bluuebunny/crossref_metadata_2025 huggingface dataset:
Europium doped CaF2 as a materials system for blue‐violet light emitting structures on Silicon
Authors: Chatterjee T. , Michellon C. , McCann P. J. , Fang X. M.
Published: April 2011

The electrical and optical properties of MBE grown Europium doped CaF2 layers onp‐ type Silicon (100) substrates reveal the possibility of using this materials system to fabricate light emitters on silicon. Low temperature MBE growth of the Eu:CaF2 layers permits the incorporation of up to 7.48 atomic weight % Eu in the epilayer without causing significant degradation of the layer ciystallinity. Strong room temperature photoluminescence in the blue‐violet spectral range has been observed in these samples, without any luminescence quenching even when the Eu concentration in the CaF2 epilayer is as high as 7.48 atomic weight percent. The current versus voltage data reveal that high current densities can be sustained through the Eu:CaF2 epilayers without causing catastrophic failure of the dielectric layer. Visible DC electroluminescence (EL) is observed by injecting electrons into Eu2+ doped CaF2 layers. High current densities up to ~50A/cm2 have been sustained through these materials with a DC bias of ~30 volts.
Safe Precursor Gas for Broad Replacement of SiH4 in Plasma Processes Employed in Integrated Circuit Production
Authors: Loboda M.J. , Seifferly J.A. , Grove C.M. , Schneider R.F.
Published: April 2011

Silane (S1H4), a pyrophoric gas, is the most widely used gas for the growth of dielectric films used in integrated circuit manufacturing. The industry has extensive experience in the handling of silane, but as process throughput continues to increase, so to do the concerns regarding safety and implementation issues involving this material. Trimethylsilane ((CH3)3SiH) is a non-pyrophoric organosilicon gas which can be used as a safe replacement for silane. Its material properties allow for standard packaging and quick integration into plasma deposition processes. The use of a non-pyrophoric gas will increase safety and process equipment uptime. By direct comparison to silane based processes, it is demonstrated that high quality films of silicon dioxide and silicon nitride can be deposited from trimethylsilane. In addition, hard, inert amorphous silicon carbide films can be deposited using the gas as a single precursor.
Gas Stream Analysis and PFC Recovery in A Semiconductor Process
Authors: Hoeymissen J.A.B. van , Daniels M. , Anderson N. , Fyen W. , Heyns M.
Published: April 2011

The performance of pressure swing adsorption (PSA) technology was assessed for recovering PFCs from the exhaust of a semiconductor plasma process. Several PSA process conditions were run to determine an optimized system. Under well defined conditions, the PSA technique was found to be effective at separating C2F6 from nitrogen, although the balance between recovery and product purity was evident. The exhaust of a plasma chamber was analysed by mass spectrometers and plasma etching conditions were varied to determine the effects on the PSA performance. A gas reactor column (GRC) was tested as pre‐treatment of the capturing system
Plasma Etching of Silicon Dioxide and Silicon Nitride with Non-Perfluorocompound Chemistries: Trifluoroacetic Anhydride and Iodofluorocarbons
Authors: Karecki Simon M. , Pruette Laura C. , Reif L. Rafael
Published: April 2011

Presently, the semiconductor industry relies almost exclusively on perfluorocompounds (e.g., tetrafluoromethane, hexafluoroethane, nitrogen trifluoride. sulfur hexafluoride, and. more recently, octafluoropropane) for the etching of silicon dioxide and silicon nitride films in wafer patterning and PECVD (plasma enhanced chemical vapor deposition) chamber cleaning applications. The use of perfluorocompounds (PFCs) by the industry is considered problematic because of the high global warming potentials (GWPs) associated with these substances. Potential replacements for perfluorocompounds are presently being evaluated at MIT. In an initial stage of the study, intended to screen potential candidates on the basis of etch performance, a large number of compounds is being tested in a commercially available magnetically enhanced reactive ion etch tool. The potential alternatives discussed in this work are trifluoroacetic anhydride (TFAA) and three members of the iodofluorocarbon (IFC) family – iodotrifluoromethane, iodopentafluorocthane, and 2-iodoheptafluoropropane. This paper will present the results of etch rate comparisons between TFAA and octafluoropropane, a perfluorinated dielectric etchant. Designed experiment (DOE) methodology, combined with neural network software, was used to study a broad parameter space of reactor conditions. The effects of pressure, magnetic field, and gas flow rates were studied. Additionally, more limited tests were carried out with the three iodofluorocarbon gases. Etch rate data, as well as Auger electron spectroscopy data from substrates exposed to IFC plasmas will be presented. All gases were evaluated using both silicon dioxide as well as silicon nitride substrates. Results indicate that these compounds may be potentially viable in plasma etching applications.
A Technique For Measuring Slurry‐Flow Dynamics During Chemical ‐ Mechanical Polishing
Authors: Coppeta J. , Rogers C. , Philipossian A. , Kaufman F.
Published: April 2011

Chemical‐Mechanical Polishing (CMP) is one of the fastest growing market segments in the semiconductor equipment industry. One of the critical consumable in CMP is a specialized solution, or slurry, which contains both free abrasives and chemicals acting together to planarize a wafer. These chemically active slurries account for approximately one fifth of the total cost of polishing a wafer. Because of the cost and potential toxicity, there are both financial and environmental pressures to reduce the amount of slurry consumed during the CMP process. To accomplish this in a systematic manner we have developed a technique for quantifying slurry flow patterns during CMP which involves using fluorescent dyes to measure slurry mixing, temperature gradients and slurry aging during the polishing. An aqueous fluorescent solution with matching viscosity is used to model the slurry, a glass window models the wafer and a commercially available polisher provides the polishing pad/table rotating work surface. This talk will focus on the diagnostic technique used to measure the slurry behavior as well as some semi‐quantitative results on both the amount and uniformity of slurry entrained beneath the wafer as a function of pad topography, injection location and pad rotation rates.
MBE Growth of InSb Based Device Structures onto InSb(111)A,(111)B and InGaSb(111)A Substrates
Authors: Johnson A D , Jefferies R , Pryce G J , Beswick J A , Ashley T , Newey J , Elliot C T , Martin T
Published: April 2011

We report on the optimum growth conditions for Molecular Beam Epitaxy (MBE) growth of InSb onto InSb (111)A and (111)B substrates. It was found that for (111)A substrates the optimum epilayer morphology was obtained for growth temperatures above 385°C and with a Sb:In ratio of 1.5:1. In contrast, for the (111)B surface, best morphology was found for growth temperatures above 385°C but with V:III ratio of ∼7.0:1. In both cases the dopant incorporation was found to be the same as the (100) surface and did not particularly depend either on V:III ratio or substrate temperature. We also describe the device characteristics of InAlSb light emitting diodes (LEDs) grown lattice matched onto ternary InGaSb(111)A substrates using the optimized growth conditions obtained.
In Situ Spectroscopic Ellipsometry for Monitoring and Control of HgCdTe Heterostructures Grown by Molecular Beam Epitaxy
Authors: Almeida L. A. , Bevan M. J. , Duncan W. M. , Shih H. D.
Published: April 2011

A major advantage of vapor phase epitaxial growth techniques is their flexibility to produce Hg1−xCdxTe layers with difFerent compositions from one run to the next, as well as the flexibility to produce compositional heterostructures of Hg1−xCdxTe in one process step. To take full advantage of this flexibility, reliable, automated control must be introduced. To this end, a phase-modulated spectroscopie ellipsometer (SE) has been implemented for use as a contactless wafer state sensor. In this work SE was used to monitor in real-time the stoichiometry of epitaxial Hg1–4CdxTe during growth by molecular beam epitaxy (MBE). SE has provided valuable information about the MBE growth process, by revealing even small fluctuations in x (± 0.002). In particular, SE has measured the compositional profiles of both LWIR/MWIR and MWIR/LWIR interfaces. Distinct profiles were revealed for interfaces created by abrupt changes in the CdTe effusion cell set-point and for interfaces created by ramping the cell temperature linearly. Ramping results in a smoothly graded interface, whose thickness may be pre-determined, though typically 2000 Å. An abrupt set-point change results in a sharper transition (∼300 Å) followed by oscillations in composition associated with the settling time of the cell (∼1500 Å). The thickness of a CdTe passivation layer grown on a LWTR layer was determined. The current status of the SE will be reported through other illustrative examples which demonstrate its utility as a diagnostic tool and as a sensor for realtime, feed-back control of the MBE process.
HgCdTe(211)B Grown on CdTe(211)B/ZnTe(211)B/Si(211) by MBE
Authors: Rujirawat S. , Wijewarnasuriya P. S. , Chen Y. P. , Aqariden F. , Sivananthan S.
Published: April 2011

We present preliminary results on HgCdTe(211)B layers grown on CdTe(211)B/ZnTe(211)B/Si substrates by molecular beam epitaxy. As-grown layers show excellent n-type characteristics as measured by Hall effect. Hall mibilities higher than 1×10 cm2/v-s have been measured at 40K for Cd composition ∼24% with doping level ∼ 3×1015 cm−3. Obtained RHEED patterns during the growth shows very smooth surface morphology.
Raman Scattering Study of H2O2-Etched Zn0.1Cd0.9Te Surfaces
Authors: Rai Brajesh K. , Katiyar R. S. , Chen K. -T. , Chen H. , Burger A.
Published: April 2011

Raman study of as-grown and H2O2-etched surfaces of Zn0.1Cd0.9 Te single crystal has been performed. A distribution of Te precipitates on the surface of as-grown ZCT, which increases after etching, has been encountered. With high irradiation powers, due to the oxidation of the surfaces, new bands of TeO32− are evolved. A downward shift in the peak position, as well as a halfwidth broadening, of all Raman modes has been observed with increasing laser power. The phenomenon, due to the formation of insulating oxide of tellurium in a dispersion of Te precipitates and vice-versa, has been attributed to the quantum confinement of phonons.
IR Sources and Modulators Based on InAs/GaSb/AlSb-Family Quantum Wells
Authors: Meyer J. R. , Felix C. L. , Malin J. I. , Vurgaftman I. , Lin C.-H. , Yang R. Q. , Pei S.-S. , Ram-Mohan L. R.
Published: April 2011

We review recent applications of wavefunction engineering to the design of antimonide quantum heterostructures with favorable properties for infrared devices. Examples include electro-optical and all-optical modulators based on Г-L intervalley transfer, type-II quantum well lasers with enhanced gain per injected carrier, and type-II interband cascade lasers predicted to combine low thresholds and high output powers.
Melt Growth of ZnGeP2: Homogeneity Range and Thermochemical Properties
Authors: Fiechter S. , Castleberry R. H. , Angelov M. , Bachmann K. J.
Published: April 2011

ZnGeP2 crystallized from the melt via horizontal gradient freezing shows the tendency to decompose into Ge and GeP when the equilibrium vapor pressure is not exactly controlled during the entire crystallization process. Using differential thermal analysis (DTA) it was found that ZnGeP2 has a truly congruent melting point of 1311 K. Adding small amounts of the elements and binaries in the ternary system Zn-Ge-P to stoichiometric ZnGeP2 a significant deflection of the liquidus curve was observed at the melting point of ZnGeP2- From DTA, X-ray diffractometry (XRD), photoluminescence (PL), transmission and conductivity measurements it was concluded that the melt grown material was highly compensated. The presence of a broad acceptor and donor band in the band gap could be associated with phosphorous and zinc point defects in the crystal lattice. It is assumed that the defect concentrations are of the order 1019 cm−3.
Electron Paramagnetic Resonance and Photoluminescence Studies of Point Defects in Zinc Germanium Phosphide (ZnGeP2)
Authors: Setzler S. D. , Halliburton L. E. , Giles N. C. , Schunemann P. G. , Pollak T. M.
Published: April 2011

Electron paramagnetic resonance (EPR) has been used to monitor native defects, both acceptors and donors, in ZnGeP2 crystals grown by the horizontal gradient freeze technique. These active centers include singly ionized zinc vacancies (Vzn-), neutral phosphorus vacancies (VP0), and neutral phosphorus antisite defects (PGe0). The concentration of Vzn− acceptors correlates with the near-infrared optical absorption present in all ZnGeP2 crystals. A photoluminescence band near 1.4 eV is shown to be polarized and is attributed to donor-acceptor-pair (DAP) recombination. Preliminary time-decay measurements support this assignment. Observation of the EPR spectrum of Mn2+ is also reported.
Photoluminescence Study of p-ZnGeP2 Crystals
Authors: Rud Yurri V. , Yu Vasilii , Ohmer M. C. , Shunemann P. G.
Published: April 2011

Photoluminescence (PL) steady-state spectra of p-ZnGeP2 (ZGP) single crystals grown by high- and low-temperature directed crystallization have been investigated. It is determined that the long-wavelength component PL with a maximum in the interval 1.2–1.5 eV for different crystals quenched in the temperature range 77–300 K. The long-wavelength component PL are due to donor-acceptor pair transitions. At room temperature the short-wavelength PL with a maximum near 1.85 eV becomes the determining component. The nature of this band discussed. The use of low-temperature directed crystallization reduces the concentration of lattice defects in ZGP single crystals and opens up the new possibilities for increasing the conversion efficiencies of nonlinear devices.
Modeling of Be Diffusion in InGaAs Epitaxial Structures
Authors: Gautier S. , Koumetz S. , Marcon J. , Ketata K. , Ketata M. , Launay P.
Published: April 2011

The subject of this work is the simulation of Be diffusion during post-growth Rapid Thermal Annealing (RTA) of InGaAs epitaxial layers grown by Chemical Beam Epitaxy (CBE). This diffusion may occur during thermal treatments of InGaAs/InP Heterojunction Bipolar Transistors (HBT's), which contributes to limit the frequency performances of these devices. In order to characterize the Be depth profiles, Secondary Ion Mass Spectrometry (SIMS) has been used. The concentration dependent diffusivity has been covered to perform an improved data fitting of Be diffusion profiles. In a first step, the solid state diffusion mechanisms have been developed, including the Substitutional-Interstitial Diffusion (SID) and, in particular, Kick-out mechanism. To explain the observed concentration profiles and related diffusion mechanisms, a Generalized Substitutional-Interstitial Diffusion model is proposed. A simultaneous diffusion by Dissociative and Kick-out mechanisms is suggested. Good agreements between experimental depth profiles and simulated curves have been obtained.
Room Temperature led's for the MID-Infrared Based on in(AS,SB) Strained Layer Superlattices
Authors: Phillips C. C. , Tang P. J. P. , Puliin M. J. , Hardaway H. R. , Chung S. J. , Yuen W. T. , Stradling R. A. , Li Y. B. , Hart L.
Published: April 2011

Arsenic-rich InAs/InAs1−x Sbx strained-layer superlattices (SLS's) are studied in time-resolved optical, and CW magneto-optical spectroscopies. A pronounced type-II offset, with electrons confined to the alloy layers, is found. High radiative efficiencies at wavelengths well into the mid-IR, and the suppression of Auger recombination yield LED's operating at 3–10 μm. Present room temperature powers are ∼30 μW, probably limited by inadequate carrier confinement.
Theoretical Performance of MID-IR Broken-Gap Superlattice Quantum Well Lasers
Authors: Flatté Michael E. , Grein C. H. , Olesberg J. T. , Boggess T. F.
Published: April 2011

We will present calculations of the ideal performance of mid-infrared InAs/InGaSb superlattice quantum well lasers. For these systems several periods of an InAs/InGaSb type-II superlattice are grown in quantum wells. Calculations of the non-radiative and radiative lifetimes of the carriers utilize the full non-parabolic band structure and momentum-dependent matrix elements calculated from a semi-empirical multilayer K · P theory. From these lifetimes, threshold current densities have been evaluated for laser structures. We find serious problems with the hole and electron confinement in the superlattice quantum wells grown to date, and propose a four-layer superlattice structure which corrects these problems.
Low-Loss, Broadened-Waveguide, High-Power 2-μm AlGaAsSb/InGaAsSb/GaSb Separate Confinement Quantum-Well Lasers
Authors: Menna R. J. , Garbuzov D. Z. , Martinelli R. U. , Lee H. , York P. K. , Connolly J. C. , Narayan S. Y.
Published: April 2011

(Al, In)GaAsSb/GaSb MQW lasers with a broadened waveguide have been used to fabricate 2-μm diode lasers with CW output power of 1.2 W. 2-μm linear arrays have output powers of 11 W and an efficiency of 0.13 W/A.
New Low Temperature Phases of Tungsten Oxynitride Stabilized by Doping with Fe, Co, and Ni
Authors: Chen F. , Aitken J. , Parasher S.
Published: April 2011

Several low temperature tungsten-containing oxynitride phases were isolated and stabilized by doping with Fe, Co, and Ni. These Phases have the rocksalt structure and form around 420 °C by reacting MWO4 (M=Fe, Co, Ni) with dry ammonia. They served as intermediates in the formation of the hexagonal ternary nitrides (MWN2). X-ray powder diffraction analyses of these phases indicate that W0.62(NO) could be the parent structure type in each case. The incorporation of group VIIIB elements in the W0.62(NO) structure may play an important role in the formation and stabilization of these low temperature phases.
A Priori Prediction of Crystal Structures
Authors: Brown I. D.
Published: April 2011

The arrangement of atoms in a crystal is determined by two factors, the bonding preferences of individual atoms (giving rise to short range order), and the translational symmetry operations of the space group (giving rise to long range order). Chemical rules can be used to determine which atoms are bonded, and hence the maximum possible symmetry of the formula unit. Space group theory is then used to find the space groups that are compatible with this symmetry. In favourable cases, using the principle of maximum symmetry, the structure can be completely determined, but in all cases the analysis yields insights into the restrictions that determine what crystal structures might be possible.
Effect of Chemistry and Structure on Voltage of Li Intercalation Oxides
Authors: Aydinol M. K. , Ceder G. , Kohan A. F.
Published: April 2011

With the aid of today's powerful computers, quantum mechanical methods are becoming accurate enough to determine the properties of materials before going into laborious and expensive synthesis processes. These “computer experiments” do not require any input other than the atomic numbers of the constituent species. In addition, they allow full control over the “experimental” parameters. In this way the effect of any parameter on the materials properties can be investigated, which is usually not possible in traditional experiments.

We used the ab initio pseudopotential method to study the effects of chemistry and structure on the voltage obtained from intercalating Li ions into transition metal oxides. The effect of transition metal and anion chemistry was systematically studied by changing M in LiMO2, (M=Ti, V, Mn, Co, Ni, Cu and Zn) and X in LiCoX2 (X=Se, S and O), keeping the structure fixed at α-NaFeO2 layered structure. In addition, the effect of structure was studied by performing computer experiments on LiCoO2 and LiMnO2 in α-NaFeO2, LiScO2 and Al2MgO4(spinel) structures.

The computed voltages are in good agreement with experimental values. We found that, the electronic band structure and the extent of charge transfer between Li and O ions is correlated to the output voltage. We will explain how the output voltage is affected by the chemistry of the transition metal.
Lattice Dynamical Prediction of the Elastic Constants of Diamond
Authors: Reeber Robert R.
Published: April 2011

The thermophysical properties of diamond, a metastable material at room temperature, are difficult to measure at high temperatures. These properties are of interest for testing equation of state and interatomic potential models. Here we utilize a geometrical lattice transformation, one dimensional lattice dynamical theory, and the principle of corresponding states to calculate the elastic constants of diamond over an extended temperature range.
Crystal Growth at Low Temperatures - Solvothermal Synthesis and Crystal Structures of Two Mercury Tellurides
Authors: Li Jing , Chen Zhen , Kelley Jamal L. , Proserpio Davide M.
Published: April 2011

Two mercury tellurium compounds [Mn(en)3]2Hg2Te9 and {[Mn(en)3]2Cl2}(Hg2Te4) have been synthesized at 180°C by solvothermal reactions using ethylenediamine as solvent. Single crystal X-ray diffraction analyses show that both compounds crystallize in monoclinic system, space group P21/c (no. 14) with four formula units in the unit cell. The cell dimensions are: a = 12.019(1) Å, b = 28.731(4) Å, c = 18.267(4) Å, β = 98.04(1)°, V = 6246(2) Å3 for [Mn(en)3]2Hg2Te9 and a = 15.720(3) Å, b = 16.812(3) Å, c = 15.224(3) Å, β= 114.31(1)°, V = 3668(1) Å3 for {[Mn(en)3]2Cl2}(Hg2Te4).[Mn(en)3]2Hg2Te9 contains pseudo one-dimensional chains of weakly bound (Hg2Te9)4− Zintl anions. The structure of {[Mn(en)3]2Cl2}(Hg2Te4) contains one-dimensional chains of Zintl anion 1∞ [(Hg2Te4)2−] formed by linking five-membered rings Hg2Te3 through bridging Te atoms. In both structures ethylenediamine incorporates into the manganese complex cation as bidentate ligand.
Layered Cuprates
Authors: Salvador P. A. , Otzschi K. , Zhang H. , Mawdsley J. R. , Greenwood K. B. , Dabrowsi B. M. , Marks L. D. , Mason T. O. , Poeppelmeier K. R.
Published: April 2011

Layered copper-oxide superconductors exhibit the highest critical transition temperatures of any materials. Yet all of the known double perovskites A′A″B′B″O6 containing copper have a random or rock salt distribution of the B cations with the exception of the unique layered arrangement found in La2CuSnO6. Only the layered arrangement contains the CuO22- planes which are necessary for high-temperature superconductivity. The occurrence of layered or two dimensional structures increases markedly when vacancies are introduced on the oxygen sublattice, as evidenced in Ln2AEmCu2TimO5+3m (Ln = lanthanide, Y: AE = Ba, Ca: 2 ≤ m ≤ 4). Similarities among oxygen-deficient structures, especially those with two-dimensional solid-state features, are discussed. Combined conductivity and thermopower analysis are presented to elucidate their unique internal chemistry, defect structure, and conduction parameters. In particular, data for La2-xSrxCuSnO6 are presented and related to the crystal chemistry of the copper-oxygen layer. These data are compared with La2Ba2Cu2Sn2O11 and La2Ba2Cu2Ti2O11 to illustrate the significance of oxygen vacancies on the properties of the copper oxygen planes. New layered cuprates are discussed including the mixed A-site stoichiometries Ln′Ln″AEmCu2TimO5+3m (Ln = lanthanide, Y: AE = Ba, Ca: 2 ≤ m ≤ 4) which contain the smaller lanthanide (Ln″) ordered between the closely spaced, facing sheets of Cu-O square pyramids.
Controlled Temperature Coefficient of Dielectric Constant Through Phase Transformation in (Ba, Sr)(Mg1/3Ta2/3)O3
Authors: Nagai T. , Sugiyama M. , Sando M. , Niihara K.
Published: April 2011

A structural phase transformation from hexagonal to monoclinic has been found in an ordered perovskite compound (Ba, Sr)(Mg1/3Ta2/3)O3, (BSMT). The transformation temperature of BSMT increases and the dielectric constant also changes from 24 to 27 with an increase in Sr concentration. The temperature coefficient of the dielectric constant is also changed with the variation of Sr content. In order to apply BSMT for practical use of dielectric resonators these changes in the dielectric properties, which is dominated by the phase transformation, must be controlled. In order to clarify the relation between the dielectric constant change and the structural phase transformation, phonon mode of BSMT has been studied using Raman spectroscopy. Change in the Raman spectrum of BSMT is classified into four steps. The first and the fourth steps correspond to the phase transformation. The change in the phonon mode detected by Raman spectroscopy is discussed in connection with the structural change.
Fabrication and Dielectric Properties of Phase-Pure Ba2Ti9O20 Microwave Resonators
Authors: Lin Wen-Yi , Gerhardt Rosario A. , Speyer Robert F. , Hackenberger Wesley S. , Shrout Thomas R.
Published: April 2011

The thermal processing schedules necessary to form phase pure Ba2TigO20, with and without substitutional solid solution were investigated. Undoped compositions formed the compound most easily under rapid (500°C/min) heating rates, where diffusional agglomeration of the. TiO2 batch constituent was minimized. The compound formed most easily with minor (0.82%) substitutions of SnO2 and ZrO2 for TiO2. The solubility of Sn in Ba2Ti9O20 was higher than that of Zr. Extended heat treatment (16 vs. 6 h at 1390°C) resulted in volitalization of grain boundary liquid phase, leading to a more porous and slightly degraded resonators. The effects of dopant concentrations and soak periods at 1390°C on dielectric constants and temperature-dependent quality factors are reported.
Defect Structure of the Mixed-Conducting Sr-Fe-Co-O System
Authors: Ma B. , Balachandran U. , Chao C.-C. , Park J.-H.
Published: April 2011

Electrical conductivity of the mixed-conducting Sr-Fe-Co-O system was investigated at elevated temperatures and various oxygen partial pressures (pO2). The system exhibits not only high combined electrical and oxygen ionic conductivities but also structural stability in both oxidizing and reducing environments. The conductivity of SrFeCo0.5Ox increases with increasing temperature and increasing pO2, within our experimental pO2 range (1 ≥ pO2 ≥ 1O-18 atm). p-type conduction behavior was observed. The activation energy of which increases with decreasing pO2. A model of the defect chemistry in the Sr-Fe-Co-O system is proposed. The pO2-dependent conducting behavior can be understood by considering the trivalent-to-divalent transition of the transition metal ions in the system.
Synthesis, Structure, Lattice Dynamics and Electrochemistry of Lithiated Manganese Spinel, LiMn2O4
Authors: Julien C. , Rougier A. , Nazri G. A.
Published: April 2011

We report synthesis, crystal structure, lattice dynamics, and electrochemical features of the lithiated manganese oxide spinel prepared through solid state reaction by careful selection of precursors and synthesis conditions. Elemental analysis shows that the material is a lithium-rich spinel phase. X-ray diffraction data and Rietveld refinement indicate formation of a single phase, impurity free, normal spinel of LiMn2O4. Lattice dynamics have been investigated by vibrational spectroscopy and group theoretical analysis has been carried out. Electrochemical performances of the lithiated spinel manganese oxide have been investigated, and the voltage profile of the cathode during lithium intercalation-deintercalation processes, close to equilibrium, has been obtained. The upper 4-volt plateau provides over 130 mA h/g with an excellent cyclability.
Solid-State Reactions in Model Oxide Systems
Authors: Johnson Matthew T. , Kotula Paul G. , Thompson Ryan S. , Barry Carter C.
Published: April 2011

The kinetics of thin-film solid-state reactions have been investigated in two model spinel forming oxide systems, NiO/Al2O3 and MgO/Fe2O3. In the NiO/Al2O3 system, thin-films of epitactic NiO were reacted with (0001), , and orientated Al2O3 (corundum). The kinetics of the spinel forming reaction for this system were found to be linear-parabolic in nature. Additionally, it was found that the kinetics of the spinel-forming reaction varied by nearly two orders of magnitude between the fastest and slowest diffusion couples. The substrate determines the orientation of the overlayers and thereby the structure of the phase boundaries. In the MgO/Fe-oxide system, thin films of epitactic Fe oxide were reacted with {001} MgO. The kinetics of this spinel forming reaction were parabolic in nature, indicative of diffusion control. In contrast to the N1O/Al2O3 system, the movement of phase boundaries are not the step controlling the reaction rate, but rather the diffusion of one of the cations across the reaction layer. In comparing the reaction rates for the two systems the activation energy for the formation of the spinel product in the MgO/Fe-oxide system was found to be almost a factor of 4 lower in comparison to the NiO/Al2O3 system.
Quantitative Interfacial Chemistry and Bonding in Ceramic Materials
Authors: Gu Hui
Published: April 2011

Internal interfaces, between the same phase (grain boundary) or two different phases, often play an essential role in controlling various properties in ceramic materials. Analysis of such interfaces can achieve various newly available quantitative information on a sub-nanometer scale, as well as bonding picture associated with these interfaces. This analysis combines EELS spectrum profiling and advanced near-edge structure (ELNES) data processing, taking advantage from both the high spatial and energy resolutions provided by a dedicated STEM instrument. Demonstrated by chemical and structural study of gram boundary and inter-phase interfaces in Si3N4 ceramics where ∼1 ran thick amorphous phases cover every crystalline boundaries, it reveals that the amorphous boundary films are substantially different to bulk amorphous phase and to the interface between crystalline and amorphous phases. Moreover, the boundaries between two different crystalline phases were found covered with two thin amorphous layers of different composition and bonding. These observations can shed further light on the influence of interfaces on the macroscopic properties of these ceramic materials. This interfacial analuysis method can be extended to broader research area in solid state physics and chemistry.
Surface Stability of Siderite Under Acidic Atmosphere: an Atomic Force Microscopy Study
Authors: Weaver R. M. , Grandstaff D. E. , Myer G. H.
Published: April 2011

The reactivity of siderite (FeCO3) was investigated under ambient atmosphere and acidic aerosols using an atomic force microscope (AFM). Scans of freshly cleaved siderite crystals showed a relatively irregular microtopography, consisting of high-density kink-steps, compared to other isostructural carbonates (e.g. Iceland-spar calcite). Under ambient conditions siderite is inert with no spontaneous surface reconstruction as is reported for calcite. Under controlled conditions of pH and humidity, siderite was exposed to mists of HC1 and H2CO3 and the reaction was imaged with submicron resolution. The kinetics of the reaction varied with pH, humidity levels, and also as a function of the initial microtopography. Preferential growth and dissolution were observed as a function of initial topography and due to crystallographic anisotropies. Although extreme reaction conditions were excluded by certain aspects of AFM (high capillary forces, tip corrosion, charged surface), this technique has allowed real-time, in situ observations of surface reactions.
Influence of Hydrogen Incorporation and Oxygen Removal on Superconducting YBa2Cu3O7-δ
Authors: Hirata T.
Published: April 2011

The influence of hydrogen incorporation and oxygen removal on superconducting YBa2Cu3O7-δ is discussed in comparison with their respective effects. Both hydrogen incorporation and oxygen removal induce the orthorhombic (O)-to-tetragonal (T) transition and antiferromagnetic ordering as well. However, there exist no consistent changes in the c-axis for the O-to-T transition and the superconducting transition temperature Tc upon hydrogen incorporation in YBa2Cu3O7-δ on the other hand, the c-axis certainly increases in the corresponding transition driven by oxygen nonstoichiometry and Tc decreases with increasing δ in YBa2Cu3O7-δ. Plots of Tc vs. the lattice parameter c reveal no significant suppression in Tc upon hydrogenation than oxygen removal. It is concluded that the Cu-O bond distances or the Cu-Cu plane spacings along the c-axis change somewhat differently in two cases; it is believed that the charge-carrier concentration is reduced less significantly upon hydrogenation than oxygen removal in YBa2Cu3O7-δ, giving rise to the aforementioned finding.
Application of a Knowledge-Based Expert System for Assisting in Catalyst Design
Authors: Körting E. , Baerns M.
Published: April 2011

The prototype expert system ESYCAD (expert system for catalyst design) was set up for assisting in the design of heterogeneous catalysts. It selects materials as catalyst components which have all required properties for the various (elementary) steps of a target reaction but which do not catalyze undesired side reactions. If necessary, also secondary catalytic components or promoters are selected; furthermore, reaction conditions are proposed if required by catalyst properties. The application of the system is illustrated by examples for CO-hydrogenation, alkane dehydrogenation, and for oxidative coupling of methane.
A Micro-Raman Study of Niobium Titanium Oxide Powders Obtained by Laser-Induced Synthesis
Authors: Depero L. E. , Sangaletti L. , Bontempi E. , Salari R. , Casale C. , Musci M. , Notaro M.
Published: April 2011

Microraman and scanning electron microscopy studies have been performed on pure TiO2 and Nb-Ti-O nanopowders obtained by laser induced synthesis. The effect of Nb content on the temperature of the anatase to rutile phase transformation, induced by annealing in air at different temperatures, has been evidenced and related to the changes in the particle size distributions obtained from a Fourier analysis of the X-ray diffraction patterns.
Rapid Thermal Response Catalyst for Treatment of Automotive Exhaust
Authors: Carter Robert N. , Roychoudhury Subir , Muench George , Karim Hasan , Pfefferle William
Published: April 2011

To meet the increasingly strict automobile emissions requirements for conventional vehicles, considerable improvements in catalyst technology are required. It is now recognized that a primary challenge in meeting the ultra-low emissions vehicle standards (ULEV) for automobiles is in reducing cold-start emissions, and this generally requires a catalytic converter that has a rapid temperature response. Conventional converters (typically made from ceramic or metal monoliths) have a relatively slow temperature response due to their high thermal mass and limited heat transfer characteristics. We present details of a novel catalyst technology (Microlith™) that offers considerable advantages for this application because of greatly enhanced heat and mass transfer characteristics. Results of performance tests are also presented that demonstrate this catalyst's effectiveness. The effects of thermal aging on microstructure and catalyst performance are also discussed.
Enhanced Catalytic Performances by Desilication and Subsequent Steam Treatment of ZSM-5 Zeolite
Authors: Le Van Mao R. , Borsuk N. , Ohayon D. , Ramsaran A. , Le S. T. , Denes G.
Published: April 2011

Controlled desilication of ZSM-5 zeolite increases the acid site density of its acid form. A subsequent treatment with steam at 300 °C results in a material with single-sized and slightly larger micropores when compared to the parent zeolite. This is likely the cause of a second increase of the yields of MTBE (methyl terbutyl ether) and ethylene when the steamed desilicated zeolite is used as catalyst in the MTBE synthesis and ethanol dehydration, respectively. Steam appears to be capable of “healing” the zeolite framework at a temperature much lower than that normally required when the desilicated ZSM-5 zeolite is solely heated in air.
Mesoporous Activated Carbon Filaments
Authors: Lu Weiming , Chung D. D. L.
Published: April 2011

Activated carbon filaments of diameter ∼0.1 μm, main pore size (BJH) 55 Å, specific surface area 1310 m2/g and yield 36.2% were obtained by activating carbon filaments of diameter ∼ 0.1 urn in C02 + N2 (1:1) at 970°C for 80 min. Prior to this activation, the filaments were surface oxidized by exposure to ozone.
1/f Dielectric Fluctuations at the Glass Transition
Authors: Israeloff N. E. , Wang W.
Published: April 2011

The temperature and frequency dependence of thermal dielectric polarization noise was investigated in glycerol and PVC in the vicinity of their glass transitions. Polarization fluctuations were observed via voltage noise which was produced within a sample capacitance cell. The high sensitivity and accuracy of the technique provides a powerful probe of dynamics in low-loss regimes of various materials. Noise spectra had 1/fβ form at lower temperatures just below the glass transition. In glycerol, the spectral exponent decreased smoothly with temperature, extrapolating to 1, i.e. 1/f noise, near T° where relaxation times diverge. The results support the idea that a glassy phase transition occurs in the static limit.
Protein Dynamics from Intramolecular Electron Transfer
Authors: Nienhaus G. U. , McMahon B. H. , Müller J. D. , Wraight C. A.
Published: April 2011

Proteins are complex systems that share essential properties with viscous liquids and polymers. Structure, dynamics, and function of proteins are strongly interrelated, and structural and dynamic aspects can be revealed by studying protein function. Here we report measurements of the kinetics of intramolecular electron transfer (ET) from the primary quinone (QA) to the special pair (P) of reaction center (RC) proteins from Rhodobacter sphaeroides as a function of temperature (5 to 300 K) and illumination protocol (cooled in the dark and under illumination from 280 K). From the data, information about structural heterogeneity, relaxations and fluctuations of these molecules is obtained.
Intermediate Range Order in Sodium Tellurite Glasses
Authors: Zwanziger J. W. , McLaughlin J. C. , Tagg S. L.
Published: April 2011

Information about the spatial distribution of sodium cations in sodium tellurite glasses is obtained from the decay rate of sodium spin echoes. The spin echoes decay due to the magnetic dipole coupling between sodium nuclei, with each pair contributing to the rate in proportion to 1/r6, where r is the distance between the pair. The experiment is used to probe the sodium distributions in sodium tellurite glasses as a function of sodium oxide content, and the resulting distance distributions are interpreted by comparison with model distributions. At low sodium contents the distribution is similar to that of a random model in which the sodium ions are constrained to be no closer than a minimum cut-off distance. At higher contents the distributions deviate significantly from the random model, suggesting the onset of medium range order in the distribution of sodium ions. This order is most pronounced at 20% sodium oxide content, the composition at which this glass has been claimed to have maximum stability against devitrification.
Effect of Size Dispersity on the Melting Transition
Authors: Sadr-Lahijany M. R. , Ray P. , Harrington S. T. , Stanley H. E.
Published: April 2011

We present a molecular dynamics simulation study of the liquid-solid transition in a two dimensional system consisting of particles of two different sizes interacting via a truncated Lennard-Jones potential. We work with equal number of particles of each kind and the dispersity Δ in the sizes of the particles is varied by changing the ratio of the particle sizes only. For the monodisperse case (Δ = 0) and for small values of Δ, we find a first order liquid-solid transition on increasing the volume fraction p of the particles. As we increase Δ, the first-order transition coexistence region weakens gradually and completely disappears at high dispersities around Δ = 0.10. At these values of dispersity the high density phase lacks long range translational order but possesses orientational order with a large but finite correlation length. The consequences of this effect of dispersity on the glass transition and on the melting transition in general are discussed.
Liquid-Liquid Phase Separation of Melts and Glasses in Ferric Ferrous Oxide-Silica System
Authors: Yasumori A. , Koike A. , Kameshima Y. , Okada K. , Yano T. , Yamane M. , Inoue S.
Published: April 2011

The existence of liquid-liquid miscibility gap in ferric ferrous oxide-silica system has been reported, however, the phase separation phenomena and the derived morphology of the phase separated glasses are uncertain. In this study, the melt-quenched samples of 5 Fe3O4-95 SiO2 and 15 Fe3O4-85 SiO2 (mol%) were prepared by melting at 2300°C or 2200°C (expected to be above miscibility gap), and subsequently at 1800°C or 1750°C (in immiscible region) by use of infrared image furnace and quenching at the rate of ≈102 K/sec. The glassy materials exhibited phase separation having discrete spherical particles or interconnected structure due to the composition, melting temperature and time. Also, the segregation of Fe component occurred during melting, which was caused by the difference of specific gravity of components in the melt.
Optical Spectroscopy of Pentavalent Chromium Ions in Glass
Authors: Yuan Huabiao , Jia Weiyi , Cohen D. , Yen W. M. , Aitken B. G.
Published: April 2011

In this work, we report the first spectroscopie observation of octahedrally coordinated pentavalent chromium ions in BaCaMg aluminate glasses. A broad band emission peaking at 780 nm with band width of 3000 cm−1 has been observed at 12K. The measurements of fluorescence decay, time-resolved emission and excitation spectra reveal that the emission band is an overlapped luminescence originating from both the 2E to 2T2 transition of octahedrally coordinated Cr5+ and a charge transfer transition of Cr6+O4 groups.
Formation and Properties of Amorphous and Nanocrystalline Phases in Mechanically Alloyed Fe-Based Multicomponent Alloys
Authors: Schlorke N. , Eckert J. , Schultz L.
Published: April 2011

Multicomponent Fe-Al-P-C-B alloys have been prepared by mechanical alloying of elemental powder mixtures. X-ray diffraction data were recorded to monitor the structural development of the powders. Coexistent amorphous and nanoscale crystalline phases are found for a variety of alloys. Some alloys exhibit an extended supercooled liquid region before crystallization. The compositional dependence of glass formation and the thermal stability of the resulting phases were investigated by constant-rate heating differential scanning calorimetry (DSC), isothermal annealing experiments, and thermomechanical analysis (TMA). The results are compared with data for melt-spun ribbons.
Tendency and Scale of Chemistry and Bonding Changes at SrTiO3 Grain Boundaries by Fe Segregation
Authors: Gu Hui
Published: April 2011

Using a new EELS analysis method the local chemical and structural changes induced by Fe segregation to two types of grain boundaries in SrTiO3 were studied. At Σ5 boundary in bicrystals Fe segregation lowers O/Ti ratio but increases substantially Ti and O concentrations in boundary region. Sr-O bond has been severely changed by the segregation as revealed by ELNES. Grain boundaries in a polycrystalline sample were covered with titania-based amorphous films where Fe content is higher but Ti and O concentrations are both lower than the bulk levels, which are strikingly different from the bicrtysal. More dopants segregated to glass pockets at triple junctions. SiO2 was detected in one of the large pocket but not at the grain boundary films within the detection limit. These observations suggest the equilibrium defect chemistry and the related space charge theory may not be the only explanation for the grain boundary segregation in SrTiO3 Local structure modification at gram boundaries can trigger dramatical change of the chemistry to a degree higher than the segregation level. The existence of titania-based amorphous films at general grain boundaries makes it better to understand Fe segregation from the two phase (SrTiO3-TiO2) equilibrium.
The Adhesion Nature of Ag/MgO Interface: Hartree-Fock Study
Authors: Heifets E. , Kotomin E. A.
Published: April 2011

The atomic and electronic structure of the Ag/MgO interface are calculated using the ab initio Hartree-Fock approach and a supercell model. The electronic density distribution is analyzed in detail for isolated and interacting slabs of a metal and MgO. The energetically most favorable adsorption position for Ag atoms is found to be above the O atoms. The binding energy is 0.20 eV (0.41 eV) for one and three Ag layers atop MgO substrate, respectively. The relevant equilibrium Ag-O distance is 2.64 Å(2.41 Å). Neither appreciable charge transfer in the interfacial region, nor considerable population of bonds between the silver layer and the insulating substrate take place. The adhesion energy arises mainly due to the electrostatic interaction of substrate atoms with a complicated charge redistribution in the metal monolayer, characterized by large quadrupole moments and electron density redistribution towards gap position in the middle of nearest Ag atoms.
Analysis of Adhesion and Interface Debonding in Laminated Safety Glass
Authors: Sha Y. , Hui C. Y. , Kramer E. J. , Garrett P. D. , Knapczyk J. W.
Published: April 2011

A tension adhesion test is developed to measure the adhesion of a polymer interlayer to the glass plates in laminated glass. The polymer adhesive is bonded between two cracked glass plates and is loaded under a remote tension P. Typically, a peak load P* exists and its value depends on the adhesion between the polymer interlayer and the glass. The peak load P* is often used to characterize the adhesion strength of the interface. The experimental data is analyzed using a micromechanical model of debonding and simulated using finite element computation. Our analysis allow us to determine the shear and normal strength of the interface and the relation between the peak load and the mechanism of debonding.
Wheel Abrasion Experiment Metals Selection for Mars Pathfinder Mission
Authors: Hepp Aloysius F. , Fatemi Navid S. , Wilt David M. , Ferguson Dale C. , Hoffman Richard W. , Hill Maria M. , Kaloyeros Alain E.
Published: April 2011

A series of metals was examined for suitability for the Wheel Abrasion Experiment, one of ten microrover experiments of the Mars Pathfinder Mission. The seven candidate metals were: Ag, Al, Au, Cu, Ni, Pt, and W. Thin films of candidate metals from 0.1 to 1.0 micrometer thick were deposited on black anodized aluminum coupons by e-beam and resistive evaporation and chemical vapor deposition. Optical, corrosion, abrasion, and adhesion criteria were used to select Al, Ni, and Pt. A description is given of the deposition and testing of thin films, followed by a presentation of experimental data and a brief discussion of follow-on testing and flight qualification.