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Annihilation
Kinds of Annihilation Terms modified by Annihilation Selected AbstractsCorrelation Between Triplet,Triplet Annihilation and Electroluminescence Efficiency in Doped Fluorescent Organic Light-Emitting DevicesADVANCED FUNCTIONAL MATERIALS, Issue 8 2010Yichun Luo Abstract Triplet,triplet annihilation (TTA) is studied in a wide range of fluorescent host:guest emitter systems used in organic light-emitting devices (OLEDs). Strong TTA is observed in host:guest systems in which the dopant has a limited charge-trapping capability. On the other hand, systems in which the dopant can efficiently trap charges show insignificant TTA, an effect that is due, in part, to the efficient quenching of triplet excitons by the trapped charges. Fluorescent host:guest systems with the strongest TTA are found to give the highest OLED electroluminescence efficiency, a phenomenon attributed to the role of TTA in converting triplet excitons into additional singlet excitons, thus appreciably contributing to the light output of OLEDs. The results shed light on and give direct evidence for the phenomena behind the recently reported very high efficiencies attainable in fluorescent host:guest OLEDs with quantum efficiencies exceeding the classical 25% theoretical limit. [source] Exciton,Exciton Annihilation in Mixed-Phase Polyfluorene FilmsADVANCED FUNCTIONAL MATERIALS, Issue 1 2010Paul E. Shaw Abstract Singlet,singlet annihilation is studied in polyfluorene (PFO) films containing different fractions of , -phase chains using time-resolved fluorescence. On a timescale of >15,ps after excitation, the results are fitted well by a time-independent annihilation rate, which indicates that annihilation is controlled by 3D exciton diffusion. A time-dependent annihilation rate is observed during the first 15,ps in the glassy phase and in the , -phase rich films, which can be explained by the slowdown of exciton diffusion after excitons reach low-energy sites. The annihilation rate in the mixed-phase films increases with increasing fraction of , -phase present, indicating enhanced exciton diffusion. The observed trend agrees well with a model of fully dispersed, -phase chromophores in the surrounding glassy phase with the exciton diffusion described using the line-dipole approximation for an exciton wavefunction extending over 2.5,nm. The results indicate that glassy and, -phase chromophores are intimately mixed rather than clustered or phase-separated. [source] Place Annihilation and Urban Reconstruction: The Experience of Four Towns in Brittany, 1940 to 1960GEOGRAFISKA ANNALER SERIES B: HUMAN GEOGRAPHY, Issue 3 2000Hugh Clout Devastation, revival and reconstruction form guiding themes in this discussion of annihilated settlements in north-west France. For reasons of deep-water access and strategic location, the German occupiers decided to construct massive submarine bases at Brest, Lorient and Saint-Nazaire. Allied bombardment devastated the towns that surrounded them during the Second World War, while the heavily defended walled port of Saint-Malo was annihilated in 1944. With peace restored, prisoners of war and local labourers cleared mines, removed debris and installed large quantities of temporary housing. Development plans, drawn up in the interwar years, provided an important starting point for subsequent master plans which shaped postwar reconstruction. Working under the guidance of the Ministry of Reconstruction and Urbanism, chief planners, architects and reconstruction cooperatives refashioned property units and engineered the rebuilding of Brest, Lorient and Saint-Nazaire along thoroughly modern lines; by contrast, Saint-Malo was rebuilt much as it had been before the war. Many of the buildings of the 1950s now require refurbishment, and urgent initiatives need to be taken to revitalise the local economies of these reconstructed towns, whose role as naval bases, military arsenals and shipbuilding centres has contracted in the wake of political détente and deindustrialisation. [source] Annihilation: the Sense and Significance of Death , Christopher BelshawTHE PHILOSOPHICAL QUARTERLY, Issue 238 2010Steven Luper No abstract is available for this article. [source] Strain Hardening Behavior of Ultrafine- Grained Cu by Analyzing the Tensile Stress-Strain Curve,ADVANCED ENGINEERING MATERIALS, Issue 5 2008C.-X. Huang UFG Cu was found to experience two stages of strain hardening processes under uniaxial tensile stress, which was similar to the Stage,IV and V of CG Cu after large plastic deformation. The storage of dislocations in small grains and dynamic recovery caused by annihilation of dislocations and GB-mediated processes were responsible for the different stages of strain hardening behavior. Improvement of strain hardening capability for UFG metals should be based on the mechanisms of strain hardening. [source] Correlation Between Triplet,Triplet Annihilation and Electroluminescence Efficiency in Doped Fluorescent Organic Light-Emitting DevicesADVANCED FUNCTIONAL MATERIALS, Issue 8 2010Yichun Luo Abstract Triplet,triplet annihilation (TTA) is studied in a wide range of fluorescent host:guest emitter systems used in organic light-emitting devices (OLEDs). Strong TTA is observed in host:guest systems in which the dopant has a limited charge-trapping capability. On the other hand, systems in which the dopant can efficiently trap charges show insignificant TTA, an effect that is due, in part, to the efficient quenching of triplet excitons by the trapped charges. Fluorescent host:guest systems with the strongest TTA are found to give the highest OLED electroluminescence efficiency, a phenomenon attributed to the role of TTA in converting triplet excitons into additional singlet excitons, thus appreciably contributing to the light output of OLEDs. The results shed light on and give direct evidence for the phenomena behind the recently reported very high efficiencies attainable in fluorescent host:guest OLEDs with quantum efficiencies exceeding the classical 25% theoretical limit. [source] Exciton,Exciton Annihilation in Mixed-Phase Polyfluorene FilmsADVANCED FUNCTIONAL MATERIALS, Issue 1 2010Paul E. Shaw Abstract Singlet,singlet annihilation is studied in polyfluorene (PFO) films containing different fractions of , -phase chains using time-resolved fluorescence. On a timescale of >15,ps after excitation, the results are fitted well by a time-independent annihilation rate, which indicates that annihilation is controlled by 3D exciton diffusion. A time-dependent annihilation rate is observed during the first 15,ps in the glassy phase and in the , -phase rich films, which can be explained by the slowdown of exciton diffusion after excitons reach low-energy sites. The annihilation rate in the mixed-phase films increases with increasing fraction of , -phase present, indicating enhanced exciton diffusion. The observed trend agrees well with a model of fully dispersed, -phase chromophores in the surrounding glassy phase with the exciton diffusion described using the line-dipole approximation for an exciton wavefunction extending over 2.5,nm. The results indicate that glassy and, -phase chromophores are intimately mixed rather than clustered or phase-separated. [source] PHOTOGRAPHS, SYMBOLIC IMAGES, AND THE HOLOCAUST: ON THE (IM)POSSIBILITY OF DEPICTING HISTORICAL TRUTHHISTORY AND THEORY, Issue 2 2009JUDITH KEILBACH ABSTRACT Photography has often been scrutinized regarding its relationship to reality or historical truth. This includes not only the indexicality of photography, but also the question of how structures and processes that comprise history and historical events can be depicted. In this context, the Holocaust provides a particular challenge to photography. As has been discussed in numerous publications, this historic event marks the "limits of representation." Nevertheless there are many photographs "showing" the Holocaust that have been produced in different contexts that bespeak the photographers' gaze and the circumstances of the photographs' production. Some of the pictures have become very well known due to their frequent reproduction, even though they often do not show the annihilation itself, but situations different from that; their interpretation as Holocaust pictures results rather from a metonymic deferral. When these pictures are frequently reproduced they are transformed into symbolic images, that is, images that can be removed from their specific context, and in this way they come to signify abstract concepts such as "evil." Despite being removed from their specific context these images can, as this essay argues, refer to historical truth. First, I explore the arguments of some key theorists of photography (Benjamin, Kracauer, Sontag, Barthes) to investigate the relationship between photography and reality in general, looking at their different concepts of reality, history, and historical truth, as well as the question of the meaning of images. Second, I describe the individual circumstances in which some famous Holocaust pictures were taken in order to analyze, by means of three examples, the question what makes these specific pictures so particularly suitable to becoming symbolic images and why they may,despite their abstract meaning,be able to depict historical truth. [source] High-Gain Broadband Solid-State Optical Amplifier using a Semiconducting Copolymer,ADVANCED MATERIALS, Issue 1 2009Dimali Amarasinghe A dilute fluorene copolymer produces enhanced optical amplification. High gain with 1000 times optical amplification and a long lifetime is achieve in only 1mm of the material, and exciton,exciton annihilation is suppressed. [source] Bcl- XL and MCL-1 constitute pertinent targets in ovarian carcinoma and their concomitant inhibition is sufficient to induce apoptosisINTERNATIONAL JOURNAL OF CANCER, Issue 4 2010Emilie Brotin Abstract In ovarian carcinomas, recurrence and acquired chemoresistance are the first leading causes of therapeutic failure and are responsible for the poor overall survival rate. Cisplatin exposure of sensitive cells has been previously associated with a down-regulation of Bcl- XL expression and apoptosis, whereas recurrence was systematically observed when Bcl- XL expression was maintained. Bcl- XL down-regulation could thus constitute an interesting chemosensitizing strategy. We showed that a Bcl- XLtargeted RNA interference strategy efficiently sensitized chemoresistant ovarian carcinoma cells to cisplatin, but some of them were still able to re-proliferate. Considering the possible cooperation between Bcl- XLand MCL-1, we investigated the possibility to avoid recurrence in vitro using a multi-targeted RNAi strategy directed against these two anti-apoptotic proteins. We showed that their concomitant inhibition lead to massive apoptosis in absence of cisplatin, this multi-targeted RNAi approach being much more efficient than conventional chemotherapy. We thus demonstrated that Bcl- XL and MCL-1 cooperate to constitute together a strong molecular "bolt", which elimination could be sufficient to allow chemoresistant ovarian carcinoma cells apoptosis. Moreover, we demonstrated that in presence of a low concentration of cisplatin, the concomitant down-regulation of Bcl- XL and MCL-1 allowed a complete annihilation of tumour cells population thus avoiding subsequent recurrence in vitro in cell lines highly refractory to any type of conventional chemotherapy. Therefore, Bcl- XL and MCL-1 targeted strategies could constitute an efficient therapeutic tool for the treatment of chemoresistant ovarian carcinoma, in association with conventional chemotherapy. [source] Radical annihilation of ,-ray-irradiated contact lens blanks made of a 2-hydroxyethyl methacrylate copolymer at elevated temperaturesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010Young-Shang Lin Abstract The annihilation of the radicals in irradiated 2-hydroxyethyl methacrylate copolymer was analyzed by the use of electron paramagnetic resonance (EPR) spectroscopy. The EPR spectra were deconvoluted into three radicals: a quartet (Ra), a triplet (Rb), and a broad singlet (Rc). Radical Ra was attributed to coupling with a methyl radical and/or a doublet or triplet with about the same hyperfine coupling due to a methylene radical. Radical Rb was due to a methylene radical produced by main-chain scission. Radical Rc was attributed to various free radicals without coupling to protons. By comparing the EPR spectra of radicals Ra, Rb, and Rc with the spectrum of a 2,2-diphenyl-1-picrylhydrazyl (DPPH) standard with a known spin number, we calculated the spin numbers of the radicals, which decreased with time in the temperature range 25,45°C, regardless of the irradiation dose. The annealing of Ra and Rb and the annealing of Rc at longer times followed second-order kinetics; these were different from the kinetics for the color formation and defect-controlled hardening of polymers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Effects of bivalve shell particles of hyriopsis cumingii on the performances of epoxy resin studied by positron annihilationJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008Xudong Sun Abstract Mussel shell particles sized in micrometer level have been prepared with a ball mill. The X-ray powder diffractrometer (XRD) and Fourier transform infrared (FTIR) results proved that the shell particles contained mainly CaCO3 in the form of aragonite, together with small amount of organic phase. EP modified with shell particles showed a much rougher fracture surface than unfilled EP. The mechanical properties have been improved obviously by adding the shell particles in EP from 1% to 5%. The particle would occupy a number of free volume holes of the EP matrix. This would lead to a decrease in the total free volume concentration of the composites. The particles acted as a bridge to make more molecules interconnected for the good interfacial adhesion, resulting in a reduction of the free volume hole size in the interfacial layers. I2 reached its highest value when 3% shell particles were added and then decreased as the shellparticles content increased. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] An improved model for boron diffusion and activation in siliconAICHE JOURNAL, Issue 2 2010Charlotte T. M. Kwok Abstract Technologies such as solid-phase epitaxial regrowth and millisecond annealing techniques have led to a wide range of maximum temperatures and heating rates for activating dopants and eliminating ion implantation damage for transistor junction formation. Developing suitable annealing strategies depends on mathematical models that incorporate accurate defect physics. The present work describes a model that includes a newly discovered representation of defect annihilation at surfaces and of near-surface band bending, together with an improved representation of interstitial clustering. Key parameters are determined by maximum likelihood (ML) estimation and maximum a posteriori (MAP) estimation. The model yields a substantially improved ability to model the behavior of implanted boron over a wide range of annealing conditions. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Electrogenerated chemiluminescence of benzo 15-crown-5 derivativesJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 1 2009Xiao Jiang Abstract Novel electrogenerated chemiluminescence (ECL) reagents C1, C2, and C3 with high fluorescence quantum yields bearing 15-crown-5 moiety have been synthesized and characterized. The photophysical, electrochemical, and ECL characters of these compounds have been studied in a 1:1 (v/v) PhH/MeCN mixed solvent. The ECL intensity is enhanced distinctly with the increase in the fluorescence quantum yield. Their ECL behaviors have been studied using annihilation and co-reactant methods (tri- n -propylamine (TPrA) was used as a co-reactant), respectively. The stable ECL emissions of compounds C1,C3 can be ascribed to the typical and simple monomer ECL emission via S-route. Copyright © 2008 John Wiley & Sons, Ltd. [source] The Tully,Fisher relation and its implications for the halo density profile and self-interacting dark matterMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2000H. J. Mo We show that the Tully,Fisher relation observed for spiral galaxies can be explained in the current scenario of galaxy formation without invoking subtle assumptions, provided that galactic-sized dark haloes have low concentrations which do not change significantly with halo circular velocity. This conclusion does not depend significantly on whether haloes have cuspy or flat profiles in the inner region. In such a system, both the disc and the halo may contribute significantly to the maximum rotation of the disc, and the gravitational interaction between the disc and halo components leads to a tight relation between the disc mass and maximum rotation velocity. The model can therefore be tested by studying the Tully,Fisher zero points for galaxies with different disc mass-to-light ratios. With model parameters (such as the ratio between disc and halo mass, the specific angular momentum of disc material, disc formation time) chosen in plausible ranges, the model can well accommodate the zero-point, slope and scatter of the observed Tully,Fisher relation, as well as the observed large range of disc surface densities and sizes. In particular, the model predicts that low surface brightness disc galaxies obey a Tully,Fisher relation very similar to that of normal discs, if the disc mass-to-light ratio is properly taken into account. About half of the gravitational force at maximum rotation comes from the disc component for normal discs, while the disc contribution is lower for galaxies with a lower surface density. The halo profile required by the Tully,Fisher relation is as concentrated as that required by the observed rotation curves of faint discs, but less concentrated than that given by current simulations of cold dark matter (CDM) models. We discuss the implication of such profiles for structure formation in the Universe and for the properties of dark matter. Our results cannot be explained by some of the recent proposals for resolving the conflict between conventional CDM models and the observed rotation-curve shapes of faint galaxies. If dark matter self-interaction (either scattering or annihilation) is responsible for the shallow profile, the observed Tully,Fisher relation requires the interaction cross-section ,X to satisfy ,,X|v|,/mX,10,16 cm3 s,1 GeV,1, where mX is the mass of a dark matter particle. [source] 5.,The Project of Reconciliation and the Road to Redemption: Hegel's Social Philosophy and Nietzsche's CritiqueAMERICAN JOURNAL OF ECONOMICS AND SOCIOLOGY, Issue 1 2009Steven V. Hicks Arthur Schopenhauer once observed: "A Philosophy in between the pages of which one does not hear the tears, the weeping and gnashing of teeth and the terrible din of mutual universal murder is no [genuine] philosophy."1 Certainly, the unforgettable events of the twentieth and early twenty-first centuries, which bear the names Auschwitz, Hiroshima, Rwanda, and Darfur, pose a challenge for philosophical thinking to prove itself equal to what emerges from these horrific events. To that end, my paper looks back to the philosophies of G. W. F. Hegel and Friedrich Nietzsche,in particular to their vision of a social reconciliation and cultural redemption,as a source of inspiration in our efforts to meet the challenges posed for a philosophy of the future by the global scale of violence, human suffering, and alienation. In what follows, I first offer a comparative analysis of Hegel's "project of reconciliation" with Nietzsche's "project of redemption." I then consider whether or not either philosopher can provide us with a coherent and attractive ethical/sociopolitical alternative for our postmodern world,a world still characterized by global violence, injustice, genocide, ecological degradation, and the prospect of nuclear annihilation. [source] Interrogating Security: A Life Story in HistoryPEACE & CHANGE, Issue 3 2000Geoffrey S. Smith This essay seeks to synthesize personal memoir and history by focusing on the author's life experiences during his first thirteen years. Interrogating security suggests the ways in which big issues,war, peace, the threatof nuclear annihilation, security and secrecy, and youthful masculinity,hit home close to home as well as in the larger political arena. The essay also indicates important continuities between hot and cold war and,in microcosm,some of the costs of developments during the late 1940s and early 1950s. In sum, it proposes some reasons why a young boynurtured in a patriotic ambience became a ,subversive' adult. [source] Deep levels associated with dislocation annihilation by Al pre-seeding and silicon delta doping in GaN grown on Si(111) substratesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 2 2008C. B. Soh Abstract The introduction of Si burst during the growth of GaN film on Si(111) substrate by MOCVD formed a Six Ny layer which leads to an effective reduction in the density of screw dislocations. The reduction is associated with bending of screw dislocations to form a square dislocation loop when neighbouring dislocations with opposite Burger's vector paired up. The concentration of electron traps Ec,Et ,0.17,0.26 eV which is associated with screw dislocations is substantially reduced and a kink is left at the silicon rich position. The mixed-edge dislocation, however, is not annihilated by the Six Ny layer. Addition of TMAl burst for the AlN growth leads to a substantial reduction in trap concentration associated with the nitrogen vacancies, VN, and antisite of nitrogen, NAl, at Ec,Et ,0.10 eV and Ec,Et , 0.60 eV respectively. This improves the quality of the subsequent layer of HT-GaN grown and is useful for device fabrication. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effects of water vapor introduction during Cu(In1,xGax)Se2 deposition on thin film properties and solar cell performancePHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2006S. Ishizuka Abstract The effects of water vapor introduction during the growth of Cu(In1,xGax)Se2, specifically CuInSe2 (CISe), Cu(In,Ga)Se2 (CIGSe), and CuGaSe2 (CGSe) thin films were studied. We have developed thus far a novel technique to improve CIGSe (x , 0.5) cell performance by means of water vapor introduction during CIGSe deposition. In this study, we have examined the effectiveness of water vapor introduction for other x -compositions (CISe and CGSe). Variations in the electrical properties observed in CIGSe (x , 0.5), that is, increasing hole density and conductivity with water vapor introduction, were also observed in CISe and CGSe. Water vapor introduction affected solar cell performance as well; open circuit voltages, short circuit current densities, and efficiencies were improved. The improvements in cell performance are thought to be related to annihilation of donor defects arising from Se-vacancies by incorporation of oxygen from the water vapor. In addition to this, the sodium content in the CIGSe layers was found to depend on the partial pressure of water vapor during deposition. This result suggests that the improvement mechanism is also related with the so-called ,Na-effects'. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Atomic structure of pyramidal defects in GaN:Mg: Influence of annealingPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2006Z. Liliental-Weber Abstract The atomic structure of the characteristic defects (Mg-rich hexagonal pyramids) in p-doped bulk and MOCVD GaN:Mg thin films grown with Ga polarity was determined at atomic resolution by direct reconstruction of the scattered electron wave in a transmission electron microscope. Small cavities were present inside the defects, confirmed also with positron annihilation. The inside walls of the cavities were covered by GaN of reverse polarity compared to the matrix. Annealing of the MOCVD layers lead to slight increase of the defect size and an increase of the room temperature photoluminescence intensity. Positron annihilation confirms presence of vacancy clusters of different sizes triggered by the Mg doping in as-grown samples and decrease of their concentration upon annealing at 900 and 1000 °C. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Vacancy-type defects and electronic structure of perovskite-oxide SrTiO3 from positron annihilationPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 2 2006A. S. Hamid Abstract The vacancy-type defects in Nb-doped SrTiO3 and in undoped SrTiO3, annealed in H2 flow, were investigated by means of positron lifetime and 2D angular correlation of annihilation radiation (ACAR) experiments. The calculations of the lifetime of positron were performed by using atomic superposition (AT-SUP) method. The results showed that positrons annihilate from a free state in the Nb-doped SrTiO3. The trapping centers in the annealed sample were found to be oxygen vacancies VO associated with relaxation of the surrounding ions. Moreover, the momentum distributions of the samples studied were correlated to the variation of their electronic structure. It was proposed from the drastic change in the momentum distribution upon introduction of VO, that 2D-ACAR technique is a sensitive tool for acquiring information on the electronic and bond structure of the perovskite-oxides. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effect of magnetic field on the corrosion of iron and St20 steel as studied by positron annihilationPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2010Ryszard Pietrzak Abstract Lifetime spectra of positron annihilation in iron and St20 steel corroded in the water solution of HCl and in vapour above its surface have been investigated with emphasis on the effect of corrosion time and environment (solution or vapour) as well as of the presence and orientation of the magnetic field on the measured positron annihilation parameters. All the registered positron lifetime spectra consist of two components. For corroded samples the intensities of the two components as well as the corresponding values of the mean positron lifetime, differ from those for uncorroded material. The corrosion-induced changes in the positron annihilation parameters depend on the corrosion environment (solution or vapour) and on the presence and direction of external magnetic field. [source] Positron preferential annihilation in Bi,Sb alloysPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2009Jerzy Dryzek Abstract We report the measurements of the positron annihilation characteristics, i.e., positron lifetime and coincidence Doppler broadening spectra performed on five Bi,Sb alloys having a Bi content between 12.5 and 81,at.%. The strong effect of the preferential annihilation of positrons with the electrons of the Bi atoms has been revealed in these alloys. [source] Molecular dynamics simulation of annihilation of 60° dislocations in Si crystalsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2009Qingyuan Meng Abstract The annihilation of two 60° shuffle dislocations is studied via the molecular dynamics method. The Stillinger,Weber (SW) potential and environment-dependent interatomic potential (EDIP) are used to describe the atomic interactions. The simulation results show that the complete annihilation of the 60° dislocations takes place only when the two dislocations lie on the same slip plane. The annihilation process may occur without external shear stress when the temperature is higher than a critical value. It is found that the critical temperature increases exponentially as a function of distance between the two dislocations. Also revealed in this simulation is an incomplete annihilation occurring when the distance between the slip planes of the two dislocations is less than about 1 nm. If the distance between the two slip planes is larger than about 1 nm, the dislocations will glide on their own slip planes as if no interaction exists between them. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Antisite defect-related luminescence in (LaLu)3Lu2Ga3O12 garnet single crystalsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 9 2007Yu. Zorenko Abstract Intrinsic luminescence of the undoped (LaLu)3Lu2Ga3O12 garnet (LLGG) single crystals with high concentration of LuLa antisite defects (AD) has been studied for the first time under excitation by 1.5 ns pulse X-ray radiation. It has been found that the host luminescence of LLGG crystal consists of two emission bands in the UV range. The band peaked at 3.80 eV at 77 K has been related to the luminescence of localized excitons (LE) perturbed by the presence of AD whereas the band peaked at 3.37 eV has been related to the radiative annihilation of bound-state excitons localized directly at LuLa AD. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Positron annihilation at grain boundaries in metalsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2007J. Kuriplach Abstract Positron annihilation at selected tilt and twist grain boundaries in iron and nickel is examined theoretically. First the atomic structure of studied perfect and imperfect grain boundaries is obtained using molecular dynamics simulations. Characteristics of positrons trapped at such GBs are then calculated employing the atomic superposition method and are related to free volumes found at GBs. It is observed that in some cases vacancies introduced into ideal grain boundaries do not result in an increase of the positron lifetime. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Density change of ion irradiated polystyrene studied by positron annihilation and SAICASPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2007F. Saito Abstract Ion-irradiated polystyrene was investigated using positron annihilation DBS, AFM and SAICAS. SAICAS revealed effective crosslink formation and molecular chain scission. Due to efective crooslink formation, the subsidence of the surface hardly produced as shown in the AFM image. From positron annilation and SAICAS, the density of the irradiated layer was estimated to be 0.8 and 0.6 g/cm3 for the ion irradiation of fluence 5×1015 and 1×1016 ions/cm2, respectively, while the density of the as received sample was 1.02 g/cm3. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structural heterogeneity in glassy polymeric materials revealed by positron annihilation and other supplementary techniquesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2007V. P. Shantarovich Abstract A disagreement between effective sizes of elementary free volumes found from the four component PATFIT analyses of positronium annihilation lifetime spectra and experiments on low temperature sorption for two membrane materials of internal microporosity poly(tri-methyl-silyl-propyne) PTMSP and spiro-linked benzodioxane polymer PIM-1 is described and discussed. This disagreement can be minimized essentially using the fifth lifetime component but not the Gaussian distribution of the fourth component. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Verifying the RTE model: ortho-positronium lifetime measurement on controlled pore glassesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2007S. Thraenert Abstract In porous media, the vacuum lifetime of ortho-positronium (o-Ps) of , = 142 ns can be reduced markedly by pick-off annihilation (interaction with electrons of the host material). So the o-Ps lifetime is determined by the pore size which can be extracted by utilising approved models like the Tao-Eldrup model for pore sizes smaller than 1 nm and the Tokyo model or RTE model for larger pore sizes. The RTE model contains an explicit temperature dependence of the o-Ps lifetime. Experiments on controlled pore glasses (CPG) with different pore sizes (2-70 nm) at different temperatures (50-500 K) were performed to verify the RTE model. A general agreement for T = 300 K could be found. The temperature dependence of the lifetime, especially for low temperatures, could not be approved sufficiently. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Lattice-matched boronphosphide (BP)/hexagonal GaN heterostructure for inhibition of dislocation penetrationPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2003T. Udagawa Abstract The crystallographic feature of a metal-organic CVD grown zinc-blende BP/wurtzite-GaN heterostructure was characterized utilizing high-resolution TEM and TED techniques. On the heterostructure system, the epitaxial relationship was revealed to be (0001), ,a -axis,-GaN//(111), ,110,-BP. (111)-BP was also found to be orientated in the "double positioning" with tracing hexagonal shape of (0001)-GaN probably because of the matching in the spacings between the a -axis of GaN (a = 0.319 nm) and the {110}-planes of BP (= 0.320 nm). (111)-BP was additionally recognized to stack in the c -direction of GaN with period of just half value of the c -axis (c = 0.518 nm). In addition to the matching property, (111)-BP joined with (0001)-GaN was found to be effective for annihilation of dislocations penetrating from the underneath GaN. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||||||||