bluuebunny/crossref_metadata_2025_split huggingface dataset:
New Covalent Ceramics: MgSiN2
Authors: Groen Wilhelm A. , Kraan Marcel J. , de With Gijsbertus , Viegers Mathias P.A 
Published: March 2011

AbstractThe ternary nitride MgSiN2 crystallizes in a diamond-like structure with a band gap of 4.8 eV. These characteristics make the compound promising for a variety of applications. Recently we succeeded in preparing fully dense ceramics by sintering at 1550°C. Phase composition, chemical properties and the mechanical properties of the as-prepared ceramics are described. The ceramics are resistant to oxidation in air at least up to 920°C. The thermal conductivity at room temperature has been found to be 20 W/m·K. A considerable improvement of the thermal conductivity is expected when improved processing conditions, well within reach, are realized. A reasonable strength of 270 MPa and a fairly good fracture toughness of about 4.3 MPa·m½ are obtained. A hardness of about 15 GPa and a Young's modulus of 235 GPa have been measured. These new ceramics show that it is still possible to find improved materials as compared to the usual oxide and non-oxide ceramics.
Carbon Nitride Thin Films Grown by Pulsed Laser Deposition
Authors: Treece Randolph E. , Horwitz James S. , Chrisey Douglas B. 
Published: March 2011

AbstractThin films of diamond and diamond-like carbon (DLC) are technologically important materials that serve as hard, scratch resistant and chemically inert coatings for tools and optics. Recent calculations suggest that β-C3N4 should be harder than diamond. We have deposited carbon nitride (CNx) thin films by pulsed laser deposition. The films were grown from a graphite target in a nitrogen background. The nitrogen source was either (a) a N2 gas atmosphere, or (b) a N2+/N+ ion beam generated by a Kaufman ion gun. A wide range of deposition parameters were investigated, such as deposition pressure (0.3-900 mTorr N2), substrate temperature (50 and 600°C), and laser fluence (1-4 J/cm2) and laser repetition rate (1-10 Hz). The films have been characterized by Rutherford Backscattering Spectroscopy, thin-film X-ray diffraction, scanning electron microscopy, and micro-Raman spectroscopy. In general, the films were nitrogen deficient with a maximum nitrogen to carbon ratio (N/C) of 0.45 and a shift in the G band Raman peak consistent with amorphous CNx (a-CNx).
Chemical Vapor Infiltration of Non-Oxide Ceramic Matrix Composites
Authors: Besmann Theodore M. , Stinton David P. , Lowden Richard A. 
Published: March 2011

AbstractContinuous fiber ceramic composites are enabling new, high temperature structural applications. Chemical vapor infiltration methods for producing these composites are being investigated, with the complexity of filament weaves and deposition chemistry merged with standard heat and mass transport relationships. Silicon carbide-based materials are, by far, the most mature, and are already being used in aerospace applications. This paper addresses the state-of-the art of the technology and outlines current issues.
Textures in AiN-SiC Composite Ceramics
Authors: Sandlin Michael S. , Bowman Keith J. 
Published: March 2011

AbstractHistorically, texture analysis has been useful in explaining processing-induced property anisotropy in metals and deformation history in geological materials. Texture analysis, however, has not been fully utilized in explaining similar phenomena in ceramic systems. The scarcity of texture analysis in ceramic systems could conceivably stem from the classical conception that textures rarely develop in ceramic materials because of their lack of plasticity. While it is true that slip-based textures occur in only a limited number of ceramic systems, textures occur in a multitude of ceramic systems in which dislocation plasticity is not observed. The most prominent non-slip-based texture development mechanism in ceramic systems is grain rotation during processing. Other possible mechanisms for texture development in ceramics are seeded solid solution formation and oriented grain growth. These non-slip-based texture development mechanisms and other phenomena related to the measurement of textures in covalent ceramics are discussed in the context of the A1N-SiC system.
Reconstructions at Si- and C-Terminated Surfaces of 2H-SiC: an ab Initio Molecular Dynamics Study
Authors: Hwang Yong Gyoo , Chen Bin , Boguslawski Piotr , Bernholc J. 
Published: March 2011

AbstractThe reconstruction patterns of Si- and C-terminated surfaces of wurtzite SiC are studied by ab initio molecular dynamics. The (1×1) relaxed, (1×2) buckled, and (2×1) л-bonded chain geometries are considered. In the (l×1) geometry, inward relaxation of the C-terminated surface is much stronger than that of the Si-terminated surface. The C-terminated surface is stable with respect to (2×1) buckled reconstruction, but the Si-terminated surface is not. At both surfaces, the (2×1) л-bonded chain geometry is energetically the most favorable. The Si-C л-bonded chains are buckled and slightly dimerized. In both cases, the outermost atoms are carbons, due to the bond length constraints of the л-bonded chain reconstruction.
Interface Roughness Effects on Adhesion of Ta2N Films.
Authors: Moody N. R. , Venkataraman S. , Nelson J. , Worobey W. , Gerberich W. W. 
Published: March 2011

AbstractIn this study, we employed continuous microscratch testing to determine the effects of interface roughness on adhesion and fracture toughness of thin Ta2N films. These films were sputterdeposited on single crystal sapphire and polycrystal alumina substrates to a thickness of 0.5 μm. Comparison of the results showed that the interfacial fracture energy increased from 0.4 J/m2 for films on the single crystals to 1.5 J/m2 for films on the polycrystals with a corresponding increase in fracture toughness values. These results are consistent with crack deflection and interface roughness models and are useful for understanding adhesion and toughness on the submicron scale. The results also show that the continuous microscratch technique is a viable approach to determining adhesion and toughness of bi-material systems.
Properties and Thermal Behaviour of Si3N4 Thin Films
Authors: Knotek O. , LÖffler F. , Wolkers L. 
Published: March 2011

AbstractThe applications of thin film technologies are increasing. A variety of different ceramic and hard coating materials are deposited. Silicon nitride is one of the materials which seems to be quite interesting for the use as coating material. An use as a wear and corrosion protective coating seems to be conceivable. Silicon nitride is known to have a good thermalshock resistivity, thermal and chemical stability and good mechanical and wear resistant properties. If these properties are also given for deposited metastable PVD Si-N-coatings has to be evaluated yet.This paper describes the influence of different coating process parameters of the MSIP process like DC and RF mode, reactive and non reactive sputter processes and target orientation on the properties of silicon nitride films. It is shown, that coatings deposited with a 100 oriented single crystal target have the highest deposition rate and the best mechanical properties. The thermal stability of these thin films is insufficient although it can be improved by a carbon incorporation.
Group 12 Thiolates: Syntheses, Characterization and Decomposition Pathways
Authors: KrÄuter Gertrud , Goedken Virgil L. , NeumÜller Bernhard , Rees W. S. 
Published: March 2011

AbstractZinc- and cadmium bis(alkylthiolate) compounds have been prepared and converted into the appropriate binary metal sulfides by thermal treatment. Several mercury chlorothiolates have been synthesized and characterized by single crystal X-ray diffraction. Their decomposition pathways are discussed. The prepared binary metal sulfides have been studied by XRPD and - in selected cases - by particle size determination. The volatile co-products have been isolated and characterized by GC/MS.
Why Covalent Ceramics are Hard
Authors: Gilman John J. 
Published: March 2011

AbstractPure metals with nearly the same elastic properties as hard, covalent ceramics are often very soft, even at low temperatures. Why the difference? “Directed bonds” is the common answer. Or, “the Peierls-Nabarro stress is large”. However, the former is only qualitative, while the latter does not distinguish between covalent and metallic bonding, and is quantitatively incorrect. The rules of quantum chemistry, as developed to account for chemical reaction rates, indicate why dislocation mobilities are low in crystals bonded through hybrid sp and spd orbitals. Resistance to the motion of kinks on dislocation lines arises from the way in which the initial electronic states of these kinks are correlated with the final states (after a unit of motion has occurred). The initial bonding states correlate with the final antibonding states, and vice versa. Thus, the correlation lines cross, creating substantial barriers to the motion. The barrier magnitudes can be calculated from the energy gaps (e.g., for Sic, the HOMO-LUMO gap); together with the quadratic dependencies of bond energy on bond-bending. The calculated results agree with observations. A second prototype, TiC is also discussed.
The Electronic Structure of Carbon Nitride
Authors: Valladares Ariel A. , Sansores L. Enrique 
Published: March 2011

AbstractRecently there has been very much interest in understanding the structure of amorphous carbon nitride thin films, it has been shown that the introduction of nitrogen in amorphous carbon leads to better properties. In this paper we use four different cluster to study the changes in the local density of states at the carbon and nitrogen sites introduced by different environments. The method used is a SCF Hartree-Fock using pseudo potentials. We have considered carbons with sp3 and nitrogens with sp2 and sp3 hybridization. The results show that when N occupies a tetrahedral position (sp3) it introduces a localized state in the gap, while in the sp2 configuration, it introduces states near the edges of the bands.
Processing of Cunse2 Films for Photovoltaics
Authors: Basol BÜlent M. , Kapur Vijay K. 
Published: March 2011

AbstractCuInSe2and related I-HI-VI2 compound semiconductors containing Ga and S are important photovoltaic materials with electrical and optical properties that can be tuned for optimum device performance. Polycrystalline thin films of ternary and multinary compounds from the Cu(In,Ga)(Se,S)2family have already yielded laboratory size solar cells with over 15 % efficiency. Large area photovoltaic modules with over 10% efficiency have also been demonstrated using these materials. In this contribution we present a brief review of the CuInSe2 material characteristics which are important to solar cell performance and their correlation with the processing variables. We concentrate on films obtained by the selenization technique. Selenization of Cu-In precursors is an approach that has yielded good quality CuInSe2films which have been used for the fabrication of high efficiency solar cells.
Room-Temperature Synthesis of CuInQ2 (Q = S or Se) in Non-Aqueous Solution Using an Organoindium Reagent
Authors: Hepp Aloysius F. , Andras Maria T. , Landry Christopher C. , Barron Andrew R. 
Published: March 2011

AbstractWe have discovered a novel two-phase synthesis of CuInSe2 at 25° from Cu2Se and (C5H5)3In in 4-methylpyridine (4-MePy). An analogous reaction to produce CulnS2 must be run at 140°C in refluxing 4-MePy in the presence of 2-mercaptopyridine. Microscopy of CuInSe2 produced at 25°C shows it to be platelet-shaped crystallites with an approximate particle size of 10 microns, less than 2% C and H, with a small amount of unidentified crystalline impurity. Our results demonstrate that it is possible to produce from solution a material that is ordinarily synthesized in bulk or films at much higher temperatures or using extraneous reagents and/or electrons.
Luminescence Behavior of Self-Assembled Multilayer Heterostructures of Poly (Phenylenevinylene)
Authors: Ferreira Marysilvia , Rubner M. F. , Hsieh B. R. 
Published: March 2011

ABSTRACTMultilayer thin film heterostrutuctures comprised of alternating layers of a poly (phenylene vinylene) (PPV) precursor and various polyanions were fabricated using a new self-assembly technique. Thermal treatment of these films produced multilayers of the fully conjugated form of PPV. Alternating Multilayers fabricated with inert polyanions such as sulfonated polystyrene exhibited a very strong photoluminescence whereas alternating multilayers fabricated with electron acceptor polyanions such as sulfonated C?O and poly (thiophene acetic acid) displayed a highly quenched luminescence. This latter behavior suggests that self-assembled Multilayers can be used to examine photoinduced charge transfer interactions between PPV and various electron acceptors.
Urea Crystals Grown by Physical Vapour Transport
Authors: Paorici C. , Zanotti L. , Zha M. , Franzosi P. 
Published: March 2011

ABSTRACTA new facility for growing single crystals of urea by physical vapour transport in effusive cells is reported. The best crystals, as characterised by X-ray diffraction topography, are largely dislocation-free and do not contain microprocipitates.
Molecular Composites Based on Rigid Rod Polymers for Electrooptical Applications
Authors: Wegner Gerhard , Neher D. , Heldmann C. , Servay Th.K. , Winkelhahn H.-J. , Schulze M. , Kang C.-S. 
Published: March 2011

ABSTRACTNovel rigid rod polymers substituted with NLO-active chromophores have been developed towards application in electrooptical signal Modulation. The Materials are based on rigid polyesters and polyesteramids, in which the chromophores are either covalently linked to the backbone by short flexible spacers or directly incorporated into the main chain. In the bulk these systems form macroscopically ordered structures with layers of rigid rod backbones separated by the side chain segments. The properties and stability of the induced polar order can thus be adjusted by morphological parameters like the layer distance or the orientation of the main chains relative to the substrate. The relaxation of the NLO activity with time is described by a Multi-exponential decay and shows enhanced time-temperature stability even above 100°C. The temperature dependence of the relaxation times exhibits unusual features that distinguishes these systems from conventional NLO side chain polymers.
Oligomers Containing Mixed Thiophene and Pyrrole Units
Authors: Cava Michael P. , Parakka James P. , Lakshmikantham M. V. 
Published: March 2011

ABSTRACTThe synthesis and properties of polythiophenes, polypyrroles and their oligomers has evolved into a major area of conducting polymer research. Mixed systems containing both thiophene and pyrrole units have received much less attention. In this paper, the chemistry of thiophene-pyrrole oligomers containing up to seven heterocyclic units is reviewed.
Optical Absorption, Luminescence, And Redox Switching Properties Of Polyphenylene Derivatives
Authors: Reynolds John R. , Child Andrew D. , Ruiz Jose P. , Musfeldt Janice L. , Sankaran Bala , Larmat Fernando , Balanda Peter , Tanner David B. 
Published: March 2011

ABSTRACTA series of polyphenylene derivative polymers with a variety of heterocyclic units along the main chain, and various pendant groups, have been synthesized and their optoelectrochemical properties examined. Polyphenylenes containing electronically isolated emitter centers have optical absorption and luminescence characteristics which are a function of the length of the conjugated unit. A water soluble electroactive rigid-rod poly (p-phenylene), specifically Poly[2,5-bis (propoxy-3-sulfonate)-1,4-phenylene-alt,4-phenylene], has been prepared. Solution cast films of this polymer exhibit optical evidence for bipolarons via both p-type and n-type electrochemical doping. Further poly (p-phenylene) (PPP) derivatives are being pursued, including PPP's bearing pendant donor molecules for charge transfer complex formation. A series of polymers containing alternating p-phenylene units with bithienylene and bifuranylene units, specifically poly[1,4-bis (2-heterocycle)-2,5-disubstituted-1,4-phenylenes], have been synthesized with both alkyl and alkoxy pendant groups. Steric interactions disrupt the ability of the redox doped polymers to attain planarity, strongly affecting the polymer's oxidation potentials and DC conductivities. The substituent length has little effect on the electronic properties of the polymer, but greatly affects the polymer's solubility and transport properties during redox switching.
Polyaniline Surface Morphology During The Doping Process Using Atomic Force Microscopy
Authors: Buckley Leonard J. 
Published: March 2011

ABSTRACTChemically synthesized polyaniline films were studied during the doping and dedoping process by imaging the polymer surface using in-situ Atomic Force Microscopy (AFM). The polymer, which was initially in the base non-conducting form was doped using aqueous acidic solutions of both tosylic (pH=0.2) and HCl (pH of 0.2 and 1.0). Dedoping was accomplished by exposing the same doped polymer surface to NH4OH (pH=12) base solution. AFM images showed that it was necessary to cycle the polymer surface 3 times between acid and base before a reproducible surface morphology was established between the doped and dedoped states. For the case of doping with tosylic acid AFM images showed that the polyaniline surface was immediately roughened. In addition there appeared to be an increase in the size of surface channels and cracks. When doping with HC1 (pH=1.0), no change in surface morphology was observed; however, noticeable surface roughening occurred over 10 Minutes for the case of the lower pH=0.2 solution. The complex permittivity and DC conductivity was measured to estimate the level of protonation in the AFM samples.
Influence of Structural Parameters of Conducting Polymers on their Microwave Properties
Authors: Hourquebie P. 
Published: March 2011

ABSTRACTThe complex dielectric constant ε* (ε* = ε′-iε″) of conducting polymers (polyaniline and poly (3-alkyl thiophene)) is studied over a frequency range spanning from 130 MHz to 20 GHz. The effects of structural parameters (counter-anion size, Molar Mass, length of the alkyl chain on the substituted Monomer) on electrical properties (σdc and ε* values) have been investigated.
Mps3 Layered Intercalates as Insulating Magnets: Towards Nanocomposites Associating Ferrimagnetism and Non-Linear Optical Properties
Authors: Clement Rene , Lacroix Pascal G. 
Published: March 2011

ABSTRACTThe layered MIIPS3 compounds posess a unique cation exchange intercalation chemistry, which allows the synthesis of a wide range of air stable M1-xPS3G2x intercalates (G stands here for a Monocation). The positive charge of the guest cations is counterbalanced by intralayer metallic vacancies.Intercalation exerts a dramatic influence on the magnetic properties of these compounds. Whereas pristine MPS3 compounds order antiferromagnetically (M = Mn, Fe‥), Many intercalates become magnets below an ordering temperature that can be as high as 92 K. The role of intercalation is discussed in terms of the creation of intralayer metallic vacancies, which destroy the spin balance that prevails in pristine MPS3 compounds.The MPS3 host lattice has the capability of causing spontaneous poling of the dimethylamino-N-Methyl stilbazolium chromophore (DAMS), leading to materials that exhibit strong second harmonic generation. (SHG). Inserting DAMS into MnPS3 therefore leads to a composite that possess both spontaneous Magnetization (below Tc = 40 K) and a strong efficiency for SHG.
Fermi Surface Study Of An Organic Superconductor θ- (Bedt-Ttf)2I3
Authors: Tamura M. , Kuroda H. , Uji S. , Aoki H. , Tokumoto M. , Swanson A. G. , Brooks J. S. , Agosta C. C. , Hannahs S. T. 
Published: March 2011

ABSTRACTThe temperature and field dependence of the de Haas-van Alphen oscillations in θ- (BEDT-TTF)2l3 is analyzed. The cyclotron masses are estimated to be 2.0 Me and 3.6 me for slow and fast oscillations, respectively. The indication of magnetic breakdown effect is discussed in terms of the geometry of the Fermi surface. The results are compared with those of the infrared reflectance spectra.
Optoelectronic and Structural Properties of Vacuum-Deposited Crystalline Organic Thin Films
Authors: Forrest S. R. , Burrows P. E. , Haskal E. I. , Zhang Y. 
Published: March 2011

ABSTRACTRecently, it has been discovered that crystalline organic thin films can be deposited in nearly single crystalline form on a variety of substrates such as glass, polymers, etc. Since then, this discovery has led to the growth of crystalline organic quantum wells, waveguides, coupler/switches, and organic/ inorganic heterojunction devices such as field effect transistors and avalanche photodiodes. Organic light emitting diodes (LEDs) which luminesce in the red, green and blue have also been demonstrated. In this paper, we will report on several recent advances in the growth of organic thin films deposited by organic molecular beam deposition. We report on modeling of organic monolayer growth based on the atom-atom potential Method. The Model provides insight into the factors which control “quasi-epitaxial growth” i.e. the ordered growth of one layer of an organic film which is incommensurate with the substrate lattice. We also observe large optical nonlinearities which are a feature of both single and Multi-layer crystalline organic films. The growth of organic, nonlinear optically active crystalline organic compounds are also discussed.
Molecular Design of Nonlinear Optical Polymers for Photonic Device Applications
Authors: Kaino Toshikuni , Ooba Naoki , Tomaru Satoru , Kurihara Takashi , Yamamoto Takakazu 
Published: March 2011

ABSTRACTMolecular design of processable nonlinear optical (NLO) polymers is discussed for applications to devices such as ultrafast optical switches. Channel waveguides must be fabricated in order to develop polymeric NLO switching devices that can be driven with lower laser power. For these purposes, we propose molecular structures that reduce attenuation loss and allow the development of highly processable NLO polymers. Third-order nonlinear optical properties, χ(3), of the novel NLO polymers are around 10−10 esu in the 1.5 μm wavelength region. Even in off-resonant regions, the χ(3) values are around 5 × 10−11 esu. Single Mode channel waveguides of the polymers are fabricated using a standard photo-process. Attenuation loss through a film and also for a single mode waveguide at 1.32 μm wavelength is Measured. Nonlinear optical properties of novel, processable, heteroaromatic polymers with large χ(3) are also discussed. Several types of heteroaromatic polymers are developed with a structure in which π-electron excessive heteroaromatic compounds and π-electron deficient heteroaromatic compounds are combined to induce strong nonlinearity. The charge transfer between heteroaromatic rings on the π-conjugated sequences is thought to influence the properties of certain excited states that enhance χ(3) These polymers have excellent potential for use in fabrication of optical switching devices.
Second-Order Nonlinear Optical Properties Of Thiophene Containing Chromophores With Extended Conjugation
Authors: Gilmour Sandra , Jen Alex K-Y. , Marder Seth R. , Jennifer-Neissink A. , Perry Joseph W. , Skindhøj Jørgen , Cai Young Ming 
Published: March 2011

ABSTRACTThe synthesis and first hyperpolarizabilities (β) of various donor-acceptor substituted thiophene containing compounds with extended conjugation are reported. Results indicate that replacing phenyl rings with less aromatic thiophene moieties enhances the second-order hyperpolarizability. Incorporating the acceptor group, N,N' diethylthiobarbituric acid, that can gain aromaticity upon charge-separation has also led to an increase in the nonlinearity. Some of the molecules have been incorporated into poIy (Methyl Methacrylate) and the electro-optic coefficients of these host-guest polymers were Measured.