bluuebunny/crossref_metadata_2025 huggingface dataset:
Improved Reliability With a New Plasma Nh3 Process for 0.35μιη P+ Poly-Gate Nitrided Oxide P-Mosfet's
Authors: Bravaix A. , Vuillaume D. , Goguenheim D. , Lasserre V. , Straboni A. , Haond M.
Published: April 2011

The electrical properties and the hot-carrier reliability of P+ poly-gate P-MOSFET's are investigated for advanced 0.35 μπι LDD CMOS technologies. It is shown that surface-channel p-devices with an optimized plasma NH3 nitrided gate-oxide have good barrier properties and electrical performances which lead to a higher hot-carrier immunity in 8nm thick nitrided gate-oxides than in pure oxides using DC and AC experiments. The AC stressing shows that reducing the gate-oxide thickness leads to a larger influence of electron detrapping inducing a stronger influence of donor type interface traps than the usual build-up of negative charges. These distinct degradation mechanisms are less significant in nitrided oxide p-MOSFET's due to the lower lateral electric field leading to a lower amount of trapped charges which are quickly suppressed during subsequent detrapping phases leaving the main influence of the interface traps.
A Plasma Reactor for Solid Waste Treatment on Pecvd Production Systems
Authors: Raoux S. , Fodor M. A. , Taylor W. N. , Cheung D. , Fairbairn K.
Published: April 2011

The growth of particulates within a PECVD (Plasma Enhanced Chemical Vapor Deposition) reactor has been extensively studied in recent years. As one of the early concerns was wafer particle contamination, the attention of industry also shifted to environmental issues. In the particular case of Si3N4 film deposition, the amount of dust particles created within the plasma is great and a significant amount of dust is dragged out of the RF interelectrode region along with the exhausted process gases. On a production system, this results in solid residues accumulation in the exhaust line (or foreline), frequent maintenance and poor vacuum pump lifetime. We developed a DPA (Downstream Plasma Apparatus) placed downstream of the deposition chamber to solve the issue of solid waste treatment for thin films applications such as SiO2, Si3N4, SiC, SiOxNy,…, α‐Si,…). The DPA is designed to capture all the residue during deposition, using both a passive and an active mode. It consists of two labyrinth‐shaped electrodes that can trap particles by gravitation (passive) and electrostatically (active) by application of a DC electric field. The second function of the device is to vaporize the previously trapped residues using a periodic plasma assisted clean. The vaporization process is performed by re‐ionizing the effluent PFCs gas (PerFluoro‐Coumpounds) from the processing chamber. All byproducts of the reaction are gaseous and water soluble. This results in the elimination of solid waste as well as improving vacuum pump lifetime. There is also better clean gas utilization and the emission of PFCs in the atmosphere is reduced. In this paper, we review the particulate formation, their size and composition. We describe the DPA reactor designed to trap charged particulates with closed to 100% efficiency. We examine the plasma‐assisted cleaning process and the implications of the device in terms of solid waste treatment and environmental impact.
Point-of-Use Silicon Sources for Cvd
Authors: Saulys D.A. , Safvi S.A. , Pauly N. , Dopke J.A. , Preston B.R. , Gaines D.F. , Kuech T.F.
Published: April 2011

The reliance of the semiconductor industry on pyrophoric silane gas as the primary source of silicon entails high risk and attendant cost. In order to enhance safety and improve control we are engaged in a systematic study of the decomposition characteristics of alkyl silanes with a focus on chemical species and conditions that exhibit silane type behavior or that actually produce silane. We have prepared a series of air stable innocuous liquid alkyl silanes, RSiH3, that generate silane and stable organic (R-H) byproducts upon flow tube pyrolysis. T-buty1, t-hexy1, and t-decyl silane as well as the corresponding R-H products exhibit a range of physical properties : room temperature vapor pressures, for example, range from several Torr to over an atmosphere. Relevant physical properties as well as kinetics and mechanisms of the hydride transfer process will be described and correlated with structural characteristics of the RSiH3 precursors.
PFC Emission Control Options for Plasma Processing Tools: A Current Assessment
Authors: Mocella M. T.
Published: April 2011

Perfluorocompounds (PFCs) are critical processing gases for a number of plasma-based IC processing steps, especially dry etching and in situ CVD chamber cleaning. The long atmospheric lifetimes and large infrared absorption cross sections for such gases (which include CF4, C2F6, C3F8, NF3, SF6, and CHF3) have raised concerns about the contributions of PFC emissions to possible global warming. Global regulatory policies on greenhouse gases are expected to include the PFCs, and the specific attention given to these gases in negotiations between the U.S. government and the semiconductor industry may expand internationally as well.

Several options exist for PFC emission control, including process optimization, chemical substitution, capture/recovery/recycle, and destructive abatement (including combustion, reactive adsorption, and plasma decomposition). An assessment of each option will be made in terms of both technical effectiveness (i.e., PFC reduction achievable) as well as implementation issues (e.g., commercialization timing, cost of ownership). PFC users can expect to have several commercial options to choose from to meet future PFC emission control requirements.
Environmental Issues of Perfluorocompounds in the Semiconductor Industry
Authors: Williams Jeffrey D.
Published: April 2011

A critical class of semiconductor manufacturing compounds is the family of perfluorocompounds, or PFCs. Originally thought to be environmentally benign compounds, they are likely long-lived atmospheric compounds with high global warming potentials. This paper reviews the options available to industry to reduce PFC emissions. Process optimization, chemical substitution, abatement, and recovery will be discussed as they relate to specific processes. Each will be reviewed with respect to the particular gas affected and the potential impact realized. Collateral environmental impacts will also be discussed. Finally, the voluntary EPA program, the PFC Emission Reduction Partnership for the Semiconductor Industry, will be presented.
High Power InAsSb/InAsSbP Laser Diodes Emitting at 3 ∼ 5 μm Range
Authors: Razeghi M. , Diaz J. , Yi H. J. , Wu D. , Lane B. , Rybaltowski A. , Xiao Y. , Jeon H.
Published: April 2011

We report metalorganic chemical vapor deposition-grown double heterostructure and multiple quantum well InAsSb/InAsSbP laser diodes emitting at 3 to 4 μm and light emitting diodes up to 5 μm. Maximum output power up to 1 W (from two facets) with differential efficiency above 70 % up to 150 K was obtained from a MQW laser with stripe width of 100 μm and cavity length of 700 μm for emitting wavelength of 3.6 μm at 90 K. Maximum operating temperature up to 220 K with threshold current density of 40 A/cm2 at 78 K were achieved from the double-heterostructure lasers emitting at 3.2 μm. The far-field beam divergence as narrow as 24° was achieved with the use of higher energy gap barrier layers, i.e., lower effective refractive index, in MQW active region. We also discuss the effect of composition-fluctuation in the InAsSb active region on the gain and threshold current of the lasers.
Single Mode Operation of Impurity-Induced Disordering Large Area Vertical Cavity Surface Emitting Lasers
Authors: Lo C. W. , Yu S. F.
Published: April 2011

Vertical-cavity surface-emitting lasers (VCSELs) with suitable interdiffusion quantum wells profile by the use of selective impurity-induced disordering is proposed for high power single mode operation in large area devices. It is shown that the transverse optical confinement in the quantum well active region formed by the diffusion profile counteracts the influence of carrier spatial hole burning for VCSELs biased at high injection current Results indicate that a single mode operation can be maintained in VCSELs with the diameter of core region equal to 50μm.
1.5 μm In0.53Al0.14Ga0.33As/In0.52Al0.48As Distributed Bragg Reflector and Single Cavity Active Layer Grown with In-Situ Double Beam Laser Reflectometry
Authors: Baek Jong-Hyeob , Lee Bun , Lee Jin Hong , Han Won Seok , Lee El-Hang
Published: April 2011

We report the highly reflecting (>99.9%) In0.53Al0.14Ga0.33As/In0.52Al0.48As 30.5 pairs distributed Bragg reflector (DBR) and the In0.53Ga0.47As/ In0.52Al0.48As active cavity layer grown at high temperature by low pressure metal organic chemical vapor deposition with in-situ double beam laser reflectometry. One of the laser wavelengths selected for in-situ measurement was same as the DBR wavelength. The growth temperature was 750 °C. Good surface morphology of the multi-layer stacks was achieved by the temperature ramping of the InP buffer layer at the beginning of a multi-layer stacks. The width of stop band edge of the DBR reflectivity spectrum was found to be 1000Å.
Intersubband Transitions, Infrared Detectors, and Optical Nonlinearities in SiGe Multiquantum Wells
Authors: Helm M. , Kruck P. , Fromherz T. , Seto M. , Bauer G. , Nützel J. F. , Abstreiter G.
Published: April 2011

A survey is given about the potential use of Si/SiGe heterostructures for applications in the mid-infrared spectral range. We discuss theoretical foundations and experiments of intersubband absorption in p-type Si/SiGe quantum wells and show that due to the complex valence-band structure, normal-incidence absorption can be observed. On the basis of these quantum wells, mid-infrared detectors were fabricated and characterized in terms of responsivity, dark current and detectivity. In asymmetric, compositionally stepped quantum wells second harmonic generation of CO2 laser radiation has been demonstrated.
P-Type Doping with Arsenic in MBE-HgCdTe Using Planar Doping Approach
Authors: Aqariden F. , Wijew Arnasuriya P. S. , Rujirawat S. , Sivananthan S.
Published: April 2011

The results of arsenic incorporation in HgCdTe (MCT) layers grown by molecular beam epitaxy (MBE) are reported. The incorporation into MBE-MCT was carried out by a technique called planar doping. Arsenic was successfully incorporated during the MBE growth or after a low temperature anneal as acceptors. These results are very promising for in-situ fabrication of advanced optoelectronic devices using HgCdTe material.
Self-Trapping of Optical Beams and Light-Induced Waveguiding in Photorefractive InP at Telecommunication Wavelengths
Authors: Chauvet M. E. , Hawkins S. A. , Salamo G. J. , Segev M. , Bliss D. F. , Bryant G.
Published: April 2011

We demonstrate self-trapping of a two-dimensional beam at 1.3 microns wavelength in resonantly-enhanced InP. The self-trapped beam also induces a two-dimensional optical waveguide in bulk InP, which guides a second beam at 1.55 micron wavelength.
Diffused Quantum Well Structures: Advances in Materials and Device Realizations
Authors: Herbert Li E.
Published: April 2011

The Diffused Quantum Well (DFQW) structures created by both impurity induced and impurity free or vacancy promoted processes have recently been advanced to a higher level. The interdiffusion mechanism is no longer confined to two constituent atoms, but consists of two or multiple phase interdiffusion as well as multiple species, such as three cations interdiffusion and two pairs of cation-anion interdiffusion. Results show that the outcome of these interdiffusions is quite different. For instance, both compressive or tensile strain materials and both blue or red shifts in the bandgap can be achieved dependent on the type of interdiffusion. The advantage of being able to tune the material properties allows the realizations of higher performance lasers and modulators. Two lasing wavelengths (60 nm apart) are produced at λ ∼ 1.55μm, on the same substrate, with threshold currents of 290mA, and an extremely large relative reflectance change (over 10000) is predicted with power consumption reduced by 67%. A six fold enhancement of the third order susceptibility over that of the bulk materials can be achieved by using the inter-subband transitions in the DFQW at λ ∼ μm. Broadband (1000nm) detectors have also been realized due to the wide DFQW spectral bandwidth. Several state-of-the-art results of the DFQW will be summarized with an emphasis on the future developments and directions of the DFQW.
Interdiffusion in Quantum Wells: Mixing Mechanisms and Energy Levels
Authors: Gass Richard G , Jackson Howard E , Hughes P J , Weiss Bernard L
Published: April 2011

Compositional interdiffusion in Al0.3Ga0.7As/GaAs superlattice structures with equal 3.5 nm barrier and well widths induced by Si focused ion beam implantation and subsequent rapid thermal annealing has been modeled. A strong depth dependence of the mixing process is observed at a Si++ energy of 100 keV and at a dose of 1×1014 cm−2; this depth dependence is modeled by considering the second derivative of the vacancy profile. That is the maximum in the vacancy injection generated by the transient vacancy concentration gradient. We have included the dynamics of the spatial vacancy profile in the model and find good agreement with experimental results.

Interdiffusion across the well/barrier interfaces modifies the subband structure in AlGaAs/GaAs single quantum well (QW) structures. We have investigated the interrelated changes in both confinement energy of the subband states and the composition dependence of the bandgap energy in the QW, both of which are a strong function of the initial well width. Higher order transitions are found to be more sensitive than the ground state transitions to interdiffusion especially during the early stages of interdiffusion. These calculations model the experimental measurements (photoluminescence and photoreflectance) which are used to characterize interdiffused QW structures.
Polarization Insensitivity in Interdiffused, Strained InGaAs/InP Quantum Wells
Authors: Micallef Joseph , Borg James L. , Shiu Wai-Chee
Published: April 2011

Theoretical results are presented showing how quantum well disordering affects the TE and TM absorption coefficient spectra of In0.53Ga0.47As/InP single quantum wells. An error function distribution is used to model the constituent atom composition after interdiffusion. Different interdiffusion rates on the group V and group III sublattices are considered resulting in a strained structure. With a suitable interdiffusion process the heavy hole and light hole ground state, excitonic transition energies merge and the absorption coefficient spectra near the fundamental absorption edge become polarization insensitive. The results also show that this polarization insensitivity can persist with the application of an electric field, which is of considerable interest in waveguide modulators.
The Confinement Profile of As-Grown Movpe AlGaAs/GaAs Quantum Well Structures
Authors: Choy W. C. H. , Hughes P. J. , Weiss B. L.
Published: April 2011

Interband transitions of a series of as-grown AlGaAs/GaAs quantum well structures grown by MOVPE have been studied using photoreflectance to determine their well shape. The transition energies calculated using three different quantum well profiles are compared to those obtained using photoreflectance. The results show that the shape of these structures is best represented by an exponential potential profile.
Preparation of AlAsSb and Mid-Infrared (3–5μm) Lasers By Metal-Organic Chemical Vapor Deposition
Authors: Allerman A. A. , Biefeld R. M. , Kurtz S. R.
Published: April 2011

Mid-infrared (3–5 μm) infrared lasers and LEDs are being developed for use in chemical sensor systems. As-rich, InAsSb heterostructures display unique electronic properties that are beneficial to the performance of these midwave infrared emitters. We have grown AlAs1−xSbx epitaxial layers by metal-organic chemical vapor deposition using trimethylamine (TMAA) or ethyldimethylamine alane (EDMAA), triethylantimony (TESb) and arsine. We examined the growth of AlAsl−xSbx using temperatures of 500 to 600 °C, pressures of 70 to 630 torr, V/III ratios of 1–27, and growth rates of 0.3 to 2.7 μm/hour in a horizontal quartz reactor. The semi-metal properties of a p-GaAsSb/n-InAs heterojunction are utilized as a source for injection of electrons into the active region of lasers. A regrowth technique has been used to fabricate gain-guided lasers using AlAs1−xSbx for optical confinement with either a strained InAsSb/InAs multi-quantum well (MQW) or an InAsSb/InAsP strained layer superlattice (SLS) as the active region. Under pulsed injection, the InAsSb/InAs MQW laser operated up to 210K with an emission wavelength of 3.8–3.9 μm. Under pulsed optical pumping, the InAsSb/InAsP SLS operated to 240K with an emission wavelength of 3.5–3.7 μm. LED emission has been observed with both active regions in both p-n junction and semi-metal injection structures.
The Profile Design of Strained Sige-Channel P-Type Modulation Doped Fet
Authors: Hsu Klaus Y.J. , Huang S. M.
Published: April 2011

To improve the performance of p-type SiGe-channel FEPs is important for Si-based high-speed/high-frequency applications. This work discusses the design of germamium profiles in the strained Si1−xGex channel region of p-type SiGe modulation doped FET's and studies its effect on device performance. Two-dimensional device simulator is used to simulate the large-signal device performance for various Ge distributions including triangular, trapezoidal, and flat profiles. In particular, the thickness of the strained SiGe channel layer is 15 nm and a 5 ran thick Si cap layer is on top of the channel. It is found that with the same integrated Ge content in the strained channel, graded Ge profiles lead to higher transconductances and larger threshold voltage windows than those of flat profiles, due to deeper potential wells and better carrier confinement ability. For triangularly graded profiles, the peak position must be located in the upper half portion of the channel layer to result in superior performance. By adding more Ge to extend the peak region, triangular profiles become trapezoidal ones. However, more Ge content does not necessarily produce better performance. If the well depth of trapezoidal profile is the same as that of triangular profile and if the trapezoid plateau begins at the same position as that of triangle peak, the device performance is almost the same for both profiles.
Examples of Hydrothermal Titration and Real Time X-Ray Diffraction in the Synthesis of Open Frameworks
Authors: Parise J. B. , Tan K. , Norby P. , Ko Y. , Cahill C.
Published: April 2011

Hydrothermal titration (HTT) techniques represent a new synthetic strategy for the production of open frameworks. As an example, initial digestion of amorphous GeS2 in the presence of tetraethyl ammonium hydroxide (TEAOH) at 100°C is followed by injection of Ag+ into this mixture to condense the [Ge4S10]4− clusters and form a framework consisting of 8-ring channels bounded by alternating GeS-clusters and Ag+. The rational use of this apparatus depends upon determining the timing of injection. Insight into the changes occurring during reactant digestion is provided by real time synchrotron X-ray powder diffraction. Changes in the the system dimethylamine-Sb-S have been followed in real time at different temperatures. The transformation from mixtures of DMA, Sb and S to the known open phase DMA-SbS-SB8 was followed by observing monochromatic X-ray scattering detected on an imaging plates over a 8 hr period with one continuous exposure.
The System Li3SbO4 - CuO
Authors: Castellanos R. M. A. , Trujillo T. S. , Skakle J. M. S. , West A. R.
Published: April 2011

Phase formation in the system Li3SbO4-CuO has been studied by solid state chemistry reaction, at temperatures between 650° and 1150°C. Two new complex oxides were found and characterized by X-ray powder diffraction (XRD), Li3CuSbO5 (O) and Li3Cu2SbO6 (S). The latter exhibits a new partially ordered rock salt structure and shows a low level of electronic conductivity [1]. The crystal structure of Li3SbO4was determined [2].
Long-Range Order Effects in Ferroelectric Pb(Zr1/2Ti1/2)O3
Authors: Sághi-Szabó G. , Cohen Ronald E.
Published: April 2011

The local orbital extension of the Linearized Augmented Planewave (LAPW+LO) method within the local density and general gradient approximations was used to optimize internal coordinates and calculate total energies of Pb(Zri1/2Ti1/2)O3 (PZT) superlattices with B site cations ordered along the [001] and [111] directions. Ferroelectric structures and bond-length distributions similar to those obtained from experimental data were found for all three investigated chemically ordered phases. The Ti atom sits in an off-center position of a slightly distorted TiO6 octahedron, the structure of which is mostly independent of the chemical ordering pattern. Coupling between the Ti and Zr containing octahedra results in highly distorted ZrO6 units. This relatively high energy part of the structure could decrease the stability of these perovskite compounds against zone-boundary rotations of the BO6 octahedra. Polar, zone-center only distortions result in lower energy [111] ordered superstructures when compared to the [001] ordered structure. The lowest energy chemically ordered PZT is the one with B-site cations ordered along the [111] direction and has 14mm symmetry. Our total energy results and a simple statistical model predict a wide miscibility gap PZT at the morphotropic composition is therefore likely a multiphase or metastable material which may be responsible for its sensitivity to synthesis and annealing conditions.
First Principles Computer Simulation of the Defect Chemistry of Rutile TiO2
Authors: Dawson I. , Bristowe P. D. , White J. A. , Payne M. C.
Published: April 2011

There exists a long-standing controversy concerning the nature of the dominant point defect mechanism in rutile TiO2. Previous classical shell model calculations by Catlow el al [1] find a strong preference for Schottky as opposed to Frenkel-type defects, lending support for oxygen vacancy rather than titanium interstitial compensation in reduced rutile. However, reviews of experimental studies [2], show that many conflicting conclusions have been reached. Ab initio total-energy calculations have been performed on a parallel computer to help resolve this controversy. First results indicate a Schottky formation energy (of the bound Schottky trio) consistent with the Mott-Littleton values of Catlow et al [1]. A first attempt is made at calculating the heat of reduction through determination of the formation energy of a neutral oxygen atom vacancy. As a. result some interesting insight is gained into the redox chemistry of reduced rutile.
Hydrogen Vibration in Cubic Dihydrides MH2 (M=Ti, Zr), and Localization in Cubic Laves Phases ZrM2H1/2 (M=V, Cr, Fe, Co)
Authors: Elsässer C. , Schweizer S. , Fähnle M.
Published: April 2011

A study of cubic dihydrides TiH2 and ZrH2 and of H in cubic Laves-phase compounds by means of ab-initio total-energy calculations in the local density-functional approximation is presented. First, for optic vibrational modes in the two dihydrides the calculated local potentials and excitation energies are compared to experimental results obtained by inelastic neutron scattering. Second, the relative stabilities of H on three types of interstitial sites in the cubic Laves-phase compounds, denoted by b, e and g, are investigated. Theoretically, a preference of g sites is found for M=V, Cr, and of e sites for M=Fe, Co. These results are discussed with respect to experimental observations and to empirical criteria for H accomodation in transition-metal compounds.
The Effects of Domain Structure on the Electro-Optic Response of Potassium Niobate Thin Films
Authors: Nystrom M. J. , Wessels B. W.
Published: April 2011

Epitaxial potassium niobate films have been deposited by metalorganic chemical vapor deposition (MOCVD). X-ray diffraction of the films deposited on (100) spinel substrates shows (110) and (001) reflections, indicating a multidomain structure. The electro-optic properties of the thin films were measured using a transmission technique. Effective electro-optic coefficients as large as 470 pm/V were observed. The observed electro-optic response was dominated by domain reorientation effects.
About Chemical Bonds in Misfit Layer Chalcogenides
Authors: Rouxel J. , Meerschaut A.
Published: April 2011

On the basis of crystal structures and electronic properties, a critical discussion of the nature of chemical bonds in misfit layered chalcogenides is given. It concerns also the various mechanisms of non-stoichiometry that are present in these incommensurate structures. Misfit chalcogenides with a LnY slab opposed to TY2ones (T = Ti, V, Cr, Nb, Ta) appear as infinite two-dimensional intercalation compounds with an electron donation from LnY to TY2. In case of PbY or SnY slabs a more complex mechanism involving coupled substitutions in both slabs seems to prevail.
Phase Equilibria and Dielectric Properties of Rare Earth Containing BaTiO3 Ceramics
Authors: Kolar D.
Published: April 2011

Addition of rare earth oxides affects several properties of barium titanate ceramics such as dielectric constant, Curie temperature and electrical conductivity. Electrical properties depend on the composition, firing conditions and mode of incorporation of rare earth ions into perovskite or perovskite-like lattice.

Incorporation of rare earth ions into the BaTiO3 lattice was studied by quantitative wavelength dispersive spectroscopy in combination with scanning electron microscopy and X-ray powder diffraction. Broad solubility regions between rare earth titanates and barium titanate were detected, influencing the properties.

In present review, phase equilibria and properties of rare earth (La,Nd,Ce) containing BaTiO3 ceramics are compared with particular emphasis on preparation conditions.
Formation and Characterization of “1:1” Ordered Phases in Am4+O3- A(B2+1/3Ta2/3)O3(A= Ba, Sr; B2+= Mg, Zn; M4+= Ti, Sn, Zr, Ce) Perovskites
Authors: Chai L. , Akbas M. A. , Davies P. K.
Published: April 2011

Previous research has demonstrated that the formation of nano-sized “1:1” cation ordered domains in Zr4+substituted Ba(Zn1/3Ta2/3)O3may be responsible for the anomalies in the dielectric loss properties of these perovskite ceramics. To explore the structure and crystal chemistry of these phases, the effect of a series of M4+substitutions (Zr4+, Ce4+, Sn4+, and Ti4+) on the B-site cation ordering in Ba(Zn1/3Ta2/3)O3, Ba(Mg1/3Ta2/3)O3, and Sr(Mg1/3Ta2/3)O3has been examined. In all cases the substitution of low levels (∼ 5 mole %) of “over-sized” tetravalent cations (e.g. Zr4+, Ce4+) promotes a transformation to a 1:1 ordered phase, while the introduction of “under-sized” cations (e.g. Ti4+) stabilizes a disordered perovskite. Using Rietveld methods the structures of the 1:1 ordered A(βI1/2βII1/2)O3phases were found to conform to a “random layer” model in which the βIIpositions are occupied by Ta, and the βIsites by a random distribution of the Mg(Zn), M4+and residual Ta cations.
Investigation of Polarization Mechanism of Relaxor Ferroelectrics
Authors: Cheng Z. -Y. , Katiyar R. S. , Xi Yao
Published: April 2011

Addition to thermally activated flips of polar regions in relaxor ferroelectrics, a new polarization mechanism, which originates from the vibrations (breathing) of surface of polar regions, is introduced to explain the dielectric behavior of relaxor ferroelectrics. This new mechanism plays an important role in the dielectric behavior of such materials at low temperature. Based on the above assumption and general dielectric theory, a formula is given to characterize the temperature dependence of the dielectric constant. The correctness of the formula is verified by using it to fit the experimental results of the two typical relaxors. The fitted results show that the method is of high precision and that the temperature of the dielectric constant maximum is decided by the two polarization behavior. It also indicates that the new polarization is a resonance polarization.
Non-Stoichiometry and Structure of SrCe1-xYbxO3 Perovskite-Type Oxides
Authors: Kosacki Igor , Shumsky Mark , Anderson Harlan U.
Published: April 2011

The structural and electrical properties of SrCe1-xYbxO3 ceramics have been studied as a function of temperature and Yb-concentration using x-ray diffraction and impedance techniques. The influence of Yb-dopants on electrical transport and structural disorder has been studied. A correlation between the structural properties, electrical conductivity is observed and discussed. These measurements allow us to determine the mechanism of charge carrier compensation and also the concentration and mobility of the electrical species.
Electrical Conductivity and Nonstoichiometry in Pr0.545Ce0.455O2-x
Authors: Porat O. , Tuller H. L. , Shelef M. , Logothetis E. M.
Published: April 2011

The oxygen nonstoichiometry of Pr0.545Ce0.455O2-x was studied by solid state coulometric titration and was found to be extensive (0 ≤ y ≤ 0.28) at temperatures of 400–600 °C. The Po2 - x curves showed evidence of the existence of a number of single and two phase regions. Electrical conductivity measurements, performed under similar conditions, exhibited a p-n transition for temperature of 500 °C and below. The activated p-type conductivity was modeled in terms of the small polaron hopping mechanism. The p-n transition was correlated with the onset of phase separation.
Grain boundary conductivity and microstructure study of 4% Y2O3 doped CeO2 thin films
Authors: Tian Chunyan , Chan Siu-Wai
Published: April 2011

The thin films of 4% Y2O3 doped CeO2 have been deposited on different substrates of Pd film/(001) LaAlO3, Pd film/r-cut sapphire, and Pd film/Quartz using an e-beam deposition technique. The microstructures and electrical properties of the films were investigated by means of x-ray diffraction, transmission electron microscopy, and ac impedance spectroscopy. Both textured and polycrystalline films were produced on different substrates. A brick layer model was adopted to correlate the micro structure and electrical property of the films. Only the grain boundary arc was observed in the film complex impedance plots. The conductivities of the films were similar to the conductivity of 6% Y2O3 doped CeO2 bulk grain boundary because of lower preexponential factor, although the activation energies were smaller than that of bulk grain boundary. The resistive gram boundaries were found to dominate the conductivities of the films.
Synthesis, Characterization, and Electrochemical Performances of Substituted Layered Transition Metal Oxides. LiM1-yM'yO2. (M=Ni and Co. M'= B and AI)
Authors: Nazri G. A. , Rougier A. , Kia K. F.
Published: April 2011

The synthesis, characterization and electrochemical performances of lithiated nickelate and cobaltate doped with Al and B are reported. The synthesis involves solid state reaction between lithium hydroxide, nickel or cobalt oxides and several sources of aluminum and boron. Careful selection of precursors and heat treatment conditions are required to prepare single phase impurity free samples. X-ray diffraction and Rietveld refinement analysis indicate that the layered structure is preserved upon considerable substitution of aluminum and boron. X-ray diffraction line intensities and positions remained in good agreement with the space group. The IR spectra of the samples indicate formation of compressed CoO6 and NiO6, and elongated LiO6 octahedra. The IR vibrational mode of the LiO6 remains in the 200–300 cm-1 and the vibrational modes of the MO6 expand over 400–650 cm-1. Results of long charge-discharge cycling of the samples as cathode materials in lithium cells showed long cycle life. The capacity of the electrodes upon substitution were reduced almost linearly as the concentration of substitution was increased. The solubility limit for the formation of solid solutions upon substitution of Al and B in LiNiO2 and LiCoO2 was found to be around 25%. Specific capacities of the samples were between 120 to 160 mAh/g depending on the amount of substitution.
Ordering in Lithium and Sodium Inserted W18O49
Authors: Martinez De La Cruz A. , Torres-Martinez Leticia M. , Garcia-Alvarado F. , Moran E. , Alario-Franco M. A.
Published: April 2011

The insertion of alkali metals in W18O49 is governed by size of the cations. In this way, lithium insertion ( rVI = 0.76 Å ) seems to be optimal and a maximum of 23.5 lithium per formula can be reached before the irreversible reduction of W18O49. On the other hand, when sodium is inserted ( rVI = 1.02 Å ) an order of magnitude decrease in the amount inserted is observed and a maximum of only 1.8 sodium per formula can be intercalated. On the basis of the different phases that we have previously detected by electrochemical methods in the Li / W18O49 and Na / W18O49 systems, we have started a structural characterization by electron diffraction techniques. These studies have revealed some lithium and sodium ordering states for certain compositions; this can be explained taking into account the different types of tunnels present in W18O49.
Kinetics of Electrochromic Effect in Amorphous Tungsten Trioxide Films
Authors: Konovalov I. A. , Nechitajlo V. B. , Shushakova E.
Published: April 2011

Reversible coloration occurs in tungsten trioxide (WO3) films when double injection of electrons and ions is provided in its volume. Experiments were performed in electrochemical cell with liquid electrolyte, where protons were used for injection in amorphous WO3 films. Kinetics of electrochromic coloration process was studied in spectral range of 300 nm to 1200 nm. Dependence of optical density on injected charge was found to be different in various spectral regions for coloring and bleaching. Infrared vibrational spectra of electro-chemically colored crystalline and amorphous WO3 were obtained. Electronic structure features of amorphous WO3 related to electorchromism are discussed.
Chemistry and Structure of Internal Interfaces in Inorganic Materials
Authors: Rühle M. , Recnik A. , Ceh M.
Published: April 2011

Physical properties of polycrystalline materials are controlled by intergranular as well as intragranular effects. In most cases materials' properties adhere to the bonding character of internal interfaces and plasticity of bulk parts. The nature of interfaces is in general difficult to understand, although they have far reaching consequences to overall properties of processed materials. To properly understand the effects brought by such interfaces one has to correlate particular properties with their local chemistry and structure. The availability of modern instrumentation that can provide a detailed chemical and structural information down to a subnanometer scale has helped greatly in tackling many fundamental problems in materials science. Our systematic studies of several metal/ceramic and ceramic/ceramic interfaces has given us a wealth of information that brings us closer to the answer on the formation mechanisms of the internal interfaces and other structural transformations in materials.
Synthesis of Inorganic Aromatic Hydrocarbon Polymers on Metal Surfaces
Authors: Perry Dale L. , Lewis Crystal , Pugh Mishi
Published: April 2011

Films of copper(II) imidazolate, an aromatic, heterocyclic hydrocarbon polymer, have been synthesized in situ at room temperature on copper surfaces. The films were made using a copper(II) salt formed as a thin film on an metallic copper substrate with subsequent complexation and deprotonation of the imidazole molecule. The in-situ formed copper(II) imidazolate polymer films have been studied by elemental analyses, scanning electron microscopy, and x-ray photoelectron and Auger spectroscopy. The copper Auger parameter has been derived for the films.
Synthesis of New Alkali-Metal-Intercalated Layered-Silicate Compounds and Their Magnetic Properties
Authors: Wada N. , Okui Hideaki , Omura Yasuyuki , Fujiwara Akihiko , Suematsu Hiroyoshi , Murakami Youichi
Published: April 2011

Single crystals and powders of vermiculite are dehydrated and then intercalated with alkali metals (K and Rb) using a two-temperature-zone furnace. The samples, originally transparent, exhibit metallic silver color upon intercalation. Our x-ray diffraction experiments indicate that the c-axis lattice constant becomes smaller after the intercalation process. A SQUID magnetometer is used to measure the magnetization of the samples as functions of temperature and magnetic field. Evidence for Pauli paramagnetism and enhancement of ferromagnetism are found in the Rb- and K-intercalated compounds, in addition to Curie paramagnetism due to iron impurities in the original vermiculite.
Synthesis of Carbon Spheres/Tubes Using a Mixed-Valent Oxide-Catalytic Carbonization Process
Authors: Kang Z. C. , Wang Z. L.
Published: April 2011

A mixed-valent oxide-catalytic carbonization (MVOCC) process is described for synthesizing monodispersed carbon spheres (or tubes) in macroscopic quantities at low cost. The technique uses natural gas and reusable catalysts and produces no environmental waste or pollution. The product is controlled to be either all of spheres (∼ 210 nm) or all of tubes with high purity (> 95 %). In spherical form, the product is solid and comprised of layered graphitic flakes containing paired pentagonal-heptagonal carbon-rings. In spiral tube form, the product is composed of twisted graphitic helix layers containing spherical nodes. A growth mechanism has been proposed, in which the pairing of pentagonal and heptagonal carbon-rings plays an important role. It is concluded that a change in fraction and nucleation rates of pentagonal, hexagonal and heptagonal carbon-rings results in the growth of different geometrical shapes. The success of using mixed-valence metal oxides as catalysts has opened a new field in catalysis research and applications.
Reforming with Novel Borosilicate Molecular Sieve Catalysts
Authors: Chen C. Y. , Rainis A. , Zones S.I.
Published: April 2011

In recent years the cost of research is increasingly dear to the sponsoring organizations, whether we speak of the public or private sector. Yet to meet the demand to make advances in product-generating technologies and to do so with slimmer margins, cost savings have to be developed along the chain of process events needed for production. In addition, the public atlarge has voiced their mandate for more environmentally benign operations. One look at the program for the 5th World Congress of Chemical Engineering (San Diego, 1996) would quickly show this trend. Both of the above-mentioned concerns merge together in the world of the chemical producer, generating a call for breakthroughs in the synergy of combining advanced catalytic materials with novel engineering processes. Thus, catalysis remains a focal point for technological progress [1].

Zeolites continue to be used as advanced catalytic materials, their contribution of molecular size discrimination, potential stability and high activity highlighting them as candidates for use in developing new process chemistry. Production of alkyl aromatics has seen recent trends in the replacement of existing corrosive catalyst technology by the safer solid acid zeolite catalysts [2]. The lube oil business has experienced the introduction of new Isodewaxing catalysts, capable of producing higher yields of desired product, and thereby reducing waste loss in the overall process scheme [3].
Activation of Oxidation Catalysts by Solvation
Authors: Eddowes Annette D. , Stallings Dana , Hightower Caprice L. , Jansen Susan A.
Published: April 2011

The versatility of heteropolyanions implies many different uses for Keggin type catalysts. However, new roles for these catalysts must first be preceeded by further understanding of the mechanisms by which they operate. It has been observed that the solvation and/or complexation of heteropolyanions promotes or limits activity in homogeneous chemistry. For this reason the solution state and the solvation characteristics of the catalyst were studied in oxidation and photochemical reactions. Simple oxidation reactions provide a system by which the solution state of the catalyst can be studied. The catalyst used for these mechanistic studies is the Keggin ion (PMo10V2O40)−5.
Automotive Applications of Sol-Gel Processed Materials: Novel, Low Power Consumption, Electrically Heatable Catalyst Devices
Authors: Nakouzi S. R. , McBride J. R. , Nietering K. E. , Visser J. H. , Adamczyk A. A. , Narula C. K.
Published: April 2011

Exhaust gas heat is the primary source of warming in a conventional automotive exhaust catalyst. It typically becomes operational within minutes after the initial start-up of an engine, when it attains temperatures greater than approximately 350°C. However, around 70% of the total hydrocarbon and carbon monoxide (CO) emissions of a modern gasoline powered vehicle, under a normal driving cycle, are released during this period of cold-start. One of the strategies suggested to treat the pollutants during the first minute after initial start-up involves electrically heating the catalyst. However, devices developed for this purpose are power intensive, can require a second battery and can reduce fuel economy. The increased weight, in turn, results in increased pollution. Here we describe a low power consumption prototype which contains a conducting layer beneath the washcoat. The prototype [4 cm2] was tested at a gas flow rate of 100 seem and required less than 5 Watts to attain temperatures greater than 350°C in less than 10 seconds. The prototype was tested in a flow reactor and found to rapidly heat up to light-off temperatures where the conversion of the hydrocarbons and CO takes place. We also summarize progress made in our laboratory in the fabrication of a test device employing sol-gel processed metal oxide films.
Effective Decomposition of Nitric Oxide Using Pd/YSZ/Au Electrochemical Membrane Reactor
Authors: Kanai Y. , Ichimura H. , Kawakami H.
Published: April 2011

The direct decomposition of NO (2NO → N2+02) has been carried out using an electrochemical membrane reactor composed of an yttria-stabilized zirconia (YSZ) disc deposited with Pd and Au metal films at reaction temperature of 773∼1023 K and applying voltage of 0∼1.8 V. N2 and O2 were continuously produced in the cathode and anode chambers, respectively. NO decomposition activity increased by applying electrical potential. It was clearly shown that the enhancement of the catalytic activity was due to electrochemical pumping, by which the surface oxygen species formed by the dissociation of NO were transported from cathode to anode through YSZ. By comparing the catalytic activity between Pd/YSZ/Au and Au/YSZ/Au systems, it is suggested that the NO decomposition occurs mainly on the Pd surface, and YSZ itself did not catalyze the reaction at lower temperature. The rate-determining step for the reaction was the adsorption of NO at 973 K, while at 773 K, the step was either a diffusion of O2- in YSZ or a migration of surface oxygen species on the Pd surface. The surface observation of Pd films by SEM showed that many microvoids were created throughout the Pd surface after the reaction. The creation of the microvoids results in an increase in the number of three-phase boundary sites, which will play an important role for the enhancement of the NO decomposition. Moreover, it was found that Pd/YSZ/Au resisted a serious degradation of the activity in the presence of O2 in the feed stream.
Catalytic Properties of Vanadium Nitride and the Effect of Preparative Parameters on its Microstructure
Authors: Kwon Heock-Hoi , Thompson Levi T.
Published: April 2011

In this paper we describe the synthesis, morphologies, and catalytic properties of vanadium nitrides prepared via the temperature programmed reaction (TPR) of V2O5 (7 m2/gr) with ammonia. This reaction yielded VN with surface areas up to 60 m2/gr. Among the synthesis parameters, the molar hourly space velocity had the most significant influence on the BET surface areas, crystallite sizes, and pore size distributions. Thermal gravimetric analysis (TGA) and x-ray diffraction indicated that the solid state reaction of V2O5 with NH3 occurred as follows: V2O5 → V4O9 → VO2 → V2O3 → VO0.9 → V.N. Scanning electron microscopy revealed that the surface roughness increased as the transformation proceeded, which corresponds to the increase in surface area. The vanadium nitrides were exceptionally active for the dehydrogenation of butane with selectivities greater than 98 % to C4 olefins. The deactivation was very slow for these catalysts. The reaction rates increased with increasing surface area and were comparable to that of a commercial Pt-Sn/Al2O3 dehydrogenation catalyst.
Preparation of Ti/B Binary Oxides by Sol-Gel Method and Their Photocatalytic Activity for Stoichiometric H2O Decomposition
Authors: Moon S. C. , Tabata S. , Okada K. , Fujiki M. , Mametsuka H.
Published: April 2011

A titanium-boron binary oxide has been prepared by the sol-gel method and characterized using SEM, TEM, UV-VIS reflectance, and X-ray diffraction spectroscopies. These measurements indicated that the obtained Ti/B gel with no treatment exhibited an amorphous structure. After calcination in O2, the crystalline structure of titanium oxide species in the Ti/B binary oxide was changed while boron oxide species maintained in the state of amorphous. Titanium oxide species in the Ti/B binary oxide calcined at 673 K showed an anatase phase of TiO2, and changed with the calcination temperatures from anatase phase to rutile phase. The Pt loaded Ti/B photocatalysts in aqueous suspension system decomposed water stoichiometrically under UV-irradiation. Their photocatalytic activities decreased with increasing the calcination temperature, indicating the photocatalytic activities of the Ti/B binary oxides were depended on the crystal phase of titanium oxide in the Ti/B photocatalysts.
A Model for Relaxation in Supercooled Liquids and Polymer Melts
Authors: Pakula T. , Teichmann J.
Published: April 2011

A new model for molecular rearrangements in liquids is proposed. The liquids are regarded as dense ensembles of vibrating molecules satisfying the excluded volume condition. A continuity condition is applied on the molecular scale of such systems and is regarded as controlling rearrangements leading to translations of molecules beyond the range of their vibration amplitude. It results in cooperative rearrangements which are considered as taking place in systems with fluctuating density. Rates of rearrangements are considered as being controlled by thermal activation with activation energy barriers dependent on local density. Various dependencies of the activation energy barriers on local density are examined. It is shown, that the model is able to reproduce the extremal cases of temperature dependencies of relaxation times represented on one edge by the Arrhenius relation and on the other edge by the Vogel-Fulcher-Tamman relation. The model can, however, provide a broad spectrum of other dependencies filling the gap between these extremes. All cases are based on the uniform microscopic picture of cooperative molecular rearrangements resulting from system continuity. The model is implemented as a simulation algorithm (Dynamic Lattice Liquid - DLL algorithm) which is used to simulate dynamic properties of liquids and polymer melts. Simulation results obtained for polymers are compared with experimental results obtained by means of the dynamic mechanical measurements on polyisobutylene samples with various molecular weights.