bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Variational Solution of the Thermoelectric Transport Properties of Two-Component Nanocomposite Systems
Authors: Garrity Patrick L. , Stokes Kevin L. 
Published: April 2011

ABSTRACTThe successful fabrication of a nanocomposite in bulk form consisting of a randomly oriented assembly of nanoscale sized core-shell particles has required an increased understanding of the theoretical aspects of the thermoelectric transport properties. Our particular nanocomposite consists of a nanorod core in 1D quantum confinement coated with an outer conducting polymer shell. Upon fabrication of the bulk composite, these nanorods are embedded within a three-dimensional conducting polymer matrix. We address the nanorod thermoelectric components by assuming a single parabolic band within the one-dimension density of states. Both elastic and inelastic scattering of electrons or holes is accommodated by solving the variational form of the Boltzmann transport equation. An altered lattice thermal conductivity for the confined nanorods is calculated separately to account for boundary scattering that is important in low dimension structures. Exact expressions for the bulk effective electrical and thermal conductivities, Seebeck coefficient and figure of merit are then obtained through the field decoupling transformation, which is a special case of two-component composites. Our method is easily generalized to any two component composite of spherical or cylindrical microstructure and is independent of the materials bulk geometry. The results similarly apply to one, two or three dimensional transport regimes with or without quantum confinement merely by solving the appropriate fundamental transport equations for each constituent material. Comparison to experimental data is then presented which helps validate the nanocomposite theory.
Thermoelectric Properties of the cubic AgPb10SbTe12
Authors: Hsu Kuei-Fang , Loo Sim , Chen Wei , Uher Ctirad , Hogan Tim , Kanatzidis Mercouri G 
Published: April 2011

ABSTRACTAgPb10SbTe12 is one member of the cubic family of materials AgPbmSbTem+2, which adopts NaCl structure where Ag, Pb and Sb atoms occupy the Na site and Te atoms occupy the Cl site. Ingots of this compound were prepared by a solid state reaction for thermoelectric measurements. AgPb10SbTe12 is a narrow band gap semiconductor with Eg∼0.26 eV. In order to optimize the ZT of this member, compositions with deficiency of Ag and Bi-substitution were examined and found to exhibit enhanced power factor at 300 K. The Bi-substituted ingot had ZT∼0.39 at 300 K and ZT∼0.68 at 400 K. Carrier concentration and the mobility measurements are reported.
Thermal Conductivity Reduction of SiGe Nanocomposites
Authors: Harris T. , Lee H. , Wang D. Z. , Huang J. Y. , Ren Z. F. , Klotz B. , Dowding R. , Dresselhaus M. S. , Chen G. 
Published: April 2011

ABSTRACTHigh figure of merit has been reported in superlattice structures in recent years mainly due to a large reduction in thermal conductivity, while maintaining or even enhancing the power factor. These findings suggest the possibility of using nanocomposites to reduce a material's thermal conductivity and thereby increasing the thermoelectric figure of merit. The current work reports on the thermal conductivity of various Si-Ge nanocomposites synthesized in a simple and straightforward process that allows one to exploit nanoscale physics while rapidly producing macroscale devices. Composite synthesis consisted of combining Si nanoparticles approximately 70 nm in diameter with micron-sized Ge particles in various atomic ratios via hotpressing to form macroscale samples. Room-temperature thermal conductivity was measured for each of the nanocomposite samples and compared with the values of SiGe bulk alloys. In this preliminary work, we observed a significant reduction in bulk thermal conductivity in such materials.
Development of Experimental Techniques for Thermoelectric Properties Characterization of Low-Dimensional Structures
Authors: Hapenciuc Claudiu L. , Khan Fazeel J. , Borca-Tasciuc Theodorian , Wang Gwo-Ching 
Published: April 2011

ABSTRACTThis work reports current efforts in developing experimental techniques applicable for thermoelectric properties characterization at micro and nanoscale. A one-dimensional transport model was used to asses the effects of heat leakage, non-symmetric boundary conditions, and electrical contact resistance, on thermoelectric properties measurements performed by transient Harman method. If the above effects are important, the thermoelectric figure of merit cannot be extracted directly from the ratio between the Seebeck voltage and the resistive voltage drop across the sample. On the other hand, measurements of both thermal conductivity and Seebeck coefficient can be performed if the temperature drop across the sample is acquired simultaneously with the voltage drop. The theoretical model and the experimental technique are validated by measurements performed on bulk calibration samples. Furthermore, this work shows that the spatial resolution of thermoelectric properties characterization methods can be enhanced by using scanning probe based techniques. Preliminary results are presented for Seebeck coefficient measurements of p-type or n-type calibration samples performed using an AFM probe instrumented with a temperature sensor.
Discussion on plasma shock waves generated by high-power pulsed laser
Authors: Li ZhiHua , Zhang DuanMing , Guan Li 
Published: April 2011

ABSTRACTSedov-Taylor theory is modified to describe plasma shock waves generated in a pulsed laser ablating process. Under the reasonable asymptotic behavior and boundary conditions, the propagating rules in the global free space (including close areas and mid-far areas) of pulsed-laser-induced shock waves are established for the first time. In particular, the temporal behavior of energy causing the difference of the propagation characteristics between the practical plasma shock wave and the ideal shock wave in point explosion model is discussed in detail.
Thermoelectric Properties of Hot-Pressed GaN and InN
Authors: Yamamoto A. , Yamaguchi S. 
Published: April 2011

ABSTRACTAn attempt was made to obtain bulk III-nitride semiconductors such as InN, GaN and InxGa1−xN alloy using hot-press method in order to test their high temperature thermoelectric properties. The Seebeck coefficient and the resistivity were –10μV/K and 1.8×10−6Ωm for InN, and –50μV/K and 1.9×10−4Ωm for GaN at 300K, respectively. Thermal conductivity determined by laser flash method with porosity correction was 17W/mK for InN and 2.6W/mK for GaN. For InN the Seebeck coefficient and the resistivity increased monotonously with increasing temperature, which indicates that InN is a metal or a degenerately doped semiconductor. The power factor and the figure of merit were 2.1 × 10−4W/mK2and 1.5×10−5K−1for InN and 6.9 × 10−5W/mK2and 2.6×10−5K−1for GaN at 650K, respectively.
Investigation of the Properties of Electrochemically Deposited Semiconductor Materials for Thermoelectric Applications
Authors: Huang C.-K. , Herman J.A. , Myung N. , Lim J. R. , Fleurial J.-P. 
Published: April 2011

ABSTRACTAt JPL, it is our desire to fabricate thermoelectric micro-devices for power generation and cooling applications using an electrochemical deposition (ECD) technique. We believe that the performance of our current micro-device developed is limited by the properties of the ECD materials. Therefore, the objective of this study is to develop ECD methods for obtaining n-type Bi2Te3and p-type Bi2-xSbxTe3thermoelectric materials with near bulk properties, as well as optimizing morphology and transport properties. The films of Bi2Te3and Bi2-xSbxTe3were initially obtained under various ECD conditions. Seebeck coefficients and transport properties were then measured along the direction parallel to the substrates before and after annealing at 250°C for 2hrs. From the data obtained, ECD n-Bi2Te3material can achieve a high Seebeck coefficient (-189 μV/K) when it is deposited at –200 mV vs. SCE. The in-plane resistivity, in-plane mobility, and carrier concentration are 3.0 mohm-cm, 31 cm2V−1S−1, and 6.79 × 1019cm−3, respectively. As for the p-type Bi2-xSbxTe3, it is possible to achieve a high Seebeck coefficient (+295 μV/K) when it is deposited at 0.3 mA/cm2. The in-plane resistivity, in-plane mobility, and carrier concentration are 9.8374 mohm-cm, 66.58 cm2V−1S−1, and 9.54 × 1018cm−3, respectively. From the results of our preliminary study, we have found the conditions for depositing high quality Bi2Te3and Bi2-xSbxTe3materials with thermoelectric properties comparable to those of their state-of-the-art bulk samples.
Theoretical Study of Electronic Structures of Bi2Te3/Sb2Te3 Superlattices
Authors: Li Hong , Bilc Daniel , Mahanti S. D. 
Published: April 2011

ABSTRACTTo understand thermoelectric properties of multiplayer Bi2Te3/Sb2Te3 superlattices, especially their charge transport properties, electronic structure calculations were carried out using ab-initio gradient corrected density functional theory. The superlattice structures of (1,1) and (1,2) Bi2Te3/Sb2Te3 multilayers were optimized and their band structures were compared with each other. Different lattice relaxation effects are observed for the two structures. The cross-plane and inplane effective masses for both these systems are found to be comparable, consistent with experimental mobility measurements.
Synthesis and Thermoelectric Properties of AgBi3S5
Authors: Kim Jun-Ho , Bilc Daniel , Loo Sim , Short Jarrod , Mahanti S. D. , Hogan Tim , Kanatzidis Mercouri G. 
Published: April 2011

ABSTRACTThe known mineral Pavonite AgBi3S5 shows a complex structure composed of NaCl type fragments but has not been studied from the thermoelectric point of view. We present initial results on the synthesis and themoelectric properties of synthetic AgBi3S5, which shows n-type metallic conductivity. In addition, the examination of the solid solutions AgSbxBi3-xS5 (x=0.3) is reported.
Calculating Seebeck Coefficients for Arbitrary Temperature Gradients
Authors: Radkowski Peter P. F. , Sands Timothy D. 
Published: April 2011

ABSTRACTA novel computational scheme has been used to predict the electric potentials generated by arbitrary temperature gradients in semiconductor materials. Written in object-oriented code, the Discrete State Simulation (DSS) is a coupled cellular automata simulator that builds upon the objects and rules of quantum mechanics. The DSS represents global non-equilibrium processes as patterns that emerge through an ensemble of scattering events that are localized at vibronic nodes. By tracking the energy-momentum-position coordinates of the individual particles that define the vibronic state at a node, the DSS undercuts equilibrium concepts such as temperature. Consequently, the DSS can represent physical systems that are described by more than one temperature or that contain physical features that defy definitions of temperature. Using modified bootstrap sampling algorithms, the DSS depicted (1) shifts in distribution functions induced by external fields and temperature gradients, (2) field-dependent transitions from linear mobility to non-linear mobility, (3) saturation velocities, (4) non-exponential decay functions generated by multiple phonon scattering modes, and (5) charge separations and electric potentials generated by temperature gradients. Ensemble averages were sensitive to the structure of dispersion relations, to the energy of the system, and to quantum coupling strengths. Seebeck coefficients were sensitive to the features of the electronic and the vibrational band structures, and their associated coupling coefficients.
X-ray Microbeam Diffraction Measurements in Polycrystalline Aluminum and Copper Thin Films
Authors: Moyer L. E. , Cargill G. S. , Yang W. , Larson B. C. , Ice G. E. 
Published: April 2011

ABSTRACTThermally induced residual strains in polycrystalline Cu and Al films on single crystal Si and glass substrates, respectively, have been examined on a grain-by-grain basis by x-ray microbeam diffraction. The crystallographic orientation and the deviatoric strain tensor, εij*, are determined for each grain by white beam Laue diffraction. From grain orientation mapping and strain tensor measurements, information is obtained about the distributions of strains for similarly oriented grains, about strain variations within single grains, and about grain-to-grain correlations of strains. This type of information may be useful in developing and testing theories for intergrain effects in strain evolution in polycrystals.
Early yielding and stress recovery in (111) and (100) texture components in Cu thin films determined using synchrotron x-ray diffraction
Authors: Nowak D. E. , Baker S. P. 
Published: April 2011

ABSTRACTSynchrotron x-ray diffraction experiments were used to study the thermomechanical behavior of individual texture components in passivated Cu thin films. Films were deposited to a thickness of 500 nm on SiNx barrier layers on Si substrates and then passivated with SiNx. The films were highly textured with grains having (111) or (100) planes parallel to the plane of the film. In-plane film stresses were determined separately in the two texture components as a function of temperature during thermal cycles and also during isothermal holds at 140°C. The results are compared to models of yield behavior and anelastic recovery.
Thermal-Mechanical Evaluation of Plated Electro-Magnetic NiFe for MEMS Generators
Authors: Xue Yibin , Hillman Keithan , Veazie David 
Published: April 2011

ABSTRACTIn micro-electro-mechanical system (MEMS) devices that contain multi-layers of metallic, ceramic, and polymeric materials, acquiring a complete understanding of the mechanical properties and interfacial strength are critical in designing the devices. In general, these layered materials are specially fabricated with thickness of each layer on submicron and/or micron scale. Particularly, the properties of these layered materials strongly depend on the fabrication processes and subsequent treatments. In this paper, we study the magnetic metallic films, NiFe (80/20 in weight), for MEMS generator/motor applications. A set of tensile tests was conducted on the plated nickel-iron metallic films of various thicknesses and subjected to various annealing conditions. Distinctive differences in mechanical behaviors between the electroplated films and the corresponding bulk alloys were observed. Furthermore, the NiFe film as-deposited exhibits almost pure elastic deformation and brittle fracture at room temperature; whereas the NiFe film subjected to annealing exhibits strain hardening and ductile fracture when tested at room temperature. X-ray diffraction was used to capture the variation of crystalline structure and the residual stresses in the electroplated films as deposited and after annealing. An atomic force microscope was used to obtain the surface morphology of the films as deposited and after annealing.
Design Maps for the Tensile Yield Strength of Nanoscale Metallic Multilayers
Authors: Lamm Adrienne V. , Anderson Peter M. 
Published: April 2011

ABSTRACTMetallic nanolayered composite materials can exhibit yield strengths one and a half to two times that of the constituents from which they are constructed. However, experimental data frequently show that there is a critical bi-layer period Λ below which the strength no longer increases with decreasing Λ To help understand the origins of this behavior and to guide future design of multilayers, maps of the internal stress and overall tensile macroyield stress are calculated as functions of the volume fractions of the two alternating constituents and bi-layer period, for a given lattice parameter ratio and elastic modulus ratio. Adopted here is a premise suggested by embedded atom simulations of Cu/Nb multilayers and recent experimental work on γ -Ni/γ-Ni3Al multilayers that the overall tensile strength is determined by the applied stress needed to eliminate the compressive bi-axial stress in the alternating layers. The results indicate that indeed, there is a critical bi-layer period below which the strength is independent of bi-layer period. In this regime, multilayer tensile strength is most effectively improved by increasing the stored compressive stress. This is achieved by decreasing the volume fraction of the compressively stressed phase. This manuscript extends previous work by providing closed-form expressions for the macroyield strength of free-standing multilayered thin films.
Thin Film Herringbone Buckling Patterns
Authors: Chen Xi , Hutchinson John W. 
Published: April 2011

ABSTRACTThin metal film deposited on compliant substrate undergoes equi-biaxial compression and buckles into a highly ordered herringbone pattern [1,2]. In this study, it is shown that compare with the bifurcation competing modes, the herringbone mode has the lowest strain energy and therefore it is the preferred buckling pattern in the thin film.
The Effect of Oxygen on Adhesion of Thin Copper Films to Silicon Nitride
Authors: Pang Mengzhi , Backhaus-Ricoult Monika , Baker Shefford P. 
Published: April 2011

ABSTRACTThe effect of oxygen on adhesion and chemistry at interfaces between Cu thin films and SiNx barrier layers on Si substrates was investigated. Films were deposited in an ultra-high-vacuum sputter deposition chamber with good control of oxygen content. Adhesion was measured using a high throughput driver film method. Microstructure and bonding were investigated using transmission electron microscopy and electron energy loss spectroscopy, respectively, on sample cross sections. For films to which a small amount of oxygen was added during deposition, oxygen segregated to Cu/SiNx interfaces during thermal cycling, where it induced charge transfer and the presence of Cu+ interfacial states, and significantly reduced the work of adhesion.
Toughness and Contact Behavior of Conventional and Low-k Dielectric Thin Films
Authors: Cook Robert F. , Morris Dylan J. , Thurn Jeremy 
Published: April 2011

ABSTRACTA comprehensive indentation fracture mechanics framework is established that allows the fracture properties of thin films to be determined. The framework is composed of four stress-intensity factors characterizing the stress fields arising from (i) elastic contact, (ii) wedging, (iii) residual elastic-plastic mismatch and (iv) pre-existing film stress. The amplitudes of the stress-intensity factors depend on the deformation properties of the film and vary throughout the indentation cycle. The toughness values of a PVD alumina, for which (iii) and (iv) are dominant, and a low-k film, for which (i), (ii) and (iv) are dominant, are evaluated.
Scratch Test Measurements on CrNx Coatings
Authors: Hoy R. , van Essen P. , Kamminga J.-D. , Janssen G. C. A. M. , Ehiasarian A. P. 
Published: April 2011

ABSTRACTHard CrNx coatings of various composition were deposited on hot work tool steel by means of reactive sputter deposition in an industrial PVD reactor. All deposited coatings (thickness 3–4 micron) were under compressive stress. The coatings were subjected to scratch testing with a diamond stylus. Two critical loads were determined. The first critical load, Lc1, indicates the onset of chipping and/or spalling. The second critical load, Lc2, indicates complete coating removal inside the track. Micrographs showing the coating failure are presented. Stoichiomeric CrN coatings outperform understoichiometric CrN0.6 coatings in scratch tests. It was found that for all specimens the coating-to-substrate adhesion is very good, independent on composition. Although the values of Lc1 and Lc2 are distinctly different, their dependence on composition is similar.
Resistance to cracking of a stretchable semiconductor: Speed of crack propagation for varying energy release rate
Authors: Liu Sheng , Lim Hee C. , Qu Min , Federici John F. , Thomas Gordon A. , Gleskova Helena , Wagner Sigurd 
Published: April 2011

ABSTRACTWe have measured and calculated the propagation velocity of successive cracks in a single sample of amorphous SiNx as a function of energy release rate. We have obtained the conditions for controlled, repetitive crack formation by using a substrate of compliant plastic that survives the cracking of a thin film formed on it. We have recorded the crack velocity curves using high-speed micro-photography using dark field illumination. Under uniform, uniaxial tensile strain, the films crack in an array of essentially straight, parallel lines, if the increase of the strain density is slow. We find reasonable agreement in the comparison of theory and experiment and find a linear relationship between the initial velocity and energy release rate threshold. Consequently, in cases where the theoretical agreement with the data is reasonable, the successive cracks show velocity curves that scale with each other.
Preparation of Oxygen Ion Conducting Doped Lanthanum Gallate Thin Films on Amorphous and Single Crystal Substrates by Pulsed Laser Deposition
Authors: Mitsugi Fumiaki , Kanazawa Seiji , Ohkubo Toshikazu , Nomoto Yukiharu , Takita Yusaku , Ishihara Tatsumi 
Published: April 2011

ABSTRACTAn La1-xSrxGa1-y-zMgyCozO3-(x+y+z)/2 (LSGMCO) has attracted much attention because it can be useable as an electrolyte of a solid oxide fuel cell due to its high oxide ion conductivity. We prepared LSGMCO thin films on silica glass and LaAlO3 single crystal substrates by pulsed laser deposition and evaluated their properties. LSGMCO thin films deposited at 800°C were poly-crystal and the deposition pressure affected their surface morphologies. In the case of the LaAlO3 single crystal substrate, a c-axis oriented LSGMCO thin film was obtained. DC conductivity and complex impedance of LSGMCO thin films were measured in vacuum atmosphere to investigate the effect of the crystal orientation on the oxide ion conductivity. It was revealed that resistance at a grain boundary of films is more dominant compare with the grain interior.
Electrical Properties of β-FeSi2 Thin Films on Insulating Substrates
Authors: Akiyama Kensuke , Kimura Takeshi , Nishiyama Shin , Hattori Takeo , Ohashi Naoki , Funakubo Hiroshi 
Published: April 2011

ABSTRACTIron silicide thin films were prepared on insulating substrates using RF magnetron sputtering method. Amorphous, polycrystalline and epitaxial β-FeSi2 were obtained on MgO(001), Al2O3(110) and Al2O3(001) substrates, respectively. Electrical conductivities of these films showed similar temperature dependence. Intrinsic band conduction and hopping conduction mechanism were predominant above and below 600K, respectively. The localized ordering in the polycrystalline and epitaxial films that controled the movement of carriers were as low as in the amorphous film. For the epitaxial β-FeSi2 film, electrical conductivity below 600K were affected by atomic ratio of silicon to iron (Si/Fe) in the films, because the localized ordering in the films decreased as Si/Fe atomic ratio decreased.
Role of Interface Quality and Film Doping Density in Amorphous Si / Crystalline Si Heterojunctions for Photovoltaic Applications
Authors: Farrokh Baroughi M. , Sivoththaman S. 
Published: April 2011

ABSTRACTWe have studied some key aspects of the (n+)a-Si/(p)c-Si heterojunction structures photovoltaic applications. The importance of the hetero-interface quality has been studied by both theoretical simulations and experimental characterization. The surface treatment prior to the film deposition is very critical. Even though H-plasma passivation can help passivate bulk defects in low quality Si, extreme care should be taken to avoid plasma induced surface damage which will result in a defective hetero-interface. Furthermore, (n+) a-Si films with different doping levels have also been characterized and their influence on the device performance has been studied.