bluuebunny/crossref_metadata_2025 huggingface dataset:
Glassy and Crystalline States in a Model without Disorder: Spin Analog of a Structural Glass
Authors: Gu Lei , Chakraborty Bulbul
Published: April 2011

We have analyzed a non-randomly frustrated spin model which exhibits behavior remarkably similar to the phenomenology of structural glasses. The high-temperature disordered phase undergoes a strong first-order transition to a long-range ordered structure. Using Monte Carlo simulations, we have studied the behavior of the supercooled state by quenching to temperatures below this transition temperature. For a range of supercooling, the system remains ergodic and exhibits dynamics characteristic of supercooled liquids. Below a certain characteristic temperature, however, the system freezes into a “glassy” phase. In this phase, the system is non-ergodic and evolves through a distribution of traps characterized by a power-law distribution of trapping times. This change in the dynamic behavior is concurrent with the appearance of a shear instability.
Local Structure of MD Simulated Soda-Lime-Silicate Glass
Authors: Yuan Xianglong , Cormack Alastair N.
Published: April 2011

Simulation of soda-lime-silicate (sis) glass has been performed using molecular dynamics (MD). The local structure of each component is analyzed extensively in terms of total radial distribution function and coordination number and found to be insensitive to the composition change. Because of its big size, Na+/Ca2+ shows a behavior rather like O2− instead of Si4+. It is evident that the CN and local structure of Na+ with O2− are similar to those in crystalline a-Na2Si2O5. Finally, the Na+/Ca2+ cluster phenomenon is discussed.
Simulation of Pressure Effects on Glasses
Authors: Kogure Y. , Doyama M.
Published: April 2011

Glass transition and effects of pressure and shear stress on atomic configuration are investigated by means of molecular dynamics simulation. An embedded atom method potential is used for the atomic interaction. A model crystal for Cu is melted and quenched to realize the glass state. Atomic configuration in the glass is examined through the radial distribution function. External stress is applied and displacement of atoms is monitored to investigate the mechanism of mechanical relaxation. Larger displacement of atoms is observed under a shear stress.
Crystallization Pathway in the Bulk Metallic Glass Zr41.2Ti13.8Cu12.5Ni10Be22.5
Authors: Schneider S. , Thiyagarajan P. , Geyer U. , Johnson W. L.
Published: April 2011

A new family of multicomponent metallic alloys exhibits an excellent glass forming ability at moderate cooling rates of about 10K/s and a wide supercooled liquid region. These glasses are eutectic or nearly eutectic, thus far away from the compositions of competing crystalline phases. The nucleation of crystals from the homogeneous amorphous phase requires large thermally activated composition fluctuations for which the time scale is relatively long, even in the supercooled liquid. In the Zr41.2Ti13.8Cu12.5Ni10Be22.5 alloy therefore a different pathway to crystallization is observed. The initially homogeneous alloy separates into two amorphous phases. In the decomposed regions, crystallization probability increases and finally polymorphic crystallization occurs. The evolution of decomposition and succeeding primary crystallization in the bulk amorphous Zr41.2Ti13.8Cu12.5Ni10Be22.5 alloy have been studied by small angle neutron. Samples annealed isothermally in the supercooled liquid and in the solid state exhibit interference peaks indicating quasiperiodic inhomogeneities in the scattering length density. The related wavelengths increase with temperature according to the linear Cahn-Hilliard theory for spinodal decomposition. Also the time evolution of the interference peaks in the early stages is consistent with this theory. At later stages, X-ray diffraction and transmission electron microscopy investigations confirm the formation of nanocrystals in the decomposed regions.
Electron Speckle and Higher-Order Correlation Functions from Amorphous Thin Films
Authors: Murray Gibson J. , Treacy M. M. J. , Loretto D.
Published: April 2011

We obtain valuable information about medium-range order in amorphous semiconductors from variable coherence microscopy, a new quantitative approach to TEM. The technique reveals three-body and higher-order atomic correlation functions, which are sensitive to medium-range order. Preliminary experimental evidence for structural changes on annealing has been found for amorphous semiconductor films, with pronounced medium-range order seen only in unannealed films.
Network Structure of Oxide Glasses Containing Alkali & Other Ions by Diffraction and MD Simulations
Authors: Yasui Itaru , Nagasawa H. , Matsumoto H. , Mabuchi T.
Published: April 2011

Network structures of several kinds of oxide glasses were analyzed by means of neutron or x-ray diffraction method and molecular dynamics (MD) simulations including silicate, borate and tellurite glasses. The basic scheme of the structure highly depends on the bonding nature of network forming oxide, but the size of the alkali ions is another important factor to control the network structure of the glass. Structures of silicate glasses are rather easily reproduced by means of MD simulation, whereas borate or tellurite glass structures are hard to be constructed by MD calculation with only 2-body potentials. It is necessary to use adequate potentials to control the bonding angles of O-M-O or M-O-M. The network structure of tellurite glass seems very complex because of the shape of structural units with low symmetry, the use of a new kind of potential was found indispensable to reproduce the glass structure by MD.

In addition to the network structure, the polarization of ions seems to be important to understand the whole vision of oxide glass structures. A new kind of MD was developed which took polarization of ions into account to understand the mixed alkali effects in silicate glasses.
Two Species/Nonideal Solution Model for Amorphous/Amorphous Phase Transitions
Authors: Moynihan Cornelius T.
Published: April 2011

A simple macroscopic thermodynamic model for first order transitions between two amorphous phases in a one component liquid is reviewed, augmented and evaluated. The model presumes the existence in the liquid of two species, whose concentrations are temperature and pressure dependent and which form a solution with large, positive deviations from ideality. Application of the model to recent data indicates that water can undergo an amorphous/amorphous phase transition below a critical temperature Tc of 217K and above a critical pressure Pc of 380 atm.
Interfacial Segregation in Ionic Conductors: Ceria
Authors: Blom D. A. , Chiang Y.-M.
Published: April 2011

Grain boundary segregation in cerium dioxide doped with varying amounts of gadolinium oxide and tantalum oxide has been measured with x-ray energy dispersive spectroscopy using a Vacuum Generators HB603 Scanning Transmission Electron Microscope (STEM). The data has been analyzed in the framework of both elastic relaxation and space charge segregation forces with a limited number of surface sites. Results show that multiple driving forces must be taken into account to explain aliovalent solute segregation.
Grain Boundary Engineering in Ordered Ni3Al for Improving Ductility
Authors: Chaki T. K.
Published: April 2011

Several techniques of grain boundary engineering for improving ductility in polycrystalline Ni3Al are discussed with the plausible mechanism. Single crystals of Ni3Al are ductile at room temperature, but polycrstalline Ni3Al fails intergranularly with little elongation. The grain boundaries are also embrittled by environmental moisture. The weakness of the boundaries is attributed to the presence of crack-like microcavities at the boundaries. Microalloying with B closes up the microcavities by enhancing relaxation of Ni and Al atoms, thereby improving ductility. In directionally solidified Ni3Al containing low-angle boundaries, large ductility has been reported. Polycrystalline N?3AI produced by recrystallization of rolled single crystals contains a large fraction of Σ3 boundaries and exhibits large ductility. Due to good matching, the low-angle and Σ3 grain boundaries do not contain microcavities and consequently are strong.
A Grain Boundary Engineering Approach to Materials Reliability
Authors: Palumbo G. , Lehockey E. M. , Lin P. , Erb U. , Aust K. T.
Published: April 2011

Intergranular degradation processes, (e.g., corrosion, stress corrosion, cracking, creep cracking) are a frequent cause of premature and unpredictable service failure of engineering components. Recent advances in (1) understanding structure-property relationships for grain boundaries, and (2) characterization techniques for grain boundaries in polycrystalline materials, have provided the means for improved component lifetime prediction, and the opportunity to engineer intergranular-degradation resistant microstructures.

In this work, we present our previously developed geometric models for grain boundary structure and grain size effects on intergranular degradation susceptibility. Specific examples are presented of the successful application of the ‘grain boundary engineering’ approach to the prediction and mitigation of intergranular corrosion, stress corrosion cracking, and creep cracking in Ni-based materials.
Interfacial Segregation in Bicrystals: A Database for Grain Boundary Design of Polycrystals
Authors: Lejček Pavel
Published: April 2011

Physical meaning of thermodynamic parameters of segregation obtained from measurements of chemical composition of grain boundaries in poly crystals and bi crystals, and calculated for individual grain boundary sites is discussed. It is shown that the mean values of these parameters determined from the measurements on polycrystals can in exceptional cases represent the behavior of general grain boundaries. On the other hand, measurements of grain boundary segregation at individual grain boundaries can provide the values of segregation enthalpies and entropies representing behavior of a specific single grain boundary site. The latter data are appropriate for the use in the grain boundary design concept.
Ab Initio Calculations for Grain Boundaries in Covalent Ceramics
Authors: Kohyama Masanori
Published: April 2011

Ab initio calculations of grain boundaries in SiC have been performed for the first time by using the first-principles molecular dynamics (FPMD) method. Four-fold coordinated models of polar and non-polar interfaces of the {122}Σ = 9 boundary in SiC have been examined. Interfacial C-C and Si-Si wrong bonds have bond lengths and bond charges similar to those in bulk diamond and Si. The C-C bonds generate greatly localized states at the valence-band edges, which have features similar to the bulk band-edge states of diamond. The wrong bonds have significant effects on the properties of grain boundaries in SiC.
Perpendicular Magnetic Anisotropy and Magneto-Optical Properties of Sputtered Re-Tm(CoGd)/Pd Multilayered Films
Authors: Yang T. , Soe W. H. , Liu B. X. , Yamamoto R.
Published: April 2011

The magnetic properties of sputtered RE-TM(CoGd)/Pd multilayered films were studied. CoGd layers with high Gd concentration were amorphous. Reducing the Gd concentration, CoGd layers changed from amorphous to crystalline gradually. Like in the crystalline Co/Pd multilayered films, perpendicular magnetic anisotropy(PMA) was observed only for CoGd/Pd multilayered films with thin magnetic layer. It is interesting to note that critical magnetic layer thickness, below which the easy magnetization axis is perpendicular to the film plane, reaches 2.5nm for CoGd/Pd multilayered films with amorphous CoGd layers and is larger than that of Co/Pd multilayered films. Kerr rotation was found decreased with the adding of Gd.
Reactive-Sputter Deposition of TiN/ZrN and TiN/CrN Multilayers: Structural and Mechanical Properties
Authors: Soe W.-H. , Kitagaki T. , Ueda H. , Shima N. , Otsuka M. , Yamamoto R.
Published: April 2011

Polycrystalline TiN/ZrN multilayers with a 7.5% lattice mismatch between the layers and TiN/CrN multilayers with a 2.3% mismatch were grown by reactive magnetron sputtering on WC/Co sintered hard alloy substrates. Multilayer structure and composition modulation amplitudes were studied using x-ray diffraction method. Hardness and elastic modulus were measured by nanoindentation testing. Hardness of TiN/ZrN multilayers decreased rapidly with increasing bilayer thickness (Λ), peaking at hardness values ≈30% lower than rul e-of-mixtures values at Λ=30 Å, before increasing slightly with further increases in Λ. A comparison with other lattice mismatched systems, TiN/VN and TiN/NbN, showed a similar hardness variation, but a sign was negative. The results suggest that coherency strains were responsible for the larger hardness change. Nanoindenter elastic modulus results showed the same behavior with hardness dependence, i.e., elastic softening at Λ=30 Å. The results of TiN/CrN systems showed no hardness and elastic anomalies within boundaries corresponding to individual values. It was thought too large the difference between hardness (or modulus) of TiN and CrN.
Characterization of TiO2 Thick Films Photoelectrodes Prepared by the Plasma-Spray Coating
Authors: Kubota N. , Ayabe M. , Fukuda T. , Akashi M.
Published: April 2011

Semiconducting TiO2 has some photoelectrochemical reactions under ultra-violet irradiation. These photoelectrochemical behaviors studied as possible protection from corrosion. TiO2 thick films were prepared on stainless steel by plasma-spray coating. The film thicknesses were 50∼100μm. The films were characterized by X-ray diffraction, and the diffraction patterns clearly showed a rutile type structure. The crystallization of the films depends on the spray coating conditions. We have investigated the protection properties of the films by measuring the electrode potential. The electrode potential of the films were reduced by about 250m V under ultra-violet irradiation. This potential drop value is sufficient for protection from the corrosion.
Measurement of the Fracture Energy of SiO2/TiN Interfaces Using the Residually-Stressed Thin-Film Micro-Strip Test
Authors: Xu Guanghai , Ragan D. D. , Clarke D. R. , He Ming Y. , Ma Qing , Fujimoto H.
Published: April 2011

One of the key factors affecting the long-term reliability of thin film structures in microelectronics devices is the fracture resistance of their interfaces. Of the many different interfaces formed during device fabrication, the SiO2/TiN interface is amongst the most common. In order to measure the fracture energy of this interface, we have been utilizing a test in which a narrow strip of a material, having a large intrinsic tensile stress, is deposited and lithographically defined onto the SiO2/TiN/Al thin film structure. The elastic strain energy in the micro-strip provides an additional driving force to debond the weakest interface in the structure. Decohesion occurs when the thickness of the micro-strip, and hence the total elastic strain energy, exceeds a critical value. Another measure of the fracture resistance in the same test is the length of the strip that remains intact after debonding at both ends. This is a function of the intrinsic stress, the thickness of the superlayer, and the modulus ratios. In addition to presenting results on the measured fracture energy of the SiO2/TiN interface, evidence for stress-corrosion will be described.
Influence of Ca-Doping on Chemistry and Force Balance at Grain Boundary in Si3N4
Authors: Gu Hui , Rühle Manfred
Published: April 2011

High-purity HIPed Si3N4 ceramics doped systematically with Ca additives are analyzed quantitatively by EELS. Using an ELNES related method to obtain film composition, we found that the composition difference from film to film is less significant than segregation. This is interpreted as a change of film width related to grain surface faceting. The hexagonal structure associated with anisotropie dielectric function can alter van der Waals attraction for different surface structures to produce variations in film thickness with a uniform film composition. These grain boundary films are better described as a high pressure amorphous oxynitride phase that allows higher but still limited solubility of calcium nitrogen.
Modelling of Adaptive Composite Materials with Embedded Shape Memory Alloy Wires
Authors: Stalmans R. , Delaey L. , Van Humbeeck J.
Published: April 2011

Various models and calculation methods for the description of shape memory behaviour have been developed in recent years by different research groups. Some of the models have already been extended towards the thermomechanical and functional behaviour of matrix materials with embedded SMA-wires. The basic concepts of a thermomechanical model which has found widespread use in the literature on smart materials, are critically reviewed.

A recently developed model based on a generalised thermodynamic analysis of the underlying martensitic transformation is discussed more into detail. Experimental verifications indicate that this thermodynamic model can be developed to an effective tool for the materials design of matrix materials with embedded SMA-wires.
Mechanical Properties of Smart Metal Matrix Composite by Shape Memory Effects
Authors: Hamada K. , Lee J. H. , Mizuuchi K. , Taya M. , Inoue K.
Published: April 2011

The thermomechanical behavior of TiNi shape memory alloy fiber reinforced 6061 aluminum matrix smart composite is investigated experimentally and analytically. The yield stress of the composite is observed to increase with prestrain given to the composite. Analytical model is developed by utilizing a shape memory alloy constitutive model of exponential type for the thermomechanical behavior of the composite. The model predicts that the composite yield stress increases with increasing prestrain, and the key parameters in affecting the composite yield stress are prestrain and matrix heat treatment. The model predicts reasonably well the experimental results of the enhanced composite yield stress.
On the Theory of Adaptive Composites
Authors: Roytburd A. L.
Published: April 2011

Thermodynamics of an adaptive layer composite with a poldomain (polytwin) ferroelectric component is considered. It is shown that there are λ-singularities on the thickness dependencies of compliance and susceptibility at some critical thicknesses of the composite layers.
Experimental Analysis of Smart Structure with Damping Treatment and SMA
Authors: Chen Q. , Ma J. , Levy C.
Published: April 2011

The experimental results of a flexible cantilever beam with constrained viscoelastic layer and shape memory alloy layer called smart damping treatment (SDT) are presented. The upper side of the beam is bonded with a viscoelastic layer and then covered with a constraining layer. The lower side is bonded with a shape memory alloy layer, which is used as an actuator. The elastic modulus and loss factor of damping materials are functions of the temperature. The temperature effects on system frequency and loss factor due to heat cycling of SMA layer are evaluated here. It is found that temperature plays an important role on system frequency and loss factor, and thus the temperature effects must be included when discussing such an structure.
Fabrication of Pseudo One-Dimensional Photonic Band System by Grating Pair Method
Authors: Todori K. , Hayase S.
Published: April 2011

We have succeeded in forming a pseudo one-dimensional photonic band by using two gratings facing each other. This pair of gratings had a period of 278 nm. The frequency of the band edge was in the visible region. This method is useful to control the group velocity and the phase velocity of light.
Characterization of SrBi2Nb2O9 Thin Films Prepared by Sol Gel Technique
Authors: Ching-Prado E. , Pérez W. , Reynés-Figueroa A. , Katiyar R. S. , Ravichandran D. , Bhalla A. S.
Published: April 2011

Thin films of SrBi2Nb2O9 (SBN) with thicknesses of 0.1, 0.2, and 0.4 μ were grown by Sol-gel technique on silicon, and annealed at 650°C. The SBN films were investigated by Raman scatering for the first time. Raman spectra in some of the samples present bands around 60, 167, 196, 222, 302, 451, 560, 771, 837, and 863 cm−1, which correspond to the SBN formation. The study indicates that the films are inhomogeneous, and only in samples with thicknesses 0.4 μ the SBN material was found in some places. The prominent Raman band around 870 cm−1, which is the A1g mode of the orthorhombic symmetry, is assigned to the symmetric stretching of the NbO6 octahedrals. The frequency of this band is found to shift in different places in the same sample, as well as from sample to sample. The frequency shifts and the width of the Raman bands are discussed in term of ions in non-equilibrium positions. FT-IR spectra reveal a sharp peak at 1260 cm−1, and two broad bands around 995 and 772 cm−1. The bandwidths of the latter two bands are believed to be associated with the presence of a high degree of defects in the films. The experimental results of the SBN films are compared with those obtained in SBT (T=Ta) films. X-ray diffraction and SEM techniques are also used for the structural characterization.
A Technique for the Measurement of d31 Coefficient of Piezoelectric Thin Films
Authors: Shepard Joseph F. , Moses Paul J. , Trolier-McKinstry Susan
Published: April 2011

This paper describes a new technique by which the d31 coefficient of piezoelectric thin films can be characterized. Silicon substrates coated with lead-zirconate titanate (PZT) are flexed while clamped in a uniform load rig. When stressed, the PZT film produces an electric charge which is monitored together with the change in applied load. The mechanical stress and thus the transverse piezoelectric coefficient can then be calculated. Experiments were conducted as a function of poling field strength and poling time. Results are dependent upon the value of applied stress, which itself is dependent upon the mechanical properties of the silicon substrate. Because the substrate is anisotropie, limiting d31 values were calculated. In general, d31 was found to be ∼20 pC/N for field strengths above 130 kV/cm and poling times of less than 1 minute, d31 was increased more than a factor of three, to ∼77 pC/N, when poled at 200 kV/cm for ∼21 hours.
Complex Piezoelectric Coefficients of PZT Ceramics: Method for Direct Measurement of d33
Authors: Jordan T. L. , Ounaies Z. , Turner T. L.
Published: April 2011

A fiber-optic device is used to determine the magnitude and phase of the strain in the poling direction of lead zirconate titanate (PZT) ceramic wafers. This information yields the real and imaginary components of the piezoelectric strain coefficient d33. The measurement hardware and software are described and results from the measurements of d33 for PZT 4 and 5 H wafers are presented. This method has the advantages of being direct, inexpensive and relatively simple to use. Verification of the results is provided through the use of the resonance method.
Effects of Magnetic Field and Hydrostatic Pressure on Martensitic Transformations in Some Shape Memory Alloys
Authors: Kakcshita T. , Saburi T. , Shimizu K.
Published: April 2011

The recent works carried by the author's group on the effects of magnetic field and hydrostatic pressure on martensitic transformation are reviewed, which mainly concerned with some shape memory allovs, such as Fe-Pt, Fe-Co-Ni-Ti, Ti-Ni and Cu-Al-Ni alloys. The works clarify the effects of magnetic field and hydrostatic pressure on martensitic transformation temperature, magnetoelastic martensitic transformation and morphology and arrangement of martensites and transformation process of athermal transformation. That is, transformation start temperatures in Fe-Pt and Fe-Ni alloys examined increase with increasing magnetic field, but are not affected in Ti-Ni and Cu-Al-Ni alloys. On the other hand, transformation start temperature decreases with increasing hydrostatic pressure in the Fe-Ni-Co-Ti alloy, but increases in Cu-Al-Ni alloys. The magnetic field and hydrostatic pressure dependences of the martensitic start temperature are in good agreement with those calculated by the equations proposed by our group. In the work on the ausaged Fe-Ni-Co-Ti alloy, the appearance of magnetoelastic martensitic transformation is newly found. In addition, several martensite plates grow nearly parallel to the direction of applied magnetic field in the specimen of an Fe-Ni alloy single crystal. Moreover, we found that in the Cu-Al-Ni alloys exhibiting an athermal martensitic transformation, isothermal holding at a temperature above Ms makes martensitic transformation to start and the incubation time increases with increasing ΔT = T − Ms (T represents holding temperature). The above results show that the magnetic field and hydrostatic pressure effectively control not only the transformation temperature but also the morphology and distribution of martensites induced, as in the case of uniaxtial stress and compression.
The Martensitic Transformation and Extra Reflections Appearing Prior to the Transformation in AuCd Alloy
Authors: Ohba T. , Otsuka K.
Published: April 2011

AuCd alloy is a typical martensitic alloy. The crystal structural of the ζ2' (trogonal) martensite was recently determined and the analysis indicated the possibility of phonon softening. Despite a large absorption coefficient of Cd phonon softening was actually observed by using an isotope 114Cd. In the present study, precise x-ray scattering studies were performed with a rotating anode x-ray source and synchrotron radiation at Photon Factory in KEK, using small crystals. The structure factors of the parent phase and the diffraction profiles along <110> direction were measured with four circle diffractometers. The structure factors decrease when approaching the transformation temperature. Superstructure reflections were observed prior to the onset of the transformation. They are very weak and rather sharp and appear at q = (1/3,1/3,0) within the experimental error, i. e. at the commensurate position.
High Electromechanical Coupling Piezoelectrics - How High Energy Conversion Rate is Possible
Authors: Uchino Kenji
Published: April 2011

A new category of piezoelectric ceramics with very high electromechanical coupling was discovered in a lead zinc niobate:lead titanate solid solution in a single crystal form. The maximum coupling factor k33 reaches 95%, which corresponds to the energy conversion rate twice as high as the conventional lead zirconate titanate ceramics. This paper reviews the previous studies on superior piezoelectricity in relaxor ferroelectric: lead titanate solid solutions and on the possible mechanisms of this high electromechanical coupling.
Thermotracttve Titanium-Nickel thin Films Formicroelectromechanical Systems and Active Composites
Authors: Grummon D. S. , Pence T. J.
Published: April 2011

Thin films of thermoelastic titanium-nickel are of interest as a material basis for force-producing elements in microelectromechanical systems, and for active phases in mechanically-adaptive composite materials. The successful introduction of this material system into such application areas will depend on development of reliable thin film deposition protocols, together with the refinement of analytical models which successfully predict the response of active microstructures to a variety of dynamic thermal and mechanical stimuli. In the present paper we review some of our recent experimental and theoretical work which bear on these problems. With respect to thin film fabrication techniques we focus on problems of composition control and the manipulation of microstructure, with particular emphasis on opportunities afforded by amorphous precursor phases formed during low temperature processing, and the fine-grained, thermally stable crystalline microstructures obtainable using hot-substrate deposition. The films resulting from either approach retain the important thermomechanical response features of the well-known bulk-alloy system: shape memory and transformational superelasticity. The response can be modeled in terms of a continuum description augmented with internal variables that track fractional partitioning of the material between austenite and variants of the martensite.
Aging Influence on the Shape Memory Effects and Superelasticity in Titanium-Nickel Single Crystals
Authors: Chumlyakov Yu.I. , Kireeva I. V. , Lineytsev V. N. , Lwisyuk A. G.
Published: April 2011

On the Ti-50.8%Ni, Ti-51%Ni and Ti-51.3%Ni (at.%) single crystals, the investigations of the shape memory effects (SME) and superelasticity (SE) have been carried out in order to find out the dependence on a size and a volume fraction of the Ti3Ni4 dispersive particles, a crystal orientation and a sign of applied stress. It is shown, that in crystals without particles the strong dependence of SME on an orientation and a sign of applied stress takes place and SE is not observed. Precipitation of the coherent particles of Ti3Ni4 of 50–100 nm in size leads to the reduction of SME, weakening of orientation dependence of σcr interval of stress-induced martensitic transformations (MT).
Model Tracking of Stress and Temperature Induced Martensitic Transformations for Assessing Superelasticity and Shape Memory Actuation
Authors: Wu X. , Pence T. J. , Grummon D. S.
Published: April 2011

Both austenite/martensite transformations, and martensite/martensite variant reorientation are central to superelasticity and shape memory actuation. Here we discuss a simple model for tracking these transformations that is appropriate for device modeling. The approach is to augment conventional continuum mechanical descriptions with internal variables that track fractional partitioning of the material between austenite and the various martensite variants. A three-species model involving austenite and two complementary martensite variants provides sufficient generality to capture the martensite variant distributions that underlie shape memory, and the strain-accommodation associated with superelasticity. Transformations between all of these species can be tracked on the basis of triggering algorithms that reflect both tran sformation hysteresis and the variation of triggering stress with temperature. The algorithm described here is for temperature-dependent response resolved in a single direction. It requires only the following experimentally determined parameters: the four transformation temperatures Mf, Ms, As, Af, the transformation strain, the Young's modulus, and the transformation latent heat.
Compression-Induced Martensitic Transformations in Cu-Zn-Al Alloys with e/a > 1.50
Authors: Cuniberti A. , Romero R.
Published: April 2011

Results are reported about the pseudoelastic cycles β-martensite obtained by compression of β Cu-Zn-Al single crystals with electronic concentration 1.52. Stress-strain curves at different temperatures and in situ observations were carried out. The results are compared with those obtained from tension test.
The Effects of Biaxial Stress on the Ferroelectric Characteristics of PZT Thin Films
Authors: Shepard Joseph F. , Trolier-McKinstry Susan , Hendrickson Mary , Zeto Robert
Published: April 2011

The design and implementation of microelectromechanical (MEMS) systems requires a sound understanding of the influence of film stress on both the ferroelectric and piezoelectric characteristics of thin films to be used for sensing and/or actuation. Experiments were conducted in which thin film samples of sol-gel derived PZT were subjected to applied biaxial stresses from -139 to 142 MPa. Films were characterized at known stress states (derived from known values of residual stress and large deflection plate theory) in terms of their ferroelectric polarization (saturated and remnant), dielectric constants, coercive field strengths, and tan δ. Results obtained indicate that domain wall motion in thin films contributes much less to the observed response than is typical for bulk PZT materials. Alternative mechanisms are proposed in an attempt to explain the discrepancies.
Frequency Effects on the Damping Capacity of Superelastic Nitinol
Authors: Jones H. N.
Published: April 2011

The evolution of the stress-strain behavior of a superelastic NiTi alloy over a range of cyclic frequencies up to 10 Hz is presented. Due to the stress-strain hysteresis typical of these alloys work is dissipated as heat during every cycle. Also, the heat release and absorption induced by the cyclic phase transformation responsible for the superelastic effect causes the material to undergo a cyclic temperature history which is superimposed on the average temperature resulting from the dissipative nature of the stress-strain cycle. As the cyclic frequency is increased the imposed strain rate is also necessarily increased. The stress-strain loops at very low frequencies are under isothermal conditions. As the cyclic rate is increased nearly adiabatic conditions are achieved at the higher frequencies. This affects the hysteretic cyclic behavior and the damping capacity of the material.
Determination of the Upper Limit for the Cluster Moment Contributing the Giant Magneto Resistance in Laser Deposited Granular Cu-rich Thin Films
Authors: Madurga V. , Ortega R. J. , Vergara J. , Rao K. V.
Published: April 2011

We have fabricated granular Cu95Co5 thin films by laser ablation-deposition. Within a regime of annealing temperatures, these samples exhibit Giant Magneto Resistance (GMR), typically 5% in 0.5 Tesla at 5 K. The magnetic hysteresis loops are found to show finite coercive fields in the whole temperature range 2 K - 300 K. Below 9 K, the field dependence of the MR shows a split maximum. We interpret the data in terms of coercivity arising from blocking phenomenon of single domain superparamagnetic Co clusters. A quantitative determination of the upper limit for the cluster moment contributing to GMR is estimated to be 17000 μB (a cluster size of 5 nm).
Synthesis and Properties of Magnetorheological (MR) Fluids for Active Vibration Control
Authors: Phulé Pradeep P. , Ginder John M. , Jatkar Arun D.
Published: April 2011

Magnetorheological (MR) fluids represent an exciting class ofsmart materials for use in active vibration control and other applications. This paper discusses some of the fundamental materials science concepts that define the scientific basis for designing MR fluids. Preliminary experimental data and observations concerning the synthesis as well as the rheological behavior of MR fluids based on carbonyl iron and iron oxide particulates are presented and discussed.
Conformational and Dynamic Properties of Polymer Loops and Their Mixtures at an Impenetrable Interface
Authors: Gulati H. S. , Driscoll D. C. , Jones R. L. , Spontak R. J. , Hall C. K.
Published: April 2011

In this study we investigate the equilibrium conformational properties and dynamic relaxation behavior of polymer loops grafted at an interface using the discontinuous molecular dynamics simulation technique. Differences and similarities between the structural and dynamic properties of polymer loops and tails are identified. The conformational properties of mixtures of polymers loops and tails are also studied using the bond-fluctuation method. The effect of mixture composition on the conformational properties of the individual components in the mixture is discussed.
Concentrated DNA Rheology and Microrheology
Authors: Mason T. G. , Dhople A. , Wirtz D.
Published: April 2011

We present mechanical measurements of the frequency-dependent linear viscoelastic storage and loss moduli,G′(ω) and G″(ω), and the yield stress, τy, and yield strain, γy, for calf thymus DNA (13 kbp) over a range of mitotically relevant concentrations fromCDNA= 1 to 10 mg/ml. For largeCDNA, we find a dominant plateau elasticity,G′p, at high ω. As ω decreases,G′ falls until it is equal toG′ at the crossover frequency, ωc, below whichG″ dominates. We measureG′p∼CDNA2.25and ωc∼CDNA−2.4, consistent with scaling exponents for classical polymer solutions. The mechanical |G*(ω)| agree well with those measured using a new microrheological technique based on video tracking microscopy of thermally-driven fluorescent colloidal spheres and a frequency-dependent Stokes-Einstein equation. We have developed this technique to probe how enzymes, typically available in small quantities, can affect the rheology of the DNA. Using it, we report preliminary measurements of a higher ωcfor a DNA network in which the ATP-powered enzyme Topoisomerase II transiently cuts and rebinds the DNA, thereby relaxing entanglements.
Late Stages of the Pearling Instability in Lipid Bilayers
Authors: Goveas J. L. , Milner S. T. , Russel W. B.
Published: April 2011

We have studied the late stages of the “pearling instability” in lipid bilayers, which is brought on by applying laser tweezers to a cylindrical vesicle. This produces a front that propagates down the vesicle, leaving behind it bilayer-covered droplets separated by thin tubes, which appear under the microscope as pearls on a string. At later times, the “pearls” are observed to drift slowly towards the “trap” (the spot where the tweezers are applied, into which the surfactant is drawn). We model the hydrodynamics of the drifting pearls as a combination of translation of the string of pearls, and “slipping” of the bilayer skin over the pearls, to relate the speed of the pearls to the underlying flux of the surfactant into the trap.
Depinning of Fracture Fronts
Authors: Daguier P. , Nghiem B. , Bouchaud E. , Creuzet F.
Published: April 2011

By studying the morphology of the fracture surfaces of both a metallic alloy and of a silicate glass for various very low crack propagation velocities, it is shown that the pin-ning/depinning scenario of a line moving through randomly distributed obstacles seems well adapted to describe fracture of heterogeneous materials. The crossover length separating the large length scales regime characterised by a roughness index ζ ≃ 0.78 and the small length scales one, for which ζc ≃ 0.5, is shown to decrease with the measured crack velocity as a power law, ξc ∞ v−φ, with ζ ≃ 1. ξc and v also vary with the pulling force as power laws, and the measured values of exponents ν and β are close to: ν ≃ 2 and β ≃ 2.
Temperature and Chemistry Effects in Porous-Media Electrokinetics
Authors: Pengra David B. , Wong Po-Zen
Published: April 2011

Electrokinetic phenomena in brine-saturated porous media, such as electroosmosis (fluid-flow induced by applied electric fields) and streaming current (the complementary process) depend on the density of ions adsorbed on the pore surface and the characteristic thickness of the diffuse space-charge layer λ. These, in turn, depend on brine chemistry, ambient temperature and possibly other parameters. We report on a series of measurements of natural rock and synthetic glass-bead samples: for one sample group, we varied the temperature over 0–50 ° C; for another, we changed the brine cation species. We find that the electrokinetic coefficients depend only weakly on temperature; this is shown to follow from the expected trends in λ, η, and σ. The chemistry dependence follows qualitatively but not quantitatively the predictions of the Debye-Hiickel approximation.
Annular Ringlike Arrays from Mixtures of Metal Nanoparticles
Authors: Ohara P. C. , Heath J. R. , Gelbart W. M.
Published: April 2011

We describe a theory for hole nucleation in volatile, wetting, thin liquid films. Hole nucleation in this system can occur due to two independent driving forces: evaporation (volatile hole nucleation) and by disjoining pressure effects (non-volatile hole nucleation). Although a concerted combination of these two can be in effect, the cases are treated separately here and will be treated jointly in the context of a simulation elsewhere. Growing holes – dry areas of the solid surface which are otherwise wet by solvent – are conjectured to be responsible for the formation of close-packed 2D annular ringlike arrays from dilute solutions of nearly monodisperse, large (3–5nm diameter), organically passivated metal particles [1]. When organic solutions of these nanoparticles are evaporated on a solid carbon substrate (a TEM grid), the resulting sub-monolayer structures are annular ringlike arrays due to the pinning of the rim of an opening hole by a sufficient collection of particles.
Uncoiling of DNA by Double Chained Cationic Surfactants
Authors: Paradies H. H. , Clancy S. F.
Published: April 2011

Distearyldimethylammonium (DSDMA) X (X− = OH, H2PO4) interact with double stranded T4 DNA (166 kilobase pairs) below and above the CMC (1.5×10−6). Below the CMC of either DSDMA X where the cationic double-chained surfactants are in the monomeric state, T4 DNA and DSDMA+form a compact complex where all surfactant molecules are bound. Close to the CMC, particularly for DSDMA OH but also in the presence of , T4 DNA exhibits a condensed (globule) conformation, though some DNA molecules are in the more extended DNA conformation. Above the CMC of DSDMA X a plateau is reached (up to 3.0 × 10−6 M surfactant) revealing a penetration of DSDMA molecules into the DNA globules resulting in a loosening of the tightened state of DNA. The various stages of the transition from the condensed coil to the extended state of T4 DNA with changing DSDMA X concentrations was monitored by static and inelastic light scattering experiments which were supplemented by small-angle X-ray scattering measurements.
Photon Correlation Spectroscopy of Liquid Crystals Confined in Porous Matrices with Different Structure and Pore Size
Authors: Aliev F.M. , Plechakov I.V.
Published: April 2011

We present the results of photon correlation spectroscopy investigations of the influence of confinement, interface, porous matrix structure, pore size and shape on the dynamic behavior of nematic liquid crystals (LC) dispersed in porous matrices with randomly oriented, interconnected pores (porous glasses) and parallel cylindrical pores (Anopore membranes). Investigations of LC in cylindrical pores together with studies in random porous matrices, makes it possible to separate the role of random structure and domain formation from the contributions due to existence of LC - solid pore wall interface and pure finite size effect in relaxation of order parameter or director fluctuations. In the temperature range below nematic - isotropie phase transition temperature we observed two overlapping relaxational processes which are satisfactorily described by the decay functionf(q,t) =a·exp(–t/τ1) + (1–a)·exp(–xz), wherex=ln(t/τ0)/ln(τ2/τ0) and τ0= 10−8s. For LC in 100 Å random pores the second term describing the slow process dominates, whereas for 200 Å and 2000 Å cylindrical pores as well as 1000 Å random pores the contribution from the first term (fast process) is more visible. Since the slow relaxational process which does not exist in the bulk LC and broad spectrum of relaxation times (10−6- 10)s appear not only for LC in random pores but in cylindrical as well, we conclude that differences in dynamical behavior of confined LC from that in the bulk are mainly due to the existence of the interface.
Molecular Configurations and Solvation Forces of Confined i-Tetradecane Jee-Ching Wang
Authors: Fichthorn Kristen A.
Published: April 2011

This work is a molecular-dynamics simulation study of the influence of chain branching on the molecular configuration in confined tetradecane thin films. Simulations of layered interfacial films of n- and i-tetradecane on Pt(111) show, in contrast to experiments, that a side methyl group does not impart sufficient asymmetry to alter the solvation force law from oscillatory to non-oscillatory. Based on previous experimental findings, a novel vertical structure resembling a self-assembled monolayer, is proposed for confined, long-chain iso-alkanes. Simulations show that i-tetradecane in this structure is stableover the time scales that can be probed by molecular dynamics and that vertical films have a lower energy per molecule than layered films. With this structure, many experimental features, including the non-oscillatory solvation forces, of confined iso-alkanes are explainable andwill be discussed in this paper.
Dynamics of Air-Water Contact Lines and Interfaces Near the Pinning Threshold
Authors: Wong Po-Zen , Schäffer Erik , Pengra David B.
Published: April 2011

We report a study of the dynamics of capillary rise of water in glass tubes and glass bead packs. The water column height h is measured as a function of time t byvideo imaging. Analyzing the late time data in terms of critical pinning, dh/dt ∞ (P – Pc)β, we find an anomalously large exponent β for interfaces in bead packs and β ≈ 1 for contact lines in capillary tubes. Repetitive rise and fall experiments in capillary tubes suggests that thinning of the wetting film plays an important role in the dynamics. We discuss these findings in light of recent theories and experiments.
High Electric field effects on the Thermal Generation in Hydrogenated Amorphous Silicon
Authors: Ilie A. , Equer B.
Published: April 2011

We have studied the electric field dependence of the electron-hole thermal generation process in hydrogenated amorphous silicon. A model was developed which takes into account the Poole-Frenkel effect and the thermally assisted tunneling. In order to explain the experimental results it was necessary to consider a strong electron-lattice interaction describing the carrier tunneling mechanism. Deep defects relaxation is also discussed.
Effects of Synchrotron X-Rays on PVD Deposited and Ion Implanted α-Si
Authors: Yu Kin Man , Wang Lei , Walukiewicz W. , Muto S. , McCormick S. , Abelson J. R.
Published: April 2011

We have studied the effects of intense x-ray irradiation on the stucture of amorphous Si films. The films were obtained by either physical vapor deposition or by implantation of high energy ions into crystalline Si. They were exposed to different total doses of synchrotron x-rays. From the EXAFS and EXELFS measurements we find that an exposure to x-rays increases the Si coordination number. Also in the PVD films a prolonged x-ray exposure enlarges, by about 2 %, the Si-Si bond length. Raman spectroscopy shows that Si amorphized with high energy ions contains small residual amounts of crystalline material. Irradiation of such films with x-rays annihilates those crystallites resulting in homogenously amorphous layer with a close to four-fold coordination of Si atoms. This rearangement of the local structure has a pronounced effect on the crystallization process of the amorphous films. Thermal annealing of x-ray irradiated ion amorphized films leads to nearly defect free solid phase epitaxy at 500°C. Also we observe a delay in the onset of the crystallization process in x-ray irradiated PVD films. We associate this with a reduced concentration of nucleation centers in the x-ray treated materials.
Observation of Coulomb Blockade Effect in Silicon Nanocrystallites at room Temperature
Authors: Gu Xiaofeng , Qin Hua , Lu Hai , Xu Jun , Chen Kunji
Published: April 2011

We report the fabrication and electrical characteristics of an ultrathin nanocrystalline-silicon/amorphous silicon oxide double barrier resonant tunneling diode. The cross-section high resolution TEM photographs indicate the layered structure and the crystallinity of nanocrystalline Si with an average grain size of 10 nm. In this prototype device, a series of reproducible conductance peaks have been observed as a function of the applied gate bias at room temperature. The real voltage spacing of 0.38V between the peaks is determined from an equivalent circuit. The results are in agreement with the theory of Coulomb blockade effect using 1.1 aF of capacitance in single Si nanocrystallite. We conclude that the observed behavior results from resonant tunneling, which is strongly influenced by Coulomb blockade effect, through the zero-dimensional states in the well isolated silicon quantum dots.