bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling the Rheology of Commercial Long Chain Branched Polymer Melts
Authors: Park Seung Joon , Larson Ronald G.
Published: April 2011

The predictions of a general “hierarchical model” for the rheology of general mixtures of linear and branched polymers are compared to experimental data for well-defined long-chain branched polymers. For a wide range of branched polymer melts, which include star-linear blends, H-polymers, and comb polymers, the predictions of the model agree well with experimental data. We apply the hierarchical model to metallocene-catalyzed polyethylenes (mPEs), in which the branched structures are generated by a Monte Carlo method based on the known reaction kinetics. The hierarchical model captures the shape of the curves of viscoelastic moduli vs. frequency of mPEs well and predicts accurately the effect of long chain branching on the linear viscoelastic properties. The quantitative agreement of the hierarchical model prediction with experimental data of well-defined long-chain branched polymers and mPEs shows that information on branching structure could be inferred from rheological measurements on combinatorial sets of mixtures of an unknown branched with different combinations of linear polymers.
High Throughput Screening of the Thermal Stability of Colorants in a Polycarbonate Matrix
Authors: Whisenhunt Donald W. , Carter Randall , Shaffer Ron , Bulsiewicz William , Flanagan William
Published: April 2011

The relative thermal stability of 44 colorants of interest to GE Plastics as polymer colorants was determined. The effects of common (non-colorant) additives on the thermal stability in a polymer matrix were also determined. The measurements were carried out by reflectance spectrometry on thin films of polymers that had been subjected to heating cycles. The change in the visible spectrum was used as an indicator of thermal stability. This paper discusses the method and overall results for the experiments.
Fiber-Optic Sensor Technology and Combinatorial Chemistry
Authors: Geissinger Peter , Prince Barry J. , Kaltcheva Nadejda T. , Prince Maureen J. , Schwabacher Alan W.
Published: April 2011

Our recently introduced “Fiber-Optic Combinatorial Chemistry” technique combines combinatorial synthetic methods and optical fiber sensor technologies. Our one-dimensional combinatorial chemistry method allows for synthesis of large compound libraries in a linear format, for example in the cladding of optical fibers. Subjecting these libraries to assays that indicate positive identification of a library member by the binding of a fluorescent group, produces, in effect, an optical fiber sensor array. The location of a particular fluorescent region along the optical fiber can be determined through the optical time-of-flight technique, in which laser pulses propagating through the fiber core probe through their evanescent fields the fluorescent properties of the compounds located in the fiber cladding. It is a virtue of our combinatorial synthetic procedure that with the location of a compound on the fiber, its synthetic history is immediately known. We demonstrated that limitations on the spatial resolution of compounds along the fiber due to the excited state lifetimes of the fluorescent marker molecules can be overcome by the use of a second fiber - evanescently coupled to the first one - as an optical delay.

The existing claddings of optical fibers severely restrict the range of chemistries for the synthesis of combinatorial libraries. Therefore, in order to make our method more generally applicable, the existing fiber cladding has to be replaced by a porous material that can act as solid support for reactions and at the same time preserve the optical guiding conditions of the fiber. In this contribution we discuss the requirements for such a replacement cladding and evaluate the general suitability of a functionalized candidate material.
Controlled deposition of wedge-shaped profiles for thin (∼10Å) layers by pulsed laser deposition
Authors: Christen H.M. , Ohkubo I.
Published: April 2011

A method yielding precisely controlled thickness profiles in thin-film growth is necessary for continuous compositional spread techniques. While multiple approaches have been introduced and successfully tested, some specific applications require the use of very thin “wedge”-type profiles (∼10 Å at the thickest point), while at the same time yielding lateral sample sizes of several centimeters. Here we introduce the basic principles of a pulsed-laser deposition based approach utilizing the translation of the substrate behind a slit-shaped aperture and demonstrate by simple calculations that this method can satisfy these requirements.
Preparation of ternary alloy libraries by means of thick film deposition and interdiffusion: structure and mechanical properties
Authors: Rar A. , Specht E. D. , Meyer H. M. , Santella M. L. , George E.P. , Pharr G. M.
Published: April 2011

A method of preparing ternary alloy libraries for combinatorial materials development based on thick film deposition and interdiffusion was studied, using the Ni-Fe-Cr ternary system. Specimens were prepared by depositing films onto sapphire substrates with an e-beam evaporation system followed by annealing in a vacuum for interdiffusion. The specimens were examined using cross sectional scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), scanning Auger microanalysis (SAM), angular resolved x-ray fluorescence (AR-XRF), x-ray diffraction (XRD), and nanoindentation. The method proved an effective way to make the alloy libraries for screening mechanical properties by means of nanoindentation.
High-Throughput Screening of Flux Materials for Single Crystal Growth by Combinatorial Pulsed Laser Deposition
Authors: Takahashi R. , Tanigawa T. , Yamamoto Y. , Yonezawa Y. , Matsumoto Y. , Koinuma H.
Published: April 2011

We propose a new concept and method for high throughput screening of flux materials used in the bulk single crystal growth. The concept of our tri-phase epitaxy has been generalized as the flux-mediated epitaxy with the aid of quick optimization of flux materials in the combinatorial thin-film technology. Here, we report on the successful discovery of a new flux composition of Bi-Ti-Cu-O for the growth of high-quality Bi4Ti3O12 bulk crystal and thin film.
Analytical TEM Observations of Combinatorial Catalyst Libraries for Hydrogen Production – As a Part of “MATERIOMICS”–
Authors: Akita T. , Ueda A. , Yamada Y. , Ichikawa S. , Tanaka K. , Kohyama M. , Kobayashi T.
Published: April 2011

Materiomicsis a new approach combining combinatorial surveys and precise structure analyses in order to develop new functional materials efficiently. In this paper, we show the first stage of materiomics applied to metal/metal oxide catalysts. The catalytic activities of various metal/metal oxide catalysts for hydrogen production have been examined by a combinatorial method, and TEM observations have been performed for the selected catalysts from the libraries in order to estimate the structures in the combinatorial surveys. A Pd/MnO2catalyst shows the high activity for the water gas shift reaction, where thin Pd oxide layers about 1–2nm thickness are formed on the flat MnO2surface. However, Pd oxide layers are reduced and metallic Pd particles 2–3nm in diameter with narrow size distribution are formed after hydrogen reduction. The structure of manganese oxide support also changes after hydrogen reduction. On the other hand, both Pd particles with diameters of 2–3nm and 10–20nm on SiO2show low activity for the water gas shift reaction. Thus, it is concluded that the catalytic activity does not simply depend on the particle size of metals, but that the interaction between metals and metal oxide supports is also important for the catalytic performance.
Search and Synthesis of New Family of Quasicrystals
Authors: Ishimasa Tsutomu , Kashimoto Shiro , Maezawa Ryo
Published: April 2011

Starting from the Zn17Sc3 cubic approximant, new icosahedral quasicrystal was searched by substituting Zn by other metals, M, at the alloy composition of Zn75M10Sc15. In the cases of M = Mn, Fe, Co, Ni, Pd, Pt, Ag and Au, new P-type quasicrystals were discovered in as-cast alloys. In the cases of M = Fe, Co, Ni, Pd and Ag, the quasicrystals are thermodynamically stable at approximately 700 °C. This result indicates that use of an approximant crystal as a starting material is very efficient way to search new quasicrystal alloy, and many kinds of metals stabilize the quasicrystal structures; i.e. noble metals and transition elements including Mn, Fe, Co and Ni in addition to Mg. Taking the variety in base metals of Tsai-type approximants into account, this variety in additional components suggests many possibilities of undiscovered quasicrystals. The equality ofthe electron concentration, ela ≈ 2.1, in Hume-Rothery rule may be a guide to these quasicrystals.
Synthesis of Quasicrystal Phases by Mechanical Alloying of Ti45+xZr38-XNi17 (-4≤ X ≤16) Powder Mixtures, and Their Hydrogen Storage Properties
Authors: Takasaki Akito , Imai Naoki , Kelton Kenneth F.
Published: April 2011

Mechanical alloying of Ti45+xZr38-xNi17 (-4 ≤ x ≤ 16) elemental powder mixtures leads to the formation the amorphous phase, but subsequent annealing at 833 K causes the formation of icosahedral (i) quasicrystal and the Ti2Ni-type crystal phases. The α-Ti phase is also produced in Ti-rich powders after annealing. Both the quasilattice constant of the i-phase and the lattice parameter of the Ti2Ni-type crystal phase decrease monotonically with increasing substituted amount of Ti because of the smaller radius of the Ti atom. The maximum hydrogen concentration in the i-phase in all powder compacts, after electrochemical hydrogenation in a KOH solution, is almost the same, about 63 at% ([H] / [M] ≈ 1.7). The onset temperature of hydrogen desorption is about 570 K (at a heating rate of 5 K/min) for all powders, but the temperature for the maximum hydrogen desorption rate increases with increasing Ti concentration in the powders, suggesting that some hydrogen atoms might be more strongly bound in the quasilattice where the original Zr sites become occupied by Ti atoms.
Hydrogen Diffusion in Quasicrystalline ZrCuNiA1
Authors: Apih T. , Klanjsek M. , Khare Varsha , Jeglic P. , Dolinsek J.
Published: April 2011

The hydrogen diffusion constant D in the hydrogenated quasicrystalline alloy ZrCuNiAl has been determined using the technique of NMR diffusion in a static fringe field of a superconducting magnet. The diffusion constant of partially quasicrystalline Zr69.5Cu12Ni11Al7.5 exhibits a significant decrease with increasing hydrogen-to-metal ratio H/M, owing to creation of defects in the lattice during hydrogen loading, which dominates over the site-blocking effect. The actual alloy structure—the amorphous, icosahedral or approximant—appears to be less important for the hydrogen diffusivity.
Path to Strong Insulating Transport Properties in Bulk AlPdRe Samples
Authors: Rosenbaum Ralph , Zhong Yuan-Liang , Lina Juhn-Jong
Published: April 2011

Electronic transport measurements have been made on bulk icosahedral Al70Pd22.5Re7.5 quasicrystal (QC's) samples, having increasingly larger resistance temperature ratios, rT = R(4.2 K)/R(292 K). Data were taken between 0.023 K to 292 K and in magnetic fields up to 17.9 T. Both the zero field resistivity and the magnetoresistance (MR) changed from metallic behavior to weakly insulating behavior to highly insulating behavior, as the resistance temperature ratios rT's of the samples were made larger. For the insulating samples, the resistivities ρ's followed simple inverse temperature power laws above 50 K going as ρ(T) = a0/Tz, where z = 1 ± 0.1.The insulating QC samples exhibited saturation behaviors of their resistivities below 2 K. Below 0.3 K, the strongly insulating QC's displayed activated variable-range hopping (VRH) laws in their conductivity; the hopping exponents y's in the VRH laws varied between 0.19 ≤ y ≤ 0.43. A simple model including conductivity contributions both from the primary insulating QC phase and from a secondary metallic phase yielded good fits to the resistivity and MR data.
Topological and Chemical Short-Range Order in Undercooled and Stable Melts of Al13(Co,Fe)4 Alloys
Authors: Holland-Moritz Dirk , Schenk Thomas , Simonet Virginie , Bellissent Robert
Published: April 2011

The short-range order of stable and deeply undercooled liquids of Al13(Co,Fe)4 alloys forming polytetrahedral phases is investigated by combining the containerless processing technique of electromagnetic levitation with elastic neutron scattering. Partial structure factors were inferred from the diffraction data which allow an analysis of both, the topological and the chemical short-range order of these alloy melts as a function of the temperature.
Metastable States During Devitrification of a Zr70Pd20Cu10 Metallic Glass
Authors: Kramer M. J. , Sordelet D. J.
Published: April 2011

High energy synchrotron x-rays (124.63 keV) are used to investigate the initial stages of the devitrification for the Zr70Pd20Cu10 metallic glass prepared by melt-spinning (MS). Due to the excellent signal:noise, we are able to determine the initial nucleating phase by analyzing the differences in the total scattering function S(Q) as a function of time at a temperature ∼ 50 K below the crystallization temperature. The alloy undergoes a structural relaxation prior to nucleation and growth. Devitrification proceeds from nucleation of the icosahedral phase. The differential pair distribution function (dPDF) indicates that the as-quenched alloy may have icosahedral-like order which undergoes local rearrangement to true icosahedral order at an annealing temperature 50 K below the crystallization temperature. More importantly, time-resolved high-energy synchrotron is shown to have excellent sensitivity to the initial atomic rearrangements preceding nucleation in metallic glasses.
The ω Phase Formation during Laser Cladding and Remelting of Quasicrystal Forming AlCuFe on Pure Aluminum
Authors: Biswas Krishanu , Chattopadhyay Kamanio , Galun Rolf , Mordike Barry L.
Published: April 2011

We report the formation ω phase in the remelted layers during laser cladding and remelting of quasicrystal forming Al65Cu23.3Fe11.7 alloy on pure aluminum. The ω phase is absent in the clad layers. In the remelted layer, the phase nucleates at the periphery of the primary icosahedral phase particles. A large number of ω phase particles forms enveloping the icosahedral phase growing into aluminum rich melt, which solidify as α-Al solid solution. On the other side it develops an interface with aluminum. A detailed transmission electron microscopic analysis shows that ω phase exhibits orientation relationship with icosahedral phase. The composition analysis performed using energy dispersive x-ray analyzer suggests that this phase has composition higher aluminum than the icosahedral phase. The analysis of the available phase diagram information indicates that the present results represent large departure from equilibrium conditions. A possible scenario of the evolution of the ω phase has been suggested.
Morphology of Sn Films Grown on the Fivefold Surface of Icosahedral Al63Cu24Fe13 Investigated by Scanning Tunneling Microscopy
Authors: Sharma H. R. , Shimoda M. , Barrow J. A. , Ross A. R. , Lograsso T. A. , Tsai A. P.
Published: April 2011

Sn film growth on the fivefold surface of icosahedral Al63Cu24Fe13 has been investigated by employing scanning tunneling microscopy. For about monolayer coverage, the deposited Sn forms a layer of monoatomic height. A Fourier transform of the layer's structure reveals quasicrystalline long range order. At higher coverage, flat-topped clusters of uniform heights are formed. The clusters preferentially grow at the step edges.
Swift Heavy Ion Irradiation on Quasicrystals
Authors: Chatterjee Ratnamala
Published: April 2011

The present level of understanding of the effects of irradiation of quasicrystalline targets with swift heavy ions has been reviewed here. The results of systematic deposition of large amount of energy densities (12 keV/nm < (dE/dx)e < 40 keV/nm) in Al-Cu-Fe based system are discussed in terms of resistivity measurements (in-situ measurements of resistivity changes with increasing flux (ions/cm2) and ex-situ resistivity vs temperature measurements before and after irradiation) & standard and high-resolution X-ray diffraction measurements made before and after irradiation. The studies are aimed at understanding the changes that may occur in these alloys as a result of the relaxation of such highly excited states of matter. Also, we attempt to learn whether such changes are typical to the long-range quasicrystallinity of the system or not.
Microstructural Design by Controlled Crystallization of Metallic Glasses
Authors: Köster Uwe , Janlewing Rainer
Published: April 2011

Nanocrystalline materials can be produced e.g. by high energy ball milling or vacuum condensation; these methods require powder compaction as a final step. In another route - the nano-crystallization - metallic glasses are used as precursors for nanocrystalline materials without any porosity. The conditions for achieving an ultra-fine grained material by crystallization are small growth, but large nucleation rates. Whereas in Fe-Ni-B glasses the finest microstructure is produced at annealing temperatures above the glass transition close to the maximum of the nucleation rate, in Zr-based metallic glasses nanocrystallization was found to proceed only at relatively low temperatures below the glass transition. The aim of this contribution is to study systematically the micromechanisms involved in the microstructural design.

Crystallization was studied in detail in Fe-Ni-B and Zr-based metallic glasses by means of TEM, X-ray diffraction and DSC. Nucleation and growth rates were estimated from crystallization statistics. By modeling the obtained time-dependent nucleation rates in the framework of diffusion controlled classical nucleation all relevant crystallization parameter could be derived. Using these data TTT-diagrams could be drawn and annealing conditions deducted, e.g. for the formation of a nanocrystalline alloy.

Isothermal DSC plots for polymorphic crystallization can only be explained with a very significant decrease in the growth rate at later stages. Such a decrease is assumed to result from stresses building up during crystallization beyond the percolation limit for the crystalline phase; under this condition stresses resulting from the volume change during crystallization cannot be compensated by viscous flow as in the case of isolated crystals in an amorphous matrix.
Catalytic Properties of High-Density Monodispersive Metal Nanostructures
Authors: Gurevich Sergey A. , Yassievich Irina N. , Kozhevin Vladimir M. , Yavsin Denis A. , Zabelin Mihail A. , Tret'yakov Pavel A. , Rostovshikova Tat'yana N. , Smirnov Vladimir V.
Published: April 2011

We report on ultra-high catalytic activity of high-density monodispersive Cu and Ni nanostructures fabricated by newly developed laser electrodispersion technique. In these structures the particle sizes are 5 nm for Cu and 2.5 nm for Ni (relative size dispersion is less than 20%). Due to fast cooling during particle formation Cu and Ni grains have amorphous structure. The catalytic activity of Cu-based structures were studied in chlorohydrocarbons transformations reactions, while Ni structures were tested in the reaction of 1-nonene hydrogenation. The measured catalytic activity vs. particle surface density dependencies exhibit a maximum corresponding to densely packed one-layer granulated films. About an order of magnitude increase in the catalytic activity is observed when increasing the dielectric permittivity of the reactant solution. It is suggested that the observed high catalytic activity is due to thermally activated interparticle electron tunneling, which results in the appearance of negatively and positively charged particles in densely packed granulated films.
Development of Amorphous Metals Using High Throughput Experiments
Authors: Eric Ramberg C. , Wang Y. , Fan Q. , McDermott E. , Wang J. , Kenyon K. , Hornbostel M. , Guan S. , Nguyen S.
Published: April 2011

High throughput, thin film synthesis and screening methods have been developed to investigate potential bulk metallic glass (BMG) compositions. Physical vapor deposition (PVD) was used for sample synthesis. A novel screening tool was developed to measure changes in resistance vs. temperature of these thin film samples. Example data for 34 compositions in the Mg-rich region of the Mg-Cu-Y ternary system are presented.
New Calcium Based Bulk Metallic Glasses
Authors: Senkov Oleg N. , Mike Scott J.
Published: April 2011

Thermal properties of a number of new Ca-based bulk metallic glasses are reported and discussed here. The compositional range of the new metallic glasses follows the formula:

CaA(Y,Ln)B(Mg,Sn)C(Ga,Zn,Al,Ag)D(Cu,Ni)E,

where A ranges from 0.40 to 0.70, B = 0 to 0.25, C = 0 to 0.25, D = 0 to 0.35, E = 0 to 0.35, A+B+C+D+E=1, and Ln represents the La group elements. The alloys have been developed based on specific criteria predicted from Senkov-Miracle topological and thermodynamic models for metallic glass formation, which narrow the compositional range for searching new metallic glasses.
Quenched-in Free Volume Vf, Deformation-induced Free Volume, the Glass Transition Tg and Thermal Expansion in glassy ZrNbCuNiAl measured by Time-resolved Diffraction in Transmission
Authors: Yavari A. R. , Tonegaru M. , Lupu N. , Inoue A , Matsubara E. , Vaughan G. , Kvick Å. , Botta W.J.
Published: April 2011

Using high-precision X-ray dilatometry, we have succeeded in directly measuring excess quenched-in free-volume Vf in metallic glasses. The method was applied to the very easy glass forming Zr57Nb5Cu15.4Ni12.6Al10 (Vit 106). The annealing out of the order of 0.5% free volume was observed during heat treatment of rapidly solidified glassy ribbons. Excess free volume was also generated by heavy deformation and observed to anneal out during heat treatment. Once the excess free volume anneals out, the glass transition Tg appears clearly as a break in the x-ray dilatation curves as the glass goes over to the supercooled liquid region prior to crystallization at Tx.
Topological and Chemical Short-Range Order in Undercooled and Stable Melts of Al13 (Co,Fe)4 Alloys
Authors: Holland-Moritz Dirk , Schenk Thomas , Simonet Virginie , Bellissent Robert
Published: April 2011

The short-range order of stable and deeply undercooled liquids of Al13(Co,Fe)4 alloys forming polytetrahedral phases is investigated by combining the containerless processing technique of electromagnetic levitation with elastic neutron scattering. Partial structure factors were inferred from the diffraction data which allow an analysis of both, the topological and the chemical short-range order of these alloy melts as a function of the temperature.
Fatigue Study of a Zr-Ti-Ni-Cu-Be Bulk Metallic Glass
Authors: Wang G. Y. , Liaw P. K. , Peker A. , Yang B. , Benson M. L. , Yuan W. , Peter W. H. , Huang L. , Freels M. , Buchanan R. A. , Liu C. T. , Brooks C. R.
Published: April 2011

High-cycle fatigue (HCF) studies were performed on zirconium (Zr)-based bulk metallic glasses (BMGs): Zr41.2Ti13.8Ni10Cu12.5Be22.5, in atomic percent. The HCF experiments were conducted using an electrohydraulic machine at a frequency of 10 Hz with a R ratio of 0.1 and under tension-tension loading, where R = σmin./σmax., where σmin. and σmax. are the applied minimum and maximum stresses, respectively. The test environment was air. A high-speed and high-sensitivity thermographic-infrared (IR) imaging system has been used for nondestructive evaluation of temperature evolution during fatigue testing of BMGs. Limited temperature evolution was observed during fatigue. However, no sparking phenomenon was observed at the final moment of fracture of this BMG. At high stress levels (σmax. > 864 MPa), the fatigue lives of Batch 59 are longer than those of Batch 94 due to the presence of oxides in Batch 94. Moreover, the fatigue-endurance limit of Batch 59 (703 MPa) is somewhat greater than that of Bath 94 (615 MPa) in air. The fatigue-endurance limit of Ti-6–4 is greater than this BMG, but Al 7075 has the lowest fatigue life. The vein pattern with a melted appearance were observed in the apparent melting region. The fracture morphology indicates that fatigue cracks initiate from some defects.
Evolution of the Free Volume during Homogeneous Flow of a Metallic Glass
Authors: Heggen M. , Spaepen F. , Feuerbacher M.
Published: April 2011

Glassy Pd41Ni10Cu29P20 was creep-tested in compression at constant true stress. The defect concentrations were shown to be reversible with reproducible kinetics. The results could be fit better with a defect creation rate that is proportional to the applied power density than with one that depends on the strain rate only. The dilatation mechanism for creation of free volume is inefficient in energy and generation of free volume.
MECHANICAL BEHAVIOR OF BULK GLASSY Fe65.5Cr4Mo4Ga4P12C5B5.5
Authors: Stoica Mihai , Radtke Nicolle , Eckert Jürgen , Roth Stefan , Alcalá Germán , Gebert Annett , Schultz Ludwig , Wang Wei Hua , Zhao Yan Hui
Published: April 2011

The bulk amorphous Fe-based alloy with the nominal composition Fe65.5Cr4Mo4Ga4P12C5B5.5 was obtained by copper mold casting in different shapes: cylindrical rods with diameters up to 2.5 mm and discs with 10 mm diameter and 1 mm thickness. This alloy exhibits good soft magnetic properties. Using electrochemical investigations we found that the corrosion resistance of this alloy is better than that of usual FeSi steel used for magnetic applications. Beside magnetic properties and corrosion resistance, this alloy exhibits also good mechanical properties. These were investigated by compression tests, nanoindentation and by an ultrasonic technique. The Young's modulus E was found to be around 160 GPa, the yield strength σy is around 2.3 GPa and the fracture strength σf is around 3.23 GPa, together with an elastic strain εe= 1.5% and a fracture strain εf= 2.3%. The hardness was found to be around 10 GPa.
Phase Transitions in Al87Ni7Nd6
Authors: Louca Despina , Ahn K. , Soper A. K. , Poon S. J. , Shiflet G. J.
Published: April 2011

The local atomic structure of Al87Ni7Nd6 amorphous metallic glass was determined upon heating by neutron diffraction and the pair density function (PDF) analysis. Two isotopes of Ni with very different scattering intensities were used (58Ni and 60Ni) to separate the local environment of the transition metal. A distinct pre-peak observed in reciprocal space arises because of chemical clustering of Ni atoms. With increasing temperature the coherence length of this peak increases indicating an enhancement in atomic clustering. In addition, precipitation of Al metal is first observed at 200 °C with heating. Binary and ternary Al phases form as the temperature increases further to 500 °C although the majority crystalline phase is Al. The local atomic topology at the intermediate temperatures can be represented with a model that is a combination of the atomic structure at room temperature plus Al.
On the Structural Characterization of a Series of Novel Ni-Nb-Sn Refractory Alloy Glasses
Authors: Tokarz Michelle L. , Bilello John C.
Published: April 2011

Recently refractory alloy glasses of varying Ni, Nb and Sn concentrations were prepared and studied via several characterization methods, including x-ray diffraction via standard lab and synchrotron radiation sources, SEM, and other complementary techniques. A comparison between x-ray diffraction results obtained from synchrotron sources vs. standard lab sources shows the necessity of a low-divergence source in order to distinguish nanoscale crystallites present within an amorphous matrix. The divergence of both sources was determined by comparing the diffraction patterns of a LaB6standard and noting the deviation from ideal or theoretical Bragg peaks. The crystallites in these glasses comprised between 0 and 7.5 percent by volume, depending upon the specific composition. The results presented here also show a very good sample-to-sample consistency for any given alloy composition. While x-ray diffraction results give information about the average structure, SEM was also performed to understand aspects of individual crystallite size and distribution. By studying results of varying alloy concentrations, it is seen that a very small composition range exists for near-perfect glass formers (as defined by a near zero percentage crystallinity). Radial distribution analysis was also performed for each composition and compared to hard sphere models for each alloy composition. This analysis indicated the presence of intermediate range order beyond the first nearest neighbors as indicated by the divergence of the experimental reduced radial distribution functions from that predicted by the accompanying hard sphere models.
Impact of Ge diffusion and wafer cross hatching on strained Si MOSFET electrical parameters
Authors: L. Driscoll , S. Olsen , S. Chattopadhyay , A. O'Neill , K. Kwa , P. Dobrosz , S. Bull
Published: April 2011

A contender for future generations of CMOS technology is the strained silicon (S-Si) MOSFET. The mobility enhancement in S-Si can be exploited to maintain the performance enhancements demanded by Moore's law with reduced critical dimensions. S-Si is obtained by growth of a thin Si layer over a thick virtual substrate (VS) of relaxed silicon-germanium (SiGe). The mobility of a surface channel MOSFET is dependent on the quality of the silicon-oxide (Si/SiO2) interface. Ge may out diffuse from the virtual substrate to the oxide interface causing an increase in trapping density. As the Ge content in the virtual substrate increases surface roughness also increases. These phenomena both lead to a reduction in mobility.

The study of a matrix of devices having variable Ge composition and S-Si thickness is crucial in deconvolving the contributions of Ge diffusion and wafer cross-hatching roughness on electrical parameters. Increasing VS Ge composition increases the Ge concentration at the SSi/SiO2 interface and cross-hatching amplitude whereas reducing S-Si channel thickness only increases Ge concentration at the S-Si/SiO2 interface and does not increase cross-hatch amplitude. Interface state density, drive current, gate leakage current, transconductance and carrier mobility data are presented for this two-dimensional space of VS composition and S-Si thickness. The relative importance of Ge diffusion and cross-hatching roughness can be seen in this data. The results of this study indicate a lower limit of 7 nm for the S-Si thickness and an upper limit of approximately 20 % Ge in the virtual substrate for the current processing technology. Understanding the performance-limiting mechanisms in S-Si is crucial in the optimisation of VS Ge composition and S-Si thickness for current and future generations of S-Si CMOS.
Material and optical properties of GaAs grown on (001) Ge/Si pseudo-substrate
Authors: Chriqui Yves , Largeau Ludovic , Patriarche Gilles , Saint-Girons Guillaume , Bouchoule Sophie , Bensahel Daniel , Campidelli Yves , Kermarrec Olivier , Sagnes Isabelle
Published: April 2011

One of the major challenges during recent years was to achieve the compatibility of III-V semiconductor epitaxy on silicon substrates to combine opto-electronics with high speed circuit technology. However, the growth of high quality epitaxial GaAs on Si is not straightforward due to the intrinsic differences in lattice parameters and thermal expansion coefficients of the two materials. Moreover, antiphase boundaries (APBs) appear that are disadvantageous for the fabrication of light emitting devices. Recently the successful fabrication of high quality germanium layers on exact (001) Si by chemical vapor deposition (CVD) was reported. Due to the germanium seed layer the lattice parameter is matched to the one of GaAs providing for excellent conditions for the subsequent GaAs growth. We have studied the material morphology of GaAs grown on Ge/Si PS using atomic layer epitaxy (ALE) at the interface between Ge and GaAs. We present results on the reduction of APBs and dislocation density on (001) Ge/Si PS when ALE is applied. The ALE allows the reduction of the residual dislocation density in the GaAs layers to 105 cm−2 (one order of magnitude as compared to the dislocation density of the Ge/Si PS). The optical properties are improved (ie. increased photoluminescence intensity). Using ALE, light emitting diodes based on strained InGaAs/GaAs quantum well as well as of In(Ga)As quantum dots on an exactly oriented (001) Ge/Si pseudo-substrate were fabricated and characterized.
Measurement of the residual macro and microstrain in strained Si/SiGe using Raman spectroscopy
Authors: Dobrosz P. , Bull S.J. , Olsen S.H. , O'Neill A.G.
Published: April 2011

The use of laser Raman spectroscopy to assess the residual strain in strained silicon/silicon germanium devices is well established. The peak shift associated with the 520cm−1 silicon peak can be used to directly measure the strain in the cap layer provided that the strained silicon peak can be deconvoluted from the more intense Si in SiGe peak which occurs at slightly lower wavenumbers. However, though peak position gives a measure of the macrostrains in the layer it is not useful for the assessment of microstrains associated with point defects which may also influence device performance; such microstrains influence the intensity of the Raman peaks and can, in principle, be monitored by this method. In this study we have undertaken a study of peak shape as a function of processing conditions for strained silicon on SiGe. Changes in peak position may be correlated with macrostrains and macrostrain relaxation around extended defects such as dislocations. Changes in peak width can be correlated with processes which lead to changes in composition (e.g. germanium build-up in the surface after etching) and microstrain. Such changes are not necessarily correlated with changes in macrostrain but indicate that microstrain could also be an important factor influencing device performance.
Retarded Growth of Sputtered HfO2 Films on Germanium
Authors: Kita Koji , Sasagawa Masashi , Toyama Masahiro , Kyuno Kentaro , Toriumi Akira
Published: April 2011

HfO2 films were deposited by reactive sputtering on Ge and Si substrates simultaneously, and we found not only the interface layer but the HfO2 film was thinner on Ge substrate compared with that on Si substrate. A metallic Hf layer has a crucial role for the thickness differences of both interface layer and HfO2 film, since those thickness differences were observed only when an ultrathin metallic Hf layer was predeposited before HfO2 film deposition. The role of metallic Hf is understandable by assuming a formation of volatile Hf-Ge-O ternary compounds at the early stage of film growth. These results show an advantage of HfO2/Ge over HfO2/Si systems from the viewpoint of further scaling of electrical equivalent thickness of the gate oxide films.
Diffusion of ion-implanted Boron and Silicon in Germanium
Authors: Uppal Suresh , Willoughby A. F. W. , Bonar J. M. , cowern N. E. B. , Morris R. J. H. , Dowsett M. G.
Published: April 2011

The diffusion of B and Si in Ge is studied using implantation doping. Concentration profiles after furnace annealing in the temperature range 800–900 °C were obtained using high resolution secondary ion mass spectroscopy (SIMS). Diffusion coefficients are calculated by fitting the annealed profiles. For B, we obtain diRusivity values which are two orders of magnitude slower than previously reported in literature. An activation energy of 4.65(±0.3) eV is calculated for B diffusion in Ge. The results suggest that diffusion mechanism other than vacancy should be considered for B diffusion in Ge. For Si diffusion in Ge, the diffusivity values calculated in the temperature range 750–875 °C are in agreement with previous work. The activation energy of 3.2(±0.3) eV for Si diffusion is closer to that for Ge self-diffusion which suggests that Si diffusion in Ge occurs via the same mechanism as in Ge self-diffusion.
Influence of He implantation conditions on strain relaxation and threading dislocation density in Si0.8Ge0.2 virtual substrates
Authors: Cai J. , Mooney P. M. , Christiansen S. H. , Chen H. , Chu J. O. , Ott J. A.
Published: April 2011

The strain relaxation and threading dislocation density of He-implanted and annealed SiGe/Si heterostructures have been studied. For He doses above a threshold of 8×1015 cm−2, the degree of strain relaxation depends primarily on the SiGe layer thickness; a similar degree of strain relaxation is obtained when the He dose and energy are varied over a relatively wide range. In contrast, the threading dislocation density is strongly influenced by the implantation depth. There is a strong correlation between the parameter He(SiGe), the He dose in the SiGe layer calculated from He profiles simulated using the program Stopping and Range of Ions in Matter (SRIM), and the threading dislocation density. We find that to achieve a low threading dislocation density, <5×107 cm−2, He(SiGe) must be less than 1015 cm−2. The strain relaxation mechanism is also discussed.
Structure of Sc2O3 Films Epitaxially Grown on α-Al2O3 (111)
Authors: Kortan A. R. , Hong M. , Kwo J. , Chang P. , Chen C. P. , Mannaerts J. P. , Liou S. H.
Published: April 2011

We have characterized the structure of the epitaxial Sc2O3 films grown on a α-Al2O3 (111) substrate using molecular beam epitaxy (MBE) techniques. The Sc2O3 films grow in the bulk bixbyite phase with a very uniform thickness, and a high structural perfection. They grow with their cubic (111) axis parallel to the rhombohedral (111) axis of the sapphire substrate. The in-plane orientation of the films, however, is rotated by ±30 degrees with respect to the substrate rhombohedral axes. This is explained by the presence of two equivalent orientations of the 3-fold axis of the film on the quasi 6-fold surface of the substrate.
Photo-induced magnetism of Pr0.65Ca0.35MnO3 in powder and thin films
Authors: Otagiri Takanobu , Arai Masato , Kodaira Masakazu , Yanagisawa Osami , Izumi Mitsuru
Published: April 2011

The photo-induced magnetism was originally found in Pr0.65Ca0.35MnO3 powder by the ESR and x-ray diffraction studies. However, the mechanism of the photo-induce magnetism was under cover for a long time. Now, D.C. magnetization measurement under a near infrared pulsed laser irradiation (hν = 1.18 eV) reveals the mechanism. The D.C. magnetization prominently increases (approximately 6 %) under the laser irradiation, especially around 90 K near the canted antiferromagnetic (CAF) – antiferromagnetic (AF) transition. The result is consistent with the previous studies and indicates that a CAF – ferromagnetic transition is caused associating with the charge-order (CO) – charge-delocalize (CD) (insulator – metal) transition by the laser irradiation. As the second step for development, the thin films were prepared with the pellet of Pr0.65Ca0.35MnO3 in the on-axis and off-axis geometry of RF magnetron sputtering deposition. The off-axis geometry provides the Pr0.65Ca0.35MnO3 film same as powder composition and the on-axis sputtering fortunately provides the Pr0.99Ca0.01MnO3 film. Both films show photo-induced magnetism. The present photo-induced magnetism is coming from a spin-canted phase in both compounds.
Persistent Electronic Conduction in 12CaO7Al2O3 Thin Films Produced by Ar Ion Implantation: Selective Kick-Out Effect Leads to Electride Thin Films
Authors: Miyakawa Masashi , Hayashi Katsuro , Toda Yoshitake , Kamiya Toshio , Hirano Masahiro , Hosono Hideo
Published: April 2011

A new method to convert 12CaO7Al2O3 (C12A7) thin films to electronic conductor by hot Ar+ ion implantation has been developed and its mechanism is discussed. It was found that hot Ar+ ion implantation extruded free O2- ions in C12A7 films by kick-out effects at fluences higher than 1×1017 cm−2, which left electrons in the cages embedded in C12A7 crystal and produced high concentration F+-like centers (∼1.4×1021 cm−3). The resulting films show coloration and persistent electronic conduction with conductivities up to ∼1 Scm−1. On the other hand, fluences less than 1×1017 cm−2 kept the films transparent and insulating.
High Mobility Nanocrystalline Indium Zinc Oxide Deposited at Room Temperature
Authors: Fortunato E. , Pimentel A. , Gonçalves A. , Marques A. , Martins R.
Published: April 2011

In this paper we present results of indium doped zinc oxide deposited at room temperature by rf magnetron sputtering, with electron mobility as high as 60 cm2/Vs. The films present a resistivity as low as 5 × 10-4 ωcm with an optical transmittance of 85%. The structure of these films look-like polymorphous (mixed of different amorphous and nanocrystalline phases from different origins) as detected from XRD patterns (no clear peak exists) with a high smooth surface, as detected from SEM micrographs, highly important to ensure long life time when used in display devices.
Guided Control of Cu2O Nanodot Self-Assembly on SrTiO3 (100)
Authors: Du Yingge , Atha Surajit , Hull Robert , Groves James F. , Lyubinetsky Igor , Baer Donald R.
Published: April 2011

A method has been developed for specifying the growth location of Cu2O nanodotson SrTiO3 (100) substrates. Growth location has been specified by using a focused ion beam (FIB) to modify microscopic and nanoscopic regions of the SrTiO3substrate prior to Cu2O deposition. Deposition onto the modified regions under carefully selected process conditions has generated nanodot growth at the edge of microscopic FIB-induced features and on top of nanoscopic FIB-induced features. For this work, an array of evenly spaced FIB implants was first patterned into several regions of each substrate. Within each sub-division of the array, the FIB implants were identical in Ga+ energy and dosage and implant diameter and spacing. After FIB surface modification and subsequent in-situ substrate cleaning, Cu2O nanodots were synthesized on the patterned SrTiO3 substrates using oxygen plasma assisted molecular beam epitaxy. The substrates and nanodots were characterized using atomic force microscopy at various stages of the process; in-situ X-ray photoelectron spectroscopy and Auger electron spectroscopy analysis demonstrated that the final stoichiometry of the nanodots was Cu2O. The photocatalytic decomposition of water on Cu2O under visible light irradiation has been reported. If the Cu2O can be located in the form ofislands on a carefully selected substrate, then it could be possible to greatly enhance the efficiency of the photochemical process.
Hydrogen induced degradation in GaInP/GaAs HBTs revealed by low frequency noise measurements
Authors: Tartarin J.G. , Escotte L. , Borgarino M. , Plana R. , Graffeuil J.
Published: April 2011

One of today's challenges to enable the improved electrical performances and reliability of microelectronic devices consists in controlling impurities contamination: hydrogen appears to be present in most (if not all) the processes steps of the devices making (ambient atmosphere, or associated with AsH3 -VPE or AsCl3 -VPE for example in GaAs based devices,…). Hydrogen induced reliability has already been investigated for many Si or GaAs based technologies ((C)MOS, FET, HEMT, PHEMT as well as HBT devices). These effects of hydrogen on electrical behavior and on long term reliability are very difficult to understand because of the different nature and ionic association of hydrogen (H, H+, H-, H2, or associated with impurities (Ge-H, Be-H, C-H,…). Most of these studies make use of IR, SIMS, Hall measurements: in this paper, we use low frequency noise measurements, associated with static as well as dynamic characterization to identify the degradation process in GaInP/GaAs Heterojunction Bipolar Transistors (HBT supplied by Thomson LCR). The presence of Hydrogen has been identified by DLTS at the LPSC laboratory (Meudon, France). The influence of passivation (SiN and GaInP ledge) on the reliability associated with Hydrogen has been one of the first improvements on HBT devices. Low-frequency noise measurements have been performed in the range of 250Hz to 100 kHz. The noise spectra evolutions (current and voltage noise sources at the input of the devices) allowed us to identify the activation process responsible of the static and dynamic rise and fall of the HBT's current gain. Chemical reactions of C-H complexes have been proved to be the processes responsible of this degradation. Additive reliability tests have been performed on two sets of devices (featuring different emitter length) under two distinct stocking conditions (temperature and biasing of the devices) leading to different junctions temperatures: low-frequency (LF) noise measurements, associated with static and dynamic S parameter measurements led to the same conclusion about the involved chemical reaction. We found that C-H complexes break, and H diffusion towards the extrinsic surface of the device has been observed on the measured leakage currents. Sealed devices have proved to get the same degradation signature than on wafer devices: Hydrogen is assumed to be present in high concentration levels in the device layers, and reacts under thermal and electrical stress.
Deciphering the Vibrational Spectrum of Interstitial H2 in Si
Authors: Stavola Michael , Chen E Elinor , Fowler W. Beall
Published: April 2011

H2 is a fascinating molecule whose properties revealed the influence of nuclear spin on the molecular wave function in the 1920s. As an interstitial defect in Si, the H2 molecule has given rise to a number of perplexing puzzles since the discovery of its vibrational spectrum. The absence of an ortho-para splitting for the H2 vibrational line and an apparent low symmetry found in stress experiments misled several researchers into thinking that interstitial H2 in Si must have a barrier to rotation. Our discovery of a new vibrational line for HD in Si and its interpretation, along with the recognition that certain transitions are possible for HD, but not for H2 or D2, establish that H2 in Si is a nearly free rotator after all. Additional puzzles such as the anomalous intensity of the HD line, the absence of an isotope dependence for the uniaxial stress splitting of the H2 and D2 vibrational lines, and the properties of an O-H2 complex are also explained naturally. Recent Raman studies confirm that interstitial H2 in Si is a free rotator but raise interesting new questions about the diffusivities of the ortho and para species.
Origin of the Hydrogen/Deuterium (H/D) Isotope Effect of Hot-Electron Degradation of MOS Devices
Authors: Chen Zhi , Guo Jun , Ong Pangleen
Published: April 2011

In order to verify Van de Walle and Jackson's theory on the isotope effect of the Si-H/D bonds resistant to hot-electron excitation [Appl. Phys. Lett., 69, 2441 (1996)], we measured the Si-H, Si-D, and other vibrational modes in oxidized silicon wafers annealed in hydrogen and deuterium using Fourier Transform Infrared (FTIR) spectrometry. Our FTIR data suggest that the frequency for the Si-D bending mode at the SiO2/Si interface is 490 cm−1. Our experimental data support Van de Walle and Jackson's theory with some modification. Their theory is correct for the experiments of breaking Si-H/D bonds using scanning tunneling microscope (STM) where no oxide is involved. In the SiO2/Si case, the de-excitation of the Si-D bond may be due to the energy coupling from the Si-D bending mode to two vibrational modes; i.e., the Si-O TO mode and the Si-Si TO phonon mode. Van de Walle and Jackson only pointed out coupling to the Si-Si TO phonon mode. The strongest coupling might happen between the Si-D mode and the Si-O TO mode. Therefore, the oxide may play a crucial role in energy dissipation of the Si-D bond in metal-oxide-semiconductor (MOS) devices.