bluuebunny/crossref_metadata_2025_split huggingface dataset:
Infra-Red Tunneling Absorption in Semiconductor Double Quantum Wells in Tilted Magnetic Fields
Authors: Lyo S. K. 
Published: April 2011

ABSTRACTUsing a linear response theory, interwell-tunneling absorption of infra-red photons is calculated in a double-quantum-well structure with a wide center barrier in tilted magnetic fields. Tunneling occurs between the ground sublevels of the two quantum wells, with an energy difference that is tunable. The absorption intensity depends strongly on the temperature and the carrier densities. The resonance width is narrow even at high temperatures due to the two-dimensional phase restriction for tunneling. In magnetic fields, both the in-plane and perpendicular components of the field sensitively control and tune the absorption lineshape in very different ways, affecting the absorption threshold, the resonance energy of absorption, and the linewidth.
Resonant-Cavity Infrared Devices
Authors: Pautrat J. L. , Hadji E. , Mula G. , Bleuse J. , Magnea N. 
Published: April 2011

ABSTRACTThe CdxHg1−x Te compounds are well suited to the design of semiconducting devices incorporating an optical microresonator since they display a wide variation of bandgap and refractive index with composition x, while the lattice parameter remains practically unchanged. It is then possible to create a specific optical function by stacking high quality pseudomorphic layers on a crystalline substrate.Microcavities resonating in the 3–5 μm range have been made by growing a lower Bragg mirror (10.5 periods) and a nominally undoped cavity medium containing a 50 nm active layer (CdTe-HgTe pseudo-alloy). The upper mirror is a gold layer deposited on the cavity. The emission of these Resonant Cavity Light Emitting Diodes has been observed in the 3–4.5 μm range up to room temperature. It coincides with the cavity resonance mode (linewidth 8 meV). With the addition of a ZnS/YF3 upper mirror, a Vertical Cavity Surface Emitting Laser at 3.06 μm has also been demonstrated.The microcavity concept appears to be very useful for designing new devices for the 3–5 μm range.
Spectroscopic Ellipsometry Study of HgCdTe Epilayer Surfaces During Electron Cyclotron Resonance Plasma Etching
Authors: Johnson J. N. , Dinan J. H. , Singley K. M. , Martinka M. , Johs B. 
Published: April 2011

ABSTRACTSpectroscopie ellipsometry has been used to monitor optical characteristics of HgCdTe surfaces during plasma etching in an electron cyclotron resonance reactor. Commonly used process conditions were found to induce changes in the ellipsometric parameters Δ and φ. A model was constructed to account for these changes in terms of process-induced roughness and mercury depleted sub-surface layers An independent characterization of the near-surface region was earned out ex situ after etching using Auger spectroscopy and x-ray photoelectron spectroscopy. Plasma process parameters were varied to isolate their influence on surface conditions and a set of parameters is given for which changes are minimized.
InAsSb/InAlAsSb Quantum-Well Diode Lasers Emitting Between 3 and 4 μm
Authors: Turner G. W. , Choi H. K. , Manfra M. J. , Connors M. K. 
Published: April 2011

ABSTRACTRecently, mid-infrared diode lasers fabricated from the antimonide-based III-V compounds have been receiving increased attention for potential applications in trace gas detection, spectroscopy, pollution monitoring, and military systems. In this paper we will report the growth, fabrication, and modeling of high performance diode lasers with wavelengths longer than 3 μm. Molecular beam epitaxy (MBE) has been employed for the growth of these Type-I, strained quantum-well (QW) laser structures on GaSb and InAs substrates. The lasers consist of compressively strained InAsSb wells, tensile-strained InAlAsSb barriers, and lattice-matched AlAsSb cladding layers. QW lasers grown on GaSb substrates, with emission wavelengths of ∼3.9 μm, have operated pulsed up to 165 K. At 80 K, cw power of 30 mW/Facet has been obtained. Ridge-waveguide lasers have operated cw up to 128K. QW lasers grown on InAs substrates have emission wavelengths between 3.2 and 3.55 μm. Broad-stripe lasers on InAs have exhibited cw power of 215 mW/facet at 80 K, pulsed threshold current density as low as 30 A/cm2 at 80 K, characteristic temperatures (TO) between 30 and 40 K, and maximum pulsed operating temperature of 225 K. Ridge-waveguide lasers on InAs have cw threshold current of 12 mA at 100 K, and a maximum cw operating temperature of 175 K. In this paper we will present some of the key issues regarding the MBE growth, fabrication, and modeling of such lasers and discuss future directions for improved device performance.
Composition of the Equilibrium Vapor Phase Over ZnGeP2 and Thermal Stability
Authors: Rechter S. , Kurzweil A. , Castleberry R. H. , Bachmann K. J. 
Published: April 2011

ABSTRACTZnGeP2 can be transported by chemical vapor transport (CVT) using phosphorus or ZnP2 as transporting agent. Since germanium has a seven order of magnitude smaller partial pressure than zinc and phosphorus solely the formation of a volatile GePy (y≥l) species can explain the CVT-growth which was observed in a temperature range from 973 to 1573 K. To stabilize this species phosphorus pressures in the bar range are needed. Using absorption spectroscopy to analyze the equilibrium vapor phase composition over P, GeP and ZnGeP2, absorption lines were found adjacent to P2 band heads in the wavelength range from 180 to 260 nm which were addressed as band heads of an unknown GePy species. Quadrupole mass spectroscopy (QMS) measurements revealed that this species is not stable at lower pressures decomposing presynthesized GeP and ZnGeP2 in a Knudsen cell. In the temperature range from 550 to 800 K at total pressures of 10−7 to 10−6 mbar, ZnGeP2 decomposes into Zn and P4 whereas Zn is the dominant gas phase species. Under vacuum ZnGeP2 starts to decompose at 600 K while in a N2 atmosphere decomposition occurs at 923 K. By adding ZnP2 (5mg/cm3) to polycrystalline ZnGeP2, which was placed in an evacuated and closed quartz glass ampoule, red transparent crystals were yielded in a temperature gradient ΔT= 1073–1023 K.
Integrated All-Optical Devices Fabricated Using Area-Selective Disordering of Multiple Quantum Well Structures
Authors: LiKamWa Patrick , Kan'an Ayman , Dutta Mitra , Pamulapati Jagadeesh 
Published: April 2011

ABSTRACTWe describe a method of silicon oxide capped disordering of GaAs /AlGaAs multiple quantum wells (MQW) and its application to the fabrication of passive waveguides integrated with nonlinear switching sections. The silicon oxide cap in this work was formed by spinning a solution of glass forming compound and curing it. The characteristics of the disordering process has been studied by monitoring the shift of the photoluminescence as a function of rapid thermal annealing temperature and fitting the n=1 electron heavy-hole level to that calculated from an error function diffusion profile. Our results indicate a Ga-Al inter-diffusion constant of 8×10−16 cm2s−1 at 980°C and an activation energy of 4.4eV which is similar to values reported by other researchers.The disordering process is then used to define selected areas of disordered and non-disordered MQWs and ridge waveguide structures were fabricated by conventional photolithography and wet chemical etching. Two structures have been studied. One is the nonlinear zero-gap directional coupler with disordered input and output branching waveguides, and the other is the symmetric nonlinear integrated Mach-Zehnder interferometer with one arm containing a non-intermixed MQW section. The devices investigated using a pump-probe set-up, exhibited strong all-optical switching behavior with a contrast ratio of 15:1.
LPE Growth of Mixed Composition HI-V “Virtual Substrates” for MID-Infrared Optoelectronic Devices
Authors: Mao Y. , Krier A. 
Published: April 2011

ABSTRACTLiquid phase epitaxy can be effectively used to grow a thick graded ternary or quaternary buffer layer to provide a “virtual substrate” for subsequent device epitaxy. Grading characteristics of InGaAs, InAsSb and InAsSbP epitaxial layers grown by LPE are discussed. The effects of the principal LPE growth parameters on epiiayer thickness, surface morphology and composition, lattice-mismatch and photoluminescence efficiency were investigated and are described.
Optical Characterization and Mapping of Four INCH InSb Epitaxial thin Films Grown on GaAs by Turbo Disk Metalorganic Chemical Vapor Deposition
Authors: Feng Z. C. , Beckham C. , Schumaker P. , Ferguson I. , Stall R. A. , Schumaker N. , Povioski M. , Whitley A. 
Published: April 2011

ABSTRACTA large number of 4 inch (100 mm) diameter 1–2 μm thick InSb films have been grown on GaAs by low pressure metalorganic chemical vapor deposition (MOCVD) turbo disk technology. Raman scattering microscopy was used to study the effects of III-V source ratios on the film crystalline quality and to optimize the growth parameters. Multi-point Raman measurements over the entire 4” wafer were performed to exhibit the uniformity distribution of the film crystalline quality. A FTIR reflectance mapping system has been established to map the film thickness distribution. Good uniformity of the film thickness and crystalline perfection was obtained. Raman and FTIR are showing useful tools for non-destructive characterization of large area wafers for industrial mass production.
Hydrothermal Synthesis of Novel Vanadium Oxides
Authors: Stanley Whittingham M. , Boylan Elizabeth , Chen Rongji , Chirayil Thomas , Zhang Fan , Zavalij Peter Y. 
Published: April 2011

AbstractExtending our prior work on tungsten and molybdenum oxides, we have found that a wide variety of vanadium oxides can be prepared using hydrothermal methods. These include a number of layer compounds as well as cluster complexes. The starting reaction medium usually contained vanadium pentoxide, an alkali containing compound such as LiOH, an organic template such as tetramethylammonium, and the pH of the whole was controlled by the addition of acid. Reaction temperature was 150°C to 200°C, and time was up to 3 days. A new lithium vanadium oxide, which has the simplest structure of any layered vanadium oxide, was formed. The lithium could be readily removed leading to a new form of vanadium dioxide. This vanadium oxide was also capable of intercalating a variety of other ionic and molecular species. Several other new vanadium oxides containing the TMA cation were also formed; one of these TMAV3O7 readily absorbed oxygen to form TMAV3O8. Addition of zinc or iron to the reaction medium caused the formation of layer structures containing double V2O5 layers; for iron the TMA was retained in the structure whereas for zinc the TMA was excluded. Changing the organic entity resulted in other new structures, for example methylamine and dimethylamine gave tetragonal structures.
Synthesis and Structure of a Metal-Organic Solid Having the Cadmium(II) Sulfate Net
Authors: Yaghi O. M. , Li Hailian , O'Keeffe M. 
Published: April 2011

AbstractReaction of silver(I) nitrate and hexamethylenetetramine (HMTA) gives crystals of Ag2(HMTA)(NO3)2, which was formulated by elemental microanalysis and a single crystal x-ray study. Its Ag2(HMTA) open-framework is the first example of a decorated CdSO4net. The relative orientation of the tetrahedral HMTA building blocks in this structure point to numerous opportunities toward constructing novel chiral and polar porous frameworks.
Hydrothermal Synthesis of Vanadium Oxides
Authors: Chirayil Thomas , Zavalij Peter , Stanley Whittingham M. 
Published: April 2011

AbstractThe pH of the reaction media is a critical factor in the formation of new vanadium oxides with the tetramethylammonium (TMA) ion via the conventional hydrothermal method. New vanadium oxides; TMAV3O7, Li0.6V2−δO4−δ·H2O and Li0.6V2−δO4−δ, TMAV4O10, and two more new vanadium phases with d spacings of 11.5Å and 19.1Å are formed as the pH is varied with acetic acid. The synthesis and characterization of TMAV3O7, a new vanadium oxide with tetramethylammonium ions residing between its layers is discussed. The intercalation of alkylamines, DMSO, and water into Li0.6V2−δO4−δ·H2O is described. Microwave hydrothermal synthesis is a new and alternate soft chemistry technique used to accelerate the synthesis of TMAV4O10. This method also aided in the formation of a new cluster compound, [Li(H2O)4]2TMA(V10O28)·4H2O.
Nonstoichiometry and Doping of Zinc Oxide
Authors: Sleight Arthur W. , Wang Ruiping 
Published: April 2011

AbstractContrary to the commonly accepted model, we conclude that the zinc interstitials in Zn1+xO are not ionized. Instead, the electron pair associated with the interstitial zinc is trapped in a metal—metal bond. The increase in conductivity on initial reduction of zinc oxide is associated with impurities such as silicon which are compensated by extra oxygen unless removed by reduction. Zinc oxide powders and thin films were prepared with the dopants B, Al, Ga, In, and Ge. By using high temperatures and highly reducing conditions, conductivities 1000 times higher than previously reported for powders were obtained for some of our powders.
Layered CMR Manganites: Structure, Properties, and Unconventional Magnetism
Authors: Mitchell J. F. , Argyriou D. N. , Potter C. D. , Jorgensen J. D. , Hinks D. G. , Bader S. D. 
Published: April 2011

AbstractNeutron powder diffraction studies of the layered compounds R1.2Sr1.8Mn2O7, (R = La,Pr, Nd), RSr2Mn2O7 (R = Pr,Nd),and La1.4Sr1.6Mn2O7 show that the degree of distortion of the MnO6 octahcdra do not correlate with the appearance of a metal-insulator (MI) transition in these compounds. Instead, the in-plane Mn-O bond length appears to be a better indicator of the electronic behavior. Detailed bulk magnetization studies on single crystal La1.2Sr1.8Mn2O7 show thai there are three magnetic regimes as a function of temperature: paramagnetic insulator, short-range ordered (SRO) fcrrromangct, and long-range ordered (LRO) fcrromagnct. Scaling analysis indicates that a 2D finite-size XY model is an appropriate description of the magnetic state in the SRO regime.
Lithium Doping in La2CuO4 and La2NiO4
Authors: Sarrao J. L. , Torelli M. E. , Fisk Z. 
Published: April 2011

AbstractWe have studied the effect of hole doping via Li substitution in La2CuO4 and La2NiO4. The response to hole doping of the Ni (S=1) sublattice is distinct from that of the Cu (S=1/2) sublattice. These effects are seen most clearly for La2Cu0.5Li0.5O4 and La2Ni0.5Li0.5O4 in which the Li ions form an ordered superlattice. It appears that Ni is in a low-spin d7 configuration whereas Cu is in a d9-ligand “Zhang-Rice” configuration. Despite this difference, the response of both La2CuO4 and La2NiO4 to hole doping is surprisingly independent of whether Sr (which substitutes out of plane for La) or Li (which substitutes in the plane for Cu/Ni) is used as the dopant.
Layered 3-D Ferromagnets and Antiferromagnets, M2+(ReO4)2 (M = Mn, Fe, Co, Ni, Cu): Importance of Dipolar Interactions
Authors: Torardi C. C. , Reiff W. M. , Dodrill B. C. , Vogt T. 
Published: April 2011

AbstractPowder samples of the anhydrous compounds M2+(ReO4)2 (M = Mn, Fe, Co, Ni, and Cu) were prepared. All have trigonal symmetry, except M = Cu which is Jahn-Teller distorted to monoclinic symmetry, I2/m. Single crystals of the Fe and Cu compounds were grown by vapor transport and their layered structures determined. Ferromagnetism, deduced from ac susceptibility and dc magnetization studies, is exhibited by the Fe (TCurie = 8.5 K), Co (TCurie = 4.7 K), and Ni (TCurie = 12.5 K) phases. They show 2-D ferromagnetic (intralayer) interactions as well as a 3-D ferromagnetic (interlayer) ground state with both of these effects obvious in the heat capacity of Ni(ReO4)2. Low-temperature powder neutron diffraction confirms the ferromagnetism of Ni(ReO4)2 below 12 K, and also reveals a structural phase transition occurring between room temperature and 77 K. The origin of the 3-D ferromagnetic ground states of the Fe, Co, and Ni perrhenates is the result of dipolar interlay er interactions, as opposed to superexchange between the layers. Susceptibility results of the Cu perrhenate indicate intralayer ferromagnetism and any long-range 3-D order occurring at T ≤ 1.5 K. The Mn compound is antiferromagnetic.
Consequences of Fluorine Atom Bridging and Increasing Metal Atom Spin Density for the Low Temperature Magnetism of the Series. Na3[FeF6],[NH4]3[FeF6], [Co(NH3)6][FeF6] and [NH4CoFeF6]
Authors: Reiff W. M. , Kweicien M. J. , Subramanian M. A. 
Published: April 2011

AbstractAspects of the low temperature magnetism of some distorted cryolite-like compounds of high-spin iron III, namely Na3[FeF6], [NH4]3[FeF6] are presented. The behavior of these systems is compared to iron-57 Mössbauer spectroscopy and ac-susceptibility results for the related [Co(NH3)6][FeF6] and the modified pyrochlore [NH4CoFeF6] obtained via thermolysis of [Co(NH3)6][FeF6] under nitrogen.
Correlation Between Structural Parameters, Polarisabilities and Dielectric Properties in Non-Ferroelectric Complex Perovskites
Authors: Colla E. L. , Setter N. 
Published: April 2011

AbstractA combination of different empirical methods which allow the prediction of the dielectric properties of non-ferroelectric complex perovskites has been proposed and its present limits verified. The long term purpose is to engineer new microwave materials with increased relative permittivity ε0 and low thermal coefficient of the resonant frequency τf.The estimation of the dielectric properties has been accomplished by means of structural predictions based on the tolerance factor and a microscopic model. Furthermore, the optical permittivity based on the Gladstone-Dale relation and the total polarisability according to the molecular/ion additivity rule were also estimated. Ceramics of new compositions were then fabricated and analysed to verify the dielectric properties predicted by the empirical methods. Results show good agreement with the expected structural features and optical permittivities, and the method is sufficiently reliable to estimate the end values, or at least to estimate trends of the dielectric properties induced by partial substitution of cations on site A. The importance of the electronic polarisability on the end value of τε has been demonstrated.
Effect of Divalent Dopants on Properties of Ba3.75Nd9.5Ti18O54 Microwave Dielectric Resonators
Authors: Ubic R. , Reaney I. M. , Lee W. E. , Samuels J. , Evangelinost E. 
Published: April 2011

AbstractPellets in the ternary solid-solution Ba6–3xNd8+2xTi18O54 (x=0.75) have been processed to near theoretical density by mixed-oxide synthesis, and their dielectric properties determined to be εr≈89, Qf> 10,000, and τf≈+60ppm/°C at microwave frequencies. Similar ceramics with Ca, Sr, and Pb partially substituted for Ba were also processed and analysed. Both Ca and Sr were found to increase εr to 100–105 but significantly lower Qf and inflate τf. While Pb substitution also lowered Qf, it had no significant effect on εr and beneficially suppressed τf to values from -16 to +8ppm/°C, tunable with Pb content, strongly suggesting that these materials may be useful for commercial applications.
On the Structures of Mo2O5(OCH3)2 and Mo2O5(OCH3)2 ·2CH3OH
Authors: McCarron E. M. , Harlow R. L. , Li Z. G. , Suto C. , Yuen Y. 
Published: April 2011

AbstractThe reaction of molybdenum trioxide dihydrate, MoO3·2H2O, with methanol produces the title compounds. That these molybdenum oxy-methoxides decompose with liberation of CH2O suggests that they represent exquisite models for selective oxidation of methanol to formaldehyde over molybdate catalysts. While a number of physical techniques have been employed to elucidate certain of their structural aspects, unfortunately, the detailed structures of these materials remain unknown. Problems, both physical and crystallographic, encountered in attempts to determine these structures are discussed. Also discussed is the recent progress made by employing the complimentary nature of electron and powder diffraction techniques.
Electrochemical Characterization of Mixed Conducting Ba(Ce1-(x+y)PryGdx)O3-x/2 Cathodes
Authors: Mukundan R. , Davies P. K. , Worrell W. L. 
Published: April 2011

ABSTRACTThe high protonie conductivities of barium cerium gadolinium perovskites (Ba(Ce1-xGdx)O3-x/2, O < x < 0.2) has led to their incorporation as electrolytes in fuel cells operating at 873–1073K. In an effort to develop new mixed-conducting electrodes that are compatible with the cerate electrolyte, we have examined the electrochemical properties of Pr-doped barium gadolinium cerate. The Pr doping increases the electronic contribution to the total conductivity and for Ba(Ce0.5Pr04Gd0.1)O2.95, a conductivity exceeding ≈ 0.1 S/cm at 1173K in dry air has been obtained. EMF measurements indicate the presence of both protonie and oxygen ionic contributions to the conductivity in the Pr substituted samples. The cathodic overpotentials of Ba(Ce1-(x+y)PryGdx)O3-x/2 mixed conductors on a Ba(Ce0.8Gd0.2)O2.9 electrolyte have been measured. Ba(Pr0.8Gd0.2)O2.9 has the best cathodic performance and could be a viable alternative to Pt cathode for a barium cerate based fuel cell.
Conduction Properties of Na+-ion Implanted Glass-Ceramics in the System Na2O-R2O3-P2O5-SiO2 (R=Rare Earth)
Authors: Okura Toshinori , Tanaka Miki , Sudoh Giichi 
Published: April 2011

AbstractThe glass-ceramics of the phosphorus containing Na5RSi4O12type (R=rare earth) Na+-superionic conductors (Narpsio-V) in the system Na2O-Sm2O3-P2O5-SiO2 were prepared by crystallization of glasses with the composition Na3+3x-ySm1-xPySi3-yO9. The optimum conditions for crystallization were discussed with reference to the conduction properties and the preparation of uncracked bulky glass-ceramic Narpsio-V. The ionic conductivity of the glass-ceramic Na3.9Sm0.6P0.3Si2.7O9 at 300°C was drastically enhanced from 2.38×10-2 S/cm to 7.15×10-2 S/cm upon implantation of 200 keV Na+ ions to a fluence of 1 × 1015 cm-2.
Predominant Factors of Lithium Ion Conductivity in Perovskite-Type Oxides
Authors: Inaguma Y. , Katsumata T. , Yu J. , Itoh M. 
Published: April 2011

AbstractThe relation between the structure and the lithium ion conductivity in perovskite-type oxides ABO3was investigated from the viewpoint of the the arrangement of A-site ions. It was showed that the conductivity in La2/3-xLi3x□1/3–2xTiO3is strongly influenced by not only the concentration but also the ordered arrangement of skeletal A-site ions. Further the activation energy for ion conduction was found to be dominated by the covalency of B-O bond in addition to the bottleneck size.
New Manganese Oxides by Hydrothermal Reaction of Permanganates
Authors: Chen Rongji , Zavalj Peter , Stanley Whittingham M. 
Published: April 2011

AbstractThe mild hydrothermal decomposition of aqueous permanganate solutions has been found to lead to new layered manganes oxides. In the case of alkali permanganates, AMnO4, layered birnessite-type compounds are formed with the general formula - AxMnO2•nH2O. These compounds have R 3 m rhombohedral structures analogous to the layered disulfides. The water is reversibly lost on heating, and the compounds readily intercalate lithium ions in a reversible manner. In the case of the hydrothermal decomposition of tetramethylammonium permanganate in the presence of nickel, the new compound NiMnO3is formed that has a novel structure. This compound also has interesting magnetic properties, being a paramagnet above 111K and a ferromagnetic below that temperature.