bluuebunny/crossref_metadata_2025 huggingface dataset:
The Creep Behaviors of Two Fine-grained XD TiAl Alloys Produced by Similar Heat Treatments
Authors: Zhu Hanliang , Seo Dongyi , Maruyama Kouichi , Au Peter
Published: April 2011

The microstructural characteristics and creep behavior of two fine-grained XD TiAl alloys, Ti-45Al and 47Al–2Nb–2Mn+0.8vol%TiB2 (at%), were investigated. A nearly lamellar structure (NL) and two kinds of fully lamellar (FL) structures in both alloys were prepared by selected heat treatments. The results of microstructural examination and tensile creep tests indicate that the 45XD alloy with a NL structure possesses an inferior creep resistance due to its coarse lamellar spacing and larger amount of equiaxed γ grains at the grain boundaries, whereas the same alloy in a FL condition with fine lamellar spacing lowers the minimum creep rates. Contrary to 45XD, the 47XD alloy with a NL structure exhibits the best creep resistance. However, 47XD with a FL structure with finer lamellar spacing shows inferior creep resistance. On the basis of microstructural deformation characteristics, it is suggested that the well-interlocked grain boundary and relatively coarse colony size in FL and NL 47XD inhibit sliding and microstructural degradation at the grain boundaries during creep deformation, resulting in better creep resistance. Therefore, good microstructural stability is essential for improving the creep resistance of these alloys.
Formation and Morphology of Kurnakov Type D022Compound in Disordered fcc γ-(Ni, Fe) Matrix Alloys
Authors: Suzuki Akane , Takeyama Masao
Published: April 2011

Formation and morphology of D022compound Ni3V in γ-fcc alloys were investigated as a model case in order to understand fundamentals for microstructure control of new class of austenitic steels strengthened by Kurnakov-type GCP intermetallic compound. The formation process of the D022phase in γ matrix varies, depending on the composition and heat treatment temperature, and precipitation of D022takes place at temperature above T0in the γ+D022two phase region. The morphology of coherent precipitates of the D022compound is sensitive to misfit strains against matrix and can be controlled by alloying addition. The habit planes between the two phases become irrational, parallel to both directions of the invariant line and an a-axis of D022, since the lattice misfit becomes negative along a-axis (δa) and positive along c-axis (δc) of the D022. The calculation based on the lattice invariant theory as well as experimental results clearly demonstrate that the misfit strain ratio δc/δais a dominant factor to determine the habit plane. In addition, the shape of D022phase, either prism or plate, depends strongly on the magnitude of |δa|. These findings will extend to Ni-Fe-Nb-V quaternary system, by partial replacement of Ni with Fe and that of V with Nb.
Rationalization of the plastic flow behavior of Polysynthetically-twinned (PST) TiAl crystals based on slip mode observation using AFM and Schmid's law
Authors: Chen Yali , Pope David P.
Published: April 2011

PST TiAl samples of different orientations were prepared and deformed by compression at room temperature. The deformation structures on the free surfaces were scanned using an AFM. It was found that when the angle between the lamellar interfaces and the loading axis is between 20 degree and 80 degree, PST samples deform primarily by shear in slip planes parallel to the lamellar interfaces. When the angle is below 20 degree, both the gamma phase and the alpha 2 phase deform by shear in slip planes inclined with the lamellar interfaces, but the shear vectors lie in the interface. When the angle is close to 90 degree, complex deformation behavior occurs. Shear in planes parallel to the lamellar interfaces contributes more to the overall strain in the directions perpendicular to the loading axis and the out-of-plane shear contributes to the strain in the compression direction. The characteristic U-shape curve of the yield stress versus the angle between the loading axis and the lamellar interfaces can be explained quite well using different C.R.S.S. for the three different deformation modes.
Fatigue Testing of microsized samples of γ-TiAl based material
Authors: Halford Timothy P. , Takashima Kazuki , Higo Yakichi
Published: April 2011

High strength γ-TiAl based alloys, such as Ti-46Al-5Nb-1W (Alloy 7), which were originally developed for gas turbine and automotive applications are now being considered for application in Micro Electro Mechanical Systems (MEMS). This requires the evaluation of these materials upon the microscale. As international standards do not currently exist for the evaluation of the mechanical properties of samples with dimensions equivalent to those required by MEMS devices, the development of new methods was required. The method developed here is intended for the fatigue testing of samples measuring ≈ 10μm (B) × 20μm (W) × 40μm (L). This is completed using a machine recently developed at Tokyo Institute of Technology to load samples of lamellar γ-TiAl based material to failure in compressive bending. This method is intended to work alongside methods previously developed for the fracture toughness testing of similar microsized cantilever bend specimens.

In this work sample cantilevers of Alloy 7 are Focussed Ion Beam (FIB) machined from foil ≈ 20μm thick and their stress - life (S-N) fatigue behaviour evaluated. The dependence of fatigue life upon lamellar orientation for a given peak stress / stress range is considered. The effect of the reduced scale of these samples upon the mean and scatter of these sample lifetimes is also considered through comparison with previous data obtained from the S-N testing of macrosized samples of the same material.
An Electron Microscope Study of Mechanical Twinning in a Precipitation–Hardened TiAl Alloy
Authors: Appel Fritz
Published: April 2011

The high temperature capability of TiAl alloys can be significantly improved by the implementation of precipitation reactions. From the engineering viewpoint the challenge is to establish the hardening mechanism without compromising desirable low temperature properties such as ductility and toughness. With this perspective in mind, twin structures were investigated in a TiAl alloy containing Ti3AlC carbides, in order to identify mitigation strategies for overcoming precipitation induced embrittlement. The study is focussed on the nucleation and immobilization of twins at precipitates. The results are discussed in the context of the plastic anisotropy and fracture behaviour of TiAl alloys.
Internal Friction of a High-Nb Gamma-TiAl-Based Alloy with Different Microstructures
Authors: Weller M. , Clemens H. , Dehm G. , Haneczok G. , Bystrzanowski S. , Bartels A. , Gerling R. , Arzt E.
Published: April 2011

An intermetallic Ti-46Al-9Nb (at%) alloy with different microstructures (near gamma, duplex, and fully lamellar) was studied by internal friction measurements at 300 K to 1280 K using different frequency ranges: (I) 0.01 Hz to 10 Hz and (II) around 2 kHz. The loss spectra in range I show (i) a loss peak of Debye type at T ≈ 1000 K which is only present in duplex and fully lamellar samples; (ii) a high-temperature damping background above ≈ 1100 K. The activation enthalpies determined from the frequency shift are H = 2.9 eV for the loss peak and H = 4.1–4.3 eV for the high-temperature damping background. The activation enthalpies for the visco-elastic high-temperature damping background agree well with values obtained from creep experiments and are in the range of those determined for self-diffusion of Al in TiAl. These results indicate that both properties (high-temperature damping background and creep) are controlled by volume diffusion-assisted climb of dislocations. The loss peak is assigned to diffusion-controlled local glide of dislocation segments which, as indicated by transmission electron microscopy observations, are pinned at lamella interfaces.
Impact Properties of Hot-Worked Gamma Alloys with BCC β-Ti Phase
Authors: Shindo Kentaro , Tetsui Toshimitsu , Kobayashi Toshiro , Morita Shigeki , Kobayashi Satoru , Takeyama Masao
Published: April 2011

Impact resistance of a hot-forged TiAl alloy with a composition of Ti-42∼44Al-5∼10M: M=V, Mn(at%), consisting of lamellar, γ and β grain of which the hot-workability was improved by introducing β phase, has been investigated using an instrumented Charpy impact test, tensile test at high strain rate and foreign object attack test. In instrumented Charpy impact test the absorbed energies for crack initiation and propagation were measured, and the effect of microstructure on the absorbed energies has been analyzed, by paying attention to the grain size, interlamellar spacing and lamellar area fraction. In tensile test at high strain rate, the dependence of strain rate of hot-extruded TiAl alloy is obtained and compared with that of Nickel based superalloy, Inconel 713C. In foreign object attack test with taper plate specimen modified turbine blade and brass ball as foreign object, the relation between impact damage and thickness of specimen at attack point is investigated. A limit of impact energy, at which there isn't a crack on buck of attack point, is obtained with each thickness about hot-forged TiAl alloy, Ti-42Al-5Mn. Therefore, the method of improvement of toughness and assessment of impact resistance of TiAl alloy is shown in this study.
Effects of long-period superstructures on plastic properties in Al-rich TiAl single crystals
Authors: Nakano Takayoshi , Hayashi Koutaro , Umakoshi Yukichi , Chiu Yu-Lung , Veyssière Patrick
Published: April 2011

In Al-rich TiAl crystals, several long-period superstructures may appear depending on Al composition, annealing temperature and annealing time. Amongst these, Al5Ti3 and h-Al2Ti contain pure Al (002) layers, as in the L10 structure of the matrix, alternating with Ti (002) layers that exhibit an ordered arrangement of the Al atoms in excess. In single crystals with compositions ranging from Ti-54.7at.%Al to Ti-62.5at.%Al annealed at 1200°C, the Al5Ti3 long-period superstructure embedded in the L10 matrix develops with increasing Al concentration to finally transform fully into h-Al2Ti for Ti-62.5at.%Al. On the other hand, Al5Ti3 precipitates grow with annealing time at 500°C in Ti-58.0at.%Al.

The effects of the Al5Ti3 and h-Al2Ti superstructures on slip properties of 1/2<110] ordinary dislocations are examined both at a macroscopic and a microscopic level. The CRSS for 1/2<110] ordinary slip increases with Al5Ti3 ordering depending on Al composition, or of annealing time in the case of Ti-58.0at.%Al. Dislocations with 1/2<110] Burgers vector group into fourfold configurations to avoid the trailing of extended APBs in Al5Ti3. The CRSS for slip in the <110] direction further increases with the formation of h-Al2Ti particles within the L10 matrix in Ti-62.5at.%Al. By contrast, Ti-62.5at.%Al fully transformed into Al5Ti3 exhibits a CRSS significantly lower than that of the two-phase alloy.
Influence of Micro-alloying on Oxidation Behavior of TiAl
Authors: Yoshihara Michiko , Taniguchi Shigeji
Published: April 2011

The influence of a wide range of elements on oxidation behavior of TiAl was investigated by micro-alloying using ion implantation with ion doses of 1019 to 1022 m−2 and at acceleration voltages of 40 to 340kV. The oxidation resistance was assessed by a cyclic oxidation test at 1200K in a flow of purified oxygen under atmospheric pressure. The implanted elements can be classified into several groups according to their effect and mechanism. The mechanisms by which the oxidation resistance is improved are as follows: (1) Formation of a protective Al2O3 layer through β-phase formation, which was confirmed by TEM observations, in the modified surface layer by the implantation. (2) Reduction of TiO2 growth rate due to doping effect of the implanted element. (3) Protective Al2O3 layer formation through migration of volatile halide. (4) Enrichment of oxide of the implanted element in the scale. On the other hand, the oxidation resistance is decreased by (1) enhanced TiO2 growth due to doping effect, (2) lattice defects induced by the implantation, and (3) decreased scale strength and enhanced scale spallation.
Carbon Nanotube Reinforced Bombyx mori Nanofiber Composites by the Electrospinning Process
Authors: Ayutsede Jonathan , Gandhi Milind , Sukigara Sachiko , Ko Frank
Published: April 2011

A nanocomposite of silkworm silk and single wall carbon nanotubes (SWNT) was produced by the electrospinning process. Regenerated silk fibroin dissolved in a dispersion of carbon nanotubes in formic acid was electrospun and the morphological, chemical and mechanical properties of the electrospun nanofibers were examined. The mechanical properties of the SWNT reinforced fiber show increases in Young's modulus up to 460 % in comparison with the un-reinforced aligned fiber.
Nanoindentation of Bone in a Physiological Environment
Authors: Akhtar R. , Morse S. , Mummery P.M.
Published: April 2011

Nanoindentation has been established as an effective method to measure the mechanical properties of bone tissue at the micron and sub-micron length scale. Although it is well-documented that the mechanical properties of macroscopic bone specimens vary depending on whether the samples are tested dry or wet, nanoindentation is generally conducted on dehydrated bone tissue at room temperature, primarily because nanoindentation systems are extremely sensitive to changes in environmental conditions such as humidity and temperature. In this study, these problems were overcome by using a specially constructed liquid cell with an extension piece that allowed the indenter tip to be submerged under 5 mm of liquid. The custom setup was used to test cortical bovine bone and cancellous human bone specimens in three distinct conditions – dehydrated, rehydrated in simulated body fluid (SBF) at 20°C, and rehydrated in SBF at 37.5°C. A heating element with a temperature control unit was used to test at 37.5°C. The hardness and elastic modulus of the bone samples were found to decrease when dry specimens were rehydrated and tested in physiological conditions. It is suggested that nanoindentation in physiological conditions gives a better estimate of the mechanical properties of the microstructural components of bone in vivo rather than nanoindentation under conventional conditions.
Lessons for New Classes of Inorganic/Organic Composites from the Spicules and Skeleton of the Sea Sponge Euplectella aspergillum
Authors: Mayer G. , Trejo R. , Lara-Curzio E. , Rodriguez M. , Tran K. , Song H. , Ma W. H.
Published: April 2011

Studies have been carried out on the structures and mechanical characteristics of an unusual family of sea sponges under the classification of Hexactinellida, genus Euplectella. The sponge spicules have been of interest to materials scientists because of their potentially important optical, coupled with mechanical, properties. The structures of the class Hexactinellida are characterized by a concentric ring appearance in the cross-section, which is a composite of hydrated silica, coupled with silicatein as a thin layer at the ring interfaces. The mechanical behavior and the toughness of the spicules have been examined with the aid of a special fiber testing method, coupled with scanning electrom microscopy (SEM) observations. It appears that there may be common mechanisms underlying toughness in rigid natural composites with high ratios of mineral/organic phase. In addition, novel pressurization tests of a portion of the sponge skeleton have provided information about the resilience of the skeleton, which resembles a selfsupporting glass winding of a cylindrical composite structure.
A continuum model for two-dimensional fiber networks
Authors: Baesu Eveline , Zheng Minrong , Beljic Doina
Published: April 2011

Elastic-plastic deformation of a continuum formed by continuously distributed fibers is described. Applications to the mechanical characterization of nanofibers, and to biological materials such as cellular cytoskeleton and tissue scaffolds are indicated.
Mechanical Properties of Biomimetic Composites for Bone Tissue Engineering
Authors: Verma Devendra , Katti Kalpana S. , Mohanty Bedabibhas
Published: April 2011

A biomimetic process involving in situ mineralization of hydroxyapatite (HAP) is used to design new composite biomaterials for bone tissue engineering. Surface and bulk properties of HAP composites have been studied for hydroxyapatite mineralized in absence (ex situ) of polyacrylic acid (PAAc) and in presence (in situ) of PAAc. XRD studies show existence of structural disorder within in situ HAP. It has been observed that PAAc increases the rate of crystallization. FTIR studies indicate calcium deficiency in structure of both in situ and ex situ HAP. PAAc provides favorable sites for nucleation of HAP. During crystallization of HAP, PAAc dissociates to form carboxylate ion, which binds to HAP. Porous and solid composites of in situ and ex situ HAP with polycaprolactone (PCL) in 50:50 ratio have been made to evaluate their applicability as bone scaffold. Mechanical tests on solid samples indicate ex situ HAP/PCL composites have higher elastic modulus (1.16 GPa) than in situ HAP/PCL composites (0.82 GPa). However, in case of porous composites, in situ HAP/PCL composites are found to have higher elastic modulus (29.5 MPa) than ex situ HAP/PCL composites (10.4 MPa). Nanoindentation tests were also performed at different loads to evaluate mechanical properties of the composites. In situ HAP mineralized using non-degradable polymers has thus been shown to improve mechanical response in porous composites.
Mechanical Response of Porous and Dense NiTi-TiC Composites
Authors: Burkes Douglas E. , Gottoli Guglielmo , Moore John J. , Ayers Reed A.
Published: April 2011

The Center for Commercial Applications of Combustion in Space (CCACS) at the Colorado School of Mines is currently using combustion synthesis to produce several advanced materials. These materials include ceramic, intermetallic, and metal-matrix composites in both porous and dense form. Currently, NiTi – TiC intermetallic ceramic composites are under investigation for use as a bone replacement material. The NiTi intermetallic has the potential to provide a surface that is capable of readily producing an oxide layer for corrosion resistance. The TiC ceramic has the potential to increase the hardness and wear resistance of the bulk material that can improve the performance lifetime of the implant. Processing parameters are critical to the production of the NiTi – TiC composite and will be discussed. These parameters can lead to the formation of substoichiometric TiC and nickel rich NiTi that changes the overall mechanical and material properties. In addition, the size of the TiC particles present within the bulk product varies with porosity. Both porous and dense samples have been mechanically analyzed employing micro-indentation techniques as well as compression tests in an attempt to characterize the mechanical response of these composites. The effects of the TiC particles, the formation of Ni3Ti intermetallic and the effects of porosity on the overall mechanical and material properties will be discussed.
Mechanical Properties of Nacre Constituents: An Inverse Method Approach
Authors: Barthelat Francois , Espinosa Horacio D.
Published: April 2011

Nacre, also known as mother-of-pearl, is the iridescent layer found inside some mollusk species such as oyster or abalone. It is made of relatively weak materials, but its hierarchical microstructure is so well optimized that its macroscopic mechanical properties are far superior to those of its constituents. For this reason there is a great interest in nacre as a source of inspiration for novel designs of composites. Despite many years of research on nacre, an accurate characterization of its constituents is lacking. In this work nacre was tested as a layered composite material using low depth indentation and uniaxial compression. The first test was modeled using finite element analysis and the second test was modeled as a Reuss composite in compression. A micromechanical model of the interface was also pursued to gain insight on the relevance of the interface features such as tablet roughness and biopolymer hydrated response. The results of the two experiments were combined to solve an inverse problem that yielded the needed properties for tablets and interfaces. These findings are expected to make possible computational models of nacre with a new degree of accuracy and therefore contribute to a better understanding of the mechanisms leading to its remarkable properties.
Spectral profiles of two-photon absorption: Coherent versus two-step two-photon absorption
Authors: Polyutov S. , Minkov I. , Gel'mukhanov F. , Kamada K. , Baev A. , Ågren H.
Published: April 2011

We present a theory of two-photon absorption in solutions which addresses the formation of spectral shapes taking account of the vibrational degrees of freedom. The theory is used to rationalize observed differences between spectral shapes of one- and two-photon absorption. We elaborate on two underlying causes, one trivial and one non-trivial, behind these differences. The first refers simply to the fact that the set of excited electronic states constituting the spectra will have different relative cross sections for one-and two- photon absorption. The second reason is that the two-step and coherent two-photon absorption processes are competing, making the one-and two-photon spectral bands different even considering a single final state. The theory is applied to the N-101 molecule [di-phenyl-amino-nitro-stilbene] which was recently studied experimentally in the paper [ T.-C. Lin, G.S. He, P.N. Prasad, and L.-S. Tan, J. Mater. Chem., 14, 982, 2004.]
Effects of Deposition Angle on the Optical Properties of Helically Structured Films
Authors: Sorge Jason B. , van Popta Andy C. , Sit Jeremy C. , Brett Michael J.
Published: April 2011

Glancing-angle deposition (GLAD) is a fabrication method capable of producing thin films with variable porosity. The GLAD process exploits substrate shadowing and limited adatom diffusion to create isolated columns of material that collectively comprise a highly porous thin film. GLAD can be used to create chiral or helical structures with a wide range of porosity through variation of the substrate tilt angle and controlled substrate rotation. We present the effect of the deposition angle on the selective transmittance of circularly polarized light in helical thin films fabricated with the GLAD process. Transmission measurements of titanium dioxide helical films reveal two regimes of enhanced selective transmittance: one corresponding to a substrate tilt angle that produces a maximum circular birefringence and another corresponding to strong anisotropic scattering.
Degradation of Ru(bpy)32+-based OLEDs
Authors: Goldberg Velda , Kaplan Michael , Soltzberg Leonard , Genevich Joseph , Berry Rebecca , Bukhari Alma , Chan Sherina , Damour Megan , Friguglietti Leigh , Gunn Erica , Ho Karen , Johnson Ashley , Lin Yin Yin , Lowenthal Alisabet , Suth Seiyam , To Regina , Yopak Regina , Slinker Jason D. , Malliaras George G. , Flores-Torres Samuel , Abruña Hector D.
Published: April 2011

Analysis of the possible mechanisms of degradation of Ru(bpy)32+-based OLEDs has led to the idea of quencher formation in the metalloorganic area close to the cathode. It has been suggested that the quencher results from an electrochemical process where one of the bipyridine (bpy) groups is replaced with two water molecules [1] or from reduction of Ru(bpy)32+ to Ru(bpy)30 [2]. We have tested these and other degradation ideas for Ru(bpy)32+-based OLEDs, both prepared and tested with considerable exposure to the ambient environment and using materials and procedures that emphasize cost of preparation rather than overall efficiency. In order to understand the mechanisms involved in these particular devices, we have correlated changes in the devices' electrical and optical properties with MALDI-TOF mass spectra and UV-vis absorption and fluorescence spectra.
Fast-Switching, High-Contrast Electrochromic Thin Films Prepared Using Layer-by-Layer Assembly of Charged Species
Authors: Grunlan Jaime C.
Published: April 2011

Thin films were prepared by depositing alternating layers of tungstate anion (WO42-) and poly(4-vinylpyridine-co-styrene) (PVP-S) onto an electrode from aqueous solutions. These films have very high contrast (CR > 8) relative to equivalent films prepared using poly(ethylene dioxythiophene) (PEDOT), but suffer from slow color change due to poor electrical conductivity. The switching time of the tungstate-based films was decreased by an order of magnitude, from 30 seconds down to three, by adding layers of indium tin oxide (ITO) particles stabilized with poly(diallyldimethylammonium chloride) (PDDA). In this case, a four-layer repeating structure was created (i.e., PVP-S and PDDA-ITO were each deposited every fourth layer). Unlike tungstate, ITO has a high intrinsic conductivity (∼ 104 S/cm) that accounts for the dramatic increase in the switching speed. It is only through the nanometer-scale control of film architecture, provided with the layer-by-layer (LbL) deposition process, that switching speed and contrast ratio can be optimized simultaneously.
Optical Responses of Conjugated Polymers by TDDFT in Real-Space and Real-Time Approach
Authors: Akino Nobuhiko , Zempo Yasunari
Published: April 2011

The time dependent density functional theory (TDDFT) has applied to study the optical responses of the conjugated polymers such as poly(p-phenylenevinylene) and poly(9, 9-dialkyl-fluorene). In our study, the real-space grid representation is used for the electron wavefunctions in contrast to a conventional basis set on each atom. In the calculations of the optical responses, the real-time approach is employed, where we follow the linear responses of the systems under externally applied perturbations in the real time. Since a real polymer is too large to handle, we have calculated the oligomers with different length and observed the spectrum peak is redshifted as the length of oligomer increases. The property of the polymer is extrapolated as the infinitely long oligomer. The estimated polymer spectra agree with the experiments reasonably well.
Linear and Nonlinear Transmission of Surface Plasmon Polaritons in an Optical Nanowire
Authors: Panoiu N. C. , Osgood R. M.
Published: April 2011

Polymer-metal composites offer the possibility of strongly enhanced nonlinear optical properties, which can be used for ultrasmall photonic devices. In this paper, we investigate numerically, by means of the finite-difference time-domain (FDTD) method, the propagation characteristics of surface plasmon polariton (SPP) modes excited in an optical nanowire consisting of a chain of either metallic cylinders or metallic spheres embedded in dielectric shells made of polymers (or other material) with optical Kerr nonlinearity. Our FDTD calculations incorporate both the nonlinear optical response of the dielectrics as well as the frequency dispersion of the metals, which is considered to obey a Drude-like model. It is demonstrated that, in the linear limit, the nanowire supports two SPP modes, a transverse and a longitudinal one, separated by Δλ = 20 nm. Furthermore, the dependence of the transmission of these SPP modes, on both the pulse peak power and Kerr coefficient of the dielectric shell, is investigated. Nonlinear optical phenomena, such as power-dependent mode frequency, switching, or optical limiting, are observed.
Coherent Oscillations of Breathing Modes in Metal Nanoshells
Authors: Kirakosyan Arman S. , Shahbazyan Tigran V.
Published: April 2011

We study coherent oscillations of radial breathing modes in metal nanoparticles with a dielectric core. Vibrational modes are impulsively excited by a rapid heating of the particle lattice that occurs after laser excitation, while the energy transfer to a surrounding dielectric leads to a damping of the oscillations. In nanoshells, the presence of two metal surfaces leads to a substantially different energy spectrum of acoustic vibrations. The lowest and first excited modes correspond to in-phase (n=0) and anti-phase (n=1) contractions of shell-core and shell-matrix interfaces respectively. We calculated the energy spectrum as well as the damping of nanoshell vibrational modes in the presence of surrounding medium, and found that the size-dependences of in-phase and anti-phase modes are different. At the same time, the oscillator strength of the symmetric mode is larger than that in solid nanoparticles leading to stronger oscillations in thin nanoshells.
Current-voltage characteristics in organic semiconductor crystals: space charge vs. contact-limited carrier transport
Authors: Reynaert J. , Arkhipov V. I. , Genoe J. , Borghs G. , Heremans P.
Published: April 2011

Numerous experimental studies, mostly based on the time-of flight (TOF) technique, showed that the conductivity in organic crystals can be analysed in terms of (trap-controlled) band transport. However, recent comparative studies of TOF signals and space charge limited currents (SCLCs) in tetracene crystals revealed a striking difference in carrier mobilities estimated from TOF current transients and from SCLC curves. The analysis of the SCLC curves yielded the mobilities wildly varying within 6 orders of magnitude. Therefore, it is not always clear whether the measured current-voltage (IV) device characteristics are controlled by charge injection or by transport in the bulk. In this work, we formulate a model of dopant-assisted carrier injection across a metal/organics interface and use this model for the analysis of IV curves measured on a tetracene and perylene crystal. The model suggests the occurrence of an energetically disordered layer at the surface of an organic crystal. This might be either an amorphous phase of the same material or a crystalline layer with a high density of defects and/or impurities. Since, at variance with bulk properties, the surface of an organic crystal is poorly controlled and can be strongly modified upon the contact deposition, the model of injection-controlled IV characteristics can explain the striking difference between the TOF mobility and the apparent ‘SCLC mobility’ measured in tetracene crystals. In order to give more credence to the role of surface defects states in the dark charge transport, we compare IV characteristics measured on sandwich and coplanar structures. In the latter structure, surface states show a major contribution to the conductivity.
Luminescence properties of Eu3+:Y2O3 and Eu3+:Lu2O3 nanoparticles, ceramics and thin films
Authors: Zhang Kai , Hunter D. , Mohanty S. , Dadson J. B. , Barnakov Y. , Pradhan A. K.
Published: April 2011

Eu3+ doped Y2O3 and Lu2O3 nanocrystalline powders were synthesized via combustion technique using urea as a fuel and the metal nitrates as oxidants. The compacted nanopowders were vacuum sintered in order to form the translucent ceramics. A significant enhancement of emission characteristics was observed from the ceramics synthesized from the nanoparticles by controlling the vacuum-sintering conditions. Although the processed ceramics display superior emission characteristics, the nanocrystalline phosphor powders also display reasonably good emission characteristics. Highly epitaxial Y2O3:Eu3+ and Lu2O3:Eu3+ films were deposited on various substrates under different growth and optimization conditions using pulsed-laser deposition technique using high-density translucent ceramic target. Superior spectroscopic performance was obtained on films grown on sapphire substrates due to high-quality and epitaxial nature of the film.
Synthesis of nanomaterials in Highly Swollen Liquid Crystals
Authors: Tokumoto Myriam , Surendran Geetarani , Santos Eduardo Pena dos , Kooyman Patricia , Remita Hynd , Ramos Laurence , Prouzet Eric
Published: April 2011

Highly Swollen Liquid Crystals (SLC) that exhibit hexagonal, cubic or lamellar symmetry have been demonstrated to form a new type of soft nanoreactors. These mesophases are formed by a quaternary mixture combining a surfactant, an aqueous solution of inorganic salt, cyclohexane as a hydrophobic swelling solvent and pentanol-1 as a co-surfactant. Unlike previous works that used a “nanocasting” approach in a binary liquid crystal, the composition of these SLC allows syntheses to be proceeded inside the aqueous and/or the organic phase. Therefore inorganic, metallic or organic materials can be prepared and the geometry of the SLC controls the final shape of the prepared by this approach. We will describe various materials that were obtained by different processes in these SLCs: rod-like nanoaggregates of metal nanoparticles were synthesized by chemical reduction in the aqueous part of the hexagonal mesophase, microrods of zirconia were obtained by slow crystallogenesis from hydrated zirconium oxychloride, mesoporous zirconia was prepared by a faster hydrolysis and polymer micro- and nano-fibers were obtained in the organic phase by photopolymerization or radiolysis. We will show how the changements in the SLC structure can modify the structure of the compounds synthesized inside and that this system constitutes a quite universal medium for the preparation of nanomaterials or nanostructured systems.
Electrochemical Characterization of Phosphosilicate-modified Nafion Membranes
Authors: Klein L. C. , Aparicio M.
Published: April 2011

Hybrid membranes containing Nafion and phosphosilicate gels were prepared using infiltration and recasting methods. The hybrid membranes were investigated using complex impedance spectroscopy. Conductivities were determined as a function of relative humidity. Infiltrated membranes, which contained gel in more or less discrete particles, were compared with recast membranes where the gel was more evenly distributed. Both of the modified membranes were compared to unmodified Nafion. The impedance spectra were analyzed to distinguish electrode interface effects from bulk transport phenomena.
Two Synthetic Routes to The Formation of Tungsten Oxide Hybrid Compounds
Authors: Chong S.V. , Ingham B. , Tallon J.L.
Published: April 2011

The syntheses of tungsten oxide-organic amine hybrids via homogenous and heterogeneous routes were explored and compared. In the former case, tungstic acid (H2WO4) and an appropriate amine were dissolved in ammonia solution under nitrogen atmosphere, and the product was precipitated out via evaporation of the solvent. In heterogeneous synthesis, a non-aqueous approach was employed in which H2WO4 powder was aged in a solution consisting of the amine dissolved in an appropriate organic solvent. XRD and FTIR showed that the hybrid materials obtained from the two different methods are identical. Based on these findings, we were able to prepare tungsten oxide hybrid films for the first time, by dip-coating tungstic acid films prepared from sol-gel techniques, in a non-aqueous diamine solution. The XRD spectra of these films exhibit a series of harmonic peaks, indexed as [00k ], which correspond to the Bragg peaks for the hybrid compounds. SEM shows the morphology of tungstic acid changes from the irregularly shaped platelets to a needle-like structure of the hybrids and resulted in a loosely packed coating.
Fabrication of Organic/Inorganic Nanocomposites Using Pulsed Laser Ablation of Zinc in Aqueous Solutions
Authors: Sasaki Takeshi , Liang Changhao , Usui Hiroyuki , Shimizu Yoshiki , Koshizaki Naoto
Published: April 2011

Hybrid organic/inorganic nanocomposites composed of zinc hydroxide and surfactant molecule, and/or zinc oxide nanoparticles were fabricated using pulsed laser ablation of zinc in aqueous solutions of various surfactants. A Zn plate was ablated by a pulsed Nd:YAG laser in four types of surfactant solutions with different concentrations. Zinc oxide nanoparticles with average diameter of 10–40 nm were obtained in cationic, amphoteric and nonionic surfactant solutions. Unique layered organic/inorganic nanocomposites composed of zinc hydroxide layers and surfactant molecules were obtained in aqueous solutions of the anionic surfactants, sodium alkyl sulfate (CnH2n+1SO4-·Na+). The carbon number, n, in the alkyl sulfate family is very important for the formation and structure of the layered nanocomposites. The layered organic/inorganic nanocomposite can be obtained only in the specific sodium alkyl sulfates (n = 12, 13, 14 and 16) and the layer spacing of the nanocomposites increased with n from 26.8 Å to 42.0 Å. It is shown that the structures of ZnO nanoparticles and layered organic/inorganic nanocomposites can be controlled by the type of surfactants in solution.
Self-Assembled Monolayers of 12-Mercaptododecylphosphonic Acid on Titania Particles; Application to the Extraction of Heavy Metals
Authors: Anthérieu Sébastien , Brodard-Séverac Florence , Guerrero Gilles , Hubert Mutin P.
Published: April 2011

Titania particles (P25 DEGUSSA AG) were treated by a solution of 12-mercaptododecyl-phosphonic acid (MDPA) in toluene to obtain an organic-inorganic hybrid material with thiol functions at the surface. This material was characterized by chemical analysis, solid state 31P MAS NMR and FTIR spectroscopies, and XPS. Reaction of the phosphonic acid end of MDPA with the TiO2 surface led to the formation of a relatively dense and well-ordered self-assembled monolayer (SAM), with a density of about 3.9 SH functions per nm2. This material was tested for the extraction of mercury in water at pH 7, 9, and 11. Chemical analysis indicated no loss of SH functionality, even at pH 11. The best extraction results were obtained at pH 9 and 11, with a metal extraction ability between 85 and 90%.
B and P Glass Formers as Stabilizers of Luminescent Ce(III) in Silica-Based Glasses
Authors: Canevali C. , Mattoni M. , Morazzoni F. , Scotti R. , Krsmanovic R. , Polizzi S. , Bettinelli M. , Speghini A.
Published: April 2011

Ce3+-doped boro, phospho and borophosphosilicate monolithic glasses (BSG, PSG and BPSG) were prepared by sol-gel method. The inclusion of the glass formers P and B in silica lowered the tendency of rare earth (RE) to segregate as CeO2 with respect to pure SiO2 matrix (SG). In PSG and BPSG, Ce3+ co-ordination to P=O groups was responsible for the inhibition of both CeO2 segregation and oxidation of isolated Ce3+ ions to Ce4+. The better ion dispersion in the host matrix and the stabilization of Ce3+ oxidation state improved PSG and BPSG luminescence properties with respect to BSG and SG.
Molybdenum Dioxide and Vanadium-Doped Molybdenum Dioxide Microcrystals in a Polymer Container.
Authors: Pavel Alexandru C. , Romanovicz Dwight K. , McDevitt John T.
Published: April 2011

Molybdenum dioxide and vanadium-doped molybdenum dioxide microcrystals were synthesized by a totally new method involving a redox-active monomer route. The two related dioxides had virtually identical crystal structures and the three precursors used in the process could be subsequently divided in two subgroups of two members each, based on their strong similarities in composition and crystal structure, respectively. Molybdenum trioxide (orthorhombic and hexagonal forms) and the vanadium-doped (10%, molar) molybdenum trioxide (hexagonal form) were used in the redox process with excess pyrrole, and at relatively high temperature (325°C) and long reaction time (12 days), formed a heterogeneous new type of organic-inorganic microcomposite. The new material could be described as a molybdenum dioxide crystal in a polymer box, with the size of the crystallite grain depending on the dimensions of the initial molybdenum trioxide grain and the ratio between the unit cell volumes of the initial and final oxide. The procedure took advantage of the relatively high reduction potentials of the Mo6+and V5+oxide surface centers towards the oxidative polymerization of pyrrole at intermediate temperatures, and the high catalytic activity of the metal cations in the molybdenum trioxide-based materials towards the total oxidation of the carbon atoms in the organic moiety, at elevated temperatures. This new synthetic route offers good perspectives as precursor composites for nanocrystal engineering in practical applications like heterogeneous catalysis, chemical sensing, nanostructured metallic catalysts, etc.
Preparation of Particulate Core-Shell Metal Oxide-Polymer Nanocomposites by a Sol-Gel Approach
Authors: Kickelbick Guido , Holzinger Dieter
Published: April 2011

Two general microemulsion-based routes towards surface-functionalized metal oxide nanoparticles serving as macroinitiators in “grafting from” atom transfer radical polymerization (ATRP), are presented. Metal alkoxides modified with several β-diketone derivatives carrying potential ATRP-initiating sites served as precursors for the particle formation leading in an solgel process to in situ-functionalized titanium-, zirconium-, tantalum-, vanadium-, yttrium-, and iron oxide nanoparticles. The obtained systems were compared with metal oxide nanoparticles prepared by using metal salts as precursors which were functionalized in a second step with ATRP-initiator containing silane coupling agents. The obtained particles had diameters between 5 nm and 640 nm and served as multifunctional polymerization initiators in ATRP using styrene and methyl methacrylate as monomers.
In situ SAXS/XRD on mesoscopically ordered surfactant-silica mesophases; What can we learn?
Authors: Lindén Mika , Teixeira Cilaine V. , Amenitsch Heinz , Alfredsson Viveka , Kleitz Freddy
Published: April 2011

In situ investigations have proven to be a very useful means of understanding the different processes involved in the formation of mesoporous materials. In this communication, we demonstrate the potential of in situ small angle x-ray scattering, SAXS and x-ray diffraction, XRD, measurements for giving both qualitative and quantitative results on the structural evolution during the early stages of the surfactant-silicate composite formation. The examples given are based on results obtained for 2D hexagonal structures, synthesized both under acidic and alkaline conditions. Careful analysis of both the scattering and diffraction patterns allows the different stages of the formation to be described in some detail. Thus, new synthesis approaches can be foreseen that allow the structure of the final hybrid mesophase to be rationally controlled.
Fabrication of Nanocomposite Thin Film of Hydroxyapatite and Polyvinylalcohol and its Ionic Conductive Properties
Authors: Takaki Toshihiko , Fukuda Kazuyuki , Tajitsu Yoshiro
Published: April 2011

A hydroxyapatite (HAp)-polyvinylalcohol (PVA) nanocomposite was prepared by the in-situ method. When the HAp was synthesized by reacting Ca(OH)2 with H3PO4 in the presence of PVA having carboxyl groups, the interaction between the carboxylic groups of PVA and calcium ions of HAp led to the formation of nanometer-sized spindle HAp particles (long axis ca. 80 nm and short axis ca. 25 nm). The reactant was stable and formed transparent thin films by the casting method. Nanometer-sized HAp particles were uniformly dispersed in PVA film. Properties of the HAp-PVA nanocomposite film, such as tensile strength, gas barrier, and pencil hardness, were superior to those of the pure PVA. Furthermore, the nanocomposite film had high ionic conductivity compared to pure PVA and traditional composite. The ionic conductivity of the stretched film (PVA: HAp = 1:1) with 35wt % content of LiN(CF3SO2)2 was about 10-3 S/m at room temperature. Regarding the mechanism of this study, we believe that the HAp particles play a crucial role in increasing the free lithium cations to accelerate the ionic conductivity, according to the ionic interaction on the HAp surface.
Morphology and Polymorph Selectivity Control in Calcium Carbonate Mineralization
Authors: Sindhu Swaminathan , Ajikumar Parayil K. , Jegadesan Subbiah , Valiyaveettil Suresh
Published: April 2011

The present paper describes the mineralization of calcium carbonate at a low temperature (4 °C) and in presence of additives. Aspartic acid immobilized polyacrylic acid (PA-Asp) induced the nucleation of spherical vaterite polymorph at 4 °C. But at room temperature, a thin film of calcite was deposited. Moreover, stable amorphous calcium carbonate was precipitated in presence of magnesium at low temperature. The observed results show that low temperature and presence of additives influence the nucleation, polymorph selectivity and morphology of the precipitated calcium carbonate.
Real-time observation of ion beam eroded silicon surfaces: Ripple propagation, coherence and noise effects in surface erosion
Authors: Habenicht S. , Lieb K. P.
Published: April 2011

The evolution of ion beam eroded Silicon surfaces was measured in real-time by combining focused ion beam technology with scanning electron microscopy. By detecting the secondary electrons emitted during implantation the surface was monitored in-situ during the erosion process of a Gallium focused ion beam. Repetitive scanning of the ion beam over the surface effectuates a coherent erosion of the exposed surface area, with the continuum theory of erosion as the ergodic limitation. Surface ripple as proposed by linear erosion theory were observed for oblique incidence of the ion beam and their propagation with progressing erosion time as well as their velocity dispersion were monitored. The ripple wavelength has been observed to increase with the erosion time and the value of the ripple velocity was observed to agree qualitatively with the results of Monte-Carlo simulations of the erosion process.

Noise effects acompanying the erosion process are found to be responsible for the reorientation of the ripples when the orientation of the ion beam onto the surface is varied. This mechanism is discussed to stimulate further efforts in this field of surface erosion.
Nanostructure analysis of protein thin film prepared by wet and dry processes
Authors: Taketani I. , Nakayama S. , Nagare S. , Senna M.
Published: April 2011

Silk fibroin (SF) and bovine serum albumin (BSA) thin films were deposited on Si(100) substrate either by colloid casting method or by pulsed laser deposition (PLD). Emphasis is laid on the comparison of nanostructures, which developed during the deposition. AFM diagrams were evaluated to quantify the nanostructures, parallel and perpendicular to the substrate, by the average wavelength of the profilogram (Wa ) and surface roughness (Rrms ), respectively. The film thickness increased with increasing the concentration of colloids or laser deposition time. The value of Wa increased with the film thickness. We note, however, that the value Wa becomes much less sensitive with decreasing the scanning area due to decreasing probability of the abnormally large agglomerates of the nanometric units. Probability of the agglomeration growth as a consequence of the surface adhesion is higher with higher concentration of random coil, followed by β-sheet and α-helix. BSA with smaller primary units and lower probability of agglomeration give more uniform films.