bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synchrotron white beam x-ray topography (SWBXT) and high resolution triple axis diffraction studies on AlN layers grown on 4H- and 6H-SiC seeds
Authors: Raghothamachar Balaji , Dudley Michael , Dalmau Rafael , Schlesser Raoul , Sitar Zlatko 
Published: April 2011

ABSTRACTFor nitride based devices such as LEDs, high power FETs and laser diodes, single crystal substrates of AlN are highly desirable. While the sublimation technique is suitable for growing bulk AlN crystals, appropriate seeds are also necessary for growing large diameter oriented boules. 4H- and 6H-SiC substrates which are readily available commercially can potentially be implemented as seeds for bulk AlN growth. However, issues regarding SiC decomposition at high temperatures, thermal expansion mismatch, single crystal growth, etc. need to be addressed. Towards this end, a series of growth experiments have been carried out in a resistively heated reactor using on and off-axis 4H- and 6H-SiC substrates as seeds for AlN growth from the vapor phase. Several hundred microns thick AlN layers have been grown under different growth conditions. Synchrotron white beam x-ray topography (SWBXT) has been used to map the defect distribution in the grown layers and high resolution triple axis x-ray diffraction (HRTXD) experiments were carried out to record reciprocal space maps from which tilt, mismatch and strain data can be obtained. These results are analyzed with respect to the growth conditions in order to gain a better understanding of this growth process.
Improvement of Operating Voltage and Luminescent Properties in Nanocrystalline Silicon Electroluminescent Device
Authors: Sato K. , Hirakuri K. , Izumi T. 
Published: April 2011

ABSTRACTWe have investigated direct current (DC) operating voltage and luminescence properties of electroluminescent (EL) devices with and/or without a silicon dioxide (SiO2) layer in nanocrystalline Si (nc-Si) region/Si substrate interface. The device with the SiO2 layer showed red luminescence with a peak at 670 nm by applying the DC operating voltage above 4.0 V. When the SiO2 layer in the device was completely removed by the hydrofluoric acid (HF) treatment, the red luminescence from the device was observed at the DC operating voltage of 2.0 V. Moreover, the luminescent intensity was also increased more than one order of magnitude, because carriers were efficiently and easily injected into the nc-Si region by the removal of SiO2 layer. The red luminescence from the device could be clearly seen with the naked eye under the DC operating voltage above 3.0 V. These results indicate that the removal of SiO2 layer leads to the lowering of DC operating voltage and increase of luminance for the nc-Si based EL device.
Hydrogen Passivation of Er and Si Nanocrystallites in Er-doped SiO2- Increase in Photoluminescence-
Authors: Fukata N. , Li C. , Uematsu H. , Arai T. , Makimura T. , Murakami K. 
Published: April 2011

ABSTRACTHydrogen passivation effect on the enhancement of photoluminescence (PL) of Er ions in SiO2films contained Si nanocrystallites (nc-Si) has been investigated. Er-doped SiO2films were fabricated by laser ablation of Er-deposited Si substrate in oxygen gas atmosphere. The PL intensity of Er ions and nc-Si were increased by hydrogen gas treatments, while ESR signal intensity of residual defects located at the interfaces between nc-Si and SiO2was decreased. These results indicate that hydrogen passivation of residual defects is useful for the enhancement of the Er PL.
Charge Transport in Silicon Nanocrystal Arrays
Authors: Krishnan R. , Xie Q. , Kulik J. , Wang X.D. , Krauss T.D. , Fauchet P.M. 
Published: April 2011

ABSTRACTSingle layers of isolated, size-controlled silicon nanocrystals were prepared by thermal crystallization of a thin amorphous silicon layer sandwiched between silicon dioxide layers. A subsequent oxidation treatment ensured controlled increase in their lateral separation. The size of the nanocrystals, separation of the nanocrystals (from < 1 nm to ∼ 4 nm), stoichiometry of the resulting oxide and surface morphology were monitored with transmission electron microscopy, scanning transmission electron microscopy, atomic force microscopy, and x-ray photoelectron spectroscopy. Mesoscopic charge transport studies performed with an electrostatic force microscope (EFM) revealed rapid lateral transport of charges when the nanocrystals were tightly packed (< 1 nm average separation) and interconnected. As the inter-nanocrystal separation was increased, lateral charge transport was rapidly suppressed. Nanocrystals separated by up to 3.6 nm retained the injected charges in a well-defined localized region (∼ 62 nm diameter region) for a time of the order of several days. The ability to switch from a very short to a very long retention time using the same structure by simply changing the post-growth processing conditions is attractive for various applications involving charge transport and localization.
Uniform dome-shaped self-assembled Ge islands by UHV/CVD after boron pre-deposition
Authors: Deng Ning , Huang Wentao , Chen Peiyi 
Published: April 2011

AbstratEffect of pre-deposited boron atoms on self-assembled growth of Ge islands on Si(100) substrate by UHV/CVD was investigated by atomic force microscopy (AFM). Proportion of dome-shaped Ge islands increases with the increasing of flux of B2H6. Quite uniform dome-shaped Ge quantum dots with size distribution of less than ±3%, which is narrower than the size distribution of typical bimodal self-assembled Ge dots, were obtained after appropriate boron pre-deposition. Based on the shape transition model we proposed before, the uniform size and shape distributions after boron pre-deposition were explained. The results show that boron pre-deposition can be used to fabricate uniform Ge quantum dots to meet the requirements of opto-electronic devices.
Tribological Applications of Shape Memory and Superelastic Effects
Authors: Ni Wangyang , Cheng Yang-Tse , Grummon David S. 
Published: April 2011

ABSTRACTWe provide an overview of our recent studies on novel tribological applications of shape memory and superelastic effects: (i) the use of shape memory NiTi alloys as self- healing surfaces, and (ii) the use of the superelastic NiTi as an interlayer between a hard coating and a soft substrate to improve interfacial adhesion, decrease friction coefficient, and improve wear resistance.
Patterning of Cells on Bioresist for Tissue Engineering Applications
Authors: Umar Yusif , Thiyagarajan Muthiah , Halberstadt Craig , Gonsalves K. E. 
Published: April 2011

Engineering functional tissues and organs successfully depends on the ability to control cell orientation and distribution. Materials used for such purposes therefore have to be designed to facilitate cell distribution and eventually guide tissue regeneration in 3D.The field of tissue engineering hinges on developing degradable polymeric scaffolds that promote cell proliferation and expression of desired physiological behaviors through careful control of the polymer surface.The development of materials for tissue engineering and guided tissue regeneration has accelerated over the last decade.[1] It has been demonstrated that non-patterned cells are effectively not tissue. “Tissues require that cells be placed and hold precise places often with precise orientations” [2–3]. Cell patterning is therefore very important for tissue engineering. We have developed a biocompatible, biostable chemically amplified bioresist, with which patterns are generated without involving harsh chemical treatment.
Synthesis, Sintering and Microstructural Characterization of Nanocrystalline Hydroxyapatite Composites
Authors: Viswanath B. , Ravishankar N. , Nayar Suprabha , Sinha Arvind 
Published: April 2011

ABSTRACTNanocrystalline hydroxyapatite (HAp) exhibits better bioactivity and biocompatibility with enhanced mechanical properties compared to the microcrystalline counterpart. In the present work, nanocrystalline hydroxyapatite was synthesized by wet chemical method. Sintering was carried out with nanocrystalline alumina as additive, the content of alumina being varied from 10 to 30 wt% in the composite. For 20 and 30 wt % Al2O3, hydroxyapatite decomposed into tricalcium phosphate (TCP) above the sintering temperature of 1100°C. The fracture toughness of nano HAp-nano Al2O3 composite is anisotropic in nature and reached a maximum value of 6.9 MPa m1/2.
Biomedical Applications of Gold Nanoparticles Functionalized Using Hetero-Bifunctional Poly(ethylene glycol) Spacer
Authors: Fu Wei , Shenoy Dinesh , Li Jane , Crasto Curtis , Jones Graham , Dimarzio Charles , Sridhar Srinivas , Amiji Mansoor 
Published: April 2011

ABSTRACTTo increase the targeting potential, circulation time, and the flexibility of surface-attached biomedically-relevant ligands on gold nanoparticles, hetero-bifunctional poly(ethylene glycol) (PEG, MW 1, 500) was synthesized having a thiol group on one terminus and a reactive functional group on the other. Coumarin, a model fluorescent dye, was conjugated to the PEG spacer and gold nanoparticles were modified with coumarin-PEG-thiol. Surface attachment of coumarin through the PEG spacer decreases the fluorescence quenching effect of gold nanoparticles. The results of cellular cytotoxicity and fluorescence confocal analyses showed that the PEG spacer modified nanoparticles were essentially non-toxic and could be efficiently internalized in the cells within one hour of incubation.
The Stability and Oxidation Resistance of Iron- and Cobalt-Based Magnetic Nanoparticle Fluids Fabricated by Inert-Gas Condensation
Authors: Hai Nguyen H. , Lemoine Raymond , Remboldt Shaina , Strand Michelle A. , Wignall Steve , Shield Jeffrey E. , Leslie-Pelecky Diandra 
Published: April 2011

ABSTRACTMagnetic nanoparticle fluids have numerous biomedical applications, including magnetic imaging, drug delivery, and hyperthermia treatment for cancer. Ideal magnetic nanoparticle fluids have well-separated, biocompatible nanoparticles with a small size distribution that form a stable colloid. We have combined inert-gas condensation, which produces nanoparticles with low polydispersity, with deposition directly into a surfactant-laden fluid to prevent agglomeration. Iron, cobalt, and iron-nitride nanoparticle fluids fabricated using inert-gas condensation have with mean particle sizes from 5–50 nm and remain stable over long periods of time. Iron and cobalt nanoparticles oxidize on exposure to air, with oxidation rates dependent on surfactant type and concentration. Iron-nitride fluids are more oxidation and corrosion resistant, while retaining the same high degree of colloidal stability. Magnetic properties vary depending on the nanoparticle size and material, but can be varied from superparamagnetic to ferromagnetic with coercivities on the order of 1000 Oe. In addition to future biomedical applications, inertgas condensation into fluids offers the opportunity to study interparticle interactions over a broad range of intrinsic materials parameters and interparticle separations.
Titanium Nanosurface Modification by Anodization for Orthopedic Applications
Authors: Yao Chang , Slamovich Elliott B. , Webster Thomas J. 
Published: April 2011

ABSTRACTTitanium is broadly used in orthopedic and dental applications mainly because of its optimal mechanical properties in load-bearing applications. However, insufficient new bone formation is frequently observed on titanium which sometimes leads to implant loosening and failure. For this reason, the objective of the present in vitro study was to modify the surface of conventional titanium to include nanostructured surface features that promote the functions of osteoblasts (bone-forming cells). This study focused on creating nanostructured titanium surfaces since bone itself has a large degree of nanostructured roughness that bone cells are accustomed to interacting with. In this study, the surface of titanium was modified by anodic oxidation techniques. The electrolyte used for anodization was hydrofluoric acid. Depending on acid concentration and anodization time, two kinds of different nano-architectures, either particulate or tube-like structures, were formed on the titanium surface. X-ray diffraction results confirmed that the titanium oxide formed on the surface of titanium was amorphous. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to characterize the surface morphology. Cell adhesion studies showed that the anodized nanostructured titanium surface promoted osteoblast adhesion compared to non-anodized titanium. This result indicated that anodization may be a simple method to modify the surface of titanium implants to enhance bone-forming cell function thereby increasing orthopedic implant efficacy.
Structures and Physical Properties of Ternary Antimonides RE3MSb5 (M = Zr, Hf), U3MSb5 (M = Zr, Hf, Nb), and YbCrSb3
Authors: Tkachuk Andriy V. , Crerar Shane J. , Wu Xing , Muirhead Craig P. T. , Deakin Laura , Mar Arthur 
Published: April 2011

ABSTRACTTernary rare-earth transition-metal antimonides RExMySbz have provided fertile ground for discovering materials with varied electrical and magnetic properties such as superconductivity and ferromagnetism. The properties of two important classes of these compounds, RE3TiSb5 and RECrSb3, have been previously investigated. These studies have now been extended to RE3MSb5 (M = Zr, Hf), which show anomalies in their resistivity curves suggestive of electronic transitions, and YbCrSb3, which undergoes long-range magnetic ordering at 285 K, the highest Tc observed so far of all RECrSb3 members. Strong magnetic exchange interactions develop through coupling of f and d electrons in these compounds. The substitution of uranium for rare earth in RE3MSb5 results in the compounds U3MSb5 (M = Zr, Hf, Nb), which also display prominent transitions in their electrical resistivity and magnetic susceptibility curves.
Structure and Properties of the Semiconductors Tl2SnAs2Q6 (Q = S, Se)
Authors: Iyer Ratnasabapathy G. , Bilc Daniel , Mahanti S. D. , Kanatzidis Mercouri G. 
Published: April 2011

ABSTRACTWe describe the Tl2SnAs2Q6, (Q= S, Se) compounds which consist of [SnAs2S6]2- layers with the Tl+ cations lying in between. Tl2SnAs2S6 and Tl2SnAs2Se6 crystallize in the space group P-3 with a = 6.706(4) Å, c = 7.187(6) Å and a = 6.996(3) Å, c = 7.232(4) Å respectively. These compounds are semiconductors with band gaps of 1.68 eV for the sulfide and 1.08 eV for selenide corresponding to their dark red and black colors respectively. Band structure calculations suggest indirect band gaps in these materials.
High Throughput Synthesis of Pigments by Solution Deposition
Authors: Henderson Stuart J. , Hector Andrew L. , Weller Mark T. 
Published: April 2011

ABSTRACTCombinatorial and high throughput methods have been utilised in the pharmaceutical industry for many years. The process involves the simultaneous synthesis of libraries containing thousands of compounds, which can then be screened for desirable properties. More recently the concepts of parallel synthesis and high-throughput screening have emerged as effective strategies in the search for novel inorganic materials. We report the development of high throughput methods, which have been used for the synthesis and preliminary characterisation of ceramic oxide pigments on an alumina substrate. This methodology has been utilised to prepare compounds with the spinel structure in the series Cu1-xZnxAl2-yCryO4 (0≤x≤1, 0≤y≤2) at a range of temperatures. The materials are analysed by rapid sequential X-ray diffraction and a simple colour measurement technique. The optical properties across the quaternary landscape can therefore be mapped as a function of composition, structure and annealing temperature.
Inducing Magnetism in Wide Band Gap Hosts
Authors: Seshadri Ram , Risbud Aditi S. , Lawes Gavin 
Published: April 2011

ABSTRACTWe have used precursor routes to prepare magnetic transition metal ion (tM) substituted wurtzite ZnO powders with up to 15% tM substitution (tM = Co and Mn) on the cation site. Careful magnetic studies reveal these samples show no cooperative magnetic ordering, and certainly no ferromagnetism. Instead, the nearest-neighbor coupling is actually antiferromagnetic. Modeling of the temperature dependence of the magnetic susceptibility indicates the difficulty in inducing ferromagnetism, in keeping with the results of density functional calculations. The alternate strategy of inducing dilute ferri magnetism in wide band gap spinel hosts with two cation sites has been more successful; dilute magnets based on tM substitution in spinel ZnGa2O4 seem promising, displaying magnetic hysteresis in nearly transparent samples.
Synthesis of Three Layer NaxCoO2(x=0.3, 0.5, 0.6, 0.75, 1.0) and Superconductivity in Three Layer Na0.3CoO2•1.3H2O
Authors: Foo M.L. , Klimczuk T. , Li L. , Ong N.P. , Cava R.J. , Huang Q. , Lynn J.W. , Zandbergen H.W. 
Published: April 2011

ABSTRACTThe synthesis of three layer sodium cobalt oxide, NaxCoO2(x=0.3, 0.5, 0.6, 0.75 and 1.0) is reported. For x=0.6, 0.75, and 1.0, conventional solid-state synthesis was employed. x=0.3 and 0.5 were obtained via oxidative deintercalation of sodium at room temperature. x=0.3 can be hydrated to Na0.3CoO2•1.3H2O which is superconducting with a Tcof 4.3 K. Although having the same chemical stiochiometry as the previously reported two layer superconductor, it has a different stacking sequence of CoO2layers making it structurally distinct. Crystals of three layer NaCoO2show triangular morphology compared to hexagonal morphology for two layer Na0.7CoO2.
Optical Property of Vanadium Oxide Nanotube Suspensions
Authors: Mai L. Q. , Chen W. , Yu H. , Qi Y. Y , Dai Y , Peng J. F. 
Published: April 2011

ABSTRACTVanadium oxide nanotube dispersions were investigated in water suspensions and characterized by TEM, absorption spectroscopy and optical limiting testing. The results show that the nanotubes are unrolled and oxidized after 6-day aging, resulting in some change of optical limiting property at the two wavelengths (532 and 1064 nm). The 1.27-eV absorption band is assigned as a superposition of both V d→d and V4+→V5+ charge-transfer excitations, and the features at 2.9 eV are attributed to O 2p→V 3d charge-transfer excitations.
Structural properties of amorphous aluminum and aluminum-nitrogen alloys. Computer simulations
Authors: Valladares Ariel A. , Valladares Alexander , Valladares R. M. , Calles A. 
Published: April 2011

AbstractLiquid and amorphous metallic systems have proven difficult to model. Some efforts have relied on the use of parameterized classical potentials of the Lennard-Jones type or geometric hard sphere simulations, but first principles approaches have been rarely used. Clearly a knowledge of atomic structures is paramount for calculating physical properties. In this work we apply our recently developed ab initio DFT approach (A. A. Valladares et al., Eur. Phys. J. 22 (2001) 443) for the generation of amorphous semiconducting materials, to amorphize aluminum and an aluminum-nitrogen alloy. We report radial distribution functions (RDFs) and specific atomic structures of periodic amorphous/liquid cubic supercells of 108 atoms with a volume of (12.1485 Å)3, generated using the Harris functional.
Generation of New Nanomaterials by Interfering Femtosecond Laser Processing
Authors: Nakata Yoshiki , Tatsuo Okada 
Published: April 2011

ABSTRACTNew nanomaterials such as nanobump array, nanomesh, nanobelt were generated from thin film processed by interfering femtosecond laser beams. Metallic single- or multi-layered film deposited on a silica substrate was used as a raw thin film. With four interfering femtosecond laser beams, a conical nanobump arrayed in a matrix was generated with single laser shot. As the femtosecond laser fluence increased, the nanobump increased in diameter and height, and a bead was found at the top. Moreover, with three or two interfering femtosecond laser beams, ellipsoidal or linear nanobump array was generated. As an application of a conical nanobump array, field emission from the nanobump array was demonstrated, and the I-V characteristics were measured. On the other hand, with much higher fluence and four interfering femtosecond laser beams, a nanohole array was generated. A nanomesh was also generated from the nanohole array by exfoliating the film. A grating was generated with two interfering femtosecond laser beams, and nanobelts were generated from the grating by exfoliating. Bimetallic nanobelt was also generated from multi-layered thin film.
Micro- and Nano-Structured Optical Fibers - Artificial Media for Amplification of Light.
Authors: Tünnermann A. , Röser F. , Schreiber T. , Limpert J. , Liem A. , Reich M. , Höfer S. , Zellmer H. , Burghoff J. , Will M. , Nolte S. 
Published: April 2011

ABSTRACTIn experiments with rare-earth-doped fibers impressively results have been demonstrated and shown that fiber lasers and amplifiers are an attractive and power scalable solid-state laser concept. With ytterbium-doped large-mode-area double-clad fibers, output powers approaching the kW-range with diffraction limited beam quality have been realized in the continuous regime. Also in the pulsed regime, even for femtosecond pulse duration average output powers in the range of 100 W have been demonstrated. Further power scaling is limited by the end facets damage, thermo-optical problems or nonlinear effects. To overcome these restrictions microstructured fibers can be used. This type of fibers has several new preferable features. In our contribution we will discuss the advantages of microstructured fibers to reduce nonlinear effects inside the fiber and the possibility to scale the output power of fiber lasers and amplifiers with excellent beam quality. We also show fiber based chirped pulse amplification system (CPA-System) with ultra short pulses, pulse energies of up to 100 μJ and high repetition rates.
A Hypothesis of Interaction of Composites Filler Particles with Polymeric Matrix
Authors: V.K. Makaryan 
Published: April 2011

ABSTRACTIn order to determine the adhesion of filler particles to polymeric matrix a set of tests on the tensile strength of composite materials based on CFD and PPS has been performed. The best results were observed for composites with nanosized amorphous fillers Mo and MoO2. The strength of composites filled with such fillers increased up to 2 times compared to the pure polymer value. The effect of using fine-ground mineral fillers is less – about 1.5 times. Coarse fractions of mineral fillers (50μm) do not have positive effect on the composite tensile strength. Thus, the effect of fillers on the mechanical properties of polymer-based composites depends heavily on the nature and dispersivity of the filler and is apparently determined by the behavior of chemical and mechanical bonds occurring on the phase boundaries. The large number of bonds for nanosized fillers is promoted by the high specific (to surface area) number of radicals on their surface, which results in strong bounding of particle to matrix, besides the polymeric material close to the phase boundary gains additional properties.Since the size of nanoparticles is proportional to the thickness of interphase boundary layer, the considerable portion of the composite material transforms to a boundary interphase state, which properties, being different from both filler and polymer properties, determine the new characteristics of the composite material.