bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Comparison of an Improved Design for Two Integrated Optical Isolators Based on Nonreciprocal Mach-Zehnder Interferometry
Authors: Bahlmann N. , Lohmeyer M. , Wallenhorst M. , Dötsch H. , Hertel P. 
Published: April 2011

AbstractNonreciprocal rib waveguide structures can be used to realize integrated optical isolators. The nonreciprocal phase shift is the difference between the forward and backward propagation constants of TM modes in magneto-optic waveguides. It can be optimized with respect to absolute value and temperature dependence if double layer waveguides with different magnetic and nonmagnetic layers are prepared. In this paper we propose an improved design for two different Mach-Zehnder interferometer isolators the nonreciprocal parts of which are formed by such double layer waveguides. One concept utilizes a nonreciprocal and a reciprocal arm. In the other case both arms are nonreciprocal but with opposite sign of the nonreciprocal phase shift. A particular property of both concepts is that the lengths of the nonreciprocal arms are well defined. The rest of the interferometer is made by reciprocal rib waveguides. Therefore, the nonreciprocal phase shift is well known. The concepts are compared with regard to isolation ratio, forward losses and fabrication tolerances. Moreover, we simulate the entire isolator by a finite difference beam propagation calculation.
Magneto-Static Wave Oscillator-Based Integrated Magneto-Optic Bragg Cell Modulator*
Authors: Su Jun , Tsai Chen S. 
Published: April 2011

AbstractA novel magnetooptic (MO) Bragg cell modulator that utilizes a magnetostatic forward volume wave (MSFVW) oscillator is presented. The carrier frequency of the MSFVW signals involved in the MO interaction is tuned linearly from 2.112 to 3.274 GHz by increasing an external bias magnetic field from 2350 to 2900 Oe. Compared with a conventional magnetostatic wave (MSW) delay line-based MO Bragg cell modulator, the proposed modulator can provide significantly higher diffraction efficiency owing to reduction of insertion losses in the MSFVW oscillator. Furthermore, the oscillator-type MO modulator can be more easily integrated with other MMIC devices.
Synthesis and Characterization of Nanosized NiAl Particles
Authors: Chen T. , Hampikian J.M. 
Published: April 2011

ABSTRACTNanophase NiAl powders were synthesized by solid state reaction via ball milling of elemental Ni and Al powders under an argon atmosphere for 0-8 h, 16 h, 24 h, and 48 h. Structural characterization of the nanophase NiAI was performed by x-ray diffraction and transmission electron microscopy. The oxidation behavior of the powders was studied by thermogravimetric analysis. It was found that the Ni + Al = NiAl solid state reaction took place between 4 and 5 hours of mechanical alloying. After 5 h or more of mechanical alloying, the phase of the ball milled particles was the B2 structure, with average grain sizes which decreased with increasing mechanical alloying times. The relationship between the long-range-order parameters and mechanical alloying time was studied. After 5 h, 6 h, 8 h, 16 h, 24 h, and 48 h mechanical alloying, the long-range-order parameter was determined to be approximately 0.82, 0.75, 0.75, 0.75, 0.71, and 0.63, respectively. Iron contamination was observed, resulting from wear of the steel vial and balls. In the mechanically alloyed NiAl nanoparticles, edge dislocations, shear bands, subgrains, distorted regions, and a large number of grain boundaries were observed.
Production of Nanocrystalline Sulfated Zirconia Catalysts via a Flow-Through Hydrothermal Process
Authors: Matson D.W. , Darab J.G. , Brewer T.D. , Kaviratna P.D. 
Published: April 2011

ABSTRACTNanocrystalline sulfated zirconia catalysts were prepared using the rapid thermal decomposition of precursors in solution (RTDS) powder formation process. Zirconia gel formation, initial crystallization, and sulfate incorporation occurred during a brief exposure to hydrothermal conditions in the RTDS reactor. The partially crystalline zirconia solid was collected as a suspension, separated by centrifugation, and subjected to calcination to achieve full catalytic activity. Crystallinity, sulfate content, and catalytic activity of the calcined powders toward butane isomerization varied according to the hydrothermal conditions at which the zirconia powders were originally precipitated. The powders were characterized using powder XRD, FTIR, and XAS.
Metallograpiuc Study of Gasar Porous Magnesium
Authors: Park Chanman , Nutt Steven R. 
Published: April 2011

ABSTRACTOne of the promising techniques for making porous metals is the so-called GASAR process. In principle, the process affords considerable control over pore size, shape, and distribution. However, in practice, the pore microstructure is difficult to control, and a clearer understanding of microstructural evolution would be helpful. In this study, we undertake a detailed microstructural study of a porous Mg and AZ31 Mg alloy synthesized by the GASAR process. Microscopic studies demonstrated the presence of different pore size ranges. The pore distribution depended on the distance from the chill end of ingots. TEM observations revealed apparent crack lines (gas tracks) near the pores and ternary intermetallic phases in the alloy.
Annealing Studies on Low Energy As+ and As2+ Implants
Authors: Srinivasa Raghu , Agarwal Vikas , Liu Jinning , Downey Daniel F. , Banerjee Sanjay 
Published: April 2011

ABSTRACT2 keV to 10 keV arsenic, As+, and arsenic dimer ions, As 2+, were implanted into silicon at a dose of le15 cm-2 and 3e 15 cm-2 at 0° and 7°' tilt angles. For bare wafers, a low concentration of oxygen is required to provide sufficient capping during anneal to minimize out-diffusion. In the presence of oxygen, enhanced diffusion occurs during the anneal, the extent of which is a function of the concentration of oxygen and the temperature of anneal. The oxidation enhanced diffusion (OED) is significant at anneal temperatures above 1050°C. The extent of OED is observed to be more significant for the samples with lower energy As+ implants. An alternative technique for minimizing OED, without much out-diffusion, is the use of higher energy, 5 keV implants through a screen oxide. For identical anneal conditions, 5 keV As+ implants through a 40 Å screen oxide offer junction depth and sheet resistance values equivalent to that of 2 keV implants into bare silicon. As the screen oxide is sufficient to cap the out-diffusion of dopants, a nitrogen ambient or a lower temperature could be employed to get shallower junctions without much degradation in the sheet resistance. Further reduction in junction depths can be achieved by using the As 2+ implants.
A Novel Low Temperature Self-Aligned Ti Silicide Technology for Sub-0.18 μm Cmos Devices
Authors: Ren L. P. , Liu P. , Pan G. Z. , Woo Jason C. S. 
Published: April 2011

ABSTRACTA novel low temperature self-aligned Ti silicidation with Ge+ pre-amorphization implant (PAI) is presented. Compared to conventional high temperature PAM silicidation, the advantages of Ti salicidation at temperatures below the recrystallization of a pre-amorphized layer are: (1) C49 TiSi2 silicide formation occurs only in the pre-amorphized layer so that the silicide depth can be well controlled, forming a very sharp interface between the silicide and the Si substrate; (2) Ti just reacts with the amorphous layer, avoiding the so-called bridging issue in which the silicide grows laterally over the isolation or spacer; (3) the effects of metal thickness and substrate doping on silicide formation are suppressed.
In Situ Wafer Cleaning Prior to Selective HemiSpherical Grain (HSG) Poly-Silicon Deposition Using RT-CVD
Authors: Brosilow B. J. , Levy S. , Gilboa Y. E. 
Published: April 2011

ABSTRACTHemispherical grained (HSG) polycrystalline-silicon surfaces are used in DRAM manufacturing to enhance cell capacitance by increasing the surface area of the capacitor electrodes. We study the formation of HSG poly-silicon in a Rapid Thermal CVD (RT-CVD) cluster tool with in-situ native oxide removal. Compared to conventional ex-situ wet cleaning procedures, use of the in-situ native oxide removal both decreases the process temperature at which HSG formation occurs and increases the width of the temperature window within which desirable HSG layers are formed.
SiGe Heteroepitaxy for High Frequency Circuits
Authors: Tillack B. , Bolze D. , Fischer G. , Kissinger G. , Knoll D. , Ritter G. , Schley P. , Wolansky D. 
Published: April 2011

ABSTRACTWe have determined the process capability of Low Pressure (Rapid Thermal) Chemical Vapor Deposition (LP(RT)CVD) of epitaxial Si/SiGe/Si stacks for heterojunction bipolar transistors (HIBTs). The transistor parameters primarily influenced by the epitaxial characteristics were measured for 600 identically processed 4” wafers. The results demonstrate that it is possible to control accurately the epitaxial process for a 25 nm thick graded SiGe base profile with 20 % Ge and very narrow B doping (5 nm). The pipe limited device yield of about 90 % for an emitter area of 104 μm2 indicates a very low defect density in the epitaxial layer stack. The process capability indices determined from about 40,000 data points demonstrate the stability and capability of the LP(RT)CVD epitaxy with regard to manufacturing requirements.
Island-Size Distributions for Submonolayer Epitaxy: Rate Equations and Beyond
Authors: Vvedensky D.D. , Caflisch R.E. , Gyure M.F. , Merriman B. , Osher S. , Ratsch C. , Zinck J.J. 
Published: April 2011

AbstractThe scanning tunnelling microscope has revolutionized the quantitative analysis of epitaxial phenomena. This, in turn, has spawned a huge theoretical effort aimed at analyzing various aspects of the morphology of growing surfaces. One of the most important general approaches to have emerged from this effort is based on the application of scaling concepts to epitaxial island-size distributions in the regime of submonolayer coverage prior to coalescence. We first discuss the analytical basis for scaling solutions to rate equations. In the limit of irreversible aggregation, a solution is obtained in terms of the capture numbers which agrees with previous work. For reversible aggregation, we identify a new quantity that may be regarded as a continuous analogue of a critical island size. We then examine the influence of spatial correlations by introducing a method for modeling epitaxial phenomena in terms of the motion of island boundaries, which is implemented numerically using the level set method. This island dynamics model is continuous in the lateral directions, but retains atomic scale discreteness in the growth direction. Several choices for the island boundary velocity are discussed and computations of the island dynamics model using the level set method are presented.
Scaling and Coarsening in Epitaxial Growth
Authors: Family Fereydoon , Amar Jacques G. 
Published: April 2011

AbstractThe results of recent theoretical and simulational studies of submonolayer and multilayer homoepitaxial growth are discussed. In the submonolayer regime, the results of kinetic Monte Carlo simulations are presented and shown to provide a quantitative explanation for the variation of the submonolayer island density, critical island size, island-size distribution and morphology as a function of temperature and deposition rate found in recent experiments. In multilayer growth, a realistic model for homoepitaxial growth on fcc and bcc lattices which takes into account the correct crystal structure is reviewed. The effects of instabilities which lead to mound formation and coarsening are discussed and a unified picture of the effects of attractive and repulsive interactions at ascending and descending steps on surface morphology and island nucleation is presented. An accurate prediction of the observed mound angle for Fe/Fe(100) deposition is obtained analytically and by kinetic Monte Carlo simulations. The general dependence of the mound angle, and mound coarsening behavior on temperature, deposition rate, and strength of the step barrier in bcc(100) and fcc(100) growth is also presented and compared with recent experiments.
Mathematical Modelling of Roughness-Temperature Evolution
Authors: Nedelcu S. , Moldovan N. 
Published: April 2011

AbstractOrientation -dependent etching of silicon in alkaline solutions is close to get a satisfactory model by considering the random Si-Si bond breaking algorithms (BBA). Here we report our progress regarding the simulation of the atomic-scale roughness of the etched surface, by considering the influence of the processing temperature. We chose the model parameters to fit the experimental data for the etching rate angular dependence for 80°C. We supposed an Arrhenius type dependence on temperature for the basic bond-breaking probabilities and obtained the etching rate and roughness dependence on temperature. The temperature dependence of the etching rates showed the main features of the experimental data: an increase of the etching rate with temperature, a slight change of anisotropy and an increase of the roughness. Further investigations showed we could be close to a roughening transition, which manifests mainly along the directions of the etching rate maxima.
Plastic Packaging Reliability of Optoelectronic Devices for Telecom Use
Authors: Fukuda Mitsuo , Kato Kuniharu 
Published: April 2011

AbstractTwo types of plastic modules for laser diodes and photodiodes are developed and tested under various environmental conditions. The stable operations for both types of modules are confirmed under various long-term aging tests, high humidity high temperature tests (85°C, 85% RH), and temperature cycling tests (-40 / +85°C). These plastic moduless are potentially suitable for economic access networks.
Durability and Reliability of Semiconductor Devices
Authors: Sidorov V. G. , Sokolov V. I. , Sidorov D. V. 
Published: April 2011

AbstractThe aim of the study is to discuss the most general aspects of semiconductor devices durability and reliability. The life time of a semiconductor device is related to the defect structure evolution of the crystalline and noncrystalline components involved. The driving force for the evolution of defect device structure is associated with relaxation processes of internal mechanical stresses. In this report the degradational effects in LEDs based on GaAs(Si) have been analyzed. The discussion of the necessity for research on composite materials creation is also included.
Characterization of Embedded Optical Fiber Bragg Grating Sensors
Authors: Frank A. , Nellen Ph. M. , Sennhauser U. 
Published: April 2011

AbstractFiber reinforced structural elements equipped with optical fiber sensors are of potential interest for long term surveillance of bridges, dams, and other civil engineering applications. We report herein on the embedding of optical fiber Bragg grating sensors into continuously pultruded glass fiber reinforced epoxy material (GFRP) rods used as structural elements.Two fibers, one with acrylic, one with polyimide coating, and fiber Bragg gratings were extensively characterized. The residual axial strain after embedding was measured. Temperature and strain coefficients of Bragg gratings during quasi-static cycling and temperature cycling tests were monitored and compared to extensometric and resistance strain gauge measurements.The effect of fiber embedding was also studied with push-out tests giving information about adhesion properties like surface bond energy, lateral stress, and coefficient of friction.For sensor purposes long term characteristics of the conversion factor between the measured Bragg grating wavelength and strain or temperature in the specimen have to be known to identify best-suited coatings for embedding and protecting fiber sensors and for obtaining reliability data on sensor performance.
Evaluation of B-Values Of Telecom Fibers, Objectives and Methods
Authors: Svensson Torbjörn 
Published: April 2011

AbstractStress corrosion in silica may end the lifetime of optical fibers in telecom networks. Since the lifetime demanded usually exceeds 25 years, a careful strategy is necessary in order to preserve cable reliability. The toolbox therefore includes equations for estimating lifetime of fibers, some of them related to the so-called B-parameter. The lifetime is proportional to B, but a value specific for the environment andfiber used has turned out to be difficult to achieve.Among various experimental methods proposed, the mechanical testing at high stress rates is a physically sound way to confirm the B-value of coated fibers, since testing can be made under similar conditions as prevail during network application. Fatigue tests including high-speed tensile tests have been run on coated silica fibers for a long time. Lately, a new high-stress-rate bending method has been investigated, pushing forward the previous experimental limits.Values of B from tensile- and bending tests are presented, being 0.004 - 0.10 GPa2 s in tension and considerably less in bending, about 0.0007 GPa2s. A study on some acrylate-coated silica fibers including draw-abraded fibers indicates that the B-value also depends on fiber strength.
The Mechanical Behavior of Optical Fiber as a Function of Dew Point Temperature
Authors: Armstrong J. L. , Matthewson M. J. , Kurkjian C. R. 
Published: April 2011

AbstractThe dew point temperature (DPT) is defined as the temperature at which condensation will form from a gas containing moisture. The DPT, which is a measure of the water vapor reactivity, depends on the relative humidity (RH) and the temperature of the gas. The strength of optical fiber has been shown to have a dependence on the humidity and the temperature of the test environment. The results of one study imply that the strength over a range of temperature and humidity can be expressed as a function of the DPT only. While attractive for its simplicity, this idea suggests that the strength depends only on the thermodynamics of the equilibrium between the vapor and condensed phases of water and does not depend on the kinetics of the reaction between water and silica. In the work described here, the strength has been measured at various humidities and temperatures in order to test the dependence on dew point temperature. It was found that the strength degradation is not solely described by the DPT. The strength and dynamic fatigue data were also interpreted by a stress assisted chemical kinetics model. The degradation reaction order with respect to humidity at different air temperatures was found to be approximately two.
Improvement of Crystalline Quality of Group III Nitrides on Sapphire Using Low Temperature Interlayers
Authors: Amano H. , Iwaya M. , Hayashi N. , Kashima T. , Katsuragawa M. , Takeuchi T. , Wetzel C. , Akasaki I. 
Published: April 2011

AbstractIn organometallic vapor phase epitaxial growth of group III nitrides on sapphire, insertion of a low temperature interlayer is found to improve crystalline quality of AlxGalxN layer with x from 0 to 1. Here the effects of the low temperature deposited GaN or AIN interlayers on the structural quality of group III nitrides is discussed.
Focused Ion Beam Micromachining of GaN Photonic Devices
Authors: Chyr Irving , Steckl A. J. 
Published: April 2011

AbstractGa+ and Au+ focused ion beams (FIB) are used to micromachine GaN films. The GaN micromachining has been studied at energies from 30-90 keV, incident angle from 0-30°, and number of repetitive scans from 10 to 50 scans. Trenches milled in GaN have vertical and smooth side-walls and very smooth bottoms. The micromachining rate was found to be fairly independent of ion dose, ranging from 0.4 to 0.6 μm3/nC for Ga+ and I to 2 Pm3/nC for Au+. This translates into an effective yield of of 6-7 atoms/ion for Ga+ and 21-26 atoms/ion for Au+. This represents the highest direct FIB removal yield reported to date. We have also investigated the micromachining of GaN substrate material: c-face sapphire. Using FIB Ga+, sapphire has an effective yield of ∼2-2.5 atoms/ion, or approximately 1/3 of the GaN sputtering yield. For the materials investigated, we found the sputtering yield to be inversely proportional to the strength of the material chemical bond. We also describe the application of the FIB μmachining technique to the fabrication of small period Distributed Bragg Reflector (DBR) mirrors for a short cavity GaN laser structure.
Optical Characterization of Erbium Doped III-Nitrides Prepared by Metalorganic Molecular Beam Epitaxy
Authors: Hommerich U. , Seo J. T. , Thaik Myo , MacKenzie J. D. , Abernathy C. R. , Pearton S.J. , Wilsont R.G. , Zavadat J. M. 
Published: April 2011

AbstractWe are currently engaged in a systematic study of the optical properties of Er doped III-nitrides prepared by metalorganic molecular beam epitaxy (MOMBE). Under below-gap excitation it was observed that GaN: Er samples with [O]∼1020 cm-3 and [C]∼1021 cm-3 luminesce at 1540 nm with an intensity of more than two orders of magnitude greater than samples with low oxygen and carbon concentrations (< 1019 cm-3). Associated with the different oxygen and carbon concentrations were different thermal quenching behaviors and below-gap absorption bands. Interestingly, for above-gap excitation only small differences in absolute Er3+ PL intensity and quenching behavior were observed for samples of varying 0 and C content. Initial lifetime studies were performed and showed a rather unusual short decay time of ∼100 μts at room temperature. In order to gain more insight in the Er3+ PL, a comparison of the integrated PL intensity and lifetime was performed for the temperature range 15-500K. The result reveals that the Er3+ PL quenches above room temperature due to the onset of non-radiative decay and the reduction in excitation efficiency. All samples were also investigated for visible luminescence. Red luminescence was observed from GaN: Er on sapphire substrates under below-gap excitation.
Growth of Oriented Thick Films of Gallium Nitride From the Melt
Authors: Dyck Jeffrey S. , Kash Kathleen , Grossner Michael T. , Hayman Cliff C. , Argoitia Alberto , Yang Nan , Hong Moon-Hi , Kordesch Martin E. , Angus John C. 
Published: April 2011

AbstractWhile significant strides have been made in the optimization of GaN-based devices on foreign substrates, a more attractive alternative would be homoepitaxy on GaN substrates. The primary motivation of this work is to explore the growth of thick films of GaN from the melt for the ultimate use as substrate material. We have previously demonstrated the synthesis of polycrystalline, wurtzitic gallium nitride and indium nitride by saturating gallium metal and indium metal with atomic nitrogen from a microwave plasma source. Plasma synthesis avoids the high equilibrium pressures required when molecular nitrogen is used as the nitrogen source. Here we report the growth of thick oriented GaN layers using the same technique by the introduction of (0001) sapphire into the melt to serve as a substrate. The mechanism of this growth is not established, but may involve transport of the metal as a liquid film onto the sapphire and subsequent reaction with atomic nitrogen. The films were characterized by x-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. X-ray diffraction showed that the GaN films were oriented with their c-axes parallel to the sapphire c-axis. The TEM analysis confirmed the orientation and revealed a dislocation density of approximately 1010 cm-2. The E2 Raman active phonon modes were observed in the GaN films.