bluuebunny/crossref_metadata_2025_split huggingface dataset:
Combustion for the Synthesis of β-SiC and Diamond/SiC Composite
Authors: Raghunathan Rohini , Chowdhury Rina , Narayan Jagdish 
Published: March 2011

AbstractCubic β-SiC was processed under conditions of self-propagating high-temperature synthesis, based on the exothermic reaction between elemental Si and C powders. The set up for the synthesis of SiC using a mixture of Si and C is described. X-Ray and Raman spectroscopy studies were performed to characterize the quality of the β-SiC produced using the new set up. Scanning Electron Microscopy and Transmission Electron Microscopy studies were also carried out to study the mechanism of the formation of β-SiC from the elemental powders. The density of the compact and grain size of the graphite was found to be critical in the formation of the SiC. Diamond seeds were also implanted on the SiC pellet while compaction and this implanted diamond provided the necessary seed for the growth of a thick diamond film. The adhesion of the film is good because of its growth from the implanted diamond. Diamond films were grown on SiC using HFCVD. The quality and the adhesion of the diamond films on SiC were studied using SEM.
Copper-Containing Ceramic Precursor Synthesis: Solid-State Transformations and Materials Technology
Authors: Hepp Aloysius F. , Eckles William E. , Duraj Stan A. , Andras Maria T. , Fanwick Phillip E. , Richman Robert M. , Sabat Michael L. , Power Michael B. , Gordon Edward M. , Barron Andrew R. 
Published: March 2011

AbstractThree copper systems with relevance to materials technology are discussed. In the first, a CuS precursor, Cu4S 10(4-methylpyridine)4 (4-MePy), was prepared by three routes: reaction of Cu2S, reaction of CuBr•SMe2 and oxidation of copper powder with excess sulfur in 4-methylpyridine by sulfur. In the second, copper powder was found to react with excess thiourea (H2NC(S)NH2) in 4-methylpyridine to produce thiocyanate (NCS-) complexes. Three isolated and characterized compounds are: Cu(NCS)(4-MePy)2, a polymer, [4-MePy•H][Cu(NCS)3(4-MePy)2], a salt, and t-Cu(NCS)2(4-MePy)4. Finally, an attempt to produce a mixed-metal sulfide precursor of Cu and Ga in N-methylimidazole (N-MeIm) resulted in the synthesis of a Cu-containing polymer, Cu(S04)(N-Melm). The structures are presented; the chemistry will be briefly discussed in the context of preparation and processing of copper-containing materials for aerospace applications.
Processing and Property Evaluation of Si(N,C) Coatings on Silica Glass/Quartz Substrates
Authors: Gonsalves Kenneth E. , Xiao Tongsan D. , Strutt Peter R. 
Published: March 2011

AbstractThis investigation outlines a process for the synthesis of preceramic/ceramic hard coatings on glass substrates. The precursor used was an organosilazane monomer [CH3SiHNH]n, with n=3 or 4. The glass substrates were dip coated in organosilazane solutions. The coated samples were then heat treated in different gaseous environments to produce the desired preceramic and ceramic coatings. The mechanical properties of the coatings were evaluated, such as rupture strength and microhardness. The former was measured using a four-point bend test (ASTM c150). Vicker's hardness rupture strength measurement were performed on both coated and uncoated specimens subjected to the heat treatment conditions. Microstructural examination was performed using a SEM. Chemical information, such as bonding was investigated via FTIR spectroscopy.
Stresses and Adhesion of Thin Polycrystalline 3C SiC Films Grown by CVD on Silicon Substrates
Authors: Ivanova L.M. , Kovalenko V.V. , Tkacheva T.M. 
Published: March 2011

AbstractSiC thin films less than 1 μm thick are grown by thermal decomposition of CH3SiC13 in a hydrogen atmosphere in an open CVD system. The interface stress is shown to be depend on the growth conditions. The optimal conditions for the preparation of uniform SiC films have been determined. Thermal annealing of the films has also been studied, and the conditions that provide for relaxation of the interface stresses are determined.
Surface and Bulk Interactions in M-SiC Systems (M = Au, Cu, Ni).
Authors: Rado C. , Kalogeropoulou S. , Eustathopoulos N. 
Published: March 2011

AbstractSurface and bulk interactions between a metal M (M = Au, Cu or Ni) and monocrystalline α-SiC are studied. Surface interactions are quantified by the work of adhesion measured by the sessile drop technique under high vacuum. Products of M-SiC bulk reactions are characterised by electron microscopy and microprobe analysis. Interpretation of experimental results is based on classical thermodynamics for equilibria of bulk phases and on interfacial thermodynamics for adsorption phenomena and wetting.
X-ray Absorption Study of Pulsed Laser Deposited Boron Nitride Films
Authors: Chaiken A. , Terminello L.J. , Wong J. , Doll G.L. , Sato T. 
Published: March 2011

AbstractB and N K-edge x-ray absorption spectroscopy measurements have been performed on three BN thin films grown on Si substrates using ion-assisted pulsed laser deposition. Comparison of the films’ spectra to those of several single-phase BN powder standards shows that the films consist primarily of sp2 bonds. Other features in the films’ spectra suggest the presence of secondary phases, possibly cubic or rhombohedral BN. Films grown at higher deposition rates and higher ion-beam voltages are found to be more disordered, in agreement with previous work.
The Effect of Impurities on the Ideal Tensile Strength of Covalent Crystals - Ab-Initio Quantum Molecular Dynamics Calculations
Authors: Huang Y.M. , Spence J.C.H. , Sankey Otto F. 
Published: March 2011

AbstractUsing first-principles electronic structure calculations in the local density approximation combined with lattice dynamics, we investigate the effect of III/V impurities on the ideal strength of covalent solids (C, Si, and Ge). Our results show that undoped crystalline solids are stronger in tension along [111] than n-type crystalline solids. P doping has a negligible effect on ideal tensile strength, while n-type doping causes a small reduction in strength of about 6%. The n-type impurity effect is due to the negative (repulsive) contribution from the bottom state of the distorted conduction band to the ideal strength of the solid.
Physical Properties of Nanocrystalline MoS2 and WS2 Particles Produced by CO2 Laser Pyrolysis
Authors: Bi Xiang-Xin , Wang Ying , Lee W. T. , Wang Kai-An , Bandow S. , Eklund P. C. 
Published: March 2011

AbstractNanocrystalline powders of 2H-MoS2 and 2H-WS2 with average particle size 5 and 9 nm, respectively, have been produced using C02laser pyrolysis. Typical production rate for these nanoparticles is 2g/hr. Particle size, crystallite size, and the structural phase were determined using X-ray diffraction(XRD), transmission electron microscopy(TEM), and Raman scattering. Particle size effects may have been observed in the Raman-active modes (WS2 and MoS2) and in the band-edge excitons (MoS2).
Hafnium Nitride Dielectric Phase Films Fabricated by Ion-Beam Sputtering
Authors: Klemm Karl. A. , Johnson L. F. , Kosik W. E. , Mckenzie D. R. , Perez I. , Pontelandolfo M. 
Published: March 2011

AbstractHafnium nitride films were deposited by ion-beam sputtering, and characterized for their composition, electrical, structural, mechanical and optical characteristics. Films were found to vary widely in their properties, based upon the parameters under which they were deposited. The films were found to have a nitrogen to hafnium ratio of up to 1.45:1, resistivity varying from 10−2 to 105 Ω-cm, as well as widely variable optical characteristics, depending on process variables. Structural characterization of the dielectric phase HfNx (x>l) material by X-ray and electron diffraction reveals a distortion of the hafnium mononitride rock salt structure with increasing amounts of nitrogen, in accordance with previous findings. Infrared spectroscopic characterization of the thin film dielectric phase hafnium nitride optical properties reveals the likely existence of multiple bonding between nitrogen in the material.
Nonthermochromic Forms of the Polydiacetylene ETCD
Authors: Sandman Daniel J. , Downey Milton J. , Hankin Sandra H.W. 
Published: March 2011

ABSTRACTSubjecting crystals of the thermochromic polydiacetylene (PDA) from the bis (ethyl ure thane) of 5,7-dodecadiyne-1, 12-diol (ETCD) to the solvents chlorobenzene and ?,?-dimethylformamide above the thermochromic transition temperature of PDA-ETCD irreversibly converts the material to nonthermochromic forms. These new forms have been characterized by their structural, thermal, and spectral properties. The materials isolated after exposure to chlorobenzene are highly crystalline with a structure that has expanded and disordered, yet is still related to that of the pristine polymer. The observed properties are discussed in the framework of the crystal structure-thermochromism relationship for urethane-substituted PDA.
The Metallic State of Conducting Polymers: Microwave Dielectric Response and Optical Conductivity
Authors: Epstein A. J. , Joo J. , Kohlman R. S. , Macdiarmid A. G. , Weisinger J. M. , Min Y. , Pouget J. P. , Tsukamoto J. 
Published: March 2011

ABSTRACTRecent advances in processing of polyaniline and polyacetylene have resulted in a new generation of conducting polymers with higher dc conductivities. We present the temperature (T) dependent microwave frequency dielectric constant, dc conductivity, and Kramers-Kronig analysis of conducting polyaniline and polyacetylene. The low temperature dielectric constant, ε, increases with the square of the x-ray crystalline domain length for preparations of HCl protonated polyaniline. For the highest crystalline polyaniline samples, ε increases dramatically with increasing T, supporting formation of three-dimensional (3-D) coupled “mesoscopic” Metallic regions. A “metallic” negative ε is observed for d,1-camphor sulfonie acid doped polyaniline prepared in m-cresol. Optical studies show a linear increase in reflectivity below 7000 cm-1. Below 600 cm-1 the reflectance increases rapidly. Kramers-Kronig analysis of the ir-visible results are presented. Highly conducting polyaniline is shown to have two plasma frequencies, one at ∼ 1.1 eV involving all the conduction band electrons, and one at ∼0.015 eV (120 cm-1) that is suggested to arise from the most delocalized electrons. The concept of inhomogeneous disorder is introduced. The results for polyaniline are compared to those of highly doped polyacetylene which also show metallic negative ε demonstrating the intrinsic metallic nature of the new generation of conducting polymers.
Synthesis and Physical Properties of Self-Orienting Head-To-Tail Polythiophenes.
Authors: McCullough Richard D. , Williams Shawn P. , Jayaraman Manikandan , Reddinger Jerry , Miller Lynnette , Tristram-Nagle Stephanie 
Published: March 2011

ABSTRACTDesigned synthesis and architectural assembly of head-to-tail polythiophene derivatives provide the ability to control π orbital topology and orbital interactions in conjugated polymers. The preparation of polythiophene derivatives with essentially 100% head-to tail (HT) couplings leads to defect free polythiophenes. These new HT polythiophenes can undergo macromolecular self-assembly to give self-oriented conducting polymers. Study of these materials has led to new insights on structure-property relationships in this class of Materials. In addition, these results show that the molecular orbital overlap, the band dimensionality, and the solid state structure are quite sensitive to the nature of the side chains attached to the polymer's backbone. In addition, we have now synthesized the first heteroatom functionalized HT polythiophenes. These polythiophene derivatives can bind cations, and ion recognition can be used to tune conjugation lengths and properties in polythiophenes. Also presented are a class of random HT coupled 3-alkylthiophenes whose optical and electrochemical properties and possibly electronic properties can be altered by recipe.
A New Dithiophene Fused p-Phenylene Vinylene Conducting Polymer. Synthesis and Study
Authors: Pomerantz Martin , Wang Jiping , Seong Seeyearl , Starkey Kyle P. , Nguyen Long , Marynick Dennis S. 
Published: March 2011

ABSTRACTA new conducting polymer, poly (benzo[1,2-b:4,5-b′]dithiophene-4,8-diyl vinylene) (1), has been prepared by pyrolysis of a precursor polymer 2, which, in turn, was prepared by a multistep synthetic sequence (Scheme 1). The polymer has a UV-vis spectral maximum at 501 nm (2.48 eV), band-gap (band edge) of 1.92 eV and with FeC?3 doping a conductivity of 15 S cm1. Quantum Mechanical calculations using PRDDO, ab-initio and modified extended Hiickel Methodology on the Monomers, trimers and polymers, both aromatic and quinoid, provided structures and an absorption maximum band-gap which is consistent with either a planar aromatic polymer or a polymer which has both aromatic and quinoid units.
Soluble Conducting Polythiophenes for Charge Dissipation in Electron Beam Lithography
Authors: Huang Wu-Song 
Published: March 2011

ABSTRACTIn electron beam lithography, charging on photoresist usually causes image distortion and placement error. To dissipate the charge, a conductive polymeric layer can be introduced either over or under the photoresist coating. In this paper, we will discuss the approach of using toluene and xylene soluble polyalkylthiophcne in combination with photoacid generator as a discharge underlayer or interlayer beneath photoresist to dissipate the accumulated charge during li-bcam exposure. We will also discuss the use of water soluble acid or ammonium salt form of poly 3- (cthanesulfonate) thiophene as discharge. toplayer. During the resist image developing process, the toplayer will be removed by aqueous base. Therefore, it is advantageous to use discharge toplayer due to its simplicity. In this study, the salt and acid form of poly 3- (ethanesulfonate) thiophene was synthesized through chemical polymerization of the corresponding methanesulfonate ester. It exhibits the same properties as that of electrochemically synthesized polymer reported in the literature.
Characterization And Photoconductive Properties Of Highly Oriented Thin Films Of Oxotitanium Phthalocyanine Prepared By Vacuum Deposition Technique
Authors: Yonehara Hisatomo , Pac Chyongjin 
Published: March 2011

ABSTRACTThin films of oxotitanium phthalocyanine were grown on optical flat PYREX glass substrates at 0.05 – 1.5 nm/s under 2×l0-4Pa. The films were analyzed by X-ray diffraction patterns (XRD) and polarized absorption spectra to reveal a preferred molecular orientation in the films evaporated at 0.05 nm/s, but amorphous nature of the films prepared at higher deposition rates. All the films were changed in the crystallinity to α-form Microcrystals upon exposure to vapor of methylene chloride or tetrahydrofuran. XRD analysis of the vapor-treated films at 0.05 nm/s showed only an intense peak at 2θ = 7.50°, demonstrating that the (010) face of the α-form crystal is highly oriented perpendicularly to the substrate surface. The Molecular orientation was again demonstrated by polarized absorption spectra. The photoconductive behavior of the films was found to depend on the deposition rates as well as on the vapor treatment.
Influence of Anisotropic Scattering Along the 2D-Fermi Surface on Transport Properties in an Asymmetric-Donor-Based Molecular Crystal
Authors: Fortune Nathanael A. , Murata K. , Papavassjuou G. C. , Lagouvardos D. J. , Zambounis J. S. 
Published: March 2011

ABSTRACTWe report our results for the temperature dependence of the Hall coefficient and in-plane resistivity for the asymmetric-donor-based quasi-2D Molecular crystal τ- (P-S,S-DMEDT-TTF)2 (AuBr2)1(AuBr2)y (y≈0.75). Using a recent “geometrical representation” of the weak-field 2D Hall conductivity developed by N.P. Ong [Phys. Rev. B 43, 193 (1991)], we model the temperature dependence of these electronic transport properties in terms of the temperature dependence of the scattering path length and its anisotropy along the 2D Fermi surface.
Fermi Surface and Magnetoresistance in an Organic Metal β″ -(BEDT-TTF)2AuBr2
Authors: Uji S. , Aoki H. , Tokumoto M. , Ugawa A. , YakushP K. 
Published: March 2011

ABSTRACTThe Shubnikov-de Haas (SdH) and Magnetoresistance Measurements have been performed in an organic Metal β″ (BEDT-TTF)2AuBr2. Absence of saturation in the magnetoresistance up to 13T suggests that this salt is a compensated Metal. The SdH oscillations are consistently understood by assuming that three cylindrical Fermi surfaces are present. The frequencies of the SdH oscillations corresponding to the Fermi surfaces are determined to be 41.5 T, 139 T, and 181 T for H//b*-axis. An anomalous maximum in the resistance is found at about 9.5 K for H//b*-axis although no anomaly is observed for H//plane.
Synthesis, Layer Assembly, And Fluorescence Dynamics Of Poly (Phenylenevinylene) Oligomer Phosphonates
Authors: Katz H. E. , Shane S. F. , Wilson W. L. , Schilling M. L. , Ungashe S. B. 
Published: March 2011

ABSTRACTThe title oligomers have been incorporated in Zr-based layers on quartz substrates. Absorbance and emission spectra and fluorescence decays have been measured on these films and compared with data from solutions, powders, and PPV. The samples may be divided into those with “liquid-like” behavior and “solid-like” behavior; the latter is characterized by blue-shifted absorbance, red-shifted emission, and more complex decay dynamics than the former. By these criteria, the layers and PPV itself are decidedly “solid-like’.
Light-Emitting Diodes Using Semiconducting Oligothiophenes
Authors: Uchiyama K. , Akimichi H. , Hotta S. , Noge H. , Sakaki H. 
Published: March 2011

ABSTRACTThe light-emitting diodes (LEDs) using semiconducting oligothiophenes, dimethylquater-thiophene (DMQtT, tetramer), dimethylquinquethiophene (DMQqT, pentamer) and dimethyl-sexithiophene (DMSxT, hexamer), have been investigated. These oligomers were deposited on ITO-coated glass in ultra high vacuum and an aluminum electrode was subsequently vacuum-deposited on top of the oligomers. These structures have the diode configuration with Schottky barrier between the oligomers and aluminum.The LED using DMSxT shows good rectifying feature with the rectifying ratio of 1500 at ±10V.Red-orange emission is clearly observed above 4V bias. In this LED, DMSxT acts not only as an emitting layer but also as a hole transport layer. We have also fabricated and studied alternate layered structures of DMSxT/DMQtT and DMSxT/DMQqT as the emitting layer. In these configurations, the carrier recombination can be modulated because both DMQtT and DMQqT have energy gaps wider than that of DMSxT.The quantum efficiencies (photons emitted per carriers injected) of the LEDs using DMSxT/DMQtT and DMSxT/DMQqT are about one hundred times and one thousand times larger than that of the LED solely based on DMSxT, respectively. These results indicate that the layered structures are advantageous in increasing quantum efficiency of the emission.
New Developments in Second-Order Nonlinear Optical Polymeric Materials
Authors: Tripathy S. K. , Kim W. H. , Bihari B. , Cheong D. W. , Kumar J. 
Published: March 2011

ABSTRACTSecond harmonic generation from the spin coated films of an asymmetrically substituted polydiacetylene, namely poly ((8-butoxy carbonyl) Methyl urethanyl) l- (5-pyrimidyl) -octa-l,3-diyne (BPOD) is reported for the first time. The Macromolecules assemble to produce the organization responsible for SHG without recourse to poling. d33 of the spin coated film (0.19–0.31 μm thickness) are between 0.78–0.88 pm/V without absorption correction and 3.32–5.57 pm/V after correction. Angular and polarization dependence study of the second harmonic response suggests that the film has in-plane isotropy as a whole and the net dipole is nearly perpendicular to the film surface. Spontaneous orientation of the polymer chains during the film formation seems to be responsible for the noncentrosymmetric alignment of the polymer. SHG from the Langmuir Blodgett films are also reported.
Control of the Mesoscopic Organization of Conjugated Thiophene Oligomers, Induced by Self-Assembly Properties
Authors: Garnier Francis , Yassar A. , Hajlaoui R. , Horowitz G. , Deloffre F. 
Published: March 2011

ABSTRACTConjugated oligomers form a fascinating class of molecular semiconductors, which open the perspective of control of electronic and structural properties through the variation of their chemical structure. For analysing the correlation between charge transport and structural properties, sexithiophene, 6T, was substituted by hexyl groups, both on the terminal α positions (α,ωDH6T) and as pendant groups in β position (β,β′DH6T). Structural characterizations by X-ray diffraction show that vacuum evaporated thin films of 6T and α,ωDH6T consist of layered structure in a monoclinic arrangement, with all-planar Molecules standing on the substrate, and that a much longer range ordering is observed when passing from 6T to α,ωDH6T, evidencing a large increase of molecular organization at the mesoscopic level. Electrical characterizations also indicate a significant enhancement of anisotropy of conductivity, with a ratio of 120 in favor of the conductivity along the stacking axis for α,ωDH6T. The charge carrier mobility, measured on field-effect transistors fabricated from these conjugated oligomers, also shows a large increase by a factor of 25 when passing from 6T to α,ωDH6T, and reaches a value close to 10-1cm2V-1s-1. In contrast, ββ′DH6T presents very low conductivity and mobility. These observations are attributed to the self-assembly properties brought by alkyl groups in α,ω position, and confirm the large potential of molecular engineering of organic semiconductors.
Polyimide/Norganic Composite - Interpenetrating Polymer Network For Stable Second-Order Nonlinear Optics
Authors: Marturunkakul Sutiyao , Chen Jeng-I , Li Lian , Jiang Xin Li , Jeng Ru Jong , Kumar Jayant , Tripathy Sukant K. 
Published: March 2011

ABSTRACTA new class of IPN system has been prepared and investigated. This IPN system combines the polybismaleinimide network and the NLO-active phenoxysilicon network. The second-order NLO coefficients, d33, values of the samples range from 2.5 to 6.7 pm/V depending on the composition and the processing conditions. The temporal stability of the second-order nonlinearities for these samples at 110 °C varies from 47 to 88 % retention after 274 h.
Nonlinear Optical Properties Of Substituted Stilbazolium-MPS3 Intercalation Compounds
Authors: Lacroix Pascal G. , Clement Rene , Nakatani Keitaro , Ledoux Isabelle , Zyss Joseph 
Published: March 2011

ABSTRACTWe have investigated intercalation into optically transparent MPS3 (M = Mn, Cd) phases as a way towards spontaneous poling of cationic chromophores. Two nano-composite Materials of formula M0.86PS3 (dimethylamino-N-Methyl stilbazolium)0.28 were synthezised, and an efficiency up to 750 times that of urea was recorded in the cadmium intercalate. An additional interest arises from the possibility to associate NLO properties with the magnetization of the host lattice in the case of MnPS3 below 40 K.