bluuebunny/crossref_metadata_2025 huggingface dataset:
Energetic Particle Synthesis of Metastable Layers for Superior Mechancial Properties
Authors: Follstaedt D. M. , Knapp J. A. , Myers S. M. , Dugger M. T. , Friedmann T. A. , Sullivan J. P. , Monteiro O. R. , Ager J. W. , Brown I. G. , Christenson T.
Published: April 2011

Energetic particle methods have been used to synthesize two metastable layers with superior mechanical properties: amorphous Ni implanted with overlapping Ti and C, and amorphous diamond-like carbon (DLC) formed by vacuum-arc deposition or pulsed laser deposition. Elastic modulus, yield stress and hardness were reliably determined for both materials by fitting finiteelement simulations to the observed layer/substrate responses during nanoindentation. Both materials show exceptional properties, i.e., the yield stress of amorphous Ni(Ti,C) exceeds that of hardened steels and other metallic glasses, and the hardness of DLC (up to 88 GPa) approaches that of crystalline diamond (∼100 GPa). Tribological performance of the layers during unlubricated sliding contact appears favorable for treating Ni-based micro-electromechanical systems: stick-slip adhesion to Ni is eliminated, giving a low coefficient of friction (∼0.3–0.2) and greatly reduced wear. We discuss how energetic particle synthesis is critical to forming these phases and manipulating their properties for optimum performance.
Tribological Properties of Si-DLC Coatings Synthesized with Nitrogen, Argon Plus Nitrogen, and Argon Ion Beams
Authors: Fountzoulas C. G. , Demaree J. D. , Sengupta L. C. , Hirvonen J. K. , Dimitrov D.
Published: April 2011

Hard, adherent, and low-friction silicon-containing diamond-like carbon coatings (Si-DLC) have been synthesized at room temperature by 40 keV (N+ plus N2+), 50%Ar+/50% (N+ plus N2+), and Ar+ ion beam assisted deposition (IBAD) of a tetraphenyl-tetramethyl-trisiloxane oil on silicon and sapphire substrates. X-ray diffraction analysis indicated that all coatings were amorphous. The average coating wear rate and the average unlubricated steel ball-on-disk friction coefficient, μ, decreased with increasing fraction of nitrogen in the ion beam, along with an increase in the average coating growth rate. The Knoop microhardness and nanohardness values of the coatings synthesized by the mixed argon and nitrogen ion beam were higher than the values for the coatings synthesized with 100% nitrogen or 100%argon ion beams. These friction/wear improvements are tentatively attributed to both increased hardening due to greater penetration and ionization induced hardening by the lighter (N) ions and to the presence of Si02 on the surface of N-bombarded samples.
Mesoscale Engineering of Nanocomposite Nonlinear Optical Materials
Authors: Haglund R. F. , Afonso C. N. , Feldman L. C. , Gonella F. , Luepke G. , Magruder R. H. , Mazzoldi P. , Osborne D. H. , Solis J. , Zuhr R. A.
Published: April 2011

Complex nonlinear optical materials comprising elemental, compound or alloy quantum dots embedded in appropriate dielectric or semiconducting hosts may be suitable for deployment in photonic devices. Ion implantation, ion exchange followed by ion implantation, and pulsed laser deposition have all been used to synthesize these materials. However, the correlation between the parameters of energetic-beam synthesis and the nonlinear optical properties is still very rudimentary when one starts to ask what is happening at nanoscale dimensions. Systems integration of corplex nonlinear optical materials requires that the mesoscale materials science be well understood within the context of device structures. We discuss the effects of beam energy and energy density on quantum-dot size and spatial distribution, thermal conductivity, quantum-dot composition, crystallinity and defects — and, in turn, on the third-order optical susceptibility of the composite material. Examples from recent work in our laboratories are used to illustrate these effects.
Ion Assisted Reaction In Polymer And Ceramics
Authors: Koh S. K. , Choi S. C. , Han. S. , Jung H-J
Published: April 2011

Abstracr

Ion assisted reaction (IAR), which was firstly presented in 1995 MRS Fall meeting, has been reviewed for the surface modifications of polymer and ceramics. The reaction is assisted by energetic ions from 0.5 to 1.5 keV, doses 1014 to 1017 ions/cm2, and blowing rate of oxygen 0 ∼ 8 ml/min. Hydrophilic surfaces of polymers (wetting angle < 20° and surface energy 60 ∼ 70 erg/cm2) have been accomplished by the reaction, and an improvement of wettability and an increment of the surface energy are mainly due to the polar force and hydrophilic functional groups such as C=O, (C=O)-O, C-O, etc., without surface damage. The IAR was also applied on aluminum nitride in an O2 environment and AMON on AIN is formed by the Ar+ irradiation. The improvement of bond strength of Cu films on the AIN surface resulted from the interface bonds between Cu and the surface layers. Comparisons between the conventional surface treatments and the IAR are described in terms of physical bombardment, surface damage, functional group, and chain mobility in polymer.
Atomistic simulation of defect production in β-SiC
Authors: Devanathan R. , Weber W. J. , de la Rubia T. Diaz
Published: April 2011

The process of defect formation and the threshold energies for Si and C displacements along various crystallographic directions in cubic silicon carbide (β-SiC) have been examined using molecular dynamics simulations. A combination of Tersoff and first-principles potentials was used to model the inter-atomic interactions. The lowest threshold energies for C and Si displacements were found to be 28 and 36 eV, respectively. These displacement threshold energies show excellent agreement with the results of recent first-principles calculations in SiC and with experimental observations. Simulation of a 10 keV Si cascade yielded values of about 0.1 ps for the cascade lifetime and about 3.5 for the ratio of the number of surviving C defects to Si defects. Anti-site defects were found on both Si and C sublattices. These defects may play an important role in the amorphization of SiC by energetic particle irradiation.
Suppression of Antiphase Disorder in GaAs Grown on Relaxed GeSi Buffers by Metal-Organic Chemical Vapor Deposition
Authors: Ting S. M. , Samavedam Srikanth B. , Currie Matthew T. , Langdo Thomas A. , Fitzgerald E. A.
Published: April 2011

Due to the prohibitively high 4.1% lattice mismatch, direct growth of GaAs on Si invariably leads to very high dislocation densities (> 108/cm2) which have precluded its use in device applications despite numerous attempts. However, the growth of low threading dislocation density (∼2 × 106/cm2) relaxed graded Ge/GexSi1−x/Si heterostructures can bridge the gap between lattice constants by replacing the high mismatch GaAs/Si interface with a low mismatch (< 0.1%) GaAs/Ge interface. Although the lattice mismatch problem is thus eliminated, the heterovalent GaAs/Ge interface remains highly susceptible to antiphase disorder. Since antiphase boundaries (APBs) nucleated at the GaAs/Ge interface act as scattering and nonradiative recombination centers, growth of device quality GaAs on Ge/GexSi1−x/Si demands effective suppression of antiphase disorder. The current work investigates the sublattice location of GaAs on 6° offcut (001) Ge/GexSi1−x/Si substrates as a function of atmospheric pressure metal-organic chemical vapor deposition (MOCVD) growth initiation parameters. Two distinct GaAs phases are observed, one dominant at temperatures > 600°C and another at temperatures <500°C. Incomplete phase transitions during pre-growth thermal cycling account for the appearance of localized bands of anti-phase disorder where the polarity of the GaAs film switches. We suspect that background arsenic levels in the MOCVD system are largely responsible for inducing the observed phase transitions. The complete suppression of antiphase disorder under optimized growth conditions is demonstrated by transmission electron microscopy (TEM)
Control of The Sb Redistribution in Strained SiGe Layers Using Point Defect Injection
Authors: Kuznetsovl A.Yu. , Cardenast J. , Grahnt J.V. , Svensson B.G. , Nylandsted Larsenl A. , Lundsgaard Hansen J.
Published: April 2011

Sb diffusion in strained Si1−xGex (x = 0.1 and 0.2) layers during nitridation (in NH3, 810 °C) and oxidation (in dry O2, 825 and 900 °C) of Si/Si1−xGex/Si heterostructures is measured and, subsequently, compared with that obtained for treatments in vacuum. An enhancement (ν) or retardation (η) of Sb diffusion in strained Si1−xGex after nitridation/oxidation anneals is detected. For example, 810 (NH3) and 900 °C (O2) anneals results in ν ∼ 2 and η ∼ 0.15 in strained Si0.9Ge0.1, respectively. The retardation of Sb diffusion is attributed to the injection of excess self-interstitials (I) and strongly indicating low interstitialcy fraction of Sb diffusion in strained Si1−xGex. The enhancement of Sb diffusion may be due to direct injection of vacancies (V), but only if the V diffusivities are significantly different in Si and Si1−xGex, or depletion of I in the strained Si1−xGex layers caused by the excess V concentration at the top surface of silicon layer
Electronically Enhanced Reaction of Process-Induced Defects in GaAs
Authors: Wada K. , Nakanishi H. , Yamada K. , Kimerling L.C.
Published: April 2011

The present paper reviews current understanding on enhanced reactions of process-induced defects in GaAs under electronic excitation. Device processing to be employed for point defect generation is Be ion implantation and Ar plasma etching. It is shown that reduction of electronic active centers is clearly enhanced by annealing under forward bias application and by annealing under reverse bias application at temperature as low as 200°C. The enhancement mechanisms are discussed in terms of recombination-enhanced defect reaction and structural instability induced by charge state effect.
Gettering of Iron and Surface Oxygen by High-Energy Boron ion Implantation in Silicon
Authors: Jain Amitabh , Mercer Douglas E. , Yu Ning , Lowell John K.
Published: April 2011

The gettering of transition metals in silicon presents new challenges since older schemes such as internal gettering cease to be effective with newer technologies. The oxygen concentration in active regions is also a matter of concern when denuding cycles are not employed. Implantation of a deep layer of boron is a promising technique. The effects of boron implants at 1.7 MeV in the dose range 1014 – 1015 at./cm2 were studied with regard to the redistribution of both Fe and 0 after a thermal cycle. Fe was introduced onto the front surface of wafers by deposition after boron implantation. The redistribution of these species was monitored through SIMS depth profiles. In addition, diffusion length measurements from the back surface of the wafers were employed as a new means of assessing Fe gettering. In general there is a lowering of the surface oxygen concentration that increases with dose, or with temperature in the range 850-1000°C. The oxygen concentration can be lowered to a level comparable to denuded wafers at the upper end of this range. The amount of Fe gettering is higher after 850°C than after 1000°C at a given dose. Diffusion length measurements correlate well with SIMS data and provide a convenient method of investigating Fe gettering. This study has demonstrated the feasibility of optimizing a combination of dose and temperature for the gettering of Fe and the lowering of surface oxygen concentration to an acceptable level for device fabrication.
Charge Redistribution and Defect Relaxation in Heavily Damaged Silicon Studied Using Time Analyzed Transient Spectroscopy
Authors: Mohapatra Y.N. , Giri P.K.
Published: April 2011

We have carried out electrical characterization of defects in heavily damaged silicon, where damage is created by MeV heavy ions at doses near but below amorphization threshold. Trapping kinetics over several orders of magnitude in time have been monitored using isothermal spectroscopy called Time Analyzed Transient Spectroscopy (TATS). Two distinct effects regarding the nature of changes in density of states in the gap have been demonstrated. Firstly, we show that charge redistribution among multiple traps occur such that only the occupancy of the deeper states increase at the cost of shallower ones for long time filling. Secondly, a novel defect relaxation mechanism is observed for samples with relatively lower damage. A trap is seen to exhibit progressive deepening in energy with increase in filling time, finally stabilizing for large filling times. From the athermal nature of associated TATS peaks, it is argued that the relaxation involves large entropic contribution to free energy. The necessity of using a time domain relaxation spectroscopy such as TATS in the study of different mechanisms of relaxation is demonstrated.
Hydrogen Enhanced Defect Reactions in Silicon: Interstitial Atom - Vacancy
Authors: Nazarov A.N. , Pinchuk V.M. , Yanchuk T.V. , Lysenko V.S.
Published: April 2011

In the paper the model of interaction of the hydrogenated vacancy with silicon interstitial and different dopants (B, P and As) in crystalline silicon is considered. Quantum chemical calculations using the SCF MO LCAO technique in the NDDO valence approach show that the hydrogenation of the vacancy leads to the considerable decrease of the energy barrier height for the interstitial atom incorporation into the vacancy site of the crystalline lattice. The potential barriers for incorporation of the interstitial into the site and for leaving the atoms from the site have been calculated as a function of hydrogen localization in the vicinity of the vacancy (inside and outside of the vacancy), the charge state of hydrogen localized outside the vacancy (HO, H+ and H-) and the transport direction (<111>, <110> and <100>) of the atoms both to the vacancy and out from it. The theory is compared with the reported experimental results.
An Investigation of the Limit of Detection and the Scattering Dependence of the Optical Precipitate Profiler (OPP)
Authors: Mule'stagno L. , Hill D.E. , Standley R. , Olmo M. , Holzer J.C. , Falster R. , Fraundorf P.
Published: April 2011

The Optical Precipitate Profiler (OPP) and similar instruments are establishing themselves as routine techniques for measuring bulk micro-defect density (BMD) and denuded zone depths in semiconductor wafers. This task has traditionally been done by means of the cleave-and-etch technique in which defects are counted on a cleaved edge of an etched wafer using an optical microscope. The OPP makes this task faster, simpler and more accurate. In addition it can perform the measurement on a whole wafer.

We have used the OPP to measure defect density and scattering intensities from a set of silicon wafers with different precipitate sizes. The wafers were all given the same nucleation heat treatment but the precipitates were then grown at 1000°C for 1, 2, 4, 8, 16 and 32 hours. The size distributions and densities of the precipitates in each wafer were determined by Transmission Electron Microscopy (TEM). In a second experiment wafers with precipitate densities varying over four orders of magnitude as determined by cleaveand-etch were also measured by the OPP.

From these experiments we have estimated that the OPP can detect defects with an equivalent radius of 16 ± 8 nm and larger. We have also found that the scattering voltage (strength) depends on the precipitate radius, r3, as approximately r3 and that there is an upper number density limit above which the OPP is unable to measure the precipitate density accurately. For our setup this upper density limit was about 1.5 - 2.0 × 1010 defects/cm3 as measured by cleave-and-etch.
Compliant Substrates With an Embedded Twist Boundary
Authors: Lo Y. H. , Zhu Z. H.
Published: April 2011

In this article, we propose a new model to explain how heteroepitaxial layers grown on a twist-bonded thin layer may have a significantly reduced number of threading dislocations even if the strain in the epitaxial layers is relaxed. We first point out the deficiency in the existing compliant substrate theory by showing that all the synthesized “compliant substrates” fail to behave as “ideal” free-standing templates assumed by the current theory. Our new model is constructed on the base of stress field interactions between the heteroepitaxial layer and the embedded twist boundary. In the new model, the reduction in threading dislocation density originates from the extension of the dislocation half loops due to the effect of misfit dislocation pinning by the twist boundary. When the average size of the dislocation half loops increases substantially from micrometers to millimeters or even to the size of the wafer, the density of threading dislocations drops significantly. This model does not require any “macroscopic” motion between the bonded thin layer and the handle wafer as the current theory does, which makes it more agreeable with the experimental results
Experimental Characterization of Material Properties of 63Sn37Pb Flip Chip Solder Joints
Authors: Wiese S. , Feustel F. , Rzepka S. , Meusel E.
Published: April 2011

The paper presents new material data of real flip chip solder joints. A testing apparatus was designed to perform reversible shear tests on flip chip joints. In contrast to previous test setups for similar purposes this tester provides an infinite stiffness, a very high precision force (1 mN resolution) and displacement (20 nm resolution) measurement. The experimental program included cyclic shear tests for elastic plastic material data as well as a newly developed reversal creep and relaxation test for time depended material properties. A subsequent FEM simulation was applied to evaluate experimental raw data and to determine the parameters of material models provided by ANSYSTM. A user defined creep model had been added to the source code, in order to receive a convenient solder model for FE-Analysis of SnPb37 flip chip solder joints under thermomechanical stresses in electronic packages. The results of this study shows that the material behavior of flip chip solder joints is much more like that of bulk samples with a comparable micro structure than it is commonly believed up to now, because of the previously published data.
Magnetic Order of Co0.1Pt0.9 in Proximity of CoPt3
Authors: Shapiro A.L. , Hellman F. , Fitzsimmons M.R.
Published: April 2011

A polarized neutron reflectometry study of the magnetization density depth profile of a Co0.1Pt0.9-CoPt3 bilayer film found evidence for an induced moment in the Co0.1Pt0.9 overlayer in close proximity to the CoPt3 underlayer. If the moment of Co in these films is that of the bulk, then the μpt = 0.09(1)μB in the overlayer, and μpt = 0.04(1)μB, in the underlayer. In addition, ferromagnetic order of the Co0.1Pt0.9 overlayer was observed 8K above Tc for the material in the bulk.
Patterned Garnet Films on Substrates with Ion-Beam Bombarded Micropatterns
Authors: Okamura Yasuyuki , Yamamoto Sadahiko
Published: April 2011

We report the selected-area epitaxy of rare-earth iron garnet crystalline and amorphous straight ridge patterns, from 4μm to 8μm in width, deposited on Gd3Ga5O12 single crystal substrates. These samples were fabricated via a sputter epitaxial method on substrates that were partially etched by ion-beam bombardment. The strip pattern direction has given the considerable influence on the crystal-graphic formation of the sidewall of the grown ridge. The ridge shapes were similar to results that have been reported for the dissolution forms of garnet crystals in phosphoric acid and the facet of garnet crystals grown from flux. Furthermore, we have successfully grown both an epitaxial garnet film onto an amorphous film and an amorphous straight ridge with a triangular shape surrounded by crystal.
Integrated Nonreciprocal Devices for Application in Optical Communication Systems
Authors: Shintaku T. , Sugimoto N. , Tate A. , Kubota E. , Kozawaguchi H. , Katoh Y.
Published: April 2011

We describe our recently developed integrated isolators. Their structure is simple, in that it consists solely of a single-mode channel magneto-optic waveguide. The operating principle is that a backward fundamental TM mode wave is converted to higher-order or radiation TE modes while a forward fundamental TM mode wave propagates with no mode conversion. These isolators are realized using a single-mode rib channel waveguide in Ce-substituted yttrium iron garnet which has a very large Faraday rotation. We obtain 13-27 dB isolation around a wavelength of 1.55 μm. We also review our recent study on a hybrid-integrated polarization-independent optical circulator based on a nonreciprocal Mach-Zehnder interferometer which does not need a polarization-beam splitter. We obtain 14.1-23.7 dB isolation at λ = 1.55 μm.
Recent Advances in Magnetostatic Waves-Based Integrated Magnetooptic Bragg Cell Modulators in Yig-Ggg Waveguides
Authors: Tsai Chen S.
Published: April 2011

The most recent advances in the integration architecture and diffraction efficiency of magnetostatic wave (MSW)-based guided-wave magnetooptic (MO) Bragg cell modulators in yttrium iron garnet-gadolinium gallium garnet (YIG-GGG) waveguides are reported. A curved ion-milled hybrid waveguide lens pair has been integrated with a MO Bragg cell modulator in a taper waveguide with dimensions of 6.0x16.0mm2 to facilitate the collimation and focusing functions. An enhancement in the Bragg diffraction efficiency by two-to six-fold has been accomplished using a non-uniform bias magnetic field. An oscillator-based MO Bragg cell modulator has also been constructed and has provided a Bragg diffraction efficiency which is higher by a factor of two to four than that of a conventional delayline-based modulator.
Colloidal Particles: Spherical Yttrium Iron Garnet
Authors: Godoi R.H.M. , Jafelicci M. , Marques R.F.C. , Varanda L.C.
Published: April 2011

The purpose of this work is to obtain spherical particles YIG from micrometric to nanometric scales. The spherical particles were obtained from cation hydrolysis in acid medium by adding urea or ammonia in order to carry out a homogeneous nucleation process up to 90°C. Different composition and morphology were achieved by changing reactant concentrations, precipitation agent and stabilizing agent. X-ray diffractometry, electrophoretic mobility, transmission and scanning electron microscopies were carried out on these particles to investigate the phase identification, mobility, morphology and particle size. Crystalline YIG, with spherical characteristics, was obtained. The surface potential presented different characteristics for different dispersion media.
Nonlinear Magneto-Optical Kerr Effect in Gd-Containing Langmuir-Blodgett Films
Authors: Didenko N.V. , Fedyanisn A.A. , Khomutov G.B. , Murzina T.V. , Aktsipetrov O.A.
Published: April 2011

Magnetization induced second harmonic generation (MSHG) is observed in Gd-containing Langmuir-Blodgett (LB) films. The nonlinear optical studies reveal significant alterations in the second harmonic generation (SHG) intensity and in the polarization and phase of the second harmonic (SH) wave induced by application of DC magnetic field. The violation of polarization selection rules and the diffusenes of the MSHG intensity indicates the inhomogeneity of LB structure and the hyper-Rayleigh scattering mechanism of MSHG. The latter proofs the existence of 2D-islands of Gd ions in the structural unit of the LB films which is composed by monolayer of rare-earth ions compressed between two layers of stearic acid molecules.
Synthesis of nanostructured silica powders by a room temperature aerosol process
Authors: Hyeon-Lee Jingyu , Beaucage Gregory , Pratsinis Sotiris. E.
Published: April 2011

Nano-sized porous silica powders are synthesized by a room temperature aerosol process. Reactant mixing configuration, reactant temperature, and drying temperature effects on the physical and morphological features of these powders are studied by nitrogen adsorption and small angle xray scattering techniques. These silica powders have high specific surface areas up to 600 m2/g, and show narrowly confined mesoporous characteristics. The powders display some structural change with temperature. The morphological features are modeled as mass fractals by small angle x-ray scattering. Measured fractal dimensions are around 2.8, indicating diffusion limited growth processes.
Schnell Gel: Rapid Formation of Low Density Gels from a Tetra(Fluoroalkoxy)Silane
Authors: Sharp Kenneth G.
Published: April 2011

A new family of simple precursors to silica gel has been developed. The gel precursors are tetra(polyfluoroalkoxy)silanes, the prototype being Si(OCH2CF3)4. Formation of transparent monolithic gels with no added catalyst can be six orders of magnitude faster than comparable reactions of Si(OCH2CH3)4[TEOS]. Extremely low density gels can be generated in minutes at concentrations at which TEOS does not gel at all. Pore sizes in the wet gels were estimated from hydrodynamic relaxation in a beam-bending experiment on cylindrical logs. In a gel at 1% solids, the pore size was approximately 100 nm. Monolithic gels can be created at concentrations at least as low as 0.1% solids and have higher moduli than predicted. NMR and GC/IR evidence indicates extremely facile hydrolysis and condensation pathways and very few silanol or cyclic intermediates in the sol. The chemistry can also be conducted in perfluorinated solvents, enabling synthesis of silica/fluoropolymer nanocomposites.
Drying of Nano-Size Materials
Authors: Maskara A. , Menon V. , Wallace S. , Smith D.M.
Published: April 2011

The physics and chemistry of drying of nano-size materials (porous solids or particles with characteristic dimensions less than 100 nm) is considered. Approaches for reducing capillary pressure and surface passivation in an effort to avoid shrinkage are presented. In addition, the effect of key variables on drying costs (both capital and operating/energy) is presented.
Ultrasonic Treatment of Nanostructured Powders for the Production of Zirconia Ceramics
Authors: Khasanov O.L. , Pokholkov Yu.P. , Sokolov V.M. , Dvilis E.S. , Strutz V.K. , Ivanov Yu.F. , Dedov N.V.
Published: April 2011

The structure and mechanical properties of Y-TZP nanoceramics produced by ultrasonic (US) action on nanostructured ZrO2 – 5.4wt% Y2O3 powder have been analyzed. The influence of powder US-treatment on elastic aftereffect of a compact, uniformity of ceramics volumetric shrinkage, on ceramic nanostructure forming and as a result on its density, hardness, impact strength was shown. The optimum of power level of US-action was defined.
Microstructures and Photoluminescence in Nanocrystalline Barium Titanate
Authors: Zhang M. S. , Yu J. , Zhang W. F. , Yin Z. , Chen W. C.
Published: April 2011

Barium titanate ultrafine particles are prepared by hydrothermal method at low temperature. Their phase structures and photoluminescence (PL) properties are examined by X-ray diffraction and Raman spectroscopy. The critical size of the cubic-tetragonal phase transition is about 48 nm and the lattice parameter ratio c/a equals 1.003. Strong photoluminescence is observed with central frequency located at 695 nm. The spectral behaviors at different annealing times and temperatures are studied. We attribute them to the semiconducting hexagonal phase embeded in the nanophase cubic BaTiO3to form trap centers and cause PL process.
Crystal Growth Studies During Aerosol Synthesis of Nanostructured Fullerene Particles
Authors: Joutsensaari J. , Kauppinen E.I. , Bernaerts D. , Van Tendeloo G.
Published: April 2011

We have studied crystal growth during aerosol synthesis of nanostructured C60, C70 and mixed fullerene particles. Fullerene particles have been produced by aerosol droplet drying and crystallization as well as via vapor condensation starting from solutions of fullerenes in toluene. Morphology, crystallinity and crystal structure of fullerene particles produced in various processing temperatures were studied by scanning and transmission electron microscopy. The results show that both highly disordered and single crystal particles with a size of about 100 nm are formed at reactor operating temperatures of 500 °C and above. The ultrafine particles formed via vapor condensation are mostly polycrystalline. Many of crystalline particles have perfectly faceted morphology, i.e., hexagonal plate-like, decahedral and icosahedral shapes. The plate-like particles are lamellar-twinned and the decahedral and icosahedral particles are multiply twinned. Crystallite formation and growth mechanisms of the particles are discussed. In addition, electron diffraction results show that fullerene alloys with fcc structure can be produced via aerosol synthesis methods.
The Effect of Oxide Layers on Gas-Generating Hydride Particles During Production of Aluminium Foams
Authors: Gergely V. , Clyne T. W.
Published: April 2011

Melt routes to metallic foam production offer attractions of low cost and the potential for good microstructural control. In situ gas generation may be preferable to external gas injection in terms of the important objective of generating a fine and uniform cell structure. The main difficulty with this approach has been that of ensuring that the gas-generating powder is suitably dispersed throughout the melt before the gas is released and the cells are formed.

In the present paper, procedures are outlined for preparation of powders for use in aluminium melts, where gas will be released only after a suitable delay, allowing the powders to first become well-dispersed in the melt and solidification to start. Pre-treatment of the foaming agent also facilitates a flexible production of castings with various porosity at the same processing conditions simply by varying the thickness of a diffusion barrier layer on the gas-releasing agent. The role of the melt viscosity history, as a function of a heat extraction rate from the solidifying melt and an alloy composition, on the final porosity of the castings is also briefly discussed.
Lvophilic Liouid Porosimetry and a New Liouid Autoporosimeter
Authors: Tyomkin I.
Published: April 2011

Lyophilic liquid porosimetry determines the volumes of different size pores by measuring the amount of liquid in these pores, thus, providing pore volume distribution (PVD) data for porous structures. Any liquid that wets the sample may be used. This opens unique opportunities for porous structure evaluation. It provides realistic PVD analysis when the liquid of interest changes the porous structure. It determines uptake/drainage hysteresis of real liquids. It allows direct measurements of uptake and retention capillary pressures with different amounts of liquid in a sample. Lyophilic liquid porosimetry determines liquid/solid contact angles of different size pores within the sample. It can also be used for PVD analysis of both soft, brittle materials and porous metal materials.
Process Modeling of Ti-6Al-4V SPM Materials
Authors: Ahmed S. S. , Huang G. , Gegel H. , Barker D.
Published: April 2011

Structural Porous Metals (SPM) was specifically designed to offer large weight reductions in structural applications. The pores of gas are incorporated into the SPM during hot isostatic pressing. Since the gas in the pores are at high pressure and are closed isolated pores, SPM can be processed by standard methods such as rolling or forging without collapsing the gas pores. The objective of this paper is to show that the combination of computer simulation and intrinsic workability modeling provide a rapid and cost-effective way, for understanding the process and selecting the process parameters. This paper explains how SPM material data and developed material density updating scheme can be used in conjunction with the existing theory and FEM model.
Parameters of Construction for Applications of Metal Foams
Authors: Neugebauer R. , Hipke Th.
Published: April 2011

This article will present characteristics that have great importance for the industrial use of metal foam structures. In detail, these are

Design criteria for detachable joint connections

Investigation of the thermal behavior of sandwich composites
Compressive Deformation and Yielding Mechanisms in Cellular Al Alloys Determined Using X-ray Tomography and Surface Strain Mapping
Authors: Bart-Smith H. , Bastawros A.-F. , Mumm D. R. , Evans A. G. , Sypeck D. J. , Wadley H. N. G.
Published: April 2011

The mechanisms of compressive deformation that occur in closed cell Al alloys have been established. This has been achieved by using x-ray computed tomography (CT) and surface strain mapping to determine the deformation modes and the cell morphologies that control the onset of yielding. The deformation is found to localize in narrow bands having width of order of a cell diameter. Outside the bands, the material remains elastic. The cells within the bands that experience large permanent strains are primarily elliptical. A group of cells work collectively to allow large localized deformation. Size does not appear to be the initiator of the deformation bands. Equiaxed cells remain elastic. The implications for manufacturing materials with superior mechanical properties are discussed. Visualization of internal deformation of a closed cell Al alloy core, as part of a sandwich panel construction, is also possible using x-ray tomography. Preliminary results for a punch indentation test are presented.
Model Based Temperature Control in RTP Yielding ±0.1 °C accuracy on A 1000 °C, 2 second, 100 °C/s Spike Anneal
Authors: Vandenabeele Peter , Renken Wayne
Published: April 2011

A Model Based Control method is presented for accurate control of RTP systems. The model uses 4 states: lamp filament temperature, wafer temperature, quartz temperature and TC temperature. A set of 4 first order, nonlinear differential equations describes the model. Feedback is achieved by updating the model, based on a comparison between actual (measured) system response and modeled system response.
Partial Transparency Effects of Silicon During Rapid Thermal Processing
Authors: Abramson A. R. , Tadal H. , Nieva P. , Zavracky P. , Miaoulis I. N. , Wong P. Y.
Published: April 2011

The radiative properties of a silicon wafer undergoing Rapid Thermal Processing (RTP) are contingent upon the doping level of the silicon substrate and film structure on the wafer, and fluctuate drastically with temperature and wavelength. For a lightly doped substrate, partial transparency effects must be considered that significantly affect absorption characteristics. Band gap, free carrier, and lattice absorption are the dominant absorption mechanisms and either individually or in concert have considerable effect on the overall absorption coefficient of the silicon wafer. At high doping levels, partial transparency effects dissipate, and the substrate may be considered optically thick. A numerical model has been developed to examine partial transparency effects, and to compare lightly doped (partially transparent) and heavily doped (opaque) silicon wafers with a multilayer film structure during RTP.
Evaluation Of 2.0 nm Grown and Deposited Dielectrics in 0.1 μm PMOSFETs
Authors: Srivastava A. , Heinisch H. H. , Vogel E. , Parker C. , Osburn C. M. , Masnari N. A. , Wortman J. J. , Hauser J. R.
Published: April 2011

The quality and composition of ultra-thin 2.0 nm gate dielectrics advocated for the 0.1 μm technology regime is expected to significantly impact gate tunneling currents, P+-gate dopant depletion effects and boron penetration into the substrate in PMOSFETs. This paper presents a comparative assessment of alternative grown and deposited gate dielectrics in sub-micron fabricated devices. High quality rapid-thermal CVD oxides and oxynitrides are examined as alternatives to conventional furnace grown gate oxides. An alternative gate process using in-situ boron doped and RTCVD deposited poly-Si is explored. PMOSFETs with Leff down to 0.06 μm were fabricated using a 0.1 μm technology. Electrical characterization of fabricated devices revealed excellent control of gate-boron depletion with the in-situ gate deposition process in all devices. Boron penetration of 2.0 nm gate oxides was effectively controlled by the use of a lower temperature RTA process. The direct tunneling leakage, although significant at these thicknesses, was less than 1 mA/cm2 at Vd = −1.2 V for all dielectrics. MOSFETs with comparable drive currents and excellent junction and off-state leakages were obtained with each dielectric.
The Effects of Small Concentrations of Oxygen in RTP Annealing of Low Energy Boron, BF2 and Arsenic Ion Implants
Authors: Downey Daniel F. , Chow Judy W. , Lerch Wilfried , Niess Juergen , Marcus Steven D.
Published: April 2011

Ion implants of 1.0 keV 11B+, 5 keV BF 2+, and 2.0 keV As+ at a dose of IeI5/cm2 were rapid thermal annealed (RTA) in a STEAG AST-2800µ with varying percents of oxygen in N2, ranging from 0-lppm to 50,000 ppm to investigate the effects of low concentrations of oxygen during anneal. Sheet resistance (Rs), ellipsometry, SIMS, Tapered Groove Profilometry (TGP), and Scanning Force Microscopy (SFM) were employed to characterize these layers. For each of these implant cases, an optimal RTA condition is established which maximizes retained dose while still producing shallow junctions. As a function of O2 content, anneal temperature and implant condition, three regimes are observed that affect after anneal retained dose. These regimes are: dopant loss to the ambient resulting from etching of Si, dopant loss by out-diffusion from evaporation/chemical reactions, a capping regime that minimizes out-diffusion. In this later regime the dopant loss results from consumption into the RTA grown oxide. In addition, this paper also discusses oxidation enhanced diffusion (OED) and identifies its extent as a function of temperature and O2 content of the anneal for the three implant conditions investigated. For example, a 1.0 keV 11B+wafer annealed at 1050°C lOs in a controlled 33 ppm of O2 in N2 yields a SIMS junction depth 320 Å shallower than previously reported by others.
Control and Impact of Processing Ambient During Rapid Thermal Silicidation
Authors: Maex K. , Kondoh E. , Lauwers A. , Steegen A. , De Potter M. , Besser P. , Proost J.
Published: April 2011

The introduction of rapid thermal processing for silicide formation has triggered a lot of research to temperature uniformity and reproducibility in RTP systems. In addition to the temperature, the ambient control is to be taken into account. Although gasses are specified to a low level of contaminants, the RTP step needs to be optimised for optimal contaminant reduction. Besides, the process wafer itself is a source of contamination.

In this paper an overview will be given of the role of RTP ambient on the silicidation processes. The effect of the wafer on ambient purity will be highlighted. It will be shown that the use of a reactive capping layer during silicidation represents an adequate solution for both sources of contamination.
Development and Characterization of a Cvd System for Thin-Film Solar Cell Manufacturing
Authors: Faller F. R. , Hurrle A. , Schillinger N.
Published: April 2011

With the development of crystalline-silicon thin-film solar cells (c-SiTFC) CVD has gained importance in a new field of application. In recent years research resulted in a large variety of different concepts of c-SiTFCs. Many of these concepts require the deposition of a silicon film of good quality. i.e., at high temperature. However, little effort has been made up to this point to develop a suitable apparatus for that purpose, especially for the case of mass production of such cells. In this paper we present a self-constructed CVD system that we believe has the potential to meet the goals of an economical production of c-SiTFCs. An extension of the existing apparatus into a system in which the substrates enter the reactor at one side and leave it at the other side in a continuous way is feasable.

The present system is characterized according to its behavior when typical CVD parameters are changed, the silicon conversion yield was investigated, and solar cells with a maximum efficiency of 15.3% were fabricated from epitaxial layers deposited on various substrates
RTP Calibration Wafer using thin-film Thermocouples
Authors: Kreider K. G. , Dewitt D. P. , Tsai B. K. , Lovas F. J. , Allen D. W.
Published: April 2011

Rapid thermal processing (RTP) is a key technology for the cluster tool, single wafer manufacturing approach that is used to produce integrated circuits at lower cost with reduced line widths and thermal budgets. However, various problems associated with wafer temperature measurements and dynamic temperature uniformity have hindered the widespread use of RTP in semiconductor device manufacturing. The current technology for calibrating the radiometers employs a thermocouple instrumented wafer. We have accomplished improvements in the accuracy of these measurements through the use of thin-film thermocouples and the new Pt/Pd thermocouple system. These new calibration wafers can reduce the uncertainty in wafer temperature measurement technology by (1) reducing the perturbation due to heat transfer at the thermocouple junctions and (2) replacing conventional thermocouples with the superior Pt/Pd system. The thin-film thermocouples were calibrated using proof specimens fabricated with the Si 200 mm wafers and evaluated in the NIST RTP sensor test bed.

The commercial type K thermocouples yielded temperature measurements within 4 °C of the thin-film Rh/Pt and Pt/Pd thermocouples on the 200 mm calibration wafer between 725°C and 875 °C. The Pt/Pd thin-film thermocouples proved less durable than the Rh/Pt thin films and the limitations of these systems are discussed. We also present a comparison of the radiometric measurements with the thermocouple measurements using a model estimating the wafer temperature from its spectral radiance temperature.
On the Interaction of Insoluble Spherical Particles with a Solidifying Interface in the Presence of Morphological Instabilities
Authors: Hadji L. , Davis A.M.J.
Published: April 2011

The interaction of a dilute suspension of spherical particles with a moving solidifying front is investigated analytically. The front emerges during the unidirectional solidification of a dilute binary alloy. A linear stability analysis of the planar interface reveals that the presence of the particles has a destabilizing effect, i.e. the critical value of the control parameter, taken here to be the concentration faraway from the interface, for the onset of the Mullins-Sekerka instability is lowered due to the particles' presence.
The Microstructure of Portland Cement-Based Materials: Computer Simulation and Percolation Theory
Authors: Garboczi Edward J. , Bentz Dale P.
Published: April 2011

Portland cement-based materials are usually composites, where the matrix consists of portland cement paste. Cement paste is a material formed from the hydration reaction of portland cement, usually a calcium silicate material, with water. The microstructure of cement paste changes drastically over a time period of about one week, with slower changes occurring over subsequent weeks to months. The effect of this hydration process on the changing microstructure can be represented using computer simulation techniques applied to three dimensional digital image-based models. Percolation theory can be used to understand the evolving microstructure in terms of the three percolation thresholds that are of importance in the cement paste microstructure: the set point, capillary porosity percolation, and the percolation of the C-S-H phase.
High-Temperature Ageing of Modern Polymer-Coated Optical Fibres
Authors: Mauron P. , Nellen Ph. M. , Sennhauser U.
Published: April 2011

Reliability and durability are essential for optical fibres in both telecommunication networks and sensor applications. We report on stress-free accelerated ageing of modem telecommunication fibres in a temperature range from 60 °C to 150 °;C in dry air, relative humidity (rh) up to 85 %, and deionised water. Fibre fracture stress was measured by dynamic tensile testing according to IEC 60793-1-3 standard requirements. Ambient humidity effects on fibre fracture strength are shown. High temperature and relative humidity ageing behaviour of fibres and acrylate coatings is discussed. Fibre fracture strengths were fitted as functions of ageing time and ageing temperature using single process Arrhenius-based models. Acceleration factors can differ by several orders of magnitude, depending on the activation energy of the process. High temperatures damage acrylate coatings, which might deteriorate its adhesion to the fibre, thus introducing new ageing mechanisms not experienced under service conditions. Nevertheless, short time ageing at high temperature is useful for estimating relative lifetime of different products and for optimizing production process.
Effect of Mechanical Stripping and Arc-Fusion on the Strength and Aging of a Spliced Recoated Optical Fiber
Authors: Volotinen T. , Zimnol M. , Tomozawa M. , Lee Y.-K. , Raine K.
Published: April 2011

Median strength 4 GPa and Weibull slope 5 were obtained after stripping the coating from fibers with a mechanical stripping technique. However, the median strength was found to decrease to 1.6 GPa following fusion splicing. Most of the fractures in a tensile test occurred at a distance of 1 mm from the splice point. The internal axial tensile stress in the fiber cladding was found to be removed over a 2 mm section over the splice point. The surface fictive temperature was found to be decreased only at the zones where the fibers fracture. The reason for the fiber weakening during fusion is therefore thought to be due to the intrinsic structural changes in the silica indicated by the fictive temperature decrease. The magnitude of the decrease can be reduced by using a quicker fusion process. The corrosion velocity around a fusion splice point during aging in hot tap water was found to be significantly higher than along the fiber elsewhere. Silica layers with a thickness of hundreds nanometers were removed uniformly. However, the weakest points (roughest surface) after water aging were located in the ends of the recoated section.
Packaging of Fiber Sensors for Civil Engineering Applications
Authors: Brönnimann R. , Nellen Ph. M. , Anderegg P. , Sennhauser U.
Published: April 2011

Many optical fiber sensor systems in outdoor applications are in operation and reliability aspects are a major concern. We installed multiplexed fiber optical Bragg grating sensor systems in a stay cable bridge and in a power dam both operational for about two years now. We report on design aspects of such systems which have several constraints: First, the sensing parts of a single multiplexed fiber had to be located at certain positions and in a specific orientation. Further, the sensors must be compensated for environmental influence, the fibers were not allowed to be bent too tightly, and the fibers had to be embedded and protected in a sensor body in a way to survive its installation in the monitored structure. Finally the sensor must be reliable to be a useful measurement device.

We present long term monitoring data and test results concerning the reliability of our systems and discuss benefits and disadvantages of the various applied sensor designs.
Contact Issues of GaN Technology
Authors: Qiao D. , Yu L.S. , Lau S. S. , Sullivan G. J. , Ruvimov S. , Liliental-Weber Z.
Published: April 2011

In this paper, we discuss the issue of fabricating reliable and reproducible ohmic contacts on AlGaN HFET structures. During the course of our investigation of fabricating contacts to HFETs, we found that the contact properties could vary significantly from one sample to another, even though they were nominally the same. This problem was prominently manifested in the ohmic contact behavior. The origin of this problem was traced back to the variation of the HFET structure during growth. In this paper, we report an attempt to fabricate reproducible ohmic contacts of these structures.