bluuebunny/crossref_metadata_2025 huggingface dataset:
Bending Stress in an Optical Fiber Interconnect Experiencing Significant Ends Off-Set
Authors: Suhir E.
Published: April 2011

A solution to the nonlinear problem of bending of an optical fiber interconnect is considered for the case when the interconnect experiences large deflections due to a significant lateral ends off-set. Thissolution can be helpful in the analysis and design of interconnects subjected to a significant ends off-set. It can be used also to assess the accuracy of the predictions, based on the linear approach.
High Precision Silicon Platform Using Self-Alignment Process
Authors: Sakushima S , Nakashima K , Masuda Y , Abe S , Takemura K , Kyomasu M
Published: April 2011

Silicon platforms were fabricated for optical modules and realize sub-micron precision using self-alignment process. This paper features a self-alignment process and use of precision platforms.
Critical issues In The Mechanical Reliability of Lightguide Fibers
Authors: Kurkjian C. R.
Published: April 2011

In order to guarantee a minimum initial strength, lightguide fibers are proof-tested. However, the strength of these fibers is known to depend on time (due to fatigue and aging) and this time-dependence must be taken into account in the calculation of fiber lifetimes. While hermetic coatings can be applied to eliminate strength degradation with time, they are rarely used. It is thus necessary to understand the time-dependent behavior well enough to ensure a desired lifetime (without an excessive and costly safety factor), or alternatively, it is necessary to validate a fundamental strength limit. This paper discusses the progress that has been made on issues related to such fiber lifetime predictions. In particular, it is pointed out that the possible variations in flaw character and coating chemistry make simple generalizations difficult and require that fundamental understandings be developed.
Mechanism of Motion of an Optical Fiber Aligned by a Solder Droplet
Authors: Powell Adam , Warren James , Bailey Christopher
Published: April 2011

Solder is often used as an adhesive to attach optical fibers to a circuit board. In this proceeding we will discuss efforts to model the motion of an optical fiber during the wetting and solidification of the adhesive solder droplet. The extent of motion is determined by several competing forces, during three “stages” of solder joint formation. First, capillary forces of the liquid phase control the fiber position. Second, during solidification, the presence of the liquid-solid-vapor triple line as well as a reduced liquid solder volume leads to a change in the net capillary force on the optical fiber. Finally, the solidification front itself impinges on the fiber. Publicly-available finite element models are used to calculate the time-dependent position of the solidification front and shape of the free surface.
Dry and Wet Etching for Group III – Nitrides
Authors: Adesida I. , Youtsey C. , Ping A. T. , Khan F. , Romano L. T. , Bulman G.
Published: April 2011

The group-III nitrides have become versatile semiconductors for short wavelength emitters, high temperature microwave transistors, photodetectors, and field emission tips. The processing of these materials is significant due to the unusually high bond energies that they possess. The dry and wet etching methods developed for these materials over the last few years are reviewed. High etch rates and highly anisotropic profiles obtained by inductively-coupled-plasma reactive ion etching are presented. Photoenhanced wet etching provides an alternative path to obtaining high etch rates without ion-induced damage. This method is shown to be suitable for device fabrication as well as for the estimation of dislocation densities in n-GaN. This has the potential of developing into a method for rapid evaluation of materials.
Carrier Dynamics of Abnormal Temperature-Dependent Emission Shift in Mocvd-Grown InGaN Epilayers and InGaN/GaN Quantum Wells
Authors: Cho Yong-Hoon , Little B. D. , Gainer G. H. , Song J. J. , Keller S. , Mishra U. K. , DenBaars S. P.
Published: April 2011

Temperature-dependent photoluminescence (PL) studies have been performed on InGaN epilayers and InGaN/GaN multiple quantum wells (MQWs) grown by metalorganic chemical vapor deposition. We observed anomalous temperature dependent emission behavior (specifically an S-shaped decrease-increase-decrease) of the peak energy (EpL) of the InGaN-related PL emission with increasing temperature. In the case of the InGaN epilayer, EPL decreases in the temperature range of 10 - 50 K, increases for 50 - 110 K, and decreases again for 110 - 300 K with increasing temperature. For the InGaN/GaN MQWs, EPL decreases from 10 - 70 K, increases from 70 - 150 K, then decreases again for 150 - 300 K. The actual temperature dependence of the PL emission was estimated with respect to the bandgap energy determined by photoreflectance spectra. We observed that the PL peak emission shift has an excellent correlation with a change in carrier lifetime with temperature. We demonstrate that the temperature-induced S-shaped PL shift is caused by the change in carrier recombination dynamics with increasing temperature due to inhomogeneities in the InGaN structures.
Electrical and Photoelectrical Characterization of Deep Defects in Cubic GaN on GaAs
Authors: Lisker M. , Krtschil A. , Witte H. , Christen J. , As D.J. , Schöttker B. , Lischka K.
Published: April 2011

Nominally undoped cubic GaN epilayers deposited by rf-plasma assisted molecular beam epitaxy on semi-insulating GaAs substrates were investigated by electric and photoelectric spectroscopical methods. As a consequence of the existence of deep levels in the GaAs-substrate itself, special care has to be taken to separate the contributions of the substrate from that of the cubic GaN epilayer in the various spectra. Two different contact configurations (coplanar and sandwich structures) were successfully used to perform this separation. In the cubic GaN epilayer a trap with a thermal activation energy of (85±20)meV was found by thermal admittance spectroscopy and thermal stimulated currents. Optical admittance spectroscopy and photocurrent measurements furthermore revealed defects at EG -(0.04-0.13) eV, EG-(0.21-0.82) eV and two additional deeper defects at 1.91 Ev and 2.1 eV, respectively. These defect related transitions are very similar to those observed in hexagonal GaN.
P- and N-Type Doping of Mbe Grown Cubic GaN/GaAs Epilayers
Authors: As D.J. , Simonsmeier T. , Busch J. , Schöttker B. , Lübbers M. , Mimkes J. , Schikora D. , Lischka K. , Kriegseis W. , Burkhardt W. , Meyer B.K.
Published: April 2011

P-type doping with Mg and n-type doping with Si of cubic GaN (c-GaN) epilayers is reported. Cubic GaN films are grown by if-plasma assisted MBE on semi-insulating GaAs (001) substrates at a substrate temperature of 720°C. Elemental Mg and Si are evaporated from thermal effusions cells. Secondary ion mass spectroscopy (SIMS), low temperature photoluminescence (PL) and temperature dependent Hall-effect measurements are used to study the incorporation, optical and electrical properties. A Mg related shallow donor-acceptor transiton at 3.04 eV with an acceptor activation energy of EA= 0.230 eV is observed by low temperature PL. At Mg concentrations above 1018 cm-3 the dominance of a broad blue band indicates that also in c-GaN Mg is incorporated at different lattice sites or forms complexes. Si-doped c-GaN epilayers are n-type with electron concentrations up to 5*1019 cm-3. The incorporation of Si follows exactly the vapor pressure curve of Si, indicating a sticking coefficient of I for Si in c-GaN. With increasing Si-concentration the intensity of the near-band luminescence continuously increases and broadens.
Effects of Susceptor Geometry on GaN Growth on SI(111) with a New Mocvd Reactor
Authors: Gao Yungeng , Gulino Daniel A. , Higgins Ryan
Published: April 2011

High quality GaN films on AIN buffer layers were grown on Si(111) with a new, commercial, two-injector vertical rotating disk MOCVD reactor (CVD, Inc.). It was found that the geometry of the susceptor greatly affected the structural quality of the epilayers on Si. For the original susceptor geometry, though single crystal GaN films could be obtained, the films were dark gray in appearance with a rough morphology, and the best x-ray rocking curve FWHM was 2.33°. After modifying the susceptor geometry, transparent, mirror-like single crystal GaN films were obtained with the best x-ray rocking curve FWHM being 0.24°. Photoluminescence (PL) and infrared reflectance (IR) spectra of the grown films were compared. The film growth rate was found to increase with decrease of the growth pressure. A 2-D simulation of the flow, heat transfer, and chemical species transport in the reactor showed a more symmetric flow, larger velocity gradient, and lower upward velocity with the modified susceptor, which may be the main reason for the improvement of the structural quality of the films.
Process Routes for Low Defect-Density GaN on Various Substrates Employing Pendeo-Epitaxial Growth Techniques
Authors: Linthicum K.J. , Gehrke T. , Thomson D.B. , Tracy K.M. , Carlson E.P. , Smith T. P. , Zheleva T.S. , Zorman C.A. , Mehregany M. , Davis R.F.
Published: April 2011

GaN films have been grown on 6H-SiC substrates employing a new form of selective lateral epitaxy, namely pendeo-epitaxy. This technique forces regrowth to start exclusively on sidewalls of GaN seed structures. Both discrete pendeo-epitaxial microstructures and coalesced single crystal layers of GaN have been achieved. SEM and TEM analysis are used to evaluate the morphology of the resulting GaN films. Process routes leading to GaN pendeo-epitaxial growth using silicon substrates have also been achieved and the preliminary results are discussed.
Absorption Coefficient and Refractive Index of GaN, AIN and AlGaN Alloys
Authors: Muth J. F. , Brown J. D. , Johnson M. A. L. , Yu Zhonghai , Kolbas R. M. , Cook J. W. , Schetzina J. F.
Published: April 2011

The design of optoelectronic devices fabricated from III-nitride materials is aided by knowledge of the refractive index and absorption coefficient of these materials. The optical properties of GaN, AIN and A1GaN grown by MOVPE on sapphire substrates were investigated by means of transmittance and reflectance measurements. Thin (less than 0.5 μm) single crystal films were employed to insure that transmission measurements could be obtained well above the optical band gap. The influence of alloy broadening on the absorption edge was investigated by using a series of AlGaN alloy samples with a range of Al compositions. The optical absorption coefficient above the band gap was obtained for AIGaN having up to 38% Al composition. The refractive index below the band gap was determined for the same series of samples. These properties provide information critical to the optimal design of solar blind detectors or other optoelectronic devices.
Role of the Substitutional Oxygen Donor in the Residual N-Type Conductivity in GaN
Authors: Chen W.M. , Buyanova I.A. , Wagner Mt. , Monemar B. , Lindstrom J.L. , Amano H. , Akasaki I.
Published: April 2011

A detailed photoluminescence (PL) study reveals a striking similarity in local vibrational properties of a defect center in GaN as compared to that for the substitutional Op donor in GaP. This observation could be interpreted as if the center is in fact related to the substitutional oxygen donor in GaN. The deep-level nature experimentally determined for the defect center calls for caution of a commonly referred model that the substitutional oxygen donor is responsible for the residual n-type conductivity in GaN.
Electrical Characterization of Defects Introduced in n-GaN During High Energy Proton and He-Ion Irradiation
Authors: Goodman S. A. , Auret F. D. , Koschnick F. K. , Spaeth J.-M. , Beaumont B. , Gibart P.
Published: April 2011

We report on the electrical properties of defects as determined by deep level transient spectroscopy (DLTS) introduced in epitaxially grown n-GaN by 2.0 MeV protons and 5.4 MeV He-ions. After He-ion bombardment three electron traps ER3 (Ec - 0.196 eV), ER4 (Ec - 0.78 eV), and ER5 (Ec - 0.95 eV) were introduced uniformly in the region profiled by DLTS with introduction rates of 3270 ± 200, 1510 ± 300, and 3030 ± 500 cm-1 respectively. Capture cross section measurements revealed that the electron capture kinetics of ER5 is similar to that of a line defect. A defect with similar electronic properties as ER3 is observed after 2.0 MeV proton irradiation. The emission rate of ER3 depends on the electric field strength in the space-charge region. This emission rate is modelled according to the Poole-Frenkel distortion of a square well with a radius of 20 ± 2 Å or alternatively, a Gaussian well with a characteristic width of 6.0 ± 1 Å. Hence, we conclude that ER1 is a point defect which appears to have an acceptor like character. Two additional electron traps, ER1 (Ec -0.13 eV) and ER2 (Ec - 0.16eV) with introduction rates of 30 ± 10 and 600 ± 100 cm-1 not thusfar observed after electron or He-ion bombardment were observed after proton irradiation.
Inductively Coupled Plasma Etching of III-Nitrides in Cl2/Xe, Cl2/Ar AND Cl2/He
Authors: Cho Hyun , Hahn Y.B. , Hays D.C. , Jung K.B. , Donovan S.M. , Abernathy C.R. , Pearton S.J. , Shul R.J.
Published: April 2011

The role of additive noble gases He, Ar and Xe to Cl2-based Inductively Coupled Plasmas for etching of GaN, AIN and InN were examined. The etch rates were a strong function of chlorine concentration, rf chuck power and ICP source power. The highest etch rates for InN were obtained with Cl2/Xe, while the highest rates for AIN and GaN were obtained with Cl2/He. Efficient breaking of the III-nitrogen bond is crucial for attaining high etch rates. The InN etching was dominated by physical sputtering, in contrast to GaN and AIN. In the latter cases, the etch rates were limited by initial breaking of the III-nitrogen bond. Maximum selectivities of ∼ 80 for InN to GaN and InN to AIN were obtained.
Scanning Tunneling Microscopy Studies of InGaN Growth by Molecular Beam Epitaxy
Authors: Chen Huajie , Smith A. R. , Feenstra R. M. , Greve D. W. , Northrup J. E.
Published: April 2011

InGaN alloys with indium compositions ranging from 0–40% have been grown by molecular beam epitaxy. The dependence of the indium incorporation on growth temperature and group III/group V ratio has been studied. Scanning tunneling microscopy images, interpreted using first-principles theoretical computations, show that there is strong indium surface segregation on InGaN. Based on this surface segregation, a qualitative model is proposed to explain the observed indium incorporation dependence on the growth parameters.
Fiber Debonding Along a Crack Front in Paper
Authors: Kettunen H. , Niskanen K. J.
Published: April 2011

We follow the accumulation of microscopic damage ahead the crack tip in paper. The fiber debonding process varies even within each specimen because of large variation in fiber and bond properties. In general, stiff and weakly bonded fibers tend to debond as a rigid body while ductile or well bonded fibers pull out gradually in a process that propagates from the crack line to the fiber ends. Particularly in the latter case the network ruptures coherently rather than through debonding of single fibers. Experimental analysis and simulations show that fracture energy correlates closely with the size of the fracture process zone (FPZ) irrespective the nature of the debonding process. Only the cases of low bonding and stiff fibers seem to make an exception in that FPZ can grow in size without a corresponding increase in fracture energy.
Cracks in Nano-Ceramic thin Layers Produced by Laser Treatments
Authors: De Hosson J.Th.M. , Teeuw D.H.J.
Published: April 2011

Sol-gel derived thin nano-ceramic layers of TiO2 and Al2O3 are studied using scanning electron microscopy to reveal the microstructure and morphologies of the layers. The low-voltage scanning electron microscope with a field emission gun is equipped with an especially designed lens, where the specimen is placed at the location where the magnetic field is the largest. In such a way a maximum resolving power could be attained of 1.5 nm at 3kV accelerating voltage. The melt-spun layers were treated differently afterwards, i.e. by furnace and by laser curing. These heat treatments appeared to dictate the final morphologies of the layers to a large extent. Grain growth is observed for the furnace as well as the laser cured layers. The activation energy for grain growth of these layers is determined. Homogeneous dense layers may be obtained if the parameters in the curing process are selected adequately. If the parameters are chosen incorrectly, severely debonded layers may be obtained. Pre-heating the layers resulted in less blister formation. The mechanisms which may cause the layers to fail were examined in more detail.
Long Distance Roughness of Fracture Surfaces in Heterogeneous Materials
Authors: Hinojosa M. , Bouchaud E. , Nghiem B.
Published: April 2011

The long distance roughness of fatigue fracture surfaces of a nickel-based superalloy is reported for two samples of different grain size. Statistical analysis over a wide range of length scales, from a few nanometers to a few millimeters, using scanning electron microscopy and atomic force microscopy allows to obtain accurately the self-affine correlation length. Long distance fracture profiles of 14,000 points were obtained and digitized from overlapping electron micrographs at a resolution of 0.22 micrometers/point. We have also analyzed the long distance roughness of the mirror zone on a soda-lime glass using atomic force microscopy. In the case of the nickel superalloy, correlation lengths are found to correspond well to the grain size. This result gives information about the mechanism of crack propagation in heterogeneous materials and shows that the correlation length of fracture surfaces is of the order of the largest microstructural heterogeneity.
Quantitative Modeling and Measurement of Copper Thin Film Adhesion
Authors: Volinsky A.A. , Tymiak N.I. , Kriese M.D. , Gerberich W.W. , Hutchinson J.W.
Published: April 2011

Numerous mechanisms have been identified as fundamental to the adhesion of thin metallic films. The primary mechanism is the thermodynamic work of adhesion of the interface, which in its most basic description is the difference between the surface energies of the two materials and that of the interface. This quantity is often described as leveraging the contributions of other mechanisms. One of the more important mechanisms is that of plasticity occurring in a process zone in the vicinity of the delamination boundary. A quantitative model to characterize the contributions of plastic energy dissipation has been developed and used to rationalize experimental adhesion assessments. This model incorporates the functional dependence of the film thickness and constitutive properties. Orders of magnitude increases in the practical work of adhesion were both observed and predicted. Experimentally, the films used for model comparison were sputter-deposited copper ranging from 40 to 3300 nm in thickness, with and without a thin 10 nm Ti underlayer. Nanoindentation induced delamination of the Cu from SiO2/Si wafers were evaluated in the context of composite laminate theory to determine adhesion energies ranging from 0.6 to 100 J/m2 for bare Cu and from 4 to 110 J/m2 for Cu with the Ti underlayer.
Novel Precursors for MOCVD of Thin Films of Metal Oxides Containing Early Transition Metals
Authors: Davies Hywel O. , Fleeting Kirsty A. , Leedham Timothy J. , Jones Anthony C. , O'Brien Paul , Otway David J.
Published: April 2011

MOCVD is a useful method for the deposition of thin films of metal oxides containing early transition metals,e.g., lead zirconium titanate, (PZT), because of its good step coverage and control of composition. Results are presented on a number of novel compounds which may be, or are, good MOCVD precursors. The compounds studied are in several general classes and include M(←diket)x, M(OR)x, M(←diket)x(OR)y[where M = Ti, Zr, Hf, Ta; ←-diket = tmhd (2,2,6,6-tetramethylheptane-3,5-dione), acac (acetylacetonate), hfac (1,1,1,5,5,5-hexafluoroacetylacetonate); R = Me, Et, Pr1, Butt]. We have sought to modify the precursors through chemical methods and have synthesized a number of novel, volatile, and intrinsically thermally stable MOCVD precursors. Full chemical characterization of the precursors (NMR, IR, MS, CHN, TGA/DSC, Single Crystal X-ray diffraction) has been undertaken.
Crystallization Kinetics and Texture of Sol-Gel PZT Thin Films
Authors: Shur V.Ya. , Blankova E.B. , Subbotin A.L. , Borisova E.A. , Bolten D. , Gerhardt R. , Waser R.
Published: April 2011

The morphology and phase evolution of sol-gel PZT thin films during rapid thermal annealing are investigated by in situ recording of scattered light intensity measured in reflected mode and momentary patterns visualized by optical microscope. In addition the texture and fractions of growing phases and the angular dependence of the scattered light are studied in partly annealed films. The kinetic parameters characterizing the transition from pyrochlore to perovskite phase are extracted by mathematical treatment of experimental data. It is shown that the film's texture and the transformation kinetics strongly depend on pyrolysis temperature. A mechanism of texture formation is proposed.
Pyroelectric Effects on 1T-1C Fram and 1Tr Fram
Authors: Yoo In Kyeong , Chung I.S. , Kim C.J. , Lee J.K. , Jeon B.K. , Desu S.B.
Published: April 2011

Pyroelectric effect on ferroelectricity was examined for PZT capacitors with diodes in series. It was observed that the magnitude of the polarization reversal increases as heating rate increases. The polarization reversal begins to decrease as heating rate becomes very high, which may stem from the fact that pyroelectric charges flow through the PZT film at high temperature as the film loses its resistance at the elevated temperature. A pure remanent polarization reversal model is suggested for the polarization reversal caused by pyroelectric charges. Based on the above results, a thermal shock test method is proposed for quality control of FRAM products. The thermal shock test reveals that pyroelectric effect can be minimized by controlling process for 1T-1C FRAM. It was also observed, by the thermal shock test, that imprint dominates pyroelectric effect in 1Tr cell with MFIS structure.
Low-Frequency Dielectric Properties of Sol-Gel Derived BaTiO3 Thin Films
Authors: Lee Su-Jae , Kang Kwang-Yong , Kim Jin-Woo , Han Seok Kil , Jeong Sang-Don
Published: April 2011

Ferroelectric BaTiO 3 thin films with perovskite structure were grown by sol-gel spin-on processing onto (111)Pt/Ti/SiO2/Si substrates. In order to investigate the effects of space charge in BaTiO3 thin films, we measured the relative dielectric constant and the ac conductivity of the films as a function of frequency, ac oscillation amplitude and temperature. Dielectric constant and dielectric loss were 147 and 0.03 at 100 kHz, respectively. Also, BaTiO3 thin films exhibited marked dielectric relaxation above the Curie temperature and in the low frequency region below 100 Hz. This low frequency dielectric relaxation is attributed to the ionized space charge carriers such as oxygen vacancies and defects in BaTiO3 film and the interfaical polarization. The thermal activation energy for the relaxation process of the ionized space charge carriers was 0.72 eV.
X-Ray Diffraction Method for Determining Textured Volume Fractions in PZT Thin Films
Authors: Fox G.R.
Published: April 2011

The crystallographic texture of PZT thin films has been proven to play a critical role in the electrical performance of PZT used in non-volatile FRAM. During both development and production of FRAM, PZT texture must be monitored to assure ferroelectric performance. A common method for monitoring texture is to use normalized intensities collected from X-ray diffraction 2-theta scans. Although this method can reveal thin film texture, it does not give a quantitative measure of the volume of textured and/or random material. In addition, this method can only be used to compare films with constant thickness since differences in X-ray absorption are not taken into account. A new method for calculating the volume fractions of textured and randomly oriented material in PZT thin films has been developed. This new method for calculating textured volume fractions still utilizes integrated intensities from 2-theta scans, but the calculations include corrections for film thickness and geometrical factors. The calculated volume fractions obtained from this new method of data analysis can be used directly for physical evaluation of PZT thin film ferroelectric performance.
Electromechanical Properties of Pb(Mg1/3Nb2/3)O3 Thin Film Capacitors
Authors: Catalan G. , Corbett M.H. , Bowman R.M. , Gregg J.M.
Published: April 2011

Pulsed Laser Deposition was used to grow Pb(Mg1/3Nb2/3)O3 (PMN) thin film planar capacitor structures. PMN crystallography was verified by x-ray diffraction and plan-view Transmission Electron Microscopy (TEM). Capacitance of the thin film structures was measured as a function of temperature and frequency. Leakage current was also measured for each capacitor. A DC field was subsequently applied and crystallographic strain was monitored in-situ by X-ray diffraction. The electromechanical strain was found to strongly depend on the deposition conditions for each capacitor. Tensile strains of ∼0.2% and compressive strains of ∼0.3% parallel to the applied field were measured for capacitors of different oxygen contents and thicknesses. We propose that the compressive strain is caused by the combined effect of joule heating of the capacitor structure, caused by large leakage currents, and epitaxial coupling between substrate and films. Electrostrictive tensile strains are of the same order as observed inbulk.
Evidence for the Presence of a Twist-Grain-Boundary Structure in Confined Hybrid Non-Chiral Smectic Liquid Crystal Films
Authors: Hu Y. , Martinez-Miranda L. J.
Published: April 2011

We have used Grazing Incidence X-ray Scattering to study the depth dependence of the interfacial structure of smectic liquid crystal (8CB) hybrid films. These films are bounded by a grated glass substrate and air, and have been studied as a function of both temperature and thickness. Our measurements indicate the presence of both a chevron structure and a structure similar to the helical twist-grain-boundary (TGB) phase. Our measurements constitute the first to show that this structure can also be observed in hybrid smectic liquid crystal films. The twisted structure is the result of anchoring at two dissimilar competing confining surfaces.
A Direct Method of Studying Polymer Adsorption on to Mica Surfaces Using a Commercial Mettler Ultramicrobalance
Authors: Terashima H.
Published: April 2011

A simple and direct method has been developed of determining absolute values of adsorbance, i.e. mass per unit area, of polymers adsorbed from solution on to mica surfaces. A commercially available Mettler UMT2 ultramicrobalance is used to measure the weight of mica sheets before and after the immersion of the mica sheets into polymer solution for a given period of time. The increase in weight of mica sheets is divided by the total area of mica surfaces to derive the adsorbance. Practically measurable change in adsorbance was evaluated to be 0.1 mg m2. As an example of the practical application of the present method, an experimental result is presented of the adsorption kinetics of polystyrene (M=66,000) adsorbed from cyclohexane on to mica surfaces at the 0 -temperature.
Energy Transfer in Organic Dendrimer Antenna Funnel and Anti-Funnel Supermolecules
Authors: Swallen Stephen F. , Kopelman Raoul , Moore Jeffrey S.
Published: April 2011

The photophysics of exciton localization and energy transfer are examined in two unique classes of phenylacetylene dendrimers. One set of supermolecules is observed to efficiently and rapidly funnel absorbed radiation toward the molecular locus, while a slight change in molecular structure creates an effective “anti-funnel”, greatly reducing the efficiency of energy trapping. Lifetime-based and steady state fluorescence studies are used to determine the rates of intramolecular energy transfer and to glean information on molecular geometry and intermolecular interactions in two solvents.
Friction Based Segregation Of 2D Granular Assembly
Authors: Kondic L. , Tennakoon S. G. K. , Painter B. , Behringer R.
Published: April 2011

We present theoretical, computational (molecular dynamics), and experimental results describing the dynamical properties of a set of monodisperse, spherical particles confined to a two dimensional surface. An interaction model, which includes the interaction between the particles via collisions as well as the interaction with the substrate, shows that the properties of this granular system are influenced significantly by the latter. In particular, we analyze in detail the effects of slipping and rolling friction, which are usually overlooked. Theoretically, we explore the possibility of formulating a continuum, hydrodynamic-like theory applicable to this system. Further, we apply our model to the particular problem of a system of two kinds of particles with different frictional properties. Our experiments have found that friction-based segregation of particles moving on a horizontally shaken substrate can be achieved. Computational results give further insight into this novel segregation mechanism and confirm that careful and realistic modeling is needed in order to understand this effect.
Structure Stability in Plasma Chemistry
Authors: Wang Ji-Tao , Zhang David Wei , Liu Zhi-Jie , Zhang Jian-Yun , Ding Shi-Jin , Wang Peng-Fei
Published: April 2011

Diamond is a metastable phase, while graphite is a stable phase in low pressure equilibrium phase diagrams of carbon. However, diamond with saturated structure of π bonds is more stable than graphite with unsaturated structure of n bonds during the existence of activated particles generated by plasma. That provides an excellent explanation for the plasma and other activated CVD diamond growth under low pressure taking place with simultaneous graphite etching.
Plasma Polymerization of Low Dielectric Constant Fluoro-Hydrocarbon Film
Authors: Lee Wei William , Tyndall George , Zehringer Raymond , Crowder Mark
Published: April 2011

Low dielectric constant fluoro-hydrocarbon polymer films were deposited using an electron cyclotron resonance (ECR) plasma source with pentafluorostyrene as a precursor. The pentafluorostyrene is a cyclic liquid monomer with relative high vapor pressure. The chemical structure of the deposited films were characterized by X-ray photoelectron spectroscopy, infrared spectroscopy and Rutherford backscattering spectroscopy. The structure of deposited films studies gave an insight of the fluorohydrocarbon polymer formation regarding to deposition conditions. The dielectric constant of the film was found in the range of 2.2 to 2.4. The influence of deposition conditions on chemical, physical and electrical properties of the resulting films were evaluated.
Surface Modifaction of Ultra High Molecular Weight Polyethylene by Low Energy DC Plasma Discharge
Authors: Hargreaves M. S. , Hussey D. S. , Leuchtner R. E.
Published: April 2011

Surface effects produced by plasma processing Ultra High Molecular Weight polyethylene (UHMW) were examined. The goal was to enhance adhesion of UHMW to a variety of polar polymers. This research focussed on enhancing adhesion to polyurethane. UHMW samples were immersed in a DC discharge and subjected to various processing conditions. The background gases experimented with were oxygen, nitrogen, and argon, and the pressure was varied between 6-67 Pa. The processing time, discharge current and discharge potential were also varied. A polar polymer (polyurethane) was subsequently applied to the processed UHMW samples and the tensile strength of the bonds was measured. Standard dogbone specimens were fabricated, and the polymer interfaces placed in the middle of the gage section and oriented normal to the tensile axis. The specimens were tested to failure in displacement control at an approximate strain rate of 0.2% per sec. In general, significant enhancement in yield strength was observed over unprocessed samples, where essentially no bonding occurred. Samples subjected to plasma processing in oxygen showed the strongest adhesion, while those in argon were almost as good, followed by nitrogen.

The contact angle of water on the processed UHMW samples ranged from about 45° to less than 2°, while unprocessed samples had a contact angle of about 70°. These data correlated with the yield tests. XPS was used to examine the composition of the UHMW surfaces before and after plasma processing with oxygen. It is believed that the plasma etched off surface layers, creating unsaturated carbon bonds that can chemically react with polar polymer groups. Precast, processed UItMW surfaces were found to be reactive for periods of up to one week. Optimum conditions of plasma processing were identified, and will be discussed in light of the chemistry occurring at the interface.
Comparison of Proliferation and Growth of Human Keratinocytes on Plasma CO-Polymers of Acrylic acid/1,7- Octadiene and Self Assembled Monolayers
Authors: Haddow D. B. , France R. M. , Short R. D. , Macneil S. , Dawson R. A.
Published: April 2011

Human keratinocytes have been cultured on plasma co-polymers (PCPs), self assembled monolayers (SAMs), tissue culture poly(styrene) (TCPS) and collagen I. The degree of keratinocyte attachment was measured over 24 hours and cell proliferation and growth monitored over 7 days using optical microscopy and DNA concentrations. Cell attachment and proliferation and growth on the PCP surfaces were compared with 2 self assembled monolayer (SAM) systems. PCP surfaces containing carboxylic acid functionalities promoted keratinocyte attachment, with optimum attachment levels seen on surfaces containing less than 5% acid groups. The level of attachment on these surfaces was comparable to that seen on collagen I, a preferred substratum for the culturing of keratinocytes. After several days in culture the cells were well attached and proliferative. Keratinocytes attached well to acidterminated SAMs but attached poorly to methyl-terminated SAMs.
Boron Containing Polyimides for Aerospace Radiation Shielding
Authors: Ko Stephen C. , Pugh Christopher S. , Kiefer Richard L. , Orwoll Robert A. , VA Williamsburg , Thibeault Sheila A. , King Glen C.
Published: April 2011

In interplanetary travel and high altitude flight, humans will be exposed to high energy charged particles from solar flares and galactic cosmic rays. These particles lose energy in a material by Coulomb interactions and nuclear collisions. In nuclear collisions, large amounts of energy are transferred and secondary particles are formed from both the projectile and the struck nucleus. A significant portion of these particles are neutrons which can only lose energy by collisions or reactions with a nucleus. Hydrogen-containing materials, such as polymers, are most effective in reducing the neutron energy. When reduced to very low energies, neutrons have a high probability of reacting with a nucleus. Such reactions are dangerous in the human body, and can cause electronic equipment failure. Low energy neutrons react particularly well with a stable isotope of boron, 10B. To test structural materials which contain both hydrogen to reduce the energy of neutrons and boron to absorb neutrons of reduced energy, samples of two polyimides were made which contained varying amounts of either amorphous boron powder or boron carbide whiskers. The polymers used were a thermoset, PETI-5 from Imitec, and a thermoplastic, K3B from Fiberite. Both materials were made in pure form and with up to 20% by weight of the boron additives. The addition of boron in either form did not change the thermal properties of these materials significantly. However, the compressive yield strength and the tensile strength were both affected by the addition of the boron materials. A neutron absorption test using a PuBe thermal neutron source showed that a 0.5 cm thick sample of K3B containing 15% amorphous boron powder absorbed over 90% of the incident neutrons.
Multilayer Coatings for Focusing Hard X-ray Telescopes
Authors: Ivan A. , Bruni R. , Byun K. , Everett J. , Gorenstein P. , Romaine S.
Published: April 2011

Several multilayer test coatings for hard X-ray telescopes were fabricated using DC magnetron sputtering. The process parameters were selected from a series of trials of single layer depositions. The samples were characterized using X-ray specular reflectivity scans, AFM, and cross-sectional TEM. Additional measurements (stylus profilometry, RBS, and Auger analysis) were used in the optimization of the deposition rate and of the thin film properties (density, composition, surface/interface microroughness). The X-ray reflectivity scans showed that the combinations of reflector and spacer materials tested so far (W/Si and W/C) are suited for graded d-spacing multilayer coatings that present a constant reflectivity bandpass up to 70 keV.
Intrinsic Misfit Dislocations on 120° Interface in TiAl
Authors: Paidar V. , Zghal S. , Couret A.
Published: April 2011

The misfit between 120° rotational variants of the lamellar structure in γ-phase TiAl with the ordered L10 lattice is analysed. It is shown that such a misfit on the (111) interface plane, which has a shear character, can be accommodated by one, two or three arrays of interface intrinsic dislocations. One example of interface dislocation structure observed by transmission electron microscopy is presented.
Deformation of Bi-PST Crystals of TiAl Produced by Diffusion Bonding
Authors: Imamura D. , Hoshikawa H. , Kishida K. , Inui H. , Yamaguchi M.
Published: April 2011

Diffusion bonded bi-PST crystals of three different series were prepared and they were deformed in tension at room temperature. Yield stress and elongation exhibited by bi-PST crystals consisting of component crystals with the lamellar microstructure aligned along the tensile axis do not significantly differ from those of component crystals. Plastic strain incompatibility at the interface exerts a strong influence on the deformation behavior of bi-PST crystals when the incompatibility activates additional deformation modes which are much harder than deformation modes operative in each component crystal.
Hexagonal Stacking at Order Interfaces Between Lamellae in TiAl
Authors: Inkson B. J.
Published: April 2011

Stacking faults at order interfaces in TiAl have been examined by HREM. In addition to very extensive OCISF formation, C-core dislocation complexes spread over two parallel { 111 } planes have been observed at order interfaces lying predominantly parallel to the original (0002)α, planes. Such C-cores, corresponding to 1/2<211] and 1/2<112] interfacial dislocations, have been observed with localised regions of both extrinsic and hexagonal stacking.
Mechanical Disordering of Cubic Intermetallics By Unconventional Methods of Cold-Work and Their Reordering Upon Annealing
Authors: Varin R. A. , Bystrzycki J. , Calka A.
Published: April 2011

Two unconventional methods of cold-work: (a) controlled mechanical (ball) milling (under shear conditions), and (b) shock-wave (explosive) loading at ˜5 GPa shock pressure were applied to two cubic intermetallics: (a) Mn-stabilized cubic (L12) titanium trialuminide (AI3Ti(Mn)) and (b) B2 iron aluminide (FeAl). The long-range order (LRO) parameter S of both intermetallics decreases and their lattice constants increase with increasing milling time providing strong evidence that the mechanical milling disorder is due to antisite-atom pairs. A nanocrystalline structure is being formed in both intermetallics upon milling. A shock-wave loading gives rise to only a partial disorder of both A13Ti(Mn) and FeAl but their lattice constants are not affected (no point defects formation). Annealing at 600°C results in the restoration of LRO and lattice constants as well as microstructural evolution in Fe-45A1.
The Role of Computational Modeling Processes in the Development and Understanding of NiAl-Based Ordered Intermetallic Alloys
Authors: Bozzolo Guillermo , Noebe Ronald D , Honecy Frank S , Good Brian S
Published: April 2011

A detailed understanding of the structure of ordered intermetallic systems is difficult at best, causing a serious disconnect in the typical process-structure-properties approach to alloy development. Basic information, like the site substitution schemes of various alloying elements, partitioning behavior in multiphase alloys, and the dependence of these phenomena with concentration and higher order alloying additions is necessary to predict and understand the effect of various alloying schemes on the physical and mechanical properties of a material. It is only recently that theoretical methods can begin to provide useful insight in these areas, as most current techniques suffer from strong limitations including the type and number of elements that can be considered and the crystallographic structure of the resulting phases. The Bozzolo-Ferrante-Smith (BFS) method for alloys was designed to overcome these limitations, with the intent of providing a useful tool for the theoretical prediction of fundamental properties and the structure of multi-component systems. The role or potential contributions of theoretical procedures like the BFS method to the alloy design process are discussed with a specific emphasis on work that has been conducted on NiAl-based alloys. After a brief description of the method and its range of applications, we will concentrate on the usefulness of BFS as an alloy design tool. The theoretical determination of site substitution schemes for individual as well as collective alloying additions to NiAl, the resulting behavior with respect to solubility limits and second phase formation, and the concentration dependence of the lattice parameter will be demonstrated.
Selective Growth Of Decagonal Ai-Co Thin Films By Reactive Diffusion: Kinetic And Thermodynamic Aspects
Authors: Emeric E. , Bergman C. , Clugnet G. , Gas P.
Published: April 2011

We report on the formation by reactive diffusion of a pure decagonal quasicrystalline film in Al/Co bilayer and multilayer structures of overall composition Al13CO4. We show that this method is highly selective since several stable phases which exist around this composition are never observed. The quasicrystal is not the first reaction product but is obtained as a second reaction step by a peritectoid reaction between Al9Co2 and the remaining cobalt. DSC analysis allows the determination of both the enthalpy of formation of the decagonal quasicrystal (ΔHf = -31500 ± 2000 J/g-atom) and its activation energy of growth (2.6 ± 0.5 eV).
Plastic Deformation Of AI-Cu-Fe Icosahedral Quasicrystals
Authors: Giacometti E. , Baluc N. , Bonneville J.
Published: April 2011

Poly-quasicrystalline specimens of the Al-Cu-Fe system have been pre-strained and further deformed at various temperatures, above and below the brittle-to-ductile transition temperature, under constant strain-rate conditions. The experiments have been specially designed to examine the respective contributions of the thermally reversible and structural dependent parts to the total flow stress. We show that the so-called internal stress, which results from the deformation builtin microstructure, has a rather low value, if any. In addition, the flow stress is found to be fully temperature reversible, if one takes into account previous plastic strains. We suggest that these results can be explained by a weakening of the friction stress, due to the formation of soft slip bands.
Observations Of Pure Climb Dislocation Movements IN Al-Pd-Mn
Authors: Caillard D. , Vanderschaeve G. , Bresson L. , Gratias D.
Published: April 2011

TEM observations of dislocations and faults in an as-grown Al-Pd-Mn single crystal show that dislocation movements have occurred by pure climb in mirror planes. A comparison with creep properties of h.c.p. metals along their c-axis indicates that pure climb is a realistic deformation mode when glide is inhibited at high temperature.
Growth and Structure of Metallic Barrier Layers and Interconnect Films II: Atomistic Simulations of Film Deposition onto Inclined Surfaces
Authors: Torre J. Dalla , Gilmer G. H. , Windt D. L. , Baumann F. H. , Kalyanaraman R. , Huang Hanchen , Rubia T. Díaz de la , Rouhani M. Djafari
Published: April 2011

We present three dimensional lattice Monte Carlo simulations of sputter deposition onto inclined surfaces. For this purpose, we use a model of an fcc material and we vary the substrate inclination, the texture, and the atomic mobility. In this way we can examine different conditions and mechanisms involved in depositing barrier layer and interconnect films. We obtain results on the density and the roughness of the films. We find that the film texture has dramatic effects on the film density and smoothness. Surprisingly, we find that the surface diffusion coefficients may not be critical parameters; changes in the coefficients by several orders of magnitude may cause only a small change in the film morphology when depositing onto non-wetting substrates.
PVD Growth of FCC Metal Films On Single Crystal Si And Ge Substrates
Authors: Westmacott K. H. , Hinderberger S. , Radetic T. , Dahmen U.
Published: April 2011

Epitaxial films of the fcc metals Al, Au, Ag and Ni were grown by physical vapor deposition on Si and Ge (111), (110) and (100) substrates at different deposition temperatures. The epitaxial relationships and morphological features of these films were characterized by transmission electron microscopy and diffraction in plan view and cross section. Ag formed single crystal films on all substrates at all temperatures. Au and Al could be grown as bicrystals, and under some conditions, Al and Ni grew as tricrystal films. The morphological effects of diffusion at the metal/substrate interface are ascribed to diffusion induced grain boundary migration.
Effect of Particle Size During Tungsten Chemical Mechanical Polishing
Authors: Bielmann Marc , Mahajan Uday , Singh Rajiv K.
Published: April 2011

Abrasive particle size plays a critical role in controlling the polishing rate and the surface roughness during chemical mechanical polishing (CMP) of interconnect materials during semiconductor processing. Earlier reports on the effect of particle size on polishing of silica show contradictory conclusions. We have conducted controlled measurements to determine the effect of alumina particle size during polishing of tungsten. Alumina particles of similar phase and shape with size varying from 0.1 μm to 10 μm diameter have been used in these experiments. The polishing experiments showed that the local roughness of the polished tungsten surfaces was insensitive to alumina particle size. The tungsten removal rate was found to increase with decreasing particle size and increased solids loading. These results suggest that the removal rate mechanism is not a scratching type process, but may be related to the contact surface area between particles and polished surface controlling the reaction rate. The concept developed in our work showing that the removal rate is controlled by the contact surface area between particles and polished surface is in agreement with the different explanations for tungsten removal.
Electrochemical Behavior of Copper in Tetramethyl Ammonium Hydroxide Based Solutions
Authors: Huang W. H. , Raghavan S. , Fang Y. , Zhang L.
Published: April 2011

An investigation was undertaken to characterize the electrochemical behavior of copper in tetramethyl ammonium hydroxide (TMAH) based solutions. The effect of hydrogen peroxide and abrasion with a polyvinyl alcohol (PVA) brush on the corrosion of copper in alkaline solutions were characterized. Galvanic interactions between copper and tantalum in TMAH as well as in ammonium hydroxide (NH4OH) solutions were investigated. The experimental results have shown that the corrosion of copper in TMAH is lower than that in NH4OH, especially at pH values higher than 10. Even in the presence of hydrogen peroxide, TMAH corrodes copper at a lower rate than NH4OH.