bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental Tests of Possible Mechanisms for the Organic Magnetoresistive Effect
Authors: Nguyen Tho Duc , Rybicki James , Sheng Yugang , Wohlgenannt Markus 
Published: April 2011

AbstractWe experimentally test three existing models of organic magnetoresistance (OMAR) which are all based on carrier spin dynamics. We first prove that hyperfine field originating from the hydrogen nuclei in organic materials is necessary for observing OMAR by studying C60 sandwich devices using several different electrode materials. We show that C60, unlike many other organic semiconductors, does not exhibit any intrinsic OMAR effect. However, we find that as soon as the carriers in C60 are brought in proximity with hydrogen-containing compounds, either in the form of a polymeric electrode, or side-chain substituents, a weak OMAR effect is observed. Next, we perform charge-induced absorption and electroluminescence spectroscopy in a polyfluorene organic magnetoresistive device. Our experiments allow us to measure the singlet exciton, triplet exciton and polaron densities in a live device under an applied magnetic field, and to distinguish between three models of OMAR. These models are based on different spin-dependent interactions, namely exciton formation, triplet exciton-polaron quenching and bipolaron formation. We show that the singlet exciton, triplet exciton and polaron densities and conductivity all increase with increasing magnetic field. Our data are inconsistent with the exciton formation and triplet-exciton polaron quenching models.
Magnetism and Recoilless Fraction of Cerium-Doped Hematite Nanoparticles System
Authors: Sorescu Monica , Diamandescu Lucian 
Published: April 2011

AbstractCerium-doped hematite particles of the type xCeO2-(1-x)α-Fe2O3 (x=0.1, 0.5) were synthesized using mechanochemical activation and characterized by X-ray diffraction (XRD) and Mössbauer spectroscopy. XRD patterns yielded the dependence of lattice parameters and particle size as a function of ball milling time for each value of the molar concentration x. For x=0.1, the Mössbauer spectra were fitted with one or alternatively, two sextets, corresponding to Ce ions substituting Fe ions in the hematite structure. For x=0.5, Mössbauer spectra fitting required the addition of a quadrupole-split doublet, representing Fe substituting Ce in the CeO2 lattice. We evidenced this transition using our recently developed method for precise determination of the recoilless fraction in a single room-temperature transmission Mössbauer measurement of a two-absorber sample. We observed the occurrence of a minimum in the values of the recoilless fraction for t=4 hours of milling, followed by a further decrease of the f factor due to the appearance of nanoparticles in the system.
Magnetization and Magnetotransport Properties of Thermally Evaporated Co-Sn-Co Trilayer
Authors: Chiolerio Alessandro , Allia Paolo , Coisson Marco , Tiberto Paola 
Published: April 2011

AbstractWe report on growth, morphology and magnetic behavior of the pseudo spin-valve (PSV) Si/Co(15 nm)/Sn(50 nm)/Co(15 nm). Thermal evaporation was chosen as experimental deposition technique for its versatility and cost effectiveness. Magnetisation and magnetotransport measurements performed at low temperature showed that the sample has a complex behaviour related to the different morphology and thickness of the outer Co layers. Combining magnetic and magnetotransport data, a model based on three magnetic phases has been developed, associating them to the Co underlayer, to the Co cap layer and to possible nanometre-sized Co islands embedded in the Sn layer, respectively. A three-phase model coherently explains both magnetisation and magnetoresistance datasets.
Development of Strategies to Improvement Ordering and Perpendicular Alignment of Cylinder Phase Block Copolymers Used as Templates for Bit Patterned Media
Authors: Garrett Seth , Franco Vincent , Snowden Timothy , Redden Chris , Warke Vishal , Bakker Martin Gerard 
Published: April 2011

AbstractBit patterned media, including media fabricated with a gradient in composition, is being developed as a potential path to higher information storage density. The noise level in such media is significantly impacted by the precision of the ordering of the individual bits and by the narrowness of their size distribution. Block copolymers that phase separate on the appropriate length scale are one method of pattern generation that is receiving considerable attention. For cylinder forming block copolymer phases the ordering and degree of perpendicular alignment is largely determined by the matching of the substrate surface to the block copolymer. If the chemical properties of the substrate surface match the average for the block copolymer, then thin films of the block copolymer align perpendicularly on annealing. Although there are a number of examples where the substrate surface fortuitously matches the block copolymer, in general an orienting layer is necessary to provide the appropriate match. The most popular approach has been to synthesize a random copolymer with the same average composition as the block copolymer. In order to produce suitably thin orienting layers it has been necessary to chemically tether the random copolymer to the substrate. Previously used chemistry has not been suitable for noble metal substrates such as platinum. We have been developing an alternate approach using thiol functional groups which we anticipate will be more suitable for Pt capped substrates.
Stress Dependence of Crystal Structure of Polycrystalline BiFeO3 Thin Films on Membrane Structure Prepared by Pulsed Laser Deposition
Authors: Nakashima Seiji , Ricinschi Dan , Nakamura Yoshitaka , Okuyama Masanori , Fujisawa Hironori , Shimizu Masaru 
Published: April 2011

AbstractAn Influence of stress of crystal structure of polycrystalline BiFeO3 (BFO) thin film on membrane structure has been investigated. To confirm the stress dependence of the crystal structure, reciprocal space mapping measurement of polycrystalline BFO thin films on Pt (200 nm)/TiO2 (50 nm)/SiO2 (600 nm)/Si (625 μm) plate substrate and Pt (200 nm)/TiO2 (50 nm)/SiO2 (600 nm)/Si (15 μm) membrane substrate have been performed. These BFO thin films have been prepared by pulsed laser deposition (PLD). The obtained BFO thin films were polycrystalline and mainly oriented to (001) and (110) plane. From reciprocal space mapping measurement, (110) oriented BFO grains on Pt/TiO2/SiO2/Si (15 μm) membrane substrate were expanded perpendicularly to the film plane about 0.15% and compressed in parallel to the film plane about 0.7% comparing to that on Pt/TiO2/SiO2/Si (625 μm) plate substrate. And (001) oriented BFO grains on the Pt/TiO2/SiO2/Si membrane substrate were expanded about 0.20% perpendicularly to the film plane and compressed about 1.3% in parallel to the film plane comparing to that on Pt/TiO2/SiO2/Si (625 μm) plate substrat
Microscopic Mechanism and Domain Formation in the Paraelectric to Ferroelectric Phase Transitions in BaTiO3
Authors: Pasciak Marek , Leoni Stefano 
Published: April 2011

AbstractA design approach to ferroelectric materials critically depends on an accurate description of the microscopic features associated with paraelectric-to-ferroelectric phase transitions. The fine structures of domains, domain walls, and domain boundary dynamics as well as a precise understanding of local atomic displacements can be accessed using adequate potential models based on ab initio calculations and advanced molecular dynamics simulations. For BaTiO3 a complex scenario of microscopic domains in the paraelectric (cubic) phase and in the ferroelectric (tetragonal) phase is obtained. Therein, the static and dynamic role of domain/antidomain features, as well as their dependence on Ti displacements around the <111> manifold is clearly emerging.
Characteristics of BST Capacitors with Aluminum Electrode and Iridium Oxide Barrier Layers
Authors: Kalkur Thottam , Troung Troung 
Published: April 2011

AbstractThe high frequency operation of BST capacitors necessitates the development of low series resistance electrodes. As an alternative to platinum, DC magnetron sputtered IrO2/Aluminum top electrode metallization for BST capacitors has been proposed. The capacitance voltage characteristics of BST capacitors did not change significantly due to the deposition of aluminum on iridium oxide. Post annealing in nitrogen environment shows that IrO2/Al metallization does not degrade annealing temperature up to 450 oC.
X-ray Analysis of Strain Relaxed Domain Structure in (100)/(001)-oriented epitaxial PbTiO3 thick films grown on (100)SrTiO3 substrates
Authors: Funakubo Hiroshi , Kim Yong Kwan , Yokoyama Shintaro , Ikariyama Rikyu , Funakubo Hiroshi , Streiffer S. K. , Nishida Ken , Saito Keisuke 
Published: April 2011

AbstractCrystal structure of epitaxially grown (100)/(100)-oriented PbTiO3 films on (100)SrTiO3 substrates with 3.8 μm in thickness was investigated by the XRD reciprocal space mapping techniques. The observed poles of PbTiO3004, 400, 204, 402 and 420 scans can be successfully explained using the model consisting with the one type of (001) domain and three types of (100) domains in good agreement with the estimation from the scanning probe microscopy in conjunction with the in-plane and out-of plain XRD analysis.
Ferroelectric Thin Films Grown on Base-Metal Foils for Embedded Passives
Authors: Ma Beihai , Kwon Do-Kyun , Narayanan Manoj , Balachandran U. 
Published: April 2011

AbstractDevelopment of electronic devices with higher performance and smaller size requires the passive components to be embedded within a printed wire board (PWB). The “film-on-foil” approach is the most viable method to fabricate suitable passive components. We have deposited high-permittivity thin films of ferroelectric Pb0.92La0.08Zr0.52Ti0.48O3 (PLZT) on base metal foils by chemical solution deposition. These capacitors could be embedded into PWBs. However, formation of a parasitic low-permittivity interfacial layer of nickel oxide during thermal processing of the PLZT films considerably reduces the capacitance density. Two approaches were taken to overcome the problem. In the first, a conductive buffer layer of lanthanum nickel oxide (LNO) was inserted between the PLZT film and the nickel foil to hinder the formation of deleterious interfacial oxide. In the second, high temperature processing was done under low oxygen partial pressure such that no interfacial oxide was formed. By these approaches, we have grown high-quality ferroelectric PLZT films on nickel and copper foils. With samples of PLZT grown on LNO-buffered Ni, we measured a dielectric constant of 1300 (at 25°C) and 1800 (at 150°C), leakage current density of 6.6 × 10−9 A/cm2 (at 25°C) and 1.4 × 10−8 A/cm2 (at 150°C), and breakdown field strength >1.2 MV/cm. With samples of PLZT on Cu, we obtained encouraging initial results of dielectric constant >450 and dielectric loss tan(δ) ≈0.04.
Effect of Diamagnetic A2+ Substitution on the Magnetic and Ferroelectric Properties of the Bi1−xAxFeO3 Multiferroics
Authors: Khomchenko V. A. , Kiselev D. A. , Vieira J. M. , Jian Li , Lopes A. M. L. , Pogorelov Y. G. , Araujo J. P. , Kholkin A. L. 
Published: April 2011

AbstractInvestigation of crystal structure, magnetic and local ferroelectric properties of the diamagnetically-doped Bi1−xAxFeO3 (A= Ca, Sr, Pb, Ba; x= 0.2, 0.3) ceramic samples has been carried out. It has been shown that the solid solutions have a rhombohedrally distorted perovskite structure described by the space group R3c. Piezoresponse force microscopy data have revealed the existence of the spontaneous ferroelectric polarization in the samples at room temperature. Magnetization measurements have shown that the magnetic state of these compounds is determined by the ionic radius of the substituting elements. A-site substitution with the biggest ionic radius ions has been found to suppress the spiral spin structure of BiFeO3 and to result in the appearance of weak ferromagnetism. The magnetic properties have been discussed in terms of doping- induced changes in the magnetic anisotropy.
Energy Harvesting From PZT Nanofibers
Authors: Shi Yong , Shi Yong 
Published: April 2011

AbstractIn this paper, we demonstrated that Lead Zirconate Titanate (PZT) nanofibers can be used to harvest energy from dynamic loading and mechanical vibration. PZT nanofibers were fabricated by electrospinning process. SEM image of PZT nanofibers has shown that the average diameter of these fibers is about 150nm, which can be tuned from 50nm to 200 nm by varying the composition and viscosity of the precursor for electrospining. Titanium substrate with ZrO2 layer was used to collect the PZT nanofibers for the demonstration of energy harvesting from dynamic loading. The largest output voltage is 170mV under 0.5% strain; the frequency of the output voltage is the same as that of the input loading. Silicon substrate with trenches was used to collect the nanofibers for energy harvesting from vibration. The output voltage generated from 150Hz sinusoid vibration source has peak voltages of 64.9mV and -95.9mV. These experimental results suggest that PZT nanofibers have great potentials for energy harvesting from environments and being used as nanogenerators. Further study is under the way to optimize the design and improve the efficiency.
Microwave Growth of ZnO Bulk Crystals
Authors: Cheng Jiping , Zhang Yunjin , Guo Ruyan 
Published: April 2011

AbstractA novel approach for fabricating ZnO crystals using self-encapsulated microwave melt growth technique is developed, which permits idealized temperature profile for the nucleation of the ZnO crystals and their growth in a contamination-free environment. This paper reports that both un-doped ZnO and p-type doped ZnO (by P or Li:N doping) single crystals were successfully fabricated by this technique. The as-grown ZnO crystals were of light brown to clear in color depending on processing conditions. Their transparency and colorless form were restored after post-growth annealing in oxygen.
Direct Fabrication of ZnO Whiskers Bridging Between Micron-gap Electrodes in Aqueous Solution for Highly Gas Sensing
Authors: Reiko Hattori , KAMETANI Keisuke , IMAMOTO Hiroshi , FUJITA Shizuo 
Published: April 2011

AbstractA simple but convenient method for fabricating ZnO micro-sized structure selectively and artificially between two micron-gap electrodes was proposed and investigated. The technique is based on electrolytic deposition in aqueous solution of zinc nitrate or zinc acetate, which selectively occurs between the electrodes being enhanced by electric field. The deposition characteristics were investigated in terms of the deposition conditions, and under the optimized condition ZnO micro-sized structure was obtained with bridging between the electrodes. The gas sensing characteristics of the structure was investigated by exposing to a 500 ppm H2 gas, resulting in 23% variation of the resistance at room temperature. The device dimensions can be downsized to nanometer scale by applying nano-gap electrodes, and therefore this technique is promising for fabrication of highly functional nano-sized sensors at low cost, contributing to mass applications.
A Theoretical Study of Ultra-Thin Films with the Wurtzite and Zinc Blende Structures
Authors: Claeyssens Frederik , Freeman Colin L. , Harding John H. , Allan Neil L. 
Published: April 2011

AbstractResults of periodic ab initio density functional theory calculations on thin films of (i) wurtzite ZnO (hexagonal) which terminate with the non-polar (1010) surface, and with the polar (0001) and (0001) surfaces (ii) zinc blende (cubic) ZnO which terminate with the non-polar (110) and with the polar (111) surfaces. Thin (less than18 layer) films of wurtzite ZnO which terminate with the polar (0001) and (0001) surfaces are found to be higher in energy than corresponding films in which these polar surfaces flatten out forming a new planar ‘graphitic’-like structure in which the Zn and O atoms are coplanar and the dipole is removed. This is the lowest energy surface for ultra-thin films. For zinc-blende ZnO a graphitic-type solution, but with a different stacking of ZnO layers, is also comparable to energy to the non-polar (110) and polar (111) solutions. Consequences for crystal growth and the stabilization of thin films and nanostructures are discussed.
InGaN Layers Grown on Al2O3/ZnO Substrates Prepared by Atomic Layer Deposition
Authors: Li Nola , Wang Shen-Jie , Nause Jeff , Valencia Adriana , Summers Christopher , Ferguson Ian 
Published: April 2011

AbstractAtomic layer deposition (ALD) of Al2O3 is used as a passivation layer on ZnO substrates before nitride growth by metalorganic chemical vapor deposition (MOCVD). This layer is being used to prevent Zn diffusion from the substrate, protect the ZnO surface from H2 back etching, and promote high quality nitride growth. ALD-Al2O3 films were grown at 100°C and then annealed in a furnace at various times at 1100°C for crystallization of the passivation layer. XRD results showed both Al2O3 and ZnAl2O4 phases at different intensities for 50 and 20nm ALD-AlM2O3 films. In addition, the InGaN layer has been successfully grown on the passivated ZnO substrate. Findings show that a short annealing time for the ALD-Al2O3 layer will be optimal for InGaN growth.
Applications of First Principles Theory to Inorganic Radiation Detection Materials
Authors: Singh David Joseph , Takenaka H. , Jellison G. E. , Boatner Lynn A. 
Published: April 2011

AbstractApplications of first principles methods to understand properties of several known and potential scintillators for radiation detection are described. These include results for rare earth and Pb-based phosphates, rare-earth trihalides, ZnO, perovskites and tungstates.
Effects of Gamma Irradiation on Optical Properties of Colloidal Nanocrystals
Authors: Withers Nathan J , Sankar Krishnaprasad , Akins Brian A. , Memon Tosifa A. , Gu Jiangjiang , Gu Tingyi , Bowers Shin T. , Greenberg Melisa R. , Smolyakov Gennady A. , Busch Robert D. , Osinski Marek 
Published: April 2011

AbstractThe effects of 137Cs gamma irradiation on photoluminescence properties, such as spectra, light output, and lifetime, of several types of colloidal nanocrystals have been investigated. Irradiation-induced damage testing was performed on CdSe/ZnS, LaF3:Eu, LaF3:Ce, ZnO, and PbI2 nanocrystals synthesized on a Schlenk line using appropriate solvents and precursors. Optical degradation of the nanocrystals was evaluated based on the measured dependence of their photoluminescence intensity on the irradiation dose. Radiation hardness varies significantly between various nanocrystalline material systems.
Diamond Nanoparticles as Photoluminescent Nanoprobes for Biology
Authors: Faklaris Orestis , Elli Alexandra , Joshi Vandana , Sauvage Thierry , Boudou Jean-Paul , Roch Jean-François , Curmi Patrick , Treussart François 
Published: April 2011

AbstractThe present work reports our attempt in developing diamond nanoparticles with size<50 nm as photoluminescent nanoprobes for biological applications like biomolecule tracking in living cell.
Single Crystal CVD Diamond Detectors: Position and Temporal Response Measurements using a Synchrotron Microbeam Probe
Authors: Morse John , Salomé Murielle , Berdermann Eleni , Pomorski Michal , Grant James , O'Shea Val , Ilinski Petr 
Published: April 2011

AbstractUltrapure, homoeptaxially grown CVD single crystal diamond is a material with great potential for the fabrication of ionizing radiation detectors for high energy, heavy ion physics, and realtime dosimetry for radiotherapy. Only diamond has suitable transmission properties and can offer the required radiation hardness for synchrotron X-ray beam monitoring applications. We report on experiments made using a synchrotron X-ray microbeam probe to investigate the performance of single crystal diamonds operated as position sensitive, solid state ‘ionization chambers’. We show that for a wide range of electric fields >0.3Vµm−1, suitably prepared devices give excellent spatial response uniformity and time stability. With an applied field of 2Vµm−1 complete charge collection times are ∼1nsec for a diamond plate thickness of 100µm. Position sensitivity was obtained for an X-ray beam incident on the isolation gap between adjacent electrodes of a quadrant device: here, a crossover response region that results from charge carrier diffusion extends over ∼20µm. Using GHz bandwidth signal processing electronics, the signal charge collection process was measured with spatial and temporal resolutions of 1µm and <50ps.
Single Crystal CVD Diamond Growth for Detection Device Fabrication
Authors: Nicolas Tranchant , Tromson Dominique , Bergonzo Philippe , Nesladek Milos 
Published: April 2011

AbstractSingle crystal (SC) CVD diamond is known to exhibit superior electronic properties than polycrystalline ones for detection applications. In our study, tested samples were grown using CVD in an ASTEX type reactor, at various microwave powers and keeping all other parameters constant. The crystalline quality and purity of the samples were investigated using Raman spectroscopy and birefringence microscopy measurements.The diamonds layers were chemically cleaned and oxidized, towards ionization chamber fabrication using Ni and Au contacts for rectifying properties. The devices electronics and detection properties were then evaluated: leakage currents were probed from I(V) measurements and the contacts behavior were tested under 60Co source at various dose rates. Time Of Flight (TOF) and Charge Collection Efficiency (CCE) measurements were evaluated under an 241Am alpha source and enabled the measurement of the mobility, carrier diffusion lengths and lifetime as a function of the growth parameters. Moreover the response under a UV pulsed flash lamp was probed in order to appreciate the CCE as a function of the repetition rate. The measurements demonstrated the importance of the power density during growth on the detection properties.
STM Characterization of Low Dimensional Surface Electronic Properties of Undoped Diamond in Buffer Solutions
Authors: Yang Nianjun , Uetsuka Hiroshi , Yamada Takatoshi , Nebel Christoph E. 
Published: April 2011

AbstractDiamond is a promising semiconductor which shows some unique surface electronic features if grown optimized with low bulk and surface defect densities. The appearance of a highly conducting surface layer if immersed into electrolyte solution is maybe the most striking feature. Scanning tunneling microscopy experiments on diamond in electrolyte solutions are applied to determine the electronic properties governing these transition. These experiments reveal the formation of unoccupied quantized electronic states in the valence band close to the surface. A two-dimensional density of state distribution with three levels from light-, heavy-, and split-off-band holes is detected. Removal of the electrolyte causes a reversible transition into the insulating state and vice versa.
Synthesis of Nanocrystalline Hexagonal Diamond Films in Organic Solvents by Femtosecond Laser Irradiation
Authors: Hu Anming , Duley Walt W. 
Published: April 2011

AbstractNanocrystalline diamond films have been synthesized on various substrates by 800 nm fs laser irradiation of a variety of organic solvents including acetone, pentane, hexane, heptane, octane, dodecane, and hexadecane in the presence of a transition metal catalyst. 632 nm Raman spectra display a strong vibration mode at 1308 cm−1 characteristic of hexagonal diamond. X-ray photoelectron spectra confirm that the film is mainly sp3-bonded carbon containing a low concentration of sp2-bonded inclusions. Film microstructure shows that these films are assembled from nanoparticles having an average size of < 100 nm. Analysis of the liquid after irradiation using HPLC techniques indicates that polyyne molecules are also synthesized during irradiation. It is possible that these species are formed as the products of ion chemistry following Coulomb explosion. This process may enable a new method for the creation of nanocrystalline hexagonal diamond layers for micro-electronic and other applications.