bluuebunny/crossref_metadata_2025_split huggingface dataset:
Defects in Low—Temperature—Grown MBE GaAs
Authors: Look David C. 
Published: March 2011

AbstractDefect concentrations in molecular beam epitaxial (MBE) GaAs range from 1012 to 1020 cm-3 as the growth temperature is lowered from 600 to 200 °C; however, very high quality layers can be grown over this whole range. The dominant defect is the As antisite, but there is also good evidence for As interstitials and gallium vacancies. The particular form of the As antisite center in low—temperature (LT) MBE GaAs is not known at this time, but it is definitely not EL2, because both the thermal activation energy and the electron capture cross section differ significantly. However, other features, such as the EPR spectrum and metastable—to—normal recovery kinetics are identical to those of EL2. The donor (As antisite) to acceptor ratio seems to hold at about one order of magnitude as growth temperature is varied from 200 — 400 °C; thus, the Fermi level stays near mid—gap over this whole range. However, hopping conduction among the As antisite centers is strong for samples grown between 200 and 300 °C and keeps the material from being semi—insulating, while for those grown between 350 — 480 °C, the resistivity is greater than 107 Ω cm. The annealing dynamics are particularly interesting and include such features as the mobility going through a sharp maximum at an annealing temperature of 400 °C for a layer grown at 200 °C. The donor and acceptor concentrations can be determined both by Hall effect and absorption measurements as the layer is annealed up to 600 °C. Above 550 °C, large precipitates are formed. The relative roles of the precipitates and point defects in influencing compensation, lifetime, and device characteristics are a source of much controversy and will be discussed.
Clusters and the Nature of Superconductivity in Ltmbe-GaAs
Authors: Bert N.A. , Chaldyshev V.V. , Goloshchapov S.I. , Kozyrev S.V. , Kunitsyn A.E. , Tretyakov V.V. , Veinger A.I. , Ivonin I.V. , Lavrentieva L.G. , Vilisova M.D. , Yakubenya M.P. , Lubyshev D.I. , Preobrazhenskii V.V. , Semyagin B.R. 
Published: March 2011

AbstractThe structure and properties of GaAs layers grown by molecular-beam epitaxy at low temperature (150-250 °C) have been studied. The samples were found to contain up to 1.5 at.% extra As, which formed nano-scale clusters under annealing. The dependences of the excessive As concentration and As-cluster size and density on the growth and annealing conditions were established. LT-GaAs layers were found to have high electrical resistivity, however, our investigations of microwave absorption in a weak magnetic field revealed a characteristic signal usually attributed to the superconducting phase. It has been proved that this microwave absorption is unlikely to be due to either the arsenic clusters in LT-GaAs films or indium in the substrate, as it was assumed previously. We suggest a new hypothesis that the superconducting phase in LT-GaAs is Ga nanoclusters formed on the growth surface.
Effects of Defects in GaAs/AlGaAs Quantum Wells
Authors: Russo O.L. , Rehn V. , Nee T.W. , Dumas K.A. 
Published: March 2011

AbstractHigh Resolution transmission electron microscopy (HRTEM) and electroreflectance (ER) were used to explain the role of point defects in the molecular beam epitaxy (MBE) grown PIN structure containing five coupled (50Å/28Å) GaAs/AlxGa1−xAs quantum wells with x = 0.25. The ER data were taken at 300K and 77K for energies from 1.4 to 2.1 eV from which sub-band energy transitions were determined. Data at 300K showed three transitions whereas four were readily resolved at 77K. HRTEM data determined the uniformity of both the wells and barriers to be within ± 2Å, which neither caused appreciable broadening nor a decrease in the transition probability. However, the data at different temperatures suggest that point defects may be responsible for the decrease in the transition probability.
Temperature and Polarization Dependence of the Optical Absorption in ZnGeP2 at two Micrometers
Authors: Shah M. , Ohmer M. C. , Fischer D. W. , Fernelius N. C. , Manasreh M. O. , Schunemann P. G. , Pollak T. M. 
Published: March 2011

AbstractThe temperature and polarization dependence of the optical absorption in ZnGeP2 at two micrometers is reported for the first time over the temperature range from 10K to 300K. The radiation was normally incident upon the face of a cubic sample which contained the c-axis. The absorption of o-rays (E parallel to c), and erays (E perpendicular to c) was determined. It was found that the e-ray absorption coefficient was always significantly larger than the o-ray absorption coefficient and that it had a less significant temperature dependence. For example, the ratio of e-ray to o-ray absorption coefficient was approximately two at 300K and five at 77K. Correspondingly the o-ray absorption coefficients were reduced upon cooling to 77K by a factor of 2.5, while the e-ray absorption coefficients were reduced only slightly (10%-20%). These results indicate that for Type I optical parametric oscillators (OPOs) which use an oray pump beam, that performance may be improved by cooling the crystal.
A Tight-Binding Theory of the Electronic Structures for Rhombohedral Semimetals and Sb/GaSb, Sb/AlSb Superlattices
Authors: Xu J.H. , Wang E.G. , Ting C.S. , Su W.P. 
Published: March 2011

AbstractThe band structures of three group-V semimetals As, Sb, and Bi with rhombohedral A7 symmetry are studied using a second-neighbor tight-binding model including spin-orbit interaction with an sp3s* basis. Then the bulk tight-binding parameters are used to investigate the electronic properties of semimetal-semiconductor superlattices made of alternating (111) layers of Sb and GaSb or AlSb. It is found that the band gap can be adjustable depending primarily on the thickness of the Sb layers. An interface state is observed in the region of the gap.
Cathodoluminescence Spectroscopy Studies of Growth Induced Deep Levels at GaInP.
Authors: Enrique Viturro R. , Varriano John D. , Wicks Gary W. 
Published: March 2011

AbstractWe report a cathodoluminescence spectroscopy study of growth-induced deep levels at GaInP epilayers grown by Molecular Beam Epitaxy under various conditions. This approach allows the identification of deep levels which appear to play an important role in the band to band radiative recombination efficiency of these GaInP films. Control of these electronic defects is crucial for the performance of visible optoelectronic devices.
Fabrication of Quantum Wires by Wet Etching Techniques
Authors: Yang H. W. , Horng S. F. , Hwang H. L. 
Published: March 2011

AbstractQuantum Wires Structures Were Fabricated By Patterning Quantum Well Samples With Electron Beam Lithography And Various Wet Chemical Etching Procedures. Wire Structures With 800Å Wire Width Were Achieved By Wet Etching In Nh4Oh / H2O2/ H2O (20:7:973). These Samples Were Characterized By Scanning Electron Microscopy (Sem), Photoluminescence (Pl), And Polarization-Dependent Photoluminescence Excitation (Ple) Measurements. The Pl Spectra Show Significantly Strongpr Peaks Than That Taken From An En-Etched Quantum Well Sample. A Wire Width Of 400Å Was Estimated From The Blue Shift Of Pl Peaks. A 22% Anisotropy Was Observed From Polarization-Dependent Ple Spectra, Further Corroborating The Existence Of Two-Dimensional Quantum Confinement.
The Organometallic Chemical Vapor Deposition of Transition Metal Carbides: the Use of Homoleptic Alkyls
Authors: Healy Matthew D. , Smith David C. , Rubiano Rodrigo R. , Springer Robert W. , Parmeter John E. 
Published: March 2011

AbstractThe organometallic chemical vapor deposition (OMCVD) of transition metal carbides (M = Ti, Zr, Hf, and Cr) from tetraneopentyl-metal precursors has been carried out. Metal carbides can be deposited on Si, A120 3, and stainless steel substrates from M[CH 2C(CH3)3]4 at temperatures in the range of 300 to 750 "C and pressures from 10-2 to 10-4 Torr. Thin films have also been grown using a carrier gas (Ar, H2). The effects of variation of the metal center, deposition conditions, and reactor design on the resulting material have been examined by SEM, XPS, XRD, ERD and AES. Hydrocarbon fragments generated in the deposition chamber have been studied by in-situ mass spectrometry. Complimentary studies examining the UHV surface decomposition of Zr[CH2C(CH3)3]4 have allowed for a better understanding of the mechanism leading to film growth.
Synthesis and Characterization of a New Ternary Transition Metal Nitride, FeWN2, from the Transition Metal Oxide Precursor, FeWO4
Authors: Bem David S. , Houmes Joel D. , Loye Hans-Conrad Zur 
Published: March 2011

AbstractThe ternary nitride, FeWN2, has been synthesized via ammonolysis of the transition metal tungstate, FeWO4. FeWN2 is hexagonal with a unit cell of a = 2.8724(1) Å and c =10.973(4) A. Rietveld refinements were performed in the space group P3–1C with Rwp=9.91%, and Rp=7.23%. The structure consist of alternating octahedrally coordinated iron-nitrogen layers and trigonal prismatically coordinated tungsten-nitrogen layers. Mössbauer data at 250K indicates an isomer shift δ=0.85 and shows no quadrupole splitting, which is consistent with the octahedral iron coordination in the proposed structure.
New Organosilicon Polymers for Ceramics Applications
Authors: Seyferth Dietmar , Strohmann Carsten , Dando Neal R. , Perrotta Anthony J. , Gardner James P. 
Published: March 2011

AbstractThe preparation, characterization and pyrolytic conversion to silicon-containing ceramics of two types of polymers – a series of poly(ureidosilazanes) and poly(silylenecarbodiimides) – are described. The former appears to have some promise as a preceramic polymer.
Oxygen Sinks in SiC-Based Ceramics
Authors: Braue Wolfgang , Chowdhury K. Das , Carpenter Ray W. 
Published: March 2011

AbstractDuring an HREM/AEM investigation, two different oxygen sinks were identified for a variety of SiC-ceramics involving different sintering mechanisms: segregation of oxygen to i) internal interfaces, and ii) “excess-carbon” secondary phases consisting of basically turbostratic graphite and an intermediate amorphous Si-C-O phase. Si-C-O glasses and polycarbosilanebased nonstoichiometric SiC materials (Nicalon fibers) are well suited as model systems to evaluate the structure and the stability range of the amorphous Si-C-O phase in SiC-based ceramics.
Synthesis and Characterization of Nanophase Metal, M and Metal Carbide, M2C Particles of The Group 6 Elements, Cr, Mo and W.
Authors: Zeng D. , Hampden-Smith M. J. 
Published: March 2011

AbstractReduction of MCln, n = 3 for M = Cr, Mo, n = 4 for W with LiBEt3H in THF results in formation of nanometer-sized crystalline metal carbide, M2C particles whereas the same reduction reaction in toluene results in formation of the corresponding metal particles. As an example of this methodology, the reduction of MoC13(THF)3 and WC14 in THF by Li/C10H8 is described in detail. Reduction of MoC13(THF)3 in THF by Li/C10H8 resulted in formation of a black suspension from which black powder can be isolated. Electron diffraction and X-ray powder diffraction data showed the black powder is amorphous. Energy dispersive spectroscopy confirmed the presence of molybdenum, and no chlorine was detected. Ex-situ variable temperature X-ray powder diffraction experiments showed the presence of fec Mo2C which upon further heating underwent a phase transformation to hexagonal Mo2C. Crystalline molybdenum was also observed after heating to 750°C for 3 hours. Reduction of WC14 in THF by Li/C10H8 results in formation of a black powder which on heating underwent phase transitions from amorphous to fcc W2C to hexagonal W2C as determined by X-ray powder diffraction.
Microstructure and Mechanical Properties of Hot-Pressed and Pressureless Sintered WC-Al2O3 Ceramic Composites
Authors: Endo Hidehiro , Ueki Masanori 
Published: March 2011

AbstractFully densified WC-A12O3 composites were successfully consolidated by both hot-pressing and pressureless sintering. The optimum hot-pressing condition for the composites was 1700°C for 2h under a pressure of 40MPa. A remarkable improvement in mechanical properties was achieved in the composite system, especially in WC-30 and -70vol%A12O3, compared to the monolithic WC and A12O3 ceramics. The addition of MgO as a sintering aid had a great effect on the properties of the composites. WC-30vol%A12O3 composite with 1.Owt% MgO addition exhibited flexural strength higher than 1000MPa up to 1200°C, fracture toughness; KIC≥7MPa√m, and hardness; HV ≥2450. In pressureless sintering with the addition of MgO as a sintering aid and subsequent HIP treatment, the WC-30vol%A12O3 composite exhibited the flexural strength higher than 900MPa up to 1200°C.
Intercalation of Li into Single Crystals of MoS2
Authors: Papageorgopoulos C. A. , Jaegermann W. 
Published: March 2011

AbstractIn this paper we study in situ the intercalation of Li across and along the van der Waals planes of MoS2 single crystals. Li is intercalated according to the band model. The intercalation reaction is inhibited by a Li-S interaction. This interaction is negligible when Li is deposited along the van der Waals planes. The dominance of the intercalation reaction of Li into MoS2 is dependent on the flux of the deposited Li and the substrate temperature.
Conducting Polymer with Improved Long-Time Stability: Polyaniline-Polyelectrolyte Complex
Authors: Sun Linfeng , Yang Sze C. , Liu Jia-Ming 
Published: March 2011

ABSTRACTConducting polymers, e.g. polyaniline, generally lack stability in their electrically conductive form due to heat and moisture induced loss of dopant. Using a template-guided synthesis scheme, we synthesized a polymeric complex of polyaniline and polyelectrolyte that showed stability against dedoping by moisture and heat. The polymeric complex consists of a strand of polyaniline twisted tightly with a strand of polyelectrolyte. The polyelectrolyte in the complex serves as a macromolecular dopant for polyaniline. These two components of the complex are tightly bound so that the dopant is not lost during tests for thermal stability and stability in water and Moisture. Since the dopant is a polyelectrolyte with high linear anion charge density, the complex resists deprotonation by water or weak base (pH < 10).
Electrically Conducting Compatible Blends Of Polyaniline / Poly (Vinyl Pyrrolidone)
Authors: Stockton William B. , Rubner M. F. 
Published: March 2011

ABSTRACTBlending polyaniline (PAn) with a host polymer has the advantage of reducing the amount of polyaniline necessary for conductivity, increasing the stability of this conduction, and enhancing the overall mechanical integrity, versatility, and processability of PAn. PAn blends have generally been observed to be immiscible, reducing many of the above mentioned advantages. In this work, PAn was solution blended with poly (vinyl pyrrolidone) (PVP) in either NMP or DMAc, both polar solvents with an amide linkage. We have found PAn to be miscible with PVP under certain processing conditions. The extent of this compatibility and resulting mechanical properties were assessed by DMA, DSC, TGA, SAXS, and light Microscopy. DSC thermograms exhibit a single Tg for all blends ranging from 3 to 30 % by weight PAn. Light Microscopy and SAXS also suggest no phase separation. TGA results show that NMP binds very tightly to both PAn and PVP, with solvent cast blends retaining up to 20 wt% NMP, even after relatively vigorous drying. Electrical conductivity measurements of cast films show conductivity to range from 10-3to 2 S/cm over the same composition range.
Electrophysical Properties of Iodine Doped Acetylene/Ethylene Copolymers
Authors: Aleshin A. N. , Guk E. G. , Marikhin V. A. , Myasnikova L. P. , Belov D. G. 
Published: March 2011

ABSTRACTA new oxydative-resistant, fusible and processible ethylene/acetylene copolymer has been synthesized. The content of rigid (acetylene) and flexible (ethylene) fragments has been widely varied. The structure of the nascent powders and the films compressed at room temperature have been investigated by SEM and WAXS. DSC has been used for studying the thermal properties. DC conductivity of the iodine doped samples has been measured as a function of temperature. It is shown that the doping leads to arising conductivity in the samples even at 10 Mol % acetylene fragments in copolymer. The conductivity up to 10−3 S/cm is reached for the samples with acetylene fragment concentration about 20 Mol %. It is found that a charge carrier transport in investigated copolymers is caused by doped polyacetylene fragments and described by the hopping Mechanism.
Optical And Magnetic Properties Of Rigid Rod Conjugated Molecules
Authors: Wautelet P. , Le Moigne J. , Turek P. 
Published: March 2011

ABSTRACTA series of new stable fiinctionalised aryl ethynyl compounds bearing nitronyl-nitroxy and galvinoxyl radicals were synthesised as potential organic magnets with optical properties. Our goal is to construct biradicals in linear or broken rod molecules with the aim of probing i) the efficiency of the conjugation for the intramolecular spin exchange, and / or ii) the inter-Molecular Magnetic interaction between the neighboring radicals in the solid state Materials.We focused our attention on the preparation of phenoxy, and galvinoxyl biradicals of the conjugated phenyl and thienyl diethynyl Moieties. The synthesis of these new components will be presented. Their optical and magnetic properties will be discussed both in solution and in the solid state.
Cyano-Derivatives Of Poly (P-Phenylene Vinylene) For Use In Thin-Film Light-Emitting Diodes
Authors: Greenham N. C. , Cacialli F. , Bradley D. D. C. , Friend R. H. , Moratti S. C. , Holmes A. B. 
Published: March 2011

ABSTRACTConjugated polymers can be use to provide charge transport and emissive layers in a range of thin-film electroluminescent devices. Electroluminescence results from radiative decay of excitons which are formed by electron-hole capture. Device efficiency is particularly sensitive to the balancing of electron and hole currents injected from opposite electrodes, and this is best achieved at the heterojunction between two polymer layers with different electronegativities. We report here the properties of a conjugated polymer with high electron affinity, a cyano derivative of poly (p-phenylene vinylene), PPV. This polymer shows an electron affinity considerably higher than than that of PPV, and is therefore suitable for use as the electron transporting layer in heterostructure LEDs. It shows efficient photoluminescence due to radiative decay of singlet excitons, and photoinduced absorption in the IR, similar to that in PPV, which we attribute to excitations of photogenerated triplet excitons. EL devices formed with a heterojunction between PPV and this cyano derivative of PPV, with indium/tin oxide as positive electrode, PPV, cyano-PPV layers and an aluminium negative electrode, show internal quantum efficiencies as high as 4%.
Thermally Stable Poled Polymers: Highly Efficient Heteroaromatic Chromophores In High Temperature Polyimides
Authors: Jen Alex K-Y. , Wong K. Y. , Pushkara Rao V. , Drost K. , Cai Y. M. , Caldwell B. , Mininni R. M. 
Published: March 2011

ABSTRACTIn this paper, we report our recent developments in achieving thermally stable polyimides that possess large second order nonlinear optical activity. We have developed several classes of novel chromophores based on the combination of efficient thiophene conjugating units and novel electron-donating and electron-accepting functional groups. Through these developments, we have synthesized chromophores that possess non-resonant βμ values as high as 9,100 × 10−48 esu measured at 1.9 μm. These chromophores also possess improved thermal and chemical stabilities. The incorporation of these chromophores in high temperature polyimides produces E-O Materials with high linear electro-optic coefficients (in excess of 15 pm/V at 1.3 μm) and long-term temporal stability at an elevated temperature of 150°C for more than 800 hours.
Novel Experimental Protocol for Studying Temporal Decay of Second-Order Nonlinear Optical Polymer Properties: Quantitative Analysis of Coupling to Polymer Dynamics and Conditions for Temporal Stability
Authors: Dhinojwala Ali , Hooker Jacob C. , Torkelson John M. 
Published: March 2011

ABSTRACTA new experimental approach has been developed which allows characterization of rotational dynamics of NLO chromophores in amorphous polymers over 12 decades in time, from 10-6 to 106 sec. Measurements over such a broad distribution in relaxation times are important not only in determining how the chromophore orientational dynamics are coupled to polymer dynamics but also in making accurate predictions of the temporal stability of technological interest. In particular, accurate characterization over a broad range of time scales reveals that NLO polymers meet technological requirements more easily than is predicted using a less complete characterization.
Photonic Polymers For Optical Switching
Authors: Horsthuis Winfried H.G. 
Published: March 2011

ABSTRACTPhotonic polymers and devices with improved performances are reported. Optical losses in electro-opic polymers below 0.5 dB/cm at 1.3 and 1.6 μm have been realized. IMprovements in thermal stability have led to poled polymers exhibiting a relaxation time of 1 12 days at 125°C. The thermo-optic switches reported here are close to the requirements in telecommunications, and electro-optic devices with low switching voltages and high extinction coefficients are described as well.
Relaxation Phenomena in Poled Electro-Optic Polymers
Authors: Singer K. D. , Dureiko R. , Khaydarov J. , Fuerst R. 
Published: March 2011

ABSTRACTThe relaxation of the nonlinear optical coefficient of poled electro-optic polymers remains an important issue in the potential application of these Materials. This relaxation is due to the homogenization of the orientational distribution function of nonlinear chromophores in the polymer glass over time. We have measured the relaxation using optical second harmonic generation as a function of temperature for doped polymer materials over a range of temperatures deep in the glassy state. We relate the data to widely used physical models of the glassy state which indicate that the relaxation process occurs over a considerable range of time scales. It has been found that the decay of the nonlinear polarization exhibits two mechanisms depending on the time and temperature scales over which measurements are performed. We have carried out measurements over a range of times and show that a broad distribution of relaxation times characterizes the data. This broad distribution is an appealing model in that it not only fits the data well, but is well connected to accepted physical models of the relaxation behavior of glasses. The characteristic energy of the relaxation can be estimated from the temperature dependence and is found to be equal to or less than the energy characterizing the polymer Motion, and agrees with dielectric studies. This indicates that the chromophores are more or less coupled to the dynamics of the polymer chain. A figure of merit for the coupling of the chromophore to the polymer chain is proposed.
Blue Second-Harmonic Light Generation From A New Organic Single Crystal, 8-(4′-Acetylphenyl)-1,4-Dioxa-8-Azaspiro[4.5]Decane(Apda)
Authors: Sagawa Masakazu , Kagawa Hiroyuki , Kakuta Atsushi , Kaji Makoto 
Published: March 2011

ABSTRACTA new second-order nonlinear optical organic Material, 8-(4′-acetylphenyl)-l,4-dioxa-8-azaspiro[4.5]decane (APDA) was synthesized as a frequency doubler emitting blue light. Its crystal growth, linear and non-linear optical properties were evaluated. The APDA crystal has a short cutoff wavelength of 384 nm and high nonlinear optical coefficients d33=50 pm/V and d32=7 pm/V. The crystal is phase matchable below wavelengths of 800nm, and its maximum effective nonlinear coefficient is 14.9 pm/V. Type I phase-Matched second harmonic generations can be carried out with YAG and Ti-sapphire laser pumping.