bluuebunny/crossref_metadata_2025 huggingface dataset:
Electronic Structure Under Extreme Uniaxial Strains: Conductance in Metallic Nanocontacts.
Authors: Sánchez-Portal Daniel , Untiedt Carlos , Soler José M. , Sáenz Juan J. , Agraït Nicolas
Published: April 2011

In this work we address the behaviour of electronic structure under uniaxial stress, by first-principles calculations and experiments of conductance in nanometer-sized metallic contactes of Au and Al. These contacts are shown to be specially suitable for this purpose. The conductance behaviour is related to the change with strain of Fermi surface. Both experimental and theoretically Au behaves like the free electron gas but Al has the opposite behaviour.
High-Pressure, High-Temperature Syntheses of Super-Hard α-Rhombohedral Boron-rich Solids in the B-C-N-O
Authors: Hubert Hervé , Garvie Laurence A.J. , Devouard Bertrand , McMillan Paul F.
Published: April 2011

We prepared α-rhombohedral (α-rh.) B-rich materials in the B-C-N-O system at high-pressures and temperatures. Samples were synthesized using a multianvil device and characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and parallel electron energy-loss spectroscopy (PEELS). The B-C-O compounds were obtained by reducing B2O3 with B, or mixtures of B and C between 1 to 10 GPa and 1200° and 1800° C In the B-O system we synthesized boron suboxide (nominally B6O) of high purity, crystallinity, and close to stoichiometric. Quantitative analyses give B6O0.95 and B6O0.77 for high-pressure and room-pressure samples, respectively. Between 4 to 5.5 GPa, B6O formed as macroscopic near-perfect regular icosahedra (to 30 μm in diameter). In the B-C-O system, intermediate phases were prepared showing evidence of solid solution between B4C and B6O. Boron carbide crystals, to 20 μm, containing a significant amount of O, typically B6C1.1O0.33 and B6C1.28O0.31, were grown for mixtures in which B and C were reacted with excess B2O3 at 7.5 GPa and 1700 °C. We also report the first conclusive bulk synthesis of a new boron nitride, B6N1-x. This subnitride was synthesized from B and hexagonal BN at 7.5 GPa and 1700 °C. XRD and PEELS shows that the boron subnitride has the α-rh. B structure and average composition B6N0.92
Progress in the Search for Metallic Hydrogen: 342 GPa
Authors: Narayna Chandrabhas , Orloff Jon , Ruoff Arthur L.
Published: April 2011

The experimental search for metallic hydrogen has been active for over two decades with the first claims being published in 1975, followed by several others all of which failed to pass the test of time. The present paper describes experiments in which several important changes were made in the experiment, compared to those performed previously, which enabled us to reach a pressure of 342 GPa. The path was strewn with 15 pairs of carefully chosen diamonds. At 342 GPa visible light was readily transmitted through the sample proving that it was not yet an alkali metal. The reasons why it has been so difficult to achieve the required pressure for metallization will be discussed.
Controlling the surface cleanliness of nanostructured alpha-iron and M50 type steel (Fe-Cr-Mo-V-C) powders
Authors: Schady S. F. , Law C. C. , Gell M. , Gonsalves K. E. , Morral J. E. , Rangarajan S. P.
Published: April 2011

The cleaning effectiveness of flowing hydrogen to remove oxygen (adsorbed and metal oxide) and carbon (elemental, carbides and carbon-hydrogen complex) from the surface of nanostructured alpha-iron and M50 type steel (Fe-Cr-Mo-V-C) alloy powders was investigated. The hydrogen treated powders and consolidated material were examined by bulk chemical analysis and metallographic examination. The trends in the cleaning effectiveness compared favorably with predictions from Richardson and Jeffies plots of metal-metal oxide equilibria.
Incorporation of nano-particle sites in polymer matrix by Metal ion imprinting
Authors: Singh Alok , Puranik Dhananjay , Guo Yan , Zabetakis Daniel , Chang Eddie L.
Published: April 2011

We present an approach for synthesizing polymer matrices that have been pre-organized to bind metal ions selectively. The acyclic chelator, triethylenetetramine, was modified to include a polymerizable functional group and then complexed with a target metal ion. Unlike macro cyclic ligands, the acyclic chelators have the flexibility to form chelation rings that are dependent on metal-ion size and geometry. Therefore, we have used the complexation step as a means to optimize the chelator conformation for a particular metal ion. The resulting complex was then cross linked with the matrix monomer, TRIM (2-ethyl-2-(hydroxymethyl)propane-1,3-diol trimethacrylate), to provide a rigid polymer matrix for stabilization of the conformation for the metal-ligand site. These sites were then tested for selectivity towards the imprinted metal ion. Unlike imprinting for larger molecules, the relatively smaller size of the metal ions facilitated their access to the imprinted sites embedded in the porous polymers. In addition to metal-binding applications, polymeric materials doped with metal nanoparticles and metal ions can exhibit interesting physical, chemical, optical and electronic properties.
Microscopic role of a surfactant in epitaxial crystal growth
Authors: Lee Seung Mi , Lee Young Hee
Published: April 2011

We have investigated the kinetic role of a surfactant in the epitaxial crystal growth of Si/Ge using an ab initio molecular dynamics approach. We find that adsorption and diffusion of an adatom on monohydride Si(001) surface is drastically altered from that on a clean surface in several ways. We particularly emphasize the role of H as a surfactant, and this is further compared to typical group V materials.
Mechanically assisted surface modification of polymer particles with superfine calcium phosphates
Authors: Liao Jiefan
Published: April 2011

A mechanical route plays an important role in particulate coatings and synthesis. A type of particulate surface modification, i.e., oriented coating of fine particles onto the surface of a core particle, is proposed. For achieving this concept, the author has developed a two-step process involving mechanical and chemical methods. As an example, needle-like dicalcium phosphate fine particles were coated, in a standing-up state, onto the surface of nylon-12 core particles (avg 50um). The effect of the crystal structure of dicalcium phosphate on the particulate oriented coating was investigated.
Effects of Heavy-Ion Cascade Volume on the Suppression of Radiation-Induced Segregation in Alloys
Authors: Giacobbe M. J. , Rehn L. E. , Lam N. Q. , Okamoto P. R. , Funk L. , Baldo P. , McCormick A. , Stubbins J. F.
Published: April 2011

The interactions of cascade remnants with freely migrating defects (FMDs) during dual light and heavy-ion irradiations in Cu-lat.%Au at 400°C were investigated using Rutherford backscattering spectrometry. Near-surface Au depletion driven by 1.5-MeV He ion irradiation was suppressed by concurrent bombardment with 1.2-MeV Ag ions. The dual irradiation effect suggests that shortlived cascade remnants created by heavy ions act as recombination centers for FMDs, reducing radiation-induced segregation (RIS). The effects of the total cascade volume generated by heavyion beams on the suppression of RIS were examined. The investigation revealed when 800-keV Cu and 1.2-MeV Ag ion beams produce nearly the same total cascade volume per second, their suppression effects on 1.5-MeV He-induced Au transport are also nearly equal even though the total cascade volume produced per ion for each are different. This result indicates that the suppression effect of cascade remnants produced by heavy ions depends on the total cascade volume induced per unit time and not on the total cascade volume per ion generated by individual ions of different mass and energy.
Characterization of Vacancy-Type Defects in Ion Implanted and Annealed SiC by Positron Annihilation Spectroscopy
Authors: Anwand W. , Brauer G. , Coleman P. G. , Skorupa W.
Published: April 2011

New examples of characterization of vacancy-type defects in ion implanted and annealed SiC by the established technique of slow positron implantation spectroscopy are presented. In particular, the estimation of the depths of damaged regions and their change (a) after post-irradiation annealing, or (b) due to variation of substrate temperature during implantation, is addressed.
Oxide and Nitride Formation and Segregation of Metals During Oxygen and Nitrogen Bombardment of Silicon
Authors: Williams J. S. , Petravic M. , Conway M. , Fu L. , Chivers D. J.
Published: April 2011

This study compares oxide and nitride formation during oxygen and nitrogen bombardment of Si. Ion bombardment is carried out both in a SIMS machine and in a conventional implanter at various temperatures. Stoichiometric SiO2 and slightly N-rich Si3N4 are formed during bombardment even at cryogenic temperatures. Implanted metals were found to have a strong tendency to be segregated at a moving Si-SiO2 interface during oxygen bombardment but little segregation is observed at a Si-Si3N4 interface.
Modeling Collision Cascade Structure of SiO2, Si3N4 and SiC using Local Topological Approaches
Authors: Jesurum C. Esther , Pulimt Vinay , Hobbs Linn W. , Berger Bonnie
Published: April 2011

Many crystalline ceramics can be amorphized within high-energy collision cascades whose overlap leads to global structural amorphization. Because the structural rearrangements amount to topological disordering, we have chosen to model these rearrangements using a topological modeling tool as an alternative to molecular dynamics simulations. We focus on the tetrahedral network compounds SiO2, Si3N4, and SiC, each compound comprising corner-sharing tetrahedral units, because they represent increasingly topologically constrained structures. SiO2 and SiC are easily amorphized experimentally, whereas Si 3N4 proves very difficult to amorphize. In this model, we consider the tetrahedron as the base unit, whose identity is largely retained throughout. In a collision cascade, all bonds in the neighborhood of a designated tetrahedron are broken, and we reform bonds in this region according to a set of local rules appropriate to crystalline assembly, each tetrahedron coordinating with available neighboring tetrahedra (insofar as is possible) in accordance with these rules. We generate fairly well connected amorphized structures for SiO2, but run into underconnected networks for Si3N4 and SiC which are irreparable without rebreaking and reforming primary tetrahedral bonds. The resulting structures are analyzed for ring content and bond angle distributions for comparison to the crystalline precursors.
Ion Beam Effects on the Formation of Semiconductor Nanoclusters
Authors: Schiestel S. , Carosella C. A. , Stroud R. , Guha S. , Cotell C. M. , Grabowski K. S.
Published: April 2011

Silicon rich silica films were deposited by coevaporation of silica and silicon with and without simultaneous ion bombardment. The Si-silica ratios are correlated to changes of index of refraction and shifts in an asymmetric stretching mode IR absorption. Photoluminescence between 550 and 600 nm is observed for all films which is attributed to SiO2 defects. After annealing this photoluminescence peak shows a shift to 750 nm and an increase in intensity, indicating the formation of silicon nanoclusters. This effect is more pronounced for samples prepared without ion beam treatment. ERD measurements show a correlation of photoluminescence with the presence of hydrogen in the films. The microstructure of these films were investigated by TEM. Photoluminescence from the Si nanoclusters in the films is optimized when the arrival rate of Si/silica is slightly less than 0.4.
Limiting Factors of Backside External Gettering by Nanocavities and Aluminum-Silicon Alloying in Silicon Wafers
Authors: Gay Henquinet N. , Martinuzzi S.
Published: April 2011

Float zone silicon single crystalline wafers are submitted to He ion implantations at various energy levels and fluences in the ranges 40 to 120 keV and 1016 to 1017 cm−2, respectively. Cavities are formed after annealing at 900°C for 1 h in argon. Al-Si gettering results from the deposition of a backside 1 µm thick Al wafer and annealing at 900'C for 4 h in argon. The wafers are voluntarily contaminated by 1014 to 1017 cm−3nickel atoms and diffusion length of minority carriers is determined by SPV technique and measured before and after gettering.

It is found that gettering by cavities works fairly well provided the fluence is 1017 cm−2. The gettering efficiency decreases in heavily contaminated samples suggesting that the capture of impurities by the cavities is limited by the saturation of their internal surface. Al-Si alloying appears more efficient at higher contamination levels. This is most likely due to the high solubility of metal atoms in the liquid Al-Si alloy formed during the annealing.
Characterisation of the Subthreshold Damage in MeV Ion Implanted p Si
Authors: Fatima Shabih , Wong-Leung Jennifer , Fitz Gerald John , Jagadish C.
Published: April 2011

Subthreshold damage in p-type Si implanted and annealed at elevated temperature is characterized using deep level transient spectroscopy (DLTS) and transmission electron microscopy (TEM). P-type Si is implanted with Si, Ge and Sn with energies in the range of 4 to 8.5 MeV, doses from 7 × 1012to 1×1014cm−2and all annealed at 800°C for 15 min. For each implanted specie, DLTS spectra show a transition dose called threshold dose above which point defects transform in to extended defects. DLTS measurements have shown for the doses below threshold, a sharp peak, corresponding to the signature of point defects and for doses above threshold a broad peak indicating the presence of extended defects. This is found to be consistent with TEM analyses where no defects are seen for the doses below threshold and the presence of extended defects for the doses above threshold. This suggests a defect transformation regime where point defects present below threshold are acting like nucleating sites for the extended defects. Also the mass dependence on the damage evolution has been observed, where rod-like defects are observed in the case of Si and (rod-like defects and loops) for Ge and Sn despite the fact that peak concentration of vacancies for Ge and Sn are normalized to the peak number of vacancies for Si.
Characterization of a Metastable Defect Introduced In Epitaxially Grown Boron Doped Si by 5.4 Mev α-Particles
Authors: Mamor M. , Auret F.D. , Goodman S.A. , Meyer W.E.
Published: April 2011

Deep level transient spectroscopy (DLTS) was used to examine the metastability of a defect configuration in epitaxially grown boron-doped p-type Si. We report the detection of a new metastable defect Hα2 in p-Si following room temperature alpha particle irradiation. DLTS measurements coupled with bias-on/bias-off cooling cycles were used to study the annealing and introduction kinetics of this metastable defect. After removing Hα2 by zero-bias annealing at room temperature, it was re-introduced by reverse bias annealing in the 240-265 K temperature range under predominantly first order kinetics. The energy level and apparent capture cross section, as determined by DLTS, were E,+ 0.43 eV and 1.4 × 10−15 cm2, respectively.
A Nonvolatile MOSFET Memory Device Based on Mobile Protons in the Gate Dielectric
Authors: Vanheusden K. , Warren W.L. , Fleetwood D.M. , Devine R.A.B. , Draper B.L. , Schwank J.R. , Shaneyfelt M.R. , Wlnokur P.S.
Published: April 2011

Ever since the introduction of the metal-oxide-silicon field-effect-transistor (MOSFET), the nature of mobile and trapped charge in the oxide layer has been studied in great detail. For example, contamination with alkali ions such as sodium, causing instability of the flat-band voltage, was a major concern in the early days of MOS fabrication. Another SiO2 impurity of particular interest is hydrogen, because of its beneficial property of passivating charge traps. In this work we show that annealing of Si/SiO2/Si structures in forming gas (Ar:H2; 95:5) above 400 °C can introduce mobile H+ ions into the SiO2 layer. These mobile protons are confined within the oxide layer, and their space-charge distribution is well controllable and easily rearrangeable by applying a gate bias, making them potentially useful for application in a reliable nonvolatile MOSFET memory device. We present speed, retention, endurance, and radiation tolerance data showing that this non-volatile memory technology can be competitive with existing Si-based non-volatile memory technologies such as Flash.

The chemical kinetics of mobile-proton reactions in the SiO2 film are also analyzed in greater detail. Our data show that the initial buildup of mobile protons during hydrogen annealing is limited by the rate of lateral hydrogen diffusion into the buried SiO2 films. The final density of mobile protons is determined by the cooling rate which terminates the annealing process and, in the case of subsequent anneals, by the temperature of the final anneal. To explain the observations, we propose a dynamical equilibrium model. Based on these insights, the incorporation of the proton generation process into standard semiconductor process flows is discussed.
Role of n-Type Codopants on Enhancing p-Type Dopants Incorporation in p-Type Codoped Znse
Authors: Yamamoto T. , Katayama-Yoshida H.
Published: April 2011

We propose materials design for the fabrication of low-resistivity p-type ZnSe crystals using a new doping method which involves simultaneous codoping of both n- and p-type dopants, based on the ab initio electronic band structure calculations. We have clarified that while doping of acceptor dopants, Lizn and Nse, leads to the destabilization of the ionic charge distributions in p-type ZnSe crystals, doping of donor dopants, Inzn, ClSe or ISe gives rise to n-type doped ZnSe with high donor concentration due to a large decrease in the Madelung energy. The codoping of the n- and p-type dopants (the ratio of their concentrations is 1:2) enhances the incorporation of the acceptors in p-type ZnSe crystals due to a decrease in the Madelung energy, resulting in the formation of the p-n-p complexes which occupy nearest-neighbor sites. It results in an increase in the net carrier densities and the hole mobility due to a change in the scattering mechanism from that caused by long-range Coulomb scatters to that by short-range dipole-like ones
Novel, Matched CTE Integrated Substrates for Power Electronics
Authors: Kowbel W. , Xia X. , Bruce C. , Withers J. C.
Published: April 2011

Rapid advances in high power electronic packaging require the development of new heat-sink/substrate materials. Advanced composites designed to provide thermal control as well as improved thermal conductivity have the potential to provide benefits in the removal of excess heat from electronic devices. Carbon-carbon (C-C)composites are under consideration for numerous electronic packaging applications. A new manufacturing process has been developed to produce high thermal conductivity (400 W/mK) C-C composites at greatly reduced cost (less than $50/lb). However, low CTE (0.25 × 10−6cm/cm °C) of C-C composites results in reduced fatigue life in chipon- board (COB) applications with silicon chips (CTE ≈ 2.6 × 10−6 cm/cm °C). A novel process was developed to convert the carbon matrix into the SiC matrix which retains the overall high composite thermal conductivity. This novel technology is well-suited for COB applications. Several types of coatings, such as CVD AIN, CVD Si and a polymer slurry-based low dielectric coating were applied to the C-SiC composite. Processing schemes were developed to produce crack-free coatings. Metallization of the dielectric coating was performed for the process integration with electronic devices. Thus, integrated substrates for power electronics were fabricated without the need of conventional metal/ceramic joining and associated high stresses. The properties of this new composite material for power electronics substrates are presented.
Experimental Investigation on Interfacial Adhesion in Microelectronic Assemblies
Authors: Dai Xiang , Brillhart Mark V. , Ho Paul S.
Published: April 2011

In this paper, we report recent studies on interface adhesion in flip-chip packaging. The adhesion energies of underfill interfaces found in typical flip-chip packaging pplications are characterized and presented using a racture-mechanics approach. The effects of underfill formulations and changes in polymer top-layer on PCB and chip passivation are also evaluated. The effects of underfill organosilane content, ubstrate surface chemistry and morphology, and underfill filler content are discussed in terms of fundamental mechanisms of adhesion.
Efficient Interfacial Design - A Multidisciplinary View
Authors: Shih C. F , Chen W. T. , Cotterell B. , Lahiri S. K. , Zhang Y.W.
Published: April 2011

One of the most important mechanical features in microelectronic packaging is the nterface. Recent developments in modelling interfacial fracture and the easurement of interfacial toughness relevant to microelectronic packaging are discussed.
Adhesion and Subcritical Debonding of Polymer Interfaces for Microelectronic Packaging
Authors: Snodgrass J. M. , Hotchkiss G. , Dauskardt R. H.
Published: April 2011

Techniques are discussed for evaluating both critical interface adhesion values as well as the sub-critical debond behavior of polymer/silicon and polymer/polymer interfaces. Sub-critical debonding behavior is expected to be most relevant in predicting the in-service lifetime of microelectronic packages. Our research characterizes the debonding of a benzocyclobutene overlayer, as well as a technologically relevant epoxy underfill/polyimide/silicon interface system. Adhesion values are measured in a double cantilevered beam (DCB) and four-point bend fracture mechanics geometries by driving a stable debond along the relevant interfaces. The effect of temperature on subcritical debonding in an underfill/polyimide interface is described. Issues of crack path selection involving the selection of microstructurally weak paths in the layered system are considered.
Chromium Distribution in CoCrTa/Cr Longitudinal Recording Media
Authors: Wittig J.E. , Nolan T.P. , Sinclair R. , Bentley J.
Published: April 2011

The current study of CoCr12Ta4/Cr longitudinal recording media combines high resolution electron microscopy (HRTEM) with nanoprobe energy dispersive spectroscopy (EDS) and energy-filtered imaging (EFTEM) to correlate the Cr distribution with specific microstructural features. EFTEM images show Cr enrichment at grain boundaries, both random angle boundaries and 90° bicrystal boundaries. Cr segregation within grains is also observed in the elemental maps. This intragrain segregation often occurs at a series of defects that may define separately nucleated grains having 00 misorientation. Nanoprobe EDS measurements indicate that these defects contain localized concentrations of 25 to 30 % Cr. The random angle grain boundary Cr concentration occurs with a wide range, 19 to 36 at% (mean 22%) whereas the more crystallographically related 900 boundaries contain less Cr with less variation, 15 to 21 at% (mean 17% Cr). Composition profiles across grain boundaries using both nanoprobe EDS and EFTEM images show the full-width-half-maximum of the segregation to be approximately 4 nm, with Cr depleted regions next to the grain boundary having less than 7 at% Cr. The Ta concentration revealed no statistical evidence of segregation.
The Application of Amine - Quinone Polymers in High Density Recording Media for Improved Corrosion Protection
Authors: Sharma Rahul , Warren G. W. , Nikles D. , Hu Y. , Street S.
Published: April 2011

High density, metal particle recording media consists of micron-sized iron particles in a polyurethane based polymer binder. In order to improve the corrosion resistance of the particles, two new amine-quinone (AQ) polymers, AQPU15 and AQPU100, have been investigated. Electrochemical impedance spectroscopy (EIS) was used to evaluate the corrosion behavior of iron substrates coated with two different thicknesses of each polymer. Results showed that the AQ polymers provide better protection compared with commercial polyurethane. The nature of the interaction at the polymer/metal interface has been investigated by FTIR-RA and XPS, which indicate that bonding probably occurs through the n system of the AQ functional group and the nitrogen of the soft segment, and through the quinone carbonyl functional group.
Metalorganic Chemical Vapor Deposition of Magneto-Optical Ce:YIG Thin Films
Authors: Li Yi-Qun , Cherif Mondher , Huang Jankang , Liu Wayne , Chen Qiushui
Published: April 2011

The deposition technologies of rare-earth substituted yttrium iron garnet (RE:YIG) thin films with a large Faraday rotation and their applications are briefly overviewed. Highly cerium substituted YIG films were successfully deposited on (111) GGG, (211) GGG, (100) MgO, and MgO buffered GaAs and InP substrates by single-liquid-source metalorganic chemical vapor deposition. Ce-YIG thin films can be epitaxially grown on lattice matched GGG substrates at a temperature as low as 600°C. They have excellent optical and magnetic properties along with high Faraday rotations. The films deposited on single crystal (100) MgO substrates are polycrystalline and have good magnetic properties. Sputter deposited MgO buffer layer was demonstrated for preventing the decomposition and chemical reaction of GaAs and LnP substrates resulting in successful deposition of YIG films on GaAs and InP substrates at a substrate temperature of 550°C. The films grown on MgO buffered GaAs substrates possessed good magnetic properties.
Integration of Yttrium Iron Garnet Films via Reactive RF Sputtering Bethanie
Authors: Stadler J. H. , Gopinath Anand
Published: April 2011

This work aims to equip integrated optical circuits with important magneto-optical devices, such as isolators, that are currently available only as discrete components. Reactive rf sputtering was used to grow cerium-doped yttrium iron garnet films onto a variety of substrates, including SiO2-buffered Si, fused Si02 and MgO. MgO was used because it has proven to be a good buffer material for semiconducting substrates. Ce-doping was not effective via reactive sputtering due to a scale which formed on the Ce metal that prevented sufficient contact with the rf target. The films were amorphous as deposited. Stoichiometric Y3Fe5O12 films yielded smooth, polycrystalline garnet films upon annealing. A study of the effect of fluctuations in the Y:Fe ratio revealed that oxygen content is important for the prevention of secondary phases. Therefore, a high oxygen content should be used in the sputtering gas and subsequent annealing should be performed in oxygen.
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

Nonreciprocal 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

A 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

Nanophase 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

Nanocrystalline 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

One 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

2 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

A 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

Hemispherical 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

We 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

The 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

The 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

Orientation -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

Two 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.
Study of Coating Mechanism of Non-Binding Metals Over Silica Fibers
Authors: Seo H. S. , Paek U. C. , Oh K. , Kurkjian C. R.
Published: April 2011

The mechanism of the coating of molten tin on a silica optical fiber is analyzed by a numerical method based on a three-dimensional conduction model.
Durability and Reliability of Semiconductor Devices
Authors: Sidorov V. G. , Sokolov V. I. , Sidorov D. V.
Published: April 2011

The 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

Fiber 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

Stress 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

The 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

In 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

Ga+ 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.