bluuebunny/crossref_metadata_2025 huggingface dataset:
Conjugated Polymer:TiO2 Nanocomposite Solar Cells Based on P3HT Nanoparticles
Authors: Venkatraman B. Harihara , Kokil Akshay , Satapathi Soumitra , Kumar Jayant , Venkataraman* Dhandapani
Published: April 2011

There is widespread interest in developing efficient solar cells derived from conjugated polymers and TiO2. The conjugated polymer can act as a light harvesting dye as well as a hole transport material, and can potentially replace both the ruthenium dye and the I3-/I- couple in the DSSCs. Herein, we report a novel and facile approach of using conjugated polymer nanoparticles to make conjugated polymer:TiO2 nanocomposite based solar cell. Nanoparticles from poly(3-hexylthiophene) (P3HT) were made using mini-emulsion technique. In this work we report on incorporation of these P3HT nanoparticles into nanoporous titania. Device characteristics made using P3HT nanoparticle sensitized solar cells were measured. These devices showed a short-circuit current density (Jsc) of 0.207 mA/cm2, open-circuit voltage (Voc) of 0.62 V and 0.07% (η) efficiency.
Stochastic Models of Epitaxial Growth
Authors: Margetis Dionisios , Patrone Paul N. , Einstein T. L.
Published: April 2011

We study theoretical aspects of step fluctuations on vicinal surfaces by adding conservative white noise to the Burton-Cabrera-Frank model in one spatial dimension. We consider material deposition from above, as well as entropic and elastic-dipole step repulsions. Two approaches are discussed: (i) the linearization of stochastic equations when fluctuations are small, which captures correlations; and (ii) a mean field approach, which leaves out correlations but captures nonlinearities. Comparisons to kinetic Monte-Carlo simulations are presented.
Nanostructured Broad Band Infrared Absorber
Authors: Corrigan Timothy D. , Park Dong Hun , Drew Dennis , Phaneuf Ray
Published: April 2011

We describe a near perfect broad band absorber based on a laterally nanostructured multilayer material. We present calculations of the structure that demonstrates over 99% absorption of the 500 K black body spectrum. We also show the ability to manufacture an anti-reflective layer using a nanostructured metamaterial which allows us to tailor the index of refraction using effective medium theory. The absorber can be adapted for use in any frequency range and any source type. These materials may have applications in energy harvesting and scattered light control.
Carbon-based Materials as Key-enabler for “More Than Moore”
Authors: Kreupl Franz
Published: April 2011

Carbon-based materials like nanotubes and graphene are heavily investigated as future transistor devices and in interconnect applications. While much of the interest has been devoted to the device aspects in competition to conventional transistors, the paper here will focus on some less known applications of pyrolytically deposited carbon. Proposed and demonstrated are applications in capacitors, gate materials, through-silicon vias, novel non-volatile memories, carbon-silicon Schottky diodes and sensors.
Pt/TiO2/Ti Metal-Insulator-Metal Tunnel Diodes for Rectification in an Energy Harvesting System
Authors: Chin Matthew , Nichols Barbara , Osgood Richard , Kilpatrick Stephen , Dubey Madan , Dhar Nibir
Published: April 2011

Methods for extracting or harvesting energy from the surrounding battlefield environment are of great importance to the United States Army. Scavenging energy from local environments reduces the required energy and weight transported to the theater. Micro- and nano-scale metal-insulator-metal (MIM) tunnel diodes are being developed to provide half-wave rectification as part of a “rectenna” energy harvesting system, which includes a radiation-collecting antenna, a rectifying MIM tunnel diode, and a storage capacitor. In this work, high-frequency MIM tunnel diodes for power rectification were designed, fabricated and characterized. Planar Pt/TiO2/Ti stacks are being fabricated to create a diode with highly asymmetric I-V characteristics that has a very low threshold voltage. The metals were chosen for their high work function difference, and the insulator was chosen for its barrier height, its compatibility with Ti, and its availability. The energy band diagram and the I-V characteristics were modeled to determine the feasibility of the Pt/TiO2/Ti material system for use as a rectifier diode in a rectenna system. Metals and insulator thin films were deposited onto silicon dioxide/silicon substrates. Pillars with lateral dimensions ranging from 20 μm x 20 μm up to 100 μm x 100 μm were fabricated. The dielectric thickness of the MIM diode was varied from 5 nm up to 50 nm to determine the optimal thickness for quantum tunneling. I-V measurements were taken using an electrical characterization system to confirm a non-linear, asymmetric response on a survey of devices fabricated with varying areas. Preliminary results exhibit asymmetric I-V characteristics with threshold voltages of less than 700 mV.
Fracture Transfer of Vertical Semiconductor Pillar Arrays to Low Cost Arbitrary Substrates for Flexible Energy Device Applications
Authors: VJ Logeeswaran , Ombaba Matthew , Islam M.Saif
Published: April 2011

In this paper, we demonstrate a heterogeneous integration technique that preserves the integrity, order, shape, and fidelity of vertically aligned single-crystal semiconductor micro- and nano- pillars by harvesting and transferring them from a single crystal substrate to a low-cost carrier substrate. The mechanism of the transfer technique exploits a combination of vertical embossing and lateral fracturing of the crystalline pillars with the assistance of a spin-coated polymer layer on a carrier substrate as well as facilitating multilayer process device integration. Specifically, the novel use of a water soluble adhesive polymer from MasterBond that acts simultaneously as a mechanical transfer polymer and as a sacrificial harvest layer further expands the versatility of this approach. Arrays of vertical micropillars of average height ~15)μm and diameter ~1.5μm on a die silicon substrate of 5mm x 5mm were fabricated via transformative top-down approaches (DRIE) on a single crystal silicon substrate and then transferred to a different target carrier substrate using the adhesive polymer assisted bendingfracturing process. The adhesive polymer is odorless, non-conducting, easy to process, spincoatable, optically transparent, resistant to heat, high mechanical strength and easily cures at room temperature. The original pillar wafers may be used repeatedly after polishing for generating more devices and are minimally consumed. Low contact resistances are formed for electrical addressing using metals and conducting thermoplastics of Ag nanoparticles. This heterogeneous integration technique potentially offers enhanced photon semiconductor interactions, while enabling multimaterial integration such as silicon with compound semiconductors (InP, GaAs etc.) for applications, including high speed electronics, low-cost and flexible electronics, displays, tactile sensors, and energy conversion systems.
Multiparameter Imaging and Understanding the Role of the Tip - Atomic Resolution Images of Rutile TiO2 (110)
Authors: O’Brien S. J. , Ozgur Ozer H. , Cross G. L. W. , Pethica J. B.
Published: April 2011

A major challenge for scanned probe microscopy is to identify structures and chemical species on a surface, which have not already been inferred from other analytical techniques. Progress is impeded by the fact that in general the structure and composition of the tip atom is not known. To illustrate some of the issues involved, we report simultaneous scanning tunneling microscopy/atomic force microscopy (STM/AFM) of the TiO2 (110) surface. The use of small amplitudes enabled the simultaneous acquisition of force gradient and barrier height images during standard STM imaging. Surprisingly, we find most STM images exhibit a corrugation contrast inverse to that usually reported in the literature. However, regardless of the contrast in STM, force gradient images always showed greater attraction over O rows. Barrier height images also show this consistency, always being greater over O rows. This supports the theoretical model of the electronic structure of the surface, but shows that the tip structure and interaction cannot be ignored in modeling STM images. We conclude that there is a fine balance between topography and local density of states (LDOS) in STM imaging of this surface; which of them dominates the STM image is determined by the tip. Simultaneous multi-parameter imaging is useful in interpreting images reliably, particularly on multi-component surfaces.
Permeability of Polymer/Clay Nanocomposites
Authors: Choudalakis Georgios A. , Gotsis Alexandros D.
Published: April 2011

Because of their large interfacial area, the presence of nanoplatelets in the polymeric matrix decelerates the process of diffusion of gases through the material. The particles are impermeable barriers to the diffusing molecules, forcing them to follow complicated paths, increasing, thus, the diffusion length. The barrier properties of the nanocomposites depend on the properties of the polymeric matrix, the volume fraction of the nanoplatelets, their aspect ratio, their orientation, and their interactions with the matrix. The mobility of the molecules is hindered by the crystallinity but it is facilitated by the free volume within the material. The size and shape of the free volume holes in the polymer affect, thus, the rate of diffusion. Interactions between the nanoparticles and the matrix may lower the barrier properties because they may increase the free volume in the material. The estimation of free volume in the nanocomposite is important for the proper choice of components and the manufacturing of nanocomposite coatings with optimum barrier properties. Detailed information about the diffusion mechanisms at atomic and molecular levels can be obtained using the approach of free volume.
Observation Of Real-Time Thin Film Evolution Using Microcantilever Sensors
Authors: Schilowitz Alan M. , Yablon Dalia G.
Published: April 2011

Adsorption and desorption kinetics of thin film formation on metal surfaces has been directly monitored in real-time by optically measuring the deflection of activated atomic force microscope microcantilevers. Microcantilever deflection is caused by stress generated during the formation of an adsorbate layer on one side of the microcantilever. In this work, rapid adsorption of carboxylic acid in hydrocarbon solvent onto a gold surface was directly observed as a compressive stress developed on the microcantilever substrate. Upon exposure to alkylthiol, acid desorbed and was displaced by alkylthiol; this process was continuously monitored in real-time. Experiments suggest that some film organization and intermolecular interaction are required before substantial surface stress can be detected.
X-Ray Study of Strained and Strain Balanced Superlattice Materials
Authors: Johnson Natee , Choa Ruth , Cheng Liwei , Choa Fow-Sen
Published: April 2011

Nano-scale superlattice (SL) based devices, such as quantum cascade lasers QCLs, have recently become very important due to their capability to identify toxic and explosive chemicals. In manufacturing these Mid-IR photonic devices, atomic-level scanning tunneling microscopes (STM) and transmission electron microscopes (TEM) have been used to characterize the growth quality of superlattice wafers. However, these methods yield observations that are localized and cannot view the entire structure and even now we have not been able to correlate these measured crystal lattice images with device performance. The x-ray scanning technique has greater likelihood of success given that it can observe not only the localized, but also the entire superlattice structure. By extracting special features and key parameters in x-ray diffraction (XRD) patterns, the epitaxial quality of QCL superlattices can be evaluated and correlated to the performance of fabricated QCL devices. We can then differentiate and classify different grades of wafers before starting device fabrication and testing.

Such an example of the usefulness of XRD can be found with strain-balanced superlattices, such as InGaAs/InAlAs, where there is notable decrease in laser performance after relaxation. It can also be found with type-II InAs/GaSb strained layer superlattice, which is currently the best candidate for room temperature mid-IR detectors and focal plane arrays. Experimentally measured x-ray patterns are compared to simulation results and problem sources are identified.
In-situ TEM Observation of Formation-Retraction-Fracture Experiment of Liquid-Like Silicon Nanocontact
Authors: Ishida Tadashi , Kakushima Kuniyuki , Fujita Hiroyuki
Published: April 2011

We have examined the change of mechanical characteristics of silicon nanocontacts with and without the pre-treatment by flowing current through the contact. The silicon nanocontact formed between silicon tips by a mechanical contact was quickly deformed during its tensile test under a transmission electron microscope, after applying over 100 μA at a high bias voltage around 15 V between tips for a short duration. In the tensile experiment, the diameter of the nanocontact easily decreased from the initial diameter of 98 nm to 30 nm and the length increased from 11 nm to 66 nm. At 30 nm in diameter, it was suddenly fractured without further elongation and became round tips with smooth surfaces. According to the close observation, the silicon nanocontact seemed amorphous. In the retraction process of the silicon nanocontact, steps moved along the surface from the neck of the nanocontact to the tip side at the speed of 7.0 nm/s. Nano-scaled round step propagations were repeated from the neck to the tip. The step propagation caused the fast thinning of the nanocontact. On the other hand, the silicon nanocontact formed at 1 V in bias voltage was gradually thinned from 42.5 nm to 1.6 nm in diameter and elongated from 2.9 nm to 61.9 nm in length. From the comparison of silicon nanocontacts with and without the pre-treatment, the silicon nanocontact after flowing substantial current showed quick deformation and had different mechanical characteristics from the silicon nanocontact without the pre-treatment.
Crosslinked Organic/Inorganic Hybrid Proton Exchange Polymeric Membranes
Authors: Di Vona Maria Luisa , Marani Debora , D'Ottavi Cadia , Trombetta Marcella , Traversa Enrico , Beurroies Isabelle , Knauth Philippe , Licoccia Silvia
Published: April 2011

A general, efficient and experimentally simple method for the synthesis of covalently crosslinked class II hybrid polymers based on PolyEtherEtherKetone (PEEK) with a high degree of sulfonation (DS = 0.8) was performed. The synthetic strategy foreseen two steps: the first one, direct sulfonation, led to the introduction of sulfonic acid groups and to the formation of sulfone bridges among repeat units. The second step, lithiation and silylation, led to the formation of covalent bonds between the organic backbone and Si(OH)3 moieties. The materials were characterized by 1H NMR Spectroscopy, ATR/FTIR Spectroscopy, Thermogravimetric Analysis (TGA) and Mass Spectrometry. Preliminary proton conduction measurements in dry conditions were performed. The introduction of silicon groups in the system improved thermal stability.
Preparation of Nano-Sized Doped Ceria for SOFC Anodes
Authors: Kobayashi Jumpei , Takamura Hitoshi , Kamegawa Atsunori , Okada Masuo
Published: April 2011

Nano-particles of Pr and Mn-doped ceria have been prepared by mixing nitrate solutions and hexamethylenetetramine as an oxidizing agent, and their thermal stability has been investigated. The particle size was evaluated by means of XRD, BET and dynamic light scattering techniques. The particle size of Pr and Mn-doped ceria was found to be approximately 3 nm as prepared. Even though the particle size of doped ceria increases with increasing annealing temperature, the size of less than 15 nm was kept after annealing at 873 K for 10 h. On the other hand, the lattice constant of nano-sized ceria, for example 0.544 nm for 3 nm-size particles, decreases and reaches to the value of bulk material (0.541 nm) as annealing temperature increases. This suggests that the valence state of cerium and the amount of oxygen vacancies strongly depend on the particle size.
The DOE National Hydrogen Storage Project: Recent Progress in On-Board Vehicular Hydrogen Storage
Authors: Read Carole , Petrovic John , Ordaz Grace , Satyapal Sunita
Published: April 2011

Hydrogen is under consideration by several countries for its potential as an energy carrier for transportation applications. In order to compete with vehicles in use today, hydrogen-powered vehicles will require a driving range of greater than 300-miles in order to meet customer needs and expectations. For the overall vehicular light-duty fleet, this dictates that a range of 5 to 13 kg of hydrogen be stored on-board (assuming a fuel cell power plant) within stringent system weight, volume, and cost constraints. Vehicular hydrogen storage thus constitutes a major scientific and technological challenge. To meet this challenge, the U.S. Department of Energy (DOE) initiated a “National Hydrogen Storage Project” with roughly 40 universities, 15 companies and 10 federal laboratories, actively engaged in hydrogen storage research. Centers of Excellence in metal hydrides, chemical hydrides, and carbon-based materials have been established, as well as independent university and industry projects in the areas of new concepts/materials, hydrogen storage testing, and storage system analysis. Recent technical progress in each of these areas is discussed.
High Throughput Screening of Complex Hydrides for Hydrogen Storage
Authors: Lewis Gregory , Sachtler J. W. Adriaan , Low John J. , Lesch David A. , Faheem Syed A. , Dosek Paul M. , Knight Lisa M. , Jensen Craig M.
Published: April 2011

The discovery that dopants, such as Ti, cause NaAlH4 to reversibly desorb H2 at mild conditions has spurred a great deal of research into complex metal hydrides. However, no complex hydride meets the targets for automotive hydrogen storage. Our approach is to accelerate the rate of discovery of improved hydrides and dopants through the combination of Virtual High Throughput Screening (VHTS) and Combinatorial Synthesis and Screening (CSS). Our CSS methods will allow us to screen thousands of samples in a year. These samples will be prepared by ball milling mixtures of hydrides and dopants similar to the established method of preparing Ti doped NaAlH4. VHTS exploits a molecular mechanics method to screen a thousand phases in a month. The combination of combinatorial methods and VHTS will help us discover the most promising complex hydrides for hydrogen storage. We will show the results of our medium throughput CSS and VHTS as applied to the NaAlH4–LiAlH4 – Mg(AlH4)2 mixed alanate compositions.
Hydrogen Storage in Carbon Nanoscrolls: A Molecular Dynamics Study
Authors: Coluci Vitor , Braga Scheila F. , Baughman Ray H. , Galvão Douglas S.
Published: April 2011

We carried out molecular dynamics simulations with Tersoff-Brenner potentials in order to investigate the hydrogen uptake mechanisms and storage capacity of carbon nanoscrolls (CNSs). CNSs are jelly roll-like structures formed by wrapping graphene layers. Interlayer adsorption is an option for this material, which does not exist for single and multiwalled carbon nanotubes. We analyzed the processes of hydrogen physisorption and uptake mechanisms. We observed incorporation of hydrogen molecules in both external and internal scroll surfaces. Insertion in the internal cavity and between the scroll layers is responsible for 40% of the total hydrogen adsorption at 77 K.
Corrosion Resistance of TiN Coatings Prepared by Filtered Cathodic Vacuum Arc Process
Authors: Wu Jin-Bao , Tsai Yin-Wen , Shih Chin-Te , Li Mei-Yi , Leu Ming-Sheng , Lai Chiou-Chu
Published: April 2011

For the purpose of developing the corrosion-resistant and low-cost metallic bipolar plates for direct methanol fuel cell (DMFC), Ti mesh, stainless steel and Si(100) were coated with TiN by using the filtered cathodic vacuum arc system (FCVA). These TiN films have received considerable attention because of its high anti-corrosion behavior and low contact-resistance. In order to improve the corrosion protective ability of TiN films and decrease pinholes of coating, growth modifications such as thickness of the coatings and bias applied to substrates have also been carried out. The microstructures and composition of TiN film were identified by the instrumental analyses such as scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The corrosion behavior of TiN coatings was studied in 0.5 M H2SO4 solutions by using potentiodynamic polarization method. The DC bias of −150 V was applied to the substrates to achieve a dense structure of approximately 400 nm coating of TiN, so that good corrosion protection of the Ti mesh and stainless steel substrates can be achieved. The TiN coating on stainless steel exhibited excellent corrosion behavior especially in lower corrosion current than 2×10−7 A/cm2.
Ruthenium-Iridium Oxide Films Prepared by MOCVD and their Electrocatalytic Activity for Oxygen Evolution
Authors: Torres M.Z. Figueroa , Garduño M. Hesiquio , Estrada E. M. Arce , García J. R. Vargas
Published: April 2011

Ruthenium-iridium oxide films were prepared in an horizontal hot-wall MOCVD apparatus and their electrocatalytic activity was investigated in the oxygen evolution reaction. Metal-acetylacetonates were used as precursors and oxygen as the reactant gas. Appropriate deposition conditions for obtaining bi-metallic oxide films were found to be deposition temperature (Tdep), 673 K and total pressure (Ptot), 133.32 Pa. X-Ray diffraction (XRD), Rietveld refinement and scanning electron microscopy (SEM) results demonstrated that the MOCVD method is a viable alternative to grow RuxIr1−xO2 films consisted of a single-phase with a very homogeneous distribution of elements. The electrocatalytic activity of the RuxIr1−xO2 films was investigated by cyclic voltammetry and anodic polarization curves in a 0.5 M H2SO4 solution at room temperature. The single-phase Ru0.4Ir0.6O2 films showed to be very promising for the oxygen evolution reaction due to a synergistic effect.
Properties of Carbon-doped TiO2 (Anatase) Photo-Electrodes
Authors: Enache Cristina S. , Schoonman Joop , van de Krol Roel
Published: April 2011

To enhance the visible light absorption of anatase TiO2 photo-electrodes, the material was doped with carbon by two different methods: i) by spray pyrolysis under a CO2 atmosphere, and ii) by a post-deposition thermal treatment in a hexane-containing environment. For the hexane-treated samples, most of the carbon is located at the surface, from which it can be removed by re-oxidation at elevated temperatures. In addition, both methods seem to result in the presence of small amounts of carbon in the bulk of the material, as deduced from a small red-shift of the absorption edge of TiO2.
New Directions for Nanoscale Thermoelectric Materials Research
Authors: Dresselhaus M. S. , Chen Gang , Tang M. Y. , Yang R. G. , Lee H. , Wang D. Z. , Ren Z. F. , Fleurial J. P. , Gogna P.
Published: April 2011

Many of the recent advances in enhancing the thermoelectric figure of merit are linked to nanoscale phenomena with both bulk samples containing nanoscale constituents and nanoscale materials exhibiting enhanced thermoelectric performance in their own right. Prior theoretical and experimental proof of principle studies on isolated quantum well and quantum wire samples have now evolved into studies on bulk samples containing nanostructured constituents. In this review, nanostructural composites are shown to exhibit nanostructures and properties that show promise for thermoelectric applications. A review of some of the results obtained to date are presented.
New Directions in Bulk Thermoelectric Materials Research: Synthesis of Nanoscale Precursors for “Bulk-Composite” Thermoelectric Materials
Authors: Tritt Terry M. , Zhang Bo , Gothard Nick , He Jian , Ji Xiaohua , Thompson Daniel , Kolis Joe
Published: April 2011

Over a decade ago it was predicted that nano-scaled thermoelectric (TE) materials might have superior properties to that of their bulk counterparts. Subsequently, a significant increase in the figure of merit, ZT (ZT > 2), has been reported for nano-scaled systems such as superlattice and quantum dot systems constituently based on those more commonly used bulk TE materials (e.g., Bi2Te3 and PbTe). However, the challenge remains to achieve these higher performance results in bulk materials in order to more rapidly incorporate them into standard TE devices. Recent theoretical work on boundary scattering of phonons in amorphous materials indicates that micron and submicron grains could be very beneficial in order to lower the lattice thermal conductivity and yet not deteriorate the electron mobility. The focus in this paper will be to highlight some of our new directions in bulk thermoelectric materials research. Thermoelectric materials are inherently difficult to characterize and these difficulties are magnified at high temperatures. Specific materials will be discussed, especially those bulk materials that exhibit favorable properties for potential high temperature power generation capabilities. One potentially fruitful research direction is to explore whether hybrid TE materials possess possible enhanced TE properties. These “engineered” hybrids include materials that exhibit sizes from on the order of a few nanometers to hundreds of nanometers of the initial materials. These initial materials are then incorporated into a bulk structure. A discussion of some of the future research directions that we are pursuing is highlighted, including some bulk materials, which are based on nano-scaled or hybrid composites. The synthesis techniques and the synthesis results of many of these nano-scale precursor materials will be a primary focus of this paper.
Thermoelectric and Thermomagnetic Transport in PbTe with Nanoscale Structures
Authors: Heremans Joseph P.
Published: April 2011

Quantum-dot superlattices (QDSLs) have demonstrated thermoelectric figure of merit (ZT) values double those of classical bulk materials, providing the proof that nanoscale materials can address this age-old limitation on thermoelectric technology. Since QDSL materials can only be obtained in thin-film form, the development of bulk materials with nanoscale inclusions would be useful for many large-scale applications. Nanometer-scale inclusions in lead chalcogenides are known to improve the thermoelectric figure of merit through a combination of two factors: a strong decrease in lattice thermal conductivity, and an increase in the Seebeck coefficient over that of bulk PbTe for a given carrier concentration. This paper focuses on experimental results obtained on two types of PbTe nanocomposites, namely samples prepared by sintering powders with nanometer-sized grains, and samples prepared with nanoprecipitates of metallic Pb. The results are analyzed using the “method of four coefficients.” At each measurement temperature there are four unknowns. These are the carrier concentration, the mobility, the carrier effective mass, and the energy dependence of the relaxation time Tau, which is modeled by a power law: Tau proportional to energy to power Lamda. Therefore, at each temperature, four measurements are taken: the electrical conductivity, and the Hall, Seebeck and transverse Nernst-Ettingshausen coefficients. This analysis concludes that the effect of the nanoscale inclusions on the power factor is due to an increase in the scattering parameter λ, and that the nanoscale inclusions affect the electron scattering in such a way as to increase the Seebeck coefficient.
Nanostructuring and its Influence on the Thermoelectric Properties of the AgSbTe2-SnTe Quaternary System
Authors: Androulakis Ioannis , Pcionek R. , Quarez E. , Palchik O. , Kong H. , Uher C. , Dangelo J. J. , Hogan T. , Tang X. , Tritt T. , Kanatzidis Mercouri
Published: April 2011

The structural and thermoelectric properties of the AgSbTe2-SnTe quaternary system were studied. Powder averaged x-ray diffraction of Ag0.85SnSb1.15Te3 indicates a cubic NaCl-type structure in contrast with the single crystal refinements, which point towards tetragonal symmetry. Furthermore, high-resolution electron microscopy imaging revealed the system to be a nano-composite formed by thermodynamically driven compositional fluctuations rather than a solid solution as it was viewed in the past. The lattice thermal conductivity attains very low values, which is in accord with recent theories on thermal transport in heterogeneous systems. The charge transport properties of the system exhibit a rich physical behavior highlighted in the coexistence of an almost metallic carrier concentration (∼5×1021 cm−3) with a large thermoelectric power response of ∼160 μV/K at 650 K. This is attributed to a heavy hole effective mass that is almost six times that of the electron rest mass.
Design of Heterostructures for High Efficiency Thermionic Emission
Authors: Bian Zhixi , Shakouri Ali
Published: April 2011

We use two heterostructure designs to improve the energy conversion efficiency of solid-state thermionic devices. The first method is to use a non-planar heterostructure with roughness in order of electron mean free path. This has some combined benefits of increased effective interface area, and reduced total internal reflection for the electron trajectories arriving at the interface. Monte Carlo simulations of various geometries show that the electrical conductivity and thermoelectric figure of merit can be improved for non-planar barrier compared to the planar counterpart. The second method is to use planar high barrier heterostructures with different effective masses for charge carriers in emitter and barrier regions. When an electron passes from a lower effective mass emitter and arrives at a barrier with higher effective mass, since both the lateral momentum and total energy are conserved, part of the lateral energy is coupled to the vertical direction and the electron gains momentum in the direction perpendicular to the interface to enter the barrier region. For high potential barriers, the improvement of thermionic current is about the same as the ratio of the effective masses of the two materials, which can be a factor of 5-10 for typical heterostructure material systems.
Characterization of Thermoelectric Power Generation Modules Made from New Materials
Authors: Short Jarrod L. , D'Angelo Jonathan , Downey Adam D. , Pajor Michael A. , Timm Ed , Schock Harold , Kanatzidis Mercouri G. , Hogan Timothy P.
Published: April 2011

Lead-Antimony-Silver-Tellurium (L-A-S-T) materials, synthesized at Michigan State University, show promising thermoelectric properties at high temperatures for use in power generation applications. Recent scaled-up quantities of L-A-S-T show a ZT=1.4 at 700 K approaching the figure of merit for samples made in small quantities. These materials are of great interest for power generation applications with hot side temperatures in the range of 600-800 K. Developing these materials into working devices requires minimization of the thermal and electrical parasitic contact resistances, so various fabrication methods are under investigation. To examine each method, a new measurement system has been developed to characterize these devices under various load and temperature gradients. An introduction to the system will be presented, as well as results for devices made of the L-A-S-T materials.
Study on the Filling Fraction Limit of Impurities in CoSb3
Authors: Shi X. , Zhang Wenqing , Chen Lidong , Yang Jihui
Published: April 2011

Complex crystals such as skutterudites have interstitial voids in the lattice that can be filled by various impurity atoms. The filling fraction limit (FFL) for the intrinsic voids in the lattice of CoSb3 is studied by density functional methods. The FFL is shown to be determined not only by the interaction between the impurity and host atoms but also by the formation of secondary phases between the impurity atoms and one of the host atoms. A model is proposed to quantitatively explain the phenomenon. The predicted FFLs for Ca, Sr, Ba, La, Ce, and Yb in CoSb3 are in excellent agreement with reported experimental data. Detailed analysis reveals the existence of a quantitative relationship between the repulsive interaction of impurity atoms and their charge state. A correlation between the FFL of an impurity atom and its charge state and electronegativity is discovered.
Synthesis and thermoelectric power factor of LSCO perovskites
Authors: Rodriguez Julio E.
Published: April 2011

Measurements of Seebeck coefficient, S(T) and electrical resistivity, ρ(T) on polycrystalline La2−xSrxCuO4+d(LSCO) (0<x≤0.2) samples are reported. The Seebeck coefficient is positive in whole measured temperature range (77K and 300K) and it decreases with Sr content. At room temperature S(T) changes from 400 μ/K for the samples with the lowest levels of Sr to 30 μV/K for the samples with the highest Sr levels. The behavior of S(T) fits to Heikes model, which describes the behavior of Seebeck coefficient in systems where the correlated hopping is present. With the Sr content, the electrical resistivity changes its behavior from semiconducting to metallic and it took values from 2.4 to 10−3Ωcm. From S(T) and rho(T) measurements the thermoelectric power factor, PF was obtained. The maximum values for PF were about 5 μW/K2cm in the samples where x= 0.03, which are comparable to the typical values for conventional thermoelectric semiconductors. The structural and morphological properties of the samples were studied by x-ray diffraction analysis and Scanning Electron Microscopy (SEM) respectively. The behavior of transport properties opens de possibility of considering this family of perovskite-compounds as a thermoelectric material which works below room temperature.
Progress on the Fabrication and Characterization of High Efficiency Thermoelectric Generators
Authors: Hogan Timothy P. , Downey Adam D. , Short Jarrod , D'Angelo Jonathan J. , Quarez Eric , Androulakis John , Poudeu Pierre F. P. , Kanatzidis Mercouri G. , Timm Ed , Sarbo Kim , Schock Harold
Published: April 2011

High efficiency thermoelectric modules are of great interest for power generation applications where hot side temperatures of approximately 800K exist. The fabrication of such modules requires a multidisciplinary effort for the optimization of the material compositions, the engineering of the module systems, modeling and fabrication of the devices, and constant feedback from characterization. Pb-Sb-Ag-Te (LAST) and Pb-Sb-Ag-Sn-Te (LASTT) compounds are among the best known materials for this temperature range. Modeling of these materials and possible cascaded structures shows efficiencies of 14% can be achieved for low resistance contacts. Using antimony we have achieved contact resistivities less than 20 µΩ·cm2. Here we give a detailed presentation on the procedures used in the fabrication of thermoelectric generators based on these new materials. We also present the characterization systems and measurements on these generators.
Electron work function at grain boundary and the corrosion behavior of nanocrystalline metallic materials
Authors: Li D. Y.
Published: April 2011

Due to their high grain boundary density, nanocrystalline materials possess unusual mechanical, physical and chemical properties. Extensive research on nanocrystalline materials has been conducted in recent years. Many studies have shown that corrosion, one of important properties of nanocrystalline materials, is crucial to their applications. In this article, the activity of electrons at grain boundaries of metallic surfaces is analyzed based the electron work function (EWF), the minimum energy required to attract electrons from inside a metal. It is demonstrated that at grain boundaries, the electron work function decreases, indicating that at a grain boundary, electrons are more active. As a result, the surface becomes more electrochemically reactive. Such increase in electrochemical reactivity has negative effect on the corrosion resistance of nanocrystalline materials. However, for a passive nanocrystalline metal or alloy, the nanocrystalline structure is beneficial to its corrosion resistance through rapid formation of a protective passive film. The mechanisms responsible for the variation in EWF at grain boundary and effects of nanocrystallization on corrosion are discussed in this article.
Statistical Mechanics: Undamaged ⇐-radiation-⇒ Damaged Atomic Lattice Density Evolution and Stochastic Deformation Functional
Authors: Stout Ray B. , Stout Natasha K.
Published: April 2011

The deformation kinematics for radiation damage response of bulk materials is presently semi-empirical and phenomenological based on a continuum mechanics supposition: there exists a function space of continuous functions to describe material displacement, strain, strain-rate metrics by using the mathematics of differential calculus. Existing data being assembled from tests on nano-length-scale(NLS) samples provide objective evidence that the continuum mechanics supposition is not an adequate generic mathematical description for radiation damage response in surface-dominated material structures at NLS. An alternative approach will be described that uses concepts and methods from classical statistical mechanics and describe deformation kinematics as a stochastic accumulation of discrete damage events at atomic lattice nano-length-scales. Although radiation damage deformation at a lattice length-scale in solids is mechanistically different from velocity scattering developed by Boltzmann for a kinetic theory of gases, the two problem areas are technically similar and in some simply cases there are useful mathematical analogs. The technical similarities and mathematical analogs will be used to define probability density functions (number per unit volume functions) for undamaged and damaged “size and size change” lattice species (similarity to a probability density function for atomic velocities in gas theory). In general, equations for undamaged and damaged lattice density function evolution are Boltzmann-type equations, which can be approximated and solved for simple cases of radiation induced material damage. Using a path integral approach and the two probability density functions, a stochastic functional will be derived for the relative deformation between any two arbitrary spatial points in a radiation damaged material. Given the relative deformation as an explicit functional of the undamaged and damaged lattice density functions, the kinematics metrics of relative velocity, strain, strain rate, etc., will also be functionals. In the case of radiation damage and annealing, the two lattice density functions are analog expressions to those commonly used to model “birth and death” population evolution.
Radiation Degradation of Nanomaterials
Authors: Raffaelle Ryne , Cress Cory D. , Wilt David M. , Bailey Sheila G.
Published: April 2011

We have been developing a variety of nanomaterials for their use in power devices. An example of this is our use of both single wall carbon nanotubes and several varieties of semiconducting quantum dots (e.g., CuInS2, CdSe, InAs) for use in space solar cells. The ability of these materials to withstand the rigors of the space radiation environment will be essential for this intended application. In addition, we have also been developing both nanostructure III-V devices and radioluminescent quantum dots for use in radioisotope batteries. In this application these nanomaterials are subjected to an extremely high radiation level. Their degradation rate will be the key to determining the ultimate lifetime of these power supplies, which in principle can have an energy density that is orders of magnitude higher than any conventional battery chemistry. The nanomaterials included in this study were subjected to alpha particles fluences and the degradation in various properties were monitored using different analytical techniques. Specifically, the radioluminescence of the quantum dot intended for use in the radioisotope batteries was monitored as a function of fluence. In the case of the III-V quantum dots, their photoluminescent degradation as a function of fluence was measured in comparison to the bulk substrate on which the quantum dots were grown. Finally for the carbon nanotubes, relative intensities of the Raman peaks associated with their inherent vibrational modes was used to monitor the effects of the alpha radiation damage. Results on the radiation tolerance of these nanomaterials and its implication with regard to their ultimately utility in power devices are presented.
Degradation of Nano-crystalline ITO Films due to Exposure to Hyperthermal Atomic Oxygen
Authors: Li Long , Harder Ross , Xu Fengting , Robinson Ian K. , Yang Judith C.
Published: April 2011

Indium tin oxide (ITO) films coated on float glass slides were exposed to 5 eV hyperthermal atomic oxygen at room temperature with increasing fluences: 2×1019, 6×1019 and 2×1020 O-atoms/cm2. We characterized the structure of the ITO films after room temperature atomic oxygen exposure with scanning electron microscope (SEM) and atomic force microscope (AFM), synchrotron X-ray diffraction (XRD), and cross-sectional transmission electron microscope (X-TEM). The unexposed ITO films were found to possess a nano-crystalline surface, and clean and abrupt ITO/SiO2 interfaces without interfacial phase. Surface roughness of the exposed ITO films increased with the increasing AO influences. The interface- sensitive peaks in XRD measurements with grazing incidence revealed that the crystallinity of the ITO was modified near the interface. Cross-sectional TEM confirmed that many ITO particles with diameters ranging from 2-10 nm formed in the SiO2 substrate near the interface after AO exposure. These findings suggest that O atoms can travel through the ITO films, where the boundaries of columnar-grown grains may supply the pathway.
Self-Lubrication of Machining Tools in Dry via In-situ Formed Tribofilms
Authors: Aizawa Tatsuhiko , Yamamoto Shigeo , Sumitomo Taro
Published: April 2011

Green manufacturing technology has become a significant innovative keyword to reduce the environmental burden and CO2 emission at the stage of manufacturing and production. In daily operations by machining, huge amount of lubricating oils and cleansing agents is wasted so that dry machining technology provides us a way to completely reduce these wastes. Among several candidates, self-lubrication via in-situ formation of lubricious oxide films is accommodated to protective coatings in order to attain low friction and wear state even at higher cutting speed range. Materials science of in-situ formed lubricious oxide tribofilms is stated with consideration of accommodation mechanism via the chlorine implantation. Mechanical characterization is made for evaluation on elasto-plastic deformation of lubricious oxides. Turning test is employed to evaluate dry machinability of various tools for wide range of cutting speed. Self-lubrication in dry machining is described both for bare WC and TiCN-coated WC tools with and without chlorine implantation. Precise microstructure analyses are made by using the laser microscope, EDS and XPS. In-situ formation of lubricous oxides proves that self-lubrication process takes place even in dry machining to reduce the flank wear and friction coefficient.
Deposition of Adherent Diamond Coatings on WC-Co Substrates
Authors: Xu Zhenqing , Lev Leonid , Lukitsch Michael , Kumar Ashok
Published: April 2011

High quality well-adhered microcrystalline diamond coatings have been produced by the microwave plasma enhanced chemical vapor deposition (MPECVD) technique on cemented carbide substrates. A multi-interlayer system Cr/CrN/Cr was deposited on the WC-Co substrate before diamond deposition to work as a diffusion barrier. The coated substrate was peened with friable diamond powder to roughen the surface resulting in high nucleation density. Adherent diamond film has been successfully deposited on the substrate at temperature around 700°C with 1.0 % CH4 in Hydrogen plasma. The surface morphology and film structure has been studied by Scanning Electron Microscopy (SEM) and X-Ray diffraction technique. The adhesion of the diamond film has been evaluated by Rockwell indentation tests.
Development of Multilayer TiAlN + γ–Al2O3 Coatings for Difficult Machining Operations
Authors: Bobzin K. , Lugscheider Erich , Knotek O. , Maes Michel , Immich Philipp , Piñero Carmen
Published: April 2011

The continuous advances in the aircraft and nuclear industry demand the development of new materials that among other properties offer a good resistance at elevated temperatures. For this reason, Ni super alloys were developed from a simple Ni-Cr matrix to multi-element, multi-phase systems. These new super alloys are specially favored for their exceptional thermal resistance and ability to retain mechanical properties at elevated temperatures. They are classified as difficult-to-machine materials due to their high shear strength, work hardening tendency, content of abrasive carbide particles within the microstructure, strong tendency to weld and to form built-up edges. Their low thermal conductivity leads to elevated temperatures during machining. Consequently, their tendency to maintain a high strength at elevated temperatures leads to elevated cutting forces. On this account, the development of an adequate coating for machining Ni alloys is today an important challenge. Nowadays, TiAlN is well known because of its excellent overall cutting performance. However, Al2O3 possesses better chemical and thermal properties than TiAlN, especially regarding hot hardness, oxidation resistance, diffusion resistance. Motivated by the advantages offered by PVD-Technology, γ-Al2O3 was synthesized by reactive bipolar pulsed magnetron sputtering in previous works. PVD-Processes allow the deposition of insulating coatings such as alumina at reduced temperatures, which implies a lower substrate thermal load. At the same time using PVD-Technology it is possible to produce high compressive stresses in the coatings (high alternating thermal stress resistance), keep sharp cutting edges, synthesize pure structures and deposit various coating combinations such as multilayer multilayer TiAlN + γ-Al2O3. Therefore, a PVD-multilayer coating TiAlN + γ-Al2O3 is very promising for machining of Ni alloys such as Inconel 718. However, due to the very different characteristics of the nitrides and oxides, particularly the good coating cohesion of this coating concept constitutes a challenge. In this work different multilayer combinations were deposited on cemented carbide cutting inserts. In order to improve the adhesion between the nitride and oxide layers and consequently the coating cohesion, a special gradation was developed. The reactive gas flows (N2 and O2) was gradually changed during the coating deposition. The result was a soft gradation consisting of different nitrides and oxides species synthesized in very thin layers. Tribological tests demonstrated that the developed soft gradation offers an important improvement of the coating cohesion and fatigue resistance. For the evaluation of the coating adhesion and cohesion calo-, Rockwell- and scratch-tests were carried out. Mechanical properties were investigated by impact.
Metal micromolding with surface engineered inserts
Authors: Cao Dongmei , Jiang J. , Meng W. J.
Published: April 2011

The LiGA (Lithographie, Galvanoformung, Abformung) technique is a leading micromanufacturing process for making polymer- and metal- based high-aspect-ratio microscale structures. Molding replication is the key LiGA step for economical mass production of metal-based HARMS. Using a hybrid technique, we have fabricated microscale Ta mold inserts. Surface engineering of Ta inserts by electrochemical polishing followed by conformal coating deposition has enabled successful high-temperature micromolding of Al and Cu. In this paper, the molding performance of Ta inserts coated with amorphous hydrogenated carbon based coatings and amorphous silicon nitride based coatings is compared. Issues of maximum molding force, demolding force, and coating durability are addressed.