bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electrical and Optical Properties of Zinc Oxide Thin Films and Heavily Aluminum-doped Zinc Oxide Thin Films Prepared by Molecular Beam Epitaxy
Authors: Ohgaki Takeshi , Kawamura Yuji , Ohashi Naoki , Kakemoto Hirofumi , Wada Satoshi , Adachi Yutaka , Haneda Hajime , Tsurumi Takaaki 
Published: April 2011

ABSTRACTZnO (ZO) and Aluminum (Al) doped ZnO (AZO) films were grown on sapphire substrate via oxygen radical assisted molecular beam epitaxy (MBE) technique. The results of XRD measurement and temperature dependent Hall measurement confirmed that the AZO films were typically highly degenerate semiconductor with good crystallinity. The resistivity of these films were closed to the theoretical lower limit. The optical properties of these films were investigated by photoluminescence (PL) spectra and absorption spectra. Strong band-edge emission was observed in the AZO films with good crystallinity in spite of high carrier concentration more than 1020 cm-3. A sift of absorption edge to higher energy side and a gradual increase of the absorption was observed for the AZO film.
A Single Source Approach To Deposition Of Nickel and Palladium Sulfide Thin Films By LP-MOCVD
Authors: Waters J. , O'Brien P. , Park J.H. 
Published: April 2011

ABSTRACTCompounds of the type M(S2CNRR’)2, M = Ni(II), Pd(II), RR' = Et2, MeEt and MenBu, have been synthesized and used as single-source precursors for the fabrication of NiS and PdS thin films via low-pressure (LP) metal-organic chemical vapour deposition (MOCVD). The phase of nickel sulfide films deposited on glass substrates was found to be NiS1.03 or a mixture of NiS1.03 and NiS, whilst palladium sulfide films were only tetragonal PdS. The films have been characterized by X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), transition electron microscopy (TEM) and energy dispersive analysis of X-rays (EDAX).
Passivation of Defects in ZnO by Hydrogen Plasma Irradiation
Authors: Ohashi Naoki , Ishigaki Takamasa , Sekiguchi Takashi , Sakaguchi Isao , Haneda Hajime 
Published: April 2011

ABSTRACTHydrogen doping effects on luminescence properties of bulk ZnO samples were examined by using a pulse-modulated plasma irradiation technique. Three kinds of ZnO samples, including both single- and poly-crystals, were employed as specimens. Secondary-ion-mass-spectroscopy analysis revealed that the surface layer to 100 nm was doped with hydrogen after the irradiation and its concentration was in the order of 1017 cm-3. The efficiency of band edge emission was increased by the hydrogenation. However, the degree of the improvements depended on impurity and defect concentration in the original samples.
Design and Fabrication of a VCSEL With Graded Bragg Mirror Interfaces for Operation at 850nm
Authors: Zhang Chichang , Christou Aris 
Published: April 2011

ABSTRACTBased on the AlxGa1-xAs/GaAs system and with graded Distributed Bragg mirrors (DBRs), a VCSEL for operation at 850–860nm is reported. The graded transition bands inside the DBRs were designed in order to achieve the tradeoff between the number of DBR layers and the low threshold current of the laser. The structure optimized had 39 pairs in the n-DBR stack and a low threshold current of 1.6mA was achieved. The device was fabricated with MBE growth, oxide confinement and RIE for MESA definition. The experimental results and physical characterization of the device are also reported to fully understand the VCSEL performance. The threshold current and other parameters predicted by the simulation are in good agreement with experimental results.
High Gain, Low Threshold Current GaInAsP Based Vcsels for Operation at 1.24UM
Authors: Tan Zhuopeng , Li Yixin , Christou Aris 
Published: April 2011

ABSTRACTAn electrically pumped 1.24um GaxIn1-xAsyP1-y Vertical Cavity Surface Emitting Laser (VCSEL) has been designed and simulated. Threshold gain of 153cm-1 and threshold current of 1.00mA was obtained. The external efficiency predicted is 0.31. Also the optimized design of VCSEL structure is presented in this article. GaInAsP and AlInAs constitute the Distributed Bragg Reflectors (DBRs) multilayer stack. Reflectivity of the top DBRs is 0.97 and reflectivity of the bottom DBRs is 0.9978 and is shown to provide a good resonant cavity and sufficient lasing intensity. Compared with other reported structures, the present VCSEL has a lower threshold current and higher threshold gain.
Trace Water Detection in Phosphine By Cavity Ring-down Spectroscopy
Authors: Lehman Susan Y. , Bertness Kris A. , Hodges Joseph T. 
Published: April 2011

ABSTRACTWe are using cavity ring-down spectroscopy (CRDS) to measure concentrations of water in nitrogen and, for the first time to our knowledge, in phosphine. Water vapor concentrations have been measured in purified and unpurified phosphine, indicating a water mole fraction of (22.0 ± 1.0) x 10-6 in unpurified phosphine. After purification with an in-line, chemically-reactive purifier, the mole fraction of water in phosphine was less than 0.1 × 10-6. Mole fractions as high as (730 ± 60) × 10-6 have been measured in unpurified phosphine, suggesting that the H2O vapor concentration increases substantially with time as the gas is stored in a cylinder. The materials properties of AlInP grown by molecular beam epitaxy (MBE) with CRDS-characterized PH3 were found to be relatively insensitive to water contamination at the 22 mol/mol level.
Stability of Non-Hydrogenated and Hydrogenated P-Channel Polycrystalline Silicon Thin-Film Transistors
Authors: Hastas N. A. , Dimitriadis C. A. , Kamarinos G. 
Published: April 2011

ABSTRACTThe effects of high gate voltage Vg stress on the stability of non-hydrogenated and hydrogenated short p-channel polysilicon thin-film transistors (TFTs) are investigated for operation in the saturation region. The degradation mechanisms were identified from the evolution with stress time of the static device parameters. In non-hydrogenated TFTs, transconductance overshoot and a turnover behavior in the threshold voltage were observed. The results indicate that hot-electron trapping near the drain dominates in the initial stages of stress and channel holes are injected into the gate oxide followed by interface states generation as the stress proceeds further. In hydrogenated TFTs, first an effective shortening of the channel length is observed due to trapping of hot-electrons. As the stress proceeds further, donor-type interface states are generated and the electric field near the drain increases due to built-up of positive charge resulted from trapping of hot-holes in these states.
Graded-Band-Gap Semiconductors: the Possibilities for Improvement of p-n Junction Performance
Authors: Sokolovskii Bogdan , Yasnytskyi Roman 
Published: April 2011

ABSTRACTThe paper theoretically analyzes properties of graded-band-gap (GBG) p-n structures in which band gap linearly enlarges with increasing the distance from the junction metallurgical edge. It is shown that by means of band-gap grading one can significantly reduce the diffusion reverse current caused by carrier thermal generation in the structure base regions and Ohmic contacts. The numerical estimations have been made for the case of p-n junction on the basis of CdHgTe solid solution.
MOCVD Growth and Characterization of GaInNAs/GaAs/InGaAs/GaAs Quantum Well Structures
Authors: El-Emawy Abdel-Rahman A. , Cao Hongjun , Nuntawong Noppadon , Liu Chiyu , Osiński Marek 
Published: April 2011

ABSTRACTEffects of MOCVD growth parameters on structural and optical properties of double-quantum-well (DQW) structures containing uncoupled GaInNAs/GaAs and InGaAs/GaAs quantum wells have been investigated. By varying growth temperature, growth rate, V/III ratio, and DMHy flow rates, we have achieved a longer-wavelength emission from a GaInNAs well than from an InGaAs well grown in the same structure. GaInNAs/GaAs multiple-quantum-well structures grown under optimum conditions emitted at 1.25 μm.
Nonstoichiometry of Epitaxial FeTiO3+δFilms
Authors: Fujii Tatsuo , Sadai Makoto , Kayano Masakazu , Nakanishi Makoto , Takada Jun 
Published: April 2011

ABSTRACTEpitaxial thin films of (001)-oriented FeTiO3+δwere prepared on α-Al2O3(001) single crystalline substrates by helicon plasma sputtering technique. The FeTiO3+δfilms had large oxygen nonstoichiometry, which seriously depended on both substrate temperature and oxygen pressure during the sputtering deposition. The valence states of Fe ions in FeTiO3+δchanged monotonically from Fe2+to Fe3+with decreasing the substrate temperature from 900 to 400°C or with increasing the oxygen pressure from 0.9 to 1.8×10-6Pa. The change of Fe valence states from Fe2+to Fe3+induced the magnetic phase transition only for the films prepared at 900°C. The films containing Fe2+were paramagnetic while those with Fe3+were antiferromagnetic at room temperature. The oxygen nonstoichiometry of the FeTiO3+δfilms was probably produced by cation vacancies and disarrangement of Fe3+and Ti4+ions, which randomly occupied both interstitial and substitutional sites of the FeTiO3related structure.
Structural Quality and Electrical Behavior of Epitaxial High-k Y2O3 / Si(001)
Authors: Vellianitis G. , Apostolopoulos G. , Dimoulas A. , Argyropoulos K. , Mereu B. , Scholz R. , Alexe M. , Hooker J. C. 
Published: April 2011

ABSTRACTY2O3 thin films were grown directly on Si (001) by MBE and annealed in-situ under UHV at various annealing temperatures. The samples were investigated in-situ by RHEED and ex-situ by HRTEM. A 7 to 15 Å thick non-uniform interfacial amorphous layer is observed in the as-grown sample. After annealing at 490°C under UHV for 30 minutes the amorphous layer is reduced and a sharp Y2O3/Si interface is obtained. At higher annealing temperatures, YSi2 islands start to form at the Y2O3/Si interface. I-V measurements performed on generic MIS structures show that the annealed samples exhibit higher leakage current density than the as-grown sample, due to reduction of the wide band gap interfacial layer. Leakage current densities in annealed samples remain below 1A/cm2, which is acceptable for future high-κ transistor fabrication.
Co-doping Deposition of p-type ZnO Thin Films using KrF Excimer Laser Ablation
Authors: Ebihara Kenji , Ohshima Tamiko , Ikegami Tomoaki , Asumussen Jes , Thareja Raj K. 
Published: April 2011

ABSTRACTWe report on the attempt to fabricate p-type ZnO thin films using various doping techniques based on the pulsed laser deposition (PLD). As an accepter, we have doped the N atom by using high purity nitric monoxide (NO) ambient gas. NO is dissociated into N and O at an energy of 6.5 eV which is lower than at N2 (9.76 eV). Moreover the dissociation reaction of NO is simpler than other nitrogenous gases such as N2O, NO2, and NH3. One of our doping techniques is co-doping of Ga and N atom by ablating ZnO:Ga target in NO gas, and another is the ablation of the metal Zn target in NO gas. Both of Ga and N co-doped ZnO films and N doped ZnO films have c-axis orientation as well as undoped ZnO films. The surfaces of these doped films are rough while the undoped ZnO thin film is very smooth and have hexagonally shaped grains. We found it possible to fabricate the p-type ZnO film by ablating the metal Zn target in NO gas.
Atomic Ordering in Self-assembled Epitaxial II-VI and IV-VI Compound Semiconductor Quantum Dot Systems
Authors: Möck Peter , Pierz Klaus , Topuria Teya , Browning Nigel D. , Wu Huizhen , McCann Patrick J. 
Published: April 2011

ABSTRACTTransmission electron microcopy (TEM) in both the parallel illumination and scanning probe mode revealed atomically ordered entities within a 5 to 250 nm range in a IV-VI and a II-VI compound semiconductor quantum dot (QD) system. While the II-VI system was a nominal [001] CdSe/(Mn0.1Zn0.9)Se multilayer structure with the QDs embedded, the IV-VI system nominally consisted of [111] PbSe islands. The comparison of photoluminescence (PL) spectra from the CdSe/(Mn0.1Zn0.9)Se structure with those of a reference structure, that was grown to the same nominal specification under otherwise identical conditions except that no Mn was incorporated into the cladding layers, revealed for the former sample two peaks at approximately 2 and 2.1 eV. We tentatively attribute these two PL peaks to two groups of atomically ordered entities.
Thermal characterization and modeling of intermediate phase formation in 20/80 nm and 10/20 nm Cu/Mg multilayers
Authors: González-Silveira M. , Rodríguez-Viejo J. , Clavaguera-Mora M.T. 
Published: April 2011

ABSTRACTThe kinetics of intermediate phase formation in the Cu/Mg multilayer system is analyzed using Differential Scanning Calorimetry. Three main exothermic processes are found during the continuous DSC treatments. The first two, significantly overlapped, are related to the same process, nucleation and growth of the Mg2Cu along the interface. We interpret differences between the Mg/Cu and Cu/Mg interfaces are at the origin of this unexpected behavior. The third exothermic reaction is due to the growth of the Mg2Cu phase perpendicular to the original interface. A kinetic model is developed which yields calorimetric traces in good agreement with the experimental data.
Rate Equation Theory for Island Sizes and Capture Zone Areas in Submonolayer Deposition: Realistic Treatment of Spatial Aspects of Nucleation
Authors: Evans J.W. , Li Maozhi , Bartelt M.C. 
Published: April 2011

ABSTRACTExtensive information on the distribution of islands formed during submonolayer deposition is provided by the joint probability distribution (JPD) for island sizes, s, and capture zone areas, A. A key ingredient determining the form of the JPD is the impact of each nucleation event on existing capture zone areas. Combining a realistic characterization of such spatial aspects of nucleation with a factorization ansatz for the JPD, we provide a concise rate equation formulation for the variation with island size of both the capture zone area and the island density.
First-principles calculation of the effect of strain on the diffusion of Ge adatoms on Si and Ge (001) surfaces
Authors: van de Walle A. , Asta M. , Voorhees P. W. 
Published: April 2011

ABSTRACTFirst-principles calculations are used to calculate the strain dependencies of the binding and diffusion-activation energies for Ge adatoms on both Si(001) and Ge(001) c(4×2) reconstructed surfaces. Our calculations reveal that over the range of strains typically sampled during quantum dot self-assembly (0 to 1% compressive strain) the binding and activation energies on a strained Ge(001) surface increase and decrease, respectively, by 0.21 eV and 0.12 eV. For a growth temperature of 600 °C, these strain-dependencies give rise to a 16-fold increase in adatom density and a 5-fold decrease in adatom diffusivity in the region of compressive strain surrounding a Ge island with a characteristic size of 10 nm lying on top of a Si substrate covered by a Ge wetting layer.
Chromium and Lanthanum on Transition Alumina Surfaces: The Role of Bulk Point-Defect Distributions on Catalytic Activity
Authors: Rashkeev S. N. , Sohlberg K. , Glazoff M. V. , Novak J. , Pennycook S. J. , Pantelides S. T. 
Published: April 2011

ABSTRACTWe employ a combination of Z-contrast scanning transmission electron microscopy (Z-STEM) and first-principles density-functional calculations to investigate the interaction between metal atoms and cubic alumina catalytic supports. We show that there are two observed La sites at the porous γ- alumina surface, and that single La atoms do not exhibit a tendency to cluster. Cr behaves very differently from La - it has a tendency to cover the alumina surface in ordered, periodic raft-like patches. The degradation of the chromia/alumina catalyst is related to the possibility for the chromium to move away from the surface into the bulk, and the activation barrier for such a process is higher in η- alumina than in γ- alumina, i.e., η- alumina is a more durable support for chromium catalyst.
Characterization of Porous Pt/Al2O3 Films Produced by Hybrid Gas-to-Particle Conversion and Chemical Vapor Deposition
Authors: Nguyen Quynh T. , Ehrman Sheryl H. 
Published: April 2011

ABSTRACTA hybrid process, based upon gas-to-particle conversion and chemical vapor deposition, is presented as an alternative technique for producing porous films with the main advantage of solvent-free, low-substrate temperature operation. Starting from precursors of platinum acetylacetonate and aluminum acetylacetonate, nanoparticles were produced by chemical reaction followed by gas-to-particle conversion. Downstream of this reaction zone, these nanoparticles were collected via thermophoresis onto a cooled substrate forming a porous, nanocermet film that may have possible uses in catalytic, sensor, or coating applications.In this study, Pt/Alumina nanocermet films were produced by two routes: either simultaneous precursor injection processing or a layer-by-layer approach. Energy-dispersive X-ray spectroscopy revealed that this hybrid process results in reasonable control of the amount of Pt within each sample. From transmission electron spectroscopy images taken of films produced by simultaneous processing, Pt nanoparticles appear to be co-agglomerated with alumina. The results may identify changes that can be made to the process to improve properties, such as catalytic activity, in the nanocermet films.
HRTEM Study of the Extended Defect Structure in Epitaxial Ba0.3Sr0.7TiO3 Thin Films Grown on (001) LaAlO3
Authors: Lu C.J. , Bendersky L.A. , Chang K. , Takeuchi I. 
Published: April 2011

ABSTRACTThe defect structure of a 350-nm-thick epitaxial Ba0.3Sr0.7TiO3 thin film grown on (001) LaAlO3 has been investigated using conventional and high-resolution transmission electron microscopy. The predominant defects in the film are threading dislocations (TDs) with Burgers vectors b = <100> and <110>. A high density of extended stacking faults (SFs) with displacement vectors R = (1/2)<110> were also observed in the near-interface region of the film. The faults are associated with dissociated dislocations and partial halfloops. Some findings about dislocation dissociation and the atomic structure of the (1/2)<110> faults are observed for the first time in perovskites to our knowledge. The mechanisms for the generation, dissociation and evolution of the TDs as well as for the formation mechanism of the SFs are discussed.
The Effect of Changing Epitaxial Strain on Colossal Magnetoresistance Thin Films
Authors: Dale Darren , Fleet Aaron , Brock J.D. , Suzuki Y. 
Published: April 2011

ABSTRACTWe have studied the properties of epitaxial La(1-x)SrxMnO3 (x=0.3, 0.5) epitaxial thin films grown on BaTiO3 and SrTiO3. Significant modifications of properties are observed in magnetization and resistivity versus temperature experiments. These modifications occur at temperatures corresponding to structural phase transitions in the substrate. The x=0.5 composition is particularly sensitive to changes in the epitaxial strain state, exhibiting a direct correlation between changes in strain, magnetization and resistivity. Strain can also be induced in BaTiO3 by the inverse piezoelectric effect, which results in as much as a 13% decrease in the resistivity of the film.
Metalorganic chemical vapor deposition of aluminum oxide on silicon nitride
Authors: Dasgupta Anindya , Chowdhuri Abhijit Roy , Takoudis Christos G. 
Published: April 2011

ABSTRACTThin films of aluminum oxide were deposited on silicon nitride thin films using trimethylaluminum and oxygen at 0.5 Torr and 300 °C. Fourier transform infrared (FTIR) and x-ray photoelectron spectroscopic (XPS) analyses of these films showed no aluminum silicate phase at the film-substrate interface. The O/Al ratio in the deposited film was found to be higher than that in stoichiometric Al2O3 indicating the presence of excess oxygen. FTIR spectroscopy and XPS of the annealed samples did not show any formation of silicon oxide, oxynitride or silicate at the aluminum oxide/silicon nitride interface. In contrast to aluminum oxide on clean silicon substrates, using ultrathin silicon nitride as a barrier layer could prevent excess oxygen migration towards the Si substrate and formation of any interfacial layers.
The Effect of the Surface Layer on the Dielectric Constant of (Pb, La)TiO3 Thin Films
Authors: Yu G.L. , Xiao D.Q. , Meng L.L. , Yu P. , Zhu J.G. 
Published: April 2011

ABSTRACT:(Pb, La)TiO3 (PLT) ferroelectric thin films are one of the promising candidates for applications in dynamic random memory and pyroelectric detectors, etc. However, the chemical composition in the surface layer of thin films is usually different from that in the “bulk” region of the thin films. For instance, it has been reported that there is Pb, Ti, or La enrichment in the surface layer of the (Pb, La)TiO3 thin films. According to a numerical modeling using effective-medium theory, which was developed in our group, we discussed the effect of the surface layer on the dielectric constant of (Pb, La)TiO3 thin films. The effect of Pb, Ti, or La enrichment in the surface layer on the dielectric constant of PLT thin films was discussed. And a case of the “upgraded” and the “down-graded” thin films was expatiated and discussed.
Nanocrystallisation and Nanoquasicrystallisation in (Ti/Hf)-Zr-(Ni/Cu) Ternary Alloys
Authors: Basu Joysurya , Louzguine D.V. , Inoue A. , Ranganathan S. 
Published: April 2011

ABSTRACTThe applicability of the confusion principle and size factor in glass formation has been explored by following different combinations of isoelectronic Ti, Zr and Hf metals. Four alloys of nominal composition Zr41.5Ti41.5Ni17, Zr41.5Hf41.5Ni17, Zr25Ti25Cu50 and Zr34Ti16Cu50 have been rapidly solidified to obtain an amorphous phase and their crystallisation behaviour has been studied. The Ti-Zr-Ni alloy crystallises in three steps. Initially this alloy precipitates icosahedral quasicrystalline phase, which on further heat treatment precipitates cF96 Zr2Ni phase. The Zr-Hf-Ni alloy can not be amorphised under the same experimental conditions. The amorphous Zr-Ti-Cu alloys at the initial stages of crystallisation phase-separateinto two amorphous phases and then on further heat treatment cF24 Cu5Zr and oC68 Cu10Zr7 phase are precipitated. The lower glass-forming abilityof Zr-Hf-Ni alloy and the crystallisation behaviour of the above alloys has been studied. The rationale behind nanoquasicrystallisation and the formation of other intermetallic phases has been explained.
Synthesis and Evaluation of Resins for Actinide Separations
Authors: Noyes K. L. , Charton N. , Draye Micheline , Czerwinski K. R. 
Published: April 2011

ABSTRACTMolecular imprinting techniques have shown great promise for applications in chemical separations, including those involving lanthanides and actinides. This work examines the production of a selective resin for Am separations. Due to practical difficulties, resins were not imprinted with Am, rather 3 resins were created with each of Sm, Nd, and Pr as the template ions. An analogous “blank” or unimprinted resin was also created. The nitrate salt of the target metal ion was dissolved in CH2Cl2 and the resin was created around the ions to provide a unique structure based upon each metal. These resins were synthesized by a radical polymerization method, producing a reusable organic solid. The resins were qualified by obtaining values for their proton exchange capacities and data to define their complexation thermodynamics. Proton exchange capacities were determined using an indirect titration and were found to be 10.08 meq/g for the Sm-imprinted resin, 7.25 meq/g for the Nd resin, and 7.14 meq/g for the Pr resin. Data for the resins' thermodynamics were obtained at pH 1–7 in steps of 0.5 units. Results show that the templated resins rapidly removed the target actinide from aqueous solution under experimental conditions. Best separation results for Am from Eu and Gd were obtained with the Nd imprinted resin.