bluuebunny/crossref_metadata_2025 huggingface dataset:
The Kinetics of Ordering in Gadolinium Zirconate: an Unusual Oxygen Ion Conductor
Authors: Haile Sossina M. , Meilicke Scott
Published: April 2011

Gadolinium zirconate, Gd2Zr2O7, undergoes an order-disorder transition at ∼1550°C, transforming from a defect fluorite structure (Fm3m) to a pyrochlore structure (Fd3m). Both cations and anions are ordered in the low-temperature, pyrochlore structure. In order to understand the interplay between anion and cation order parameters and ordering rates, the transformation kinetics of Gd2Zr2O7 have been examined via X-ray diffraction. Gadolinium zirconate is of particular interest because the oxygen ion conductivity of the ordered phase is significantly greatly than that of the disordered phase, in contrast to virtually every other known solid electrolyte. This difference in conductivity has provided a second technique for characterizing the transformation kinetics: in situ A.C. impedance spectroscopy. Results of the X-ray diffraction showed the growth of superstructure peak intensity to follow an apparent (time)½ dependence, rather than that expected from a nucleation and growth model. The impedance spectroscopy measurements, on the other hand, showed the conductivity to increase linearly with time. These results suggest the transition is second order in nature.
The Effect of Strain on Intra- and Interlayer Mass Transport in Metal Epitaxy
Authors: Brune H. , Bromann K. , Kern K.
Published: April 2011

A general concept is shown how to measure both the barriers for terrace and step-down diffusion for an epitaxial system. It is based on the application of mean-field nucleation theory to variable temperature STM data. With this approach we studied the influence of strain on intra- and interlayer diffusion for Ag self diffusion on strained and unstrained Ag(111) surfaces. The strained surface was the first Ag layer that grows pseudomorphically on Pt(111) and is thus under 4.2% compressive strain. The barrier for terrace diffusion is observed to be substantially lower on the strained, compared to the unstrained Ag/Ag(111) case, 60±10 meV and 97±10 meV, respectively. The additional barrier for interlayer diffusion decreases from 120±15 meV for Ag(111) homoepitaxy to only 30±5 meV for diffusion from the strained Ag layer down to the Pt(111) substrate. These examples illustrate the considerable effect of strain on the intra- and interlayer mass transport. They require a new concept of layer dependent nucleation kinetics for heteroepitaxial systems in general.
Pyramid Formation and Coarsening During Homoepitaxial Growth
Authors: Siegert Martin
Published: April 2011

One of the generic scenarios in molecular beam epitaxy is the growth of large scale pyramid-like three-dimensional structures. These structures are a consequence of non-equilibrium surface diffusion currents that result from a transport of adatoms in the uphill direction in regions of the surfaces that are tilted away from a high symmetry orientation. The microscopic origin of these currents are, e.g., diffusion barriers at step edges that suppress the diffusion of adatoms to lower terraces. The temporal evolution of the resulting instabilities can be described by simple continuum equations that display slope-selection, pyramid-like structures, and coarsening. We show that similar scenarios can be found in microscopic models investigated by Monte-Carlo simulations. However, crossover phenomena can complicate the comparison of the asymptotic theory with computer simulations or experiments. We therefore discuss criteria that allow to distinguish experimentally between kinetic roughening with exponents ζ ≃ 1 and unstable pyramid-like growth.
X-Ray Diffraction Analysis of the Strain of SiGeC/(100)Si Alloys
Authors: Bair A.E. , Alford T.L. , Sego S. , Atzmon Z. , Culbertson R.J.
Published: April 2011

Samples of Si1-x-YGexCy were analyzed with a triple axis high resolution x-ray diffractometer to produce reciprocal space maps. Films with compositions of approximately Si0.77Ge0.20C0.01 vvith thicknesses ranging from 120 nm to 750 nm were found to be pseudomorphic with a tetragonal distortion, εT, near 1%. The tetragonal distortion in pseudomorphic samples with compositions near Si0.47Ge0.50C0.03 with thicknesses ranging from 61 nm to 115 nm was found to be near 2%. The strain increased linearly with Ge concentration even though the Ge:C ratio remained nearly constant. The strain in samples with similar compositions was not a function of thickness. These strain measurements correlated well with results from ion channeling analysis.
Tem Study of Stacking Faults Formed in Pairs in a ZnSe Epitaxial Layer on a GaAs(00l) Buffer Layer
Authors: Tanimura J. , Wada O. , Endoh Y. , Imaizumi M. , Ogama T.
Published: April 2011

Structure of stacking faults in a ZnSe epitaxial layer grown on a GaAs(001) buffer layer was determined with transmission electron microscopy. Two stacking faults were formed in pairs on (111) and (111) planes with the same polarity and met at a point which is a few atomic layers away from the interface between ZnSe and GaAs. Partial dislocations were found to be the Shockley type ones with a Burgers vector of 1/6<211>. Atomic force microscopy showed that hillocks were formed in pairs at a surface where the pair of stacking faults existed in the layer. Moreover, it was observed that the pair of stacking faults elongated along the <110> direction by gliding on the {111} faulted planes under annealing at 200°C for 30min. Formation mechanisms of the pair of stacking faults have been discussed.
Atomistic Simulation and Elastic Theory of Surface Steps
Authors: Shilkrot L. E. , Srolovitz D. J.
Published: April 2011

Atomistic computer simulations and anisotropic elastic theory are employed to determine the elastic fields of surface steps and vicinal surfaces. The displacement field of and interaction energies between <100> steps on an {001} Ni surface are determined using atomistic simulations and EAM potentials. The step-step interaction energy found from the simulations is consistent with a surface line force dipole elastic model of a step. We derive an anisotropic form for the elastic field associated with a surface line force dipole using a two dimensional surface Green tensor for a cubic elastic half-space. Both the displacement fields and step-step interaction energy predicted by the theory are shown to be in excellent agreement with the simulations.
Interdiffusion and Stress Evolution During Solid-State Amorphization in Ni-Hf Thin-Film Diffusion Couples
Authors: Atzmon M. , Boyer W. S. L.
Published: April 2011

Using a combination of x-ray diffraction and curvature measurements, the stress evolution during solid-state amorphization in a Ni-Hf diffusion couple has been monitored. In contrast to the Co-Hf system, no dissolution of Ni in Hf is observed. During interdiffusion, the growing amorphous layer develops a large tensile stress, which subsequently relaxes by creep. Irradiation of the diffusion couple leads to an increase in tensile stress, and a further increase following a subsequent anneal. Composition measurements by Rutherford backscattering spectrometry indicate absence of an effect of the stress variations on the effective interdiffusion coefficient.
Thickness Dependent Phase Formation in Fe Thin Film and Si Substrate Solid Phase Reaction
Authors: Molnár G Y. , Pető G. , Zsoldos E. , Horváth Z. E. , Khánh N. Q.
Published: April 2011

The solid phase reaction of Fe thin films with (111) Si substrate was investigated at constant annealing temperature and time (700°C, 7 minutes) as a function of the initial iron film thickness (from 5 nm to 27.5 um in 2.5 nm steps). The formed phases were analysed by X-ray diffraction, Rutherford backscattering and transmission electron microscopy and optical microscopy.

After annealing FeSi phase was detected in the thinner samples. Samples with Fe layers thicker than 12.5 nm contained a β-FeSi2 phase. This special phase sequence was explained with the help of a nucleation controlled phase formation model, taking into consideration the critical radius of nuclei of the new phase. The advantages of using the film thickness as a variable during investigation of solid phase thin film reactions and the probable substrate effects are also discussed.
Controlled Nucleation and Growth in the Hydrothermal-Electrochemical Formation of BaTiO3 Films
Authors: Escobar I. , Silva C. , Lorca J. , Fuenzalida V. M. , Lisoni Judit. G. , Vargas T.
Published: April 2011

The influence of controlled potential conditions on the structure and phases of BaTiO3 films grown on titanium by the hydrothermal-electrochemical method was studied. The experiments were conducted using a three electrode high pressure electrochemical cell in a 0.2 M Ba(OH)2 electrolyte at 150 °C. The spontaneous initial nucleation linked to pure hydrothermal BaTiO3 formation was inhibited by cathodically protecting the titanium electrode since its immersion in the electrolyte. The application of initial nucleation pulses of varying cathodic potentials affected the grain size of the deposit. The growth of tetragonal BaTiO3 was achieved combining the initial inhibition of the pure hydrothermal growth, followed by nucleation under controlled potentiostatic conditions.
Effect of Thickness and Substrates on the Mechanical Properties of Tantalum and Tantalum Nitride Thin Films
Authors: Saha Ranjana , Inturi Rama B. , Barnard John A.
Published: April 2011

Determining the intrinsic mechanical properties of films by nanoindentation is complicated by the presence of the substrate. Generally, for very thin films (<100 nm) one unavoidably observes the properties of the film/substrate composite system. In order to determine the extent of the effect of the substrate on the mechanical properties of Ta and Ta-N thin films, we have grown these films in four different thicknesses (50, 250, 400 and 500 nm) and on three different substrates (glass, oxidized Si, and sapphire). The structure of the films was evaluated by x-ray diffraction and the mechanical properties (hardness and elastic modulus) were determined by nanoindentation.
Microstructural Characterization of Platinum Films Grown by Mocvd
Authors: Vellaikal M. , Streiffer S. K. , Woolcott R. R. , Kingon A. I.
Published: April 2011

Platinum thin films were deposited on SiO2/Si(100) by metalorganic chemical vapor deposition using Pt(acetylacetonate) and Pt(hexaflouroacetylacetonate) as precursors. The films were characterized in terms of orientation, surface roughness and morphology. As expected, Pt(111) was the preferred orientation. Higher substrate temperatures led to higher growth rates and increased surface roughness. The presence of oxygen during deposition decreased the minimum substrate temperature required for platinum deposition, indicating that oxygen played a role in the decomposition of these metalorganic compounds. Annealing platinum films at 550°C in an oxygen ambient resulted in hillock formation. Resistivity measurements showed that films deposited without oxygen were more resistive. Conformal coverage of platinum on patterned SiO2/Si substrates was investigated, and a side wall film thickness to top film thickness ratio of 0.6 for growth at 400°C was obtained. These Pt films produced by MOCVD displayed greater surface roughnesses than films grown by evaporation or sputtering.
Boron Induced Changes in the Structural Properties of Amorphous Silicon Boron Alloys
Authors: Yang G-R. , Abburi M. , Tong B. Y.
Published: April 2011

Thin films of an amorphous Si-B alloy with B contents 1–50% were deposited by low pressure chemical vapor deposition (LPCVD) from diborane (B2H6) and silane (SilH4) gases. XRD patterns of the as deposited films showed them to be completely amorphous. The films were annealed in N2 at 600–800°C for 30 minutes and characterized by Raman spectroscopy. Wet oxidation of the film was carried out 700°C for 30 minutes, and the films examined by XRD. The structural changes induced by B in the a-Si network discussed in the conceptual framework of the continuous random network (CRN) model. We conclude that the boron incorporation enhances the structural disorder and induces topological changes in the amorphous network.
Resistance Decrease of Phosphorus Ion Implanted Poly-Si Thin Films During Low Temperature Annealing
Authors: Tokioka H. , Masutani Y. , Goto Y. , Nagao S. , Kurokawa H.
Published: April 2011

During low temperature (below 450°C) annealing, the sheet resistance of phosphorus implanted poly-Si thin films (film thickness : 50nm) decreased to lE+3Ω/square. The sheet resistance after annealing decreased with annealing time and became lower when the dosing level was high enough. At the dose of 8E+14 ions/cm2 we obtained a sheet resistance of 1E+3Q/square by annealing at 450°C for 180min. We analyzed ellipsometry data assuming a two-layer model where the surface layer consists of a-Si and the lower layer of poly-Si. This analysis indicated that the surface of implanted films was amorphized by ion implantation and the amorphized layer thickness increased with dosing level. Also, it turned out that the lower poly-Si layer thickness increased from 30nm to 50nm after annealing accompanied by the conversion of a-Si layer to poly-Si layer. During annealing at low temperature, activation of phosphorus ions implanted into poly-Si and recrystallization of a-Si took place simultaneously and the sheet resistance after annealing decreased with the increase in thickness of the recrystallized region.
Stress-Temperature Behavior and Stress Relaxation in Ti/Al-0.5%Cu/TiN and TiN/W Thin Films
Authors: Doucet L. , Brun A. , Jaouen H. , Dupeux M. , Ignat M.
Published: April 2011

The stress behavior of two structures (Ti/Al-0.5%Cu/TiN and TiN/W) has been analyzed versus temperature up to 400 °C using the Flexus measurement system. Microstructure modifications induce stress variations with temperature. Furthermore, stress relaxation after annealing has been investigated. Al-based metallization stress is essentially due to thermal issues and reaches rapidly its yield strength whereas the W film exhibits high intrinsic stress. Microstructural observations afte deposition and after annealing have been conducted using a non destructive technique, the Thermal Wave Imager.
Structural and Magnetic Features of Fe-Based Multilayers with Thick Non-Magnetic Layers
Authors: Hage Y. , Nittono O.
Published: April 2011

Coercivity and microstructure were investigated in Fe-based multilayers. Coercivity of the Fe layer near the film surface differs slightly from that of the layer near the substrate. The coercivity of a given Fe layer in the multilayer is related to the thickness of the given layer and to the total thickness of the layers between the given layer and the substrate. In addition, coercivity and microstructure are influenced when various metals are combined with Fe.
Temperature and Strain Rate Effects in Grain Boundary Sliding
Authors: Molteni C. , Francis G. P. , Payne M. C. , Heine V.
Published: April 2011

We have performed total energy density functional theory calculations to investigate the sliding process at the ∑ = 5 (001) twist grain boundary in germanium. The accurate quantum mechanical description of the interatomic bonding provides valuable insights into the mechanisms of bond breaking and remaking that occur during the sliding.

In this paper we show how total energy calculations can be used to describe finite
temperature and strain rate effects in this grain boundary.
First-Principles Calculations of Heusler Phase Precursors in the Atomic Short-Range Order of Disordered BCC Ternary Alloys
Authors: Althoff Jeffrey D. , Johnson Duane D.
Published: April 2011

We apply our recently developed first-principles theory of atomic short-range order in disordered multicomponent alloys to CuAuZn2 and AgAuZn2, two alloys which display partially-ordered B2 phases as well as fully-ordered Heusler structures. The calculated Warren-Cowley pair correlation functions for both alloys peak at the special points 〈½ ½ ½〉 and 〈100〉, with the peak at 〈100〉 dominant. This is indicative of a tendency to B2 order at high temperatures, and a subsequent tendency to Heusler-type order at lower temperatures. An analysis in terms of effective interactions shows that the Au Zn interaction drives the 〈100〉 ordering tendency, while the Ag Au and Cu Au interactions contribute more to the 〈 ½ ½ ½〉ordering tendency - this effect is larger in CuAuZn2 and should lead to a slightly higher transition temperature for the B2 to Heusler transition in CuAuZn2 as compared to AgAuZn2.
Dissociative Adsorption and Desorption Processes of Cl2/GaAs(001) Surfaces
Authors: ohno Takahisa
Published: April 2011

The energetics of both dissociative adsorption of C12 molecules on reconstructed GaAs(001) surfaces and desorption of chlorides from the chlorinated GaAs(001) surfaces is theoretically investigated, employing the first-principles pseudopotential density-functional approach within the generalized gradient approximation. On the Ga-rich GaAs(001)-(4x2) surface a C12 molecule is found to dissociate with no potential barrier over a Ga dimer and the Ga dimer is also simultaneously broken upon chlorination, resulting in formation of GaC1 with two backbonds to the As layer below. The desorption energy of a GaCl molecule is smaller than that of a Cl atom, although the former involves breaking two Ga-As backbonds and the latter involves the breakup of one Ga-Cl bond. On the As-rich (2x4) surface, the dissociation of a C12 molecule over an As dimer is an activated process and the As dimer is not broken by the Cl adsorption. The desorption energy of a AsCI molecule is larger than that of a Cl atom. The obtained results are consistent with recent experiments such as temperature-programmed desorption measurements.
Hydrogenation Effects on Structures of Silicon Clusters
Authors: Miyazaki Takehide , Stich Ivan , Uda Tsuyoshi , Terakura Kiyoyuki
Published: April 2011

We have performed anab initiogeometry optimization of hydrogenated silicon clusters Si6Hx,(O ≤x≤ 12), within the generalized gradient approximation (GGA-PW91) in the density-functional theory. We have found that hydrogenation of Si6clusters provides contrasting effects on their stable structures depending onx. From calculation of zeropoint corrected formation energies, we also foundbistabilityof silicon clusters in the existence of hydrogen.
Small-Scale Simulations Of Lattice Fracture
Authors: Marder M.
Published: April 2011

Many properties of rapid fracture may profitably be studied in atomic scale computer simulations involving relatively small numbers of atoms. A first result of such a study is that qualitative properties of Mode III fracture change little when one explores various shapes of the interparticle potential, introduction of randomness, and elevated temperatures. A second result is that Mode I fracture is considerably more susceptible to instability than had previously been understood, and that to obtain stable Mode I fracture may require non-central forces between atoms.
Stability Analysis Of Cracks Propagating In Three Dimensional Solids
Authors: Larralde H. , Al-Falou A. A. , Ball R. C.
Published: April 2011

We present a theory for the morphology of the fracture surface left behind by slowly propagating cracks in linear, isotropic and homogeneous three dimensional solids. Our results are based on first order perturbation theory of the equations of elasticity for cracks whose shape is slightly perturbed from planar. For cracks propagating under pure type I loading we find that all perturbation modes are linearly stable, from which we can predict the roughness of the fracture surface induced by fluctuations in the material. We compare our results with the classical results for cracks propagating in two dimensional systems, and discuss the effects in the three dimensional analysis which result from taking into account contributions from non-singular terms of the stress field, as well as the effects arising from finite speeds of crack propagation.
Modeling Acoustic Emission In Microfracturing Phenomena
Authors: Zapperi S. , Vespignani A. , Stanley H.E.
Published: April 2011

It has been recently observed that synthetic materials subjected to an external elastic stress give rise to scaling phenomena in the acoustic emission signal. Motivated by this experimental finding we develop a mesoscopic model in order to clarify the nature of this phenomenon. We model the synthetic material by an array of resistors with random failure thresholds. The failure of a resistor produces an decrease in the conductivity and a redistribution of the disorder. By increasing the applied voltage the system organizes itself in a stationary state. The acoustic emission signal is associated with the failure events. We find scaling behavior in the amplitude of these events and in the times between different events. The model allows us to study the geometrical and topological properties of the micro-fracturing process that drives the system to the self-organized stationary state.
Fractography Of Glass At The Nanometer Scale
Authors: Guilloteau E. , Arribart H. , Creuzet F.
Published: April 2011

We present a nanometer scale description of the fracture surface of soda-lime glass. This is achieved by the use of Atomic Force Microscopy. The mirror zone is shown to be built with elementary entities, the density of which increases continuously while the mist and hackle zones are approached. Moreover, the overall picture leads to some kind of self-similarity, in the sense that small regions of the hackle zone exhibit the full set of mirror, mist and hackle areas.
Growth and Structure of Carbide Nanorods
Authors: Lieber Charles M. , Wong Eric W. , Dai Hongjie , Maynor Benjamin W. , Burns Luke D.
Published: April 2011

Recent research on the growth and structure of carbide nanorods is reviewed. Carbide nanorods have been prepared by reacting carbon nanotubes with volatile transition metal and main group oxides and halides. Using this approach it has been possible to obtain solid carbide nanorods of TiC, SiC, NbC, Fe3C, and BCx having diameters between 2 and 30 nm and lengths up to 20 µm. Structural studies of single crystal TiC nanorods obtained through reactions of TiO with carbon nanotubes show that the nanorods grow along both [110] and [111] directions, and that the rods can exhibit either smooth or saw-tooth morphologies. Crystalline SiC nanorods have been produced from reactions of carbon nanotubes with SiO and Si-iodine reactants. The preferred growth direction of these nanorods is [111], although at low reaction temperatures rods with [100] growth axes are also observed. The growth mechanisms leading to these novel nanomaterials have also been addressed. Temperature dependent growth studies of TiC nanorods produced using a Ti-iodine reactant have provided definitive proof for a template or topotactic growth mechanism, and furthermore, have yielded new TiC nanotube materials. Investigations of the growth of SiC nanorods show that in some cases a catalytic mechanism may also be operable. Future research directions and applications of these new carbide nanorod materials are discussed.
Low Temperature Mocvd Growth of V/Vi Materials VIA a Me3SiNMe2 Elimination Reaction
Authors: Groshens T. J. , Gedridge R. W. , Lowe-Ma C. K. , Cole Teresa
Published: April 2011

Films of M2Te3 (M = Sb, Bi) were grown on Si(lll) cut 4° off-axis and GaAs(100) substrates between 25°C and 150°C in a low pressure MOCVD reactor via a novel N, Ndimethylaminotrimethylsilane (Me3SiNMe2) elimination reaction using M(NMe2)3 (M = Sb, Bi) and (Me3Si)2Te. X-ray diffraction data indicated that the crystallinity and crystallite orientation of the resulting films were dependent on the substrate structure and growth temperature. Amorphous films were deposited below 50°C. Films deposited at 75°C for Sb2Te3 and 125°C for Bi2Te3 were highly oriented with the (015) reflection plane parallel to the substrate surface. Films of Sb2Te3 deposited at 150°C were highly oriented with the (00ℓ) reflection planes parallel to the substrate surface. The electrical properties and presumably the composition of Bi2Te3 films deposited on Kapton was independent of the V/VI precursor ratio used. This unique deposition reaction provides an alternative route to prepare group V chalcogenide materials which have potential applications in solar cells, reversible optical storage, and thermoelectrics.
Silicon Carbide: the Premier Paradigm for Structural and Microelectronic Device Applications in Severe Environments
Authors: Davis Robert F.
Published: April 2011

The extreme thermal, mechanical, corrosion resistant and electronic properties of SiC provide multiplicative combinations of attributes which allow a variety of products for very different applications. The emphasis herein will be the consideration of both the constant stress creep properties of several types of polycrystalline SiC materials and the characteristics of different SiC-based devices having high power, high frequency and switching applications and which are operational at ≥573K. The controlling mechanism in reaction-bonded SiC within the ranges of temperature and stress of 1848K-1923K and 110–220 MPa, respectively, is glide/climb controlled by climb. The controlling creep mechanism in CVD material at T<1873K is dislocation glide controlled by the Peierls stress; above this temperature, the evidence suggests that dislocation glide/climb controlled by climb becomes an increasingly important mechanism. For sintered α-SiC within the respective temperature and stress ranges of 1670K-2073K and 138–414 MPa, the controlling creep mechanisms are grain boundary sliding accommodated by grain boundary diffusion at T<1800K and lattice diffusion at T> 1920K. By contrast, the continual development of SiC thin film deposition and the device related technologies of doping, contacts and dry etching have culminated in a host of microelectronic devices operable at high temperatures, namely, MOSFET high power devices, MESFET high frequency devices, and switches including p-n junctions and thyristors. The properties of selected devices and circuits made from them are described with an emphasis on their operation at high temperature.
New Strategies for the Fabrication of Enzyme Electrodes
Authors: Alva K. Shridhara , Samuelsont Lynne A. , Kumar Jayant , Marx Kenneth A. , Kaplan David L. , Tripathy Sukant K.
Published: April 2011

The electrochemical properties of o-dianisidine have been studied in both aqueous and organic solvents. This aryl diamine has been electrochemically polymerized on ITO coated glass electrodes and it was determined that the optical properties of these films are influenced by the polymerization conditions. The use of this polymer film as substrate for chemical coupling of biomaterials has been demonstrated with the light harvesting protein, phycoerythrin. Fabrication and bioanalytical application of enzyme electrodes by electrochemical copolymerization of odianisidine with the enzymes glucose oxidase and horseradish peroxidase, modified with odianisidineis described.
Bioactive Void Metal Composites for Orthopedic Implant Devices
Authors: Campbell Allison A. , Graff Gordon L. , Song Lin , Sump Ken R.
Published: April 2011

Although significant advances have been made to provide mechanically strong and nontoxic metals and alloys, biological integration of devices into natural tissues remains a problem. The Surface Induced Mineralization (SIM) and Void Metal Composite (VMC) processes produce a bioactive porous metal implant coating/device which may address many of the problems associated with conventional processing methods.

The VMC process produces materials which have cylindrical pores of uniform diameter which can completely penetrate the structure of the material. The pore diameter, orientation and interconnectivety are easily controlled

The SIM process uses the idea of nature's template-mediated mineralization by chemically modifying the implant to produce a surface which induces heterogeneous nucleation from aqueous solution. SIM produced bioactive coatings provide 1) control of the thickness and density of the mineral phase, 2) a way to coat porous metals, complex shapes and large objects, 3) the ability to coat a wide variety of materials, 4) potential choice for the phase of the mineral formed.
Thin Film Phosphate Based Bioactive Substrates
Authors: Langstaff S , Sayer M , Weaver L , Pugh S , Smith T
Published: April 2011

Calcium phosphate based thin films prepared by colloidal sol-gel slow draw dipping of quartz substrates are bioactive to both osteoclast resorption and osteoblast deposition. The bioactivity is related to the presence of mixed crystalline phases in the films generated under different sintering conditions. As the sintering temperature was increased from 800°C to 1000°C, a transition in film composition from calcium hydroxylapatite to alpha-tricalcium phosphate is achieved.
Cu Deposition Characteristics into Submicron Contact Holes Employing Self-Sputtering With a High Ionization Rate
Authors: Shingubara S. , Sano A. , Sakaue H. , Takahagi T. , Horiike Y. , Radzimski Z. J. , Posadowski W. M.
Published: April 2011

Cu deposition profiles in submicron contact holes are investigated employing the Cu self-sputtering which do not need any inert gas e.g. Ar during sputtering. Excellent bottom coverage in the high aspect ratio contact holes was obtained at a large target-substrate distance in the selfsputtering due to a long mean free path of Cu ions and atoms, although a coverage is poor in Ar sputtering at 6 mTorr. It is also shown that the self-sputtering has low resputtering effect and high self-diffusivity of Cu, while the resputtering predominates in the case of Ar sputtering when DC bias is applied on the substrate. As a consequence, the bottom coverages of the self-sputtered films are much improved than the Ar sputtered ones. The present work strongly suggests that the self-sputtering is promising to fill Cu in sub micron via and contact holes.
Thermal Stability of Nickel Silicide Films
Authors: Das S. R. , XU D.-X. , Nournia M. , Lebrun L. , Naem A.
Published: April 2011

In view of their potential application in ULSI technology, nickel silicide films were formed on undoped and doped Si(100) substrates. Nickel films of varying thicknesses were sputter-deposited onto the substrates and silicidation was performed ex-situ by rapid thermal annealing in nitrogen ambient. The electrical sheet resistance of the silicides was studied as a function of film thickness and annealing temperature. The process window for forming the NiSi phase and the thermal stability of the NiSi phase were determined as a function of film thickness.
Electromigration and Diffusion in Pure Cu and Cu(Sn) Alloys
Authors: Hu C.-K. , Lee K. L. , Gupta D. , Blauner P.
Published: April 2011

Atom movements of Cu in pure Cu and Cu(0.5 to 2 wt.% Sn) alloys have been investigated using drift velocity and radioactive tracer techniques. The void growth rate in pure Cu at the cathode end, as a result of electromigration driving force, linearly increases with the applied current density. A marked decrease in the Cu grain boundary diffusivity and electromigration drift velocity is attributed to Sn trapping of Cu atoms and/or binding defects at grain boundaries. The effect is more pronounced at lower temperatures. The activation energies for electromigration and diffusion of Cu in pure Cu grain boundaries were found to be in the range of 0.7 - 0.9 eV. Addition of about 0.5 to 2 wt.% Sn increased these energies to 1.1 - 1.3 eV, respectively which resulted in enhancement of electromigration resistance by several orders of magnitude over that in pure Cu at the field operation temperature.
New Class of Microporous Materials: Porous Metal Phosphonate Thin Films
Authors: Vermeulen Lori A. , Pattanayak J. , Fisher Travis , Hansford Monica , Burgmeyer Scott J.
Published: April 2011

Solid state metal phosphonates (M(O3P-R-PO3) or M(O3P-R)2 (M = metal)) have layered structures where the metal atoms lie in planar sheets and the intervening R groups take up the interlamellar space. Microporous metal phosphonates can be prepared by reaction of the metal with a mixture of large and small phosphonates (M(O3P-LARGE)x(O3P-SMALL)2-x. The larger group acts as a pillar that holds the layers apart. Void spaces result from the presence of the smaller groups. The porous nature of these solids make them potential candidates for applications as sensors, size- and shape- selective catalysts, and chromatographic materials. Metal diphosphonates (M(O3P-R-PO3) can also be prepared one layer at a time on a surface, resulting in the construction of interesting superstructures that are not accessible through the solid state synthesis. For example, these superstructures can contain different components in sequential layers and may have applications in energy conversion, vectorial electron transport, and NLO devices. The preparation of microporous thin films would combine the desirable potential applications of the porous solids with the interesting parallel superstructures that can be prepared from the thin film assemblies. We report our progress toward the construction of microporous metal phosphonate thin films. The two methods that are currently being developed include: 1) phosphonate exchange of pre-assembled films, and 2) co-deposition of different large and small phosphonates during film assembly.
Optical Properties of Si Nanoclusters with Passivated Surfaces
Authors: Dinh L. N. , Chase L. L. , Balooch M. , Siekhaus W. J. , Wooten F.
Published: April 2011

Si nanoclusters with average size of a few nanometers have been synthesized by thermal vaporization of Si in an Ar buffer gas, and passivated with oxygen or atomic hydrogen. High resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) revealed that these nanoclusters were crystalline. All samples showed strong infrared and/or visible photoluminescence (PL) with varying decay times from nanoseconds to microseconds depending on synthesis conditions. Absorption mainly in the Si cores was observed by photoluminescence excitation (PLE) spectroscopy. The visible components of PL spectra were noted to blue shift and broaden as the size of the Si nanocrystals (nc-Si) was reduced, and there were differences in PL spectra for hydrogen and oxygen passivated nc-Si. Our data can be explained best by a model involving absorption between quantum confined states in the Si cores and emission by surface/interface states.
Graphitized Needle Cokes and Natural Graphites for Lithium Intercalation
Authors: Tran T. D. , Spellman L. M. , Pekala R. W. , Goldberger W. M. , Kinoshita K.
Published: April 2011

The microstructure of carbonaceous materials strongly affect their ability to electrochemically intercalate lithium [1]. The fractional intercalation capacity (x in LixC6) for various types of amorphous and graphitic carbons can vary over a range between 0 to 1. Capacities exceeding that of graphite (372 mAh/g or LiC6) can be obtained from chemically doped (i.e., with phosphorous [2]) materials or from carbonized organic precursors pyrolyzed at low temperatures (<900°C) [3]. Additional chemical effects apparently influence the carbon electrochemical behavior in these cases.
Photonic Band Structure of Nanochannel Glass Materials
Authors: Rosenberg A. , Tonucci R. J. , Lin H.-B.
Published: April 2011

We demonstrate that nanochannel glass (NCG) materials are ideal for investigating twodimensional (2D) photonic band-structure effects. The NCG materials we have studied consist of triangular arrays of glass cylinders embedded in a glass matrix, having center-tocenter nearest-neighbor separations from 0.54 to 1.08 μm. The indices of refraction of the two glasses differ by less than 0.02 in the relevant spectral region. Narrow attenuation features occur whenever the dispersion relation for light propagating within such a periodic dielectric structure crosses a Brillouin zone boundary. The attenuations corresponding to the first Brillouin zone appear in the near-infrared (IR), at wavelengths between 1 and 3 μm, in good agreement with calculations.
Morphological Characterization of Furfuraldehyde Resins Adsorbents
Authors: Sánchez R. , Monteiro S. N. , D'Almeida J. R.
Published: April 2011

The posibility of employing acid catalyzed fufuraldehyde resins as seletive adsorbents has arisen during a comprehensive study of physical-chemical adsorption properties of these materials. The morphology of these resins depend on the synthesis method. Scanning Electron Microscopic studies of these materials which were synthetized, in bulk (FH-M) and solution (FH-D), showed differences in surface density and particle size. Using mercury porosimeter techniques and BET adsorption methods, it was found different pore size distributions and a decrement in surface area when solvent was employed in the synthesis process. By thermogravimetric analysis it was found similar weight losses (6%) of water adsorption and a small differences in thermal stabilities.
Electrical Behaviour of Natural Manganese Dioxide (NMD)
Authors: Gorgulho H. F. , Fernandes R. Z. D. , Pernaut J. M.
Published: April 2011

NMD samples from Brazil have been submitted to magnetic and particle size separations and characterized by X-ray diffraction and fluorescence and thermogravimetric analyses. Results showed that simple physical treatments can lead to more than 60% enriched MnO2 materials which could satistify some electrochemical applications. The electrical properties of the samples conditionated as pressed pellets have been investigated by four-points direct current probe and impedance spectroscopy, varying the conditions of preparation and measurement. It is proposed that the higher frequency impedance is equivalent to the intrinsic electronic resistance of the MnO2 phases while at lower frequencies occurs an interphase charge separation coupled with a possible ionic transport. The corresponding contact resistance depends on the article size distribution of the material, the compactation pressure of pellets and the iron content of the materials. The interphase dielectric relaxation does not behave ideally; the depression of the impedance semicircles as shown in the Nyquist plane is assumed to be related to the roughness of the bulk interfaces.
Porous Materials from Fly Ash
Authors: Möller Jorge G. , Shih Wei-Heng
Published: April 2011

Large quantity of fly ash is generated every year from the electric power plants. Due to the shortage of disposal sites and tighter regulations, new viable ways of utilizing fly ash are needed. The formation of a porous material comprising fly ash was investigated. It was found that a porous material can be made by mixing fly ash with phosphoric acid, followed by heat treatment. The porous material is light-weight (bulk density ˜1 g/cm3), machinable, and with reasonable strength. Due to the high percentage of close porosity, the porous material has a great potential for thermal insulation applications.
Surface Precipitation in the Co(II)/Al2O3 Sorption System
Authors: Towle S. N. , Bargar J. R. , Persson P. , Brown G. E. , Parks G. A.
Published: April 2011

Surface precipitation is a critically important process in many systems of scientific and technological importance, such as modeling the segregation of contaminants from aqueous to solid phases in groundwater and the dispersion of active phases on catalyst supports. XAFS and TEM studies of Co(II) sorbed on Al2O3 indicate clearly that surface precipitates have formed from solutions that are undersaturated with respect to any known bulk solid Co-bearing phase. These studies indicate that the structure of the precipitates is similar to that of Co(OH)2(s), but it is disordered and has a high concentration (about 30%) of Co vacancies. Using the FEFF 6.011 multiple-scattering code, we have been able to model the XANES spectrum of the precipitate phase by making small modifications to the structure of Co(OH)2(s). The formation of this precipitate phase is consistent with the coprecipitation of Co(II) with Al(III) derived from dissolution of the substrate, forming a double hydroxide. The existence of a phase that is less soluble than the Al(OH)3 and Co(OH)2 endmembers was proved by forming a colloidal coprecipitate from a mixture of Al(III) and Co(II) aqueous solutions, at the same pH and concentration as in the sorption samples; this material was shown to have Co-XAFS similar to that of the sorption samples. We conclude, therefore, that the surface precipitation observed in the Co(II)/Al2O3 system is due to the the formation of a ternary hydroxide of Al and Co. Successful quantitative models of metal-ion transport in groundwater should include the possibility of forming ternary and higher order precipitates that include ions derived from sparingly soluble solids. For the impregnation of catalysts, the process of surface coprecipitation will make it more difficult to produce a well dispersed precursor material.
Formation and Thermal Properties of Layered Nanocomposites with Layered Double Hydroxides and Polyanions
Authors: Oriakhi C. O. , Farr I. V. , Lerner M. M.
Published: April 2011

Poly(acrylic acid), poly(vinylsulfonate), and poly(styrene sulfonate) are incorporated between the positively-charged sheets of double hydroxide layers M1-xAlx(OH)2+ (M = Mg, Ca, Co) and Zn1-xM' x(OH)2+ (M' = Al, Cr) to form layered nanocomposites. The resulting nanocomposites contain the LDH sheet structures separated by 7.6 – 17.0 Å, which is sufficient to accommodate polymer bilayers between the LDH sheets.

Phase and morphological changes during thermolysis of the nanocomposites with poly(styrenesulfonate) (PSS) are studied by X-ray powder diffraction, scanning and transmission electron micrography, (SEM and TEM) and thermal analyses. Mg4Al2(OH)12CO3·nH2O and the associated PSS / MgAl-LDH nanocomposites show comparable thermal stabilities: the layered structure is lost above 300 °C with the nucleation of MgO and MgAl2O4 phases at approximately 400 and 800 °C, respectively. The PSS / ZnAl-LDH nanocomposite shows complete oxidative pyrolysis of the polyanion at 500 °C, indicating a catalytic effect of zinc oxide on thermolysis. Crystalline oxide products are obtained at approximately 300 °C lower temperature than from thermolysis of Zn6Al2(OH)16CO3·nH2O. SEM and TEM images show that the thermolysis of LDH carbonates produces dense aggregates containing microcrystalline particles, whereas materials obtained from the PSS / MgAl-LDH nanocomposites exhibit a macroporous framework structure.
Dry Etching Issues in the Integration of Ferroelectric Thin Film Capacitors
Authors: Menk G. E. , Desu S. B. , Pan W. , Vijay D. P.
Published: April 2011

Dry etching is an area that demands a great deal of attention in the large scale integration of ferroelectric thin film capacitors for nonvolatile random access memory applications. In this review, we discuss some of the issues relating to the etching of the ferroelectric films, patterning of the electrodes, device damage caused by the etch process and post-etch residue problems. An etch process that can provide high etch rates and good etch anisotropy for the current candidate ferroelectrics including Pb(Zr, Ti)O3 and layered structure SrBi2Ta2O9 thin films using environmentally benign gases such as hydrochlorofluorocarbons is presented. The etch mechanism for both of these materials was determined to rely substantially on ion bombardment effects. For example, PZT films were etched anisotropically at rates of up to 60 nm/min using CHCIFCF3 gas under high rf power and low gas pressure conditions. Problems remain with respect to the acrosswafer differential etch rates observed when more than one phase is present in the material (e.g., amorphous/pyrochlore + perovskite phases in PZT). Damage caused by the etch process which can lead to changes in device characteristics, including hysteresis and fatigue properties, and the underlying mechanism that causes the damage are discussed. O2 was found to be a suitable etch gas for etching the conductive oxide electrode material RuO2. However, an anomaly in the etch rate was detected upon introduction of a small amount of fluorine containing gas: addition of 2% of CF3CFH2 gas to the O2 plasma increases the etch rate by a factor of four. This can be taken advantage of in obtaining high etch selectivity between the electrode and ferroelectric layers.
Domain Structure of Tetragonal Plt Epitaxial Thin Films on Mgo (001) Single Crystal Substrates
Authors: Kang Y. M. , Ku J. K. , Baik S.
Published: April 2011

Ferroelectric Pb1−xLaxTiO3 (PLT, x = 0.00 ˜ 0.28) thin films have been prepared on MgO(001) substrates using pulsed laser deposition. The degree of c-axis orientation in PLT films increased as the La concentration (x) increased with systematic changes in lattice constants and transformation strains. For x ≥ 12, the PLT films showed full c-axis orientation.

In order to understand why the domain evolution in PLT films changes with the La concentration, we have conducted high temperature X-ray diffraction to simulate the cooling process during which the domain structure is evolved. Lattice constants, degree of c-axis orientation, crystal quality of PLT films were characterized as a function of temperature. Lattice constants along substrate normal direction showed similar characteristics with those of powder. The degree of c-axis orientation just after the phase transformation at the Curie temperature also increased with La concentration. The crystal quality, which is quantified by the line width of diffraction peak, is insensitive to La concentration in paraelectric phase. However, it shows significant variation after the domain structure is evolved.
Leakage Current Behaviors of Ba0.5Sr0.5TiO3 Thin Films on Pt, RuO2, and Pt/RuO2 Bottom Electrodes
Authors: Jo W. , Kim D. C. , Lee H. M. , Kim K. Y.
Published: April 2011

Ba0.5Sr0.5TiO3 thin films were grown by rf-magnetron sputtering. Pt and RuO2 films were used as bottom electrodes of the Ba0.5Sr0.5TiO3 thin films. Further, a Pt/RuO2 hybrid electrode was adopted as an electrode for the film. Structural properties of the Ba0.5Sr0.5TiO3 thin films were found to be closely related to the type of the bottom electrodes. Dielectric constants of the films on Pt, RuO2, and Pt/RuO2 were measured as 500, 320, and 450 in the range of 100 Hz ˜ 1 MHz, respectively. Leakage current characteristics of the films were also found to be strongly dependent on the type of the electrodes and their microstructures.
The Effects of the Precursor Solutions on the Structure and the Properties of Sol-Gel Derived Bst Thin Films
Authors: Ryoo Jeong Seon , Kang Seong Jun , Yoon Yung Sup
Published: April 2011

We have studied the effects of solvents and additives in the precursor solutions on the characteristics of barium strontium titanate (BST) thin films. The solution having two solvents, ie. acetic acid for barium acetate and strontium acetate and 2-methoxyethanol for titanium isopropoxide and also having an additive of ethylene glycol shows good stability and remains homogeneous even after a month of ageing. It produces excellent BST thin film without cracks. Dielectric constant, loss tangent at 10kHz and leakage current density at 3V of the BST(70/30) thin film made from this solution are 339, 0.052 and 13.3μA/cm2, respectively. We have also found that a Ta layer is a better diffusion barrier against Si than a Ti layer and is functional up to 750°C.
Mechanics of Metal Matrix Laminates
Authors: Teply J. L.
Published: April 2011

The mechanics of fracture and fatigue crack propagation of ARALL Laminates and Discontinuously Reinforced SiC Aluminum (DRA) laminates is studied. In these two, supposedly different, material systems the fracture and fatigue performance is closely related to their capability to delaminate. The delamination shape, length, rate of growth, effect on fatigue and fracture toughness are analyzed in the both lamination systems. The similarities between these two lamination systems fatigue and fracture failure modes are determined and summarized. Design for compression is also mantioned.