 : x PbO and 10Bi2O3 : (1,x)TiO2 : xCeO2 with x = 0.25 and 0.10. No growth-related difficulties were encountered other than those typical of sillenite crystals. Samples with good optical quality were obtained and were characterized by optical absorption, dark current, spectral photocurrent dependence, optical activity and electro-optic coefficient measurements. A comparison is made of the results of the optical measurements of doped and undoped BTO crystals. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Growth and optical characterization of Cd1- xBexSe and Cd1- xMgxSe crystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 4-5 2005F. Firszt Abstract Cd1- xBexSe and Cd1- xMgxSe solid solutions were grown from the melt by the high pressure Bridgman method. Optical, luminescence and photothermal properties of these materials were investigated. Spectroscopic ellipsometry was applied for determination of the spectral dependence of the complex dielectric function (E) and refractive index n(E) at room temperature in the photon energy range 0.75-6.5 eV for samples with optic axis (c-axis) perpendicular to the air-sample interface. The critical point (CP) parameters for E0 and E1 transitions were determined using a standard excitonic CP function to fit the numerically calculated differential spectra ,2,2/,E2. The dispersion of the refractive index of the alloys was modelled using a Sellmeier-type relation. The values of fundamental and exciton band-gap energies were estimated from the ellipsometric and photoluminescence measurements. The origin of luminescence in Cd1- xBexSe and Cd1- xMgxSe was discussed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Studies on the growth and optical characterization of dysprosium gadolinium oxalate single crystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 2 2004A. Elizebeth Abstract Preparation and optical characterization of dysprosium gadolinium oxalate (DGO) single crystal is reported. The crystals were grown using silica gel technique, by the controlled reaction of rare earth nitrates with oxalic acid. Crystals were characterized using X-ray powder diffraction, optical absorption and fluorescence studies. Radiative transition probability, fluorescence branching ratio and radiative lifetime of Dy3+ in the crystal are evaluated by the parameterization of the absorption spectrum by the Judd-Ofelt theory. The recorded fluorescence spectrum showed two well resolved peaks at 480 nm and 571 nm and are assigned to the transitions from 4F9/2 , 6H15/2 and 6H13/2 of Dy3+. Stimulated emission crossection and optical gain of these transitions are also evaluated. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A Crystalline Phase Transition and Optical Properties in a CoIICuII Oxamato-Bridged Ferrimagnetic ChainEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 24 2005Cynthia L. M. Pereira Abstract The compound [CoCu(opba)(DMSO)3] (1) [opba = ortho -phenylenebis(oxamato)] has been synthesized and characterized. Its crystal structure has been analyzed by X-ray diffraction techniques at 100 and 298 K. A structural phase-transition has been detected at around 150 K. An orthorhombic crystalline system is found at both temperatures, with very similar unit-cell dimensions. At room temperature 1 crystallizes in the Pnam space group (, -1 phase), with a = 7.6712(2), b = 14.8003(3), c = 21.0028(5) Ĺ, and Z = 4, whereas at low temperature it crystallizes in the Pna21 space group (, -1 phase), with a = 7.3530(2), b = 14.5928(4), c = 21.0510(7) Ĺ, and Z = 4. Both crystalline phases consist of linearly ordered bimetallic chains with the [Cu(opba)]2, units tied by CoII ions to form a one-dimensional system. The DMSO molecules in , -1, which are coordinated to either CuII or CoII, are disordered. At low temperature, a small reorganization of the CuII and CoII environments is observed. The origin of this phase transition, which is completely reversible, is the modification of the crystalline packing with the temperature. Linear birefringence measurements were done on single crystals in the 100,300 K temperature range. Around 150 K, the linear birefringence curve shows an inflexion that is interpreted as being related to the conversion of ,-1 into , -1. Both dc and ac magnetic measurements were performed on the polycrystalline sample. The results reveal a one-dimensional ferrimagnetic behavior. Single crystal optical characterization at room temperature shows that 1 presents a very strong dichroism superposed on the linear birefringence. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Characteristics of two-segment lensed fiber collimatorMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 8 2010Yu-Cheng Lin Abstract A two-segment lensed fiber collimator using gradient index fiber (GIF) of 140 ,m diameter spliced to a coreless fiber (CLF) of 125 ,m, and a single mode fiber (SMF) is demonstrated. The CLF and GIF are treated as a beam expander and lens, respectively. The complex beam parameter method and ABCD law are applied for theoretical analysis. Both numerical and experimental data are presented for optical characterization of the divergence angle and insertion loss in lateral and axial displacement of the device. The divergence angle of 1.5 degrees is obtained for the wavelength of 1.31 ,m at the GIF length of 180 ± 5 ,m and the CLF length of 350 ,m. The variation of insertion loss due to lateral and axial displacement shows good agreement with theory. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1846,1848, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25353 [source] From the Rainbow to the Structure of AtomsPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 6 2007Gérard Gouesbet Abstract The optical rainbow is nowadays of much use, in the laboratory and in industry, in the field of optical characterization. However, the geometrical optics interpretation of the optical rainbow generates a caustic singularity which is a clue that something is wrong, and that a more fundamental theory (in practice, wave optics, or Maxwell's equations) is required to explain the optical rainbow and to accurately enough interpret experiments. There also exists a mechanical rainbow in classical mechanics, also leading to a singularity, implying that classical mechanics is wrong too. To smooth out this singularity, we have to turn to a wave mechanics. By lifting the Hamilton-Jacobi formulation of classical mechanics to a wave mechanics and looking to a time evolution equation, we may reach Schrödinger's equation. We therefore establish a beautiful connection between the rainbow in the sky, and the structure of atoms, in the sky and on earth. [source] Structural and optical characterization of pulsed laser-ablated potassium lithium niobate thin filmsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 12 2009V. Jayasree Abstract Thin films of potassium lithium niobate (K3Li2Nb5O15: KLN) have been prepared on glass substrate, as a function of substrate temperature, using a pulsed laser-deposition (PLD) technique for the first time. Grazing-incidence X-ray diffraction (GIXRD) analysis suggests that KLN films can be grown successfully at a substrate temperature as low as 300,K. The anomalous behavior of the decline of crystalline structure with increase in substrate temperature is explained. The atomic force microscopic (AFM) and scanning electron microscopic (SEM) images show an agglomerated growth mode for the films deposited at a substrate temperature of 300,K and a decrease in grain size with increase in substrate temperature. The films deposited at higher substrate temperatures show ring-like structures. The AFM analysis shows that the rms surface roughness of the film decrease with increase in substrate temperature. The UV,Vis transmission spectra suggest that the nature of the transition in the films is directly allowed. A blue shift in optical bandgap is observed for the films compared to bulk material. The changes in the optical bandgap with substrate temperature are also discussed. [source] MOVPE growth and optical characterization of GaAsN films with higher nitrogen concentrationsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2006F. Nakajima Abstract We have successfully grown high-N-content GaAsN films up to 5.1% on GaAs(001) substrates using tertiarybutylarsine (TBAs) as the As precursor by metalorganic vapour phase epitaxy (MOVPE). The narrow X-ray diffraction (XRD) peaks and clear Pendellosung fringes indicate that the GaAsN/GaAs interface is fairly flat and the GaAsN layers are uniform. By the photoluminescence (PL) measurement at 10 K, the clear PL peaks related to the near-band-edge transition could be detected and the bandgap energy was red-shifted to 1.16 eV in 1.9%-N GaAsN film. But, in higher N-content films no peak could be detected. So, post growth annealing in the reactor was applied to 4.7% and 5.1%-N films, and resulted in an enhancement of the PL peak intensity, and the bandgap energy of 5.1%-N film was consequently determined to be 0.95 eV at room temperature. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Optical super-resolution using higher harmonics and different acquisition modes in an aperture tapping SNOMPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2010Giovanni Longo Abstract Scanning near field optical microscopy (SNOM) is a well-established technique to obtain a sub-wavelength resolution optical characterization, together with nanometer-scale topography images, on any kind of biological or non-biological sample. Recently we have modified a classical SNOM unit to work in the tapping modality, ensuring stability, versatility and good optical resolution and signal to noise ratio. Exploiting the vertical tip movement, in particular, we were able to access two different optical detection modes: light modulation, which can be obtained by a mechanical chopper or by electronically switching the laser on and off; gap modulation in which the tip's vertical oscillation is used to produce, itself, a modulation of the collected light. Several biological and non-biological samples have been investigated and the data reveal that, despite the signal collected in gap-modulation is at least one order of magnitude smaller than in laser-modulation, resolution, and signal-to-noise ratio in the gap-modulated images is preferable. On the other hand, the higher intensity of the laser-modulation signal allows to deconvolve the optical information at higher harmonics of the tip oscillation frequency. This is a well-known procedure used in the apertureless-SNOM setup to enhance the near-field contribution of the scattered light and reduce the noise content. The interesting results obtained in this Aperture setup are described and commented. [source] AFM and SNOM characterization of ordinary chondrites: A contribution to solving the problem of asteroid reddeningPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2010Giuliano Pompeo Abstract Space weathering (SW) is an ensemble of processes that act on a body exposed to the space environment. Typically, the exposure to SW results in the accumulation, at the surface, of nanoparticles, that are thought to be produced through a vaporization and subsequent cooling of the metallo-silicaceous components exposed to the space environment. The presence of such nanoparticles is responsible for the so-called reddening of the asteroids' reflectance spectra (i.e., the increase in Vis,NIR reflectance with increase in wavelength) observed by remote-sensing measurements. To investigate the mechanism of formation of these nanoparticles, we have employed atomic force microscopy (AFM) and scanning near-field optical microscopy (SNOM) to morphologically and optically characterize ordinary chondrites (OC), the most abundant class of meteorites collected on Earth and whose parent bodies are the S-type asteroids. The AFM study reveals the occurrence of a diffuse nanophase (martensite) in the meteorite's metal inclusions. Since the same areas show a reddening of the reflectivity spectra, this suggests that such spectral modification is based on a shock-induced phase transformation of the metal components of the extraterrestrial body. To gain more insight into this nanophase and on its role in the SW of the asteroids, an optical characterization by SNOM has been performed on OCs. In this work we exploited the peculiarity of this technique to search for a correlation between the topography on the nanoscale and the spectral characteristics, at different wavelengths in the red-NIR range, of the observed nanophase. Indeed, a high-resolution mapping of the optical properties of the meteorite provides an interesting method to discriminate between martensite-based and Fe-silicaceous nanoparticles. [source] Structural and optical characterization of (11-22) semipolar GaN on m -plane sapphire without low temperature buffer layerPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010Sung-Nam Lee Abstract We reported the high quality semipolar (11-22) GaN grown on m-sapphire by using the novel two-step growth method without low temperature GaN or AlN buffer layer. It is found that macroscopic surface morphology of semipolar GaN epilayer was very smooth, while microscopic surface structure was arrowhead-like surface structure toward the direction of [1-21-1]. Anisotropic crystal properties of semipolar GaN/m-sapphire were also observed by two incident directions of X-ray beam. Therefore, we suggested that the anisotropic crystal properties and arrow-head like surface structure would be caused by heteroepitaxial crystallograhpic difference between semipolar GaN and m-sapphire. Additionally, photoluminescence (PL) measurements showed the strong bandedge emission of n-type semipolar GaN without yellow luminescence (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Elastic constants of aluminum nitridePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2007M. Kazan Abstract We report on the application of Brillouin spectroscopy as an approach to non-destructive optical characterization of the elastic constants of semiconductors with the wurtzite symmetry. Three different configurations were used to achieve a complete determination of the elastic stiffness constants of bulk AlN substrates grown by the Physical Vapor Transport (PVT) method. The scattering diagrams of these three configurations are presented showing the geometrical arrangements necessary to observe all the elastic stiffness constants for the partially nontransparent wurtzite type of the crystal structure. Because aluminum nitride (AlN) is a suitable material for the fabrication of light emitting devices, the characterization of its elastic constants was carried out very precisely to provide a reliable data which can be used for the determination of residual stress arising during the growth of AlN thin films or wide band gap semiconductor thin films on substrates of AlN. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structural and optical characterization of AlyInxGa1,x ,yN quantum dotsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006V. Pérez-Solórzano Abstract AlyInxGa1,x ,yN quantum dots have been grown by MOVPE on (0001) sapphire substrates. We investigated the dependence of the self-assembled quantum dot density and height on the growth conditions: the growth temperature, the amount of deposited material, and the growth rate interruption. A maximum dot density of 4 × 1010 cm,2 was achieved. The optical properties were studied after overgrowing of the QDs with a GaN cap layer. We observed very intense luminescence in the region between 2.4 and 2.8 eV and decay times of 1.8 ns under resonant excitation. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] BGO glasses: structural and optical characterizationPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2005S. Polosan Abstract Mixtures of 30% Bi2O3 and 70% GeO2 (in molar percents) were prepared followed by the solid state reaction at 700 °C for 30 min. or 24 h using an Al2O3 crucible. After melting at 1050 °C for 10 min. the melt was poured into a preheated graphite plate and then naturally cooled to room temperature (RT). X-ray diffraction measurements (XRD) on the resulting BGO glasses have been performed, and optical absorption spectra recorded at room temperature on the samples obtained using various preparation conditions. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structural and optical characterization of homogeneous monophasic Cu(In1,xGax)(Se1,ySy)2 thin filmsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2004V. Alberts Abstract Single-phase Cu(In1,xGax)(Se1,ySy)2 thin-film absorbers have been prepared by a reproducible two-stage growth method. The growth scheme is based on the selenization/sulfurization of metallic CuIn0.75Ga0.25 alloys in an atmosphere containing a mixture of H2Se/H2S/Ar gases. The degree of S incorporation was carefully controlled by the accurate manipulation of the H2Se/H2S reaction process parameters under defined conditions. Using this novel approach, pentenary alloys with varying degree of S content (i.e. S/(Se+S) ratio = 0.1,0.5) were prepared. A systematic study was conducted in order to establish the relationship between the morphological features, lattice parameters and band gap values of these classes of semiconductor materials. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Characterization of optical collectors for concentration photovoltaic applicationsPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 6 2003I. Antón Abstract The design and characterization of the collector of a photovoltaic concentrator system is commonly carried out for a given receiver, the optical parameters of the collector being linked to it. This paper, which has substantial tutorial content, deals with the characterization of collectors for concentrator photovoltaic systems, independently of any receiver, and providing the necessary parameters for the design of a system. This strategy allows the parameters related to the collector and the receiver, which are usually manufactured by different industries, to be totally separated. It also allows the optical collectors coming from non-photovoltaic industries to be evaluated. The information that the mirror and lens manufacturers should provide for a photovoltaic concentrator application can be summarized under three characteristics: overall optical efficiency; light distribution; and acceptance angle. Theory, equipment, and procedures to carry out the optical characterization of the collectors are explained. Copyright © 2003 John Wiley & Sons, Ltd. [source] Thick crack-free AlGaN films deposited by facet-controlled epitaxial lateral overgrowthPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2003R. Liu Abstract Thick crack-free AlGaN films have been grown on inclined-facet GaN templates. Light emitting diodes with , = 323 nm has been achieved on these epilayers. The GaN template was grown at a low temperature in order to obtain triangle-facet growth fronts. Subsequent growth of AlGaN on this template involving a lateral overgrowth process exhibits interesting properties. The microstructure and optical characterizations were done using transmission electron microscopy and cathodoluminescence. At the AlGaN/GaN interface, a high density of dislocations was created due to lattice mismatch strain. Another unexpected set of triangular boundaries was observed inside the AlGaN layer, which grew without any change of the growth parameters. These boundaries were found to arise from domains grown in different directions. Mono-chromatic cathodoluminescence images indicate that Al content is different between the vertically-grown and the laterally-grown domains, suggesting that lattice mismatch strain exists between them. Dislocations were created at these mismatched boundaries to relax the strain. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Long-term Reliability Prediction of 935 nm LEDs Using Failure Laws and Low Acceleration Factor Ageing TestsQUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 6 2005Y. Deshayes Abstract Numerous papers have already reported various results on electrical and optical performances of GaAs-based materials for optoelectronic applications. Other papers have proposed some methodologies for a classical estimation of reliability of GaAs compounds using life testing methods on a few thousand samples over 10,000 hours of testing. In contrast, fewer papers have studied the complete relation between degradation laws in relation to failure mechanisms and the estimation of lifetime distribution using accelerated ageing tests considering a short test duration, low acceleration factor and analytical extrapolation. In this paper, we report the results for commercial InGaAs/GaAs 935 nm packaged light emitting diodes (LEDs) using electrical and optical measurements versus ageing time. Cumulative failure distributions are calculated using degradation laws and process distribution data of optical power. A complete methodology is described proposing an accurate reliability model from experimental determination of the failure mechanisms (defect diffusion) for this technology. Electrical and optical characterizations are used with temperature dependence, short-duration accelerated tests (less than 1500 h) with an increase in bias current (up to 50%), a small number of samples (less than 20) and weak acceleration factors (up to 240). Copyright © 2005 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||