bluuebunny/crossref_metadata_2025 huggingface dataset:
Inorganic-Organic Hybrid Hierarchically Structured Methyl-modified Silica Monoliths
Authors: Brandhuber Doris , Hüsing Nicola , Peterlik Herwig
Published: April 2011

Highly porous inorganic-organic hybrid monoliths with mesopores in a macroporous network have been prepared from methyltris(2-hydroxyethoxy)silane (MeGMS) and tetrakis(2-hydroxyethoxy)silane (EGMS) in the presence of an amphiphilic block copolymer. The amount of methyltris(2-hydroxyethoxy)silane (MeGMS) in the gel has been varied from 0 to 100 %. These glycol-modified silanes have the advantage of being water-soluble and thus allowing for a direct templating of liquid-crystalline surfactant mesophases without the presence of a homogenizing organic solvent such as ethanol. The wet gels have been dried by supercritical extraction with carbon dioxide.

In the present work, the sol-gel behaviour of these glycol-modified silanes is discussed especially with a focus on the formation of the meso- and macrostructure. In addition, the influences of the varying ratios of methyltris(2-hydroxyethoxy)silane on the structural features of the gels are investigated by various analytical techniques such as small angle X-ray scattering, nitrogen sorption, and scanning electron microscopy.
Formation and Reaction of Metal-containing Nanoparticles in Organic/Inorganic Hybrid Aerogels
Authors: Yao Chunhua , Risen William M.
Published: April 2011

Synthesis of hybrid aerogel materials that contain both selectively reactive nanoparticles and nanoparticles with appreciable magnetic susceptibilities will be reported. This has been achieved by a two stages process. First silica-bioderived polymer hybrid aerogels with incorporated metal ions were synthesized and then reduced by photolytically induced chemical reductions or decompositions. For example, silica-chitosan hybrid gels were prepared, Au(III) ions were coordinated to the chitosan, and, after forming the Au(III)-silica-chitosan aerogel by SCL extraction, UV photolysis afforded gold nanoparticles of controlled size in the aerogel. Second, an iron-containing organometallic compound, such as iron carbonyl itself, was absorbed into the aerogel, and then heating or photolysis afforded reduced metal decomposition products. Ferromagnetic organic/inorganic hybrid products containing Au(0) nanoparticles were obtained. Their size (TEM), crystallographic, optical and magnetic properties are discussed. Reactions of thiol compound with the metal nanoparticles in the aerogels were studied.
Inorganic-organic Hybrid materials from Layered Double Hydroxide structure and their subsequent carbonaceous repliqua
Authors: Leroux Fabrice , Moujahid El Mostafa , Roland-Swanson Claudia , Vieille Laetitia , Taviot-Guého Christine , Besse Jean-Pierre , Raymundo-Piñero Encarnacion , Béguin François
Published: April 2011

Interleaved monomers and polymers between the sheets of layered double hydroxide (LDH) (hydrotalcite-type) materials are considered as carbonaceous source. After a charring process constituted of a carbonisation and a subsequent demineralisation, carbonaceous materials of interesting textural properties were obtained. The initial preparation of the polymer LDH hybrid phase was found to strongly orientate the textural characteristics, microporous volume and creation of mesoporosity. Several methods to assess the microporosity, t-plot, αs and Dubinin-Astakhov, are compared. Specific surface area as high as 2300 m2/g measured by BET method and microporous volume of 1.07 mL/g were obtained. The carbonaceous materials tested as supercapacitor in acidic medium present capacitances in the range 60 - 120 F/g associated to a good behavior in cycling.
Constrainment Effects of Interleaved Organic Molecules into Layered Double Hydroxides
Authors: Dubois Marc , Moujahid El Mostafa , Besse Jean-Pierre , Leroux Fabrice
Published: April 2011

Incorporation and subsequent stabilization of organic molecules into layered double hydroxide are investigated. Through two types of hybrid materials, organic dyes and aniline-based monomers interleaved between LDH materials of cation composition Zn2Al and Cu2Cr respectively, it is shown that the effect of the constrainment is revealed by the interactions different according to the molecule size and stacking as exemplified by dye molecules, orange 6 and green 25 acids and two aniline-based monomers, m-amino-4-benzenesulfonic and 3-aniline-1-propanesulfonic acids.
Influence of TiO2 on the Pore Structure and Texture of SiO2-PDMS Hybrid Materials
Authors: Téllez Lucía , Rubio Juan , Valenzuela Miguel A. , Rubio Fausto , Morales Ernesto , Oteo José L.
Published: April 2011

Porous SiO2-PDMS-TiO2 hybrid materials have been prepared by the Sol-Gel method using tetraethoxysilane (TEOS), silanol terminated-Polydimethylsiloxane (PDMS) and tetrabuthylortotitanate (TBT) as precursors. These materials were characterized by means of nitrogen adsorption, mercury porosimetry and helium picnometry. It was found that the meso and microporosity are predominant in all samples. The influence of the TBT concentration in the final pore structure and texture of SiO2-PDMS-TiO2 hybrid materials was studied. Results showed that increasing the TBT concentration decreases the pore volume of micropores, mesopores and macropores. On the other hand the specific surface areas of meso and macropores decreases with increasing TBT content, but micropore areas increase with TBT. These results are assigned to the formation of ultramicropores when TBT is added. In addition, surface roughness is found to increase with TBT concentration which is attributed to the formation of hydrous titanium oxide based nanoparticles.
The Constrained Growth and Patterned Distribution of nc-Si from a-SiNx/a-Si:H/a-SiNx: Mechanism and Experiments
Authors: Chen K. J. , Chen K. , Wu L. C. , Ma Z. Y. , Han P. G. , Li W , Zhang L , Zhang Y. J. , Huang X. F.
Published: April 2011

We get size-controlled nanocrystalline silicon (nc-Si) from a-SiNx/a-Si:H/a-SiNx sandwich structures by thermal annealing. Transmission electron microscope analyses show that the mean size and the grain size distribution (GSD) of the nc-Si are controlled by the annealing conditions and the a-Si sublayer thickness. We build a theoretical model of constrained crystallization which can well interpret the phenomena of the growth halt of nc-Si and higher crystallization temperature for the thinner a-Si sublayer. The experimental results indicate that constrained crystallization method is promising to achieve uniform and high density nc-Si array either by thermal annealing or by laser annealing. Based on this investigation we employ the method of laser interference crystallization (LIC) to fabricate nanocrystal Si with the two-dimensional (2D) patterned distribution within 10 nm thick a-Si:H single layer. Si nano-crystallites are selectively located in the discal regions within the initial a-Si:H layer. The present method is promising to fabricate various patterned nc-Si arrays for device applications simply by changing the geometry of the mask.
Nonlinear Stabilization Mechanisms in Amplitude Saturation During Sputter Ripple Formation on Silicon
Authors: Erlebacher Jonah , Brown Ari-David
Published: April 2011

Sputter rippling refers to the formation of regular surface patterns during glancing incidence energetic ion beam etching of surfaces, usually as a result of a competition between etching (from the ion beam) and capillary action (driving smoothening via surface diffusion). Many different kinds of morphologies are often observed, including ripples oriented parallel and perpendicular to the projected ion beam direction and “quantum dots” arranged in hexagonal or rectangular arrays. Theoretical analyses of ripple evolution have concentrated on the initial stages of the surface instability leading to pattern formation, and the details associated with the nonlinear mechanisms leading to amplitude saturation and pattern stabilization remain a subject of active interest. The Si(111) surface is a single component surface with isotropic surface diffusion kinetics; for these reasons, this system provides a useful probe of surface evolution without complicating effects of compositional inhomogeneities and anisotropic terrace diffusion. Our examination of the Si(111) surface indicates that step-step interactions may play an important role in the evolution of sputter ripples in this system. To argue for this conclusion, a comparison with sputter ripple evolution on Si(001) is made.
Hexagonal-arranged ZnO Nanowire Arrays by Using Au Nanohole Membranes as Fabrication Template
Authors: Fan H. J. , Lee W. , Nielsch K. , Zacharias M. , Dadgar A. , Krost A.
Published: April 2011

A new template method for large-scale fabrication of hexagonally patterned and vertically aligned ZnO nanowires is demonstrated. The process involves a novel type of metal membrane, a gold catalyst template produced using the membrane as deposition mask, and the catalyst-guided growth of ZnO nanowires. The metal membranes, composed of hexagonal nanohole arrays, are electrochemically replicated from ordered porous alumina. The ZnO nanowires obtained have a uniform alignment perpendicular to the GaN surface and a distribution according to the pattern defined by the nanohole membrane. Such periodically arranged ZnO nanowires have potential applications as sensor arrays and piezoelectric transducers.
Nano structure formation by gas cluster ion beam irradiations at oblique incidence
Authors: Toyoda Noriaki , Yamada Isao
Published: April 2011

Nano structure formations on Au surfaces by 20 keV Ar gas cluster ion beam (GCIB) irradiation at an oblique incidence were studied. When the incident angle was close to 0° from the surface normal of Au targets, the Au surface was smoothed due to the lateral sputtering effects and there were no structure formations on the surfaces. However, ripples were formed on Au surfaces at incident angle of 60° without sample rotation. When the Au samples were irradiated with Ar-GCIB at 60° with sample rotation, cone like structures with 50nm in diameters were fabricated and the surface roughness had a maximum value. However, the surface roughness suddenly decreased over incident angle of 60°. Even though the surface roughness was the same in the cases with and without sample rotations at 85° incidence, ripple structures were formed parallel to the incoming GCIB directions when there was no rotation. The incident angle dependence of the sputtering depth decreased following cosθ dependence. Very efficient surface smoothing without removing materials were realized with oblique incidence.
Irradiated Single Crystals for High Temperature Measurements in Space Applications
Authors: Volinsky Alex A. , Nikolaenko V. A. , Morozov V. A. , Timoshenko V. P.
Published: April 2011

While spacecrafts experience temperatures from -120 to 110°C on the orbit, their surface reaches extremely high temperatures, well above 1000 °C, during descent into the atmosphere due to aerodynamic heating. Sophisticated insulation systems are designed for thermal protection. One of the steps in designing a protection system is experimental temperature measurements.

Neutron flux induces point defects formation and accumulation in diamond and SiC single crystals, which causes overall lattice expansion. During thermal annealing this process is reversed, so the annealing temperature and time result in the “reduced” lattice parameter (measured by X-Ray diffraction), which allows determining the maximum temperature, if the exposure time is known. This paper describes the use of irradiated single crystal high temperature sensors for measuring temperatures in thermal protection systems during spacecraft descent, as well as other space applications. These additional applications include measuring the furnace temperature during single crystal growth in space at zero gravity, and measuring the rocket combustion chamber turbo pump temperature.
Polymeric materials for Solar Sail: The combined effects of polymer thickness, radiation, and temperature
Authors: Edwards David L. , Chipara Mircea
Published: April 2011

The feasibility and the performance of solar sail depend critically on the availability of light materials and extremely thin polymeric films. The main requirements imposed on solar sail materials are analyzed in depth. The potential effects of the space environment are discussed in detail, with emphasis on the radiation-temperature-polymeric film thickness relationships. It is shown that the radiation component of the space environment triggers two competing degradation processes (erosion and depolymerization) and that both processes act towards the decrease in the glass transition temperature.
Raman Spectroscopy for Carbon Based Amorphous Thin Films
Authors: Compagnini Giuseppe
Published: April 2011

Vibrational spectroscopies and in particular Raman spectroscopy are known to be among the most useful tools to characterize and control the properties of carbon materials. This is because of the possibility to detect and study the carbon bonding state and because of the strong correlation between shape and width of the vibrational signals and the structure of the amorphous network. The aim of this work is to present some experiments in which the formation and evolution of carbon films obtained by energetic particle irradiation of solid targets or by deposition of carbonaceous species onto suitable surfaces, are controlled and studied by these methods. Particular attention will be given to pure amorphous carbon films and carbon based binary alloys.
Radiation-Induced Modifications in Polymeric Materials
Authors: Hui David , Chipara Magdalena D.
Published: April 2011

Radiation-induced modifications in polymeric materials are briefly reviewed. The attention is paid to the effect of ionizing radiation on the mechanical properties of polymers. The competition between several parallel degradation processes in the harsh conditions of the space environment is analyzed. The need for a complex analysis of the effect of polymeric materials in simulated space environments is demonstrated.
Molecular Self-Healing Processes in Polymers
Authors: Chipara M. , Wooley K.
Published: April 2011

A critical review of self-healing processes in polymers and composites based on polymeric matrices is presented. Two self-healing processes are analyzed, one “operating” within micron range and the other at molecular scale. Preliminary data on the molecular self-healing process in living polymers, as obtained by electron spin resonance are discussed. The possibility to develop a multi-scale self-healing material is suggested.
Luminescence and Upconversion Dynamics of Praseodymium in LiLuF4 Laser Crystals
Authors: Özen Gönül , Collins John M , Forte Ottavio , Meylman Misha , Abdulsabirov R. Yu , Bartolo Baldassare Di
Published: April 2011

We have investigated the spectroscopic properties of Pr3+ ions in LiLuF4 laser host doped with 0.5% Pr3+ ions as a function of temperature. We obtained the luminescence spectra by exciting selectively the sample at 439nm into the 3P2 level and at 593nm into the 1D2 level. With excitation in the 3P2 level we obtained emission only from the 3P0 level but not from the 1D2 level at all temperatures between 24 and 300K. With excitation into the 1D2 level we observed the luminescence emitted by the same level and a strong blue up-conversion emission from the 3P0 level. We used the decay pattern inspection to assign spectral lines to specific radiative transitions and to study the dynamics of the excited ions in the crystal. Under direct excitation, the 1D2 decay curve is nonexponential at all temperatures, whereas the 3P0 decay is exponential only at low temperatures. The experimental data indicate that the 3P0 level is populated via upconversion due to mainly energy transfer.
Surface Modification of Polymers, Paints and Composite Materials Used in the Low Earth Orbit Space Environment
Authors: Kleiman Jacob I.
Published: April 2011

Many organic-based materials exposed to low Earth orbit (LEO) environment undergo dramatic changes and irreversible degradation of physical characteristics. While many protective schemes are used to reduce the effects of LEO environment, protection of such materials in LEO still remains a major challenge, especially for future long duration missions or space stations.

In addition to the traditional protective coating approaches, surface modification processes were proposed and successfully used as an approach to protect polymers, thermal control paints and other components and structures from LEO environment. Among them two surface modification processes, the Photosil™ and the Implantox™ that used new approaches in silicon functionalization, as in the Photosil™, and a modified ion implantation process, as in the Implantox™ allowed to incorporate up to 36 at.% of Si into the upper surface layer regions of the treated polymers, composite materials, thermal control paints and other high-performance organic materials.

The tests conducted in plasma and fast atomic oxygen (FAO) beam facilities at comparable to LEO fluencies (∼ (1–2)·1020 at.O/cm2 ) demonstrated erosion yields lower than −10−26 cm3at, unchanged thermal optical properties, where important, and excellent thermal match between the treated layers and the bulk of the treated materials. After FAO testing, the Implantox™ treated samples were clear and transparent, with a glassy-like shiny surface with no signs of any surface erosion.
Adhesion of Copper to Teflon ® poly(tetrafluoroethylene-co-perfluoropropyl vinyl ether) (PFA) Surfaces Modified by Vacuum UV Photo-oxidation Downstream from Argon Microwave Plasma
Authors: Dasilva W. , Entenberg A. , Kahn B. , Debies T. , Takacs G. A.
Published: April 2011

Good practical adhesion of sputter-deposited Cu is achieved to poly(tetrafluoroethylene-co-perfluoropropyl vinyl ether) (PFA) surfaces at short treatment times of vacuum UV (VUV) photo-oxidation downstream from Ar microwave (MW) plasma. Factors contributing to the adhesion include: (1) an improvement in wettability as observed by water contact angle measurements; (2) surface roughening; (3) defluorination of the surface; (4) cross-linking at the surface and (5) incorporation of oxygen as CF-O-CF2, CF2-O-CF2 and CF-O-CnF2n+1 moieties. With long treatment times, a cohesive failure occurred within the modified PFA and not at the Cu-PFA interface due to extensive chain scission weakening its mechanical properties.
Structural Characterization of Oxide layers on Aluminum Formed by Exposure to Hyperthermal Atomic Oxygen
Authors: Li Long , Wang Liang , Minton Timothy K. , Yang Judith C.
Published: April 2011

Single crystal Al (100) was exposed to 5 eV atomic oxygen beam. The sample was maintained at a temperature of 220°C and the total atomic oxygen fluence was 8×1019 atom.cm-2. We have characterized the resulting oxide and interface structures by cross-sectional (scanning) transmission electron microscopy ((S)TEM) and scanning electron microscope(SEM). Our TEM results show that an amorphous aluminum oxide layer with ∼6 nm thickness formed on the aluminum crystal, and a rough alumina/Al(100) interface forms. For a systematic study of the evolution of the oxide, a unique Physical Sciences, Inc. Pitt FASTTM AO laser detonation atomic oxygen source in a UHV chamber is employed. The system is equipped with a Maxtek RQCMTM system, a research quartz crystal microbalance (QCM) with a dual-sensor head, to dynamically measure the mass change of an aluminum film coated on the sensor crystal during exposure to atomic oxygen. The Al film initially experiences mass loss, and then parabolic mass gain. To observe the structural evolution of the oxide, a very thin Al (100) single crystal was exposed inside the AO source, characterized by SEM and TEM. The surface morphology changed from flat to rough after 5.5 minutes of exposure. This surface roughening could be related to the initial mass loss measured by QCM.
The Development and Manufacture of Aluminium Mokumé Gane (Wood-Grain Metal) Decorative Alloy
Authors: Ferguson Ian T. , Derby Brian , Thompson G.E.
Published: April 2011

The application of contemporary metallurgical knowledge and solid state bonding techniques provide for development of entirely new Mokumé Gane combinations. A multi-layered aluminium alloy is manufactured by the successive hot roll-bonding of two different aluminium alloys. The surface is then embossed with a selected pattern and machined back, exposing the various alloys. A range of suitable alloy combinations has been identified. When anodised, the surface presents the pattern as a strong contrast due to the differing anodising properties of the constituent alloy layers. The anodic coating can then be dyed with a wide range of colours to develop the decorative potential of the technique.
Optical Profilometry as a Non-Destructive Technique to Quantify Engraving on Medieval Brass Astrolabes
Authors: Newbury Brian D. , Notis Michael R.
Published: April 2011

Optical profilometry has been performed on an astrolabe dated 1556 AD and attributed to the famous maker Gualterus Arsenius of Louvain, Belgium. In this non-destructive technique, a beam of white light is impinged on the sample and combined with the chromatic aberration technique to accurately measure surface features. With machine parameters set to a vertical resolution of 0.1 μm, lateral resolution to 6 μm and a 3 mm depth of field, various engraving features on the astrolabe were studied. Both hand-scribed and stamped markings are present on the astrolabe components. Inspection of the hand-scribed date on the instrument's mater allows one to quantify the shape and dimensions of the tool used, as well as the direction and inclination of the engraving tool during inscription. The results of this analysis give information about how the astrolabe was constructed in one of the Renaissance's greatest scientific instrument workshops. The results are compared to similar engravings on an undated and unsigned Islamic astrolabe tympan.
Fiber Optics Reflectance Spectroscopy in the Entire VIS-IR Range: a Powerful Tool for the Non-invasive Characterization of Paintings
Authors: Bacci M. , Bellucci R. , Cucci C. , Frosinini C. , Picollo M. , Porcinai S. , Radicati B.
Published: April 2011

Fiber optics reflectance spectroscopy (FORS) in the entire 380 – 11, 000 nm range has been used to non-invasively characterize Leonardo's paintingMadonna of the Yarnwinder. A preliminary analysis of the recorded spectra made it possible to obtain useful information concerning the pigments used, previous restoration work, the preparatory layer, and the binding medium. In particular, it was found that Thénard's blue was used in a previous restoration instead of the original ultramarine. As regards the painting technique, typical spectral features of oil binding medium are present in the mid-IR spectra, while near IR spectra reveal the occurrence of clay in the preparatory layer.
A Parametric Analysis of Relative Humidity Effects on Traditional Panel Paintings
Authors: Hagan Eric , Quasney Evan , Mecklenburg Marion
Published: April 2011

A finite element analysis was performed on panel painting structures subjected to changes in relative humidity. Measured Young's modulus values and humidity expansion coefficients were used to define the properties of materials characteristic to northern and southern European panels. Models of northern panels simulated white oak with two layers of oil paint, while models of southern panels simulated cottonwood with gesso and two oil paint layers. In both cases, the properties of the oil paints were input for lead white and Naples yellow respectively. Influence of radial/tangential grain orientation, panel thickness, and structural support were investigated through various humidity changes. Results are presented in the form of stress in the wood, gesso, and paint layers as well as curvature of the painted surfaces. Methods of reducing panel curvature with structural support are discussed, which involve applying a frictionless cradle, wood battens, or verso gesso layer. Verification of the model was performed with a derivation of general stress equations for a cradled painting with no friction between the slider-bars and the panel. A comparison of derived and parametric results confirms accurate behavior of the model.
Craft Knowledge as an Intangible Cultural Property: A Case Study of Samarkand Tiles and Traditional Potters in Uzbekistan
Authors: Vandiver Pamela B.
Published: April 2011

Reverse engineering past craft technologies involves using the basics of materials science and engineering to a new end: their preservation and continuation. Examples are presented of the glazed tile technologies of Samarkand, Bukhara and other Silk Route cities of Uzbekistan that date from the thirteenth century A.D. but that continue to the present. The UNESCO charter for the preservation of Intangible Cultural Properties has enlightened the goals and results of the research and has linked together archaeological materials research and conservation science in an exciting new partnership.
Systematic Investigation of Exchange Coupling in Thickness Gradient Fe/Sm-Co and Co/Sm-Co Magnetic Bilayers
Authors: Yu M. H. , Hattrick-Simpers J. , Takeuchi I. , Liu J. P.
Published: April 2011

Magnetic bilayers Fe/Sm-Co and Co/Sm-Co have been fabricated with gradient thicknesses of the soft layers in order to systematically study the dependence of exchange coupling on the thickness of the soft layer. The films were deposited in a combinatorial magnetron-sputtering chamber, where the Fe and Co thickness wedges were created by the natural thickness gradient due to the deposition geometry. The soft layer was deposited at two different temperatures (150°C and 300°C) in order to study the effect of deposition temperature on the exchange coupling. The deposition of the Fe layer at the higher temperature (300°C) was found to enhance the interlayer exchange coupling between Fe and Sm-Co. The single-phase-like magnetization reversal critical thickness increases from 12 nm for Fe deposited at 150°C to 24 nm for Fe deposited at 300°C. We attribute the enhanced exchange coupling in Fe/Sm-Co bilayers to the interfacial mixing and the coherent growth of the Fe layer. On the other hand, we found that the exchange coupling between Co and Sm-Co is not sensitive to the growth temperature of the Co layer.
Magnetic and Transport Properties of Ferromagnetic-PEEK Polymer Nanocomposite Prepared via Ion-Implantation
Authors: Ghosh K. , Mishra S. R. , Losby J. , Kehl T. , Robertson B. , Kassim T. , Patel R. , Weigand M. , Curry M. , Giedd R. E.
Published: April 2011

Thin films of magnetic-nanocomposite are prepared using a novel two step ion-implantation technique. Structural assessment via TEM of the ion bombarded iron-polymer composite shows development of fine magnetic nanoparticles (20–50 A) in a carbonaceous matrix. The experimental temperature dependence of conductivity of the composite, in the temperature range 10–300 K, follows the exponential law σ = σo exp [(-To/T)γ], where To and γ are constants. The observed higher values of γ > 1 imply the presence of more than one conducting channel in the composite. The secondary conducting channels, beside hopping conductivity, may arise from the conducting graphitic matrix around Fe nanoparticles. The room temperature magneto-transport measurement indicates a 0.5% change in magnetoresistance at 0.5T field. The observed anomalous Hall voltage confirms the presence of magnetic nature of nanoparticles.
Effects of defects on the electrical and magnetic properties of Ga1−x MnxAs layer
Authors: Koh D. , Park J.-B. , Park Y. J. , Lee J. I. , Park C. , Cho H. , Kim Y. M. , Park I.-W. , Chung K. S.
Published: April 2011

We investigated the effects of V/III flux ratios on the Curie temperature, TC, in Ga1−x Mnx As layers with various Mn mole fractions of x = 0.03 and 0.05. A 75 nm thick GaMnAs layer was grown at the temperature of 250 °C with various V/III flux ratios of 25∼34. The low temperature molecular beam epitaxy (LT-MBE) method for growth of GaMnAs layer caused the defects related by excess As and Mn interstitial, and these leaded the formation of deep level. We investigated that formation of deep level was established with various Mn mole fraction for V/III flux ratio 34. The changes of TC are observed by varying V/III flux ratio with a fixed Mn mole fraction. The TC in the sample grown with a lower V/III flux ratio of 25 is found to be higher comparing to that with higher V/III flux ratio of 34 at a fixed high Mn concentration (x = 0.05). Although the Mn concentration increases, the TC is not much changed when the V/III flux ratio is high of 34. The changes of TC with various V/III flux ratios are explained by the existence of low temperature grown defects, which are clarified by the deep level transient spectroscopy measurement. The prime species of defects are found to be AsGa and MnI etc.
In-Situ Magnetic Field Induced Structure and Properties of Epitaxial Spinel Ferrite Thin Films Prepared by Pulsed Laser Deposition (PLD) (Dynamic Aurora PLD Method)
Authors: Wakiya Naoki , Nagamune Toyokazu , Shinozaki Kazuo , Mizutani Nobuyasu
Published: April 2011

The influence of an in-situ magnetic field on the plume during pulsed laser deposition (PLD) to prepare epitaxial nickel zinc ferrite (NZF) thin films were investigated. An air core coil (solenoid coil) was installed between a target and a substrate, and up to 43 mT of magnetic field was generated by direct current (DC)(Dynamic Aurora PLD method). Application of magnetic field brought about following structural and property changes;

(1) deposition rate was almost doubled, (2) the concentration of Ni and Zn in the film was decreased, (3) lattice parameter was unchanged, and (4) magnetization and coercivity was increased. Since deposition rate was increased by application of magnetic field, films with same thickness was also prepared without magnetic field, however, magnetic properties were unchanged. This indicates that application of in-situ magnetic field improved magnetic properties.
Magnetophotonic Crystals
Authors: Inoue Mitsuteru
Published: April 2011

When the constitutive materials of photonic crystals (PCs) are magnetic, or even only a defect in PCs is magnetic, the resultant PCs exhibit very unique optical and magneto-optical (MO) properties: The strong photon confinement in the vicinity of magnetic defects results in large enhancement in linear and nonlinear magneto-optical responses of the media. Novel functions, such as band Faraday effect, magnetic super-prism effect and non-reciprocal or magnetically controllable photonic band structure, are predicted to occur theoretically. All the unique features of the media arise from the existence of magnetization in media, and hence they are called magnetophotonic crystals (MPCs) providing the spin-dependent nature in PCs.
The Effects of Nanoscopic Fillers on the Viscoelastic Response of Polymers
Authors: Xavier Jean Harry , Sokolov J. , Rafailovich M.H.
Published: April 2011

We have used a technique developed by Brochard (Macromolecules, 2004, 37, 1470) using free standing thin films to study the viscoelastic response of filled-polymer films. Transmission Electron Microscopy (TEM) experiments reported that fillers were well distributed within the films, and therefore no clustering and interfacial segregation occurred. Results from Shear Modulation Force Microscopy (SMFM) measurements revealed that the glass transition temperature of the polymer (Tg) was depressed by 10°C relative to the bulk for Au (10 nm), and bulk like for Au (3 nm). The effects of colloidal fillers on the tracer diffusion coefficient (D) were studied using secondary ion mass spectrometry (SIMS), and results found that D was increased significantly for the Au 10 nm, and constant for the Au 3 nm. Values for zero shear rate viscosity extracted from the diffusion coefficient were compared to the shear strain calculated from the hole growth measurements, and theoretical predictions. Results were attributed to an increase in excluded volume when large particles were introduced into the matrix.
Thermal Stability of Nanostructured TiN-TiB2 Thin Films
Authors: Mayrhofer Paul H. , Mitterer Christian
Published: April 2011

Nanocrystalline hard films have attracted increasing interest for wear-resistant applications. Especially, films within the system Ti-B-N with its numerous different phases are ideal candidates for materials science based studies on the nanoscale. In physical vapor deposited Ti-B-N films the nanostructure arises during growth by segregation-driven renucleation resulting in 2–3 nm sized TiN and TiB2 crystals. These films exhibit a hardness of ∼ 42 GPa in the as-deposited state which increases to ∼ 52 GPa during thermal annealing in vacuum. Here we show, that as-deposited films have a remarkable fraction of disordered regions surrounding TiN and TiB2 nanocrystals. During thermal annealing, the structural rearrangement causes the formation of compact boundary areas, leading to a hardness increase. At temperatures higher than 900 °C, the occurring B-loss, grain-growth, and recrystallization cause the hardness to decrease.
Surface Instability of Microscale Multilayer Thin Film System
Authors: Wei Yueguang , Jiang Di , Cao Ajing , Zhao Haifeng
Published: April 2011

Fundamental relations of surface instability for micro-scale multilayer thin film systems are derived based on the Hill and Hutchinson bifurcation theory and the volume average integral. In the present relations, a size effect is considered through generalizing the plastic hardening modulus to include the strain gradient hardening effects. By using the model, firstly, the parameter-controlled instability region is divided and analyzed, secondly, the surface instability of the multilayer thin films are analyzed. In the surface instability analysis, several kinds of failure band formations are obtained, such as the kink bands and the compressive buckling bands in vertical direction and in inclined direction. Moreover, the failure mechanism of the multilayer thin film system due to surface instability is used to interpret the microstructure features of the surface-nanocrystallization materials.
Thermal Grooving in Single versus Multilayer Thin Films
Authors: Anderson Peter M. , Wang Jue , Narayanaswamy Sridhar
Published: April 2011

A 2D analytic result is presented for the penetration distance P of grain boundary grooves as a function of time t during heating and straining of polycrystalline multilayer thin films with immiscible phases. These grooves can ultimately pinch off individual layers. The result shows that P ∼ t0.25 initially and P ∼ t at longer time. This new analysis contrasts single- versus multilayer thin film response.
The Residual Stress Effect on Microstructure and Optical Property of ZnO Films produced by RF Sputtering
Authors: Ryu Sang , Kim Youngman
Published: April 2011

ZnO films were produced on the Si(100) and sapphire(0001) wafers by RF magnetron sputtering in terms of processing variables such as substrate temperature and RF power. The stress in films was obtained from the Stoney's formula using a laser scanning device. The stress levels in the films showed the range from ∼40MPa to ∼-1100MPa depending on processing variables.

SEM was employed to characterize the microstructure of the films. As the substrate temperature increased, the film surface became rougher and the films showed coarser grains. The optical property of the films was studied by PL measurements. At the highest substrate temperature 800°C the film exhibited sharper UV peaks unlike other conditions.
Residual stress and microstructural evolution in thin film materials for a micro solid oxide fuel cell (SOFC).
Authors: Quinn David , Mark Spearing S. , Wardle Brian L.
Published: April 2011

The stability of multilayered membrane structures is a major challenge in the development of microfabricated solid oxide fuel cells (SOFC). The work presented here explores residual stress in sputter-deposited yttria stabilized zirconia (YSZ) thin films (5nm – 1000nm thickness) as a function of deposition pressure and substrate temperature. The results indicate variations in intrinsic stress from ∼0.5GPa compressive to mildly tensile (∼50 MPa). Microstructure is characterized by x-ray diffraction (XRD). The evolution of intrinsic stress with temperature is investigated by thermally cycling YSZ films deposited on silicon wafers. Observed changes of 100s of MPa in the intrinsic stress component of the film serve as indicators of possible changes in microstructure. Such changes in microstructure are subsequently characterized using x-ray diffraction of as-deposited and annealed films. Correlations with relevant mechanisms and models of residual stress evolution are discussed. Finally, use of such residual stress data in the fabrication and design of mechanically stable multilayered membranes for micro SOFC devices is discussed.
Mode–I Fracture Toughness of Tetrahedral Amorphous Diamond-like Carbon (ta-C) MEMS
Authors: Jonnalagadda K. , Cho S.W. , Chasiotis I. , Friedmann T.A. , Sullivan J.P.
Published: April 2011

Mode-I fracture toughness studies were conducted on hydrogen-free tetrahedral amorphous diamond-like carbon (ta-C) MEMS specimens of various thicknesses. Mathematically sharp edge pre-cracks were generated through micro indentation on the Silicon dioxide sacrificial layer. An atomic force microscope (AFM) was employed to measure the precise length and orientation of each pre-crack. Upon wet etching and release the freestanding uniform width and varying thickness MEMS-scale specimens were tested in Mode-I using a custom-made micro-tensile tester. Fracture toughness values were computed from the test data using linear elastic fracture mechanics (LEFM) for a finite width specimen with an edge crack in the fixed grip loading configuration. The average Mode-I fracture toughness for 0.5 micron thick specimens was found to be while the average mode-I fracture toughness for 1 micron specimens was .
Cast NiTi Shape-Memory Alloys
Authors: Ortega Alicia M. , Frick Carl P. , Tyber Jeffrey , Gall Ken , Maier Hans J.
Published: April 2011

The purpose of this study is to investigate the structure and properties of polycrystalline NiTi in its cast form. Although it is commonly stated in the literature that cast NiTi has poor shape-memory behavior, this study demonstrates that with appropriate nano/micro structural design, cast NiTi possesses excellent shape-memory properties. Cast NiTi shape-memory alloys may give rise to a new palette of low-cost, complex-geometry components. Results from two different nominal compositions of cast NiTi are presented: 50.1 at.%Ni and 50.9 at.%Ni. The cast NiTi showed a spatial variance in grain size and a random grain orientation distribution throughout the cast material. However, small variances in the thermo-mechanical response of the cast material resulted. Transformation temperatures were slightly influenced by the radial location from which the material was extracted from the casting, showing a change in Differential Scanning Calorimetry peak diffuseness as well as a change in transformation sequence for the 50.9 at.%Ni material. Mildly aged 50.9 at.%Ni material was capable of full shape-memory strain recovery after being strained to 5% under compression, while the 50.1 at.%Ni demonstrated residual plastic strains of around 1.5%. The isotropic and symmetric response under tensile and compressive loading is a result of the measured random grain orientation distribution. The favorable recovery properties in the cast material are primarily attributed to the presence of nanometer scale precipitates, which inhibit dislocation motion and favor the martensitic transformation.
Micro-fluidic applications of telephone cord delamination blisters
Authors: Volinsky Alex A. , Waters Patrick , Wright Gregory
Published: April 2011

Argon pressure significantly affects the residual stress in sputter deposited thin films and coatings. In case of W thin films, high residual stresses on the order of 1–2 GPa are quite common. With the rest of sputtering parameters being equal, argon pressure determines the sign and the value of residual stress.

When the amount of stored elastic energy in the film due to the residual stress exceeds the interfacial toughness, fracture normally occurs. Telephone cord buckling delamination blisters are commonly observed in compressed thin films. These mechanically active features form by a loss of adhesion between the film and the substrate due to residual stress relief, and exhibit directional growth under certain conditions. This paper considers telephone cord delamination channels for micro-fluidics applications, as this could to be a valuable, reliable, and inexpensive method of forming open channels.
Electrochemical Tuning of Single-Wall Carbon Nanotube Mat and Investigations on Actuator Mechanism
Authors: Gupta S. , Hughes M. , Robertson J.
Published: April 2011

Electrochemical tuning of single-wall carbon nanotubes has been investigated using in situ Raman spectroscopy. We built a linear actuator from single-wall carbon nanotube mat and studied in several alkali metal (Li, Na, and K) and alkaline earth (Ca) halide solutions. The variation of bonding with electrochemical biasing was monitored using in situ Raman. This is since Raman can detect changes in C-C bond length: the radial breathing mode (RBM) at ∼190 cm−1 varies inversely with the nanotube diameter and the G band at ∼1590 cm−1 varies with the axial bond length. In addition, the intensities of both the modes vary significantly in a nonmonotonic manner pointing at the emptying/depleting or filling of the bonding and anti-bonding states - electrochemical charge injection. We discuss the variation of spectroscopic observables (intensity/frequency) of these modes providing valuable information on the charge transfer dynamics on the single-wall carbon nanotubes mat surface. We found the in-plane compressive strain (∼ -0.25%) and the charge transfer per carbon atom (fc ∼ -0.005) as an upper bound for the electrolytes used i.e. CaCl2. These results can be quantitatively understood in terms of the changes in the energy gaps between the one-dimensional van Hove singularities in the electron density of states arising possibly due to the alterations in the overlap integral of π bonds between the p orbitals of the adjacent carbon atoms. Moreover, the extent of variation of the absolute potential of the Fermi level or alternatively modification of band gap is estimated from modeling Raman intensity to be around 0.1 eV as an upper bound for CaCl2.
Kinematic and Topological Models of Martensitic Interfaces
Authors: Pond Robert C. , Ma Xiao , Chai Yaw W. , Hirth John P.
Published: April 2011

The Phenomenological Theory of Martensite Crystallography, developed fifty years ago, envisages martensitic interfaces to be invariant planes of the shape transformation. This theory has been very successful, but neither incorporates the notion of atomic relaxations at martensitic interfaces, nor explicitly demonstrates that such interfaces are glissile. A new model, called the Topological Model, is proposed that addresses these issues. Predictions of the habit plane and relative orientation of the crystals according to the two models are compared and contrasted.
A Unified Model for Hysteresis in Ferroic Materials
Authors: Seelecke Stefan , Smith Ralph C.
Published: April 2011

This paper provides a unified modeling framework for ferroelectric, ferromagnetic and ferroelastic materials operating in hysteretic and nonlinear regimes. Whereas the physical mechanisms which produce hysteresis and constitutive nonlinearities in these materials differ at the microscopic level, shared energy relations can be derived at the lattice, or mesoscopic, scale. This yields a class of models which are appropriate for homogeneous, single crystal compounds. Stochastic homogenization techniques are then employed to construct macroscopic models suitable for nonhomogeneous, polycrystalline compounds with variable effective fields or stresses. This unified methodology for quantifying hysteresis and constitutive nonlinearities for a broad class of ferroic compounds facilitates both material characterization and subsequent model-based control design. Attributes of the models are illustrated through comparison with piezoceramic, magnetostrictive and thin film SMA data.
Anisotropic saturable absorption of single wall carbon nanotubes aligned in polyvinyl alcohol
Authors: Rozhin Aleksey G. , Sakakibara Youichi , Kataura Hiromichi , Matsuzaki Shun , Ishida Kohtaro , Achiba Yohji , Tokumoto Madoka
Published: April 2011

We report anisotropic optical absorption and saturable absorption (SA) properties of aligned single wall carbon nanotubes (SWNT) embedded in the mechanically stretched polyvinyl alcohol (PVA) film. Polarized absorption spectra of the film showed a strong anisotropy for the near-infrared band gap transition of semiconductor SWNT with a dichroic ratio of 7.4, indicating the good alignment of the embedded SWNT. The SA property of the band gap transition measured using a polarized femtosecond fiber laser showed a strong polarization angle dependence for the stretched film. When the polarization of light is parallel to the stretching direction, the absorption saturation of the stretched film became more efficient than that of the unstretched film because of the apparently stronger transition moment.
Raman studies of suspensions and solutions of singlewall carbon nanotubes
Authors: Izard N. , Pénicaud A. , Anglaret E.
Published: April 2011

Raman spectroscopy is used to probe the structure and electronic properties of nanotubes dispersed in a liquid phase. We show that the radial breathing modes are upshifted in suspensions due to the molecular pressure of the solvent. On the other hand, we directly probe charge transfer in solutions of nanotube polyelectrolytes and its reversibility after oxydation in air.
Quantitative evaluation of bundling effect on single walled carbon nanotubes by resonance Raman spectra
Authors: Luo Zhengtang , Li Rongfu , Kim Sang Nyon , Papadimitrakopoulos Fotios
Published: April 2011

The radial breathing mode (RBM) region of the resonance Raman spectra of HiPco single walled carbon nanotubes (SWNTs) was investigated as a function of aggregation. This was modeled using an energetic deviation term (ΔE), imparted to the optical transitions (Eii(n, m)) by bundling effect. Eii(n, m) values obtained from photoluminescence (PL) measurements were used to reconstruct these RBM profiles. The simulation revealed that the PL-determined Eii(n, m) set provided a good fit in terms of peak position. Providing an accurate set of Eii(n, m) values becomes available, the RBM profile reconstruction methodology discussed herein could greatly enhance our ability to model a range of physicochemical changes to the immediate environment of SWNTs.
Integration Of Carbon Nanotubes Into Device Structures
Authors: Lägel B. , Schumacher J. D. , Nguyen N. , Zivanovic B. , Schlaf R.
Published: April 2011

Carbon nanotubes have shown promising properties for applications in electronic circuits and other device structures. Several device structures have been demonstrated in recent years by manual manipulation of single nanotubes. The integration of large numbers of nanotubes on wafer size substrates, however, has been a challenge.

Our approach addressing this issue utilizes nano-patterning methods in combination with plasma enhanced chemical vapor deposition to directly assemble carbon nanotubes on wafer structures. A secondary formation step is used to actually form device structures connecting the nanotubes to electrode structures. We present first results demonstrating the feasibility of our approach. Electrode structures were prepared using multi-step electron beam lithography processes. Carbon nanotubes were grown in pre-defined locations, and contact formation procedures were carried out to establish multi-terminal contact structures.