bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermal Conductivity and Phonon Engineering in Low-Dimensional Structures
Authors: Chen G. , Volz S. G. , Borca-Tasciuc T. , Zeng T. , Song D. , Wang K. L. , Dresselhaus M. S. 
Published: April 2011

AbstractUnderstanding phonon heat conduction mechanisms in low-dimensional structures is of critical importance for low-dimensional thermoelectricity. In this paper, we discuss heat conduction mechanisms in two-dimensional (2D) and one-dimensional (1D) structures. Models based on both the phonon wave picture and particle picture are developed for heat conduction in 2D superlattices. The phonon wave model, based on the acoustic wave equations, includes the effects of phonon interference and tunneling, while the particle model, based on the Boltzmann transport equation, treats the internal as well interface scattering of phonons. For 1D systems, both the Boltzmann transport equation and molecular dynamics simulation approaches are employed. Comparing the modeling results with experimental data suggest that the interface scattering of phonons plays a crucial role in the thermal conductivity of low-dimensional structures. We also discuss the minimum thermal conductivity of low-dimensional structures based on a generalized thermal conductivity integral, and suggest that the minimum thermal conductivities of low-dimensional systems may differ from those of their corresponding bulk materials. The discussion leads to alternative ways to reduce thermal conductivity based on the propagating phonon modes.
Carrier Pocket Engineering to Design Superior Thermoelectric Materials Using GaAs/AlAs Superlattices
Authors: Koga T. , Sun X. , Cronin S. B. , Dresselhaus M. S. 
Published: April 2011

AbstractA large enhancement in the thermoelectric figure of merit for the whole superlattice, Z3DT, is predicted for short period GaAs/AlAs superlattices relative to bulk GaAs. Various superlattice parameters (superlattice growth direction, superlattice period and layer thicknesses) are explored to optimize Z3DT, including quantum wells formed at various high symmetry points in the Brillouin zone. The highest room temperature Z3DT obtained in the present calculation is 0.41 at the optimum carrier concentration for either (001) or (111) oriented GaAs(20 Å)/AIAs(20 Å) superlattices, which is about 50 times greater than the corresponding ZT for bulk GaAs obtained using the same basic model.
Thermoelectric Properties of the AIPdMn Quasicrystalline System
Authors: Pope A. L. , Tritt T. M. , Chernikov M. , feuerbacher M. , Legault S. , Gagnon R. , Strom-Olsen J. 
Published: April 2011

AbstractWe have begun a systematic investigation the electrical transport properties of the AlPdMn quasicrystalline system. Resistivity and thermopower measurements have been performed over a temperature range between 5K and 320K. In the pure, single phase Al70Pd20Mn10 we have observed thermopowers as high as +80 μV/K around room temperature with resistivities of 1.5 mΩ-cm. Thermal conductivity measurements have been performed yielding values less than 2 W/m-K for all the samples investigated to date. We will discuss how the thermopower and resistivity vary as a result of differing sample composition as well as different processing and annealing conditions. Several different preparation techniques have been employed to further understand how various factors affect the thermal and electrical properties of this quasicrystalline system and how these may be adjusted to optimize these materials for possible thermoelectric applications.
Hot Electron Effects on Thermionic Emission Cooling in Heterostructures
Authors: Zeng Taofang , Chen Gang 
Published: April 2011

AbstractThe energy conversion between electrons and phonons in a heterostructure is studied for thermionic cooling by using the hot electron approximation. Calculations show that the energy exchange rate between electrons and phonons should be small for a net cooling power, and the layer length should be in the range of submicron for effective cooling.
Anisotropic Thermal Conductivity of A Si/Ge Superlattice
Authors: Borca-Tasciuc T. , Song D. , Liu J. L. , Chen G. , Wang K. L. , Sun X. , Dresselhaus M. S. , Radetic T. , Gronsky R. 
Published: April 2011

AbstractExperimental evidence for a significant thermal conductivity reduction have been reported in recent years for GaAs/AlAs, Si/Ge, and Bi 2Te3/Sb2Te3 superlattices. In this work, we present preliminary experimental results on the reduction of the in-plane and cross-plane thermal conductivity for a symmetric Si/Ge superlattice. A differential 2-wire 3ω method is developed to perform the anisotropic thermal conductivity measurements. In this technique, a patterned heater with a width much larger than the film thickness yields the cross-plane thermal conductivity of the film. The in-plane thin film thermal conductivity is inferred from the temperature rise of a narrow width heater that can create more heat spreading in the in-plane direction of the thin film. A differential method to measure the temperature drop across the film is employed in order to increase the accuracy of the measurement.
Development of Thick-Film Thermoelectric Microcoolers Using Electrochemical Deposition
Authors: Fleurial J.-P. , Borshchevsky A. , Ryan M. A. , Phillips W. M. , Snyder J. G. , Caillat T. , Kolawa E. A. , Herman J. A. , Mueller P. , Nicolet M. 
Published: April 2011

AbstractAdvanced thermoelectric microdevices integrated into thermal management packages and low power, electrical source systems are of interest for a variety of space and terrestrial applications. By shrinking the size of the thermoelements, or legs, of these devices, it becomes possible to handle much higher heat fluxes, as well as operate at much lower currents and higher voltages that are more compatible with electronic components. The miniaturization of state-of-the-art thermoelectric module technology based on Bi2Te3 alloys is limited due to mechanical and manufacturing constraints for both leg dimensions (100–200 μm thick minimum) and the number of legs (100–200 legs maximum). We are investigating the development of novel microdevices combining high thermal conductivity substrate materials such as diamond, thin film metallization and patterning technology, and electrochemical deposition of thick thermoelectric films. It is anticipated that thermoelectric microcoolers with thousands of thermocouples and capable of pumping more than 200 W/cm2 over a 30 to 60 K temperature diffrence can be fabricated. In this paper, we report on our progress in developing an electrochemical deposition process for obtaining 10–50 μm thick films of Bi2Te3 and its solid solutions. Results presented here indicate that good quality n-type Bi2Te3, n-type Bi2Te2.95Se0.05 and p-type Bi0.5Sb1.5Te3 thick films can be deposited by this technique. Some details about the fabrication of the miniature thermoelements are also described.
Synthesis of New Thermoelectric Materials Using Modulated Elementary Reactants
Authors: Sellinschegg Heike , Williams Joshua R. , Maxwell Steven P. , Sillars Douglas , Johnson David C. 
Published: April 2011

AbstractModulated elemental reactants have been used to synthesize metastable ternary compounds with the skutterudite crystal structure. The initial reactants are made up of multiple repeats of a unit containing elemental layers of a ternary metal, iron or cobalt (or a combination of these two) and antimony. The elemental layers interdiffuse upon low temperature annealing and form amorphous reaction intermediates. In this paper we target the compounds PbxFe4−yCoySb12. On annealing at temperatures between 12° and 150° C (depending on the composition) crystallization of the skutterudite structure occurs. The compounds are only kinetically stable, decomposing into a mixture of binary compounds upon annealing past a temperature of about 600°C. Preliminary data for the Seebeck coefficient and the electrical conductivity was collected The thermoelectric properties of the lead cobalt antimony skutterudite - films were measured as a function of lead occupancy.
Chevrel Phases as Good Thermoelectric Materials
Authors: Roche C. , Pecheur P. , Riffel M. , Jenny A. , Scherrer H. , Scherrer S. 
Published: April 2011

AbstractChevrel phases have an open lattice with large voids in which cations can be inserted. These cations are good scattering centers for phonons. The thermal conductivity of these compounds must be low. Chevrel phases are generally metallic, but we calculated the density of states of several compounds and we found that Zn2Mo6Se8, Cd2Mo6Se8, TiMo6Se8 are semiconducting whereas SnMo6Se8, Cu2Mo6Se8 and CrMo6Se8 are metallic. We are currently trying to synthesize Zn2Mo6Se8 by different ways.
Extraction of the Coefficient of Thermal Expansion of Thin Films from Buckled Membranes
Authors: Ziebartl V. , Paul O. , Baltes H. 
Published: April 2011

AbstractWe report a new method to measure the temperature-dependent coefficient of thermal expansion α(T) of thin films. The method exploits the temperature dependent buckling of clamped square plates. This buckling was investigated numerically using an energy minimization method and finite element simulations. Both approaches show excellent agreement even far away from simple critical buckling. The numerical results were used to extract Cα(T) = α0+α1(T−T0 ) of PECVD silicon nitride between 20° and 140°C with α0 = (1.803±0.006)×10−6°C−1, α1 = (7.5±0.5)×10−9 °C−2, and T0 = 25°C.
Reliability and Properties of Pzt Thin Films for Mems Applications
Authors: Bahr D. F. , Merlino J. C. , Banerjee P. , Yip C. M. , Bandyopadhyay A. 
Published: April 2011

AbstractThin films of PZT have been deposited using a solution deposition method onto platinized silicon substrates. The effects of process variables, including sintering time and solution molarity, have been investigated on the resulting microstructure and electrical properties. As utilizing piezoelectric thin films in geometries for MEMS applications requires load to be transferred between the film and an underlying membrane, the adhesion of these films has been examined using nanoindentation techniques. Delaminations occur at the PZT-Pt interface, suggesting that these films may be susceptible to interfacial failure with repeated bending. Longer firing times are shown to improve the adhesion of the films, but increase the surface roughness and grain size. Film hardnesses range between 4 and 6.8 GPa; for sintering times beyond 5 minutes at 700 °C the hardness appears relatively constant. Electrical properties are shown to degrade with tine at elevated temperatures.
Fullerene Derivatives as Novel Resist Materials for Fabrication of MEMS Devices by Electron Beam Lithography
Authors: Robinson A.P.G. , Palmer R.E. , Tada T. , Kanayama T. , Shelley E.J. , Preece J. A. 
Published: April 2011

AbstractThe fabrication of MEMS and electronic devices relies heavily on lithography. We have explored the application of derivatives of C60, as high resolution, high etch durability resists. Spin coating was used to produce films of various methanofullerenes on silicon substrates, with thickness ranging from 20 to 200 nm. These films behave as effective high resolution negative tone electron beam resists allowing sub 20 nm patterning of silicon which compares favorably with other negative tone resists. Organic solvents such as monochlorobenzene and chloroform can be used to develop the exposed films. The films have sensitivities of 4 × 10−3 to 8 × 10−4 C/cm2 for 20 keV electrons, more than an order of magnitude higher than the sensitivity of C60,. The dry etch durabilities of these compounds are considerably higher than those of conventional resists. A silicon grid with hole depth 160 nm and wall thickness 20 nm has been fabricated to demonstrate the high resolution and high etch durability of these resists.
The synthesis of novel polynuclear organogold complexes
Authors: Thomson J. , Fzea A. H. , Lobban J. , McGivern P. G. , Cairns J. A. , Fitzgerald A. G. , Berry G. J. , Davidson M. R. , Fan Y. C. 
Published: April 2011

SummaryThe synthesis and peirastic characterisation of two new organogold(III) complexes with a high molar ratio of gold content is described. The proposed formulae for the complexes in the present study are [C2H2Au4F8(PPh3)4]n and [C2H2Au4F8(NCCH3)4]n (Figure 1). These complexes were found to be stable to the atmosphere. The aim of this work was to demonstrate that such materials have a high metal to ligand ratio, suitable for physical vapour deposition process (PVD) and, hence, can be used as precursors for the deposition of pure metallic features. Physical and chemical characterisation methods were employed to obtain information about i) the structures, ii) the thermal and chemical stability, iii) the volatility and iv) the adhesion of these materials to specific substrates. These include n.m.r. (1H, 19F, 13C and 31P) IR spectroscopy, EDX (Energy Dispersive X-ray analysis), DSC ( Differential Scanning Calorimetry), TGA (Thermogravimetric Analysis), Powder X-ray Diffraction and Electron Microscopy (Scanning, Transmission and Atomic Force).
New Perovskite Oxide (Tl1/2Na1/2)TiO3
Authors: Shan Yue Jin , Nakamura Tetsuro , Miyata Mayuko , Kobashi Kazuhisa , Inaguma Yoshiyuki , Itoh Mitsuru 
Published: April 2011

AbstractNew perovskite-type oxide (Tl1/2Na1/2)TiO3 was synthesized by a cubic-anvil-type high pressure apparatus at 5.5 GPa and 1273 K for 30 sec. The perovskite-phase was found to have a tetragonal symmetry with space group P4/mmm. The lattice parameters a and c are 0.3811 nm and 0.3826 nm, respectively. An insulating skin covered the sample, but real resistivity is smaller and shows a metallic behavior.
Suppression of Exaggerated Grain Growth During Sintering of Nano-Sized Barium Titanate Powders
Authors: Meyers K.S. , Speyer R.F. 
Published: April 2011

AbstractRate controlled sintering (RCS) was used to sinter nano-sized BaTiO3 particles. A distinct shift in temperature slope above 1150-1200°C during RCS implied a change in sintering mechanism, and a corresponding exaggerated grain growth (grain size ~40-50 μm). By suppression of the exaggerated grain growth by firing a specimen packed in BaCO3, these phenomena were shown to be the result of a shift in phase equilibria from the volatilization of BaO from BaTiO3; the eutectic liquid which formed permitted rapid grain growth by a dissolution and precipitation process.
Effect of MnO on the Electrical Properties of Nb-Doped SrTiO3 Varistor
Authors: Kim S.-H. , Seon H.-W. , Kim Yoonho 
Published: April 2011

AbstractThe effect of MnO on the electrical properties of Nb-doped SrTiO3 was investigated to understand the electronic states of grains and grain boundaries. Grain size and dielectric constant were decreased with increasing Mn-doped content from 0 to 0.07 mol%. However, it was observed that the non-linearity coefficient of Nb-doped SrTiO3 was changed from 5 to 43 with Mn-doped content increasing from 0 to 0.03 mol%. Current-voltage (I-V) characteristics, capacitance-voltage (C-V) measurement, complex plane analysis and impedance spectroscopy were performed to obtain the information about the electrical properties of grains and grain boundaries. The potential barrier height increased and the donor concentration decreased with increasing Mn-doped content. This phenomena, that the electrical properties of Nb-doped SrTiO3 were changed with the addition of Mn, would be determined by the effect which Mn-2-3 substituted for Ti sites. It was observed that the breakdown voltage of single grain boundary was changed from 3.8 V to 8.9 V when measured by micro-electrode method.
Crystal Chemistry of New Calcium Tantalate Dielectric Materials
Authors: Grey Ian E. , Roth Robert S. , Mumme Gus , Bendersky Leonid A. , Minor Dennis 
Published: April 2011

AbstractDoping of calcium tantalate, Ca2Ta2O7, with small amounts (<5 mole%) of Ca2Nb2O7 results in a 50% increase in the dielectric constant, K (from 23 to 35 at 1 MHz), and a zero temperature coefficient of K is achieved at about 18 mole% of Ca2Nb2O7. This opens up the possibility of applications in microwave communication devices. Crystallographic information needed to understand the structure/property relationships in this system is lacking. We have prepared samples of calcium tantalates doped with different elements including Nb, Sm, Ti, Nd and Zr, and have structurally characterised them using X-ray diffraction and transmission electron microscopy. The diffraction patterns of the tantalates all display strong subcell reflections characteristic of the trigonal weberite structure together with complex distributions of superlattice reflections that depend on the nature and concentration of the dopant and on the reaction temperature. The diffraction patterns were indexed using related trigonal or pseudo-trigonal unit cells with a ~7.3 Å, c ~ n × 6 Å. Polytypes with n = 3, 4, 5, 6 and 7 were prepared as single crystals by the flux method. Single crystal X-ray data was used in conjunction with high resolution electron microscope images to solve the structures. Details are given for a 6M polytype (M=monoclinic). A characteristic structural feature of the polytypes is a fluorite-type cation array which is periodically twinned on (111)f to give mixed cubic-hexagonal stacking of the cation layers. The structure relations with the pyrochlore and weberite structures are discussed.
Synthesis and Characterization of New Composite Oxides Related to the 2H-Perovskite Structure Type
Authors: Claridge J. B. , zur Loye H.-C. 
Published: April 2011

AbstractThe synthesis, structural characterization, and magnetic properties of three strontium rhodium oxides Sr6Rh5O15, Sr4Rh3O9+δ, and Sr9Rh7O21+δ, is presented. While Sr6Rh5O15 is an example of a commensurate n = 1 member of the A3n+3A'nBn+3O6n+9 family of oxides, Sr4Rh3O9+δ, and Sr9Rh7O21+°, are examples of incommensurate n =2 and n = 3 members. Sr6Rh5O15 crystallizes in space group R32, a = 19.3197(2) Å, c = 13.0418(1) Å. The Sr6Rh5O15 structure is a superstructure of the Ba6Ni5O15 structure type. Sr4Rh3O9+δ, and Sr9Rh7P21+δ crystallize in the superspace group with lattice parameters of a = 9.6007(6), c1 = 2.6881(2), c2 = 4.2373(3), and a = 9.6127(6), c1 = 2.6769(2), c2 = 4.252(1), respectively. Their magnetic data are consistent with antiferromagnetic coupling between the chains leading to an ordered state at low temperature.
A Coupled Compressible and Polarizable Ionic Model Applied to Oxide Crystal Structures
Authors: Marks N. A. , Fabris S. , Finnis M. W. 
Published: April 2011

AbstractCompressible and polarizable ion models parametrized by ab initio calculations represent a promising technique for simulating challenging materials such as oxides. We present a new form of such a model in which the compression and polarization effects are coupled, and the anion-anion interaction is not fixed but dependent on the ion size and polarization. These two effects provide a more physically realistic description of a system, and significantly improve the predictive power of the method. Calculations on magnesium oxide show the elastic constants and other properties to be in good agreement with experiment. The new functional form is part of an ongoing project to develop an empirical model of zirconia, an important oxide for which a satisfactory model has yet to be determined.
A New Allotropic Form of Bi2O3
Authors: Kumada N. , Kinomura N. 
Published: April 2011

AbstractSingle crystals of a new allotropic form of bismuth sesquioxide, Bi2O3 were prepared by low temperature hydrothermal reaction using hydrated sodium bismuth oxide, NaBiO3·nH2O, as a starting material. This bismuth oxide crystallized in the orthorhombic space group Pccn with a=12.732(2), b=4.955(2) and c=5.582(2)Å, z=4, and the R-factors were R=0.030 and Rw=0.030 for 1702 unique reflections. The crystal structure is built up by corner- and edge-sharing of irregular BiO5 polyhedra and the tunnel is running along the c-axis.
Effect of Potassium Carbonate Additive on CO2 Absorption in Lithium Zirconate Powder
Authors: Ohashi T. , Nakagawa K. 
Published: April 2011

AbstractLithium zirconate, which reacts with CO2 reversibly at temperatures over 500°C, is expected to find wider application than conventional CO2 absorbents, as the latter can be used only at room temperature. We examined the effect of potassium carbonate, which had usually been added to facilitate the formation of lithium zirconate in the past, on the kinetics of CO2 absorption reaction. The result shows that the CO2 absorption rate of lithium zirconate powder is extremely accelerated by the potassium carbonate additive. We conclude that this acceleration results from the formation of a eutectic carbonate composed of Li2CO3 and K2CO3.
Synthesis of Epitaxial Thin-Films of Tetragonal Perovskites Via a Solution Technique
Authors: Beach David B. , Morrell Jonathan S. , Xue Ziling B. , Specht Eliot D. 
Published: April 2011

AbstractSolution chemistry has been used to synthesize epitaxial films of SrLaGaO4, SrPrGaO4, SrLaAlO4, and SrPrAlO4 on single crystal substrates of [100] SrTiO3 and [100] LaAlO3. Precursor solutions were prepared from metal methoxyethoxides in 2-methoxyethanol. Films were prepared by spin-casting from partially hydrolyzed solutions followed by firing for 20 minutes in air at 850°C. The structure of the films was determined using X-ray diffraction. Theta/2-theta scans and omega scans (rocking curves) indicated that the films were c-axis aligned. Phi scans proved that the films were also aligned in-plane.
Preparation of YSZ Thin Film on Porous Electrode of SOFC
Authors: Nagamoto H. , Ikewaki H. 
Published: April 2011

AbstractPorous electrode substrate of La0.7Sr0.2MnO3 was used as the support for the deposition of YSZ thin films. The porosity of the electrode substrate was controlled by sintering temperature and particle size of powders. Thin films of YSZ were fabricated on the electrode by sol-gel method. The YSZ film fabricated by 10-fold coating with 0.05M YSZ sol containing TEA was continuous and crack-free one of 5 mm in thickness. However, hydrogen permeation measurement showed that there was a very small leakage of hydrogen in the fabricated film. In addition to sol-gel method, another technique such as EVD should be employed to make the film completely gas-tight.
Factors Influencing the Electrochromic Properties of Nickel Oxide Thin Films Derived from Sol-Gel Method by Dip Coating
Authors: Sharma Pramod K. , Mracia M.C.A. , Fischer H. , Craievich A. F. , Gorenstein A. 
Published: April 2011

AbstractThe synthesis of thin film of nickel oxide is important due to their potential application in eletrochromic displays which can be used in optical displays and as windows controlling the light intensity. Dip coating through sol-gel method is a possible low energy method of coating. Hence this method of film growth has been chosen under various concentration of water, catalyst (acetic acid) and precursor. The films were characterized by XRD, FTIR, thickness profiler and SEM. The films which were synthesized with the concentration of Ni=0.005 molar were found to have low positive current density while the coloration was getting dark when concentration of Ni was increased to 0.015 molar. Increase in concentration of acetic acid decreases the positive current density. Small-Angle X-ray Scattering (SAXS) and density measurements were carried out for the structural characterization of the xerogels. A denser material was obtained at high concentration of acetic acid. The physical and chemical properties of the films and xerogels are well correlated with the electrochemical properties of the films.