bluuebunny/crossref_metadata_2025 huggingface dataset:
The Domain Mode in Ferroelectric Liquid Crystals a Novel Electrooptical Process
Authors: Beresnev L. A. , Pfeiffer M. , Ptkin S. A. , Haase W.
Published: March 2011

Novel electrooptical effects in ferroelectric liquid crystals with high spontaneous polarization (Ps ) are observed. They are connected with the formation of a modulated distribution of the macroscopic dipole moments of smectic layers if going along the layer normal. The period (D) of this modulation (ferroelectric domains) near the electrode surfaces (DS) and in the bulk (DB) of a FLC-specimen can differ appreciably, depending on an applied external voltage. The main role of the value of the effective spontaneous polarization is established. A variuos number of domain structures and corresponding diffraction patterns are observed under variation of frequency and amplitude of the external electric field. A simple explanation of the new electrooptical responses is proposed on the basis of interference and incommensurability of bulk and surface domains.
Photoconductivity in an Epoxy-Based Photocrosslinkable Nonlinear Optical Polymer
Authors: Li Lian , Jeng R. J. , Lee J. Y. , Yang Y. , Kumar J. , Tripathy S. K.
Published: March 2011

Photoconductivity measurements on an epoxy-based photocrosslinkable second-order nonlinear optical (NLO) polymer - DGENC - NAC ( diglycidyl ether of nitrocatechol / nitroaniline prepolymer functionalized with cinnamoyl groups) are presented. Without introducing any sensitizer or charge carrier transport agents, large photoconductivity was obtained in this polymer system. Optical excitation of the NLO chromophores leads to photocarrier generation and it is conjectured that these NLO chromophores also play a role in the carrier transport. This polymer is one of the candidate materials for photorefraction.
Dielectric Study of a Photo-Ckosslinkable Nonlinear Optical Polymer
Authors: Chen J. I. , Moody R. A. , Chen Y. M. , Lee J. Y. , Sengupta S. K. , Kumar J. , Tripathy S. K.
Published: March 2011

Temperature and frequency dependent measurements are utilized to study the relaxation behavior of a photocrosslinking nonlinear optical (NLO) material based on a polyvinylcinnamate (PVCN) polymer matrix. 3-cinnamoyloxy-4-[4-(N, N-diethylamino)-2-cinnamoyloxy phenyl azo] nitrobenzene (CNNB-R) is used as a functionalized NLO active dye. Measurements of dielectric properties of PVCN doped with different levels of CNNB-R have been performed. NLO dye molecules were bonded to the host polymer by ultraviolet irradiation. Measurements were carried out from 50 to 200 °C and a frequency range of 30 Hz to 1 MHz. The effects of dye content and UV irradiation on the dielectric response are discussed.
Functionalizing C60 via Nucleophilic Trapping of its Radical Cations: 1. Alkoxylation and Arylation of C60; 2. Synthesis of Earmuff Ethers (Difulleroxyalkanes)
Authors: Miller Glen P. , Hsu Chang S. , Thomann Hans , Chiang Long Y. , Bernardo Marcelino
Published: March 2011

While its electrochemical oxidation is difficult, Cgg is readily oxidized in protic superacidic media. In order to exploit the reactive nature of the radical cations thus formed for the purpose of generating novel fullerene derivatives, a method involving nucleophilic trapping of oxidized Cgg has been developed. Thus, trapping oxidized Cgg with alcohols and aromatics results in the formation of alkoxylated and arylated C60, respectively, while trapping oxidized CgQ with x, y-diols results in the formation of x, y-difulleroxyalkanes (earmuff ethers).
Physical Properties of Superconducting and Ferromagnetic Materials Based on C60
Authors: Thompson J. D. , Sparn G. , Diederich F. , Grüner G. , Holczer K. , Kaner R. B. , Whetten R. L. , Allemand P.-M. , Li Q. , Wudl F.
Published: March 2011

We present results of magnetization and pressure measurements on recently discovered superconductors K3C60 and Rb3C60. as well as ferromagnetic C60TDAE, and discuss the nature of the ground state suggested by these studies.
Defective Buckyballs: Alternative Structural Isomers of C60
Authors: Raghavachari Krishnan , Rohlfing Celeste M.
Published: March 2011

Alternative isomerie structures of C60 spheroids have been investigated using semiempirical and ab initio quantum chemical techniques. Unlike the icosahedral ground state, these isomers are characterized by the presence of pentagonal rings adjacent to each other. The lowest energy alternative isomer of C60 has two such pairs of edge-sharing pentagons and lies = 2 eV higher in energy than the ground state. Isomers containing three and four pairs of adjacent pentagons have also been studied in detail. Overall, the energy contributions of these adjacent pentagonal defects are additive, with each defect making the structure less stable by = 1 eV.
Raman Scattering in MxC60 Films (M=K. Rb, Cs; ×=0, 3.6)
Authors: Wang Kai-An , Zhou Ping , Wang Ying , Holden J. M. , Ren Song-Mn , Hager G. T. , Ni H. F. , Eklund P. C. , Dresselhaus G. , Dresselhaus M. S.
Published: March 2011

The Raman-active modes of solid films of MxC60 (x-0, 6; M=K, Rb, Cs) and K3C60 have been studied experimentally. The mode-activity is dominated by intraball interactions, and the effect of the M + ions on the C60 spectrum is observed to be almost insensitive to the radius or mass of the alkali metal. Tangential modes of solid C60 are observed to soften in M660 by -60 cm−1, which can be attributed to a charge-transfer-induced elongation of the intraball bond lengths, similar to that observed in graphite intercalation compounds. Conversely, the radial modes are found to upshift slightly, indicating that a competing mechanism counteracts the effect of the bond elongation. For K3C60, six Raman lines have been observed in which the lowest frequency mode exhibits a Breit-Wigner-Fano lineshape, indicating a coupling between the lowest frequency Hq-derived intramolecular modes of C60 and a broad Raman-active continuum with the same symmetry lying lower in frequency.
In Situ Photoconductive Study of C60 and Phthalocyanine Thin Films
Authors: Minami Nobutsugu
Published: March 2011

The in situ measurement of lateral photoconductivity has been carried out on vacuum vapor deposited C60 and phthalocyanine thin films. From the photo-current increase curve during the deposition and the SEM observation of copper phthalocyanine (CuPc) thin films, it has been revealed that, at an early stage of deposition, they consist of small clusters scattered on substrate. As the thickness Increases, the clusters coalesce to eventually form continuous film. We also show that C60 thin film has considerable photoconductivity. The photo-current spectrum agrees well with the absorption one with the exception that a peak at 600 nm appears only in the former. This wavelength region corresponds to a theoretically predicted forbidden transition. An onset of photocurrent at 760 nm is assigned to the absorption edge of solid C60. The photoconductivity of C60 thin films shows a rather unusual temperature dependence In that a small drop of temperature (e.g. from 25° C to 15° C) causes a dramatic increase In photocurrent by more than two orders of magnitude.
Ferro-and Antiferromagnetic Behaviors of Some Organomatallic and Coordinated Compounds
Authors: Wei H. H. , Chang Y. F.
Published: March 2011

Several new examples of ferro- and antiferromagnetic organometallic and coordinated compounds have been investigated by means of the temperature-dependent magnetic measurements and Mössbauer spectroscopy. Above 70 K the Cu3 [Fe(CN)6] 2-4H2O compound is ferromagnetic as it obeys the Curie-Weiss experession, χm= C/(T-θ), with θ = 25 K; μeff evalued at 200 K is 4.91 μβ. Below 20 K this compound displays the onset of spontaneous magnetization in zero applied field. Above 10 K the Cu[(bpy>2] 3 [Fe(CN)6] 2.5H2O is also ferromagnetic (θ= 2.5 K). Above 20 K the antiferromagnetic [Fe(C5H4Me)2] + [TCNOJ- (θ= 3.25 K) and [Fe(C5H4Me)2]+[TCNE]- (θ= -3.64 K) obey the Curie-Weiss expression. The e.p.r. and Mössbauer spectra for these compounds have been discussed.
Design of Organic Superconductors Based on Bedt-TTF
Authors: Saito Gunzi , Komatsu Tokutaro , Nakamura Toshikazu , Yamochi Hideki
Published: March 2011

A close examination of the relation between Tc and structural characteristics of BEDT-TTF superconductors has revealed that there is a good correlation between the effective volume (VeffαVc-Vanion and Tc but no such correlation between the unit cell volume (Vc) and Tc. In order to increase Veff, it is favorable to use big but thin anion which can form a thin two-dimensional anion layer. Three-dimensional donor interactions are critical to have sizable Tc. According to the designing, two new superconductors; K-(BEDT-TTF)2CuCN[N(CN)2] (Tc=11.2K) and K'-(BEDT-TTF)2Cu2(CN)3 (Tc=3.8K), are prepared and their physical and structural properties are described. Their Tc's are discussed in terms of veff.
Cation Radical Salts of S, S-Dmbedt-TTF: Semiconductors, Metals and a new Organic Superconductor
Authors: Zambounis John S. , Mayer Carl W. , Hauenstein Kurt , Htjlti Bruno , Hofherr Walther , Pfeiffer Jürgen , Bürkle Markus , Rihs Grety
Published: March 2011

The electrical properties of cation-radical salts based on S, S-DMBEDT-TTF and their crystal structures are presented.
Fermi Surface Study of Organic Metals (Bedt-TTF)2X
Authors: Tokumoto M. , Swanson A. G. , Brooks J. S. , Agosta C. C. , Hannahs S. T. , Kinoshita N. , Anzai H. , Tamura M. , Tajima H. , Kuroda H. , Ugawa A. , Yakushi K.
Published: March 2011

Observations of Shubnikov-de Haas(SdH) and de Haas-van Alphen(dHvA) oscillations in organic metals (BEDT-TTF)2X, with X=KHg(SCN)4, θ-I3 and β″-AuBr2. are reported. In KHg(SCN)4 salt, in addition to the SdH oscillations with fundamental frequency of 670 T corresponding to about 16% of the first Brillouin zone(FBZ), we observed splitting of each SdH peak which we ascribed to “spin-splitting” We have also found that the ground state of this salt is not a simple metal but has some magnetic character. In θ-l3 salt we have succeeded in an observation of dHvA oscillations for the first time. We observed a “saw-tooth” dHvA oscillation characteristic to a highly two-dimensional and extraordinary clean electronic system. In addition to the fundamental frequency of 4170 T corresponding to 50.4 % of the FBZ and its higher harmonics, we observed an oscillation with lower frequency of 730 T corresponding to about 8.8 % of the FBZ. A new Fermi surface topology for θ-l3 salt is proposed based on the analysis of the dHvA effect. In β″-AuBr2, we observed complex dHvA oscillations, which can be explained in terms of the mixing of two fundamental frequencies of 47 and 268 T, suggesting the presence of very small pockets corresponding to 0.6 and 2.9 % of the FBZ.
Synthesis and Physical Properties of two Organic Donor Derivatives of 12-Molybdophosphate Anion [PMO12O40] n-: New Examples of Mixed-Valence Organic Donor-Inorganic Acceptor Compounds
Authors: Attanasio D. , Bellitto C. , Bonamico M. , Righini G. , Staulo G.
Published: March 2011

Tetrathiafulvalene and bis(ethylenedithio)tetrathiaful-valene radical-cation salts of the a-Keggin anion [PMo12O40] have been synthesized and characterized. They both are mixed-valence compounds and contain the paramagnetic anion [PMO12O40] 4-. The former contains irregular TTF ϱ+ chains isolated by the inorganic anions. From the IR spectrum a ϱ=+0.5 is suggested. The latter is two-dimensional, where BEDT-TTF molecules are ionised, ϱ=+0.5, and arranged in irregular chains. They show electrical conductivity typical of organic semiconductors.
Energy Band Structure for Metallic Polyacetylene
Authors: Tanaka Chizuko , Tanaka Jiro
Published: March 2011

The optimized molecular structures of doped polyacetylene model compounds are studied by the ab initio SCF MO method. The calculated structures are assigned to polaron, charged soliton and poison unit. The one dimensional energy band structures of the charged soliton-antisoliton and the polson-antipolson lattices are investigated. The latter one gives a quasi-metallic energy band. The results of the energy band calculation are consistent with the electrical properties and ultraviolet photoemission spectra of the doped polyacetylene.
Highly Conducting and Thermally Stable Conjugated Polymers
Authors: Jen Alex K-Y. , Drzewinski Michael , Chin Hui Hwui , Boara Guilio
Published: March 2011

A series of highly conductive, environmentally and thermally stable polyanilines was synthesized. These polymers, which are obtained by employing careful synthetic conditions, purification procedures, and dopant variations, show interesting morphological structures and high temperature stability. Thermal studies by TGA, DSC and DMTA show a glass transition temperature (Tg) for neutral polyaniline around 185°C. This is the same temperature at which the conductivity and crystallinity decrease. Isothermal heatings of the polyaniline tosylate at 200 and 250°C in air show significant amounts of weight loss. This is due to dopant loss through irreversible chain rearrangements and air oxidation at temperatures above Tg.
In-Situ Monitoring of the Kinetics and Mechanism of Conducting Polymer Synthesis
Authors: Fong Yoke , Chen Chengbo , Schlenoff Joseph B.
Published: March 2011

The aqueous polymerization of pyrrole and aniline by ferricyanide and persulfate, respectively, was monitored by Raman scattering and potentiometry. Raman scattering gave well-resolved signals for monomer and oxidizer. The kinetics of polypyrrole formation could be determined by both techniques, whereas only Raman scattering was suitable for the aniline system. The stoichiometry of the pyrrole polymerization remained constant at 2.5 oxidant molecules per pyrrole consumed. The aniline reaction showed an accelerated region with aniline consumption lagging persulfate use.
Electrically Conductive Composite of Polypyrrole and Liquid Crystalline Aromatic Copolyamide
Authors: Bao Jing-Sheng , Xu C. C. , Cai W. , Bi Xian-Tong
Published: March 2011

The modification of the mechanical properties of polypyrrole(PPy) by electrochemical preparation of conductive composite film from pyrrole(Py) and two kinds of liquid crystalline copolyamide of poly(p-phenylene-terephthal- amide)(PPTA) poly(p-phenyleneterephthalamide/diphenyl ether terephthal- amide) (PPTA[0]) and poly(p-phenyleneterephthalamide/diphenyl methane tere-phthalamide) (PPTA[C]) are presented.

The electrical conductivity of the PPTA[0]/PPy and PPTA[C]/PPy composites are the same order of magnitude as PPy or PPTA/PPy. The mechanical properties of the composite films are better than that of pure PPy. and the composite films have good electroactivlty and thermalstability.
Structure and Morphology of Metallic-Conductive Polyacetylene
Authors: Tsukamoto Jun , Takahashi Akio
Published: March 2011

We have carried out structural analyses of highly conductive polyacetylene in order to elucidate the relationship between stucture and electrical properties. Sharp X-ray diffraction lines were observed for the heavily iodine-doped polyacetylene showing high conductivity, in contrast with the diffused diffractions of the conventional one. SEM observation reveals that granular structure of the new polyacetylene is composed of densely packed micro-fibrils. The result from the resonance Raman analysis indicates that the new cis-polyacetylene contains more longer conjugated segments than conventional polyacetylene. The relationship between the structure and conductivity is discussed, basing on the crystal structure and morphology observed.
Ion Implantation of Conducting Ladder and Rigid-Rod Polymers
Authors: Bums A. , Wang Z. H. , Du G. , Joo J. , Epstein A. J. , Osaheni J. A. , Jenekhe S. A. , Wang C. S.
Published: March 2011

We report optical, thermal, and transport studies on Kr+ implanted ladder (BBL) and rigid-rod ( PBO and PBZT) polymers, with an ion energy of 200 keV and dosage of 4 × 1016 / cm2. Both pristine and ion implanted polymers were studied using X-ray photo-electron spectroscopy (XPS), optical spectroscopy (IR and UV-Vis), thermogravimetric analysis (TGA), and temperature dependent DC conductivity (σ(T)). The XPS and IR results show a reduction in the heteroatoms and increase in the relative carbon content. After ion implantation, each polymer had a similar electronic structure, showing broad band metallic behavior. TGA data shows that each implanted polymer retains its thermal stability. σ(T) of the implanted polymers has the weakest temperature dependence of any conducting polymer reported, in accord with a disordered metal.
Multiphoton Spectra of Conjugated Polymers
Authors: Soos Z. G. , Etemad S. , Kepler R. G.
Published: March 2011

Multiphoton excitations of conjugated polymers are related to their optical gap, Eg, which serves as an internal standard. In π-electron models with electron-hole symmetry, the alternation gap Ea is the lowest-energy two-photon absorption (TPA) and increases with the alternation δ of the transfer integrals t(l ± δ) along the backbone. Increasing electron-electron (e-e) correlations shift an intense TPA from 2Eg in the band limit to Eg in the atomic limit. Two-photon spectra and multiphoton resonances in polyenes, polydiacetylenes, and polysilanes are related to interacting electrons in Pariser-Parr-Pople(PPP) models with increasing alternation and either carbon or silicon e-e interactions. Some general features of correlated states of conjugated polymers are discussed in the rigid-lattice limit.
Unusual X-Ray Diffraction Vector Shift Observed in Heterogeneous Langmuir-Blodgett Multilayer Films
Authors: Nogami Yoshio , Ogasawara Kazuyoshi , Takeuchi Shigeki , Ishiguro Takehiko , Ohsumi Kazumasa , Shimizugawa Yutaka
Published: March 2011

Stacking of heterogeneous Langmuir-Blodgett films was studied by high resolution X-ray diffraction method using synchrotron radiation (SR) source. The diffraction patterns of the heterogeneous films formed with alternately deposited Cd salts of fatty acids with different length of alkyl chains exhibit anomalous oscillatory structure in diffraction vector.
Plasma Activated Chemical Vapor Deposition of Polythiophene Thin Films
Authors: Targove J. D. , Haaland P. D. , Kutsche C. A.
Published: March 2011

Polythiophene thin films have been deposited by a novel plasma technique which avoids the disadvantages of conventional plasma-based processes. In particular, the thiophene precursor is injected into an activated argon stream rather than into a plasma. The films produced are dense and uniform, with surface roughness of less than 1 nm. Other film properties are comparable to films deposited by more conventional methods. These films have been processed by reactive ion etching to produce micron-scale features.
High Resolution Organic Thin Film Mapping for Process Control
Authors: Denenberg David , Blew Austin R.
Published: March 2011

ABSTRACT; This paper describes the use of advanced circuitry nondestructive eddy current techniques to map organic Thin Films. Surface profiles, contour maps and diameter scans are obtained from the process wafers tested providing the necessary information to control the processes for maximum yield.
Deuelopment of a Computer Program for the Determination of Opticrl Constants of Radiation Damaged Optical Elements Using Classical Oscillator Fit to Reflectance and/or Trrnsmittrnce Data
Authors: Rahman Miftahur , Yang C. , Chiu K. S. , Karakashian A. S. , Karp C. , Mooney T. , Al-Jumaily G.
Published: March 2011

ARSTAACT

A computer program is developed using the classical oscillator model of Hans W. Verleur [1] to study the transmittance and reflectance spectra of pre- and post radiation damaged optical components such as color glass filters, multilayer bandpass filters and band reject filters irradiated by one megárad gamma radiation from a 60Co source. In the classical oscillator model, the complex dielectric constant ε(ω) is represented as the sum of classical oscillators with oscillator strength Si, resonance frequency ωi, linewidth Γi and high frequency dielectric constant ε∞ which are the adjustable parameters to fit the experimental transmittance and reflectance data over a limited range of frequency. The parameters have physical significance in the lattice vibrational region. In the spectral regions corresponding to electronic transitions, the spectra can be fitted accurately with no physical meaning associated with the parameters. The present work has concentrated on the calculations of the optical constants n and k of the radiation damaged optical components to determine the effects of 60Co gamma radiation on the optical constants of both films and substrates in these components.
Chemical Vapor Deposition Modeling for High Temperature Materials
Authors: Gokoglu Suleynaz A.
Published: March 2011

The formalism for the accurate modeling of chemical vapor deposition (CVD) processes has matured based on the well established principles of transport phenomena and chemical kinetics in the gas phase and on surfaces. The utility and limitations of such models are discussed in practical applications for high temperature structural materials. Attention is drawn to the complexities and uncertainties in chemical kinetics. Traditional approaches based on only equilibrium thermochemistry and/or transport phenomena are defended as useful tools, within their validity, for engineering purposes. The role of modeling is discussed within the context of establishing the link between CVD process parameters and material microstructures/ properties. It is argued that CVD modeling is an essential part of designing CVD equipment and controlling/optimizing CVD processes for the production and/or coating of high performance structural materials.
Modification of Optical Surfaces Employing CVD Boron Carbide Coatings
Authors: Lowden Richard A. , Riester Laura , Akerman M. Alfred
Published: March 2011

Non-reflective or high emissivity optical surfaces require materials with given roughness or surface characteristics wherein interaction with incident radiation results in the absorption and dissipation of a specific spectrum of radiation. Coatings have been used to alter optical properties, however, extreme service environments, such as experienced by satellite systems and other spacecraft, necessitate the use of materials with unique combinations of physical, chemical, and mechanical properties. Thus, ceramics such as boron carbide are leading candidates for these applications. Boron carbide was examined as a coating for optical baffle surfaces. Boron carbide coatings were deposited on graphite substrates from BCl3, CH4, and H2 gases employing chemical vapor deposition (CVD) techniques. Parameters including temperature, reactant gas compositions and flows, and pressure were explored. The structures of the coatings were characterized using electron microscopy and compositions were determined using x-ray diffraction. The optical properties of the boron carbide coatings were measured, and relationships between processing conditions, deposit morphology, and optical properties were determined.
Fiber-Reinforced Tubular Composites by Chemical Vapor Infiltration°
Authors: Stinton D. P. , Lowden R. A. , Besmann T. M.
Published: March 2011

A forced-flow thermal-gradient chemical vapor infiltration process has been developed to fabricate composites of thick-walled tubular geometry common to many components. Fibrous preforms of different fiber architectures (3-dimensionally braided and filament wound) have been investigated to accommodate components with different mechanical property requirements. This paper will discuss the fabrication of tubular, fiber-reinforced SiC matrix composites and their mechanical properties.
The CVD of Ceramic Protective Coatings on SiC Monofilaments
Authors: Choy K. L. , Derby B.
Published: March 2011

The TiB2, TiC and TiN coatings were studied as potential protective coatings for SiC fibre reinforced titanium alloys. These coatings were deposited by a CVD technique on resistively heated SiC monofilament fibres at reduced pressure in a cold wall reactor. The deposition conditions that are required to coat each of these materials were determined. The morphology, microstructure, phase composition and nature of the coatings were examined. The comparison and evaluation of the effectiveness and potential of these as protective coatings were carried out by incorporating the coated fibre into Ti-6A1–24V using the diffusion bonding method at 1100°C under 10 MPa for 1 hour.
Chemoical Vapor Deposotdoo of Tungsten and Molybdenum Folms From m(η3–C3H5)4 (M=Mo, W)
Authors: Kirss Rein U. , Chen Jian , Hallock Robert B.
Published: March 2011

Chemical vapor deposition using tetra(allyl) tungsten and molybdenum precursors yielded amorphous tungsten and molybdenum carbide films on pyrex substrates. The films were characterized by Auger, ESCA, SEM, XRD and resistivity measurements. Volatile pyrolysis products consisted primarily of propene, C3H6.
Advanced Dielectrics Deposited by LPCVD
Authors: Lane Andrew P. , Chen Arthur , Sandier Neal P. , Freeman Dean W. , Page Barry S.
Published: March 2011

Ta2O5 and Nb2O5 films were deposited using the Lam Research Integrity™ reactor. The chemical precursors used were pentaethoxides of Ta and Nb. Typical films were deposited at a rate of 4 nm/min with uniformities of <1.5% lσ in the presence of O2 at 470°C. Annealing the Ta2O5 films did not change the O/Ta ratio. Annealing the Nb2O5 films increased the O/Nb ratio to 2.5/1 at 850°C. Interfacial SiO2 grew to 4 nm after annealing at 850°C for both Ta2O5 and Nb2O5. The as-deposited films were amorphous, but became crystalline above 600°C and 700°C for the Nb2O5 and Ta2O5 films respectively. The TEM observations on crystallization is supported by x-ray diffraction data.
Pyrolytic Carbon Deposition on Graphitic Surfaces
Authors: Ismail Ismail M. K.
Published: March 2011

The present study outlines the importance of carbon active sites in controlling the kinetics of pyrolytic carbon deposition on a graphitized pitch fiber at 1025°C. Blockage of active sites with chemisorbed hydrogen retards deposition rates substantially. Removal of the chemisorbed hydrogen from the occupied sites raises deposition rates to the normal values noted on a fresh “clean” surface. The effect of surface activation prior to deposition is discussed. Activating the surface generates additional active sites and enhances the rates. However, not all the newly developed sites contribute to the kinetics. After the deposition of the first carbon layer, a fraction of those newly developed sites is instantaneously blocked and does not further contribute to subsequent deposition. The remaining fraction, along with the original sites available before activation, keeps replicating during the remaining course of deposition. That is, the disappearance of one active site after carbon deposition is associated with the generation of a new site. This trend continues up to the deposition of 60 carbon layers.
H States, Impurity Passivation and Gettering Studies in H-Implanted Si Crystals
Authors: Mukashev Bulat N. , Tokmoldin Serikbol Zh.
Published: March 2011

IR and DLTS studies of H-implanted Si crystals are performed. It is shown that H is a bistable impurity: it has an equilibrium site at a T-site for H+ and H- and at a BC-site for H°. The mechanisms of H-passivation of defects and shallow and deep impurities are discussed.
Studies of the Effects of Ion-Implantation and Electron Beam Irradiation on CuInSe2 Single Crystals
Authors: Mullan C. A. , Kiely C. J. , Rockett A. , Imanieh M. , Yakushev M. V. , Tomlinson R. D.
Published: March 2011

A series of CuInSe2 single crystals which were grown by the vertical Bridgman technique have been implanted with oxygen and xenon ions. These implants tend to cause a change from n to p-type conductivity and an enhancement of the photoconductivity. We present HREM and SIMS characterisation of the microstructural effects caused by high dose ion implants on CuInSe2. We also correlate our data with calculated ion implant profiles. In addition, we show that CuInSe2 thin foils can undergo significant degradation under the electron beam irradiation conditions which are commonly encountered in electron microscopes.
Studies of Nonthermal Effects During Intense Microwave Heating of Crystalline Solids
Authors: Booske John H. , Cooper Reid F. , McCaughan Leon , Freeman Sam , Meng Binshen
Published: March 2011

Reports of enhanced sintering rates associated with microwave heating may be due to nonthermal lattice fluctuation statistics. Recent theoretical analyses reviewed in this paper confirm the feasibility of this phenomenon for a wide variety of situations involving very different microwave absorption mechanisms. For materials with weak microwave absorption coefficients, the effect is expected to be uniformly distributed throughout the volume. For strongly absorbing materials, however, the effect is expected to be concentrated near the material surface, with a characteristic exponential penetration depth of Lnt ∼ 10 - 100 μm. An “observable” nonthermal effect depends on the relative magnitude of the microwave electric field strength |E| and the lattice ion energy relaxation rate γ with the most pronounced effects occurring for larger values of |E| and smaller values of γ.
Microwave Processing of Ceramics: Guidelines Used at the Oak Ridge National Laboratory
Authors: Janney Mark A. , Kimrey Hal D. , Kiggans James O.
Published: March 2011

To make meaningful comparisons between conventional and microwave processing of materials, one must conduct experiments that are as similar as possible in the two environments. Particular attention must be given to thermal conditions, sample parameters, and furnace environment. Under thermal conditions, one must consider temperature measurement (pyrometer or thermocouple, sheath type, and arcing of thermocouples), thermal history (heating and cooling rates, thermal gradients), and exothermic reactions. Regarding sample parameters, one must. consider sample size, and packing powders and insulation systems. With respect to furnaces, one must consider differences in atmosphere, impurities, and uniformity of heating. Examples will be drawn from diffusion, grain growth, sintering, nitridation, and drying experiments conducted at the Oak Ridge National Laboratory (ORNL) over the past six years.
Ceramic Powders Generated by Metallorganic and Microwave Processing
Authors: Willert-Porada M. , Krummel T. , Rohde B. , Moormann D.
Published: March 2011

A novel approach to synthetic ceramic powders based on microwave heating of metallorganic ceramic precursor compounds or mixtures of such compounds with a appropriate matrix material is described.

Numerous oxides as well as nonoxide powders with high specific surface area were obtained. Pyrolysis as well as enhanced reactivity is observed with microwave heating at lower temperatures than in conventional heating.
Microwave Processing of Tantalum Capacitor Anodes
Authors: Lauf R. J. , Hamby C. , Holcombe C. E. , Vierow W. F.
Published: March 2011

Porous tantalum anodes were sintered at temperatures from 1600 to 1900°C using a conventional high-vacuum furnace as well as both 2.45 GHz fixed-frequency and 4-8 GHz variable-frequency microwave furnaces. Various insulation and casketing techniques were used to couple the microwave power to the tantalum compacts. Several types of tantalum powder were used to assess the effect of microwave processing on sintered surface area and impurity levels.

Some microwave sintered anodes have an unusual surface rippling not seen on conventionally fired parts. The rippling suggests that a microscopic arcing or plasma might have been generated. Two important effects could be exploited if this phenomenon can be controlled. First, the effective tantalum surface area could be increased, yielding higher capacitance per volume. Second, surface impurities might be cleaned away, allowing the formation of a better dielectric film during the anodization process and, ultimately, higher working voltage.
An Experimental Investigation of Hybrid Convective/Microwave Drying of Electrical Porcelain
Authors: Hendrix Walter A. , Martin Tom
Published: March 2011

The drying of electrical porcelain using a combination of convection and microwave heating has been experimentally studied. To date, a total of 58 individual tests have been conducted to evaluate the effect of a range of microwave and convection conditions on the drying behavior of both solid and cavity core bodies. Preliminary indications are that order of magnitude reduction in drying time may be achieved. Furthermore, improved control over quality problems appears to be possible because of the ability of microwave heating to minimize the amount of convective surface heating.
Microwave Processing of Glass Fiber/Vinyl Ester-Vinyl Toluene Composites
Authors: Ramakrishna Dhulipala , Travis Susannah , Hawley Martin C.
Published: March 2011

Microwave processing has been investigated as an alternative to the conventional processing of polymers and polymer matrix composites. Different studies have demonstrated its viability and advantages, but various aspects related to its industrial applicability are still being investigated.

Two aspects related to the microwave curing of glass fiber/vinyl ester-vinyl toluene composites have been studied. A qualitative evaluation was done to determine the reproducibility of heating patterns of these laminates in different modes of a microwave resonant cavity. The samples were prepared to similar physical and chemical specifications and heated in different single modes of the cavity.

Another evaluation was done to compare the mechanical properties of microwave and thermally cured laminates subjected to flexural load. The samples were processed using similar cure cycles. The microwave samples were cured using a mode-switching technique and the thermal samples were cured in a temperature controlled oven. The void fractions of the samples were evaluated to develop pre-consolidation conditions that yield samples with low void fraction. Results of these two evaluations are discussed.
Microwave Processing of Foam Materials
Authors: Loock W. Van
Published: March 2011

The distinct phases in the production process of a foam material are foaming, curing and drying. Cellular materials are insulators to conventional heat. This paper discusses the effectiveness of microwave or high frequency energy for processing a layer of foam material on for example a conveyor belt. The emphasis is on the thermal and drying time constants and on the specific energy consumption. It is demonstrated that a limit is set on time gain when using microwaves.

A case study for applying microwaves in an industrial production line of foam rubber for mattresses according to the above principles is presented.
Dielectric Processing of Hazardous Materials - Present and Future Opportunities
Authors: Oda Steven J.
Published: March 2011

Dielectric heating technologies (microwave and radio-frequency, RF) bring unique capabilities to the processing of hazardous wastes. Potential opportunities for using these techniques can be described by classifying and matching waste streams to the particular features of dielectric heating. Microwave and RF applications for processing hazardous waste are at various stages of development and include: solvent recovery, regeneration of activated carbon, pyrolysis of rubber tires, soil remediation, and disinfection of hospital wastes. Other solutions to environmental problems can include the replacement of conventional fossil-fired processes (eg, RF-assisted post-baking of biscuits) and microwave heating of catalyst substrate materil for automotive emission control. Examples of dielectric heating systems that are processing hazardous waste are used to illustrate the benefits of these technologies and to characterize future opportunities.
Microwave Treatment of Hazardous Wastes: Physical Chemical Mechanisms
Authors: Dauerman Leonard , Windgasse Gabriele , Zhu Naihong , He Yaoll
Published: March 2011

The objective Is to develop processes to treat hazardous waste streams using microwave treatment. First, physical chemical mechanisms have been posited for a variety, of such waste streams including: soils contaminated with organics, and toxic heavy metals; “spent” GAC; organics in the gas phase. Second, feasibility tests are being carried out to determine if on-site field testing is warranted. In the case of microwave-induced steam distillation of volatile and semivolatile organics, pilot plant stuides indicate that the incident power cost is not prohibitive: that fear of prohibitive power costs has been thought to be the major drawback for micrwave treatment to become a competitive technology in this market.
Rapid High Temperature Measurement of Microwave Dielectric Properties
Authors: Tinga W.R.
Published: March 2011

Practical high temperature (above 500°C) dielectric measurement techniques are reviewed stating both advantages and limitations of known methods. Details of a new and practical dual frequency microwave high temperature dielectrometer are discussed. This dielectrometer technique is capable of measurements beyond 2000°C. Both heating of the small samples and the measurement of their complex dielectric constant is done simultaneously using both a medium power (60W) microwave source and a low power scalar network analyzer. Good accuracy is obtained and the measurement is capable of being totally automated. Presently, a measurement and heating cycle time of about 20 s is needed to completely characterize the sample's microwave dielectric response from 300°C to 1600°C. A second high temperature dielectrometer technique is discussed which requires only one microwave source of medium power level (60W). This method requires only the reflected power to be monitored during the microwave heating of the sample to obtain the complex permittivity versus temperature curve.
Polybenzene, A Predicted New Low Energy Form of Carbon
Authors: Adams Gary B. , O'Keeffe Michael , Sankey Otto F. , Page John B.
Published: March 2011

We have used a first principles molecular dynamics technique to find the relaxed atomic geometry and the corresponding electronic structure of a simple novel form of threecoordinated solid carbon, which we name polybenzene. The polybenzene structure is found to have a substantially lower energy per atom (by 0.23 eV) than C60, yet contains only 24 atoms per unit cell. In addition we have calculated the zero wavevector vibrational spectrum for this novel carbon structure.
Electronic Structure of Doped Buckminsterfullerene
Authors: RosÉn Arne , Östling Daniel
Published: March 2011

Molecular cluster calculations within the local density approximation have been performed in a study of the electronic structure of the C60 molecule - “Buckminsterfullerene” doped with K, B and N. Calculations for the KC60 molecule, with the K atom located at the centre of the cage as well as at different positions inside or outside the cage, show how the valence 4s electron is transferred to the LUMO state of the bare C60 molecule. Doping with a B or N atom located at the centre of the cage creates a molecule with a partly occupied level of 2p character in the HOMO and LUMO gap, similar to donor and acceptor levels in the band gap of traditionally doped semiconductors. Doping by substitution of one or two of the carbon atoms in the cage with X = B or N, as modelled with the C59 X1 or C58X2 clusters, gives a different structure with a splitting of the HOMO and LUMO levels in the pure C60 molecule and with the creation of acceptor and donor levels with the substitution of B and N, respectively.
Electron-Phonon Coupling in Superconducting Alkali-Metal Doped Fullerenes
Authors: Jishi R.A. , Dresseliiaus M.S.
Published: March 2011

The dimensionless electron-phonon coupling parameter in alkali metal-doped fullerenes isevaluated in a model whereby the electrons are treated within a tight binding formalism.The phonon mode frequencies and eigenvectors are obtained from a lattice dynamical modelwhich accurately fits all available experimental data on these modes. It is shown that the electrormphonon interaction can account for the relatively high values of the superconducting transition temperatures in alkali-metal fullerenes.
Synthesis of Fullerols from an Aqueous Acid Method
Authors: Chiang Long Y. , Swirczewski John. W. , Hsu Chang S. , Chowdhury S. K. , Cameron Steve , Creegan Andkathy
Published: March 2011

An efficient aqueous acid chemistry for the preparation of fullerols, consisting of 14-15 hydroxyl moieties in an average structure, from C60 molecules is described.
Carbon Aerogels and Xerogels
Authors: Pekala Richard W. , Alviso Cynthia T.
Published: March 2011

The aqueous polycondensation of resorcinol with formaldehyde proceeds through a sol-gel transition and results in the formation of highly crosslinked, transparent gels. If the solvent is simply evaporated from the pores of these gels, large capillary forces are exerted and a collapsed structure known as a xerogel is formed. In order to preserve the gel skeleton and minimize shrinkage, the aforementioned solvent or its substitute must be removed under supercritical conditions. The microporous material that results from this operation is known as an aerogel. Because resorcinol-formaldehyde aerogels and xerogels consist of a highly crosslinked aromatic polymer, they can be pyrolyzed in an inert atmosphere to form vitreous carbon monoliths. The resultant porous materials are black in color and no longer transparent, yet they retain the ultrafine cell size (< 50 nm), high surface area (600-800 m2 /g), and the interconnected particle morphology of their organic precursors. The thermal, acoustic, mechanical, and electrical properties of carbon aerogels/xerogels primarily depend upon polymerization conditions and pyrolysis temperature. In this paper, the chemistry-structure-property relationships of these unique materials will be discussed in detail.
Diamond Growth in an Oxy-Acetylene Flame by an Alternating Gas Ratio Technique
Authors: Sivazlian F. R. , von Windheim J. A. , Glass J.T.
Published: March 2011

Diamond films were grown using a computer controlled oxy-acetylene torch that allowed precise programming of O2 and C2H2 gas profiles. This enabled more accurate control of the diamond growth chemistry. With this torch, systematic and complex variations in gas chemistry were applied during growth and the resulting film morphology and film quality was investigated. Plan view scanning electron microscopy (SEM) revealed predominately (111) faceting as a result of a sawtooth variation in the O2:C2H2 gas ratio from 0.97 to 1.00. Raman spectroscopy indicated mostly sp3 bonding, with little non-diamond component present. Furthermore, crosssectional SEM showed small grains during normal growth (O2:C2H2 = 0.97), whereas grain size increased significantly after onset of a sawtooth variation in the gas ratio.
Scanning Atomic Force Microscopy and Scanning Electron Microscopy Study of Diamond Thin Films Grown by Microwave Plasma Enhanced Chemical Vapour Deposition
Authors: Ahn Jaeshin , Tan F.H. , Tan H.S. , Zhu W.
Published: March 2011

The early stages of diamond thin film growth under various growth conditions have been investigated using Scanning Atomic Force Microscopy and Scanning Electron Microscopy. A series of experiment with various source gas combinations, substrate surface preparation methods and different substrates have been carried out to determine the effect on the diamond nucleation. The highest early nucleation density was obtained with CH4(1%)/H2 process among other gas combinations used. It is suggested that the atomic oxygen content should be kept minimum during the initial nucleation period of CVD diamond. It has been observed that diamond nucleation does not necessarily require diamond seeding dust. The silicon substrate polished with alumina powder showed diamond nucleation along the alumina scratched lines. In the process of diamond crystal growth, screw dislocations and stacking faults have been observed.
The Role of Heavy Hydrocarbons in Cvd Diamond Growth
Authors: Wu Ching-Hsong , Potter T. J. , Tamor M. A.
Published: March 2011

A mass spectrometric analysis of heavy hydrocarbons (HHCs) during hot-filament CVD diamond growth was performed together with in situ monitoring of the growth rate. Many HHCs were detected and tentatively identified. Of all HHCs studied, only diacetylene shows good correlation with the diamond growth rate under various deposition conditions. Its possible role is discussed.
Chemical and Structural Effects on Diamond C(111)-(2×1) Surface Exposed to F, H and Hydrocarbon Species
Authors: Yramada Taro , Chuang T.J. , Seki H.
Published: March 2011

Adsorption and subsequent surface processes of hydrogen and hydrocarbon species on the diamond C(111)-(2×1) bare surface have been investigated by AES, XPS, LEED, TDS and laser non-linear spectroscopies (SHG and SFG) under ultrahigh vacuum condition. Extremely low coverage of atomic II causes the transition of the hare (2×1) surface to the (1×1) structure. Exposure of the. bare (2×1) surface to CIIx species from hot filament activated methane leads to the formation mainly of CH3 species. The conversion of the surface structure from (2×1) to (1×1) with exposure does take place but not as easily as for hydrogen. These studies are now being extended to adsorption of F by exposures to XeF2 There arc two stages of saturation for 17 adsorption on the C(111)-(2×1) surface. This is interpreted to indicate that there are at least two adsorption sites for the F atoms. Whereas adsorption of II atoms at coverages less than 5% of a monolayer causes the surface lattice transition from (2×1) to (1×1) structure, the (2×1) structure is retained at all levels of fluorine adsorption. However the C(111) (1×1) surface with over half a monolayer of II adsorption behaves quite differently with respect to F adsorption.
Molecular Dynamic Structure Investigations of the Surface Stability and Adsorption of H, H2, CH3, C2H2: (100) Diamond
Authors: Frauenheim Th. , Blaudeck P. , Porezag D.
Published: March 2011

Surface properties - stability and reconstruction - of clean and hydrogenated diamond (100) have been studied by real temperature molecular dynarnic (MD) simulations using an approximate density functional (DF) theory expanding the total electronic wave function in a minimal basis of localized atomic valence electron orbitals (LCAO - ansatz). The clean surface is highly unstable against a spontaneous dimerization resulting in a 2×1 reconstruction. Atomic hydrogen in the gas phase above the top surface at all temperatures and H2 molecules approaching the center of the dimer bond at room temperature are reactive in breaking the dimer π-bonds forming a monohydrogenated surface which maintains a stable 2×1 structure but with elongated surface C-C dimer bonds remaining stable against continuing hydrogen supply. The dihydrogenated surface taking a 1×1 structure, because of steric overcrowding dynamically becomes unstable against forming a 1×1 (alternating) di-, monohydrogenated surface. As first elementary reaction processes which may be discussed in relation to diamond growth we studied the thermal adsorption of CH3 and C2H2 onto a clean 2×l reconstructed (100) diamond surface.
Temperature Programmed Desorption of Hydrogen and Deuterium from Cvd Diamond Samples
Authors: Schulberg Michelle T. , Kubiak Glenn D. , Stulen Richard H.
Published: March 2011

The desorption kinetics of H2, HD, and D2 from a CVD-grown diamond sample have been measured using temperature programmed desorption. The sample was exposed to hydrogen and deuterium at ∼ 100 K. Molecular hydrogen does not react with the diamond surface but atomic hydrogen chemisorbs. The sample is then heated to 1500 K at a rate of 6 K/s. The hydrogen desorption spectrum from these polycrystalline specimens is surprisingly simple, consisting of a single peak near 1270 K for all coverages studied. The width of the desorption peak is ∼ 100 K. Neither the width nor the peak maximum shift with increasing hydrogen coverage. There is no isotope effect to the desorption. No other desorption products (water, small hydrocarbons) are detected. Kinetic parameters can be extracted from these spectra, and these can be compared to hydrogen desorption from natural diamond single crystal surfaces. These parameters can be used to model diamond growth processes.