bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Conductivity of Zn4−xCdxSb3 Solid Solutions
Authors: Caillat T. , Borshchevsky A. , Fleurial J. -P.
Published: April 2011

β-Zn4Sb3 was recently identified at the Jet Propulsion Laboratory as a new high performance p-type thermoelectric material with a maximum dimensionless thermoelectric figure of merit ZT of 1.4 at a temperature of 673K. A usual approach, used for many state-of-the-art thermoelectric materials, to further improve ZT values is to alloy β-Zn4Sb3 with isostructural compounds because of the expected decrease in lattice thermal conductivity. We have grown Zn4−xCdxSb3 crystals with 0.2≤x<1.2 and measured their thermal conductivity from 10 to 500K. The thermal conductivity values of Zn4−xCdxSb3 alloys are significantly lower than those measured for β-Zn4Sb3 and are comparable to its calculated minimum thermal conductivity. A strong atomic disorder is believed to be primarily at the origin of the very low thermal conductivity of these materials which are also fairly good electrical conductors and are therefore excellent candidates for thermoelectric applications.
Selection and Evaluation of Materials for Thermoelectric Applications II
Authors: Sharp Jeff W.
Published: April 2011

In good thermoelectrics phonons have short mean free paths, and charge carriers have long ones. The other requirements are a multivalley band structure and a band gap greater than 0.1 eV for the 200 to 300 K temperature range. We discuss the use of solid state physics and chemistry concepts, along with atomic and crystal structure data, to select the new materials most likely to meet these criteria.
Quantum Confinement Effects on the Thermoelectric Figure of Merit in Si/Si1−xGex System
Authors: Sun X. , Dresselhaus M. S. , Wang K. L. , Tanner M. O.
Published: April 2011

The Si/Sil−xGex quantum well system is attractive for high temperature thermoelectric applications and for demonstration of proof-of-principle for enhanced thermoelectric figure of merit Z, since the interfaces and carrier densities can be well controlled in this system. We report here theoretical calculations for Z in this system, and results from theoretical modeling of quantum confinement effects in the presence of δ-doping within the barrier layers. The δ-doping layers are introduced by growing very thin layers of wide band gap materials within the barrier layers in order to increase the effective barrier height within the barriers and thereby reduce the barrier width necessary for the quantum confinement of carriers within the quantum well. The overall figure of merit is thereby enhanced due to the reduced barrier width and hence reduced thermal conductivity, K. The δ-doping should further reduce K in the barriers by introducing phonon scattering centers within the barrier region. The temperature dependence of Z for Si quantum wells is also discussed.
Experimental Transport Phenomena and Optimization Strategies for Thermoelectrics
Authors: Ehrlich A. C. , Gillespie D. J.
Published: April 2011

When a new and promising thermoelectric material is discovered, an effort is undertaken to improve its “figure of merit”. If the effort is to be more efficient than one of trial and error with perhaps some “rule of thumb guidance” then it is important to be able to make the connection between experimental data and the underlying material characteristics, electronic and phononic, that influence the figure of merit. Transport and fermiology experimental data can be used to evaluate these material characteristics and thus establish trends as a function of some controllable parameter, such as composition. In this paper some of the generic-materials characteristics, generally believed to be required for a high figure of merit, will be discussed in terms of the experimental approach to their evaluation and optimization. Transport and fermiology experiments will be emphasized and both will be outlined in what they can reveal and what can be obscured by the simplifying assumptions generally used in their interpretation.
Analysis of Grain Boundaries, Twin Boundaries and Te Precipitates in Cd1−xZnxTe Grown by High-Pressure Bridgman Method
Authors: Heffelfinger J. R. , Medlin D. L. , James R. B.
Published: April 2011

Gtain boundaries and twin boundaries in commercial Cd1−xZnxTe, which is prepared by a high-pressure Bridgeman technique, have been investigated with transmission electron microscopy, scanning electron microscopy, infrared-light microscopy and visible-light microscopy. Boundaries inside these materials were found to be decorated with Te precipitates. The shape and local density of the precipitates were found to depend on the particular boundary. For precipitates that decorate grain boundaries, their microstructure was found to consist of a single, saucer-shaped grain of hexagonal Te (space group P3,2 1). Analysis of a Te precipate by selected-area diffraction revealed the Te to be aligned with the surrounding Cd1−xZnxTe grains. This alignment was found to match the (111) Cd1−xZxTe planes with the (0 111) planes of hexagonal Te. Crystallographic alignments between the Cd1−xZnxTe grains were also observed for a high-angle grain boundary. The structures of the grain boundaries and the Te/Cd1−xZnxTe interface are discussed.
Growth and Characterization of PbSe and Pb1−xSnxSe Layers on Si (100)
Authors: Sachar H. K. , Chao I. , Fang X. M. , Mccann P. J.
Published: April 2011

Crack-free layers of PbSe were grown on Si (100) by a combination of liquid phase epitaxy (LPE) and molecular beam epitaxy (MBE) techniques. The PbSe layer was grown by LPE on Si (100) using a MBE-grown PbSe/BaF2/CaF2 buffer layer structure. Pb1−xSnxSe layers with tin contents in the liquid growth solution equal to 3%, 5%, 6%, 7%, and 10%, respectively, were also grown by LPE on Si (100) substrates using similar buffer layer structures. The LPE-grown PbSe and Pb1−xSnxSe layers were characterized by optical Nomarski microscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Optical Nomarski characterization of the layers revealed their excellent surface morphologies and good growth solution wipe-offs. FTIR transmission experimentsshowed that the absorption edge of the Pb1−xSnxSe layers shifted to lower energies with increasing tin contents. The PbSe epilayers were also lifted-off from the Si substrate by dissolving the MBE-grown BaF2 buffer layer. SEM micrographs of the cleaved edges revealed that the lifted-off layers formed structures suitable for laser fabrication.
Nonmonotonous Behavior of Temperature-Dependence of Plasma Frequency and Effect of a Local Instability of the PbTe:In,Ga Lattice
Authors: Belogorokihov A. I. , Belogorokhova L. I. , Khokhlov D. R.
Published: April 2011

The optical spectra of PbTe:In,Ga samples were studied in the Far Infrared region at temperatures T=11 K–3 50K. Anomalous behavior of the temperature dependence of the plasma frequency at 65K–80K was observed for the first time. This is explained by means of a model of localized changes in the lead telluride lattice structure near impurity centers.
The Effect of Tensile Strain on AlGaAs/GaAsP Interdiffused Quantum Well Laser
Authors: Chan K. S. , Chan Michael C. Y.
Published: April 2011

In this paper, we study the interdiffusion of tensile strained GaAsyPi.y /A10 33Ga0 67As single QW structures with a well width of 60Å. Different P concentrations in the as-grown well are chosen to obtain different tensile strains in the QW. Interdiffusion induces changes in the tensile strains and confinement potentials, which consequently change the valence band structure and the optical gain.
Polarized Raman Scattering Study of ZnGeP2 Single Crystals
Authors: Tlali Spirit , Jackson Howard E. , Ohmer M. C. , Schunemann P. G. , Pollak T. M.
Published: April 2011

Raman scattering experiments on high quality ZnGeP2 single crystals grown by the seeded horizontal dynamic gradient technique have been carried out. Polarized Raman spectra were obtained in the backscattering geometry at both room and low temperatures for several crystal orientations and compared with group theoretical predictions. Raman spectra from as-grown and annealed samples display distinctive differences which were explored by utilizing two different excitation wavelengths: 514.3 nm and 632.8 nm; the observed differences are attributed to a surface interdiffuasion effect.
Relaxed Inx.Ga1−xas Graded Buffers Grown With Organometallic Vapor Phase Epitaxy on GaAs
Authors: Bulsara M. T. , Leitz C. , Fitzgerald E. A.
Published: April 2011

InxGa1−xAs structures with compositionally graded buffers were grown with organometallic vapor phase epitaxy (OMVPE) on GaAs substrates and characterized with plan-view and cross-sectional transmission electron microscopy (PV-TEM and X-TEM), atomic force microscopy (AFM), and x-ray diffraction (XRD). The results show that surface roughness experiences a maximum at growth temperatures where phase separation occurs in In.Gal.,As. The strain fields from misfit dislocations induce this phase separation in the <110> directions. At growth temperatures above and below this temperature, the surface roughness decreases significantly; however, only growth temperatures above this regime ensure nearly complete relaxed graded buffers with the most uniform composition caps. With the optimum growth temperature for grading InxGa1−x,As determined to be 700 °C, it was possible to produce In0.33Ga0.67As diodes on GaAs with threading dislocation densities < 8.5 × 106/cm2.
Gamma Ray Spectrometers Fabricated from Modified Bridgman/Annealed CZT Crystal Material
Authors: Chattopadhyay K. , Chen H. , Chen K-T. , Burger Arnold , Flint J. P. , Glass H. L. , James R. B.
Published: April 2011

The CZT boule was grown by a modified vertical Bridgman process using in-situ compounding, Cd over-pressure and a pyrolytic boron nitride crucible within a fused ampoule. During growth, the Cd vapor pressure was near 1 atmosphere. These growth conditions tend to give high purity, good stoichiometry, few precipitates, and dislocation densities in the low to mid-104 cm−2 range. The crystals, after polishing, were annealed in a nearly saturated Cd, Zn atmosphere to fill residual Cd-site vacancies and achieve high resistivity in the 1010 γ-cm range. Low temperature photoluminescence study shows very good crystalline quality and a very low concentration of deep level recombinations. Single crystal samples were diced into 1 cm squares for evaluation as gamma ray detectors. The best detector results (4.5% resolution at 60 keV) were achieved for a 2 hour anneal at 850°C.
Pulse Filtering and Correction For CZT Detectors Using Simple Digital Algorithms Based on The Wavelet Transform
Authors: Pérez J. M. , García-Belmonte G.
Published: April 2011

We report an approach to double gaussian filtering used in classical works as dual parameter pulse processing. This technique has been implemented by creating a bank of gaussian-like digital filters based on wavelet transforms. A simple method to correct for the charge loss inherent to room temperature semiconductor gamma detectors has been developed. This method is based on multi-resolution signal analysis. Results are reported from tests of these algorithms on commercial CZT detectors and two trapped hole charge correction levels are compared. Finally, the advantages and limitations of this new approach to detector pulse processing are discussed.
HgI2 Two-Dimensional Arrays Based on Resistive Charge Division Readout
Authors: Alfieri S. , Cesare N. De , Grassi D. , Perillo E. , Spadaccini G; , Vigilante M. , Dusi W. , Amann M. , Koebel J. M. , Siffert P.
Published: April 2011

Newly designed HgI2 two-dimensional arrays based on resistive charge division, obtained by depositing a Ge surface resistive layer between the readout Pd strips, have been fabricated. These detectors, coupled with very low noise preamplifiers, have shown a high detection efficiency over a large active area and an energy resolution of 15% for X-ray energy Ex =60 keV (241Am), becoming ≈ 9% at Ex = 122 keV (57Co). Further, a spatial sensitivity of ≈ 5 μm and a spatial resolution of ≈ 40 μim in both the directions parallel to the anode and to the cathode strips have been obtained at an energy equivalent to ≈ 40 keV, by making use, for a fine spatial characterization of the devices, of a laser beam spot with wavelength tuned to match the crystal bandgap (582 nm). These devices, with optimized cathode layer resistances, could be successfully employed in basic research (for example Bragg X-ray spectrometry) and for imaging in radiological and space applications, at least in the important energy range 40 <Ex <120 keV.
New Generations of Position Sensitive Silicon Detectors
Authors: Burger P. , Keters M. , Van Buul L. , Verplancke J.
Published: April 2011

The new generation of elementary particle and nuclear physics experiments demand instrumentation with a more precise spatial resolution and a better and faster energy response. Nuclear physics and space experiments need position sensitive pad detectors having very thin entrance windows while high energy physics and medical applications use fast microstrip or drift detectors. Silicon pixel detectors can be improved by implementing integrated electronics on it. They allow a better X-ray energy resolution and are also used in hybrid photocathode tubes for faster timing and larger dynamic range.
Radiation Damage Of InGaAs Photodiodes By High Energy Particles
Authors: Kudou T. , Ohyama H. , Simoen E. , Claeys C. , Takami Y. , Shigaki K. , Fujii A. , Sunaga H.
Published: April 2011

Results are presented of a study on the performance degradation and the induced lattice defects of In0.53Ga0.47As p-i-n photodiodes, subjected to 220-MeV carbon particles. The effects on both the dark current and the photo-current are investigated as a function of the carbon fluence and correlated with DLTS results. The device degradation is compared with the one observed after exposure to 1-MeV electrons, 1-MeV fast neutrons and 20-MeV alpha rays, respectively. The differences in damage coefficients will be explained in view of the calculated number of knock-on atoms and the nonionizing energy loss (NIEL). The recovery behavior of the diode performance and of the induced deep levels by isochronal annealing is also reported.
Properties Of Zinc Selenide Grown By Chemical Vapor Transport And Its Application To Room-Temperature Radiation Detection
Authors: Brunett B. A. , Toney J. E. , Yoon H. , Rudolph P. , Schieber M. , Schlesinger T. E. , Goorsky M. S. , James R. B.
Published: April 2011

We have characterized ZnSe material grown by chemical vapor transport in iodine using triple-axis X-ray diffraction (TAD), photo-induced current transient spectroscopy (PICTS), photoluminescence (PL), current-voltage measurements and gamma-ray spectroscopy. The material was found to have inadequate carrier transport for nuclear spectrometer use, but there was a discernible difference in performance between crystals which could be correlated with crystallinity as determined by the TAD rocking curves.
Optical and Electrical Characterization of Copper-and Chlorine-Doped Cadmium Zinc Telluride
Authors: Toney J. E. , Brunett B. A. , Schlesinger T. E. , Cross E. , Doty F. P. , James R. B.
Published: April 2011

We have used low-temperature photoluminescence spectroscopy and photo-induced current transient spectroscopy to study the properties of copper-doped Cd1−xZnxTe with x=0.1 and chlorine-doped Cd1−xZnxTe with x=0.2, 0.35 and 0.5. The current-voltage characteristics and detector response were also measured. We observed variations in charge collection and resistivity in the Cu-doped samples which was correlated with variations in PICTS spectra. The Cl-doped material was found to have insufficient resistivity for detector operation.
Growth, Characterization and Spectroscopic Investigations of InI Crystals for Optical and Radiation Detector Applications
Authors: Mandal K. C. , Klugerman M. , Cirignano L. J. , Moy L. P. , Shah K. S. , Squillante M. R. , Bhattacharyya R. N.
Published: April 2011

Single crystals of InI (Eg = 2.01 eV at 300K) have been grown by vertical Bridgman technique using zone refined (ZR) starting materials. The quality of the grown crystal has been evaluated by X-ray diffraction (XRD), Electron probe microanalysis (EPMA) and Photoelectron spectroscopy (XPS). Chemically etched crystal wafer has been used to fabricate optical and nuclear detectors. The results are presented in this paper.
Exciton Bandwidth and Coupling to Intramolecular Phonons in PTCDA
Authors: Hennessy M. H. , Soos Z. G. , Bulovic V. , Forrest S. R.
Published: April 2011

abstract

A Holstein model is introduced for PTCDA stacks forming a one-dimensional exciton system and analyzed using Merrifield's variational method. The bandwidth and hopping integral V = 0.15 eV are obtained by comparing the absorption, emission, and fluorescence excitation of PTCDA films to solution spectra.
Electronic Properties of a Novel Class of Conjugated Systems: Transition Metal Substituted Oligothiophenes
Authors: Lancellotti L. , Tubino R. , Luzzati S. , Licandro E. , Maiorana S. , Papagni A.
Published: April 2011

We report on a spectroscopical study of a novel class of push-pull molecules containing a Chromium or Tungsten atom connected to an oligothiophene through a carbenic bond. The electronic coupling between the π electrons of the conjugated system and the π electrons of the transition metal has been monitored through absorption and Raman spectra.

This interaction between d and π electrons leads to a red shift of the thienylene π-π* absorption band and to the appearance of a new strong metal to ligand charge transfer band at lower energies. In this latter transition the electrical dipole reverses its direction upon photoexcitation from the ground to the first excited state, thus accounting for the enhanced non linear optical response of these molecules. Solvatochromic effect has been used to estimate the second order molecular hyperpolarizability.
Plastic Multilayered Molecular Organic Light Emitting Diodes
Authors: Daly George M. , Murata Hideyuki , Merritt Charles D. , Kafafi Zakya H. , Inada Hiroshi , Shirota Yasuhiko
Published: April 2011

Enhanced performance has been observed for plastic molecular organic light emitting diodes (MOLEDs) consisting of two to four organic layers sequentially vacuum vapor deposited onto patterned indium-tin oxide (ITO) on polyester films. For all device structures studied, the performance of plastic diodes is comparable to or better than their analogs on glass substrates. At 100 A/m2, a luminous power efficiency of 4.4 lm/W and external quantum yield of 2.7% are measured for a device structure consisting of two hole transport layers, a doped emitting layer and an electron transport layer on a polyester substrate. The same device made on a silica substrate has a luminous power efficiency of 3.5 lm/W and external quantum yield of 2.3%. Electrical and optical performance for comparable device structures has been characterized by current-voltage-luminance measurements and electroluminescence spectra collected normal to the emitting surface. In addition, an integrating sphere was used to collect the total light emitted and to determine the optical output coupling on glass versus plastic substrates.
Multilayer Self-Assemblies as Electronic and Optical Materials
Authors: Li DeQuan , Lütt M. , Shi Xiaobo , Fitzsimmons M. R.
Published: April 2011

The layer-by-layer growth of film structures consisting of sequential depositions of oppositely charged polymers and macrocycles (ring-shaped molecules) have been constructed using molecular self-assembly techniques. These self-assembled thin films were characterized with X-ray reflectometry, which yielded (1) the average electron density, (2) the average thicknesses, and (3) the roughness of the growth surface of the self-assembled multilayer of macrocycles and polymers. These observations suggest that inorganic-organic interactions play an important role during the initial stages of thin-film growth, but less so as the thin film becomes thicker. Optical absorption techniques were also used to characterize the self-assembled multilayers. Phorphyrin and phthalocyanine derivatives were chosen as the building blocks of the self-assembled multilayers because of their interesting optical properties.
Structural and Electronic Properties of Self-Assembled Supramolecular Grid Structures: Doping of Supramolecular Thin Films
Authors: Hassmann J. , Hahn C. Y. , Waldmann O. , Volz E. , Schleemilch H-J. , Hallschmid N. , MÜller P. , Hanan G. S. , Volkmer D. , Schubert U. S. , Lehn J-M. , Mauser H. , Hirsch A. , Clark T.
Published: April 2011

Thin films of self-assembled supramolecular grid structures were prepared by electrochemical deposition. The surface structure of the films was determined by electrochemical insitu scanning tunneling microscopy (STM), revealing ordered monolayers of the grid molecules on a Au( 111) surface. The electronic structure of the films was studied by photoelectron spectroscopy. The thin films show semiconducting behavior with an insulating gap of ca. 2.5 eV. The size of insulating gap can be reduced to 0.5 eV by doping the films with additional Cd2+ ions, which is in agreement with molecular orbital calculations. Additionally, conductivity measurements were performed. By doping of the thin films, their conductivity could be increased by several orders of magnitude. This is due to additional electronic states in the insulating HOMO-LUMO gap, which is confirmed by UPS measurements.
Investigations on the Aluminum/Para-Hexaphenyl Interface in Light Emitting Devices
Authors: Koch N. , Yu L.-M. , Guyaux J.-L. , Morciaux Y. , Leising G. , Pireaux J.-J. , Demoustier G.
Published: April 2011

Blue light emitting devices (LED) with para-hexaphenyl (PHP) as the active material and aluminum as cathode exhibit very high quantum efficiencies. To further optimize device performance it is crucial to understand the physical properties of the involved interfaces. We have performed Rutherford-Backscattering experiments on actual devices to show the importance of oxygen in the interface formation at the cathode as this leads to the formation of a layer of AlxOy between PHP and aluminum. In devices, where the organic film is exposed to air before the metal electrode is evaporated, an insulating layer on the metal-side therefore is inherent. It has been shown that the introduction of an intermediate layer between active material and electrodes results in a higher quantum efficiency of the LED, the most common concepts being charge-transport-layers, or insulators on the other hand. Our results underline the need for a better control of the LED processing. Ultraviolet- and X-ray photoelectron spectroscopy in situ growth studies of thin aluminum films on PHP have been made to reveal the change in the electronic structure of the active medium in a LED in the absence of oxygen. Also the direct interaction of oxygen with this organic material is investigated by photoelectron spectroscopy.
Electroactive and Photoactive Rod-Coil Block Copolymers: Self-Organization and Photophysical Properties
Authors: Chen X. Linda , Jenekhe Samson A.
Published: April 2011

Two series of new electroactive and photoactive coil-rod-coil and rod-coil-rod triblock copolymers, poly (pentadecamethylene carboxester)-block - poly(p-phenylene benzobisthiazole) - block - poly (pentadecamethylene carboxester) (1), and poly(2,6-benzoxazole)-block poly(benzobisthiazole decamethylene)-block-poly(2,6-benzoxazole) (2), were synthesized, characterized, and used to investigate the self-assembly properties of rod-coil block copolymers. The progressive band narrowing of the absorption spectrum of thin films of 1 confirmed the effects of spatial confinement with increasing coil block size. Photoluminescence studies of thin films of 1 and 2 showed the effects of self-organization, annealing at 110 °C, block lengths, and composition on photophysical properties. Bilayer photoreceptors consisting of a layer of block copolymer as the charge generation layer and a layer of tris(p-tolyl)amine dispersed in polycarbonate as a trap-free hole transport layer were oberved to have high quantum efficiency, good photosensitivity and good dark decay.
Cascade Connected Organic El Diodes for Multi-Color Emission
Authors: Ohmori Yutaka , Tada Norio , Kurosaka Yoshitaka , Fujii Akihiko , Yoshino Katsumi
Published: April 2011

Multicolor electroluminescent (EL) device which emits red (R), green (G) and blue (B) light has been realized by stacking a two-color emission part and a single-color emission part. The former part consists of two emissive layers of red and blue light, which can be selected by changing the polarity of applied field. The latter part consists of a single emissive layer of green light. The emission color from the R-G-B emission device can be modulated by the combination of applying various voltages to the two-color and to the single-color emission parts, separately.
Photolithographic Patterning of Vacuum–Deposited Organic Light Emitting Devices
Authors: Tian P. F. , Burrows P. E. , Bulovic V. , Forrest S. R.
Published: April 2011

A photolithographic technique to fabricate vacuum-deposited organic light emitting devices has been demonstrated. The photolithographically patterned, yet unpackaged devices show no sign of deterioration in room ambient when compared with devices fabricated using shadow masks. Furthermore, the environmental robustness of the encapsulated devices makes them particularly useful in fabricating high resolution, full color displays.
Observation of the Temperature Dependence of the Dynamics of Photoexcited States in Pristine Tris(8-Hydroxyquinoline) Aluminum (Alq3)
Authors: Priestleya Richard , Walsera Ardie D. , Dorsinville Roger
Published: April 2011

We have investigated the temperature dependence of the dynamics of radiative excited states in pristine thin films of tris(8-hydroxyquinoline) aluminum (Alq3). By measuring the transient photoluminescence (PL) response with subnanosecond resolution, our results revealed an increase in the radiative excited state lifetime and fluorescence quantum yield with decreasing temperature from 300K to 77K. At low temperature we observed a decrease in the bimolecular recombination rate constant, singlet exciton diffusion coefficient and diffusion length. A singlet exciton trapping model is used to explain these results.
The Dielectric Response Of 8-Hydroxyquinoline Aluminum used in Multilayer Organic Devices
Authors: Niko A. , Hochfilzer C. , Jost T. , Graupner W. , Leising G.
Published: April 2011

We present optical measurements of 8-hydroxyquinoline aluminum (Alq3) a metal-chelate complex which is an important material used for multilayer light emitting diodes. Thin films of Alq3 produced by vacuum deposition were investigated by transmission and reflectance spectroscopy, and the dielectric coefficients in the near IR to UV-Vis energy range were calculated. Kramers-Kronig analysis was used to determine the real and imaginary dielectric spectral dependence of the thin films. Values obtained by internal field distribution measurements in organic double layer LED's are compared to those determined from optical data. A near-IR value of epsilon (real component) close to 3 was obtained from optical measurements.
Characterizing the NLO Chromophore Orientation of Polymeric Film by Electroabsorption Spectroscopy
Authors: Yang Ke , Wang Xiaogong , Kim Woohong , Jain Aloke , Li Lian , Kumar Jayant , Tripathy Sukant
Published: April 2011

The dispersion of third-order nonlinear coefficients and of three different NLO(nonlinear optical) polymer films were determined by electroabsorption spectroscopy. The first material investigated is an epoxy-based polymer BP-2A-NT, with azobenzene NLO chromophore 4-[((4-nitrophenyl)(azo)phenyl)azo)]aniline in its side chain. The other materials are two polydiacetylenes, poly(BPOD) and poly(4-BCMU), in which the( 3de)localized polymer chains contribute to the third-order nonlinearity. The complex spectrum of of each material is very similar in shape to corresponding spectrum. The ratio of to is 3.2 for BP-2ANT, 1.5 for both poly(BPOD) and poly(4-BCMU). These ratios indicate that the distribution of the side-chain NLO chromophores of BP-2A-NT is very close to three-dimensional isotropy, and the distribution of the main-chain chromophores of poly(BPOD) and poly(4-BCMU) is concentrated on the film plane.
Investigation of Dielectric Constant and Dispersion in Barium Strontium Titanate Capacitors
Authors: Zafar Sufi , Chu Peir , Remmel T. , Jones Robert E. , White Bruce , Gentile David , Jiang Bo , Melnick Bradley , Taylor Deborah , Zurcher Peter , Gillespie Sherry
Published: April 2011

The correlation between the dielectric constant and dispersion is investigated for barium strontium titanate (BST) capacitors with platinum and iridium electrodes. For platinum electrode capacitors, dispersion decreases with increasing dielectric constant. In contrast, capacitors with iridium electrodes exhibit the reverse correlation. A simple model is proposed to provide a quantitative explanation for the observed correlation for both platinum and iridium electrodes. In addition, the dependence of the dielectric constant and dispersion on varying ratios of (Ba+Sr)/Ti is also reported.
PZT Electro-Optic Waveguide Devices Fabricated by Solid-Phase Epitaxy
Authors: Nashimoto Keiichi , Nakamura Shigetoshi , Moriyama Hiroaki , Watanabe Masao , Osakabe Eisuke
Published: April 2011

High quality epitaxial PZT optical waveguides have been grown by solid-phase epitaxy based on metal alkoxide solution process. Optical propagation loss was 4 dB/cm in epitaxial PZT thin film optical waveguides grown on SrTiO3 substrates. Epitaxial PZT optical waveguides were grown on Nb doped conductive SrTiO3 substrates, since considerable reduction in drive voltage will be expected when top electrode / optical waveguide / conductive substrate structures are realized. Propagation loss was relatively large, as compared with the structure using non-dope insulative substrates. Preliminary electrooptic deflection devices were fabricated by preparing prism electrodes on the surface of the PZT optical waveguides. Efficient deflection/switching of coupled laser beam in the PZT optical waveguides as large as 26 mrad was observed by applying 70 volts between prism electrode and Nb doped SrTiO3 substrates.
Sol-Gel Derived Ferroelectric YMnO3 Films
Authors: Teowee G. , McCarthy K. C. , McCarthy F. S. , Dietz B. H. , Davis D. G. , Uhlmann D. R.
Published: April 2011

Sol-gel derived YMnO3 films have been prepared on platinized Si wafers. Crystallization took place at firing temperatures above about 750C. The crystallized films were very conductive. YMnO3 films exhibited a dielectric constant of 23, a remanent polarization of 1.0 μC/cm2 and a coercive field of 12 kV/cm, all measured at -33C The FE loop was lossy and elliptical at room temperature but became more distinct at lower measuring temperatures or at higher measuring frequencies.
Design of Catalysts with Artificially Controllable Functions Using Surface Acoustic Waves and Resonance Oscillations Generated on Ferroelectric Materials
Authors: Saito N. , Ohkawara Y. , Sato K. , Inoue Y.
Published: April 2011

A poled ferroelectric material of a LiNbO3 single crystal and a polycrystalline lead strontium zirconium titanate(PSZT) disc were employed as a catalyst substrate, on which various metals such as Pd, Ag, Ni and Pt and a WO3 oxide were deposited as a thin film catalyst. The effects of acoustic waves generated by rf power upon catalyst activation and reaction selectivity have been examined. The activity for CO oxidation of a Pt/PSZT catalyst increased by a factor of 3.9 with a thickness-extensional(TE) mode of resonance oscillation(RO) and 2.9 with a radial-extensional (RE) mode. The activation energy of the reaction was larger for the TE mode( 38 kJmol−1) than that for the RE mode(24 kJmol−1). The polarization axis-dependent changes in surface potential occurred with the TE mode, but not with the RE mode. With the TE mode, the activation energy of ethanol oxidation over a Ni/LiNbO3 and a Ag/LiNbO3 catalyst decreased from 36 to 19 kJmol−1 and from 76 to 30 kJmol−1, respectively, and the TE mode had a larger effect on the reaction with a higher activation energy. In ethanol dehydrogenation and dehydration on a WO3 / LiNbO3 catalyst, the TE mode increased remarkably the selectivity for ethylene production without giving a significant change to acetaldehyde production. The effects of acoustic wave excitations on the catalysts are discussed.
Molecular Modeling of Selective Adsorption from Mixtures
Authors: Bandosz T. J. , Blas F. J. , Gubbins K. E. , McCallum C. L. , McGrother S. C. , Sowers S. L. , Vega L. F.
Published: April 2011

Molecular simulation methods provide a means for carrying out systematic studies of the factors affecting adsorption phenomena. For selective adsorption, the selectivity is strongly affected by the interaction energy with the pore walls, molecular size and shape, site specific interactions, entropie effects, differences in diffusion rates, and networking effects. Two recent studies of site specific selectivity will be described. The first is an investigation of the effect of oxygenated surface sites on the adsorption of water vapor on activated carbons. Hydrogen-bonding sites are modeled using off-center square well interactions for both water and wall sites; wall sites are placed at the edges of the graphite micro-crystals. New experimental results for water adsorption at low pressures on carefully characterized activated carbons are reported, and are found to be in good agreement with the simulations. In the second application, we consider the separation of alkene/alkane mixtures using aluminas whose surfaces have been doped with metal ions, π-complexation between these metal ions and the alkenes can produce a highly selective separation. The simulations are found to be in good agreement with the available experimental data, and have been used to predict separations for other conditions not yet studied in the laboratory.
Characterization of Carbon Nitride Films Prepared by Magnetic Filtered Plasma Deposition
Authors: Wei Aixiang , Chen Dihu , Ke N. , Peng Shaoqi , Wong S. P.
Published: April 2011

Carbon nitride films prepared by magnetic filtered plasma deposition were characterized using Fourier transform infrared (FTIR) absorption and X-ray photoelectron spectroscopy (XPS). Characteristic bands corresponding to C-N, C=N, C=N, and C=C bonds were observed in FTIR spectra. It was found that the XPS C 1s and N 1s signals could be deconvoluted into three and two gaussian peaks, respectively. A plausible suggestion on the assignments of the XPS peaks to C3N4, CNx and ta-C phases was discussed. The relative abundance of the various CN bonds, the relative abundance of the various bonding components from XPS results, and their dependence on the nitrogen partial pressure PN during deposition were analyzed. Assuming the assignments of the XPS peaks to the various phases, the XPS results suggested that there would be an optimal PN that would favor the growth of the C3N4 phase. The electrical conductivity, the optical band gap and the Vickers hardness of these films were measured and the effects of PN on these properties were studied.
Doping Mechanism in Tetrahedral Amorphous Carbon
Authors: Chen C W , Robertson J
Published: April 2011

Doping in hydrogenated amorphous silicon occurs by a process of an ionised donor atom partially compensated by a charged dangling bond. The total energies of various dopant and dopant/bonding combinations are calculated for tetrahedral amorphous carbon. It is found that charged dangling bonds are less favoured because of the stronger Coulombic repulsion in ta-C. Instead the dopants can be compensated by weak bond states in the lower gap associated with odd-membered π-rings or odd-numbered π-chains. The effect is that the doping efficiency is low but there are not charged midgap recombination centres, to reduce photoconductivity or photoluminescence with doping, as occurs in a-Si:H.
The Effect of Bonding Disorder on the Vibrational Features of Amorphous Carbon Based Binary Alloys
Authors: Compagnini G. , Foti G.
Published: April 2011

In this work we report some results concerning Raman characterisation of covalently bonded amorphous carbon based thin films (∼ 100 nm) of binary alloys, obtained by ion implantation of carbon ions into silicon and germanium matrices. It will be shown that compositional disorder is present in our samples even below the stoichiometric concentration (∼50 carbon at.%) as deduced by the presence of three vibrational features in the Raman spectra. A quantitative measure of the compositional disorder will be also given by using either Raman or infrared spectroscopies in samples with different carbon content.
High Pressure Lattice Instabilities and Structural Phase Transformations in Solids from Ab-Initio Lattice Dynamics
Authors: Baroni Stefano , Giannozzi Paolo
Published: April 2011

This paper is devoted to some recent applications of density-functional perturbation theory to the prediction of lattice instabilities occurring in ionic solids at high pressure. We first briefly review some work aimed at understanding the interplay between shear instabilities and phonon softening in the pressure-induced phase transformations of Cesium halides and hydride. We then report on preliminary results of an attempt of ours to apply similar techniques to the long-standing problem of the pressure-induced amorphization of quartz.
Studies on Materials Under Ultrahigh P-T at the Advanced Photon Source
Authors: Shen G. , Duffy T. , Wang Y. , Rivers M. , Sutton S.
Published: April 2011

The Advanced Photon Source (APS) is a third-generation synchrotron now in operation at Ar-gonne National Laboratory. A national user facility for research in the Earth sciences is being constructed by the GeoSoilEnviro group of the Consortium for Advanced Radiation Sources (GSECARS). One component of this effort is the program for diamond anvil cell (DAC) research, to study materials at ultrahigh pressure and temperature conditions using a variety of techniques.

In this paper, we describe the DAC facility that is being developed at the GSECARS. Recent progress in developing a laser heating system is presented.
A Study of Band Alignment in GaAs/GaInP(Partially Ordered) Heterostructures with High Pressure
Authors: Uchida K. , Yu P. Y. , Zeman J. , Kwok S. H. , Teo K. L. , Su Z. P. , Martinez G. , Arai T. , Matsumoto K.
Published: April 2011

In this paper we review the use of high pressure techniques to investigate the optical properties of partially ordered GalnP epitaxial layers grown on GaAs substrates. In particular, we demonstrate the ability of high pressure to modify the band alignment at the GalnP/GaAs interface and hence to alter the optical properties of heterostructures fabricated from partially ordered GalnP on GaAs.
Pressure-Induced Amorphization and Disordering on Cooling in Semi-Crystalline Polymers; calorimetrie evidence for inverse melting in one component system
Authors: Rastogi S. , Höhne G. , Keller A.
Published: April 2011

We report some unusual phase behaviour, of general implication for condensed matter, on the polymer poly-4-methyl pentene-1 (P4MP1) induced by changes in pressure (P) and temperature (T), as observed by in-situ X-ray diffraction and high pressure DSC. Upon increasing pressure beyond a threshold value, the polymer, crystalline at ambient conditions, looses its crystalline order isothermally. The process is reversible. This behaviour is observed in two widely separated temperature regions, one below the glass transition temperature (< 50°C) and one close to the melting temperature (250°C), thus showing solid state amorphization and inversion in the melting temperature with increasing pressure. This further suggests inverse melting, i.e. re-entrant of the two widely separated liquid and amorphous phases along the T-axis at fixed P. This is confirmed experimentally as disordering in the crystalline structure on cooling. The inverse melting in P4MP1 raises the possibility of exothermic melting and endothermic crystallization as anticipated by Tammann (1903). The anticipated exothermic melting and endothermic crystallization is confirmed experimentally in the one component system P4MP1. We are observing similar features in a range of polymers.
Nanocomposite particles for the preparation of advanced nanomaterials
Authors: Somasundaran P. , Chen T.
Published: April 2011

New composites based on nano-size particles provide a promising route to the fabrication of novel materials for advanced technology applications. To produce desired materials, it is important to control the composition and distribution of nanoclusters within the bulk or surface coating of nanostructured materials. Towards this purpose, we have developed a novel method of processing nanocomposite materials utilizing colloidal chemistry techniques to tailor their microstructure. Unique composite aggregates of nanoparticles with a core-shell structure were prepared using a special scheme ofcontrolledpolymer adsorption. Polymers which specifically adsorb on both nano- and micron- size particles are used as tethers to enable desired coating of the later particles with the former and to enhance the cluster integrity. Nanocomposite particles consisting of micron-size alumina or silicon nitride as cores and nano-size alumina, titania, or iron oxide as shell particles have been successfully prepared using this process. The surface charge of the core particles is reversed after the adsorption of polyacrylic acid polymers. This promotes the interaction between the core and the shell particles and therefore nanoparticles added subsequently to the core particle suspension coat on core particles by electrostatic as well as possibly hydrogen bonding bridging mechanisms. Success of the process depends to a large extent on the absence of homoflocculation of nanoparticles and this is achieved by removing all the unadsorbed free polymers from the bulk solution before introducing them to coat on the polymer coated core particles. Coating itself is estimated by monitoring change in the zeta potential of core-shell structure. The coating scheme as well as the characterization of these nanocomposite particles are discussed in detail. This processing scheme provides a simple way for the preparation of both bulk and surface coatings with these engineered nanostructured particles as building blocks.
Nanostructured zinc sulphide phosphors
Authors: Vacassy R. , Scholz S. M. , Dutta J. , Hofmann H. , Plummer C. J. G. , Carrot G. , Hilborn J. , Akinc M.
Published: April 2011

Zinc sulphide (ZnS) particles are efficient phosphors for application in flat-panel displays. Spherical ZnS particles were prepared by precipitation from a homogeneous solution. Nanoparticles of 20 to 40 nm having a very narrow size distribution could be synthesized by using complexing chelates such as acetate and acetylacetonate. Complexing of the precipitating cation with the anions present in the system lead to a limited concentration of free cations in the solution. This strongly influences the kinetics of the primary particle agglomeration/growth, resulting in nanometer-sized ZnS particles. Nanostructured ZnS synthesized in this way are polycrystalline particles composed of crystallites of 5–10 nm. The synthesis of very small, non-agglomerated, nanocrystalline particles in the 5–10 nm size range was also possible, making use of a strong complexing ligand (thioglycerol) during the synthesis. The synthesis of controlled monosized ZnS particles will be presented and discussed. The photoluminescence characteristics of ZnS make this material a suitable candidate as phosphor for application in low voltage display technology. The effect of Mn2+ doping on the luminescence characteristics of ZnS will also be discussed.
Tin Dioxide Nano-Powders for Gas Sensor Applications
Authors: Vacassy R. , Houriet R. , Plummer C. J. G. , Dutta J. , Hofmann H.
Published: April 2011

SnO2 nanoparticles are of interest for gas sensor applications because the surface area is much larger compared to conventional powders. Thus, interactions between the material and the gases, which occur on the surface sites of the particles, are increased considerably. The preparation of SnO2 powders has been investigated following two forced precipitation systems: the hydrolysis reaction of SnC14 in an emulsion media and the hydrolysis reaction of Sn2+ in the presence of a complexing ligand (CH3COO−). Spherical nanoparticles in the 10 to 100 nm range and with a narrow size distribution were synthesized by both precipitating routes. In both cases, it has been demonstrated that the most important parameter which controlled the particle size was the nature of the associated anion. When this associated anion or ligand is able to form a strong complex with the colloidal subunits, a barrier against Van der Waals attraction is created which results in little growth. This greatly influences the agglomeration/growth kinetics during the precipitation. The effect of acetate chelating ligands which resulted in the SnO2 nano-powders formed of 5–10 nm crystallites will be presented and discussed. Preliminary results on the gas (N2, NO) adsorption studies on pellets formed from these powders are also presented.
Magnetically assisted impaction coating process to synthesize engineered particulates with controlled surface characteristics
Authors: Ata Ali , Rabinovich Ya. I. , Singh R. K. , Hendrickson W.
Published: April 2011

A novel dry coating technique called magnetically assisted impaction coating (MAIC) to synthesize engineered particulates with controlled surface coatings has been developed. In this method, the impaction of magnetic particles, core particles and secondary particles results in dry coating on the surface of the core particle. The attachment of particles to surfaces and factors affecting the efficiency of the process have been discussed.
RDF Analysis of Ion-Amorphized SiO2 and SiC from Electron Diffraction using Post-Specimen Scanning in the Field-Emission Scanning Transmission Electron Microscope
Authors: Bell David C. , Garratt-Reed Anthony J. , Hobbst Linn W.
Published: April 2011

Radial density functions (RDFs) provide important information about short- and ntermediaterange structure of topologically-disordered materials such as glasses and irradiation-amorphized materials. We have determined RDFs for irradiation-amorphized SiO2, AIPO4 and SiC by energy-filtered electron diffraction methods in a field-emission scanning transmission electron microscope (FEG-STEM) equipped with a digital parallel-detection electron energy-loss spectrometer. Post-specimen rocking was used to minimize the effects of spherical aberration in the objective lens, which interfere with the acquisition of data collected by pre-specimen rocking. Useful energy-filtered data has been collected beyond an angular range defined by q = 2 sin(Θ/2)/λ = 25 nm−1
Preparation of Hard Coatings on Polycarbonate Substrate by High Frequency Ion Beam, Deposition using CH4/H2 Gases
Authors: Kim S. R. , Song J. S. , Choi Y. J. , Kim J. H.
Published: April 2011

Polycarbonate is one of the most widely used engineering plastics because of its transparency and high impact strength. The poor wear and scratch properties of polycarbonate have limited its application in many fields. In order to improve the wear and scratch properties of polycarbonate we have deposited diamond like carbon (DLC) coatings. The diamond like carbon coatings were made using a high frequency ion beam gun by introducing H2 and CH4 gases. The coatings were characterized with scanning electron microscope, Raman spectroscopy, ellipsometer, and microscratch tester. Polymer hard coating was applied onto the polycarbonate substrate before depositing a diamond like carbon coating to see the effect of interlayer on the system's failure mechanism.