bluuebunny/crossref_metadata_2025_split huggingface dataset:
Degradation Studies Of Polypyrrole Coated Fibers For Microwave And Millimeterwave Obscurants
Authors: Buckley Leonard. J. , Eashoo Mark 
Published: April 2011

ABSTRACTMicrowave and millimeterwave obscurants based on typical millimeterwave materials do not environmentally degrade with respect to their physical and electrical properties. The use of conductive polymer coated films and fibers with inherent environmental instabilities are being investigated as possible alternatives. Achieving the optimum electrical performance is highly dependent upon the polymer/dopant combination, deposition conditions, morphology, and volume of the coating that is used. Several conductive polymer coated fiber systems were investigated via thermal analysis. The effects of processing conditions on performance and stability were studied.
Femtosecond Optical Dynamics In A Poly(Para-Phenylene)-Type Ladderpolymer
Authors: Graupner W. , Petritsch K. , Leising G. , Lanzani G. , Nisoli M. , De Silvestri S. , Scherf U. 
Published: April 2011

ABSTRACTTime-resolved femtosecond pump and probe experiments were conducted on films and solutions of poly (para-phenylene)-type ladder-homopolymers featuring a high degree of intrachain order. We find photobleaching, stimulated emission and photoinduced absorption. The spectral separation of stimulated emission and photoinduced absorption makes this polymer a promising candidate for a solid state laser.
Positron Lifetime Studies of Polyaniline Conducting Polymers
Authors: Huang C. M. , Liu J. , Sandreczki T. C. , Jean Y. C. 
Published: April 2011

ABSTRACTPositron annihilation lifetime measurements are made in a series of polyaniline polymers with different chemical compositions and protonation ratios at room temperature. Two positron lifetimes are observed in these materials: one is assigned to annihilation in the bulk and the other to voids created due to protonation. A relationship between conductivities and positron annihilation probabilities is found.
Raman spectra of charge transfer organic compounds: Conductors And Semiconductors
Authors: Gómez R. , Ridaura R. , Quintana M. , Marquina M. L. , Marquina V. , Jiménez M. , Aburto S. , Gómez-Lara J. , González-Rolón B. 
Published: April 2011

ABSTRACTA series of coordination compounds -macrocycle tetraaza derivatives with extended electronic conjugations- as molecular solids have been synthesized and analyzed by Raman spectroscopy. Their resistivity vs. temperature characteristics, measured in thin films, show three types of behavior: metallic, semiconductor and, in some cases, semiconductor with a transition to metallic below certain temperature. Room temperature Raman spectra were obtained in a FT-IR spectrometer and some stretching modes show different Raman shifts depending on the reactants. We relate these shifts with the degree of charge transfer between donor and acceptor radicals.
Characterization Of Heattreated Polyparaphenylene-Based Carbons
Authors: Matthewsa M. J. , Endo M. , Takahashi T. , Nishimura Y. , Takamuku T. , Dresselhaus M. S. 
Published: April 2011

ABSTRACTRaman spectroscopy and TEM measurements were recently performed on a series of polyparaphenylene (PPP)-based carbon samples which were heat-treated to temperatures between 600°C and 3000°C. Particular attention is focused on the development of carbonaceous structures at low heat-treatment temperatures (THT) in the range 600°C ≤ THT ≥ 800°C. PPP-based carbons heat treated in this temperature range have been found to have a very high affinity for the electrochemical introduction of lithium, which is of particular interest in ‘rocking-chair’ rechargeable Li batteries. Specific (Faradaic) capacities of up to 1120 mAh/g have been obtained for PPPbased carbon anodes with a THT of 700°C, which is about three times the capacity of GIC-based anode materials. At a heat-treatment temperature of 700° C, the PPPbased carbon has a disordered-granular appearance, as observed from TEM, while a ribbon-like graphitic structure is seen for heat treatment near 3000°C. Furthermore, Raman spectra show that, near a THT of 700° C, these PPP-based materials undergo a carbonization transformation from a mostly polymer-type extended lattice to a disordered carbon matrix, which undergoes partial graphitization at higher THT. Upon the introduction of small amounts of substitutionally-doped Boron (1% - 3% atomic), various properties are substantially modified. In this work we briefly discuss the effect of B-doping on the PPP-based carbon structure.
Erbium Tris(Amide) Compounds as Source Molecules FOR Rare Earth Doping of Semiconducting Materials
Authors: Just Oliver , Greenwald Anton C. , Rees William S. 
Published: April 2011

ABSTRACTThe homoleptic compound erbium{tris[bis (trimethylsilyl)]amide} displays high doping ability for incorporation of the rare earth element into epitaxially grown semiconducting host materials for fabrication of temperature-independent, monochromatic solid state optoelectronic devices. Electronic characteristics derived from erbium doped semiconducting films have been obtained. Several more volatile and lower melting representatives of this class of compounds have been synthesized, characterized by various analytical techniques and examined for their suitability to incorporate optically-active erbium centers into a semiconducting environment.
Liquid Delivery MOCVD of Ferroelectric PZT
Authors: Roeder J. F. , Vaartstra B. A. , Buskirk P. C. Van , Beratan H. R. 
Published: April 2011

ABSTRACTFerroelectric PbZrxTi1-x O3 (PZT) films have been deposited by chemical vapor deposition using flash vaporized metalorganic precursors. Crystalline perovskite films approximately 3000Å thick were deposited on Pt/Si substrates at 550–590°C and had dielectric coefficients in the range of 600–1900. Dielectric constant was found to increase with increasing Zr/Ti ratio, rising to the largest values near the morphotropic phase boundary. Remanent polarizations of the PZT were between 20–27 μC/cm2 and the coercive field decreased with increasing Zr/Ti ratio from 43 to 21 kV/cm. Pyroelectric coefficients were measured using the Byer-Roundy technique and ranged from 20–30 nC/cm2K. At 550°C, a direct relationship was observed between precursor composition and film composition. At 590°C, volatility of PbO became appreciable and composition of films with Zr/(Zr+Ti) = 0.3 remained near stoichiometry over a wide range of excess Pb in the precursor. However, this effect was found to diminish for higher ratios of Zr/Ti. The orientation of the PZT films deposited over a range of precursor compositions was similar with some [100] preferred orientation. In contrast, the orientation of a PbTiO3 films could be manipulated by the Pb/Ti ratio in the precursor, with [111] preferred orientations predominating at lower Pb/Ti and [ 100/001]–[111] mixed orientations at higher Pb/Ti ratios.
MOCVD OF SrS and SrS:Ce Thin Films for Eelctroluminescent Flat Panel displays
Authors: Samuels John A. , Smith David C. , Siebein Kerry N. , Salazar Kenny , Tuenge Richard T. , Schaus Christian F. , King Christopher N. , Le H. , Hitt J. , Thuemler R. L. , Wager J. F. 
Published: April 2011

ABSTRACTHigh quality SrS and SrS:Ce thin films were deposited from Sr(thd)2, Ce(thd)4 and H2S via a low pressure MOCVD process. Film characteristics were found to be insensitive to the presence of the cerium dopant in the concentration range investigated. Depositions were carried out for a wide temperature range (250–550° C). Deposition rates were found to be relatively insensitive for the temperature range investigated. The films produced were found to be highly crystalline at all temperatures investigated. Deposited material showed texturing as a function of substrate material and temperature. FWHM of the <111> reflections were found to have a 2Θ values of 0.15–0.18 deg. for all temperatures. RBS and AES shows stoichiometric 1:1 SrS with less than 2% carbon and oxygen contaminates. ERD indicates the films to have 1 – 2.5% hydrogen. Films doped with 0.019 – 0.043 atom – 250 volts.
MOCVD of Very thin Films of Lead Lanthanum Titanate
Authors: Beach David B. , Vallet Catherine E. 
Published: April 2011

ABSTRACTFilms of lead lanthanum titanate were deposited using metal-organic chemical vapor deposition (MOCVD) at temperatures between 500 and 550°C in a hot-wall reactor. The precursors used were Pb(THD)2, La(THD)3, and Ti(THD)2(I-OPr)2where THD = 2,2,6,6-tetramethyl-3,5-heptanedionate, O2C11H19, and I-OPr = isopropoxide, OC3H7. The three precursors were delivered to the reactor using a single solution containing all three precursors dissolved in tetraglyme and the precursor solution was volatilized at 225°C. Films were deposited on Si and Si/Ti/Pt substrates, and characterized using Rutherford Backscattering Spectroscopy (RBS) and X-ray diffraction(XRD). Films deposited at 550°C had a composition which was close to that of the precursor solution while films deposited at 500°C were deficient in lanthanum. Even at 500°C, the desired perovskite phase is readily observed by XRD. Subsequent rapid thermal processing of the film deposited at 500°C showed an increase in the intensity of the X-ray lines, but did not change the width of these lines, implying that grain sizes had remained unchanged.
Liquid Source Mocvd of High Quality Yba2Cu3O7−x Films on Polycrystalline And Amorphous Substrates
Authors: Studebaker D.B. , Doubinina G. , Zhang J. , Wang Y.Y. , Dravid V.P. , Marks T.J. 
Published: April 2011

ABSTRACTHigh temperature superconducting Yba2Cu3O7−x films were grown by liquid delivery metal-organic chemical vapor deposition (LDMOCVD) on silver-coated stainless steel substrates. The films are c-axis oriented, and exhibit a very low surface resistance of 110 μΩ at 77 K and 3 GHz. A two-step LDMOCVD method for growth of oriented (200) CeO2 films on amorphous substrates was also developed. Films of CeO2 for YBCO buffer layers were grown on fused silica (SiO2), polycrystalline alumina (Al2O3), and sapphire (A12O3). A highly c-axis oriented film of YBCO was grown on a fused silica substrate with a CeO2 buffer layer.
Barrier Modification In Au/IIb Semiconducting Diamond Contacts
Authors: Teklu M. , Das K. 
Published: April 2011

ABSTRACTRectifying contacts on semiconducting type IIb diamond crystals are readily established with any conducting material system including elemental metals, highly doped semiconductors, silicides and carbides. However, for a given surface preparation using oxidizing wet chemicals and in the absence of a surface reaction, barrier heights are observed to be constant regardless of the metal work function. In this report it is demonstrated that an adjustment of the barrier height can be achieved by employing a premetallization low-dose low-energy ion-implantation step.
Esr Of Defects In Surface Conduction Layer On Cvd Diamond Films
Authors: Show Y. , Iwase M. , Izumi T. 
Published: April 2011

ABSTRACTDefects in the surface conductive layer of CVD-diamond films have been investigated by ESR method. ESR analysis revealed that defect center ( Pac-center: g=2.003, ΔΔ Hpp=8 Oe ) in the non-diamond phase carbon region exists in the surface conductive layer. The Pac-center with a spin density of the order of 1020spins/cm3 or above was formed in the surface layer by hydrogen radical irradiation during the diamond deposition. Formation of the Pac-center causes the resistivity of CVD-diamond to decrease ( from 9 × 108 Ω to 1.8 × 106 Ω )
Reaction Of Diamond Surfaces With Halogen-Containing Species
Authors: Larsson K. 
Published: April 2011

ABSTRACTAn energetic and structural comparison has been made concerning adsorption processes on a diamond (111) surface from a hydrogen (H)-, halogen (X)- or H/X-carrying carbon precursors. The halogens X examined were F, Cl and Br. The quantum mechanical methods used in the investigation were the ab initio MO method as well as the LDA method. F, Cl, and H, were all shown to be able to sustain the sp3 structural configuration of the surface carbon atoms. For Br large sterical hindrances were induced and the diamond (111) surface could not be stabilized. The calculated adsorption energy of CF3 to a H-terminated diamond (111) surface was found to be numerically the largest one (489 kJ/mol on the MP2 level of theory) in comparison to the other adsorption processes studied in the present investigation. It was, in particular, much larger than the corresponding adsorption energy of CH3 (418 kJ/mol). The calculated adsorption energies do support the initial step in the growth process (adsorption) to be energetically more favourable for systems incorporating a mixture of halogen and hydrogen in the growth vapor than for corresponding systems involving unmixed halogen or hydrogen in the carbon containing precursor.
Fluoroalkyl Iodide Photodecomposition on Diamond (100) - an Efficient Route to The Fluorination of Diamond Surfaces
Authors: Smentkowski V. S. , Yates J. T. 
Published: April 2011

ABSTRACTThe photodecomposition of CF3I and C4F9I overlayers at 119 K on diamond (100) surfaces has been shown to be an efficient route to fluorination of the diamond surface. X-ray photoelectron spectroscopy (XPS) has been used for photoactivation as well as for studies of the following processes: the photodecomposition of the fluoroalkyl iodide molecules: the attachment of the photofragments to the diamond surface; and the thermal decomposition of the fluoroalkyl ligands. Chemisorbed CF3groups on diamond (100) decompose by 300 K whereas C4F9groups decompose over the temperature range of 300 K to ∼ 700 K. Both of these thermal decomposition processes produce surface C-F bonds on the diamond surface which thermally decompose over a wide temperature range extending up to 1500 K. Hydrogen passivation of the diamond surface is ineffective in preventing free radical attack from the photodissociated products of the fluoroalkyl iodides. The use of photoactivation of fluoroalkyl iodides for the fluorination of diamond surfaces provides a convenient route compared to other methods involving the direct production of atomic F, molecular fluorine, XeF2, and F containing plasmas.
Electrical Properties Of Undoped Polycrystalline Diamond Thin Films On Silicon
Authors: Jauhiainen Anders , Bengtsson Stefan , Engström Olof 
Published: April 2011

ABSTRACTWe have investigated the electrical properties of undoped polycrystalline diamond thin films deposited on (100)-oriented n-type and p-type silicon substrates. The films, intended for electronic applications, were manufactured using hot filament chemical vapour deposition (HFCVD). To a large extent the capacitance-voltage characteristics are influenced by traps located close to the interface between the diamond layer and the silicon substrate. These traps play an important role for voltage sharing between the diamond layer and the silicon space charge region. The DC current density through the diamond film has the same functional dependence on the electric field for films deposited on both n- and p-Si. The field dependency agrees with a Frenkel-Poole transport model. Further, although the DC current transport is thermally activated, it does not follow an Arrhenius relation. A possible reason is that traps within a broad range of energy levels are involved in the charge transport. Finally, current transients resulting from stepwise changes in the applied voltage follow a power law time dependence where the kinetics depend only weakly on temperature.
High Field Electrical Conductivity and Breakdown in Heteroepitaxial Diamond Films
Authors: Schröppel S. , Hessmer R. , Schreck M. , Stritzker B. 
Published: April 2011

ABSTRACTNominally undoped, heteroepitaxially nucleated diamond films have been grown on Si(001). For different temperatures ranging between room temperature and 490°C the DCconductivity through the films has been measured for field strengths up to 600kV/cm. In the framework of the Poole-Frenkel theory a fit of the curves is possible for the model of isolated as well as for the model of overlapping coulombic potentials yielding an activation energy of 1.03eV.In addition the breakdown voltage of the films has been measured as a function of the temperature. A drastic linear decrease with temperature is observed. Starting at a dielectric strength of about 1 MV/cm at room temperature the breakdown field decreases by an order of magnitude for 400°C. This observed behaviour is consistent with thermal breakdown based on Poole-Frenkel conduction in the pre-breakdown region.
Determination of Hydrogen in CVD Diamond by Notched Neutron Spectrum Technique and Ftir
Authors: Golshani F. , Miller W. H. , Prelas M. A. , Sung T. , Popovici G. , Manning G. , Loyalka S. K. , Shahedipour F. , White H. W. , Brown W. D. , Malshe A. P. , Naseem H. A. 
Published: April 2011

ABSTRACTThe hydrogen content of free-standing polycrystalline CVD diamond samples was determined by Fourier Transform Infrared (FTIR) measurements and was quantified by a notched neutron spectrum technique. The latter measures the total bonded and unbonded hydrogen. The concentration of total hydrogen in these samples was of the same order of magnitude. The FTIR measurements, which are sensitive to the bonded hydrogen, indicated different hydrogen to diamond peak ratios.
A High Performance UV Photodetector from Thin Film Diamond
Authors: Mckeag Robert D. , Whitfield Michael D. , Chan Simon Sm , Pang Lisa Ys , Jackman Richard B. 
Published: April 2011

ABSTRACTThin film diamond has been used to fabricate a photodetector which displays high sensitivity to deep UV light, with an external quantum efficiency of greater than one, a dark current of less than 0.1nA and which is near ‘blind’ to visible light.
Photoelectron Emission from the Cesiated Diamond (110) Surface
Authors: Fox C. A. , Kelly M. A. , Hagstrom S. B. , Cao R. , Vergara G. , Pianetta P. , Pan L. S. , Hsu W. L. 
Published: April 2011

ABSTRACTCesiation of type IIB diamond (110) crystals was studied using a combination of ultraviolet photoemission spectroscopy, x-ray photoemission spectroscopy, and low energy electron diffraction. The diamond (110) crystal was hydrogen treated by exposure to a hydrogen microwave discharge. Although cesium was largely unreactive with the hydrogenated diamond surface, cesiation yielded a large enhancement in the secondary electron yield of the diamond surface and the negative electron affinity (NEA) condition. An increase in the downwards band bending of approximately 0.75-0.9 eV was inferred from the shift in the valence band edge following cesiation. In addition, (lx 1) LEED patterns were observed at all cesium coverages. Exposure of the cesiated diamond surface to molecular oxygen significantly reduced the NEA peak (relative to the secondary electron background); however, recovery of the NEA peak was observed when the molecular oxygen source was removed.
On The Optimized Nucleation of Near-Single-Crystal Cvd Diamond Film
Authors: Chen L. C. , Juan C. C. , Wu J. Y. , Chen K. H. , Teng J. W. 
Published: April 2011

ABSTRACTNear-single-crystal diamond films have been obtained in a number of laboratories recently. The optimization of nucleation density by using a bias-enhanced nucleation (BEN) method is believed to be a critical step. However, the condition of optimized nucleation has never been clearly delineated. In the present report, a novel quantitative technique was established to monitor the nucleation of diamond in-situ. Specifically, the induced current was measured as a function of nucleation time during BEN. The timedependence of induced current was studied under various methane concentrations as well as substrate temperatures. The optimized nucleation condition can be unambiguously determined from the current-time plot. Besides the in-situ current probe, ex-situ x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were also used to investigate the chemical and morphological evolution. Characteristic XPS and AFM features of optimized nucleation is discussed.
Solid-Phase Thermal Decomposition of 2,4-Dinitroimidazole (2,4-DNI)
Authors: Minier Leanna , Behrens Richard , Bulusu Suryanarayana 
Published: April 2011

AbstractThe solid-phase thermal decomposition of the insensitive energetic aromatic heterocycle 2,4- dinitroimidazole (2,4-DNI: mp 265–274°C) is studied utilizing simultaneous thermogravimetric modulated beam mass spectrometry (STMBMS) between 200° and 247°C. The pyrolysis products have been identified using perdeuterated and N-labeled isotopomers. The products consist of low molecular-weight gases and a thermally stable solid residue. The major gaseous products are NO, CO2, CO, N2, HNCO and H2O. Minor gaseous products are HCN, C2N2, NO2, C3H4N2, C3H3N3O and NH3. The elemental formula of the residue is C2HN2O and FTIR analysis suggests that it is polyurea- and polycarbamate-like in nature. The rates of formation of the gaseous products and their respective quantities have been determined for a typical isothermal decomposition experiment at 235°C. The temporal behaviors of the gas formation rates indicate that the overall decomposition is characterized by a sequence of four events; 1) an early decomposition period induced by impurities and H2O, 2) an induction period where CO2 and NO are the primary products formed at relatively constant rates, 3) an autoacceleratory period that peaks when the sample is depleted and 4) a final period in which the residue decomposes. Arrhenius parameters for the induction period are Ea = 46.9 ± 0.7 kcal/mol and Log(A) = 16.3 ± 0.3. Decomposition pathways that are consistent with the data are presented.
Kinetics and Species of Flash Pyrolysis of Cellulose Acetate Butyrate: The Binder of Lova
Authors: Gongwer P. E. , Arisawa H. , Brill T. B. 
Published: April 2011

AbstractThe principal binder of many LOVA propellants is cellulose acetate butyrate (CAB). By the use of T-Jump/FTIR spectroscopy, CAB was flash-pyrolyzed to set temperatures in the 465–600°C range, while rapid-scan IR spectra were used to identify the main decomposition products and to measure the rate of formation of each product as a function of temperature. Eleven specific products, which include oligomers of CAB, acids, aldehydes, ketenes, esters, CO2 and CO, were quantified by chemometric procedures. The ketenes are the most novel products. The Arrhenius parameters reveal that below 510 ± 20°C, the rate of product evolution is controlled mainly by condensed phase reactions. Above 510 ± 20°C, the rate of product evolution is controlled by desorption/evaporation of the volatile products.
Atomic Force Microscopy of Hot Spot Reaction Sites in Impacted RDX and Laser Heated AP
Authors: Sharma J. , Coffey C. S. , Ramaswamy A. L. , Armstrong R. W. 
Published: April 2011

AbstractAn atomic force microscope (AFM) has been used to reveal residual sub-micron sized decomposition sites in drop weight impacted RDX and laser irradiated AP crystals. In impacted RDX, the small and early reaction sites observed are hemispherical craters, ranging in size from 20–300 nm. The smallest reaction site encompassed about 10,000 molecules with an expected energy evolution of 2 × 10−14 J. On a somewhat larger scale hillocks of 200–800 nm were observed, their shape giving evidence of internal reaction and hot spot melting. Dislocation densities as high as 5 × 1012 per cm2 were observed in sub-ignited RDX. High resolution AFM images of the RDX lattice structure indicate molecular rotation as well as displacements at dislocation sites. In AP, after nanosecond pulsed laser irradiation, reaction sites were trumpet shaped with a smallest size of approximately 50 nm. Most sites contained a crystallographically oriented central square lid formed above the surrounding crystal surface, probably relating to the orthorhombic to cubic phase transition documented in micron scale cracking patterns observed at the laser heated sites.