bluuebunny/crossref_metadata_2025_split huggingface dataset:
Application of Transmission Line Theory for Modeling of a Thermoelectric Module in Multiple Configurations for AC Electrical Measurements
Authors: Downey Adam Darwin , Timm Edward , Poudeu Pierre F. P. , Kanatzidis Mercouri G. , Shock Harold , Hogan Timothy P. 
Published: April 2011

ABSTRACTMeasurements of assembled thermoelectric modules commonly include investigations of the module output power versus load resistance. Such measurements include non-ideal effects such as electrical and thermal contact resistances. Using an AC electrical measurement, two models for a thermoelectric module have been developed utilizing electrical circuits for both the thermal and electrical characteristics of the module.Measurements were taken over the frequency range of 1mHz to 500Hz using lock-in amplifiers. We present data showing the extraction of ZT from such measurements on commercially available modules utilizing both the magnitude and phase of the measured impedance. Here we extend upon a simple RC equivalent circuit model by utilizing transmission line theory in electrical circuits to explain the thermal activity in a thermoelectric module. This model includes all components of a module such as nickel traces and ceramic end caps, and makes use of their corresponding thermal conductivities, thermal capacitance, and density. This model can then be applied to pn unicouples in either a standard or inline configuration, and to individual p or n legs of the module. Data is presented showing the advantages of both models. Measurements on new thermoelectric materials and modules are also presented.
Thermoelectric Properties of Bi2SrCo2O9 Tellurium-Doped Single Crystalline Whiskers
Authors: Bourne Dwayne , Tang Xiaofeng , Aaron Kelvin , Barnes Julius , Payne James , Tritt Terry M. 
Published: April 2011

ABSTRACTLong single crystalline whiskers (10-200 µm diameter) were synthesized using tellurium-doped precursors. The length of these whiskers varies from less than 1 mm up to 9 mm. The thermopower and resistivity were approximately 150 µV/K and 5 mΩ-cm respectively at 325K. The thermopower was measured using a differential technique, while the resistivity was measured using a standard four-probe method. The thermal conductivity of these small samples was measured using our parallel thermal conductance technique. The total thermal conductivity was on the order of 2 Wm−1K−1.
Effect of Rare-Earth Cation Doping on Enhancement of The Thermoelectric Power of Zinc Oxide
Authors: Fuda Kiyoshi , Sugiyama Shigeaki 
Published: April 2011

ABSTRACTWe investigated the effects of doping of rare-earth ions (Ce, Pr, Nd, Sm, and Eu) on the thermoelectric properties of ZnO, especially Seebeck coefficient in the temperature range from 100 to 800 °C. The data were scattered more or less depending on the doping species, but it was commonly found that the rare-earth doped samples showed higher Seebeck coefficients with compared to those for Al-doped samples. The highest values were observed for Nd-doped one ranging from -360 to -400μVK−1 in the temperature range observed, the lowest ones for Pr-doped one ranging from -250 to -310 μVK−1, whereas those for Al-doped one ranging from -80 to -140 μVK−1. It should also be pointed out that the power factor at 100 °C for Pr-doped ZnO was twice or more as much as that for Al-doped one. From the results it seemed that rare earth doping is effective for enhancement of thermoelectric power of ZnO.
Thermoelectric Modules For High Temperature Waste Heat
Authors: Funahashi Ryoji , Mihara Toshiyuki , Mikami Masashi , Urata Saori 
Published: April 2011

ABSTRACTA new adhesive material has been developed in order to obtain practically usable thermoelectric modules composed of oxide thermoelectric legs. The thermoelectric module composed of 8-pair oxide legs has been fabricated. Both hot- and cold-sides of the module were covered by alumina plates. Open circuit voltage VO and maximum power Pmax reach 0.38 V and 0.30 W, respectively at 803 K of a hot-side temperature TH and 362 K of a temperature differential ΔT between TH and cold-side temperature TC. Generating power was repeated 11 times at 873-993 K of TH and at 200-290 K of ΔT. The module was cooled down to room temperature after each generation. At third measurement internal resistance RI of the module increased by 30 %. This is due to destruction of junctions because of thermal strain. No deterioration, however, was observed in thermoelectric properties for the oxide legs.
Mechanical Degradation of Carbon Nanotubes: ESR Investigations
Authors: Chipara Mircea , Kukovecz Akos , Konia Zoltan , Zaleski Jeffrey M. , Chipara Magdalena 
Published: April 2011

ABSTRACTESR investigations on milled multiwalled carbon nanotubes are reported. The ESR spectra of pristine and milled nanotubes consists of two resonances, a wide line located at g>3.0 assigned to magnetic particles (catalysts residues) and a broad line with a peak to peak linewidth of about 10−2 T located at g=2.05 and assigned to the interaction between the conducting electrons delocalized over carbon nanotubes and magnetic ions. It was observed that this line depends on the milling time. For short milling times (up to 125 minutes) both the resonance linewidth and the g-factor increase as the milling time is increased. Longer milling times resulted in a decrease of both the g-factor and resonance linewidth as the milling time was increased. This behavior was assigned to the removal of the magnetic nanoparticles from nanotubes. No resonance line due to the destruction of carbon nanotubes was observed.
Photo-oxidation of Single-walled Carbon Nanotubes
Authors: Parekh B , Debies Thomas , Evans Chris , Landi Brian , Raffaelle Ryne , Takacs Gerald 
Published: April 2011

ABSTRACTUV- and vacuum UV-assisted photo-oxidation of single-walled carbon nanotube (SWNT) paper occurred with: (1) atmospheric oxygen pressure using low-pressure Hg lamps (λ = 253.7 and 184.9 nm), (2) low oxygen pressure employing emission downstream from an Ar microwave plasma (λ = 106.7 and 104.8 nm), and (3) high pressures of He in a rotating d.c. arc that was designed to produce a spectral continuum from He excimers (λ = 58 - 110 nm). The photo-oxidized materials were characterized by x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and Raman spectroscopy. UV photo-oxidation was demonstrated to be a controlled dry procedure for introducing oxygenated functional groups (C-O-C, C=O, O-C=O and O=C-O-C=O) on SWNTs.
Fire Retardancy and Morphology of Nylon 6-Clay Nanocomposite Compositions
Authors: Shanmuganathan Kadhiravan , Razdan Sandeep , Dembsey Nick , Fan Quinguo , Kim Yong K , Calvert Paul D , Warner Steven B , Patra Prabir 
Published: April 2011

ABSTRACTWe investigated the effect of organically modified clay on the thermal and flammability behavior of nylon 6 nanocomposites. We also used zinc borate along with layered silicate with an aim of achieving synergistic effect in flame retardancy. It is found that addition of 10 wt% clay reduced the onset decomposition (5% wt loss) temperature of nylon 6 by 20°C, while addition of 5 wt% zinc borate and 5 wt% clay in combination reduced it by around 10°C. Differential thermogravimetric analysis indicated that the peak decomposition temperature was not affected by the addition of clay, but the rate of weight loss decreased with increasing clay concentration. The horizontal burning behavior of the nanocomposite films of approximately 0.5mm thickness changed with additive concentration. The nanocomposites with 2.5 wt% and 5 wt% clay burned for almost the same duration as neat nylon 6 but dripping was reduced. The 10 wt% clay nanocomposite sample burned without any dripping and the flame spread rate was reduced by 25-30%. The burn rate of 5 wt % zinc borate/5 wt% clay nanocomposite sample was about 20% higher than that of 10 wt% clay nanocomposite sample, which could be attributed to varying char morphology. Scanning electron microscopy images of the 10wt% clay nanocomposite char surface and cross- section revealed an integrated layer of clay platelets with increasing density gradient from the center to the surface, while the 5 wt% zinc borate/5 wt% clay nanocomposite char appeared foamy and porous. The 5 wt% zinc borate and 5 wt% clay sample developed into a very good intumescent system in cone calorimeter test, swelling about 10-13mm height prior to ignition forming a cellular char structure. This was as effective as the 10wt% clay nanocomposite sample in reducing the heat release and mass loss rate of nylon 6 by around 65%. Fourier transform infrared spectroscopy of the 10 wt% clay nanocomposite char showed the presence of amides, indicating possible residual polymer within the shielded char.
Effects of ion-beam irradiation on the L10 phase transformation and their magnetic properties of FePt and PtMn films (Invited)
Authors: Lai Chih-Haung , Huang Sheng-Huang , Yang Cheng-Han , Chiang C.C. , Liou S. H. , Sellmyer D. J. , Yan M. L. , Yuan L. , Yokata T. 
Published: April 2011

ABSTRACTIon-beam irradiation shows enhancement or degradation of magnetic properties on L10 phase of FePt and PtMn films. A highly ordered L10 FePt phase was directly achieved by using 2 MeV He-ion irradiation without conventional postannealing. The in-plane coercivity greater than 5700 Oe can be obtained after disordered FePt films were irradiated at the beam current of several μA/cm2 with the ion does of 2.4×1016 ions/cm2. The high beam-current-density results in direct beam heating on samples. In addition, the irradiation-induced heating process provides efficient microscopic energy transfer and creates excess point defects, which significantly enhances the diffusion and promotes the formation of the ordered phase. Consequently, the direct ordering of FePt took place by using ion-irradiation heating at temperature as low as 230°C. The comparison has been made on the [Fe/Pt]10/C films by RTA and high current-density He irradiation. Although RTA and ion irradiation both reach high coercivity, ion irradiation seems to suppress the (001) texture, leading to isotropic Hc. Ion-beam irradiation can also be applied to the transformation of PtMn. An ordered PtMn phase, a large exchange field and a high GMR ratio (11%) were obtained in PtMn-based spin valves by using 1.25 μA/cm2 He-ions. On the other hand, Ge-ion and O-ion irradiation completely destroyed the ferromagnetism of FePt and GMR of PtMn-based spin valves, respectively. We propose a novel approach to achieve magnetic patterning by using ion irradiation, which can be applied for patterned media and magnetic sensors.
Large magnetoresistance in oxide based ferromagnet / superconductor spin switches
Authors: Peña V. , Nemes N. , Visani C. , Garcia-Barriocanal J. , Bruno F. , Arias D. , Sefrioui Z. , Leon C. , Te Velthuis S. G. E. , Hoffmann A. , Garcia-Hernandez M. , Santamaría Jacobo 
Published: April 2011

ABSTRACTWe report large magnetoresistance (in excess of 1000%) in ferromagnet / superconductor / ferromagnet structures made of La0.7Ca0.3MnO3 and YBa2Cu3O7 in the current in plane (CIP) geometry. This magnetoresistance has many of the ingredients of the giant magnetoresistance of metallic superlattices: it is independent on the angle between current and magnetic field, depends on the relative orientation of the magnetization in the ferromagnetic layers, and takes very large values. The origin is enhanced scattering at the F/S interface in the anti parallel configuration of the magnetizations. Furthermore, we examine the dependence of the magnetoresistance effect on the thickness of the superconducting layer, and show that the magnetoresistance dies out for thickness in excess of 30 nm, setting a length scale for the diffusion of spin polarized quasiparticles.
Diamond/Carbide Nano-Composite Gradient Films: a Route to solve the Adhesion Issues of Diamond Films
Authors: Staedler Thorsten , Vadali Srikanth , Jiang Xin 
Published: April 2011

ABSTRACTDue to their outstanding mechanical properties diamond films are ideal candidates for many cutting and machining applications. However, industrial applications of these films are limited due to poor adhesion. Two main reasons causing this poor adhesion, which are based on the extrinsic physical and chemical properties of diamond, can be identified: High mechanical stresses induced by a difference of the thermal expansion coefficient between the diamond film and the substrate as well as a catalytic effect in case of metallic substrates containing iron-, cobalt- and nickel that, in combination with a methane atmosphere during deposition, leads to soot formation. One option to overcome these difficulties is to provide an interfacial layer that acts as adhesion layer as well as barrier layer to prevent the catalytic effect of the substrate elements. Even though some successful examples exist, this approach usually requires a time consuming and expensive multi-step process.In this paper, the synthesis of nanocrystalline diamond/carbide composite films with a compositional gradient will be reported. Focusing on the example of diamond/ß-SiC the possibility to create a gradient layer ranging from ß-SiC to diamond in a controlled manner will be shown. The films are prepared by a Microwave Assisted Plasma Chemical Vapour Deposition process (MWCVD) using H2, CH4 and Tetramethylsilane (TMS) as reactive gases. The structure, grain sizes, and volume fractions of the components of these composite films, which consist of a mixture of diamond and carbide phase, can be controlled by adjusting the concentrations of the reactive gases in the gas mixture. This strategy, which handles all depositions in one process step, should allow for an improved diamond film adhesion on tools. The preparation and characterization of the composite films with special emphasize on their mechanical and tribological properties will be discussed and a short outlook on other diamond/carbide systems will be given.
The Effect of Surface Interactions on the Viscosity of Polymer Thin Films
Authors: Li Chunhua , Jiang Jun , Rafailovich Miriam J. , Sokolov Jonathan C. 
Published: April 2011

ABSTRACTPreviously, we reported that the viscosity of a polymer film can be measured in situ by observing the liquid-liquid dewetting of polymer bilayer films. In this study, we use the technique to investigate the effect of film thickness and surface interactions on the effective viscosity of polymer thin films. We found that the effective viscosity increases dramatically with decreasing the film thickness. We attribute this to the pinning of the polymer chains at the strongly interacting polymer/Silicon interface.
Thermal stability of Cr1−xAlxSiyN coatings with medium and high aluminium content prepared by arc evaporation
Authors: Karvankova Pavla , Karimi Ayat , Coddet Olivier , Cselle Tibor , Morstein Marcus 
Published: April 2011

ABSTRACTThe thermal stability of Cr1−xAlxN and Cr1−xAlxSiyN nanocomposite coatings with different composition x, Si content, and phase structure has been investigated. The coatings were deposited in an industrial unit by the cathodic arc evaporation method, using rotating cylindrical cathodes. Further sets of coated WC/Co plates were subjected to an annealing step in a forming gas (92% N2 / 8% H2) atmosphere for several hours at a constant temperature (maximum 1000°C). Chemical composition, microstructure and mechanical properties of the coatings were investigated by the RBS, XRD, TEM, SEM, XPS and nanoindentation techniques.As-deposited Cr1−xAlxSiyN coatings with Al contents x in the range of 0.4 ≤ x ≤ 0.6 showed a single-phase cubic CrAlN structure and a maximum hardness of 38 GPa. With increasing the Al content to x = 0.95 – 0.96, two-phase films consisting of hexagonal AlN and cubic CrAlN structure with hardness of about 31 GPa were obtained. The hardness of Cr1−xAlxSiyN coatings increases during annealing at temperatures in the range of 800 – 1000°C by about 1 – 4 GPa, even though the residual compressive stress in the coatings was found to relax considerably during this procedure. The addition of Si into Cr1−xAlxN delays the appearance of hcp-AlN and thereby improves the thermal stability of the coatings.
A theoretical approach to the energetic stability and geometry of hydrogen and oxygen terminated diamond (100) surfaces
Authors: Petrini Daniel , Larsson Karin 
Published: April 2011

ABSTRACTThe thermodynamic stability of diamond (100) surfaces as a function of degree of hydrogen and oxygen-related termination coverage has been theoretically studied using DFT techniques. The results show that an exchange of the hydrogen atoms with hydroxyl groups is disfavored, whereas a corresponding exchange with oxygen atoms (in the ketone or ether position) is energetically preferred. The adsorption of up to about 50 % oxygen coverage (ether position) is, however, largely disfavored compared to a fully hydrogen-terminated surface. However, this oxygen termination will be energetically improved as the coverage increases above the 50 % level. The adsorption energy per terminating species (at 100% surface coverage) is −4.13 eV, −4.30 eV, −5.95 eV and 6.21 eV for H, OH, O(ketone) and O(ether) species, respectively.
Interdiffused InGaAsP Quantum Dots Lasers on GaAs by Metal Organic Chemical Vapor Deposition
Authors: Arif Ronald A. , Kim Nam-Heon , Mawst Luke J. , Tansu Nelson 
Published: April 2011

ABSTRACTSelf-assembled InGaAs quantum dots (QD) grown by metal organic chemical vapor deposition (MOCVD) have a natural peak emission wavelength around 1150-1200-nm due to its specific composition, shapes, and sizes. In this work, a new method to engineer the emission wavelength capability of MOCVD-grown InGaAs QD on GaAs to ∼1000-nm by utilizing interdiffused InGaAsP QD has been demonstrated. Incorporation of phosphorus species from the GaAsP barriers into the MOCVD-grown self-assembled InGaAs QD is achieved by interdiffusion process. Reasonably low threshold characteristics of ∼ 200-280 A/cm2 have been obtained for interdiffused InGaAsP QD lasers emitting at 1040-nm, which corresponds to blue-shift of ∼ 85-90-nm in comparison to that of unannealed InGaAs QD laser.
Cathodoluminescence study of orientation patterned GaAs films for non linear optics
Authors: Avella Manuel , Jiménez Juan , Bliss David , Lynch Candance , Weyburne David 
Published: April 2011

ABSTRACTZincblende semiconductor materials such as GaAs and ZnSe are very promising for the generation of tunable IR signals by quasi phase-matched nonlinear optical frequency conversion. Orientation patterned GaAs crystals (OP-GaAs) were grown by low-pressure hydride vapor phase epitaxy (HVPE) on lithographically prepared templates.. Cathodoluminescence (CL) imaging was used to study these epitaxial films, which consist of periodic domains of inverted crystallographic orientation. The challenge is to achieve thick, vertical domains and to minimize sources of optical loss. Both the domain walls and crystal defects may contribute to transmission losses, therefore, a characterization of both is necessary to improve the OP-GaAs crystal performance. The stress and non radiative recombination activity of the domain walls were investigated. The presence of dislocation glide was revealed and CL spectral imaging was used to observe the stress distribution around both the domain walls and the dislocations.
Thin Multiwall Carbon Nanotube Field Emitters with Microchannel Plate for High Current Emission
Authors: Seelaboyina Raghunandan , Huang Jun , Choi Won Bong 
Published: April 2011

ABSTRACTWe report a method to amplify the electron current of carbon nanotube field emitter cathode using an electron multiplier and synthesis of thin multiwall carbon nanotubes by thermal chemical vapor deposition. A commercial microchannel plate which is an array of microscopic electron multipliers was used for this purpose. A microchannel plate placed between the cathode and anode amplified the current and also acted as protection shield for nanotubes during vacuum arcing. The turn-on field was approximately 1 V/µm for both cases, but current obtained was 3 times higher and the field was also lower. The increase in current is attributed to the electron multiplication, and to the increase in field enhancement factor from 9296 to 12815 (37%) with microchannel plate. The thin multiwall carbon nanotubes were synthesized using Mo/Fe catalyst solution. The inner and outer wall diameters of the nanotubes were in the range of 2.5-5 nm and 7-15 nm respectively, determined by Raman spectroscopy and transmission electron microscopy. The nanotubes had excellent field emission property which is attributed to their thin wall diameters ∼10 nm, high aspect ratio of 1500 and the high field enhancement factor of 9296. The emission current was stable with an average fluctuation of 2%.
Silicon Thin Film Growth by Pulsed Plasma CVD under Near-Atmospheric Pressure
Authors: Kitabatake Hirotatsu , Suemitsu Maki , Nakajima Setsuo , Uehara Tsuyoshi , Toyoshima Yasutake 
Published: April 2011

ABSTRACTSi Plasma-enhanced chemical vapor deposition (PECVD) at a near-atmospheric pressure (NAP) of 500 Torr has been conducted by using a pulsed-electric-field based NAP-PECVD system. At a growth temperature of 180°C, poly-Si films with a high Raman ratio of 7.4 are obtained on glass substrates, while epitaxial-like growth occurs when Si(100) substrates are employed, as confirmed by Raman-scattering spectroscopy, X-ray diffraction, and a cross-sectional transmission-electron microscopy.
Growth of high quality Ge epitaxial layer on Si(100) substrate using ultra thin Si0.5Ge0.5 buffer
Authors: Nakatsuru Junko , Date Hiroki , Mashiro Supika , Ikemoto Manabu 
Published: April 2011

ABSTRACTMethods for forming Ge epitaxial layer on Si (100) substrate have been vigorously sought due to potential applications of such structure as a virtual substrate for III-V devices on Si. Various methods were proposed to realize low threading dislocation density and smooth surface. To date, such methods involve more than one of thick (micrometer order) SiGe buffer growth process, high temperature annealing steps and CMP process, which could compromise reliability and suitability for production.In this study, we report feasibility of a thin (in the order of 10nm) SiGe buffer layer to realize pure Ge epitaxial layer with good crystalinity, low threading dislocation density, and smooth surface without high temperature annealing steps and CMP process.As a result, we achieved shorter time for growth of practical thickness of crystalline Ge on Si (100) substrate, and also get the high quality Ge epitaxial layer which has low threading dislocation density with very smooth surface.Ge epitaxial layer and underlying thin SixGe1−x buffer layer were grown on Si (100) substrate using a cold wall UHV-CVD system. Source gases of Si and Ge were Si2H6 and GeH4, respectively. No carrier gas was used for this process. SiGe buffer layer was grown on Si(100) substrate at 450 – 520˚C. Two-step growth process was employed to grow Ge epitaxial layer on the buffer layer. Ge seed layer was grown at a low temperature (350–400˚C), followed by Ge thick layer growth at a high temperature (550–650˚C). XRD, TEM, EPD, and AFM were used for characterization of Ge epitaxial layer.Optimization of growth temperature and source gas flow rate ratio enabled to obtain an effective buffer layer thinner than 10nm. The thin buffer layer realizes process time shortening, which is within 10min, and the smooth surface is realized without crosshatch structure. The buffer thickness is 1/160 to 1/1000 than that of previously known methods using thick SiGe buffer layers. Thin SiGe buffer also enabled process time shortening for Ge seed layer growth as two-dimensional Ge layer was formed faster on the thin SiGe buffer layer than on Si. XRD of the Ge seed layer showed 97% relaxation as grown and fully relaxed at 550˚C. The threading dislocation density of the top Ge layer was estimated below 1E7counts/cm2 by TEM and EPD.The misfit dislocations oriented along [110] at the interface between the SiGe buffer layer and the Ge layer and the distances are 9.5nm constantly in cross-sectional TEM image. We are checking the surface roughness of the Ge epitaxial layer by using AFM.