bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optical Gain in Foerster Energy Transfer Based Organic Guest-Host-Systems
Authors: Rabe Torsten , Döring Sebastian , Hildebrandt Niko , Riedl Thomas , Kowalsky Wolfgang , Scherf Ullrich 
Published: August 2010

AbstractWe study the optical gain for various doping concentrations in a dye doped polymer (poly-[9,9-dioctylfluorene] with 6,6'-[2,2'-octyloxy-1,1'-binaphthyl] spacer groups (BN-PFO) doped by the stilbene dye 1,4-bis[2-[4-[N,N-di[p-tolyl]amino]phenyl]vinyl-benzene] (DPAVB)). In such a guest-host-system (GHS) the occupation of the upper laser level (dopant site) is due to Förster energy transfer (FET), which strongly depends on the donor acceptor distance and hence on the concentration of the laser dye. Therefore, the doping concentration is varied over a wide range and the gain coefficients are measured at various excitation densities to analyze the stimulated emission cross section.For the investigated GHS maximum gain coefficients up to ∼340 1/cm were found at absorbed pump energy densities of around 50 μJ/cm2. It will be shown that the stimulated emission cross section (σ = 1.8 × 10−16 cm2) is concentration independent which is quite different to a recently investigated small molecule based GHS. These effects will be discussed considering the rate and exciton diffusion constants.
Fluorinated Poly(N-vinylcarbazole) Host for Triplet Energy Confinement on Phosphorescent Emitter in Organic Light-emitting Diodes
Authors: Mizuno Yukitami , Takasu Isao , Uchikoga Shuichi , Enomoto Shintaro , Sawabe Tomoaki , Amano Akio , Wada Atsushi , Yoshida Jiro , Ono Tomio 
Published: August 2010

AbstractFluorinated carbazoles as host materials have been investigated for highly efficient organic light emitting diodes (OLEDs). By molecular orbital calculations, we found that fluorinations at position 2, 4, 5 and 7 of carbazole ring were effective for widening HOMO-LUMO energy gap. The energy gaps of our synthesized 2,7-difluorocarbazole (F2-Cz) and 2,4,5,7-tetrafluorocarbazole (F4-Cz), were estimated to be 3.71 eV and 3.87 eV by the absorption spectra, respectively. These energy gaps were higher than that of the non-substituted carbazole (Cz, 3.59 eV). We synthesized poly(N-vinyl-2,7-difluorocarbazole) (F2-PVK) and poly(N-vinyl-2,4,5,7-tetrafluorocarbazole) (F4-PVK) as solution processable polymer host materials. However, the F4-PVK was found to be an unsolved polymer. The F2-PVK could be compared with non substituted poly(N-vinylcarbazole) (PVK) in OLEDs. The emission layer (EML) contained iridium(III) bis [(4,6-di-fluorophenyl)-pyridinato-N,C2′] picolinate (FIrpic) as a blue phosphorescent dopant, and iridium(III) bis [2-(9,9-dihexylfluorenyl)-1-pyridine] acetylacetonate as a yellow dopant. The white OLED with the F2-PVK showed 1.4 times higher luminous current efficiency (24 cd/A) than the PVK (17 cd/A). These data show that the excitation energy is confined on dopants by using fluorinated polymer host material with higher T1 corresponding to wider HOMO-LUMO energy gap.
Bright Inkjet Printed Macromolecular Organic Light emitting Diodes on Flexible Substrates
Authors: Singh Madhusudan , Chae Hyun Sik , Froehlich Jesse D. , Kondou Takashi , Li Sheng , Mochizuki Amane , Jabbour Ghassan 
Published: August 2010

AbstractWe present results of printing solution-processable organic light emitting diodes (OLEDs) based on electrophosphorescent Ir(III) stellate polyhedral oligomeric silsesquioxane (POSS) macromolecules. The macromolecules are doped into a polymer-based ink containing a hole transporting polymer, poly(9-vinylcarbazole) (PVK) and an electron transporting material, 2-4-biphenylyl-5-4-tertbutyl-phenyl-1,3,4-oxadiazole (PBD), and the resulting ink is printed on a layer of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) spin-coated on indium tin oxide (ITO). An exciton-blocking layer consisting of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) is thermally evaporated onto the printed ink layers, followed by a LiF/Al cathode. While the photoluminescence (PL) spectrum of printed ink on glass indicates a significant contribution from the PVK:PBD exciplex, electroluminescence measurements (EL) suggest a much smaller effect of these states, which implies significant charge trapping at dopant molecular sites. Our latest experiments with devices printed on PEDOT:PSS/ITO/glass indicate that the devices exhibit high luminances (∼ 13,000 cd/m2 at 70 mA/cm2) and a fairly consistent quantum efficiency (∼ 2.5%) across a wide range of luminances. The corresponding figures for spin-coated devices are expectedly higher, with efficiencies ∼ 4.5% at similar levels of brightness. We use white light interferometry as a non-contact technique to quantify surface roughness and thickness of printed layers. Our current results thus indicate that inkjet printing of macromolecular phosphor doped polymer inks is suitable for fabrication of OLEDs with high brightness, in spite of the low glass transition temperature of some of the species. Our initial work with these devices on flexible ITO-coated plastic substrates shows devices with moderately high luminance values (∼ 2,500 cd/m2 at 35 mA/cm2). Our more recent devices show higher brightnesses (∼ 9, 600 cd/m2). We are working on the development of inkjet printing materials and processes for pure macromolecular OLEDs that are not performance and reliability limited by the presence of the PVK:PBD matrix with low glass transition temperatures. This requires the development of macromolecules that subsume all the functions of the host matrix and have high enough Tg to be usable in high concentrations needed. In conjunction with the inkjet printing technology demonstrated in this work, this has the potential to yield low-cost manufacturing of these devices.
Phenyl and Halophenyl Substituted Poly(p-phenylene vinylene)s for Capacitor Dielectrics
Authors: Johnson Ross , Kholwadwala Fenil M. , Dirk Shawn M. 
Published: August 2010

AbstractConducting polymers have attracted attention in many areas of materials chemistry due to their tunability and wide range of applications. We are interested in utilizing the thermo-switchable properties of precursor PPV polymers to develop capacitor dielectrics that will fail at specific temperatures due to the material irreversibly converting from an insulating to a conducting state. Here, we report the synthesis and characterization of a new halophenyl substituted PPV polymer. We show that the precursor polymer has good dielectric properties over a range of temperatures, but will fail at high temperatures due to the polymer backbone conjugating. By utilizing thermo-switchable dielectrics in capacitors, the unintentional discharge of electricity in the event of a fire or overheating could be averted, providing a fundamental safety mechanism for high-voltage electronics.
Evaluation of Thermopower of Organic Materials Toward Flexible Thermoelectric Power Generators
Authors: Nakamura Masakazu , Hoshi Atsushi , Sakai Masatoshi , Kudo Kazuhiro 
Published: August 2010

AbstractOrganic conducting and semiconducting materials are promising as thermoelectric conversion materials in flexible and wearable electronics because they have large Seebeck coefficients and small thermal conductivities. Since there have been only a limited number of studies on the thermoelectricity of organic materials to date, precise evaluation of Seebeck coefficient and electrical conductivity of various organic conducting/semiconducting thin films is important to examine what kind of material is the most effectual. To carry out such experiments, a specially designed instrument for organic thin films has been developed. Its ability to measure Seebeck coefficients of highly resistive materials was confirmed and Seebeck coefficients and power factors of several typical organic functional materials were preliminary evaluated.
Structural Response of BaTiO3/CaTiO3 Superlattice to Applied Electric Fields
Authors: Jo Ji Young , Sichel Rebecca , Lee Ho Nyung , Dufresne Eric , Evans Paul 
Published: August 2010

AbstractThe structural response of a ferroelectric BaTiO3/dielectric CaTiO3 superlattice to the bipolar applied electric field was studied using time-resolved x-ray microdiffraction. Structural results were compared to the polarization-electric field hysteresis curve obtained from electrical measurements. The superlattice x-ray reflections were found to have a broad distribution of intensity in reciprocal space under applied electric fields exceeding the nominal coercive electric field. The broad distribution of the lattice constant at high electric fields is compared with a model in which the constituent layers of the superlattice have different coercive fields for the polarization switching.
Imaging of Hybrid-Multiferroic and Translation Domains in a Spin-Spiral Ferroelectric
Authors: Meier Dennis , Leo Naëmi , Lottermoser Thomas , Becker Petra , Bohatý Ladislav , Fiebig Manfred 
Published: August 2010

AbstractTwo fundamentally different types of domains were resolved in multiferroic MnWO4 by optical second harmonic generation (SHG). Hybrid-multiferroic (absolute) domains reflect the magnetic chirality coupled 1:1 to the spontaneous polarization because of the magnetic origin of the ferroelectric order. Magnetic translation (relative) domains reflect discontinuities in the progression of the magnetic spin spiral. SHG topography is the only experimental method so far allowing one to image both types of domains. The imaging procedure and the SHG contributions involved are therefore discussed in detail.
Leakage Current of PLD- and CSD-BiFeO3 Thin Films Observed by Current Sensitive AFM
Authors: Nakashima Seiji , Fujisawa Hironori , Park Jung Min , Kanashima Takeshi , Okuyama Masanori , Shimizu Masaru 
Published: August 2010

AbstractWe have investigated relationships between leakage current and microstructure or domain structure of BiFeO3 (BFO) thin films, and leakage current mappings of BFO thin films have been performed by current sensitive AFM. 350-nm-thick and 250-nm-thick BFO thin films were prepared on Pt/TiO2/SiO2/Si substrate by pulsed laser deposition (PLD) and chemical solution deposition (CSD), respectively. Average grain size of PLD-BFO thin film is about 480 nm, which is the same as the film thickness. From the leakage current mapping at a bias voltage of -16 Vdc, leakage current of the BFO thin film flows through not only grain boundary but also the grain itself. On the other hand, CSD-BFO thin film shows rosette structure and small size grains. From the leakage current mapping at a bias voltage of -10 Vdc, leakage current flows along boundaries of the rosette structures. These results indicate that leakage current of BFO strongly depends on its microstructure.
Structural, Magnetic and Dielectric Properties of Magnetoelectric TbMn1-xCuxO3
Authors: Ray Shishir , Buroker Larry , Williamsen Mark S , Zou Ying , Sen Somaditya , Guptasarma Prasenjit 
Published: August 2010

AbstractTbMnO3 is a multiferroic magnetoelectric material known to simultaneously exhibit antiferromagnetism below 40K and ferroelectricity below 28K in the same crystalline phase [1]. Following interesting results of Cu substitution in LaMn1-yCuyO3 [2, 3], we report a study of TbMn1-x CuxO3 (0 < x < 0.15). We describe here our results of crystal structure refinement, together with measurements of magnetic and dielectric properties in the temperature range 2 - 320 K, and magnetic field 0 - 9 T. We find no major changes in structure or symmetry upon substitution of Cu up to x = 0.15 in TbMn1-x CuxO3. Unlike LaMn1-yCuyO3, which exhibits ferromagnetism with very low values of y, we observe antiferromagnetism at x = 0.15. Our study of dielectric properties as a function of temperature suggests increased lossy behavior upon substitution of Cu at the Mn site. In our temperature dependent studies of tan δ at 1 kHz, we observe a well-defined step-like feature near 120K in both pure and substituted samples, possibly ascribable to a change in carrier mobility, or a dielectric-relaxation process mediated by ordered oxygen vacancies [4, 5], which we will continue to study.
First-principles Investigation of Edged Ferroelectric PbTiO3 Nanowires and the Role of Axial Strain
Authors: Shimada Takahiro , Tomoda Shogo , Kitamura Takayuki 
Published: August 2010

AbstractAtomistic and electronic structures of PbTiO3 nanowires with atomically sharp edges consisting of (100)/(010) surfaces using first-principles calculations. Ferroelectricity is enhanced at the PbO-terminated edge in the nanowire because the Pb-O covalent bond that predominates the ferroelectric distortions is partially strengthened. On the other hand, a significant suppression is observed in the TiO2-terminated nanowire. Surprisingly, the smallest (one-unit-cell cross- section) PbO-terminated nanowire can keep ferroelectricity, while ferroelectricity disappears in the TiO2-terminated nanowires with a diameter of smaller than 17 Å. The ferroelectricity is recovered by axial tension, where the thinner nanowire requires the higher critical strain.
First-principles study of ferromagnetic Ni2CoGa(Zn) alloys in the Heusler and the inverse Heusler structure
Authors: Dannenberg Antje , Gruner Markus Ernst , Wuttig Manfred , Entel Peter 
Published: August 2010

AbstractWe performed an ab initio characterization of ferro- and nonmagnetic Ni2CoGa and Ni2CoZn compounds with respect to their potential application as new ferromagnetic shape memory alloys. The calculation of structural energy differences and mixing energies in the common
X2YZ Heusler structure and the inverse (XY)XZ structure revealed, that both alloys are stable in the tetragonal distorted Heusler structure with a c/a ratio of 1.38 and show ferromagnetic ordering. The Curie temperatures are of the order of ≃ 250 K. Exchanging Ga with Zn improves the magnetic properties of the alloy without qualitative modiﬁcation of the structural energy landscape, but at the expense of a reduced mixing energy.
Magnetocaloric Effect in Ni-Mn-Ga and Ni-Co-Mn-In Heusler Alloys
Authors: Buchelnikov Vasiliy , Taskaev Sergey , Drobosyuk Mikhail , Sokolovskiy Vladimir , Koledov Viktor , Khovaylo Vladimir , Shavrov Vladimir , Fediy Alexander 
Published: August 2010

AbstractThe positive magnetocaloric effect (MCE) in the vicinity of the Curie point in Ni2+xMn1-xGa (x=0.33, 0.36, 0.39) Heusler alloys and the negative and positive MCE near the metamagnetostructural (MMS) transition and the Curie point, respectively, in Ni45Co5Mn36.5In13.5 Heusler alloy has been measured by a direct method. For the magnetic field change ΔH = 2 T, the maximal adiabatic temperature change ΔTad at the Curie point in Ni2+xMn1-xGa alloys is larger than 0.6 K. For Ni45Co5Mn36.5In13.5 alloy, the maximal value of ΔTad = 1.68 K (for the same magnetic field change, ΔH = 2 T) is observed at the MMS phase transition temperature.
Ni-Mn-Ga films in the austenite and the martensite structures at room temperature: Uniaxial texturation and epitaxial growth
Authors: Tillier Jérémy , Einig Antinéa , Bourgault Daniel , Odier Philippe , Ortega Luc , Pairis Sébastien , Porcar Laureline , Chometon Paul , Caillault Nathalie , Carbone Laurent 
Published: August 2010

AbstractNi-Mn-Ga films in the austenite and the martensite structures at room temperature have been obtained using the DC magnetron sputtering technique. Two elaboration processes were studied. A first batch of samples was deposited using a resist sacrificial layer in order to release the film from the substrate before vacuum annealing. This process leads to polycrystalline films with a strong (022) fiber texture. The martensitic phase transformation of such polycrystalline freestanding films has been studied by optical and scanning electron microscopy. A second batch of samples was grown epitaxially on (100)MgO substrates using different deposition temperatures. The texture has been analyzed with four-circle X-ray diffraction. Epitaxial films crystallized both in the austenite and the martensite structures at room temperature have been studied.
Galfenol-based Sensor/Actuator Devices for Smart by-Wire Steering System for Automobile Technology
Authors: Furuya Yasubumi , Saito Chihiro , Okazaki Teiko , Okada Kazumi , Sado Yusuke , Chinen Takeo , Ogasawara Naoki , Shimada Muneaki 
Published: August 2010

AbstractPolycrystalline Galfenol (Fe-Ga-X, X=Al, C, Zr etc.) alloys were fabricated as a bulk sample from ark-melted and annealing process method for enhancing various engineering applicability. (Fe-Ga0.15-Al0.05)99.0-Zr0.5-C0.5 [at.%] sample showed a maximum magnetostriction of 134 ppm as well as a tensile stress over σ=800MPa. This large magnetostriction is caused by A2 phases without the excessive precipitation of ordered phases such as fcc ordered L12 and bcc ordered D03 phases. Secondarily, we will introduce an application as a smart torque sensor by utilizing Galfenol-ring around the steering shaft for steering-by-wire system of automobile. In this system, a torque sensing system by using the magnetostrictive ring of FeGa (Galfenol) alloy was developed and magnetic flux leaked from the Galfenol ring attached on the rotating shaft was experimentally measured by using two differential Hall probe sensor. As a result, the sensitivity in (Fe0.80Ga0.15Al0.05)99Zr0.5C0.5 ring increased by 2.9 times in comparison with the (Fe0.80Ga0.15Al0.05)98.5C1.5 alloy at rotations speed 500 rpm.
Electrical properties of charging effect in Au nanoparticle memory device
Authors: Jung Sung-Mok , Kim Hyung-Jun , Kim Bong-Jin , Seo Il , Yoon Tae-Sik , Kim Yong-Sang , Lee Hyun Ho 
Published: August 2010

AbstractSemiconductors or metal nanoparticles (NPs) using their monolayer bindings with self-assembly chemicals are an attractive topic for device researchers. Electrical performance of such structures can be investigated for a particular application, such as memory device. Currently, Au NPs has been reported to show a substantial potential in the memory applications. In this study, Au NP and gluing layer were fabricated through a new method of monolayer formation of a chemical bonding or gluing.
In this study, a new NPs memory system was fabricated by using organic semiconductor, i.e., pentacene as the active layer, evaporated Au as electrode, SiO2 as the gate insulator layer on silicon wafer. In addition, Au NPs coated with binding chemicals were used as charge storage elements on an APTES (3-amino-propyltriethoxysilane) as a gluing layer. In order to investigate chemical binding of Au NP to the gate insulator layer, GPTMS (3-glycidoxy-propyltrimethoxysilane) were coated on the Au NPs. As a result of that, a layer of gold nanoparticles has been incorporated into a metal-pentacene-insulator-semiconductor (MPIS) structure. The MPIS device with the Au NP exhibited a hysteresis in its capacitance versus voltage analysis. Charge storage in the layer of nanoparticles is thought to be responsible for this effect.
Commercial Production of Silicon Solar Cell Feedstock by Upgrade of Metallurgical Grade Silicon
Authors: Mott John R , Bragagnolo Julio A , Hayes Michael P. 
Published: August 2010

AbstractThe relation between impurity content in Solar Grade Silicon (SGS) and solar cell quality is the subject of intensive research. The PV industry has developed around the use of silicon made by the Siemens process for the semiconductor industry, with impurity levels typically in the parts per billion by weight (ppbw) range. There is a growing consensus that SGS with impurities in the parts per million range (ppmw) can be obtained cost effectively from Metallurgical Grade Silicon (MGS) and used to yield solar cells with comparable performance (see for example ‘Beneficial Effects of Dopant Compensation on Carrier Lifetime in Upgraded Metallurgical Silicon’ by S. Dubois et al. in the 23rd European Photovoltaic Solar Energy Conference, Valencia, September, 2008). This provides insight on the success encountered by Timminco, an early SGS market entrant, in commercializing silicon material with [P] levels of the order of 2 ppmw.
Current Work
We have successfully reduced P to about 2 ppmw, a level that appears acceptable for solar cell fabrication, by application of a novel unidirectional solidification (UDS) technique at a 50% material yield. This is important as UDS, by its nature, implies a loss of silicon, while little or no silicon is lost in B reduction, partially achieved in this furnace using a glass slagging process. Figure 1 shows [P] data from 16 UDS runs on samples taken from the melt, before and after UDS, and a solid sample taken from the silicon frozen on the cold silicon collection surface. The error bars represent a standard 20% error value. We note that the average values of [P] in the molten silicon samples increase from 11.9 ppmw before UDS to 15.9 ppmw after UDS. The average value of [P] in the solid silicon sample is 4.9 ppmw.
The average value of the solid silicon, 4.9 ppmw P, taken with the average value of the starting silicon, 11.9 ppmw P, demonstrates an effective refining ratio of 0.41, even at a 50% solid fraction. Performing a second UDS on silicon obtained from runs in Figure 1, yields [P] around 2 ppmw (Figure 2).In addition to P and B reduction, in this paper we also discuss the hardware designed to implement this process in commercial production in volumes exceeding 4,000 MT per year. MB Scientific, the original process developer, and NC Consulting, an engineering company, have developed a plant design that can produce SGS at an estimated cost that will allow for profitable large scale production, and have joined in a new company, Silicon Forge, to commercialize the large-scale production technology.
Improving the Conversion Efficiency and Decreasing the Thickness of the HIT Solar Cell
Authors: Inoue Hirotada , Tsunomura Yasufumi , Fujishima Daisuke , Yano Ayumu , Taira Shigeharu , Ishikawa Yasuko , Nishiwaki Takeshi , Nakashima Takeshi , Asaumi Toshio , Taguchi Mikio , Sakata Hitoshi , Maruyama Eiji 
Published: August 2010

AbstractIn order to reduce the power-generating cost of silicon solar cells, it is necessary to achieve a high conversion efficiency using a thinner crystalline silicon (c-Si) substrate. The HIT (Heterojunction with Intrinsic Thin-layer) solar cell is an amorphous silicon (a-Si) / c-Si heterojunction solar cell that exhibits the potential to make this possible. Our recent R&D activities have achieved the world’s highest conversion efficiency of 23.0% with a practical sized (100.4 cm2) HIT solar cell, by improving the quality of the surface passivation, reducing the optical absorption loss and reducing the resistance loss. We have also developed a HIT solar cell with a thickness of only 98 mm, which has a very high conversion efficiency of 22.8%. This value is comparable to that of the conventional HIT solar cell, which has a thickness of more than 200 mm. Moreover, we have fabricated HIT solar cells using thinner c-Si substrates (96 to 58 μm), and found that the Voc increased with decreases in the substrate thickness, and reached an extremely high value of 0.745 V with a thickness of only 58 μm. This indicates that the surface recombination velocity of the HIT structure is extremely low due to the excellent passivation of the c-Si surface.
PV Metamaterial Based on the Nanostructured Si
Authors: Kuznicki Zbigniew T. , Meyrueis Patrick 
Published: August 2010

AbstractThere are several ways to nanostructure Si. Some of them, e.g. nanoscale Si-layerd systems buried within the n+ layer of a crystalline Si can provide an initial material with unpredicted optoelectronic behavior. Such a transformation leads to a PV Si metamaterial, whose optoelectronic properties arise from qualitatively new response functions that are (i) not observed in the constituent materials and (ii) result from the inclusion of artificially fabricated, intrinsic and extrinsic, low-dimensional components. We show that an extremely strong c-Si:P absorptance, is larger than can result from conventional conversion because the surface population increases by injection of additional carriers from a nanostratum (transformed up to a Si-metamaterial) lying just behind the top c-Si:P-layer.