bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ultraviolet Photoresponse of Pure and Al doped ZnO Polycrystalline Thin Films by Inkjet Printing
Authors: Wu Yan , Tamaki Takahiko , Voit Wolfgang , Belova Lyubov M. , Rao K. V. 
Published: June 2009

AbstractPure ZnO, and Al doped ZnO, 120 -300 nm thin films on glass substrates, were synthesized by inkjet printing technique using zinc and aluminum acetate solution as precursors and a two stage heat treatment process to obtain polycrystalline hexagonal wurtzite structure with the mean grain size of 25 and 30 nm respectively. All films exhibit a transmittance above 85-90% in the visible wavelength range below 700 nm. In the Al doped films the UV absorption spectra show a strong absorption onset below 380nm followed by shoulders centered around 325 nm depending on the film thickness. The electrical conductivity of Al doped ZnO thin films is larger by two orders of magnitude than that for pure ZnO films while the photoconductivity increases by about three orders of magnitude under UV irradiation. The photoresponse of the films with UV irradiation in terms of the rise and decay times in the frequency range from 5 to 500 Hz is also presented and discussed.
Optimization of Ce Content in CexLa1-xF3 Colloidal Nanocrystals for Gamma Radiation Detection
Authors: Withers Nathan J , Sankar Krishnaprasad , Plumley John B , Akins Brian A , Memon Tosifa A , Rivera Antonio C , Smolyakov Gennady , Osiński Marek 
Published: June 2009

AbstractWe report on experimental investigations of CexLa1-xF3 colloidal nanocrystals (CNCs) and their properties in function of Ce content. The CNCs were characterized by TEM, energy-dispersive X-ray spectroscopy (EDS), steady-state UV-VIS optical absorption and photoluminescence (PL) spectroscopy, and by PL lifetime measurements. We also report on observations of scintillation from the cerium-doped lanthanum fluoride CNC material in experiments on radiation detection.
The Influence of the Composition Ratio on CZTS-based Thin Film Solar Cells
Authors: Katagiri Hironori , Jimbo Kazuo , Tahara Masami , Araki Hideaki , Oishi Koichiro 
Published: June 2009

AbstractCu2ZnSnS4 (CZTS) thin films were fabricated by using three RF co-sputtering continued with sulfurization method. The new type of thin film solar cells using CZTS as an absorber consists of buffer-layer and window-layer on CZTS films that were fabricated on a Mo-coated Soda Lime Glass (SLG) substrate. It was confirmed that CZTS solar cells with high conversion efficiency existed in a relatively narrow composition region. In this paper, the fabrication method of CZTS-based thin film solar cells in our laboratory was stated briefly and the influence of the composition ratio on the photovoltaic properties were presented. Furthermore, the properties of a genuine non-toxic solar cell using a Cd-free buffer-layer were introduced.
Structural Properties of CdTe Thin Films for Solar Cell Applications Deposited on Flexible Foil Substrates
Authors: Palekis Vasilios , Hodges Deidra Ranel , Morel Don L , Stefanakos Lee , Ferekides Chris S 
Published: June 2009

AbstractCadmium telluride (CdTe) is a leading thin film photovoltaic (PV) material due to its near ideal band gap of 1.45 eV and its high optical absorption coefficient. The typical CdTe thin film solar cell is of the superstrate configuration where a window layer (CdS), the absorber (CdTe), and a back contact are deposited onto a glass slide coated with a transparent electrode. Substrate CdTe solar cells where the above listed films are deposited in reverse order are not common. In this study, the growth of CdTe thin films deposited on foil substrates by the close-spaced sublimation (CSS) has been investigated for the purpose of fabricating substrate based CdTe solar cells. The CdTe films were deposited at substrate temperatures (TSUB) in the range of 300 to 600°C, and source temperatures (TSRC) in the 600 to 650°C range. The effect of the substrate-source temperature variations on the growth rate, film structure and morphology were studied using XRD and SEM. It was found that for low substrate temperature and as the growth rate increases, grain size was the same but the films appeared to be more uniform and more densely packed with less or no pinholes. The growth rate increased as the source temperature increased. The substrate temperature clearly influences the grain growth and the preferred orientation. As the substrate temperature increased the growth rate decreased and the grain size varied from 2 to 6 μm. XRD analysis showed that with the increase in substrate temperature film orientation changes from preferential along the (111) direction to a mix of (111) (220) and (311).
Interdiffusion of Bi and Sb in Superlattices Built from Blocks of Bi2Te3, Sb2Te3 and TiTe2
Authors: Mortensen Clay D. , Johnson David 
Published: June 2009

AbstractThe reaction kinetics of [(Ti-Te)]x[(Sb-Te)]y, [(Bi-Te)]x[(Sb-Te)]y, [(Ti-Te)]w[(Bi-Te)]x and [(Ti-Te)]w[(Bi-Te)]x[(Ti-Te)]y[(Sb-Te)]z precursors as a function of annealing temperature and time was probed using x-ray diffraction techniques to define the parameters required to form superlattice structures. [(TiTe2)1.36]x[Sb2Te3]y and [(TiTe2)1.36]x[Bi2Te3]y superlattices were observed to form while [(Bi-Te)]x[(Sb-Te)]y precursors yielded only Bi2-xSbxTe3 alloys. This behavior was correlated with the immiscibility/miscibility of the constituents of the targeted superlattices. For the three component system, Bi and Sb were observed to interdiffuse through the Ti-Te layer over the range of Ti-Te thicknesses explored, resulting in formation of (BixSb1-x)2Te3 alloys within the superlattice structure. When the Bi2Te3 and Sb2Te3 thicknesses were equal, symmetric [{(TiTe2)}1.36]w[(Bi0.5Sb0.5)2Te3]y superlattices were formed.
Enhancement of Thermoelectric Figure-of-Merit by a Nanostructure Approach
Authors: Ren Zhifeng , Poudel Bed , Ma Yi , Lan Yucheng , Minnich Austin , Muto Andy , Yang Jian , Yu Bo , Yan Xiao , Wang Dezhi , Liu Junming , Dresselhaus Mildred , Chen Gang 
Published: June 2009

AbstractThe dimensionless thermoelectric figure-of-merit (ZT) in bulk materials has remained about 1 for many years. Here we show that a significant ZT improvement can be achieved in nanocrystalline bulk materials. These nanocrystalline bulk materials were made by hot-pressing nanopowders that are ball-milled from either crystalline ingots or elements. Electrical transport measurements, coupled with microstructure studies and modeling, show that the ZT improvement is the result of low thermal conductivity caused by the increased phonon scattering by grain boundaries and defects. More importantly, the nanostructure approach has been demonstrated in a few thermoelectric material systems, proving its generosity. The approach can be easily scaled up to multiple tons. Thermal stability studies have shown that the nanostructures are stable at the application temperature for an extended period of time. It is expected that such enhanced materials will make the existing cooling and power generation systems more efficient.
Size Effects on the Thermal Properties of Self-assembled Ge Quantum Dots in Single-crystal Silicon
Authors: Gillet Jean-Numa 
Published: June 2009

AbstractSuperlattices with an ultra-low thermal conductivity were extensively studied to design thermoelectric materials. However, since they are made up of superposed materials showing lattice mismatches, they often show cracks and dislocations. Therefore, it is challenging to fabricate superlattices with a thermoelectric figure of merit ZT higher than unity. Moreover, like nanowires, they decrease heat transport in only one main direction. Self-assembly from epitaxial layers on a Si substrate is a major bottom-up technology to fabricate 3D Ge quantum-dot (QD) arrays in Si, which have been used for 3D quantum-device applications. Using the model of the atomic-scale 3D phononic crystal, we showed that 3D high-density arrays of self-assembled Ge QDs in Si can also show an ultra-low thermal conductivity in 3D, which can be several orders of magnitude lower than that of bulk Si. As a result, they can be considered to design novel 3D thermoelectric devices showing CMOS compatibility. In an example QD crystal, the thermal conductivity can be decreased below only 0.2 W/m/K. The main objective of this paper is to show the size dependence of the thermal conductivity versus the supercell lattice parameter d. For a constant QD-crystal filling ratio x = 12.5 at%, a decrease of the thermal conductivity is observed for an increasing d. This analysis enables us to predict that the optimal d-value will be of the order of 11 nm for the given filling ratio. At this optimum, the thermal conductivity decreases to the global minimum value of 0.9 W/m/K. The presented results are a first step towards the optimal design of thermoelectric devices with a maximal ZT obtained by global optimization of the size parameters.
Rectifying Polarity Switch of Pt/TiO2-x/Pt
Authors: Zhong Ni , Shima Hisashi , Akinaga Hiro 
Published: June 2009

AbstractCurrent-voltage (I-V) characteristic of Pt/TiO2-x/Pt has been investigated. The Pt/TiO2-x/Pt devices in the initial state exhibit a rectifying I-V behavior. By applying a pulse voltage, the rectifying polarity could be switched to an opposite direction. The mechanism of the rectifying polarity switch is proposed as the local drift of defects, such as oxygen vacancies (VO), due to applying pulse voltage. It is found that the required pulse voltage height for the polarity switch (Vswitch) exhibits much dependence on the operation temperature and width of applied pulse voltage. With an increase of the pulse voltage width or the measurement temperature (T), Vswitch exhibits a decrease with increase of T. These results suggest that the rectifying polarity switch in the Pt/TiO2-x/Pt is attributed to a thermal and dynamic dependence process, which agree well with the localized migration of VO induced by applied pulse voltage.
Synthesis and Characterization of Flowerlike ZnO Nanoneedle Arrays on Si (100)
Authors: Yang Boqian , Feng Xianping 
Published: June 2009

AbstractFlowerlike ZnO nanoneedle arrays have been synthesized on Si (100) substrates by pulsed laser deposition techniques. The tips of the nanoneedles are ˜ 20- 50 nm in diameter and their roots are as thick as ˜ 50- 100 nm. The nanoneedle arrays grow preferentially along the [0001] direction. Raman spectroscopy shows three first order optical normal modes which confirm wurtzite structure of ZnO nanoneedles. In the low frequency zone, additive modes (92, 122, 163, and 275 cm-1) are observed and can be attributed to zone boundary phonons. ZnO nanoneedle arrays exhibit a strong UV luminescence emission, and two strong peaks at 3.258 eV and 3.288 eV are observed.
Tailoring TMR Ratios by Ultrathin Magnetic Interlayers: A First-principles Investigation of Fe/MgO/Fe
Authors: Bose Peter , Zahn Peter , Henk Juergen , Mertig Ingrid 
Published: June 2009

AbstractFor spintronic device applications, large and in particular tunable tunnel magnetoresistance (TMR) ratios are inevitable. Fully crystalline and epitaxially grown Fe/MgO/Fe magnetic tunnel junctions (MTJs) are well suited for this purpose and, thus, are being intensively studied [1]. However, due to imperfect interfaces it is difficult to obtain sufficiently large TMR ratios that fulfill industrial demands (e.g. [2]).A new means to increase TMR ratios is the insertion of ultra-thin metallic buffer layers at one or at both of the Fe/MgO interfaces. With regard to their magnetic and electronic properties as well as their small lattice mismatch to Fe(001), Co and Cr spacer are being preferably investigated.We report on a systematic first-principles study of the effect of Co and Cr buffers (with thicknesses up to 6 ML) in Fe/MgO/Fe magnetic tunnel junctions (MTJs) on the spin-dependent conductance. The results of the transport calculations reveal options to specifically tune the TMR ratio. Symmetric junctions, i.e. with Co buffers at both interfaces, exhibit for some thicknesses much larger TMR ratios in comparison to those obtained for Fe-only electrodes. Further, antiferromagnetic Cr films at a single interface introduce TMR oscillations with a period of 2 ML, a feature which provides another degree of freedom in device applications. The comparison of our results with experimental findings shows agreement and highlights the importance of interfaces for the TMR effect.
Quantitative Electron Diffraction for Crystal Structure Determination
Authors: Oleynikov Peter , Grüner Daniel , Zhang Daliang , Sun Junliang , Zou Xiaodong , Hovmöller Sven 
Published: June 2009

AbstractWe present a quantitative investigation of data quality using electron precession, compared to standard selected-area electron diffraction (SAED). Data can be collected on a CCD camera and automatically extracted by computer. The critical question of data quality is addressed – can electron diffraction data compete with X-ray diffraction data in terms of resolution, completeness and quality of intensities?
Comparison of two Metal Ion Implantation Techniques for Fabrication of Gold and Titanium Based Compliant Electrodes on Polydimethylsiloxane
Authors: Niklaus Muhamed , Rosset Samuel , Dubois Philippe , Shea Herbert R. 
Published: June 2009

AbstractThis study contrasts the implantation of 25 μm thick Polydimethylsiloxane (PDMS) membranes with titanium and gold ions at 10 keV and 35 keV for doses from 1×1015at/cm2to 2.5×1016at/cm2implanted with two different techniques: Filtered Cathodic Vacuum Arc (FCVA) and Low Energy Broad Ion Beam (LEI). The influence of the ion energy, ion type, and implantation tool on the Young’s modulus (E), resistivity and structural properties (nanocluster size and location, surface roughness) of PDMS membranes is reported. At a dose of 2.5×1016at/cm2and an energy of 10 keV, which for FCVA yields sheet resistance of less than 200 Ω/square, the initial value of E (0.85 MPa) increases much less for FCVA than for LEI. For gold we obtain E of 5 MPa (FCAV) compared to 86 MPa (LEI) and for titanium 0.94 MPa (FCVA) compared to 57 MPa (LEI). Resistivity measurements show better durability for LEI than for FCVA implanted samples and better time stability for gold than for titanium.
Design of Architectured Sandwich Core Materials using Topological Optimization Methods
Authors: Laszczyk Laurent , Dendievel Rémy , Bouaziz Olivier , Bréchet Yves , Parry Guillaume 
Published: June 2009

AbstractSandwich structures are especially interesting when multiple functionalities (such as stiffness and thermal insulation) are required. Properties of these structures are strongly dependent on the general geometry of the sandwich, but also on the detailed patterns of matter partitioning within the core. Therefore it seems possible to tailor the core pattern in order to obtain the desired properties. But multi-functional specifications and the infinite number of possible shapes, leads to non-trivial selection and/or optimization problems.
In this context of “material by design”, we propose a numerical approach, based on structural optimization techniques, to find the core pattern that leads to the best performances for a given set of conflicting specifications. The distribution of matter is defined thanks to a level-set function, and the convergence toward the optimized pattern is performed through the evolution of this function on a fixed grid. It is shown that the solutions of optimization are strongly dependent on the formulation of the problem, which have to be chosen with respect to the physics.
A first application of this approach is presented for the design of sandwich core materials, in order to obtain the best compromise between flexural stiffness and relative density. The influence of both the initialization (starting geometry) and the formulation of the optimization problem are detailed.
Multifunctional One-dimensional Phononic Crystal Structures Exploiting Interfacial Acoustic Waves
Authors: To Albert C , Lee Bong Jae 
Published: June 2009

AbstractThe present study demonstrates that interfacial acoustic waves can be excited at the interface between two phononic crystals. The interfacial wave existing between two phononic crystals is the counterpart of the surface electromagnetic wave existing between two photonic crystals. While past works on phononic crystals exploit the unique bandgap phenomenon in periodic structures, the present work employs the Bloch wave in the stop band to excite interfacial waves that propagate along the interface and decay away from the interface. As a result, the proposed structure can be used as a wave filter as well as a thermal barrier. In wave filter design, for instance, the incident mechanical wave energy can be guided by the interfacial wave to the lateral direction; thus, its propagation into the depth is inhibited. Similarly, in thermal barrier design, incident phonons can be coupled with the interfacial acoustic wave, and the heat will be localized and eventually dissipated at the interface between two phononic crystals. Consequently, the thermal conductivity in the direction normal to the layers can be greatly reduced. The advantage of using two phononic crystals is that the interfacial wave can be excited even at normal incidence, which is critical in many engineering applications. Since the proposed concept is based on a one-dimensional periodic structure, the analysis, design, and fabrication are relatively simple compared to other higher dimensional material designs.
Modelling the Mechanical and Thermal Properties of Cellular Materials from the Knowledge of their Architecture
Authors: Maire Eric , Caty O. , Bouchet R. , Loretz M. , Adrien J. 
Published: June 2009

AbstractThis paper shows different examples where the architecture of cellular materials has been determined exactly using 3D X ray computed tomography. The images were then subsequently used to generate FE meshes reproducing the architecture as exactly as possible. The FE meshes where in turn used to simulate the mechanical (monotonous and fatigue compression) and the thermal (radiative properties) behavior of the studied materials.
Triple-Shape Capability of Thermo-sensitive Nanocomposites from Multiphase Polymer Networks and Magnetic Nanoparticles
Authors: Uttamchand Narendra Kumar , Kratz Karl , Behl Marc , Lendlein Andreas 
Published: June 2009

AbstractThermo-sensitive multiphase polymer networks with triple-shape capability have been recently introduced as a new class of active polymers that can change on demand from a first shape A to a second shape B and from there to a permanent shape C. Such multiphase polymer networks consist of covalent cross-links that determine shape C and at least two phase-segregated domains with distinct thermal transitions Ttrans,A and Ttrans,B , that are associated to shape A and B. In general the application of a two step programming or a one step programming procedure is required for creation of triple-shape functionality. In this study we report about a series of CLEGC nanocomposites consisting of silica coated nanoparticles (SNP) incorporated in a multiphase graft polymer network matrix from crystallisable poly(ε-caprolactone) diisocyanatoethyl methacrylate (PCLDIMA) and poly(ethylene glycol) monomethyl ether monomethacrylate (PEGMA) forming crystallisable side chains. These CLEGC nanocomposites were designed to enabling non contact activation of triple-shape effect in alternating magnetic field. Composites with variable PCLDIMA content ranging from 30 wt-% and 70 wt-% and different SNP amounts (0 wt-%, 2.5 wt-%, 5 wt-% and 10 wt-%) were realized by thermally induced polymerization. The thermal and mechanical properties of the CLEG nanocomposites were explored by means of DSC, DMTA and tensile tests. The triple-shape properties were quantified in cyclic, thermomechanical experiments, which consisted of a two step programming procedure and a recovery module under stress-free conditions for recovery of shapes B and C.
While the thermal properties and the Young’s modulus of the investigated polymer networks were found to be independent from the incorporated amount of SNP, the elongation at break (εB) decreases with increasing nanoparticle content. All investigated composites exhibit excellent triple-shape properties showing a well separated two step shape recovery process.
Microfluidic Manifolds with High Dynamic Range in Structural Dimensions Replicated in Thermoplastic Materials
Authors: Becker Holger , Beckert Erik , Gärtner Claudia 
Published: June 2009

AbstractIn this paper, we present the manufacturing process of a polymer microfluidic device which is currently being used to investigate wetting properties of nanostructured microchannels replicated in hydrophobic thermoplastic materials like cyclo-olefin co-polymer (COC), polypropylene (PP) or polymethylmetacrylate (PMMA). These devices feature large structural dynamics (feature sizes between 200 μm and 200 nm). The mold insert necessary was fabricated using a combination of precision machining with single-point diamond turning (SPDT).
Polybrominated diphenyl ethers and their hydroxylated analogs in plasma of bottlenose dolphins (Tursiops truncatus) from the United States east coast
Authors: Houde Magali , Pacepavicius Grazina , Darling Colin , Fair Patricia A. , Alaee Mehran , Bossart Gregory D. , Solomon Keith R. , Letcher Robert J. , Bergman Åke , Marsh Göran , Muir Derek C.G. 
Published: June 2009

Abstract
Polybrominated diphenyl ethers (PBDEs) and hydroxylated PBDEs (OH-PBDEs) were determined in plasma of freeranging bottlenose dolphins (Tursiops truncatus) from Charleston (CHS), South Carolina, and the Indian River Lagoon (IRL), Florida, USA. Significantly lower sums (Σ) of PBDE concentrations (sum of 12 congeners) were found in animals from the IRL (arithmetic mean, 5.45 ± 4.63 ng/g wet wt) compared with those from CHS (30 ± 40 ng/g wet wt). Brominated diphenyl ether (BDE)-47 was the predominant PBDE in dolphins from the IRL (50% of the ΣPBDEs) and CHS (58%). The ΣPBDE concentrations in plasma of dolphins were negatively correlated with age at both locations. Fifteen and sixteen individual OH-PBDE congeners could be quantified in plasma of dolphins from IRL and CHS, respectively. Similar to ΣPBDE, mean ΣOH-PBDE concentrations were significantly higher in plasma of dolphins at CHS (1,150 ± 708 pg/g wet wt) compared with those at IRL (624 ± 393 pg/g wet wt). The predominant congener at both locations was 6-OH-PBDE-47 (IRL, 384 ± 319 pg/g wet wt; CHS, 541 ± 344 pg/g wet wt), representing 61.5% of total ΣOH-PBDE at IRL and 47.0% at CHS. Concentrations of ΣOH-PBDEs were weakly negatively correlated with age in dolphins from both locations (p &lt; 0.05; IRL, r2 = 0.048; CHS, r2 = 0.021). In addition to the OH-PBDE congeners identified with technical standards, eight and four unidentified OH-PBDEs were detected and quantified, respectively, in animals from CHS (sum of unidentified OH-PBDEs = 1.35 ± 0.90 pg/g wet wt) and IRL (0.73 ± 0.40 pg/g wet wt). Results of the present study suggest that, unlike OH-PCBs, OH-PBDEs in bottlenose dolphins are minor products in plasma relative to ΣPBDEs and a significant proportion may be a consequence of the dietary uptake of naturally produced methoxylated- and OH-PBDEs.