bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural and optical properties of CdSe, CdTe and CdSeTe nanoparticles dispersed in SiO2 films
Authors: Babu Dayal P. , Rama Rao N. V. , Mehta B. R. , Shivaprasad S. M. , Paulson P. D. 
Published: April 2011

ABSTRACTCdSexTe1-x nanoparticles (with different stoichiometry ratio x) dispersed in silicon dioxide films have been grown by magnetron sputtering technique followed by thermal annealing. Effect of thermal annealing conditions on the structural, compositional, optical and electronic properties of nanoparticles has been studied using GAXRD, XPS, TEM, and spectroscopic ellipsometry techniques. A structural transformation in the nanoparticle core mediated purely by surface layer effects in the case of CdTe and a spontaneous self-organization of nanoparticles into nanorods in the case of CdSe via fractal growth has been observed. Preliminary observations from the ellipsometry measurements carried out on some of these nanoparticle films shows a blue shift of absorption edge.
Optical Properties of CdSe Nanoparticle Assemblies
Authors: Rafael Leon F. , Zaitseva Natalia , Gerion Daniele , Huser Thomas , Krol Denise 
Published: April 2011

ABSTRACTWe report on three-dimensional fluorescence imaging of micron-size faceted crystals precipitated from solutions of CdSe nanocrystals. Such crystals have previously been suggested to be superlattices of CdSe quantum dots [1,2]. Possible applications for these materials include their use in optical and optoelectronic devices. The micron-size crystals were grown by slow evaporation from toluene solutions of CdSe nanocrystals in the range of 3–6 nm, produced by traditional wet-chemistry techniques. By using a confocal microscope with laser illumination, three-dimensional raster-scanning and synchronized hyper-spectral detection, we have generated spatial profiles of the fluorescence emission intensity and spectrum. The fluorescence data of the micro-crystals were compared with spectra of individual nanocrystals obtained from the same solution. The results do not support the assertion that these microcrystals consist of CdSe superlattices.
Optical Interactions and Photoluminescence Properties of Wide-Bandgap Nanocrystallites
Authors: Bergman Leah , Chen Xiang-Bai , Huso Jesse , Walker Althea , Morrison John L. , Hoeck Heather , Penner Margaret K. , Purdy Andrew P. 
Published: April 2011

ABSTRACTThe UV-photoluminescence (PL) properties of GaN and ZnO nanocrystallites and nanocrystallite ensembles were studied utilizing micro-photoluminescence. We address the origin of the light emissions of the nanocrystallite as to whether it is due a bandgap or excitonic recombination process. The other topic presented here focuses on the interaction of the laser with a collective of crystallites; we address the phenomena of intensity saturation at a high density of laser excitations as well as the impact of the vacuum state on the PL characteristics. Our analysis indicates that the PL of both GaN and ZnO nanocrysallites is excitonic-like and very similar to the behavior of the free exciton in bulk materials. Additionally, we attribute the intensity saturation of GaN and ZnO to the laser heating and heat trapping which takes place in the enclosure of the nanocrystallite ensemble. In vacuum the PL energy was found to exhibit a strong PL energy redshift relative to the PL in air. We attribute the observed shift to a thermal effect and analyze it in terms of the conditions enabling a convective cooling in the ensemble: the mean free path of air in atmospheric pressure and in vacuum relative to the interparticle separation inside the ensemble.
Superparamagnetic Iron Oxide Nanoarticles for Biomedical Applications: a focus on PVA as a coating
Authors: Chastellain M. , Petri A. , Hofmann H. 
Published: April 2011

ABSTRACTNanoscaled particles showing a superparamagnetic behavior have been intensively studied these past years for biomedical applications and water-based ferrofluids turned out to be promising candidates for various in vivo as well as in vitro applications. Nevertheless, the lack of well-defined particles remains an important problem. One of the major challenges is still the large-scale synthesis of particles with a narrow size distribution. In this work iron oxide nanoparticles are obtained by classical co-precipitation in a water-based medium and are subsequently coated with polyvinyl alcohol. The thus obtained ferrofluids are studied and a focus is made on their colloidal stability.
Controlled Structure of Gallium Oxide and Indium Oxide Nanowires
Authors: Chun Hye Jin , Bae Seung Yong , Park Jeunghee 
Published: April 2011

ABSTRACTGallium oxide (Ga2O3) and indium oxide (In2O3) nanostructures were synthesized by chemical vapor deposition (CVD). Ga2O3 nanowires were synthesized using Ga/Ga2O3 mixture and O2. The diameter of the nanowires is 30–80 nm with an average value of 50 nm. They are consisted of single-crystalline monoclinic crystal. While the nanowires grown without catalyst exhibit a significant planar defect, the nanowires grown with nickel catalytic nanoparticles are almost defect-free. The growth direction of the nanowires grown without the catalyst is uniformly [010]. In contrast, the nanowires grown with the catalyst have random growth direction. X-ray diffraction, Raman spectroscopy, and photoluminescence are well correlated with the structural characteristics of the nanowires. The result provides an evidence for the catalyst effect in controlling the structure of nanowires. In2O3 nanostructures were also synthesized in a controlled manner by selecting the catalyst. The reactants were In and In/In2O3 mixture. The nanowires were produced using catalytic Au nanoparticles and Ga. But the unique bifurcated-structure nanobelts were instead grown without Ga. The nanowires have uniform [100] growth direction with rectangular cross-section. We converted the In2O3 nanowires to In2O3-Ga2O3 nanostructures.
Diffusion-Limited Recombination in Dye-Sensitized TiO2 Solar Cells
Authors: Kopidakis Nikos , Benkstein Kurt D. , Lagemaat Jao van de , Frank Arthur J. 
Published: April 2011

ABSTRACTThe effect of doping on the electron transport dynamics and recombination kinetics in dye-sensitized solar cells was investigated. A simple electrochemical method was developed to dope TiO2 nanoparticle films with Li. Increasing the doping levels is found to slow electron diffusion. The electron diffusion time exhibits a light intensity dependence at all doping levels consistent with a multiple electron-trapping model involving native and doping-induced traps. Importantly, the diffusion time and recombination lifetime of photocarriers are observed to increase in unison with increased doping. This is the first observation that electron diffusion limits recombination with the redox electrolyte under normal working conditions of the dye cell. A model is presented that accounts for the observation. The implications of this mechanism on cell performance are also discussed.
The Magnetic Behavior of Triangular Shaped Permalloy Nanomagnet Arrays
Authors: Shiu J. Y. , Tai M. F. , Yao Y. D. , Kuo C. W. , Chen P. 
Published: April 2011

ABSTRACTDuring the past few decades, the density of magnetic storage has been improved considerably. To increase the storage capacity, it is necessary to reduce the size of magnetic grains. However, as the domain size decreases, their thermal stability will also decrease, which results in the loss of magnetization. To overcome the limit imposed by such superparamagnetic behavior, lots of recent research attentions have been focused on the patterned magnetic media. To maximize the storage density, it is preferable to create periodical magnetic patterns, in which single-domain magnetic dots are well separated from each other. In this experiment, we have utilized nanosphere lithography to create large-area well-ordered two dimension arrays of permalloy (Ni80Fe20) nanoparticles. Nanosphere lithography is an inexpensive, simple, parallel, and high throughput fabrication technique. We have employed monodisperse polystyrene beads with diameter of 650, 560, 440, 350, 280 nm to fabricate triangle-shaped permalloy (Ni80Fe20) nano-arrays with lateral dimension in the region of 170∼90 nm, and thickness in the region of 10∼50 nm. The magnetic behavior of these triangle-shaped nanomagnet arrays have been investigated by longitudinal magnetic optic Kerr effect (LMOKE) and magnetic force microscopy (MFM). It was found that the coercivity of the permalloy nanoparticle arrays increases with decreasing the thickness of the nanoparticle. This can be attributed to the interface effect between the arrays and the substrate.
Lasing from CdSe/ZnS Quantum Rods in a Cylindrical Microcavity
Authors: Kazes Miri , Lewis David Y. , Ebenstein Yuval , Mokari Taleb , Banin Uri 
Published: April 2011

ABSTRACTLasing from CdSe/ZnS quantum rods and quantum dots both in solution and in a film is studied by utilizing a high Q cylindrical microcavity, showing Whispering Gallery Mode (WGM) lasing. CdSe/ZnS quantum rods, in comparison to quantum dots, exhibited remarkably reduced lasing thresholds. In addition, polarization measurements revealed that quantum rods have a linear polarized lasing, in contrast to quantum dots that show no preferable lasing polarization. Furthermore, an efficient and reproducible method is employed for preparation of nanocrystal films inside capillaries by laser irradiation for achieving robust lasing. Further irradiation of the film resulted in a room temperature stable lasing over hundreds of pump pulses, lasing thresholds as low as 0.02mJ and lasing intensities that are three orders of magnitude larger than the saturated fluorescence intensity. This was successfully applied to CdSe/ZnS quantum rod samples of varied dimensions and was also demonstrated for quantum dot samples.
Quantum Conductivity of Spatially Inhomogeneous Systems
Authors: Pozhar Liudmila A. 
Published: April 2011

ABSTRACTA fundamental quantum theory of conductivity of spatially inhomogeneous systems in weak electro-magnetic fields has been derived using a two-time Green function (TTGF)-based technique that generalizes the original method due to Zubarev and Tserkovnikov (ZT). Quantum current and charge density evolution equations are derived in a linear approximation with regard to the field potentials. Explicit expressions for the longitudinal and transverse conductivity, and dielectric and magnetic susceptibilities have been derived in terms of charge density - charge density and microcurrent - microcurrent TTGFs. The obtained theoretical description and formulae are applicable to any inhomogeneous system, such as artificial molecules, atomic and molecular clusters, thin films, interfacial systems, etc. In particular, the theory is designed to predict charge transport properties of small semiconductor quantum dots (QDs) and wells (QWs), and is a significant step toward realization of a concept of virtual (i.e., theory-based, computational) synthesis of electronic nanomaterials of prescribed electronic properties.
The Effect of Gate Geometry on the Charging Characteristics of Metal Nanocrystal Memories
Authors: Gorur-Seetharam Anirudh , Lee Chungho , Kan Edwin C. 
Published: April 2011

ABSTRACTThis study presents the effect of gate geometry on the charging characteristics of metal nanocrystal memories. The effect is studied by varying the perimeter to area ratio, number of convex corners and concave corners of the gate of a metal-oxide-semiconductor (MOS) capacitor with embedded gold nanocrystals. It can be observed that the nanocrystal charging rate increases for a smaller perimeter to area ratio. The presence of concave and convex corners increases the nanocrystal charging rate. Based on this study it is expected that gate geometries with low perimeter to area ratio and with selected convex and concave corners would increase the nanocrystal charging rate.
Synthesis of boron nitride nanolayers encapsulating iron fine particles and boron nitride nanotubes
Authors: Tokoro Hisato , Fujii Shigeo , Oku Takeo , Muto Shunsuke 
Published: April 2011

ABSTRACTBoron nitride (BN) nanolayers encapsulating iron (Fe) fine particles have been synthesized by annealing mixtures of hematite (α-Fe2O3) and boron powders at 1373 K for 2 hours in nitrogen atmosphere. The Fe particles had an average diameter of ∼300 nm with BN nanolayers coating of ∼10 nm. The α-Fe2O3 was transformed into Fe and then Fe-B on a process of annealing. The Fe-B was decomposed into Fe and BN, and consequently Fe particles coated with BN nanolayers were synthesized. They showed soft magnetic properties with coercivity of 1.5 kA/m. The BN nanolayers encapsulation was effective on improving oxidation resistance. BN nanotubes with diameter of ∼100 nm were also synthesized as a resultant product by this method.
Aqueous Ferrofluid of Citric Acid Coated Magnetite Particles
Authors: Goodarzi A. , Sahoo Y. , Swihart M. T. , Prasad P. N. 
Published: April 2011

ABSTRACTMagnetic nanoparticles have found application in medical diagnostics such as magnetic resonance imaging and therapies such as cancer treatment. In these applications, it is imperative to have a biocompatible solvent such as water at optimum pH for possible bio-ingestion. In the present work, a synthetic methodology has been developed to get a well-dispersed and homogeneous aqueous suspension of Fe3O4 nanoparticles in the size range of 8–10 nm. The surface functionalization of the particles is provided by citric acid. The particles have been characterized using transmission electron microscopy, magnetization measurements with a superconducting quantum interference device, FTIR spectroscopy (for surfactant binding sites), thermogravimetric studies (for strength of surfactant binding), and x-ray photoelectron spectroscopy and x-ray diffraction (for composition and phase information). The carboxylate functionality on the surface provides an avenue for further surface modification with fluorescent dyes, hormone linkers etc for possible cell-binding, bioimaging, tracking, and targeting.
Atomic Organization In Magnetic Bimetallic Nanoparticles: An Experimental And Theoretical Approach
Authors: Fromen Marie-Claire , Dennler Samuel , Casanove Marie-José , Lecante Pierre , Morillo Joseph , Bayle–Guillemaud Pascale 
Published: April 2011

ABSTRACTUltrafine bimetallic CoRh nanoparticles synthesized by a soft chemical route with compositions ranging from pure cobalt to pure rhodium are investigated using high-resolution and energy filtering transmission electron microscopy techniques as well as wide angle x-ray scattering. In parallel, they are simulated with the use of an n-body semi-empirical interaction model: quenched molecular dynamics and Monte-Carlo Metropolis simulated annealing are performed on these nanoparticles in order to find their most stable isomers as a function of composition and size. A progressive evolution from an original polytetrahedral structure to the face-centered cubic structure with increasing Rh content is observed in these particles. Strong tendency to Co surface segregation is both experimentally evidenced and confirmed by the simulations.
Phonon Thermal Conductivity of Superlattice Nanowires for Thermoelectric Applications
Authors: Dames C. , Dresselhaus M. S. , Chen G. 
Published: April 2011

ABSTRACTAn incoherent particle model has been developed to predict the phonon thermal conductivity of nanowires and superlattice nanowires. It is argued that the surface roughness of most real nanowires prevents the formation of idealized confined dispersion relations for typical temperatures and diameters. Instead, the three-dimensional bulk dispersion is used, thus addressing only classical size effects. Four adjustable parameters capture the effects of diameter, superlattice, Umklapp, impurity, and alloy scattering. Predictions are compared with experimental data for nanowires and superlattice nanowires down to 22 nm diameter and 20 K, and are in good agreement above ∼40 nm diameter. The analysis suggests that ideal low thermal conductivity nanowires for thermoelectric applications would have small-diameter, alternating alloy segments that are acoustically dissimilar but electrically similar.
Influence of Stress on Thermoelectric Properties of Antimony Telluride
Authors: Mahan Gerald D. , Jeon Gun Sang , Thonhauser T. 
Published: April 2011

ABSTRACTWe present first-principles calculation for the behavior of antimony telluride under stress. We focus on the calculation of transport properties for pure Sb2Te3and the investigation of stress-induced defects. Our transport calculations were done within first-principles using the linearized-augmented plane-wave method, where we first calculated the transport distribution for several stress conditions. Next, using these stress dependent transport distributions, we derived the stress dependence of the electrical conductivity, the Seebeck coefficient, and the power factor. Our calculations for the stress-induced defects were done utilizing a pseu-dopotential method and confining ourselves to the antisite defect. In all cases, our results are in good agreement with experimentally obtained data. Furthermore, we found that hydrostatic pressure does not improve the power factor, while, on the other hand, a large increase under uniaxial stress can be observed. Also, both hydrostatic pressure and uniaxial stress are found to lower the formation energies of the antisite defects, suggesting a structural transition at high pressures.
Effect of Ni in new skutterudite compounds CaxCo4Sb12
Authors: Puyet Matthieu , Lenoir Bertrand , Dauscher Anne , Scherrer Hubert , Dehmas Moukrane , Hejtmanek Jiri , Stiewe Christian , Müller Eckhard 
Published: April 2011

ABSTRACTThe transport properties of the partially filled CaxCo4-yNiySb12 skutterudite compounds have been investigated in the 300 – 800 K temperature range. We underline the positive influence of the Ni substitution on the electrical resistivity and thermopower while the thermal properties – thermal conductivity – remains almost unaffected. These results suggest again a beneficial effect of Ni atoms on the dimensionless figure of merit in CoSb3 based compounds.
New Transition-Metal Doped Germanium Clathrates
Authors: Li Yang , Ross Joseph H. 
Published: April 2011

ABSTRACTWe have investigated transition-metal substitutions into germanium clathrates, and describe the properties of two different Fe-substituted Ge clathrates, one with the chiral Ba6Ge25-type clathrate structure, and one based on the Ba6Ga16Ge30clathrate with the type-I structure. In both cases Fe exhibits a high-spin local moment, with 5.5 μBand 5.6 μBper Fe. We observe ferromagnetic ordering, withTcup to 278 K in the most heavily substituted Ba6Ga16Ge30clathrate. X-ray powder diffraction and electron microprobe measurements confirmed the formation of these substituted phases. Ni-doped type I clathrates were found to be diamagnetic. Strong competition from Mn11Ge8makes it difficult to produce pure Mn-doped clathrates, however a composite material with partially substituted chiral structure is described. Similar efforts to produce Co, Cr, and V-substituted clathrates have not been successful.
Thermoelectric Properties of NaZn13-type Intermetallic Compounds
Authors: Amagai Y. , Yamamoto A. , Lee C. H. , Takazawa H. , Noguchi T. , Obara H. , Iida T. , Takanashi Y. 
Published: April 2011

ABSTRACTWe report the electrical resistivity and the Seebeck coefficient of AZn13(A = Sr, Ba, and La) and LaCo13measured over a wide temperature range and their thermal conductivity measured at room temperature. The electrical measurements of AZn13and LaCo13above room temperature reveal that the compounds show good metallic behavior. We find that the absolute value of Seebeck coefficient for AZn13(A = Sr, Ba, and La) increases with increasing temperature, which is a typical metallic behavior and the absolute value is less than 3μVK−1at room temperature. Accordingly, the power factor of AZn13is quite low. Temperature dependence of the Seebeck coefficient for LaCo13is similar to that of Co. The absolute value of the Seebeck coefficient for LaCo13is high as a metallic conductor and approaches -30μVK−1at 500K, which leads LaCo13to large power factor of 1.8 × 10−3Wm−1K−2. We obtained lattice components of the thermal conductivity by subtracting electronic contributions from the total thermal conductivity. The electronic components of the thermal conductivity were estimated using Wiedemann-Frantz law assumingL(Lorentz number) is 2.45 × 10−8V2K−2. The thermal conductivities of the lattice components for AZn13(A = Sr, Ba, and La) and LaCo13with NaZn13type structure are about 10 Wm−1K−1, respectively. These values are high as compared with other thermoelectric materials.
Crystallographic Features of Rhenium Disilicide
Authors: Tanaka K. , Inui H. , Ohba T. , Tsutsui S. , Mizumaki M. 
Published: April 2011

ABSTRACTCrystallographic features of Rhenium disilicide have been examined by powder and single-crystal X-ray diffractometry with a synchrotron radiation. The chemical composition of the compound is determined as Re4Si7 (ReSi2-x, x = 0.25) from lattice constants and specific density determined. The structure is defined as a vacancy ordered structure with the space group of Cm. The positions of the constituent atoms in the structure have been refined. The positions of silicon atoms apparently shift from the ideal positions of the C11b structure which is the structure without containing structural vacancies.
Hall Effect Measurements on New Thermoelectric Materials
Authors: Short Jarrod , Loo Sim , Lal Sangeeta , Hsu Kuei Fang , Quarez Eric , Kanatzidis Mercouri G. , Hogan Timothy P. 
Published: April 2011

ABSTRACTIn the field of thermoelectrics, the figure of merit of new materials is based on the electrical conductivity, thermoelectric power, and thermal conductivity of the sample, however additional insight is gained through knowledge of the carrier concentrations and mobility in the materials. The figure of merit is commonly related to the material properties through the B factor which is directly dependent on the mobility of the carriers as well as the effective mass.To gain additional insight on the new materials of interest for thermoelectric applications, a Hall Effect system has been developed for measuring the temperature dependent carrier concentrations and mobilities. In this paper, the measurement system will be described, and recent results for several new materials will be presented.
Effects of Sb-doping on electrical transport properties of Co-based half-Heusler compound
Authors: Ono Yasuhiro , Inayama Shingo , Adachi Hideaki , Yotsuhashi Satoshi , Miyazaki Yuzuru , Kajitani Tsuyoshi 
Published: April 2011

ABSTRACTElectrical transport properties of NbCoSn1−xSbx(x=0, 0.01, 0.02 and 0.05), a half-Heusler compound and its alloys, have been studied in the temperature range from 80 K to 850 K. As-prepared samples exhibit metallic conduction and similar Seebeck coefficients near 300 K (S= –100 μVK−1). Except for NbCoSn0.95Sn0.05, both electrical resistivity, ρ, and the absolute value ofSappreciably increase during the annealing for 6 days at 1123 K. Unusual increase in ρ of the annealed NbCoSn sample is found at about 200 K. ρ-T curves of the other annealed samples remain metallic over the measured temperature range and the ρ value noticeably decreases with increasing Sb content,x. Among the annealed samples, the high power factor, 25×10−4Wm−1K−2at 850 K, is obtained for NbCoSn0.95Sb0.05. The band structure of NbCoSn is calculated based on the determined crystal structure, indicating that NbCoSn is an indirect transition-type semiconductor with a band gap of approximately 1 eV. This is not consistent with the metallic behavior of ρ observed for the annealed NbCoSn sample above 400 K. Partial disordering of Nb and Co atoms is a conceivable answer.