bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis of luminescent nanoparticle embedded polymer nanocomposites for scintillation applications
Authors: Rogers Thomas , Han Chenlu , Wagner Brent , Nadler Jason , Kang Zhitao
Published: April 2011

Detecting gamma-ray emission from radionuclides hidden within containers is a significant concern to national security and can be accomplished with scintillating materials such as NaI:Tl, LaBr3:Ce crystals. However, the use of these high quality crystals limits the functionality of the detectors due to their high cost and scalability issues. Therefore the development of more durable, more easily manufactured, and more cost effective scintillating materials is desired. The incorporation of nanophosphors or Quantum Dots (QDs) into a polymer matrix to produce a transparent nanocomposite could potentially provide an alternative method to fabricate scintillating detectors. Embedded in a suitable polymer matrix, nanocomposite detectors may be easily made suitably large for portal monitors. Also, preparation of suitable particle sizes and/or compositions permits selection of a photon wavelength that optimally matches the photodetector response curve to increase the number of photons collected per pulse. In this paper a series of LaF3:Ce nanophosphors with varying doping concentrations (1–30mol%Ce) were synthesized using a chemical precipitation method. Photoluminescence and photoluminescence excitation characterizations indicated that the highest luminescent intensity was obtained from the 20%Ce doped sample with a peak emission at 325 nm. The refractive indices of the nanoparticles were identified by index matching measurements. Then an index matched epoxy was selected for incorporation of these nanoparticles to prepare transparent nanocomposite scintillators. In addition, colloidal solutions of CdTe QDs with various emitting colors were synthesized and incorporated into a Polymethyl-methacrylate (PMMA) matrix to make transparent nanocomposites. An initial evaluation of the scintillation behavior of these nanocomposites was evaluated by exposure to gamma rays.
Depth sensing indentation of nanoscale graphene platelets in nanocomposite thin films
Authors: Zandiatashbar Ardavan , Picu Catalin R. , Koratkar Nikhil
Published: April 2011

Significant improvement of mechanical properties was observed recently in graphene platelet-epoxy nanocomposites relative to unfilled epoxy, such as an increase of the fracture toughness by 50% and dramatic decrease of fatigue crack growth rate. In this work, thin films of 0.1 wt.% of graphene platelet (GPL) – epoxy nanocomposites were fabricated and the nanoscale mechanical properties of the nanocomposite were investigated by nanoindentation. This provides information about the presence of characteristic length scales induced by the microstructure and the strength of the filler-matrix interface.
Inorganic-Organic Hybrid Copolymers derived from Silsesquioxanes or Carborane Building Blocks
Authors: Gadodia Gunjan , Cardoen Gregoire , Simon Yoan , Abe Hiroshi , Coughlin E. Bryan
Published: April 2011

To explore competitive or cooperative effects novel organic-inorganic hybrid copolymers are being prepared and studied. The use of polyhedral oligomeric silsesquioxanes (POSS), a molecularly precise isotropic comonomer, is being utilized to take advantage of the inherent size scale of these particles, average diameters of 1-2 nm. The organic component selected for study in these hybrid systems are either semi-crystalline or amorphous polymers. The architectures of the hybrid copolymers range from random, to precise block copolymers, as well as telechelic and hemi-telechelic end-functionalized model compounds. The degree of POSS aggregation that occurs is found to be a function of thermal history, and processing conditions. Templating, or arresting, aggregation can be achieved using either crystalline organic polymer scaffolds in the bulk. The second inorganic comonomers for study has been constructed from icosahedral carboranes. Dicarbo-closo-decaboranes have been widely investigated for their thermal stability, chemical resistance, unique geometry, and the high cross-section for the capture of thermal neutrons. While carboranes have been widely incorporated into small molecules, metal complexes, and on a limited basis in polymer systems relatively little work exists relating their unique properties to systems with extended π-conjugation. Details of the syntheses, characterization and performance properties of both sets of hybrid systems will be discussed.
Atomic force microscopy based quantitative mapping of elastic moduli in phase separated polyurethanes and silica reinforced rubbers across the length scales
Authors: Schön Peter , Bagdi Kristóf , Molnár Kinga , Markus Patrick , Dutta Saurabh , Shirazi Morteza , Noordermeer Jacques , Pukánszky Béla , Vancso G. Julius
Published: April 2011

In the work presented here atomic force microscopy (AFM) based mechanical mapping techniques - HarmoniX imaging and Peak Force Tapping - were applied to determine the surface elastic modulus of phase separated polyurethanes and silica reinforced rubbers across the length scales. Segmented polyether polyurethanes (PUs) were prepared with varying stoichiometric ratio of the isocyanate and hydroxyl groups. The effect of molar mass, as well as the type and number of end-groups on their morphology was investigated. Smooth PU samples for AFM imaging were prepared by ultramicrotonomy. The micro phase separated morphology of the phase separated PUs showed characteristic “fingerprint” AFM phase images. Surface modulus values obtained by AFM were compared to bulk modulus values obtained by tensile testing. The moduli were mapped quantitatively with nanoscale resolution and were in excellent agreement for both AFM modes. Surface mean moduli values do not coincide with bulk values obtained via tensile testing which is attributed to fundamentally different averaging procedures and effects that lead to the respective modulus values obtained via surface and volume averaging. EPDM and SBR rubbers and rubber blends thereof were prepared with varying concentrations of silica nanoparticles and studied in order to investigate the effect of different composition on the resulting morphology (filler distribution) and elastic moduli on a specific rubber or rubber blend sample. Elastic moduli of the rubber and rubber blend samples were first measured by bulk tensile testing. The morphology of the rubber samples was visualized by height and phase imaging. Surface elastic moduli of silica reinforced rubbers and rubber blends were mapped quantitatively and compared with bulk tensile test results. AFM allowed the determination of modulus distributions at the sections imaged. As potential reasons for the observed differences between bulk and surface modulus different averaging procedures like surface and bulk averaging of AFM vs. tensile testing, different filler distributions in SBR and EPDM and the AFM modulus calibration procedures can be named.
Thermal and Mechanical Characterization of Jute-Biopol Nanophased Green Composites
Authors: Hossain Mohammad K , Dewan Mohammad W , Hosur Mahesh , Jeelani Shaik
Published: April 2011

Surface modification of jute fibers was accomplished by performing chemical treatments including detergent washing, dewaxing, alkali, and acetic acid treatment. Morphology of modified surfaces examined using scanning electron microscopy (SEM) revealed improved surfaces for better adhesion with matrix. Better thermal performance of treated fibers was found from thermogravimetric analysis (TGA). Enhanced tensile properties of treated fibers were obtained from tensile tests. Using solution intercalation technique and magnetic stirring, 2%, 3%, and 4% by weight Montmorillonite K10 nanoclay were dispersed into a biodegradable polymer, Biopol. Thermal performance of nanoclay infused Biopol characterized using dynamic scanning calorimetry (DSC) showed improved degree of crystallinity by 7%. Jute fiber reinforced Biopol biocomposites with and without nanoclay were manufactured using treated and untreated jute fibers by compression molding process. Thermal and mechanical responses of treated fiber reinforced Biopol composites (TJBC) without nanoclay evaluated using dynamic mechanical analysis (DMA) and flexure tests showed 9% and 12% increase in storage modulus and flexure strength, respectively, compared to untreated jute fiber reinforced composites (UTJBC). The respective values were 100% and 35% for 4% nanoclay infused TJBC compared to UTJBC without nanoclay.
Study ITO@PMMA Composites by Transmission Electron Microscopy
Authors: Arlindo Elen P. S. , Orlandi Marcelo O.
Published: April 2011

ITO nanowires were synthesized by carbothermal reduction process, using a co-evaporation method, and have controlled size, shape, and chemical composition. The electrical measurements of nanowires showed they have a resistance of about 102 Ω. In order to produce nanocomposites films, nanowires were dispersed in toluene using an ultrasonic cleaner, so the PMMA polymer was added, and the system was kept under agitation up to obtain a clear suspension. The PMMA polymer was filled with 1, 2, 5 and 10 % in weight of nanowires, and the films were done by tape casting. The results showed that the electrical resistance of nanocomposites changed by over 7 orders of magnitude by increasing the amount of filler, and using 5 wt% of filler the composite resistance decreased from 1010 Ω to about 104 Ω, which means that percolation threshold of wires occurred at this concentration. This is an interesting result once for nanocomposites filled with ITO nanoparticles is necessary about 18% in weight to obtain percolation. The addition of filler up to 10 wt% decreased the resistance of the composite to 103 Ω, which is a value close to the resistance of wires. The composites were also analyzed by transmission electron microscopy (TEM), and the TEM results are in agreement with the electrical ones about percolation of nanowires. These results are promising once indicates that is possible to produce conductive and transparent in the visible range films by the addition of ITO nanowires in a polymeric matrix using a simple route.
Low Temperature Phase Diagram of NH3BH3
Authors: Sundqvist Bertil , Andersson Ove , Quwar Issam , Talyzin Alexandr
Published: April 2011

The pressure-temperature (p-T) phase diagram of NH3BH3 has been investigated by thermal conductivity measurements up to 1.5 GPa at temperatures between 100 and 300 K, and the phase boundaries between the three known structural phases have been identified. The transformation between the room temperature tetragonal I4mm phase and the low temperature orthorhombic Pmn21 phase (Tc = 218 K at p = 0) shows only a small hysteresis. The transformation into the high pressure orthorhombic Cmc21 phase (at 1.0 GPa near 292 K) has a very strong hysteresis, up to Δp = 0.5 GPa, and below 230 K a fraction of this phase is metastable even at atmospheric pressure.
Optical Coating by Hybrid Sol
Authors: Wang Wei-Hong , Chen Lih-Yue
Published: April 2011

The fluorocarbon/SiO2 hybrid sol (L) for low refractive index coating was made by tetraethoxysilane (TEOS) and polytetrafluoroethylether derivative(PTFEED) with the hydrolysis and condensation in ethanol to get with coating refractive index as (nL=1.38). It can be coated on glass with single layer by quarter wave, the anti-reflective (AR) coating glass would have less than 3 % reflection. The TiO2 hybrid sol are prepared by tetraisopropyl orthotitanate(TPOT) with silane coupling agent and acrylic resin. The TiO2 hybrid sol with the coating refractive index (nH=1.75) used as high refraction coating sol (H). More acrylic resin added to get less coating refractive index (nM=1.65) used as middle refractive coating sol (M). Three layers AR coating glass can be made by M/H/L design to get 1.0 % reflection, have 3H hardness, 500g scratch resistance, and 107° water contact angle. These two kinds AR coating with fluorocarbon /SiO2 hybrid sol (L) coating on surface has anti-stain efficacy, which can be applied on the touch panel screen of flat panel display for mobile phone, PDA and e-book.
PS-TiO2 Nanocomposites: Thermal Investigations
Authors: Villegas Rafael , Zhai Yun , Xu Hailan , Chipara Dorina Magdalena , Hui David , Lozano Karen , Chipara Mircea
Published: April 2011

Nanocomposites of polystyrene loaded with various amounts of anatase (ranging between 0 % wt. and 20 % wt.) have been synthesized and investigated by thermal analysis. The research was focused on the simulation of Thermogravimetric Analysis data, aiming to a refined understanding of the interactions between of polystyrene and TiO2 nanoparticles. The dependence of the first derivative of residual mass on temperature has been used to determine more accurately the temperature at which the mass loss is maxim. Several functions have been used to simulate the dependence of the first derivative of mass loss on the temperature of the sample. The highest correlation coefficient was obtained for the asymmetric Gaussian combination, which connects two halves of a Gaussian line with different linewidth. An increase of the thermal stability of the polymeric matrix upon loading with TiO2 is reported.
Plasma Treatment of Titanium Dioxide Nanoparticle Layer for Improving Performance of Dye-sensitized Solar Cell
Authors: Kitamura Miho , Shimada Yuya , Kawabata Ryoto , Kasamatsu Toshimichi , Tokunaga Yoshiaki , Aizawa Koji
Published: April 2011

Performance on dye-sensitized solar cells (DSCs) using a titanium dioxide nanoparticle layer treated by tetrafluoromethane gas plasma was investigated through electrical properties under illumination. A 50%-increase of maximum power density was observed in the plasmatreated DSCs when RF power and processing time are 1W and 100s, respectively. We also obtain diode factor between 1 and 2 in the fabricated DSCs from a plot of short-circuit current versus open-circuit voltage and then the calculated current density-voltage curve was good agreement with the experimental data.
Thickness effect of sputtered ZnO seed layer on the fabrication of ZnO nanorods on flexible polyimide films and their ethanol gas sensing properties
Authors: Ahn Hosang , Kim Seon-Bae , Kim Dong-Joo
Published: April 2011

Controlled ZnO nanostructures were grown on a flexible substrate for the future development of smart sensing tags. Thermolysis-assisted chemical solution deposition was used to grow ZnO nanorods at 85°C from 0.01mol of Zinc nitrate hexahydrate and HMT (Hexamethyltetramine) solution. To promote and modulate the ZnO nanorods, R.F. sputtered ZnO seed layers were deposited on polyimide substrates at various film thicknesses in the range of 8 to 160 nm. The optimum processing conditions to fabricate ZnO nanostructures have been investigated to examine the growth behaviors and to correlate the process parameters with the morphological characteristics. When the ethanol gas sensitivities were measured at different thickness of ZnO seed layers before growing ZnO nanorods, the highest sensitivity was obtained at 40 nm thick ZnO film at 300°C where the film thickness is similar to the Debye length. When ZnO nanorods were grown on such a ZnO seed layer, the sensitivities were more heavily influenced by the ZnO nanostructures rather than the thickness of the seed layer probably due to the dominant proportion of carrier density involved with the gas absorption.
Nano-Flower MnO2 Coated Graphene Composite Electrodes for Energy Storage Devices
Authors: Cheng Qian , Tang Jie , Ma Jun , Zhang Han , Shinya Norio , Qin Lu-Chang
Published: April 2011

Graphene, two-dimensional layers of sp2-bonded carbon, has many unique properties. In this paper, graphene is decorated with flower-like MnO2 nanostructures for the application in energy storage devices. The as-prepared graphene and MnO2 nano-flowers, which were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), were assembled into an asymmetric supercapacitor. The specific capacitance of the graphene electrode reached 245 F/g at a charging current of 1 mA. The MnO2 nano-flowers which consisted of tiny rods with a diameter of less than 10 nm were coated onto the graphene electrodes by electrodeposition. The specific capacitance after the MnO2 deposition is 328 F/g at the charging current of 1 mA with an energy density of 11.4Wh/kg and power density of 25.8 kW/kg. This work suggests that our graphene-based electrodes can be a promising candidate for high-performance energy storage devices.
Electronic Structures of Non-Pt Carbon Alloy Catalysts for Polymer Electrolyte Membrane Fuel Cells Revealed by Synchrotron Radiation Analyses
Authors: Oshima Masaharu , Niwa Hideharu , Saito Makoto , Kobayashi Masaki. , Horiba Koji , Harada Yoshihisa , Terakura Kiyoyuki , Ikeda Takashi , Ozaki Jun-ichi , Nabae Yuta , Miyata Seizo
Published: April 2011

The oxygen reduction reaction (ORR) mechanism of non-Pt catalysts was elucidated by investigating electronic structures of carbon alloy catalysts (CACs) for polymer electrolyte membrane fuel cells (PEMFC). For metal phthalocyanine-based carbon alloy catalysts with 1-2% of nitrogen and less than 0.1% of Co or Fe, photoelectron spectroscopy, X-ray absorption spectroscopy (XAS), and X-ray Absorption Fine Structure (XAFS) have revealed that Co or Fe metal sites are not the ORR active site, whereas the carbon atoms adjacent to graphitic nitrogens at a zigzag edge of graphite may act as the ORR active site, which is in good agreement with first principles calculations. These studies have also revealed that the zigzag edges, detected as a XAS shoulder component, are well evolved for catalysts pyrolyzed at 600°C, which show the maximum ORR activity. Based on these analyses, we have realized significantly improved carbon alloy based ORR performance, up to about 70 % of that with Pt catalysts. Further, to analyze the electronic structure of CACs during operation, we constructed a new in situ soft X-ray emission spectroscopy system with very high energy resolution (ΔE) of 120 meV at 640 eV at the University of Tokyo beamline BL07LSU in SPring-8.
Electrical and photoelectrical measurements on ZnO-Nanowires coated with PEDOT:PSS for Dye-Sensitized Solar Cells
Authors: Waltermann Julia , Günther Kay-Michael , Kontermann Stefan , Waldvogel Siegfried R. , Schade Wolfgang
Published: April 2011

Dye-sensitized solar cells composed of an n-doped ZnO nanowire array and a p-doped polymer layer appears to be a promising candidate for low-cost production of environment-friendly solar cells. In this work, we investigate hybrid devices consisting of a transparent conducting oxide (TCO) substrate, ZnO-nanowires (ZnO-NW) or a sol-gel prepared ZnO layer, a ruthenium dye (N719) and a PEDOT:PSS or P3HT layer. The dense polycrystalline ZnO layer is able to prevent short circuits, which have a strong effect on the performance of the solar cells. This is demonstrated by the use of only the ZnO layer which improves the open circuit voltage by a factor of 2 and the efficiency by a factor of 1.7 compared to cells with nanowires. That indicates that the system combined with a thin but dense ZnO layer and NW grown on it will show further improvement. Furthermore three different TCO substrates were investigated. Impedance spectroscopy (IS) reveals at least one additional Schottky barrier formed with ZnO:Al substrates. Spectral photovoltage measurements clearly show distinct absorption features correlated with the ZnO and N719 dye.
SYNTHESIS OF CNT-METAL OXIDE NANO-COMPOSITE ELECTRODE MATERIALS FOR SUPERCAPACITATOR BY LOW-PRESSURE MOCVD
Authors: Arod Pallavi , Shivashankar S.A.
Published: April 2011

Homogeneous composite thin films of Fe2O3-carbon nanotube were synthesized in a novel, single-step process by metalorganic chemical vapor deposition (MOCVD) using ferric acetyl acetonate as precursor. The deposition of composite takes place in a narrow range of CVD conditions, beyond which the deposition either multiwall carbon nanotubes (MWNTs) only or hematite (α-Fe2O3) only takes place. The composite film formed on stainless steel substrates were tested for their supercapacitive properties in various aqueous electrolytes.
Polypyrrole Nanowire Array with High Aspect Ratio Fabricated by Block-Copolymer-Templated Electropolymerization
Authors: Komiyama Hideaki , Iyoda Tomokazu , Kamata Kaori
Published: April 2011

Conducting polypyrrole (PPy) nanowire array was electrochemically fabricated by using microphase-separated block copolymer (PEOm-b-PMA(Az)n) thin film as an electrode template. Electropolymerization proceeds selectively through the perpendiculary oriented PEO nanocylindrical microdomains on an ITO electrode coated by the above polymer film. The length of the PPy nanowires was controllable in range of 10-120 nm by the thickness of the coated template film and the amount of passed charge. A 10 nm of diameter, 27 nm of periodicity, and 12 of aspect ratio of the crystalline PPy nanowires were successfully achieved. Selective removal of the template is also achieved simply by rinsing with solubility-controlled mixed solvent.
Nanostructure Dependent Surface Energy of Silica Nanorod Arrays through Block Copolymer Templating Processes
Authors: Zhao Yongbin , Chen Aihua , Iyoda Tomokazu
Published: April 2011

The self-assembled block copolymer films with poly (ethylene oxide) (PEO) and hydrophobic polymetharylate (PMA) with azobenzene mesogen in the side chain, denoted as PEOm-b-PMA(Az)n, were used as the template to prepare hexagonally ordered silica nanorod arrays by immersing the template films in the silicate precursor containing tetraetoxysilane (TEOS). The diameter and the center-to-center distance of the SiO2 nanorod arrays were controlled by selecting the block copolymer with different PEO volume fraction. In addition, the contact angles of different kinds’ solvents for the SiO2 nanorod arrays were characterized. We further found, the diameter and the period distance of silica nanorods are very important factors for controlling the contact angle of different kind’s solvents on the surface of the SiO2 nanorod arrays.
Synthesis of Layered Titanate Micro/nano-materials for Efficient Pollutant Treatment in Aqueous Media
Authors: Tang Y. X. , Lai Y. K. , Gong D. G. , Dong Zhili , Chen Z.
Published: April 2011

In this work, the one dimensional (1D) titanate nanotubes (TNT)/nanowires (TNW), bulk titanate micro-particles (TMP), and three dimensional (3D) titanate microsphere particles (TMS) with high specific surface area were synthesized via different approaches. The chemical composition and structure of these products have been characterized by field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM) study and Raman scattering spectroscopy. The as-prepared TMS shows excellent adsorption performance compared with TMP, TNW and TNT when methylene blue (MB) and PbII ions are used as representative organic and inorganic pollutants.
Thermodynamic aspects of transition metals doped ZnO
Authors: Sedmidubský David , Sofer Zdeněk , Huber Štěpán , Leitner Jindřich
Published: April 2011

We present a thermodynamic study of selected transition metals (TM=Cr, Mn, Fe and Co) solubility in ZnO based on the assessment of available thermodynamic data and ab-initio calculations in the respective TM-Zn-O systems. The ab-initio DFT calculations of enthalpies of formation of the involved phases and the energies of substitution defect (TM-Zn) formation were performed using the full-potential APW+lo technique (WIEN2k code) within GGA+U approximation. The calculated energies of mixed oxides and virtual (unstable) TMO end-members of (Zn,TM)O solid solutions are referred to well established thermodynamic data of binary oxides taken from SGTE database. The assessed thermodynamic data are subsequently used for calculation of phase equilibria and construction of the respective pO2-T-x phase (FactSage software). Whereas the solubility of Mn, Fe, and Co in ZnO is found not to exceed 1 mol% at low temperatures (T<900°C), the homogeneity range is substantially enlarged at elevated temperatures (~10 mol% at the eutectic temperature). By contrast, the solubility of Cr turned out to be negligible in the relevant range of T and pO2.
Growth of Ruthenium and Ruthenium oxide nanoplates
Authors: Meda Lamartine , Stevens Geoffrey D.
Published: April 2011

By carefully manipulating and controlling the growth conditions, Ruthenium (Ru) and ruthenium oxide (RuO2) two-dimensional (2-D) nanostructure were self-assembled into a stack of plates on indium tin oxide coated glass substrate. The nanoplates were grown in a horizontal hot-wall metalorganic chemical vapor deposition (MOCVD) from ruthenocene. Each nanoplate has a thickness in the range of 25 - 60 nm and the average area is 1000 x 300 nm2. Each stack of nanoplates is approximately 1.2 m in height. A continuous layer of Ru and RuO2 thin film, which may serve as the growth template, is observed on the bottom of the nanoplate stacks. Field-emission scanning electron microscopy reveals that each stack of nanoplates was grown vertically aligned on the substrate and exhibited elongated shape. Structural properties which were examined by X-ray diffraction show that the nanoplates are polycrystalline.
Study of Silicon-metal Interaction in Adsorption Process: An Ab-initio Approach
Authors: Chakraborty Sudip , Ghaisas S. V. , Majumder Chiranjib
Published: April 2011

The formation of metal silicide plays important role in deciding the nature of the contact on silicon.Due to their chemically neautral nature,Au and Ag are used as contact metals in various devices.In particular the role of silicides is known to be crucial in defining the behavior of the electrical contact. The interaction of these metals with silicon at cluster level is still under the study.For naoscale devices, the nature at such interaction carries lot more inportance. Bulk Gold silicide(Cohesive energy ~ 3.81eV/atom) shows higher stability compared to silver silicide(Cohesive enrgy ~ 2.95 eV/atom). In the present work we show computational results based on Density Functional Theory(DFT) of Si cluster adsorption on Ag(111) surface and compare with the results of Si adsorption on Au(111). These results bring out the difference in Si cluster-metal surface interactions at the nanoscale. In particular the Si island-metal surface interaction shows island size dependence. We have presented results for most stable orientations only.
Spreading kinetics at a molecular level
Authors: Buraud Jean-Luc , Noel Olivier , Ausserre Dominique
Published: April 2011

The spreading of a smectic nanodrop (8CB liquid crystal) on a solid surface was investigated by direct and real time imaging using the Surface Enhanced Ellipsometric Contrast (SEEC) microscopy [1-2]. The spreading ends with two molecular terraces (made of one monolayer and a bilayer). Two different behaviors were observed. In the first one the upper layer stays dense while shrinking. At the end of the process, the last molecules to disappear are located at the center of the initial disk. In the second one, nucleation and growth of holes is observed in the upper layer, in addition to shrinking. A model is proposed to describe the time evolution of the late stage structure. This model gives exact solutions of the kinetic equations, it covers strongly layered liquids such as smectic liquid crystals, it introduces the two dimensional Laplace pressure as an essential motor for spreading and it takes into account the liquid/gas transition in the surface layer that was consistently reported in experiments with 8CB. This model is in remarkable agreement with the experimental data and can explain the two observed behaviors [3].
Correlation of Nanoscale Structure and Magnetic Properties in Manganese Doped Germanium Dilute Magnetic Semiconductors
Authors: He Li , Yin Wenjing , Yu Jiani , Lu Jiwei , Wolf Stuart , Hull Robert
Published: April 2011

Spintronic devices generally require the spin of carriers to be utilized in the storage or manipulation of data. One theoretical model for ferromagnetism in dilute magnetic semiconductors (DMS) results from the percolation of ferromagnetic regions around dilute dopants such as Mn atoms in III-V or group IV materials through the interaction of Mn atoms with carriers. Our work employed Mn implantation in Ge with subsequent rapid thermal annealing or TEM in-situ annealing to study the correlation between structure and magnetic properties. The magnetic properties of 300-350 ºC implanted Ge:Mn (which produced crystalline Ge films) varied significantly with implantation dose and annealing condition due to precipitation and transformation of different MnxGe1-x secondary phases. It was found that Mn substitution of Ge and MnxGe1-x secondary phases can both result in ferromagnetic properties. By combining TEM in-situ annealing and ex-situ magnetic characterization, we have demonstrated detailed correlation of magnetic properties with nanoscale structures in Mn implanted Ge DMS materials.
Building 3D materials from adjustable 2D-units; towards the Design of new Bi-based compounds
Authors: Colmont M. , Endara D. , Huvé M. , Krivovichev S.V. , Mentré O.
Published: April 2011

In the Bi2O3-MO-P2O5 diagram, on the basis of previous compounds based on 2D-ribbon like units, we have predicted and prepared the infinite term. It contains [Bi2O2]2+ planes arranged within a never-observed crystallographic form. In this series, the ribbons-like units are polycations built on the linkage of n O(Bi,M)4 tetrahedra along their width and infinite in a perpendicular dimension. Hence, this novel form completes the continuous series of analogue compounds, whose building units now extend from the single chain to the infinite plane, via a number of discrete n values (2,3,4,5,6,7,8,9,10,11). The presented materials of formulae Bi4MP2O12 (M= Zn and Mg) roughly show the same crystal structure. However different arrangements of the groups located between the [Bi2O2]2+ planes are at the origin of a complex superstructure in the case of the zinc compounds.
Silicon Micro Machining Technologies and Advanced Materials (Porous Silicon and PEEK-WC) for Realization of Micro-PEM Fuel Cells
Authors: Elena Tresso M. , Borello Luisa , Enrico Drioli , Gianolio Giuseppe , Guastella Salvatore , Perrone Denis , Quaglio Marzia , Rossi Andrea M. , Rosso Ilaria , Scaltrito Luciano , Trotta Francesco
Published: April 2011

In view of the development of a miniature PEM fuel cell operating at low temperature on hydrogen or direct methanol as anodic feed and air as cathodic feed, we present preliminary results on the performances obtained by employing silicon-based microfabrication techniques and advanced materials which can be easily integrated in silicon technologies, such as porous silicon for the electrode fabrication and PEEK-WC for membranes alternative to Nafion. Powder blasting and reactive ion etching (RIE) have been used for obtaining anode and cathode micro-channels for hydrogen and methanol, in glass and in silicon bipolar plates. Localized micro-fusion processes has been successfully employed for sealing between silicon and membrane.
PEM fuel cell electrodes using Single Wall Carbon Nanotubes
Authors: Moloney Padraig , Huffman Chad , Springer Micah , Gorelik Olga , Nikolaev Pasha , Sosa Edward , Arepalli Sivaram , Yowell Leonard
Published: April 2011

Single wall carbon nanotubes (SWCNT) have previously been considered potential catalyst supports in proton exchange membrane fuel cells (PEMFC) [1]. Earlier research and development of SWCNT for PEMFC catalyst supports has been advanced by utilizing differing SWCNT purities and carbon blacks in differing ratios. This study validates the performance of SWCNT and introduces new concepts for SWCNT membrane fabrication.
Thermal and Volumetric Studies of Complex Chemical Hydrides: Li-modified/Ti- doped Mg2FeH6, Sonicated LiNH2/LiH and Zn- doped NaBH4
Authors: Srinivasan Sesha , McElwee-White Lisa , Stefanakos Elias , Goswami Yogi , Dumbris Seth
Published: April 2011

Light weight hydrogen storage systems are indeed essential for the on-board automotive vehicular applications. Complex chemical hydrides bearing light elements such as Li, Na, Mg etc. and their catalytic doping with transition metal species are presently being investigated. The Li- modified Mg2FeH6structure have been thermally characterized using DSC and TGA techniques. It is interesting to notice that the reduction in the decomposition temperature of about 100° C has been unambiguously observed for the Li modified Mg2FeH6. Besides, there is an enhancement in sorption kinetics for the Ti- doped Mg2FeH6. The role of Ti- species on the dehydrogenation and rehdyrogenation properties of NaAlH4have been explored by heat flow measurements using high pressure differential scanning calorimetry. We have also developed the Li-amide/LiH system by sonicated process and studied their PCT characteristics. A new class of hydrogen storage system Zn(BH4)2with theoretical hydrogen capacity of 8.4 wt.% have been synthesized and we have determined their gravimetric and volumetric characteristics.
Evolved Gas Analysis of Heat-Treated Carbon Nanomaterials
Authors: Shulga Yury , Martynenko Vyacheslav M. , Loutfy R. O. , Moravsky Alex P.
Published: April 2011

Gases evolved on heat-treatment of intact fullerite C60, single-walled (SW) and multi-walled nanotubes (MWNTs) and chemically modified carbon nanomaterials (deuterofullerites C60Dx, hydrogenated SWNTs and fluorinated MWNTs) are studied by mass spectrometry.
Structure and Thermal Conductivity of Silica Aerogels from Computer Simulations
Authors: Good Brian
Published: April 2011

Aerogels are of current interest in the aerospace community due to their light weight and low thermal conductivity, making them suitable for a variety of applications, notably cryotank insulation.

These gels typically exhibit a complex structure; the smallest feature is a “primary” particle of amorphous silica, typically 2-5nm in diameter. The primary particles aggregate to form “secondary” particles, typically an order of magnitude larger, and these, in turn, form pearl-necklace structures whose details depend on the density. The gels appear to exhibit fractal dimensionality, at least over a small range of length scales.

In this work, we investigate the relationship between the structure of the gels, their dimensionality and density, and their thermal conductivity. We model the secondary-particle aggregate structure using a modified Diffusion Limited Cluster Aggregation (DLCA) model. The model produces qualitatively different structures at low and high densities that are consistent with experimental observation. At lower densities, we find evidence for a transition from fractal behavior at small length scales to approximately compact behavior at larger lengths.

We model the thermal conductivity using a variant of the random resistor network approach that has been used to describe, e.g. hopping electrical conduction in doped semiconductors. In our model, each secondary particle is assigned an effective thermal conductance that depends on the particle's size, and on the details of its contacts with neighboring particles; the conductivity of the gel network is obtained using standard numerical techniques. The scaling of the thermal conductivity with density and fractal dimension is discussed.
A Novel Two-Step Hydrogen Cycled Methane Reforming Process
Authors: Breitkopf Richard , Smalley Yardlynne , Wang Zhong-Lin , Snyder Robert , Haluska Michael
Published: April 2011

We have prepared novel transition metal fluorite materials for a 2-step hydrogen reformer process that generates low CO hydrogen for fuel cell applications. The nanopowder materials, which are converted to an oxygen vacancy rich form in the first step of the process using methane or any hydrocarbon fuel are subsequently brought back to their original state using water vapor while generating pure hydrogen in the process. We have observed large weight losses in TGA measurements below 500°C with our nanomaterials that we do not observe in similar powders with larger grain size that comprise an efficient low temperature first step. We have also observed decreases in lattice parameter in high temperature XRD measurements consistent with formation of a high concentration of oxygen vacancies. The process has produced fuel efficiencies as high as 65% with typical CO content below 30 ppm using methane fuel. Additionally, since we are using nanomaterials, we have enabled low temperature hydrogen generation with good cycling stability at 500°C.
Commercialization of Thermoelectric Technology
Authors: Stabler Francis R.
Published: April 2011

Thermoelectric technology capable of solid state electric power generation and cooling has been has been known for almost 180 years. Only in the past 50 years has this technology found its way out of the laboratory and into niche military, space, and commercial products. Most of the profitable commercial products have made their appearance in the past decade. Many of you are working hard to advance the state of the art in thermoelectric materials, and I am sure that you do not want to wait another 180 years, 50 years, or even another decade to commercialize your results. There are many potential ways to commercialize this technology, but the area that I think represents the biggest market is the automotive industry. There are over 17 million automobiles sold in the US each year and over 60 million worldwide. With the possible exception of the electric power industry, I know of no other market segment that is even close to the potential of the automotive industry for using a high volume of thermoelectric materials. Every vehicle produced has an electrical system supplied by a one to two kilowatt generator with increasing power demand as electrical features are added. A high percentage of vehicles have air conditioning systems with 3 to 5 kilowatts of cooling. Sufficiently advanced thermoelectric materials can be the heart of systems that supplement or replace the mechanical or electro-mechanical devices performing these functions today. This paper addresses the boundary conditions for the function, quantity, and value needed to commercialize thermoelectric technology. Timing to introduce subsystems with this technology is also addressed. Thermoelectric technology has to compete with the existing technologies and other emerging technologies to be successfully commercialized. While it seems out of reach today, there is even the potential that sufficiently advanced thermoelectric materials and device construction could one day replace the internal combustion engine and even rival fuel cells in energy conversion efficiency.
Microstructure of Ca3Co4O9 Single Crystals and Thin Films
Authors: Hu Yufeng , Sutter Eli , Si Weidong , Li Qiang
Published: April 2011

We present a comparative study of the microstructure of Ca3Co4O9 single crystals and c-axis oriented Ca3Co4O9 thin films grown on glass substrates. Though both crystals and films have similar values of Seekbeck coefficient and electric resistivity at room temperature, their microstructures are rather different. Extensive high resolution transmission electron microscopy (TEM) studies reveal that the films grown on glass substrates have abundant stacking faults, which is in contrast to the perfect crystalline structure found in the single crystal sample. The c-axis lattice constants derived from the x-ray diffraction (XRD) and TEM measurements for the single crystal sample and the thin film are virtually the same, suggesting that the thin film on the glass substrate was not strained.
Synthesis and Thermoelectric Properties of NaxCo2O4 Single Crystals
Authors: He Jian , Aaron Kelvin , Abbott Edward , Kolis Joseph , Tritt Terry M.
Published: April 2011

Single crystal NaCo2O4 platelets with sizes up to 6mm were synthesized by the typical high temperature NaCl flux method. The in-plane thermopower α and in-plane resistivity ρ were measured to be ∼100µV/K and 0.3mΩ-cm at 300K, respectively. The in-plane thermal conductivity κ was measured by our custom-designed “PTC” system and found to be ∼5 W-m−1K−1 at 300K, which is 2-3 times larger than the polycrystalline NaCo2O4. The in-plane phonon mean free path lph was estimated to be ∼9.5Å, which is much smaller than the in-plane mean free path of conducting carriers (la∼51Å). A novel low temperature flux method where NaCl/NaOH was used as flux and metallic Co powders as Co source was developed to successfully synthesize Na-deficient NaxCo2O4 crystals with size up to 6mm at low temperature of 550°C. The different temperature dependence in resistivity reveals that two different types of crystals can exist, one is metallic and another is semiconducting. The temperature dependence of the measured k is like that of a disordered solid and the value is found to be ∼7 W-m−1K−1 at 300K.
Synthesis of (Bi2Te3)x(TiTe2)y and (Bi2Te3)x(TiTe2)3 Superlattices
Authors: Smeller Mary , Harris Fred R. , Johnson David C.
Published: April 2011

The synthesis of (Bi2Te3)x(TiTe2)x and (Bi2Te3)x(TiTe2)3 superlattices using modulated elemental reactants was successfully accomplished. This required the calibration of the deposition parameters to achieve both the desired atomic compositions of the constituent layers and the deposition of the absolute amounts of each of the components to yield the title compounds. Proper annealing conditions were determined from an investigation of the x-ray diffraction patterns of a superlattice sample as a function of annealing temperature. The change in lattice parameters as a function of x showed the expected linear behavior with slopes consistent with values expected from the published lattice parameters of the binary components. Rietveld refinement showed that the characteristic structure of the binary components is maintained in the superlattices studied.
Evaluation of TiTe2 as a Diffusion Barrier in the Synthesis of (Bi2Te3)5(SnTe)5 Misfit Layer Compound
Authors: Li Sissi L. , Johnson David C.
Published: April 2011

The evolution of modulated reactants designed to form (Bi2Te3)5(TiTe2)5(SnTe)5(TiTe2)5 and (Bi2Te3)5(SnTe)5 are compared and contrasted. The modulated reactant designed to form (Bi2Te3)5(SnTe)5 interdiffused at 220°C forming SnBi2Te4 rather than the desired superlattice structure. The second sample was designed to have TiTe2 as a potential diffusion barrier to prevent the formation of SnBi2Te4. This second sample remained layered after annealing at 220°C. SnTe crystals are observed in the high angle diffraction pattern after this annealing, but there is evidence for the beginning of SnBi2Te4 formation. Annealing this sample at 300°C results in the formation of SnBi2Te4. The interdiffusion of Sn and Bi appears to occur before the formation of the desired TiTe2 structure.
Growth and Characterization of 1D Bi2Te3 Nanowires
Authors: Craps M. , Gothard Nick , Rao Rahul , He Jian , Hudson JoAn , Tritt Terry M. , Rao Apparao M.
Published: April 2011

Bulk bismuth telluride (Bi2Te3) is one of the best known thermoelectric materials with a figure of merit ZT ∼1 at room temperature. Theoretical studies have suggested that low-dimensional materials may exhibit ZT values that exceed 1. In this study, we used the pulsed laser vaporization (PLV) method to prepare Bi2Te3 nanowires on silicon and quartz substrates by ablating Bi2Te3 targets in an inert atmosphere. Nano-sized gold or iron catalyst particles were used to seed the growth of the Bi2Te3 nanowires. Results from electron microscopy and Raman spectroscopy are discussed.
Size-selective and High-yield Nanocrystal Growth of PbTe Compounds Using a Chemical Vapor Deposition Technique
Authors: Zhang B. , Gothard Nicholas , He Jian , Thompson Daniel , Tritt Terry M.
Published: April 2011

The nanocrystals of PbTe and related compounds (Pb1−xSnxTe, PbTe1−xSex), differing by size and composition, have been synthesized using a chemical vapor transport (CVD) technique. The size–selective precipitation mechanism relying on the variation of heating temperatures, Ar flow rates and admixture with Au particles, enables a relatively good control of particle size distribution. In addition, the doping ratios of those nanocrystals are readily modified by changing the atomic ratio in the raw starting materials. Subsequently, a yield of hundreds of milligrams of nanocrystals which exhibit narrow size distributions at 100 nm, 300 nm and 600 nm and controllable composition have been obtained. XRD patterns taken on the PbTe samples show sharp, which indicate good crystallinity of samples. According to the shift of the Bragg reflections, the lattice constants of (Sn / Se) doped PbTe change with the variation of the doping ratios.
CVD Growth of Nanostructures from Bi2Te3
Authors: Gothard N. , Zhang Bo , He Jian , Tritt Terry
Published: April 2011

Research into thermoelectric materials has recently undergone a push into lower dimensional materials in the hopes that quantum confinement effects will enhance the performance of these structures. It has already been demonstrated that 2D superlattice materials show enhanced properties. More recently, materials known to have good thermoelectric properties, such as Bi2Te3 or PbTe, have been grown in low dimensional morphologies. We investigate synthesis techniques for growing low dimensional structures of Bi-Te materials with the aim of incorporating them into a composite material alongside bulk Bi2Te3.
Solid-State and Vacuum Thermionic Energy Conversion
Authors: Shakouri Ali , Bian Z. , Singh R. , Zhang Y. , Vashaee D. , Humphrey T. E. , Schmidt H. , Zide J. M. , Zeng G. , Bahk J-H. , Gossard A. C. , Bowers J. E. , Rawat V. , Sands T. D. , Kim W. , Singer S. , Majumdar A. , Mayer P. M. , Ram R. J. , Russel K. J. , Narayanamurti V. , Koeck F. A. M. , Li X. , Park J.-S. , Smith J. R. , Bilbro G. L. , Davis R. F. , Sitar Z. , Nemanich R. J.
Published: April 2011

A brief overview of the research activities at the Thermionic Energy Conversion (TEC) Center is given. The goal is to achieve direct thermal to electric energy conversion with >20% efficiency and >1W/cm2power density at a hot side temperature of 300–650C. Thermionic emission in both vacuum and solid-state devices is investigated. In the case of solid-state devices, hot electron filtering using heterostructure barriers is used to increase the thermoelectric power factor. In order to study electron transport above the barriers and lateral momentum conservation in thermionic emission process, the current-voltage characteristic of ballistic transistor structures is investigated. Embedded ErAs nanoparticles and metal/semiconductor multilayers are used to reduce the lattice thermal conductivity. Cross-plane thermoelectric properties and the effective ZT of the thin film are analyzed using the transient Harman technique. Integrated circuit fabrication techniques are used to transfer the n- and p-type thin films on AlN substrates and make power generation modules with hundreds of thin film elements. For vacuum devices, nitrogen-doped diamond and carbon nanotubes are studied for emitters. Sb-doped highly oriented diamond and low electron affinity AlGaN are investigated for collectors. Work functions below 1.6eV and vacuum thermionic power generation at temperatures below 700C have been demonstrated.
On the optical properties of thermoelectric alkali metal chalcogenide compounds
Authors: Hatzikraniotis W. , Kyratsi Theodora , Zorba T. , Paraskevopoulos Kontantinos M. , Kanatzidis Mercouri G.
Published: April 2011

Solid solutions of K2Bi8−XSbXSe13 is an interesting series of complex bismuth-chalcogenide compounds, which are attractive for thermoelectric investigations. The highly anisotropic structure in these compounds results in needle-like morphology along the b- crystallographic axis, leaving structural tunnels where K+ ions reside. The complex electronic structure that arises from a large and low symmetry unit cell and the weakly bound K+ ions, lead to high Seebeck coefficient, highly anisotropic electrical properties and very low thermal conductivity.

Reflectivity spectra in the FIR region are presented for several members in the Sb-rich (x≥6) side. Optical investigations are carried out on crystalline and pelletized samples. The received spectra are analyzed, examined comparatively and discussed. Results indicate that upon Bi/Sb substitution in the Sb-rich region, phonons develop a mixed-mode behavior in the FIR spectral region.