bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermoelectric Properties of Ag-Tl-Te Ternary System
Authors: Kurosaki Ken , Kosuga Atsuko , Goto Keita , Muta Hiroaki , Yamanaka Shinsuke 
Published: April 2011

ABSTRACTWe have studied the thermoelectric properties of thallium compounds as novel thermoelectric materials. Especially, we focus on the Ag-Tl-Te ternary system, in which we found that Ag9TlTe5 exhibits an excellent thermoelectric figure of merit (ZT= 1.23) because of its extremely low thermal conductivity (around 0.22 Wm−1K−1). In this paper, we studied the thermal conductivity of four kinds of ternary silver thallium tellurides: AgTl3Te2, AgTlTe, Ag8Tl2Te5 and Ag9TlTe5, for which we found room temperature values of 0.39, 0.26, 0.14 and 0.21 Wm−1K−1, respectively. In order to understand the extremely low thermal conductivity, we performed an ultrasonic pulse echo measurement and evaluated some thermophysical properties.
Experimental and theoretical studies of plasma resonance and the electronic structure of binary skutterudites
Authors: Prytz Øystein , Løvvik Ole M. , Taftø Johan 
Published: April 2011

ABSTRACTWe determine the plasmon energies of the skutterudites CoP3, CoAs3 and CoSb3 by electron energy loss spectroscopy, and compare with calculated values from the Drude model and density functional theory (DFT). For these compounds, whose doped versions have potential applications as thermoelectric materials, there is a relatively large discrepancy between experiment and theory based on the Drude model as well as the DFT-calculations. We also study the transitions from occupied to unoccupied states near the Fermi-level that show up at energies lower than the plasmon energies. The features observed are in general agreement with the DFT-calculations.
Incomplete Crystallization of Skutterudites
Authors: Smalley Arwyn L. E. , Johnson David C. 
Published: April 2011

ABSTRACTA series of CexCo4Sb12 samples were synthesized, with x = 0 to 2. The crystallinity of the samples was studied using quantitative Rietveld analysis, and revealed that the samples did not crystallize completely. These data correlated with changes in the lattice parameter, DSC peak temperature, and DSC peak area. The crystallinity was confirmed using electron back-scatter diffraction (EBSD), which showed crystallites with a background of an amorphous matrix. This unusual morphology may improve thermoelectric properties by decreasing thermal conductivity.
Growth and Characterization of Germanium-based type I Clathrate Thin Films Deposited by Pulsed Laser Ablation
Authors: Witanachchi Sarath , Hyde R. , Nagaraja H. S. , Beekman M. , Nolas G. S. , Mukherjee P. 
Published: April 2011

ABSTRACTThin films of clathrate material have been grown using the laser ablation technique on a variety of substrates. Films deposited on silicon substrates exhibited a significant deficiency of Ga and Ge while the stoichiometry was preserved in films deposited on quartz, sapphire, and glass substrates. Ablation characteristics of the clathrate target for laser radiation at three different wavelengths in the UV, visible and IR were studied. The UV and IR laser wavelengths produce low ablation thresholds and high growth rates. Crystalline films were obtained above a growth temperature of 400°C. Conductivity measurements on the films at low current injection (<40 µA) showed semiconducting behavior. At high currents the films demonstrated a semiconductor-to-metal transition for temperatures lower than 150 K.
Cross-plane Thermoreflectance Imaging of Thermoelectric Elements
Authors: Mayer Peter M. , Ram Rajeev J. 
Published: April 2011

ABSTRACTThis paper presents the first cross-plane thermoreflectance image of the temperature distribution in a thermoelectric (TE) element under bias. Using the technique of lock-in CCD thermoreflectance imaging, we can map the temperature distribution of an operational device with submicron spatial resolution and a temperature resolution of 10 mK. As such it offers a complete picture of the quasi-equilibrium transport within the device. The submicron resolution of the thermoreflectance image enables clear determination of localized heating due at interfaces - for example to due contact resistance - and thermal impedance mismatch within samples. The high spatial resolution is ideal for the characterization of thin-film thermoelectric materials where data from conventional techniques (such as the transient Harman method) are difficult to interpret. This paper also presents the first thermoreflectance data we are aware of for BiTe-based material systems. Identification and separation of the Peltier and Joule components of the heating are possible, and finite difference simulations of the devices are presented for comparison with experiment. In this way it is possible to simultaneously acquire information about the Seebeck coefficient, electrical conductivity, and thermal conductivity of the thermoelectric material. The measurements demonstrate the feasibility of non-contact thermal measurements at the sub-micron scale.
Thermoelectric properties of Mg2Si1−xCx crystals grown by the vertical Bridgman method
Authors: Sakuma Takashi , Higuchi Yoshinori , Akasaka Masayasu , Iida Tsutomu , Takanashi Yoshifumu 
Published: April 2011

ABSTRACTMulticrystalline Mg2Si crystals were grown using a Brigdman method combined with a die-casting growth technique. Although molten and/or vapor-phase Mg at elevated growth temperatures exhibit high chemical reactivity with the surrounding crucible materials, the use of an alumina crucible with a BN coating allowed single phase crystal growth and Mg2Si of good crystalline quality. Incorporation of carbon into the Mg2Si was observed to form Mg2Si1−xCx. For x=0.01 and 0.03, a lower thermal conductivity and higher figure of merit than those of Mg2Si were observed in the temperature range from room temperature to 773 K. The maximum figure of merit was 0.62 at 773 K for a Mg2Si0.99C0.01 sample.
High Efficiency Thermoelectric Power Conversion
Authors: Byrnes Donald F. , Heshmatpour Ben 
Published: April 2011

ABSTRACTRecent efforts at Teledyne Energy Systems, Inc. have lead to significant improvements in thermoelectric (TE) materials and power conversion devices. A number of improved formulations have been identified for standard n-type PbTe and p-type TAGS alloys. The preliminary test results appear to show nearly a 50% increase in the dimensionless figure-of-merit, ZT, for these two alloys. The new TE material formulations also exhibit a lower sublimation rate which is likely to allow use of these materials at higher heat source temperatures and thus result in higher Carnot efficiencies. The combination of higher ZT and higher Carnot efficiency allows achievement of exceptionally high thermoelectric conversion efficiencies through small changes to proven technology. For example, a thermoelectric conversion device which uses segmented BiTe/modified PbTe/modified TAGS thermoelectric couple design and operates between 300 °K and 900 °K will have a conversion efficiency of approximately 16.2%. Effort is continuing to confirm the preliminary test results and validate the materials fabrication processes. A number of improvements have also been made in the TE device fabrication processes and assembly techniques which have reduced the internal thermal and electrical losses, increased conversion efficiency, enhanced reliability and reduced manufacturing cost for the thermoelectric devices.
Raman and Electron Spin Resonance Investigations of as Prepared and Thermal Annealed Cluster Beam Deposited Carbon Thin Films
Authors: Compagnini Giuseppe , Puglisi Orazio , Chipara Mircea 
Published: April 2011

ABSTRACTNanostructured amorphous carbon thin films deposited by a Low Energy Carbon Cluster Beam Deposition technique have been characterized by Raman spectroscopy and Electron Spin Resonance (ESR). This study focuses on the correlation between carbon cluster structure and sp2 related defects. The ESR spectrum of as prepared and thermally annealed carbon clusters is a single line located near the free electron g-factor. Resonance lines were accurately fitted by a single line symmetric and narrow Lorentzian line. The resonance line parameters (line position, line amplitude, and line width) were found to be extremely sensitive to the thermal treatment of the as deposited samples. The paramagnetic centres are randomly distributed and correlated with the nanosized nature of the investigated system. The absence of the resonance line asymmetry, typical for the ESR spectra of conducting carbaceneous materials, confirms the small size of carbon nanoclusters and indicates poor electrical contacts between them. The resonance line parameters (position, intensity, and width) are not affected by the orientation of the carbon cluster film relative to the direction of the external magnetic field. The evolution of the ESR signal upon thermal treatments is sensitive to the increase of the sp2 average domain size as revealed by Raman spectroscopy. The Raman spectrum of as obtained and thermally annealed carbon clusters, in the domain 1000 cm−1 to 2000 cm−1 shows two Lorentzian lines located at 1300 cm−1 and 1550 cm−1 representing the D and G bands. The position and amplitude of these lines were found to be affected by thermal annealing.
Effect of Nanoparticles on the Thermal Stability of Polymers
Authors: González-Irun Juan , Garcia Ana , Artiaga Ramón , Liz-Marzán Luís , Hui David , Chipara Mircea 
Published: April 2011

ABSTRACTThe thermal stability of polymethylmethacrylate loaded with silica nnaoparticles is investigated. The temperature dependence of the mass has been accurately fitted with a single Boltzmann-like dependence. The effect of surface functionalization, size of silica nanoparticles, and concentration of silica nanoparticles is analyzed. A weak increase of the thermal stability of polymethylmethacrylate has been obtained by loading the polymer matrix with nanoparticles. Surface functionalization produced a modest increase in the thermal stability (compared to composites with silica nanoparticles without surface modification).
Investigations of dc electrical properties in electron-beam modified carbon nanotube films: single- and multiwalled
Authors: Gupta Sanju , Smith N. D. , Patel R. J. , Giedd R. E. 
Published: April 2011

ABSTRACTCarbon nanotubes (CNTs) in the family of nanostructured carbon materials are of great interest because of several unique physical properties. For space applications, it needs to be shown that CNTs are physically stable and structurally unaltered when subjected to irradiation becomes indispensable. The CNT films were grown by microwave Carbon nanotubes (CNTs) in the family of nanostructured carbon materials are of great interest because of several unique physical properties. For space applications, it needs to be shown that CNTs are physically stable and structurally unaltered when subjected to irradiation becomes indispensable. The CNT films were grown by microwave plasma-assisted chemical vapor deposition (MWCVD) technique using Fe as catalyst. Synthesis of both single- and multiwalled CNTs (SW and MW, respectively) were achieved by varying the thickness of the Fe catalyst layer. To investigate the influence of electron-beam irradiation, CNTs were subjected to low and/or medium energy electron-beam irradiation continuously for a few minutes to several hours. The CNT films prior to and post-irradiation were assessed in terms of their microscopic structure and physical properties to establish property-structure correlations. The characterization tools used to establish such correlations include scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), Raman spectroscopy (RS), and current versus voltage (I-V) measuring contact resistance (two-probe) and dc conductivity (four-probe) properties. Dramatic improvement in the I-V properties for single-walled (from semiconducting to quasi-metallic) and relatively small but systematic behavior for multi-walled (from metallic to more metallic) with increasing irradiation hours is discussed in terms of critical role of defects. Alternatively, contact resistance of single-walled nanotubes decreased by two orders of magnitude on prolonged E-beam exposures. Moreover, these findings provided onset of saturation and damage/degradation in terms of both the electron beam energy and exposure times. Furthermore, these studies apparently brought out a contrasting comparison between mixed semiconducting/metallic (single-walled) and metallic (multiwalled) nanotubes in terms of their structural modifications due to electron-beam irradiation.
Degradation of Assembled Silicon Nanostructured Thin Films: a Theoretical and Experimental Study
Authors: Bertani Valeria , D'Urso Luisa , Scalisi Alfio Alessandro , Compagnini Giuseppe , Puglisi Orazio 
Published: April 2011

ABSTRACTThe study of the structures and properties of small elemental clusters has been an extremely active area of current research, due to the peculiar behavior of these species halfway between that of single atoms and of the bulk phase. In this work silicon nanoclusters are generated by ablation of a high purity polycrystalline rod with a pulsed laser vaporization source and then deposited on a support. Their structure is studied both in the gas phase by means of Time of Flight Mass Spectrometry and in the solid phase through in situ Raman and Infrared Spectroscopy. The spectra reveal that the as deposited clusters are hydrogenated with negligible amount of oxide. Degradation of silicon nanoclusters has been studied after gas exposure. In the gas of air a consistent modification was observed, leading to a near-infrared luminescent silicon nanoparticles. In the second part of the work, density functional theory is applied to investigate the geometrical structure of silicon clusters and their interaction, in term of structure and energy, with different gases. The calculations were performed with the Gaussian 03 program suite, adopting the B3LYP functional to calculate the exchange and correlation energy. Si8 has been chosen as model cluster to study the degradation of silicon clusters both kinetically and thermodynamically, in order to explain the experimental evidences. Experimental and calculated infrared spectra are compared.
Sintering of HAp precipitated from solutions containing ammonium nitrate and PVA
Authors: Safronova Tatiana Victorovna , Putlyaev Valery I. , Belyakov Alexey V. , Shekhirev Mikhail A. 
Published: April 2011

ABSTRACTBioceramics based on hydroxyapatite (HAp) is known to be a prospective material for biomedical applications. However, sintering of HAp is still understudied in sense of reasonable selection of controlling parameters. In particular, the role of impurities and co-products of powder fabrication is still questionable. The data concerning the role of ammonium nitrate coming to precipitated HAp from the mother liquor, its effect on powder compaction and subsequent sintering, are not available.Nanosized powders of HAp were fabricated via conventional wet-precipitation technique by dropwise adding of Ca(NO3)2 solution (0.25 -1.67 M) to the stock solution of (NH4)2HPO4 (0.15-1.00 M) with pre-adjusted pH at 60°C in presence of polyvinyl alcohol (PVA). PVA was added to the stock solution in order (i) to block crystal growth during synthesis , (ii) to improve stability of Hap suspension to sedimentation, (iii) to regulate an aggregation of HA nanoparticles during synthesis and in the stage of drying.NH4NO3 – a by-product of the precipitation reaction, presented in as-precipitated powder in amount of 30%, was evaluated as an additive affecting a compaction of the powder and the initial stage of a sintering. The powder samples were tested by XRD, FTIR, light-scattering , TEM and SEM/EDX to get particle sizes, morphology and chemical composition, dilatometry. Ceramics were sintered at 700-1250°C and evaluated with SEM/EDX and density measurements.Addition of PVA to the stock solution in the course of HAp precipitation is a promising technique to control an aggregation of HAp nanoparticles in the stages of drying and sintering. PVA acting as a surfactant in the solution and as a binder in dry powder can keep highly reactive small HAp particles within large agglomerates providing better molding of the powder and controllable densification of ceramics. The effect of PVA on microstructure of the HAp powder and their sintering behaviour is discussed in terms of self-organisation concept and synergetics.
Fast and Slow Magnetization Processes in Magnetic Recording Media
Authors: Zhou J. , Skomski R. , Michalski S. , Kirby R. D. , Sellmyer D. J. 
Published: April 2011

ABSTRACTInformation loss due to thermal activation is a major concern in ultrahigh-density magnetic recording media. The usually considered mechanism is thermally activated magnetization reversal over micromagnetic energy barriers. However, micromagnetic approaches ignore local anisotropy fluctuations, which translate into a time-dependent reduction of the remanent magnetization. The effect is negligibly small in macroscopic magnets but becomes important on a scale of a few nanometers.
Size Control and Spectroscopic Characterization of Monolayer Protected Gold Nanoparticles Obtained by Laser Ablation in Liquids
Authors: Compagnini Giuseppe , Scalisi Alfio Alessandro , Puglisi Orazio 
Published: April 2011

ABSTRACTIn this paper we present a study on the formation of gold colloids by laser ablation of a gold metal target in alkanes and thiol-alkane solutions. The results show a decrease of the gold particles' size up to 2 nm when thiol molecules are present in the liquid environment. In summary, we observed that laser ablation of gold targets in thiol-alkane solutions leads to the formation of stable gold clusters with size smaller than those obtained in the corresponding pure alkane. This result is a consequence of the competition between the aggregation of gold species in the plume (which allows a gold embryo to be formed and to grow) and the tendency of the dispersed thiol molecules to bond at each embryo surface stopping their growth.
Degradation of Copper-Silver Alloy Thin Films Induced by Annealing
Authors: Snyder S. T. , King Alex 
Published: April 2011

ABSTRACTCopper / silver alloy thin films form with a fine, polycrystalline, metastable crystal structure. The expected effects of annealing include grain growth, transformation into the two stable phases, coarsening of the phases, texture formation, and the formation and growth of pinholes or voids. Copper/silver alloy films were deposited on single crystal sodium chloride substrates, via pulsed laser deposition ablation of an alloy target, of the eutectic composition. Free-standing films of 20-30 nm thickness were studied as-deposited and after annealing on copper TEM grids at 100°C for various times. Although several of the expected degradation processes involve short-range diffusion – essentially single atomic jumps – these were not observed, while other, longer-range diffusion effects were clearly identifiable. In particular, void shrinkage was observed in the films at short times, and void growth occurred at longer times.
Effect of Deposition Parameters on the Microstructure and Growth Rate of CVD Mullite Environmental Barrier Coatings
Authors: Basu Soumendra , Kulkarni Tushar , Sarin Vinod 
Published: April 2011

ABSTRACTSi-based ceramics such as SiC require environmental barrier coatings to protect against hot-corrosion and recession in gas turbine applications. Dense, crystalline mullite coatings of uniform thickness have been deposited by hot-wall chemical vapor deposition (CVD) on SiC substrates, using the AlCl3-SiCl4-CO2-H2 system. The effects of the CVD deposition parameters such as temperature, total reactor pressure, and metal-chloride partial pressure on the coating microstructure and growth kinetics have been investigated, and are discussed in this paper.
Scaled Up Pulsed Deposition Technology: Carburization Resistant Ablation Coatings for Ethylene Pyrolysis Coils
Authors: Chauhan Alok , Anwar Mir , Montero Kelvin , White Henry J , Si Weidong , Bai Jianming 
Published: April 2011

ABSTRACTProducts derived from ethylene have and will continue to replace metallic materials traditionally used for transportation, building materials, and products we use in our everyday lives. As the demand continues to increase, a more suitable material for the outlet coils of ethylene pyrolysis heaters will have to be identified. In this study, we discuss utilization of scaled up pulsed deposition technology to deposit adherent carburization resistant coatings on the inner diameter of ethylene pyrolysis tubing with the intent of extending tube life. Ablation target material selection was based primarily on elevated temperature properties and the ability of the coating to prevent transformation of the inherent protective chromium oxide surface film to metal carbides while in service. The near optimal settings of the processing parameters for pulsed laser deposition of ceramic SiC on heat resistant tubing traditionally used for ethylene service were investigated using a semi quantitative controlled random search methodology. Minimization of the objective function which was based on width, thickness and coverage of the thin film resulted in an optimal deposition time of 4.3 minutes and surface finish of 272 nm.
Laser-induced patterning of Co nanostructures under ambient conditions
Authors: Favazza C. , Trice Justin , Krishna Hare , Kalyanaraman Ramki 
Published: April 2011

ABSTRACTIncreasing the efficiency and the relative ease of creating ordered nanostructures is essential to the advancement of nanotechnology. The practical benefits from ambient processing of nanostructures, like reduced complexity and increased efficiency, makes it an important avenue for investigation as nanomanufacturing processes. We have recently shown that pulsed laser melting of ultrathin metal films in vacuum leads to nanostructure ordering presumably due to metal dewetting. Here we show that UV pulsed laser irradiation (10 ns pulse width) of ultrathin Co films on SiO2 substrates under ambient conditions with a two-beam laser interference pattern generates Co nanoparticles with both long- and short-range order (LRO and SRO) and are qualitatively comparable to those created in vacuum. Furthermore, preferential etching of the metal shows that there is minimal interaction of the Co with the substrate. These results show that the presence of oxygen in the ambient does not substantially influence the resulting nanostructure formation. Therefore, ns pulsed laser processing under ambient conditions may be a practical way to realize ordered metal nanostructures.
Analysis and comparison of semiconductor materials processed at IR vs. UV laser wavelengths for DRAM yield enhancement applications
Authors: Hooper Andy E. , Kawasaki Allen , Kirby Paul , Hainsey Robert , Bang Jeongho , Shin Kyeongseon , Kang Ki Sang , Lee Kungu 
Published: April 2011

ABSTRACTThis report demonstrates the effects of IR and UV laser energy on common semiconductor layer stack materials used for DRAM laser fuses. By moving from IR to UV wavelengths it is possible to significantly shrink the laser spot diameter from ∼1.6 μm to 0.8 μm. Effects and concerns for the absorption of UV energy by Si, SiO2, nitrides, and oxynitrides are also presented.
Hydrogen Radical Etching Effect on Carbon Nanotube Growth
Authors: Nagayoshi Hiroshi , Sato Hiroaki , Nishimura Suzuka , Terashima Kazutaka 
Published: April 2011

ABSTRACTThe hydrogen microwave remote plasma CVD was introduced to fabricate carbon nanotubes(CNTs). C2H2 or CH4, used as source gas react with hydrogen radicals introduced from the cavity. In this experiment, hydrogen radical etching effect on the substrate surface could be controlled independently. We confirmed CNTs growth at 400°C under adequate hydrogen radical etching effect on the substrate surface. The result directly suggests that the etching effect of hydrogen radicals on the reaction surface contribute to the low temperature growth of CNTs. The CNT thickness did not depend on the hydrogen radical etching effect but the catalyst layer thickness.