bluuebunny/crossref_metadata_2025 huggingface dataset:
Processing of Silicon Oxides Thin Films by Thermal LPCVD Starting from Teos Mixtures
Authors: Vamvakas Vassilis Em. , Davazoglou Dimitris , Vahlas Constantin
Published: April 2011

A thermodynamic simulation is presented of the low pressure chemical vapor deposition (LPCVD) of silicon oxide thin films starting from TEOS and N2O mixtures within the temperature range 700 – 1300K, by minimizing the total Gibbs energy of the C‐H‐N‐O‐Si chemical system. It was found that at temperatures up to 1173K and N2O/TEOS molar ratios up to approximately 7, SiO2 films contain carbon impurities, while above this ratio deposits are carbon free. A corresponding experimental investigation is also presented where the obtained submicronic films are slightly substoichiometric in oxygen. They contain small carbon impurities the concentration of which decreases with the N2O/TEOS molar ratio.
Tantalum Pentoxide for Advanced DRAM Applications
Authors: McKinley K. A. , Sandier N. P.
Published: April 2011

Tantalum pentoxide (Ta2O5) films were deposited from the reaction of tantalum pentaethoxide (Ta(OC2H5)5) and oxygen (O2) using the Lam Research Corporation DSM™9800 advanced LPCVD reactor. Typical films were deposited at a rate of 0.9 – 1.1 nm/min at 400°C. The films were stoichiometric with an O/Ta ratio of 2.57/1.00 and excellent compositional uniformity. Conformity was >95% indicating that the process is surface reaction rate limited. Films with non‐uniformities <2.2% were deposited on 300 mm wafers. The deposited non‐uniformity on 150mm and 200mm wafers was <2.0% ‐1σ within a wafer, wafer to wafer within a batch, and batch to batch. The dielectric constant for as‐deposited films was 22–24, and as high as 34 for films which were heat treated. Various post deposition heat treatments were performed to improve the capacitor's electrical properties. Superior results were obtained from rapid thermal annealing (RTA) in N2O compared with RTA in O2 and two‐step UV‐O3 followed by high temperature annealing in dry O2. Values for the leakage current of <10-8 A/cm2 at 1.2 volts negative bias (worst case) and breakdown >5 MV/cm at 1.6μΑ with tegox<2.5 nm have been obtained. These values meet the requirements for 256 Mbit DRAM memory devices Bottom and top electrode formation and integration issues are also addressed.
POST‐METALLIZATION ANNEALING OF ULTRA‐THIN REMOTE PLASMA ENHANCED CVD OXIDES
Authors: Ragnarsson L‐Å , Lundgren P. , Landheer D.
Published: April 2011

A remote plasma enhanced chemical vapour deposition (RPECVD) process was used to deposit thin silicon dioxides on silicon substrates. The oxide properties were compared with thermal oxides with similar thicknesses (2.5–9 nm) using capacitance‐voltage (C‐V), current‐voltage (I‐V) and constant voltage stress measurements (I‐t). Post‐metallization annealing (PMA) showed different annealing dynamics as compared to the thermal oxides for anneal times below approximately 1000 s (at 260 °C) after which the dynamics were similar. The deposited oxides had a higher initial interface state density (Dit) than the thermal oxides, but after PMA they were found to be of the same quality as the thermal oxides. Positive charging of the deposited oxides during constant voltage stress was the same as for thermal oxides, showing that the stress endurance of the two are similar.
Electrical Properties of Batio3 thin Films Flash‐Evaporated on si and sio2/Si
Authors: Caballero J.V. , Avila R. E. , Fuenzalida V.M. , Eisele I.
Published: April 2011

BaTiO3 (BT) thin films were prepared by flash evaporation onto p‐Si and SiO2/p‐Si. The films are amorphous and remain so after a thickness reduction by 20% by annealing at 500 °C for 3 min. in O2 atmosphere. The electrical characteristics were measured at room temperature.

Electron injection at the Al to BT interface of Al/BT/Si capacitors is enhanced by the Schottky effect, yielding a value of 11.2 for the dielectric constant of BT. Modeling current‐time measurements yields a trap density of 1024 m3, 0.82 eV below the conduction band. Capacitance‐voltage curve shifts due to bias stress on AI/BT/SiO2/Si capacitors are interpreted as caused by electron injection and trapping in the BT films. Starting deposition at 170 °C or post‐deposition annealing reduces the trap density and increases the C‐V curve shifts by bias stress, from 0.3 to over 14 V at bias stress of‐10 V.
Characterization of the Thin Diamond-Like Carbon Films Deposited Using Rf Inductively Coupled Ch4- Plasma Source
Authors: Druz B. , Polyakov V.I. , Ostan E. , Hayes A. , Rukovishnikov A.I. , Rossukanyi N.M. , Khomich A.V.
Published: April 2011

Diamond-like carbon (DLC) films with 4-400 nm thickness were deposited on silicon substrates using direct ion beam from an RF inductively coupled CH4 - plasma (ICP) source. The dependence of the film electrical and photoelectrical properties on methane flow were examined. Two kinds of trapping centers with different activation energies and capture cross-sections, and very low densities were discovered by the Q-DLTS method. The influence of thermal annealing in air at 100-450°C was investigated. The current leakage and defect concentration were reduced while electrical breakdown field and photoresponse were increased in annealed films. The results obtained have been used for optimization of the technology to prepare thin films with good protective, electrically insulating, and passivating properties.
Simulation of Structure and Dynamics of Amorphous SiO2
Authors: Kogure Y. , Doyama M.
Published: April 2011

A molecular dynamics computer simulation of amorphous SiO2 has been made to investigate the structure and dynamics. The effects of the external stresses on the amorphous structure were investigated through the radial distribution function, the distribution of Si‐O‐Si bond angles, and the distribution of coordination numbers.
Surface Oxidation of Si (111) By High Purity Ozone and Negative Ions Produced by Rydberg Electron Transfer
Authors: Nonaka H. , Kurokawa A. , Nakamura K. , Ichimura S.
Published: April 2011

The sub‐initial oxidation of Si (111) surface by a high‐flux pure ozone was investigated using X‐ray photoelectron spectroscopy. In addition to the advantage of the pure ozone which can efficiently oxidize the Si surface at room temperature, the high‐flux ozone was found to further enhance the oxidation. The possibility of producing negative ions of oxidizing gases using Rydberg electron transfer was also investigated.
Chlorine Precursors For Gate Oxidation Processes
Authors: Mc Geary M.J. , Mertens P.W. , Vermeire B. , Heyns M. , Sprey H. , Lubbers A. , Schaekers M.
Published: April 2011

1,1,1‐Trichloroethane (TCA) has played a vital rôle in contemporary semiconductor fabrication as a source for chlorine during the oxidation of silicon substrates. However, TCA has been identified as an ozone depleting compound by the Montreal Protocol, and in the United States The Clean Air Act Amendments of 1990 severely restrict its use in many applications. This paper discusses oxalyl chloride (OC) and trans‐ 1,2‐dichloroethylene (DCE) as alternatives to TCA for silicon oxidation processes. Information on precursor vapor delivery, atmospheric chemistry, industrial hygiene, and combustion chemistry will be presented along with comparisons of metal decontamination efficiency and electrical properties (Qbd) for oxides grown in the presence of each precursor The suitability of OC for low temperature, ultra‐thin oxidation processes will also be addressed.
Parallel Down Flow Rinsl : Water Saving Technology in Wafer Rinse
Authors: Hiratsuka Y. , Fujikawa N.
Published: April 2011

We had proposed parallel downflow rinse which was capable of draining out chemical carried over to rinsing bath together with wafer about twice as fast as overflow rinse.
In an attempt to further improve rinsing efficiency of PDR, we have investigated (1) the effect of wafer carrier shape, and (2) removal of boundary layer on wafer surface. Boat‐type wafer holder is preferable to conventional cassette. Three stirring techniques adequate for PDR, namely, megasonic irradiation. N2 bubbling, liquid level shifting, are found effective to remove chemical ion remaining boundary layer in measuring conductivity and resistivity.
Intersubband Transitions in Microcavities with a Grating: Coupled Oscillators
Authors: Duboz J.-Y.
Published: April 2011

We theoretically study the absorption in grating coupled quantum wells in a cavity. We describe the coupling betwen the three oscillators present in the structure: The intersubband transition, the grating and cavity modes. We show that optical mode anticrossings should be observed. The splitting between the cavity mode and the intersubband transition is calculated but its experimental observation would require electronic coherence times longer than what was measured.
Emission Efficiency in InAs LEDs Controlled by Surface Recombination
Authors: Kane M J , Braithwaite G , Emeny M T , Lee D , Martin T , Wight D R
Published: April 2011

In this paper, light emitting diodes (LEDs) are used to study the recombination dynamics of minority electrons in p type InAs. The LEDs operate through injecting electrons into p type material with a free surface. When surface recombination is dominant, the output of the LEDs is shown to depend only on the strength of the radiative recombination and not on its efficiency. When surface recombination is not dominant, the dependence of the LED efficiency on the thickness of the active layer is analysed to give the minority carrier diffusion lengths and recombination efficiencies. the electron diffusion lenSgth is shown to be 3±0.5 μm in 5×10−18 cm−3 p type InAs and 6±1 pm in 2×10 cm−3 p type material. An upper limit of∼2.1×10−28 cm6 s−1 is deduced for the total Auger recombination rate constant in p type material.
GaAs/GaInP Quantum Well Intersubband Photodetectors for Focal Plane Array Infrared Imaging
Authors: Jelen C. , Slivken S. , Brown G. J. , Razeghi M.
Published: April 2011

We demonstrate long wavelength quantum well infrared photodetectors (QWIP) with GaAs quantum wells and GalnP barriers grown using gas-source molecular beam epitaxy. Wafers were grown with varying well widths. The optimum well width was 75 Å, which resulted in a detection peak at 13 μm and a cutoff wavelength of 15 μm Dark current measurements of the samples with 15 μm cutoff wavelength show low dark current densities. Preliminary focal plane array imaging is demonstrated.
A Novel Infrared Sige/Si Heterojunction Detector with an Ultrathin Phosphorus Barrier Grown by Atomic Layer Deposition
Authors: Banisch R. , Tilack B. , Pierschel M. , Pressel K. , Barth R. , Krüger D. , Ritter G.
Published: April 2011

In strained Sia−xGex heterojunction internal photoemission (HIP) photodiodes the spectral response can be tailored over a wide wavelength range by varying the Ge content. In this paper heavily in situ boron doped SiGe layers with 30% Ge were grown by low pressure rapid thermal chemical vapour deposition (LP(RT)CVD). The detectors exhibit a cut-off wavelength of 8.5 μm. A delta-like P peak, incorporated by atomic layer deposition technique, shifts the cut-off to shorter wavelengths. This shift is related to an increase of the barrier height at the SiGe/Si interface caused by the narrow n+-doped layer in agreement with device simulation. In this way the trade off between critical film thickness for high Ge content film growth and absorption depth for proper detector response can be overcome.
Defect Characterization in ZnGeP2 by Time -Resolved Photoluminescence
Authors: Dietz N. , Busse W. , Gumlich H. E. , Ruderman W. , Tsveybak I. , Wood G. , Bachmann K. J.
Published: April 2011

Steady state and time-resolved photoluminescence (PL) investigations on ZnGeP2 crystals grown from the vapor phase by high pressure physical vapor transport (HPVT) and from the melt by gradient freezing (GF) are reported. The luminescence spectra reveal a broad infrared emission with peak position at 1.2 eV that exhibits features of classical donor-acceptor recombination. The hyperbolic decay characteristic over a wide energy range, investigated from 1.2 eV up to 1.5eV, suggest that this broad emission band is related to one energetic recombination center. Higher energetic luminescence structures at 1.6eV and 1.7eV were revealed after annealing of ZnGeP2 crystals in vacuum for a longer period of time. The emission decay behavior in this energy range is characterized by two hyperbolic time constants, viewed as the supercomposition of the decay from the broad emission center peaked at 1.2eV and additional donor-acceptor recombination emissions at 1.6eV and 1.7eV, respectively. ZnGeP2 crystals grown under Ge-deficient conditions by HPVT show an additional emission structure at 1.8 eV with sharp emission fine structures at 1.778 eV related to the presence of additional donor states.
Analysis of three types of Interdiffusion Process in Ingaas/Inp Quantum-Well and their Devices Implications
Authors: Chan Michael C.Y. , Chan K. S. , Herbert Li E.
Published: April 2011

The optical properties of In0.53Ga0.47As/InP single quantum well (QW) (with an as-grown well width of 60Å structures) interdiffused with different cation and anion interdiffusion rates have been theoretically analyzed for applications in optoelectronics. The interdiffusion of TnGaAs/InP QW structures is complicated as interdifrusion can occur for either (i) only group-Ill (In,Ga), (ii) group-V (As,P), or (iii) both group-Ill and group-V sublattices. Depending on the resulting composition profiles, the shifts (blue or red) of the transition energies can be tuned to wavelengths between 1.3μm to 1.55μm for device applications. The results show that the control of the rates of cation and anion interdiffusion offers interesting possibilities for designing optoelectronic devices such as modulators and lasers.
Optical Properties of Diffused AlGaAs/GaAs Multiple Quantum Wells and their Applications in high Power Laser
Authors: Luo Yi , Jiang Ai-Qing , Hao Zhi-Biao , Wang Jian-Hua , Lai Terry W. K. , Herbert Li E.
Published: April 2011

We will present results for an Al0.24Ga0.76As/GaAs diffused multiple quantum well with five periods of 100/100 Å thick well/barrier layers grown in between Al0.24Ga0.76As guiding layers and cladded on top by a 1 μm thick p-Al0.44Ga0.56As layer and on the bottom by an n-Al0.44Ga0.56As layer of equal thickness, on a n+-GaAs buffer layer and n+-GaAs substrate. Vacancy enhanced QW diffusion is employed where a 2000 Å thick layer of SiO2 is deposited on top of the diffused multiple quantum well structure. Photoluminescence measurement and photovoltage measurement at room temperature show that after rapid thermal annealing for 30 sec at 1000 °C to 1040 °C, a bandgap shift of 30 nm is obtained for the exciton edge. Further, this technique is applied to a ridge waveguide laser structure to make two windows for high power output up to 36 mW. This device shows that the diffusion process may have practical applications.
Numerical Simulation of Electronic Behavior in a Finite Superlattice With a Tamm State: A Possible Submillimeter Wave Emitter Without Optical Pumping
Authors: Manzoli J. E. , Hipólito O.
Published: April 2011

We propose a semiconductor heterostructure consisting of six coupled quantum wells of GaAs plus a larger one, all inside Al(x)Ga(l−x)As, x=0.35. Our simulation prevents that the localized electronic eigen-state at the large well, the Tamm state, will oscillate when the voltage applied across these “finite superlattice” varies fast. We include exchange and correlation effects in the local density approximation and made the self-consistent calculations to the electrons at 77K varying the voltage in a gate contact of the device. We obtain the effective potential, the sub-bands (mini-bands) and respective electronic densities which enable us to simulate the temporal evolution of an electronic wave-packet when the gate-voltage is switched fast. Such a switching turns the Tamm eigen-state in a wave-packet. By the simulation we conclude that this wave-packet oscillates a Tera-Hertz frequency that can emit electromagnetic radiation as a charge oscillator. We estimate the finite superlattice capacitance and it confirms the possibility of changing the Hamiltonian faster than the period of the oscillation.
Group II-VI Downconverting Phosphors
Authors: Valdna V. , Gavrish T. , Hue J. , Mellikov E. , Mere A.
Published: April 2011

The efficiency of group II-VI solid solutions doped with chlorine and copper as X-ray downconverting phosphors for photodetectors is investigated. It is found that the phosphors based on the group II-VI compounds and prepared in oxygen-free medium can increase the photodetectors sensitivity to X-ray radiation more than one order of magnitude and enhance the photodetectors photovoltage versus X-ray radiant flux characteristic linearity.
Early Transition Metal Oxides and a Pinch of Salt: New Synthetic Routes to Titanates and Niobates
Authors: Geselbracht M. J. , Scarola R. J. , Ingram D. , Green C. , Caldwell J. H.
Published: April 2011

Molten salts have traditionally been used as recrystallizing solvents for the crystal growth of mixed metal oxides. In recent years, many examples of the direct preparation of mixed metal oxides from molten salt solutions have been reported. We have been exploring the use of chloride melts as a reaction media to prepare complex early transition metal oxides. Specific examples of new synthetic routes to interesting titanates and niobates will be presented. In one case, we have prepared a series of layered niobate perovskite solid acids from molten salts at temperatures well below those traditionally used in solid state syntheses. In the second case, we have discovered a new synthetic route to a poorly characterized reduced calcium titanate that is otherwise very difficult to make. The synthesis and characterization of these two classes of compounds will be described.
Controlling Defects in Double-Layer Cuprates by Chemical Modifications
Authors: Salvador P. A , Greenwood K. B. , Otzschi K. , Koenitzer J. W , Dabrowski B. M. , Poeppelmeier K. R. , Mason T. O.
Published: April 2011

In-situ high temperature electrical conductivity and thermopower have been measured simultaneously on a number of ordered perovskite-like oxides containing double CUO4/2 sheets. Equilibrium measurements have been conducted as a function of oxygen partial pressure, temperature and chemical substitution in order to understand the relationships between the chemical architecture and the transport and defect properties. Data for LaBa2Cu2NbO8 and LaCa2Cu2GaO7 are presented and compared with those of known triple perovskite superconductors, Y1−xCaxSr2Cu2GaO7 and YBa2Cu3O7−δ, and several quadruple perovskites, Ln′Ln″Ba2Cu2M2O11 (Ln = Lanthanide, Y; M = Sn, Ti). These materials belong to a general family of superconductors which are constructed from similar ‘active’ layers (double perovskite blocks of square-pyramidal copper-oxygen sheets), and interleaved with fixed valence cations in perovskite-like ‘conditioning’ layers. Similarities in the transport properties of the non-superconducting and superconducting materials at elevated temperatures are illustrated, and the amount and types of defects, including carrier concentrations, are correlated with the internal chemistry and inner architecture of each material.
Optical Properties of Lanthanide -Containing Halide-Modified Zinc Tellurite Glasses
Authors: Sidebottom D. L. , Hruschka Michael A. , Potter B. G. , Brow Richard K. , Hudgens James J.
Published: April 2011

As part of an ongoing investigation to characterize the properties and structure of zinc halide-tellurium oxide glasses, we report preliminary measurements of the optical properties of several Nd- and Er-doped tellurites. Measurements include florescence lifetimes and estimates of the theoretical radiative lifetimes (as obtained by traditional Judd-Ofelt analysis of optical absorption spectra) as well as phonon sideband studies sensitive to vibrational characteristics near the rare earth ion. The response of these optical features to the substitution of alternative halides is examined.
New Nonlinear Optical Crystals of KTiOPo4 (KTP) Family
Authors: Chani V. l. , Shimamura K. , Endo S. , Fukuda T.
Published: April 2011

Phase formation and crystal growth conditions for different combinations of cations corresponding to chemical formula of KTP were studied. Preparation of new Ti-less arsenates which arc isostructural with KTP is reported. In the single crystals grown Ti4+ cations were completely substituted with M2+ + Nb5+ (M = Mg, Zn) or M3+ + Nb5+ (M = Al, Cr, Ga, Fe, In) cation couples. The crystals were prepared by spontaneous crystallization using flux method. The structure analysis was made by X-ray powder diffraction technique. The crystals composition was measured by electron probe microanalysis (EPMA). Second harmonic generation (SHG) effect was studied by the powder technique with a pulsed YAG:Nd laser (1064 nm). SHG signal of the crystals was found to be slightly greater than that of KTiOAsO4 (KTA).
Optical Second Harmonic Generation in Transparent Tellurite Glass-Ceramics Containing BaTiO3
Authors: Tanaka Katsuhisa , Kuroda Hisako , Hirao Kazuyuki , Soga Naohiro
Published: April 2011

Optical second harmonic generation has been observed in transparent tellurite glass-ceramics of Ba0-TiO2-TeO2 system. BaTiO3 and unidentified crystalline phase precipitate from 15BaO·15TiO2·7OTeO2 glass. The temperature of maximum rate of nucleation for these crystalline phases is estimated to be 380°C. The BaTiO3 crystal precipitated is a cubic phase with lattice parameter of 0.4045 nm, which is slightly larger than the value reported in the JCPDS cards. The optical second harmonic intensity of the present transparent tellurite glass-ceramics is comparable to the intensity of poled tellurite glasses although the BaTiO3 phase precipitated is cubic and the crystal face is randomly oriented in the glass-ceramics. For instance, the second harmonic intensity of the present transparent tellurite glass-ceramics is about twice as large as that of 20WO3·80TeO2 glass poled at 280°C under the external electric field of 3 kV, the second-order nonlinear coefficient, d33, of which is 0.10 pm/V.
Application of Photostimulable Phosphor, Imaging Plate :BaFBr:Eu2+, to Image Storing for UV-VUV Radiations
Authors: Katto Masahito , Ohnishi Shunshiro , Kurioka Yutaka , Takigawa Yasuo , Kurosawa Kou
Published: April 2011

An imaging plate containing photostimulable phosphor material, BaFBr:Eu2+, was found to be applicable to store images for nanosecond pulses as well as quasi-continuous radiations in 4 – 35 eV photon energy range. The sensitivity, which was defined as photostimulated luminescence intensity for a given incident photon number increased with the photon energy and had a peak at 6.2 eV. The intensity of the luminescence was confirmed to increase in proportion to incident photon numbers of the radiation. The readout system was improved and then pattern images were successfully restored. The resolution of imaging plate was found to be lower than 100 μm with our system, which depends on the intensity of a He-Ne laser for restoring images.
Crystal Growth of Ca3(Li,Nb,Ga)5O12 Garnets from Melt
Authors: Chani V. l. , Myu Y. , Shimamura K. , Saiki Y. , Fukuda T.
Published: April 2011

Single crystals of Ca3(Li,Nb,Ga)5O12 garnets have been grown from stoichiometric melts by micro-pulling down and Czochralski methods using Pt crucibles. It was found that the mixture of oxides with atomic ratio Ca : Li : Nb : Ga = 3 : 0.275 : 1.775 : 2.95 correspond to the garnet composition which melts congruenlly at about 1450°C. Solid state reaction data of the compounds related with this material are also reported. Lattice parameter of all Ca3(Li,Nb,Ga)5O12 crystals grown was about 1.254 nm. Transparent and bubble-free crystals of Ca3LixNb1.5+xGa(3.5+x)Ga(3.5−2x)O12 (x = 0.25 and 0.275) were grown by Czochralski technique in air. An optical transmission spectrum of the crystals was studied. No absorption was detected in 400–1200 nm wavelength range.
Electron Transport Phenomena in NiS2−xSex Single Crystals
Authors: Yao X. , Ehrlich S. , Liedlb G. , Hogan T. , Kannewurf C. , Honig J. M.
Published: April 2011

Structural studies, electrical resistivity, and Seebeck coefficient measurements are reported in the range 4.2 − 300 K for single crystals of NiS2−xSex (0 ≤ x ≤ 0.71) grown from a Te melt. Over the entire temperature and composition ranges there are no large scale structural changes concomitant to a variety of magnetic ordering phenomena, and to a changeover from insulating to metallic characteristics as x increases. Thus, the evolution in transport characteristics with x can be studied without interference from the lattice; moreover, the electron count is unaffected by substitution of Se for S. The existence of anomalous peaks in resistivity as a function of temperature is attributed to significant electron correlation phenomena which allow the entropy of charge carrier to play a dominant role. The complex temperature dependence of the Seebeck coefficient is attributed to the participation of both electrons and holes in charge transport.
The Narrow-Band System La1-xSrxTiO3
Authors: Hays Charles C. , Goodenough John B. , Marken John T.
Published: April 2011

Magnetic, transport, and structural data on polycrystalline samples of the system La1-xSrxTiO3, 0 ≤ x ≤ 0.8, show an abrupt, but apparently smooth, transition from p-type polaronic conduction in a canted-spin antiferromagnetic system for x ≤ 0.04 to metallic, mass-enhanced Pauli paramagnetic behavior for x ≥ 0.1 with evidence for a spin glass and a discontinuous drop in TN in the transition range. We interpret these results as a manifestation of the coexistence of two distinguishable electronic domains within a single crystallographic phase as a result of cooperative displacements of the oxygen atoms.
Synthesis of A1–xA'xNbO3 (A=Na+, K+; A'= La3+, Sr2+) and its Electrical Properties
Authors: Sugimoto W. , Tahara T. , Sugahara Y. , Kuroda K.
Published: April 2011

Polycrystalline samples of A1–xA'xNbO3 (A=Na+, K+; A'= La3+, Sr2+) were prepared by solid-state reactions and the relationship between the structure and electrical properties was examined. Single-phase products were obtained for Na1–xLaxNbO3 (x ≤0.1), K1–xLaxNbO3 (x ≤0.15), Na1–xSrxNbO3 (x ≤0.3), and K1–xSrxNbO3 (x ≤0.5). The structures of the sodium-containing compounds and potassium-containing compounds were indexed according to a pseudocubic and cubic symmetry, respectively. The resistivity measurements showed semiconductive behavior for the lanthanum-containing samples. The strontium-containing samples showed semiconducting properties for x ≤0.2, while a transition to metallic conduction at low temperature was observed for x >0.2.
Low Temperature Magnetic Properties of Some New High-Pressure Perovskite Phases of Iron II: Observation of Novel Slow Paramagnetic Relaxation in CaFe2Ti2O6 and CaFe3Ti4O12
Authors: Reiff W. M. , Leinenweber K. , Parise J.
Published: April 2011

Results of iron-5 7 Mössbauer spectroscopy and ac and dc susceptibility study of the double perovskite phases, CaFeTi2O6 (A) and CaFe3Ti4O12 (B) are presented. Both phases exhibit spectral broadening effects with decreasing temperature and incipient magnetic hyperfine splitting attributable to novel slow paramagnetic relaxation at the tetrahedral and square planar sites of (A) and the square planar sites of (B). The temperature dependence of magnetic moment for (A) corresponds to classical single ion zero field splitting, while that of (B) indicates antiferromagnetic exchange interactions. There is no evidence of cooperative long range magnetic order in these materials.
Effects of Non-Stoichiometry on Anisotropic Magnetic Properties in CuFeO2+δ Single Crystals
Authors: Hasegawa M. , Zhao T. R. , Bartashevich M. I. , Takei H. , Goto T.
Published: April 2011

Effects of non-stoichiometry on anisotropie magnetic states in CuFeO2 with a so-called delafosite structure have been investigated using CuFeO2+δ (δ=-0.061, -0.026, 0.014, 0.085) single crystals. Each single crystal is grown using the floating zone method in each controlled atmosphere and found to have good quality. All crystals show two anisotropie successive antiferromagnetic transitions in the temperature dependence of magnetic susceptibilities. The higher antiferromagnetic transition temperature is not affected by the non-stoichiometry. On the other hand, the lower one shows distinct effects of the non-stoichiometry, depending on the kind of oxygen defects. Oxygen deficiency leads to an increase in TN2, while excess oxygen leads to a decrease. It is also found that all samples show clear anisotropie step anomalies in the magnetization curve up to 38 T and that the anomalies and hystereses depend on the nonstoichiometry.
Effect of Hydrostatic Pressure (≤2GPa) on the Transport Properties in Perovskite-Type Oxides
Authors: Itoh M. , Yu J-D. , Nishi K. , Katsumata T. , Inaguma Y. , Huang T.
Published: April 2011

A clamp-type hydrostatic pressure device for the measurement of properties of perovskite-related compounds under pressure was established in our laboratory and applied to the measurements of resistivity, AC susceptibility, Hall effect and ionic conductivity. In usual perovskite-type oxides, loading of a pressure of 1 GPa (lOkbar) corresponds to a contraction of interionic distance as large as 0.2%. This small value is not enough to evaluate the whole scheme of phase transition behavior for perovskite-type oxides but very effective for the observation of changes in interactions between electrons and ions. Some problems concerned with this method have been pointed out.
High-Resolution Electron Microscopy of Magnetic Dielectric Oxides in the Bao:TiO2Fe2O3 System
Authors: Bendersky L. A. , Vanderah T. A. , Roth R. S.
Published: April 2011

In a recent work on phase equilibria relations in the BaO:Fe2O3:TiO2 system the existence of sixteen ternary compounds was confirmed. Most of the new found compounds apparently have a new structural type. In this work we employed electron diffraction and high-resolution microscopy in attempt to understand the structures of the new compounds. Since the present work was done on the compounds prepared by solid-state reaction, it also provides a correlation with a single-crystal x-ray work on some of the similar compounds prepared by crystallization from a melt.
La2Zr2O7 Formation Between Yttria-Stabilized Zirconia and La0.85Sr0.15MnO3 at 1373 K
Authors: Mitterdorfer A. , Gauckler L. J.
Published: April 2011

Oxygen ion conducting yttria-stabilized zirconia and perovskite-type Sr-doped LaMnO3 have been widely used as solid electrolyte and cathode materials in solid oxide fuel cells. The electrochemical properties of the cathode depend largely on the nanostructure and the phase composition of the interface between cathode and electrolyte. Interfaces between single crystals of 9.5mol% Y2O3-stabilized ZrO2 and porous La0.85Sr0.15MnyO3 (y = 0.95…1.10) were investigated. Atomic force microscopy was used for interface studies of YSZ single crystals after removal of sintered perovskite cathodes. High resolution transmission electron microscopy, electron diffraction and electrochemical impedance spectroscopy were employed for interface characterization. Pyrochlore-type lanthanum zirconate formed at the interface during sintering at 1100°C. Nucleation, growth kinetics, and morphology were largely depending on cathode stoichiometry. Lanthanum zirconate formation was retarded in case of A-site deficient perovskite.
Ionic Distribution in Rare Earth Ion-Doped Na+ β"- Alumina
Authors: Wang Yuhu , Cormack Alastair N.
Published: April 2011

Structure of β"-alumina has been studied through atomistic simulation. Distribution of Mg2+ in the spinel blocks, Na+ as well as Nd3+ in the conduction planes have been calculated and compared with the structure models derived experimentally. Mg2+ ions, as the stabilizer of β"-alumina structure, prefer to occupy the tetrahedral Al(2) sites in the spinel block. Two configurations for Mg2+ distribution are proposed. Due to the presence of Mg2+, oxygen ions in or adjacent to the conduction plane, O(5), O(4) and O(3), are slightly displaced from their original sites, leading to the removal of the local symmetry at the mO site. Strongly affected by the Mg2+ distribution, Nd3+ions, originally introduced into the BR site in the conduction plane, are found to move towards the distorted mid-oxygen sites, which is in excellent agreement with the previous estimate from spectroscopie study.
Preparation and Electrical Conductivity Measurement of LiSbO3Thin Films
Authors: Ozawa K. , Sakka Y. , Amano M.
Published: April 2011

LiSbO3thin films have been prepared by the sol-gel process with metal alkoxides using a spin-coating method. The (Oll)-oriented and randomly oriented LiSbO3thin films are obtained by the precursor film crystallizing under an atmosphere of a flowing mixture of water vapor and oxygen, and an air atmosphere, respectively. The two different atmospheres also affect the crystallization temperature of the films. The electrical conductivity of the (Oll)-oriented LiSbO3thin film is approximately one order of magnitude larger than that of the randomly oriented LiSbO3thin film in the temperature range of 380 to 600°C.
A Comparative Study of Lithium and Sodium Insertion in Two Block Structure Type Phases, W3Nb14O44 and W4Nb26O77
Authors: Fuentes Antonio F. , Martinez De La Cruz A. , Torres-Martinez Leticia M.
Published: April 2011

A comparative study of lithium insertion in W4Nb26O77 and W3Nb14O44, two block structure type phases, has been carried out. This process is, in both cases, reversible for a similar number of lithium ions incorporated to total metal atoms ratio (Li/ΣM), 1.15 in W3Nb14O44 and 1.23 in W4Nb26O77. No significant structural changes are seen by X-ray diffraction upon insertion. Sodium insertion in W3Nb14O44 has been also studied observing a substantial reduction on the number of ions incorporated when compared with lithium (Na/ΣM: 0.03).
Chemical Reactivity Between Sialon Ceramics and Iron-Based Alloys
Authors: Vleugels J. , Van Der Biest O.
Published: April 2011

The chemical interaction of a number of SiAlON ceramic - iron-based alloy combinations is studied by means of static interaction couple experiments at 1200 °C. During the interaction, silicon and nitrogen from the ceramic dissolve and diffuse into the iron alloy, whereas the remaining aluminium and oxygen form Al2O3 particles. The rate controlling step of the interaction was identified and the influence of alloying elements in the iron-based alloy as well as the chemical composition of the ceramic on the reactivity was investigated. The relative reactivity measured in the interaction couples was compared with the measured wear of the ceramics in turning of steels. The predictive capabilities of the results of the interaction couple experiments on the actual cutting tool performances in turning operations is highlighted.
Reactivity of Chrysotile Asbestos in Acids: Mechanism of Transformation to Silicon Dioxide Hemihydrate Upon Leaching of Magnesium
Authors: Vaillancourt Anne , Denes Georges , Le Van Mao Raymond
Published: April 2011

Acid leaching chrysotile asbestos results in a stepwise loss of magnesium which reduces the strain locally. This results in a partial unwiding of the structural sheets which makes possible further leaching. Strong acids are used for a coarse brutal attack of the chrysotile structure, whereas weak acids allow a fine control of the magnesium leaching degree required to have the adequate properties of the partially leached asbestos which is used for the preparation of zeolites with enhanced catalytic properties. The final material is not carcinogenic. The leached materials were characterized by atomic absorption spectrometry, bulk density and BET specific surface area measurements, and X-ray diffraction.
Atomic and Electronic Structure of the Corundum (0001) Surface
Authors: Puchin V. E. , Kotomin E. A. , Shluger A. L.
Published: April 2011

The electronic structure and geometry of the Al terminated corundum (0001) surface were studied using a slab model within the ab-initio Hartree-Fock technique. The distance between the top Al plane and the next O basal plane is found to be considerably reduced on relaxation (by 0.57 Å, i.e. by 68% of the corresponding interlayer distance in the bulk). An interpretation of experimental photoelectron spectra (UPS Hel) and metastable impact electron spectra (MIES) is given. Calculated projected densities of states exhibit a strong dependence on the relaxation of surface atoms.
Microstructural Characterization of an Oriented Silicalite Film
Authors: Lovallo M. C. , Tsapatsis M.
Published: April 2011

The crystal orientation of a submicron silicalite membrane is examined using standard x-ray diffraction and pole-figure analyses. Results indicate that the crystals in the molecular sieving layer are preferentially oriented with both straight and sinusoidal channel networks of the zeolite parallel to the membrane surface. This requires that transport across the membrane proceed down the c-axis of the crystals which can occur by jumping between the two channel networks. EDAX data confirms that the molecular sieving layer is the pure silica zeolite silicalite.
Use of Graphite Nanofibers as a Novel Catalyst Support Medium for Hydrogenation Reactions
Authors: Park C. , Rodriguez N. M. , Baker R. T. K.
Published: April 2011

In this investigation we elected to use the hydrogenation of 1-butene as probe reactions in an attempt to monitor any possible changes in catalytic behavior resulting from supporting 5 wt.% nickel on different types of carbon nanofibers compared to the performance of the same metal loading on more traditional carriers, including γ-Al2O3 and active carbon. In all cases the carbon nanofiber supported nickel particles are found to exhibit superior activity and significant changes in selectivity to that found from the same metal supported on traditional carriers.
High-Energy Mechanical Synthesis of Nanophase Fluorite-Structured Mixed Oxide Catalysts with a High Redox Activity
Authors: Primavera Alessandra , Trovarelli Alessandro , Jordillorca  , Terribile Daniela , de Leitenburg Carla , Dolcetti Giuliano
Published: April 2011

A series of nanostructured, highly defective, ternary solid solutions containing CeO2, ZrO2, and MnO2 or CuO were prepared by high-energy mechanical milling of individual components. Morphological and redox properties were studied by XRD, HRTEM and temperature-programmed reduction techniques. It was shown that the introduction of small amounts of copper and manganese strongly promotes the redox behavior of cerium at lower temperatures in comparison with CeO2 and CeO2-ZrO2. High temperature treatment of up to 1400K was also shown to further promote overall redox capacity without affecting low-temperature redox behavior. Moreover, evidence is provided to show that Cu and Mn are dissolved within the CeO2 lattice structure. Addition of dopants enhances catalytic redox properties in the oxidation of CO at low temperatures, which is associated with the high concentration of oxygen vacancies that form on the introduction of aliovalent elements into the ceria-zirconia lattice.
Materials Science: A Driver for Innovation in Applied Catalysis
Authors: Maxwell I. E. , Lednor P. W.
Published: April 2011

This paper suggests that materials science is an important driver for innovation in applied catalysis. A wide range of catalytic materials is discussed in support of this thesis, with porosity as a common theme, and covering micro, meso and macro-porous materials. Applications of these materials is also wide-ranging, covering processes for the manufacture of fine chemicals or petrochemicals, and in oil refining, natural gas conversion and environmental processes. Further im-provents in the rate of innovation can be expected from new partnerships which are being formed, both at business and research levels.
Symmetry Breaking in the Transformation of Nanoporous Carbons Solids
Authors: Foley H. C. , Stevens Mark , Acharya Madhav , Kane Michael
Published: April 2011

Nanoporous carbons (NPC) or carbogenic molecular sieves (CMS) are unique materials that are able to produce shape selectivity for very precise molecular separations, such as that of oxygen from nitrogen on the basis of size. Surprisingly, the structure of NPC is globally amorphous. This seems at first irreconcilable, since regular transport behavior is expected to arise from regular porous solids such as zeolites and other crystalline molecular sieves. With this problem in mind as motivation, in this paper we describe some of the more intriguing aspects of the nanopore formation process. It is argued that at the nanoscale the NPC are both regular and structurally self similar, consisting of curved aromatic nanodomains that arise from the broken symmetry of hexagonal arrays. The symmetry breaking process is a direct result of the dissipation that takes place during pyrolysis leading to small molecules and a defect-laden carbogenic solid. In this context, some preliminary results illustrating how these NPC structures can be used to stabilize cesium for base catalysis and to prepare supported molecular sieve membranes for small molecule separations.
Dynamic Heterogeneity by Higher Moments of a Relaxing Quantity
Authors: Richert R.
Published: April 2011

A relaxation experiment usually acquires a measure for the mean energetic distance of the system from the thermodynamic equilibrium and its temporal evolution. For sufficiently small perturbations necessary to assure linear responses such data is bound to remain undecisive as regards the spatial nature of the relaxation process, heterogeneous or homogeneous. The technique of solvation dynamics near the glass transition can probe the entire distribution of site specific energies and its approach towards equilibrium, so that apart from the mean solvation energy v(t) also higher moments in terms of the inhomogeneous optical linewidth σinh(t) become accessible. While v(t) maps the dielectric relaxation behaviour of the liquid, σinh(t) is found to be sensitive to the spatial nature of the underlying process. Contrasting experiment and simulation leads to the conclusion, that the relaxation time is a site specific quantity, i.e. the heterogeneous nature is found to dominate.
Cooperative Length Scale of Aroclor Near its Dynamic Glass Transition
Authors: Rizos A. K. , Ngai K. L.
Published: April 2011

Photon correlation spectroscopy in the depolarized mode has been used to monitor the reorientational dynamics of Aroclor (A 1248) (polychlorinated biphenyls) that contain in solutions various amounts of low and high molecular weight (Mw) polymers. For the high Mw polymer/A1248 solutions we observe a very small dependence of the stretched exponential parameter β on temperature. In contrast, the low Mw polymer/A 1248 solutions display a pronounced temperature dependence of β. These preliminary experiments allow us to use the effect of modification of the solvent dynamics by added polymer to estimate the length scale of cooperative motion in glass forming systems from the size of the polymer chain.
Rotational Dynamics of a Molecular Probe in Tri-Cresyl Phosphate: From “Stick” to “Slip” Boundary Conditions
Authors: Bagliesi M. G. , Cianflone F. , Leporini D.
Published: April 2011

The rotational dynamics of a molecular probe dissolved in the glass-former tri-cresyl phospate has been studied by linear and non-linear Electron Spin Resonance spectroscopy. At the highest temperatures the Debye-Stokes-Einstein (DSE) law with stick boundary conditions holds. On cooling, a transition region is crossed and then a new regime sets in which is accounted for by the DSE law provided that slip boundary conditions are assumed. At the lowest temperatures the rotational diffusion and the shear viscosity are decoupled. The onset of the decoupling takes place close to Tc, the critical temperature predicted by the Mode Coupling Theory.
From Spin Glasses to Glasses
Authors: Bouchaud J. P. , Mezard M.
Published: April 2011

We discuss some aspects of the links between the behaviour and theory of spin glasses and that of structural glasses of the fragile type. We review the present status of the conjecture according to which a certain class of spin glass mean field theories (those with first order transitions) could provide a mean field theory for the glass transition. Recent developments pointing in that direction include the existence of spin glasses without disorder, and the general link between Mode-Coupling Theory (MCT) and the motion of a particle in a random potential. This link enables one to generalize the MCT equations for temperatures below the glass transition, and to describe aging effects. We compare these results with those obtained within more phonomonological ‘trap’ models.
Slow Dynamics in Supercooled Water
Authors: Sciortino Francesco , Tartaglia Piero , Gallo Paola , Chen Sow-Hsin
Published: April 2011

We review some recent results on the self-dynamics in deep supercooled (simulated) water, obtained by analyzing very long Molecular Dynamics simulations. We discuss the possibility of interpreting the observed slowing down of the dynamics in terms of Mode Coupling Theory for supercooled liquids and, at the same time, of associating the experimentally observed anomalies of the transport coefficients in water on lowering the temperature to the formation of long living cages. The so-called critical Angeli temperature TA in supercooled water could be interpreted as kinetic glass transition temperature, relaxing the need of a thermodynamic singularity for the explanation of the dynamic anomalies of liquid water. In the end we discuss the possibility that TA acts as cross-over temperature from fragile to strong liquid behavior.
The coupling model of relaxation: An alternative for the study of an interacting system of small particles
Authors: Castro J.
Published: April 2011

It is shown that the coupling model of relaxation accounts for the main experimental results of the magnetic relaxation in an assembly of interacting fine particles.
Dynamics at the Glass Transition in Polymers: Results from Neutron Spectroscopy
Authors: Richter D. , Arbe A. , Colmenero J.
Published: April 2011

This short review presents quasielastic neutron scattering and dielectric experiments on the α and βslow relaxation in polybutadiene and polyvinylchloride. Exploiting the momentum transfer dependent dynamic structure factor, spatial information about the underlying molecular motions is obtained. While the βSlow process reveals itself as a local jump with average jump distances of about 1.5 Å, the a relaxation is diffusive and occurs statistically independently from the βslow process. With this result a consistent interpretation of dielectric spectra on the same polymer is achieved. Finally some new results on the a process in PVC are presented.
Metastability and Properties of Metallic Bulk Glass Forming Alloys
Authors: Fecht H.-J.
Published: April 2011

Glasses are generally produced from the highly undercooled liquid state by rapid quenching methods or quasi-statically at slow cooling by the effective control of potent heterogeneous nucleation sites. For metallic systems the latter method recently has led to the development of bulk metallic glass with a complex multicomponent chemistry and advanced engineering properties. With these alloys crystallization can be avoided over a broad temperature / time window. As such, the relevant thermodynamic properties of the metastable glassy and undercooled liquid states can be directly measured below and above the glass transition temperature, respectively. The obtained data give new insight into the nature of the glass transition suggesting that it is not a phase transition in the classical sense but kinetic freezing triggered by an underlying entropie instability to avoid crystallization. Further measurements of the mechanical and wear properties point to the unique engineering properties of these highly disordered materials for technological applications.