bluuebunny/crossref_metadata_2025 huggingface dataset:
Advanced Photorefractive and Light-Emitting Organic Materials
Authors: Peyghambarian N. , Kippelen B.
Published: April 2011

The tailoring of organic molecules and polymers has enabled the recent development of multifunctional materials such as photorefractive polymers and organic electroluminescent materials. This paper presents recent advances in both areas.
High Mobility and Liquid Phase Processable Organic Semiconductors
Authors: Katz H. E. , Laquindanum J. , Lovinger A. J.
Published: April 2011

New thiophene oligomers and fused ring compounds have been designed and synthesized with the aim of maximizing semiconductor mobility in thin film transistors (TFTs) while allowing for liquid phase processability. Thiophene hexamers with alkyl side chains of various lengths, some with an ether oxygen embedded in the chain, were synthesized, as were derivatives of the novel heterocycle anthradithiophene. Mobilities of the vaporphase-deposited films ranged from 0.01 cm2/Vs for the hexamers to 0.15 cm2/Vs for dihexylanthradithiophene. The latter is the highest mobility yet reported for a polycrystalline film. Cast films of some of these compounds from solution gave mobilities within factors of 2–10 of the corresponding values from gas-phase-deposited films.
Electrical Characterization of Thin Single Crystals of Sexithiophene
Authors: Frisbie C. Daniel , Granstrom Eric L. , Loiacono Michael J.
Published: April 2011

Extremely thin, single crystals of sexithiophene (6T), 2–14 nm thick and 2–5 μm in length and width, can be grown an flat gold substrates by thermal evaporation. The thickness dimension corresponds to 1–6 monolayers (ML) of 6T molecules arranged with their long axes nearly perpendicular to the substrate. We have measured the current-voltage (I-V) characteristics through the thickness of these crystallites, after doping them with iodine, using conducting probe atomic force microscopy (CPAFM). The I-V traces are linear in the ±50 mV regime. The conductance (I/V) of the doped 6T crystals does not decrease monotonically with increasing thickness as might be expected, but instead has a maximum at 3 ML thickness, and we discuss several possible explanations for this observation.
Preparation of C60 Charge Transfer Complexes with Organic Donor Molecules and Alkali Doping
Authors: Otsuka A. , Saito G. , Hirate S. , Pac S. , Ishida T. , Zakhidov A. A. , Yakush K.
Published: April 2011

Solid charge transfer (CT) complexes of C60 with TSeC1-TTF, EDT-TTF, EOET-TTF, and TDAP (1, 3, 6, 8-tetrakis(dimethylamino)pyrene) were newly prepared. All the obtained black crystals were proved to be neutral despite of their rather strong electron donor ability. Lattice parameters of them except for EOET-TTF complex were determined together with those of HMTTeF·C60, which had been reported with different values. Rubidium doping under a mild condition was examined on the complexes of TDAP, EOET-TTF, HMTTeF, BEDT-TTF, hydroquinone and ferrocene to search for the superconductors of new crystal and electronic structures. Among them, the rubidium-doped ferrocene complex easily showed an apparent superconducting signal in SQUID magnetization measurements. The doping effect on these CT complexes is compared to that on OMTTF complex.
Morphological Effects in the Chemical and Photoluminescent Behavior of Aluminum Tris(8-Hydroxyquinoline) (Alq3)
Authors: Higginson K. A. , Zhang X.-M. , Papadimitrakopoulos F.
Published: April 2011

Aluminum tris(8-hydroxyquinoline) (Alq3) is presently considered one of the most reliable electron transporting and emitting materials for molecular-based organic light emitting diodes (OLEDs). This paper discusses the effects of sample morphology on the hydrolysis and photoluminescence response of Alq3. The evolution of 8-hydroxyquinoline (8-Hq), a volatile byproduct of the hydrolysis of Alq3, was quantified using gas chromatography/mass spectroscopy (GC/MS) analysis on samples of different morphology. Annealed (more crystalline) samples exhibited greater chemical stability than freshly sublimed films, at the expense of photoluminescence efficiency. These phenomena are discussed with respect to possible failure mechanisms that Alq3-based OLEDs might undergo during prolonged operation.
Light Emitting Devices with Molecularly Doped Polymer Layers. A New Diamine as a Hole Transporting Molecule
Authors: Fattori V. , Cocchi M. , Marco P. Di , Giro G. , Kalinowski J. , Dembech P. , Fabbri G. , Seconi G.
Published: April 2011

In the present contribution a new hole transporting molecule belonging to the triphenyldiamine family (N,N'-diphenyl-N,N'-bis(4-metylphenyl)- 1, 1'-biphenyl-4,4'- diamine) in a polycarbonate matrix is studied as the hole transport layer in a two layer device with Alq3 as emitting layer. The dependence of the electrical and emitting behaviour on the doping level is studied and compared with the vacuum deposited diamine layer also interfaced with Alq3
Injection Efficiency from Various Metals into Trap Free Molecularly Doped Polymers Evaluated from Combined Analysis of Current-Voltage and Time-of-Flight Drift Mobility Data
Authors: Abkowitz M. , Facci J. S. , Rehm J.
Published: April 2011

An experimental procedure which can provide a direct quantitative measure of contact injection efficiency into a trap free transport polymer is described. This technique combines coupled analyses of bias dependent injection current supplied by the contact under test with time-of-flight drift mobility measurements carried out on the same specimen film. This general procedure has been used in a broad range of experiments to evaluate the injection efficiencies from a series of hole injecting contacts of differing work functions into the molecularly doped polymer, TPD/Polycarbonate Two key results are emphasized: (1) Injection efficiency does scale on average with the interfacial barrier, the energy step estimated from substrate workfunction and MDP electrochemical data. In individual cases however, large variations about the norm are clearly identified and can be attributed to variations in the contact surface prior to coating, for example the relative degree of oxidation or, as TOFSIMS reveals, the interdiffusion of metal atoms from adhesive layers which secure the metal coating to a Si wafer substrate. (2) For the case of Au, the injection efficiency of a Au substrate was compared to the behavior of Au vacuum deposited onto the already formed coating under a variety of conditions. The injection efficiency from Au evaporated onto preformed coating initially varies with deposition conditions but relaxes with time under ambient conditions, eventually becoming ohmic. Significant details of this relaxation behavior are described and analyzed in an accompanying paper.
Electrical Properties of Au/Polymer Interfaces
Authors: Ioannidis A. , Facci J. S. , Abkowitz M.
Published: April 2011

A trap-free Molecularly Doped hole-transport Polymer (MDP) provides a model system for the study of metal/polymer interfaces by enabling the use of a recently developed technique that supplies a quantitative measure of contact injection efficiency. The technique combines fielddependent injection current measurements from a contact under test with time-of-flighl (TOF) mobility measurements on the same sample. In the present case, MDP films were prepared with two top vapor-deposited contacts, one of Au (test contact) and one of AI (for TOF), and a bottom carbon-loaded polyimide electriode. An unusual phenomenon is investigated whereby injection from Au is initially blocking, evolving to ohmic over time. This contrasts with the behavior expected according to the relative work-functions of Au and of the polymer whereby Au should inject holes efficiently. The samples were aged at various temperatures below the glass transition of the polymer (85°C) and the evolution of current-field measurements and of capacitance is followed in detail over time and analyzed. All Au contacts eventually achieved ohmic injection. Rapid sequence data acquisition enabled the separation of two main processes in the injection evolution. Control measurements ensure that the evolution of the electrical properties is due to the Au/polymer interface behavior and not the bulk. The behavior of Au contacts evaporated under various deposition conditions was compared. Transmission electron microscopy results at the Au/MDP interface were obtained as both a function of time and of deposition conditions. Mechanisms operating at the interface of the evaporated Au films on the polymer are discussed.
Control of the Luminescence Properties in Polythiophenes Solutions by Interring Rotational Disorder
Authors: Luzzati S. , Bongiovanni G. , Catellani M. , Loi M. A. , Milani A. , Mura A. , Piaggi A.
Published: April 2011

The photoluminescence properties of thiophene-based polymers obtained by the random copolymerization of 3,4-dibutylthiophene and 3-butylthiophene are reported. Optical absorption spectra, cw photolumninescence (PL) spectra, PL quantum efficiencies and PL decays have been measured in dilute solutions. By varying the copolymer chemical composition it is possible to tune the intensity and the color of the luminescence spectra in the whole visible range. We evidence the role of disorder, controlled by interring rotations, as the tuning factor for the disexcitation pathway of the photoexcitations in these materials.
Polarized Light-Induced Anisotropy in Polymer Films Doped with Az Dyes in the Photostationary State Studied by IR Spectroscopy
Authors: Tawa K. , Kamada K. , Sakaguchi T. , Ohta K.
Published: April 2011

The anisotropy induced in a series of methacrylate polymers doped with Disperse Orange 3 (DO3, NO2-phenyl-N=N-phenyl-NH2) was investigated by polarized FTIR spectroscopy. Three kinds of methacrylate polymers with different glass transition temperature (Tg), poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA), and poly(butyl methacrylate) (PBMA), were used as polymer matrices. Observed infrared absorption bands of DO3 in the polymer films were assigned to symmetric (NO2s) and antisymmetric (NO2as) stretching modes of NO2, and the C-N stretching mode of C-NH2 (C-N). The infrared dichroism was observed in these bands under the irradiation. The orientation factors, Kzfn, (f=x, y, z, n=trans, cis), for both isomers of DO3 were determined in the photostationary stite for every polymer matrix. The factors indicate that it is difficult for NO2 group to move in the PMMA during trans-cis-trans isomerization and that it is difficult for NH2 group to move in the PBMA. The dynamical behavior of DO3 molecules which depends on the kind of polymers could be interpreted from orientation factors. This study shows that polarized FTIR spectroscopy is one of the most powerful methods available to analyze the physical mechanisms of photoinduced anisotropy.
Dynamics of Polarons in Guest-Host-System Polymer Light Emitting Devices
Authors: List E.J.W. , Partee J. , Graupner W. , Shinar J. , Leising G.
Published: April 2011

The conjugated ladder-type poly(paraphenylene) is an attractive material for blue polymer light emitting devices (PLED). Blending the active layer with small amounts of a red emitting guest polymer, the emission shifts from blue to red with increasing guest concentration due to efficient excitation energy transfer. The results of photoluminescence detected magnetic resonance, electroluminescence detected magnetic resonance measurements and current detected magnetic resonance measurements on PLEDs based on 0.05w%/o - 2w%/o red emitting poly(perylene-co-diethynylbenzene) (PPDB) in the active layer of the PLED are presented and discussed.
Effects of Sputtered Ir and IrO2 Electrodes on the Properties of PZT Thin Films Deposited By MOCVD
Authors: Shimizu M. , Fujisawa H. , Hyodo S. , Nakashima S. , Niu H. , Okino H. , Shiosaki T.
Published: April 2011

The effect of bottom electrode thickness on the electrical properties of PZT capacitors with Ir and IrO2, electrodes was investigated, with particular attention to switching endurance characteristics. Ir and IrO2 electrodes were prepared by rf magnetron sputtering. PZT films were grown by MOCVD. Secondary ion mass spectrometry (SIMS) analysis showed thick Ir and IrO2 electrodes performed well as a barrier to the PZT elements. On the other hand, strong diffusion at the interface between PZT and the electrodes was observed, when the Ir and IrO2 electrodes were thin. From transmission electron microscope (TEM) observation, it was also found that there was an amorphous intermediate layer at the interface between the PZT and the thick Ir bottom electrode. The switching endurance characteristics were influenced by the thickness of the Ir bottom electrode.
A Study on the Responsivity of Four-Layer Pyroelectric Sensors
Authors: Samoilov Vladimir B. , Kang Seong Jun , Chang Dong Hoon , Yoon Yung Sup
Published: April 2011

The temperature distribution under periodic thermal excitation and the pyroelectric response of a four-layer system consisting of front and back semi-infinite media, a pyroelectric element, and an intermediate layer are found. Numerical results and approximate expressions are obtained for special cases, such as a detector with an air gap between the pyroelectric layer and the bulk substrate and a detector on a substrate of finite thickness an air environment. The responsivities of detectors with a lead-lanthanum-titanate (PLT) sensing element on either a Si and a SiO2 substrate are calculated as functions of the pyroelectric layer and the underlying layer thicknesses. It is found that the detector with an air gap has a frequency-independent responsivity over a wide frequency range. A correlation is found between the type of frequency response in each frequency region and the corresponding dominant mechanism for heat loss.
Reparation and Characterization of BST Thin Films with Hybrid Bottom Electrodes
Authors: Ahn Joon-Hyung , Park Jeong-Ho , Lee Won-Jae , Kim Ho-Gi
Published: April 2011

Thin platinum layer was used for the modification of the interface state between (Ba,Sr)TiO3 (BST) thin films and RuO2 bottom electrodes. Pt/RuO2 hybrid bottom electrodes were fabricated with various platinum deposition temperatures by a conventional dc magnetron sputtering method. Although the surface morphology and XRD patterns of BST thin films were not changed, the electrical properties of BST films deposited on Pt/RuO2 hybrid electrodes were improved compared to the films on RuO2 electrodes. Dielectric constant (εr) and leakage current density of BST thin films on Pt/RuO2 hybrid electrodes prepared at the platinum deposition temperature of 400°C were 498 and 8.6 × 10−8 A/cm2 at 1.5V, respectively.
Sol-Gel Synthesis of Rare Earth Aluminate Films as Buffer Layers for High Tc Superconducting Films
Authors: Beach David B. , Vallet Catherine E. , Paranthaman Mariappan , Specht Eliot D. , Morrell Jonathan S. , Xue Ziling B.
Published: April 2011

Cubic rare-earth aluminate perovskites of the general form REAIO3 have been identified as possible buffer layers for high current carrying cuprate superconductors deposited on roll-textured metals. This paper describes on-going research to develop solution routes which would avoid the use of slow and costly vacuum processing. Our research plan includes the development of an appropriate solution chemistry, studies of the crystallization behavior of powders under reducing and oxidizing conditions, deposition of polycrystalline films on silver substrates, deposition of epitaxial films on single-crystal oxide substrates, and deposition on roll textured nickel. The method is illustrated with the example of PrAlO3.
Automotive Applications of Materials Prepared by Ceramic Precursor and Sol-Gel Routes
Authors: Narula C. K. , Varshney A. , Everson M. P. , Schmitz P. , Allard L. F. , Gandopadhyay A. , Suren Lewkbandara T. , Winter C. H. , Czubarow P. , Seyferth D.
Published: April 2011

The promise of new applications continues to drive research on ceramic precursor and sol-gel routes to materials preparation. These routes offer flexibility in the fabrication of materials in forms such as films, coatings, fibers, foams, and powders, etc. Our interest in ceramic precursors stems from their potential in the low cost fabrication of films. Such films can be employed in a variety of new automotive applications. In this article, we summarize our efforts to prepare soluble ceramic precursors and their conversion to group IV metal nitrides. A comparison of some properties of electrically conducting titanium nitride films prepared by dipcoat-fire cycle and low pressure CVD is presented. We also describe the fabrication of indium tin oxide films by a sol-gel process. These films are candidates in the low cost fabrication of electrically heatable catalyst devices.
Properties of TiN and TiN Deposited by CVD on Graphite for Pyrochemical Applications
Authors: Maiya P. S. , Moon B. M.
Published: April 2011

High-density TiN (>098% of theoretical) has been prepared by hot pressing TiN powder with 2–4 wt.% Li2CO3at temperatures between 1150–1550°C and pressures of ≈40–50 MPa. The Li2CO3served as a fugitive sintering aid, enabling attainment of high density at low temperatures without adversely affecting the inherently good properties. Variation in processing variables and TiN powder characteristics resulted in material with various porosities. Measurement of mechanical properties such as flexural strength and fracture toughness showed that the high-density material has mechanical properties that are superior to those of several oxide ceramics. We have also quantified the effects of porosity on mechanical properties. In addition, adhesion and chemical stability tests were used to investigate graphite coated with TiN by chemical vapor deposition (CVD). Pin-pull tests were used to determine coating adhesion and failure stresses were analyzed by Weibull statistics. All pin-pull tests resulted in fracture of the graphite substrate, rather than separation at the TiN/graphite interface. The data showed a good fit to the two-parameter Weibull expression, with a failure strength of 16.4 MPa and Weibull modulus of 9.3. Both the high-density TiN and the TiN coating on the graphite were exposed to a corrosive molten salt CaCl2-7 wt.% CaO and a liquid metal alloy (Zn-10 wt.% Mg) at 800°C for 168 h to determine chemical interactions. No reaction was detected by scanning electron microscopy (SEM) or energy-dispersive X-ray (EDX) analysis. Thus, graphite coated with TiN by CVD combines the thermodynamic stability of TiN when exposed to reactive molten metals and salts, with the excellent machinability of graphite, and hence is promising for use in container vessels for pyrochemical processing of certain rare-earth and nuclear metals, where chemical inertness and good matching of thermal expansion coefficients are required.
Preparation of YBCO Superconducting Thin Film by Pulsed Thermal Decomposition of Ultrasonic-Misted Nitrate Solution
Authors: Kinugasa Junichi. , Hatta Akimitsu. , Ito Toshimichi.
Published: April 2011

YBa2Cu3O7-x superconducting thin films have been prepared by a new material preparation method, namely pulsed thermal decomposition of ultrasonic-misted nitrate solution. The prepared films have been studied by using powder X-ray diffraction method, scanning electron microscopy and Rutherford backscattering spectrometry. The results obtained indicate (1) that by local heating of the substrate with an infrared lamp, c-axis oriented YBa2Cu3O7-x films can be deposited without segregation of impurity phases, (2) that a high decomposition temperature is necessary to increase flatness of thin YBa2Cu3O7-x films although a sufficient margin temperature is required to obtain impurity-phase-free films, and (3) that the efficiency of the process increases if the adhesion is large between the deposited film and the substrate.
Low Temperature Remote Plasma Assisted Jet Vapor Deposition of Silicon Nitride
Authors: Veteran J. , Hobbs C. , Hegde R. , Tobin P. , Wang V. , Tseng H. , Kenig G. , Hartig M. , Tamagawa T. , Doran R. , Makowicz P. , Schmitt J. , Halpern B. , Zhang J. Z.
Published: April 2011

As MOSFET dimensions are aggressively scaled, minimizing the thermal budget becomes critical for limiting the diffusion of channel profiles. Unfortunately, high quality dielectrics with low deposition temperatures have not been readily available. Typical room temperature dielectrics are porous and electrically leaky. A promising technique for low temperature dielectric deposition is Jet Vapor Deposition (JVD). [1] Two coaxial quartz nozzles spray the process gases to the substrate surface at super-sonic speeds while a microwave cavity generates a plasma in the nozzle. [2] We have successfully deposited silicon nitride films using SiH4/He and N2/He gas mixtures. These are the first reported JVD results on 200 mm wafers.
Spectroscopic and Structural Studies of Some Precursors for the Deposition of PZT and Related Materials by MOCVD
Authors: Fleeting Kirsty A. , Jones Tony C. , Leedham Tim , Azad Malik M. , O'brien Paul , Otway David J.
Published: April 2011

MOCVD is a useful method for the deposition of thin films of lead zirconium titanate, PZT, because of its good step coverage and control of composition. Results are herein presented on a number of novel compounds which are potential MOCVD precursors. The compounds studied include Pb(tmhd)2, Zr(OBu')4 and Ti(OPr')4. Another commonly utilized precursor Zr(tmhd)4, is not ideal, in that it is a high melting point solid, and hence requires high substrate temperatures. We have sought to modify Zr precursors through chemical methods and have synthesized a number of novel, more volatile, and less intrinsically thermally stable MOCVD precursors. Full chemical characterization of the Zr precursors (NMR, IR, MS, CHN, TGA/DSC, Single Crystal X-ray diffraction) has been undertaken. We also present structural results on some related lead precursors.
Chemical Vapor Deposition of Ruthenium Dioxide Thin Films From Bis(2, 4-Dimethylpentadienyl)Ruthenium
Authors: Meda Lamartine , Breitkopf Richard C. , Haas Terry E. , Kirss Rein U.
Published: April 2011

Thin films of polycrystalline RuO2 were deposited from bis(2,4-dimethylpentadienyl) ruthenium, (η5-2, 4-Me2C5H5)2Ru (1) and ruthenocene (2) on quartz and silicon substrates between 200 and 500°C under Ar/O2 or O2. Films deposited from 1 were more adherent than those grown from 2 under the same conditions, however, none of the films were particularly adherent when O2 was used as a carrier gas. SEM revealed a columnar structure for both precursors with grain size ranging from 0.15 – 1 5μ. Crystallinity increased after annealing the films to 800°C. Resistivity decreased as the annealing temperature increased.
Precursors for Vapor Deposition of Blue Phosphors for Electroluminescent Flat Panel Displays
Authors: Rees William S. , Just Oliver , Luten Henry A. , Otway David J.
Published: April 2011

New strontium (host lattice constituent) and cerium (doping element) precursor sources have been developed and evaluated for deposition of blue color emitting SrS:Ce thin films by ALE (Atomic Layer Epitaxy). In the case of strontium, the monomeric derivative [Sr(hfac)2]*triglyme has been synthesized and structurally characterized, whereas, for cerium, the utilization of its homoleptic tris amide derivative Ce{N[Si(CH3)3]2}3 has led to a blue color emitting SrS:Ce. In a further effort, emission characteristics of SrS:Ce doped with the β-diketonate-related Ce(tmhd)4 derivative have been weighed against data obtained employing the cerium tris amide composition.
The Raft-Like Structure of Supported PtRu5
Authors: Yang J. C. , Bradley S. , Nashner M. N. , Nuzzo R. , Gibson J. M.
Published: April 2011

We have examined supported PtRus specimens by a variety of electron microscopy techniques, including high resolution, analytical and a novel mass-spectroscopic electron microscopy techniques. Analytical electron microscopy results showed that the relative atomic concentration of Pt to Ru for each PtRu5 cluster is 1 to 5. The average diameter of the clusters was a 15.6Å, and the average number of atoms was measured to be 24 atoms per cluster. The combination of these techniques demonstrate that the PtRu5 clusters are raft-like on the carbon black support.
Stability and Surface Acidity of Aluminum Oxide Grafted on Silica Gel Surface
Authors: Prado L. L. L. , Nascente P. A. P. , de Castro S. C. , Gushikem Y.
Published: April 2011

The synthesis of aluminum oxide grafted on silica gel surface was carried out by the reaction of a suitable aluminum precursor with the surface hydrolysis of the oxide support. The chemical and physical properties of the attached oxide, SiO2/ Al2O3, can be quite different than those found for bulk Al2O3. The advantage of this preparation method, compared to the conventional ones (impregnation, precipitation and calcination), is that the oxide is highly dispersed on the surface (monolayer or submonolayer). We characterized the surface oxides treated at the temperature range of 423 to 1573 K employing X-ray photoelectron spectroscopy (XPS), solid state nuclear magnetic resonance spectroscopy (NMR), and diffuse reflectance spectroscopy (DRS). XPS was used to identify the oxidation states and atomic ratios. Al27 NMR detected two species for samples heated up to 1023 K, and another one above this temperature. DRS, using pyridine as a molecular probe, showed that both Lewis and Brönsted acid sites are stable up to 1023 K. We concluded that the aluminum oxide is highly dispersed on the silica gel surface and it remains stable up to 1023 K.
Surface Characterization of W/Ni/Al2O3 Catalysts
Authors: Jordão M. H. , Assaf J. M. , Nascente P. A. P.
Published: April 2011

Catalysts containing tungsten and nickel oxides are important in hydrodesulfurization (HDS), hydrogénation (HY), and steam reforming of hydrocarbons. A series of W/Ni/Al2O3 catalysts was prepared by two different methods: (1) coprecipitation of nickel and aluminium hydroxicarbonate from their nitrates, followed by calcination and impregnation of tungsten; (2) precipitation of boehmite from aluminium nitrate, followed by impregnations of nickel, firstly, and tungsten. The nickel content was kept constant, while the amount of tungsten varied from 2.5 to 15.5 wt-%. The resulting oxides were characterized by inductively coupled plasma spectroscopy (ICP), atomic absorption spectroscopy (AAS), X-ray diffraction (XRD), temperature programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS). ICP and AAS were used to determine the W, Ni, and Al concentrations. XRD detected two phases: NiO and NiAl2O4 (no phase containing metallic tungsten was detected). Increasing the amount of W, the quantity of NiAl2O4 rose, the quantity of NiO decreased, and the particle size of NiO enlarged. The TPR profiles presented three peaks: one at about 1000 °C, associated to a very stable phase; for the samples prepared by coprecipitation, the other two peaks corresponded to “free NiO” and a nonstoichiometric aluminate. For the samples prepared by impregnation, those peaks corresponded to NiO and NiAl2O4. XPS identified Al2O3, NiAl2O4, and Al2(WO4)3 for both preparation methods. Increasing the amount of tungsten in the impregnated samples, NiWO4 was also observed.
Properties of Pure and Sulfided NiMoO4 and CoMoO4 Catalysts: Tpr, Xanes and Time-Resolved XRD Studdzs
Authors: Chaturvedi S. , Rodriguez J. A. , Hanson J. C. , Albornoz A. , Brito J. L.
Published: April 2011

X-ray absorption near-edge spectroscopy (XANES) was used to characterize the structural and electronic properties of a series of cobalt- and nickel-molybdate catalysts (AMoO4.nH20, α-AMoO4, β-AMoO4; A= Co or Ni). The results of XANES indicate that the Co and Ni atoms are in octahedral sites in all these compounds, while the coordination of Mo varies from octahedral in the a-phases to tetrahedral in the β-phases and hydrate. Time-resolved x-ray diffraction shows a direct transformation of the hydrates into the β-AMoO4 compounds (following a kinetics of first order) at temperatures between 200 and 350 °C. This is facilitated by the similarities that the AMoO4.nH20 and β-AMoO4 compounds have in their structural and electronic properties. The molybdates react with H 2 at temperatures between 400 and 600 °C, forming gaseous water and oxides in which the oxidation state of Co and Ni remains +2 while that of Mo is reduced to +5 or +4. After exposing α-NiMoO4 and P-NiMoO4 to H2S, both metals get sulfided and a NiMoSx phase is formed. For the β phase of NiMoO4 the sulfidation of Mo is more extensive than for the a phase, making the former a better precursor for catalysts of hydrodesulfurization reactions.
Electron Field Emission from Multilayered Tetrahedral Amorphous Carbon Films
Authors: Shi X. , Cheah L. K. , Silva S. R. P. , Tay B. K. , Yang H. S. , Sun Z.
Published: April 2011

The electron emission switching property of the multilayer structures, which constitute of nitrogen doped tetrahedral amorphous carbon (n+-ta-C) film and intrinsic ta-C layer fabricated by the filtered cathodic vacuum arc (FCVA) technique has been investigated. Low voltage DC bias (9V) was applied between the top and bottom layers in conjunction with the conventional electric field applied between the cathode and anode. It has been demonstrated that by varying the low DC bias polarity, the on-set electric field for the electron emission can be varied by ∼ ±6 V/μm compared to the unbiased situation. A possible mechanism for the multilayer field emission and the switching property is proposed.
Electron Emission Properties of Si Field Emitter Arrays Coated With Nanocrystalline Diamond From Fullerene Precursors
Authors: McCauley T. G. , Corrigan T. D. , Krauss A. R. , Auciello O. , Zhou D. , Gruen D. M. , Temple D. , Chang R.P.H. , English S. , Nemanich R. J.
Published: April 2011

In this paper, we report on a substantial lowering of the threshold field for electron field emission from Si field emitter arrays (FEA), which have been coated with a thin layer of nanocrystalline diamond by microwave plasma-assisted chemical vapor deposition (MPCVD) from fullerene (C60) and methane (CH4) precursors. The field emission characteristics were investigated and the emission sites imaged using photoelectron emission microscopy (PEEM). Electron emission from these Si FEAs coated with nanocrystalline diamond was observed at threshold fields as low as 3 V/μm, with effective work functions as low as 0.59 eV.
Synthesis of C-N films by hot carbon filament CVD
Authors: Watanabe Yoshihisa , Kasai Hiroshi , Kawasumi Emi , Amamoto Yoshiki , Nakamura Yoshikazu
Published: April 2011

Thin films composed of carbon and nitrogen were synthesized by hot-filament chemical vapor deposition method. Deposition method was developed by replacing a filament material from metals to graphite to ascertain two effects; (1) prevention of contamination from the filament material and (2) feasibility of synthesis of hydrogen free films without using hydrocarbon gas such as methane. Films were synthesized from pure nitrogen gas and hot graphite filament. Synthesized films were characterized by Auger electron spectroscopy, Raman spectroscopy, X ray diffraction, atomic force microscopy and nano indentations. It is found that the synthesized films are amorphous with the smooth and uniform surface and show the elastic behavior.
Doping Induced Internal Stress Reduction in Diamondlike Carbon Films Deposited by Pulsed Laser Ablation
Authors: Wei Q. , Narayan R. J. , Sharma A. K. , Sankar J. , Narayan J.
Published: April 2011

We have investigated the effect of dopants on the reduction of internal compressive stress in diamond-like carbon (DLC) films prepared by pulsed laser deposition on Si(100) substrates. A novel target configuration was used to incorporate dopants into DLC films by sequential pulsed laser ablation of two targets. These dopants include copper, titanium and silicon. The thickness of the DLC films deposited was measured in the range 400nm - 600nm using a profilometer. Raman spectroscopy was employed to analyze the chemistry of the films. The shifts of the G-peak position in the Raman spectrum, due to different concentrations of dopant, were used to estimate the internal stress changes. All of the films showed a Raman spectrum typical of DLC films containing a high fraction of sp3 species, with the G-peak centered at around 1510–1560cm−1. The shift of the G-peak due to the presence of dopants was observed for all the DLC films as compared to the undoped one. It was found that Ti has the strongest tendency to reduce the compressive stress of DLC films. This effect increases with increasing concentration of dopants. Silicon was also observed to have this effect, but the G-peak position did not appear to shift with different Si concentrations. Buckling occurred in the as-deposited, undoped DLC film because of the relief of the large compressive stress accumulated in the film, while all the doped DLC films showed good adhesion to the substrate. The results are discussed combining the atomic structure of DLC and the structure and properties of the dopants.
Equation of State of Warm Condensed Matter
Authors: Barbee T. W. , Young D. A. , Rogers F. J.
Published: April 2011

Recent advances in computational condensed matter theory have yielded accurate calculations of properties of materials. These calculations have, for the most part, focused on the low temperature (T=0) limit. An accurate determination of the equation of state (EOS) at finite temperature also requires knowledge of the behavior of the electron and ion thermal pressure as a function of T. Current approaches often interpolate between calculated T=0 results and approximations valid in the high T limit. Plasma physics-based approaches are accurate in the high temperature limit, but lose accuracy below T∼Tfermi. We seek to “connect up” these two regimes by using ab initio finite temperature methods (including linear-response[l] based phonon calculations) to derive an equation of state of condensed matter for T<Tfermi.

We will present theoretical results for the principal Hugoniot of shocked materials, including carbon and aluminum, up to pressures P>100 GPa and temperatures T> 104K, and compare our results with available experimental data.
Sintering of Compacts from Nanocrystalline Diamonds Without Sintering Agent
Authors: Witek A. , Palosz B. , Stel'Makh S. , Gierlotka S. , Pielaszek R. , Ekimov E. , Filonenko V. , Gavriliuk A. , Gryaznov V.
Published: April 2011

Compacts of polycrystalline diamond were made in toroid-type high-pressure camera under the pressure of 8 GPa using temperatures between 800 to 2150°C without the use of additive components. Nanocrystalline commercial DALAN, and microcrystalline ASM diamond powders were used. The compacts were characterized by helium pycnometry, Vickers hardness measurements, X-ray diffraction and SEM methods.

The starting and sintered nanocrystalline grain compacts were found to have strongly one-dimensionally disordered cubic modification. The nanocrystalline powder had a bimodal grain size distribution function as determined from X-ray diffraction data and ab initio intensity calculations performed with the use of Debye functions. It was found that neither the grain size nor one-dimensional disordering change under high-pressure high-temperature conditions. There is a general tendency in a decrease of density of compacts with increase in the sintering temperature what resulting partly from graphitization above 1000–1200°C. The main factor which determines the density of the diamond compacts is closed porosity. Typically, the nanocrystalline diamond compacts sintered from 30 sec. to 6 min. have densities around 90% of the theoretical value. Their Vickers microhardness is 24 GPa and less.
High Pressure - High Temperature Synthesis of Low-Compressibility Cubic C3N4
Authors: Nguyen Jeffrey H. , Caldwell Wendel A. , Benedetti Laura Robin , Kruger Michael B. , Jeanloz Raymond
Published: April 2011

We report the synthesis of a crystalline carbon-nitrogen compound having a zero-pressure bulk modulus of ∼ 249 GPa. Its crystal-structural and compressional properties are in good accord with those predicted theoretically by Teter and Hemley for a cubic C3N4 phase. Experimentally, this phase is synthesized at pressures and temperatures above 18 GPa and 2000 K. It decomposes upon pressure release below 14 GPa, and may offer a route to synthesizing other incompressible carbon nitride phases.
Infrared Optical Studies of Semiconductors at Large Hydrostatic Pressures
Authors: Haller E. E. , McCluskey M. D.
Published: April 2011

Among the various external disturbances used in the study of semiconductors, including electric and magnetic fields as well as uniaxial pressure, large hydrostatic pressures can be employed to induce dramatic changes in host lattice, dopant and defect properties. Diamond anvil cells with an appropriate pressure medium (e.g. liquid N2 or alcohol mixtures) allow the application of pressures up to hundreds of kbar. In this pressure range the global conduction band minimum of a semiconductor can become a local minimum. GaAs for example changes near 45 kbar from a direct (Γ-band) to an indirect (X-band) semiconductor. Donors in GaAs and InP transform from their shallow, hydrogenic state to the DX configuration at hydrostatic pressures near 23 and 82 kbar, respectively. This donor configuration change has been studied using local vibrational mode (LVM) spectroscopy in the far infrared region of the electromagnetic spectrum. Recently we have investigated several LVM's of H-containing complexes in GaAs as a function of hydrostatic pressure at liquid He temperatures. Depending on the specific complex we find the LVM frequencies to vary either linearly, sub- or superlinearly with hydrostatic pressure. In the case of O in Si the vibrational mode changes its character from that of a harmonic oscillator to a rotor as pressure is applied. The implications of the pressure dependences of LVM's are discussed.
Nanocrystalline Gallium Nitride from Gallium Azide Precursors
Authors: Manz A. H. , Frank A. C. , Sussek H. , Stowasser F. , Fischer R. A.
Published: April 2011

High quality nanoscale, phase-pure hexagonal gallium nitride (GaN) crystallites have been synthesized using the thermally induced explosion of the molecular precursor (Et3N)Ga(N3)3. The method allows the control of the particle size from 2 to 24 nm. X-ray diffraction and Rietveld simulations revealed a platelet-like shape of the larger particles in contrast to the rather spherical smaller crystallites. An increasing blue-shift of the high energy luminescence with decreasing crystal size was found (up to 4.4 eV at 5 K). A preliminary analysis of the surface chemistry of has been carried out based on silylation and deuteration experiments and IR spectroscopy, indicating hydrophilic, O-H and N-H terminated particles.
Microstructural Evaluation of Sintered Nanoscale Sic Powders Prepared by various Processing Routes
Authors: Schmidt W. R. , McCarthy G. , Palosz B. , Stel'makh S. , Aloshina M. , Gierlotka S. , Zinn P. , Keil D. G. , Calcote H. F.
Published: April 2011

Microstructural analysis was performed on several crystalline SiC samples previously prepared by three separate processing methods and subsequently sintered under high pressure and high temperature conditions using the cubic anvil cell MAX80 at Hasylab. Microcrystalline SiC was prepared using SHS conditions, while nanocrystalline SiC was prepared using both combustion synthesis methods and polymer precursors. High purity, highly disordered nanocrystalline SiC powders, with average particle diameters below 100 nm, were synthesized via combustion methods from precise mixtures of silane and acetylene. The properties of the silicon carbide powders prepared in this manner were dependent on the initial stoichiometry and pressure of the combustion mixture. Pyrolysis of polymer precursors to SiC was also used to fabricate ceramic powders containing uniformly-sized, highly disordered nanocrystalline SiC grains. The grain sizes ranged from approximately 3 nm to greater than 50 nm, and depended on the initial composition of the polymer, the pyrolysis conditions, as well as the annealing atmosphere, temperature and time. This paper describes the preparation methods for each of the SiC powders, the densification procedure, and preliminary results obtained primarily from transmission electron microscopy and X-ray diffraction analysis.
Detailed study on the characterization of silver nanocluster in poly(methyl methacrylate)
Authors: Yanagihara Naohisa , Uchida Kazutaka , Wakabayashi Muyuki , Hara Toru
Published: April 2011

Solid sol of silver in poly(methyl methacrylate), Ag/PMMA, was prepared by bulk polymerization of methyl methacrylate solution of silver (I) triflluoroacetate (AgTfa) and followed by postheating. The formation of the metallic Ag nanocluster was characterized by visible spectroscopy, and effects of the concentrations of AIBN and AgTfa and the heat-treatment duration on the formation of Ag cluster were investigated. Furthermore, based on the kinetic study of MMA in the presence of AgTfa, possible mechanism for the reduction and agglomeration of silver is proposed.
Particle adhesion: interaction forces and mechanical effects: extrapolation to the nanometer-size range
Authors: Rimai D. S. , Demejo L. P. , Gady B. , Quesnel D. J. , Bowen R. C. , Reifenberger R. , Busnaina A. A.
Published: April 2011

The physics of particle adhesion is a complex subject and depends on the interaction mechanisms and the mechanical properties of the contacting materials. These interactions, which tend to be caused by van der Waals and electrostatic interactions, generate stresses that, in turn, result in deformations of the contacting materials. Most of today's understanding of particle adhesion is based on theories that assume that the adhesion-induced strains are small. However, for small particles, the strains can be quite large, resulting in yielding and plastic deformations. In some instances, the entire particle can become engulfed by the substrate. This paper discusses the nature of the deformations, as are presently known, and extrapolates today's understanding of particle adhesion, which is based on the micrometer-size scale, to nanometer-size particles.
Synthesis and microstructure of conformal coatings on particulates
Authors: Rajan K. , Sajgalik P. , Singh R. K. , Kumar D. , Fitz-Gerald J.
Published: April 2011

In this paper we present an overview of two very different approaches to the synthesis of composite particulates which result in a “core-shell” type structure. It is shown that both these synthesis approaches result in very characteristic interface structures between the outer coating and the host particles. One synthesis strategy is to use laser ablation deposition on individual particles and the other is to “coat” particles ‘in-situ’ by taking advantage of solid state diffusional transformations. Examination of the interface between the outer shell and the core of the particle shows that textured or toptactical growth occurs and it is suggested that this unique crystallographic characteristic may be responsible for the properties offered by these engineered particulates. The applications of such engineered particulates is also discussed.
Optical properties of gold clusters precipitated on zirconia particles
Authors: Valmalette J.-C. , Dutta J. , Scholz S. M. , Hofmann H.
Published: April 2011

We have studied precipitation of noble metals with a view to extending these synthetic processes to other metals. In this paper we discuss the synthesis of gold clusters on the surface of oxide fine particles (in the range 60–100nm). The influence of pH of the solution, the concentration of metal and the reducing agent are discussed. The size distribution of the precipitated gold clusters, determined by transmission electron microscopy, are around 2–10 nm. The interface between the gold clusters and oxide has been investigated by HRTEM. Optical measurements of the zirconia supported gold clusters shows a significant shift in the plasmon resonance. A model based on effective medium theory is proposed taking into account the high refractive index of zirconia.
Swelling of SiO2 Quartz Induced by Energetic Heavy Ions
Authors: Trautmann C. , Costantini J. M. , Meftah A. , Schwartz K. , Stoquert J. P. , Toulemonde M.
Published: April 2011

A pronounced swelling effect occurs when irradiating SiO2 quartz with heavy ions (F, S, Cu, Kr, Xe, Ta, and Pb) in the electronic energy loss regime. Using a profilometer, the out-of-plane swelling was measured by scanning over the border line between an irradiated and a virgin area of the sample surface. The step height varied between 20 and 300 nm depending on the fluence, the electronic energy loss and the total range of the ions. From complementary Rutherford backscattering experiments under channelling condition (RBS-C), the damage fraction and corresponding track radii were extracted. Normalising the step height per incoming ion and by the projected range, a critical energy loss of 1.8 ± 0.5 keV/nm was found which is in good agreement with the threshold observed by RBS-C. Swelling can be explained by the amorphisation induced along the ion trajectories. The experimental results in quartz are compared to swelling data obtained under similar irradiation conditions in LiNbO3
Correlation of Intermediate Ion Energy Induced Extended Defect Continuity to Enhanced Pinning Potential in Tl-2212 Films
Authors: Provencio P. Newcomer , Venturini E. L. , Doyle B. L. , Brice D. K. , Schöne H.
Published: April 2011

Lattice defects are introduced into the structure to suppress the motion of magnetic vortices and enhance the critical current density in high temperature superconductors. Point defects are not very effective pinning sites for the cuprate superconductors; however, extended defects, such as linear tracks, have been shown to be strong pinning sites. We study the superconducting cuprate TI-2212 (the numbers designate Tl-Ba-Ca-Cu stoichiometry). Large enhancements of vortex pinning potential were observed in TI-2212 after high-intermediate energy heavy-ion irradiations where non-continuous extended defects were induced at dE/dx of 9 to 15.2 keV/nm (60 MeV Au, 60 MeV Cu, and 30 MeV Au) and continuous linear defects were induced at 19.5keV/nm (88MeV Au). Our research addresses the question of pinning in highly anisotropic materials like Tl-2212 where the vortices are “pancakes” rather than “rods” and suitable defect structures may be discontinuous extended damage domains. The defect microstructure and the effectiveness of the pinning potential in TI-2212 after irradiation by intermediate energy Au at lower dE/dx of 5–15 keV/nm, where recoils are more significant, is studied using high resolution transmission electron microscopy digital imaging and a SQUID magnetometer. The nature of the ion irradiation damage at these intermediate dE/dx will be correlated to the average vortex pinning potential and the TRIMRC calculations for recoils.
Transmission Electron Microscopy Study of Cascade Collapse in Copper During in- Situ Ion- Irradiation at Elevated Temperatures
Authors: Daulton T. L. , Kirk M. A. , Rehn L. E.
Published: April 2011

The basic mechanisms driving the collapse of point defects produced in collision cascades are investigated by transmission electron microscope (TEM) characterization of defect microstructures produced in fcc-Cu irradiated with low-fluences of heavy (100 keV Kr) ions at elevated temperature (23–600°C). Areal defect yields are determined from direct TEM observation of the total defect production integrated over the duration of the in-situ ion-irradiation. They are unequivocally demonstrated to decrease with increasing lattice temperature. This decrease in defect yield indicates a proportional decrease in the probability of collapse of cascade regions into defects of size where visible contrast is produced in a TEM.