bluuebunny/crossref_metadata_2025 huggingface dataset:
Factors for Controlling Martensitic Transformation Temperature of TiNi Shape Memory Alloy by Addition of Ternary Elements
Authors: Hosoda Hideki , Wakashima Kenji , Miyazaki Shuichi , Inoue Kanryu
Published: April 2011

Correlations between the changes in martensitic transformation start temperature (Ms) by addition of ternary elements X and several factors of the ternary additions were investigated for TiNi shape memory alloy. The change of Ms by addition of 1mol%X is referred to as ΔMs (in K/mol%), and ΔMs was systematically evaluated by differential scanning calorimetry experimentally using (Ti, X)50Ni50 solution-treated at 1273K for 3.6ks where the Ni content was kept constant to be 50mol%. The ternary additions X investigated are the transition metal (TM) elements selected from 4th period group (Zr, Hf) to 10th period group (Pd, Pt). The factors investigated are (1) the number of total outer d- and s-electrons (Nele), and electron hole number (NV), (2) electronegativity (EN), (3) atomic volume (VX) and (4) Mendeleev number (NM). It was found that the values of ΔMs are different even in a same period group; ΔMs of 6th period group are -133K/mol%Cr (3d-TM), -152K/mol%Mo (4d-TM) and -64K/mol%W (5d-TM) for example. The results found in the correlations between ΔMs and those factors are summarized as follows. (1) ΔMs depends on Nele and NV. However, the data are scattered because same Nele and NV are often given in a same period group. Then, other factors than Nele and NV are required for clear understanding of ΔMs. (2) ΔMs seems to become lowered slightly with increasing EN. (3) ΔMs weakly depends on atomic volume VX. Ternary addition with large VX increases ΔMs slightly, and with small VX decreases ΔMs largely. Since the stress field must be formed by substitution due to size mismatch, the type of stress field, tension/compression, may be an important role to determine the sign of ΔMs. (4) ΔMs shows a good correlation with NM as -9.4Kmol%−1/ΔNM where ΔNM is the difference in NM. This suggests that a ternary alloying element with smaller (larger) NM stabilizes the B19’ martensite (B2 parent) phase. Effect of site occupancy on Ms is also discussed only for Cr.
Advanced TEM Investigations on Ni-Ti Shape Memory Material: Strain and Concentration Gradients Surrounding Ni4Ti3 Precipitates
Authors: Schryvers Dominique , Tirry Wim , Yang Zhiqing
Published: April 2011

Lattice deformations and concentration gradients surrounding Ni4Ti3 precipitates grown by appropriate annealing in a Ni51Ti49 B2 austenite matrix are determined by a combination of TEM techniques. Quantitative Fourier analysis of HRTEM images reveals a deformed nanoscale region with lattice deformations up to 2% while EELS and EDX indicate a Ni depleted zone up to 150 nm away from the matrix-precipitate interface.
Investigation of the structure and properties of hypereutectic Ti-based bulk alloys
Authors: Louzguine-Luzgin Dmitri V. , Louzguina-Luzgina Larissa V. , Inoue Akihisa
Published: April 2011

Structure and mechanical properties of binary Ti-TM (TM-other transition metals) and ternary Ti-Fe-(TM, B or Si) alloys produced in the shape of the arc-melted ingots of about 25 mm diameter and 10 mm height are studied. The formation of high-strength and ductile hypereutectic alloys was achieved in the Ti-Fe, Ti-Fe-Cu and Ti-Fe-B systems. The structures of the high-strength and ductile hypereutectic alloys studied by X-ray diffractometry and scanning electron microscopy were found to consist of the primary cubic Pm3 m intermetallic compound (TiFe-phase or a solid solution on its base) and a dispersed eutectic consisting of this Pm3m intermetallic compound + BCC Im 3 m β-Ti supersaturated solid solution phase. The hypereutectic Ti-Fe alloy showed excellent compressive mechanical properties. The addition of Cu improves its ductility. B addition increased mechanical strength. Ni, Cr and Mn additions caused embrittlement owing to the formation of alternative intermetallic compounds. The deformation behaviour and the fractography of the Ti-based alloys were studied in details. The reasons for the high strength and good ductility of the hypereutectic alloys are discussed.
In-situ Observation of Surface Relief Formation and Disappearance during Order-Disorder Transition of Equi-atomic CuAu alloy using Laser Scanning Confocal Microscopy
Authors: Miura Seiji , Okuno Hiroyuki , Ohkubo Kenji , Mohri Tetsuo
Published: April 2011

In-situ observation of the formation and disappearance of the surface relief associated with the twinning during the order-disorder transitions among CuAu-I (L10), CuAu-II (PAP) and disordered fcc phases was conducted using Confocal Scanning Laser Microscopy equipped with a gold image furnace. The Retro effect was confirmed in poly-crystal samples, however no evidence was found in single-crystal samples. Also observed in poly-crystal samples are that the disordering temperature detected by the disappearing of relieves is different from grain to grain, and that grain boundary cracking alleviates the Retro effect. The observed phenomena were explained based on the crystallographic orientation relationship among grains investigated by FESEM/EBSD in terms of the elastic strain effect around grain boundaries induced by transition. It was confirmed that in each grain the surface relieves correspond to a set of two {011} planes having a <100> axis perpendicular to both planes in common. It was also found that the larger the average strain of two neighboring grains is, the lower the transition temperature. This observation was explained by the stress effect on the stability of a phase.
Optimisation of Precipitation for the Development of Improved Wrought Fe3Al-based Alloys
Authors: Kobayashi Satoru , Zaefferer Stefan , Schneider André
Published: April 2011

Effect of TiC precipitates on the kinetics of static recrystallisation has been studied by using a Fe-26Al-5Cr (at%) single-phase (α:A2/B2/D03) alloy and two-phase (α+TiC) alloys with different amounts of TiC precipitates. Based on the results, a desirable thermo-mechanical processing is proposed for the development of wrought Fe3Al-based alloys with strengthening MC carbides.

In the alloys with a high amount of TiC, needle-like TiC precipitates with 1–10 μm in length formed during air-cooling after homogenisation. Hot deformations with such large precipitates cause inhomogeneous deformation around the particles, leading to particle stimulated nucleation (PSN) and hence accelerate recrystallisation.

The occurrence of PSN is harmful for the embrittlement problem, i.e. ductility drastically decreases when recrystallisation occurs, but useful for grain refinement. The following process is proposed to accomplish grain refinement, strengthening by precipitates and avoidance of the embrittlement: hot deformation with a large amount of precipitates to make grain refinement possible by using PSN, followed by hot deformation with a small amount of precipitates near α single-phase region and a subsequent heat treatment to obtain fine precipitates. The fine particles would also act to pin the boundaries of growing grains, thus leading to extended recovery rather than recrystallisation. This process is difficult to carry out in the (Fe-26Al-5Cr)-TiC system because the temperature necessary to enable precipitation is very high and the kinetics is quick. The precipitation temperature is significantly decreased by replacing TiC by VC or MoC.
Application of the CSL Model to Deformation Twin Boundary in B2 Type TiNi Compound
Authors: Nishida Minoru , Matsuda Mituhiro , Morizono Yasuhiro , Fujimoto Towako , Nakashima Hideharu
Published: April 2011

The deformation structure of B2 type TiNi compound around 573 K has been investigated by transmission electron microscopy (TEM). Serrations are seen in stress-strain curve, which corresponds to the formation of various planar defects with twin relation. The dominant planar defect found in the specimens showing serration is {114} compound twin. The other defects are in mirror symmetry with respect to {113}, {115}, {447} planes and so on. These defects are considered to be <110> symmetric tilt boundaries in bcc structure by ignoring the atomic arrangement of B2 structure and are characterized with Σ value based on coincide site lattice (CSL) model. For instance, the Σ value of {114}, {113}, {115} and {447} boundaries are Σ9, Σ11, Σ27 and Σ81, respectively. Numerous (114) defects initially form at grain boundary and grow into grain interior. Some of those deflect to (-1–14) defects. In such case, the {447} Σ81defect is always observed at the interface of (114) Σ9 and (-1–14) Σ9 defects. This fact indicates that the sigma combination rule of the CSL model can be applied to the triple junction of defects. Similarly, {7710} Σ99 boundary forms at the interface of {114} Σ9 and {113} Σ11 defects. It can be concluded that the ductility of B2 type TiNi compound around 573 K is attributable to the formation of various planar defects with large shear strain and the increment of independent slip system due to the formation of planar defects, and that the arrangement of some planar defects conforms to the sigma combination rule of CSL model.
Effect of Excess Vacancies on Antiphase Domain Growth in Fe3Al
Authors: Koizumi Y. , Hagiwara T. , Minamino Y. , Tsuji N.
Published: April 2011

The growth of the D03-type antiphase domain (APD) in Fe3Al was investigated focusing on the effect of excess vacancies that were introduced during the quenching process from the disordered state. The variation in the APD size exhibited considerable deviation from the conventional “parabolic growth law” in the early stage of APD growth. This variation was numerically calculated on the assumption that the migration of the APD boundaries was enhanced by non-equilibrium excess vacancies and the vacancy concentration decreased during the isothermal annealing for the APD growth. The calculated variations in the APD size could be successfully fitted to the experimental results in cases with quenching temperatures (Tq) of 873 K or 1073 K, but not when Tq was 1273 K. The APD growth in the latter case was much slower than the expected growth derived from the calculation. This discrepancy was attributed to the rapid decrease in the vacancy concentration due to vacancy clustering since a significant amount of dotted contrasts were observed in TEM image of only the specimen quenched from 1273K.
Microstructures in Cold-Rolled Ni3Al Single Crystals
Authors: Kishida Kyosuke , Demura Masahiko , Hirano Toshiyuki
Published: April 2011

Microstructure evolution during cold rolling of binary stoichiometric Ni3Al single crystals was examined by the optical (OM) and transmission electron microscopy (TEM). In the case of the <001> initial RD, the banded structure is formed. Inside each matrix band, the localized shear deformations occur alternately on two {111} planes. In addition, huge amounts of widely extended superlattice intrinsic stacking faults (SISFs) are observed from relatively early stage of cold rolling. The occurrence of the localized shear deformation is considered to be controlled by the SISFs since they must be strong obstacles for the dislocation motion on the other glide plane. The extensive formation of the SISFs is therefore considered to be one of the most important microstructural features which control the cold rolling behavior of Ni3Al.
High-Temperature Environmental Embrittlement of Thermomechanically Processed TiAl-Based Intermetallic Alloys with Various Kinds of Microstructures
Authors: Takasugi T. , Hotta Y. , Shibuya S. , Kaneno Y. , Inoue H. , Tetsui T.
Published: April 2011

Thermomechanically processed TiAl-based intermetallic alloys with various alloy compositions and microstructures were tensile tested in various environmental media including air, water vapor and a mixture gas of 5vol.%H2+Ar as a function of temperature. All the TiAl-based intermetallic alloys showed reduced tensile fracture stress (or elongation) in air, water vapor and a mixture gas of 5vol.%H2+Ar not only at ambient temperature (RT∼600K) but also at high temperature mostly from 600K to 1000K (sometimes higher temperature than 1000K). The high-temperature environmental embrittlement of TiAl-based intermetallic alloy depended upon the microstructure. The possible species causing the high-temperature environmental embrittlement are hydrogen atoms decomposed from water vapor (H2O) or hydrogen gas (H2), similar to those causing the low-temperature environmental embrittlement.
Crystal Structure and Thermoelectric Properties of Al-containing Re Silicides
Authors: Terada Eiji , Oh Min-Wook , Wee Dang-Moon , Inui Haruyuki
Published: April 2011

The microstructure, defect structure and thermoelectric properties of Al-containing ReSi1.75 based silicides have been investigated. All the Al-containing alloys investigated contain four differently oriented domains accompanied by the twinned microstructure, as the binary alloy does. However, thin defect layers containing a kind of shear structure are locally and sporadically formed at some of twin boundaries. In the defect layer, shear occurs by the vector of [100] on either (1 09) or (107) planes. Binary ReSi1.75 exhibits nice thermoelectric properties as exemplified by the high value of dimensionless figure of merit (ZT) of 0.70 at 800 °C when measured along [001], although the ZT value along [100] is just moderately high. Al-containing Re silicides considerably increase the ZT value along [100] so that the maximum value of 0.95 is achieved at 150 °C for the ReSi1.75Al0.02 alloy. The temperature dependence of electrical resistivity changes from of semiconductor for the binary alloy to of metal for the Al-added alloys and the value of electrical resistivity is significantly reduced when compared to the binary counterpart.
Increase in γ/α2 Lamellar Boundary Density and its Effect on Creep Resistance of TiAl Alloy
Authors: Maruyama Kouichi , Matsuda Jun , Zhu Hanliang
Published: April 2011

ABTSRACT

Several lamellar microstructures of a Ti-48 % Al alloy were made by changing heating rate in the α+γ dual phase field, and their creep properties were investigated at 1150 K. Average spacing and average length of α2 lamellae decrease with increasing heating rate. The decrease of α2 lamellar spacing is most effective at lower heating rate, and minimum creep rate decreases with increasing the heating rate, since a high density of γ/α2 boundaries stabilizes lamellar microstructure during creep. On the other hand creep rate increases at high heating rate, since α2 lamellar length becomes shorter with increasing heating rate. A reduction of creep rate by one order of magnitude is achieved at the optimum heating rate providing the best combination of narrow spacing and sufficiently long length of α2 lamellae.
Effect of Molecular Interactions at Polymer-Mineral Interfaces on Mechanical Response
Authors: Bhowmik Rahul , Katti Kalpana S , Katti Dinesh R
Published: April 2011

Nanocomposites of polymer and hydroxyapatite are widely used as bone replacement materials. The mechanical responses of these nanocomposites are known to be influenced by molecular interactions at mineral polymer interface. Molecular modeling of these interactions is an area of current interest but force field parameters of such dissimilar molecules are not available for a common force field. Also, parameters for several commonly used force fields are not available in the literature for hydroxyapatite. Recently a unique force field was described in literature that represents the structure of hydroxyapatite reasonably well. Yet the applicability of this force field for studying the interaction between dissimilar materials (such as mineral and polymer) is limited as there is no accurate representation of polymer. CVFF is a commonly used force field for which parameters of many material systems are available. We have obtained the parameters of CVFF for monoclinic hydroxyapatite from the known potential energy function of apatites and from experimentally obtained infrared spectra. Validation of simulations is done by comparison of computationally obtained unit cell parameters, vibrational spectra and different atomic distances with experiments. This study represents molecular modeling of polymermineral interfaces with the known parameters of hydroxyapatite.
Nanoscale Characterisation of Salivary Pellicle
Authors: Dickinso Michelle E. , Mann Adrian B.
Published: April 2011

Salivary pellicle is an organic biofilm formed by the physisorption of proteins and carbohydrates onto the surface of dental enamel exposed to the oral environment. The pellicle has several key roles in oral physiology including lubrication and reduction of friction between teeth during mastication, as well as chemical protection of the enamel against acidic solutions. However, pellicle proteins are known to react with dietary compounds to cause extrinsic staining on the tooth surface.

In this study, nanoindentation and AFM have been used in vitro to examine the acquired salivary pellicle formed in vivo on dental enamel. The mechanical properties, growth, structure and morphology of pellicle grown in vivo on human enamel surfaces have been analysed. In addition, the effects of dietary agents such as polyphenols on the pellicle's morphology and properties have been studied.

It was found that initial adsorption of proteins on the enamel surface occurred within 30 seconds of exposure to the oral cavity, with full growth achieved within 2 hours. Differences in the properties of the pellicles such as surface adhesion, and time dependent effects due to polyphenol interaction were measured using nanoindentation. It was seen that the polyphenol interaction has a significant effect on these properties. These results suggest that the stained pellicle is mechanically stiffer, but also less viscous and more fluid like. This could explain why traditional tooth brushing techniques do not efficiently remove this layer.
Computational Mechanics Routes to Explore the Origin of Mechanical Properties in a Biological Nanocomposite: Nacre
Authors: Katti Dinesh , Katti Kalpana
Published: April 2011

Nacre, the inner layer of seashells, is a laminated nanocomposite consisting of micron sized pseudo hexagonal aragonitic calcium carbonate platelets with about 20 nanometer thick organic layer sandwiched between the platelets. This nanocomposite has been studied extensively as a model system for the design of new biomimetic nanocomposites. The nano and micro architecture of nacre has many features and nuances, which have been attributed as possible reasons for the exceptional mechanical properties. In our work, we have used computational mechanics routes to model and simulate observed macro response, to quantitatively evaluate the contribution of various components of the nano and micro architecture of nacre to the mechanical properties. We also describe our discovery of platelet interlocks and their impact on the mechanical response of nacre. Our experiments on tensile failure and scanning electron microscopy of nacre specimens, and simulations using finite element modeling, indicate that the interlocks function as a physical restraint against free relative movement of platelets. Hence, these interlocking features need to yield/break before the complete transfer of load can occur to an intervening organic. The observed interlocks play a critical role in the mechanical response of nacre. During failure the features observed in the microstructure of nacre, such as relative rotation between platelet layers, platelet penetration, and other geometrical abnormalities such as an elongated side etc., appear not to be accidents of nature; they seem to exist for a purpose. These abnormalities lead to high toughness and strength, which is necessary for protecting the organism within the seashell.
Shrinkage Of Bone
Authors: Lees Sidney
Published: April 2011

Shrinkage of bone and other mineralized Type 1 collagen tissues when the tissue is dried has been observed for a long time. It is anisotropic with respect to the orientation of the bone structure. It is linearly dependent on the inverse wet tissue density (specific volume) in the radial direction but not in the axial direction. The volume fraction of water in the tissue has also been shown to be linearly dependent on the inverse and other wet density leading to a direct relation between the shrinkage and the volume fraction of water.

Shrinkage may be determined on any scale, macroscopic to microscopic but volume fraction of water is closely related to the lateral spacing of the collagen molecules, that is on the scale of nm. The linear dependence of shrinkage on volume fraction shows the generalized packing model underlies bone structure and is due to the properties of collagen molecules assembled in sheets.
Influence of Protein Structures on Mechanical Response
Authors: Ghosh Pijush , Katti Dinesh R. , Katti Kalpana
Published: April 2011

In biological nanocomposites such as bones, teeth and seashells, proteins play an important role in their mechanical response. Proteins in nacre, the inner layer of seashells have been shown to have exceptional mechanical properties. The secondary structures, β-sheets of protein when present close to each other in multiple numbers could take the shape of a planar β-sheath like structure or a β-barrel to form a domain. In natural proteins both these types of structures are commonly found. Effort has been made through this work to study the mechanical response of these β-planar sheath and β-barrel structures when subjected to external loads. Comparative study of the stress-deformation characteristics of these two types of structures has been made. The influence of shear force on the conformation of planar and barrel structure is investigated. Both these structures with almost similar number of amino acids have been extracted from one single spinach protein, Ferredoxin Reductase (1FNR). Steered molecular dynamics has been used to conduct these studies. The paper deals with the separation of the two domains from the main protein, simulation details and results comparing the responses.
Continuous force-displacement relationships for the human red blood cell at different erythrocytic developmental stages ofPlasmodium falciparummalaria parasite
Authors: Mills John P. , Qie Lan , Dao Ming , Tan Kevin S. W. , Lim Chwee Teck , Suresh Subra
Published: April 2011

Prior work involving either aspiration of infected cells into micropipette under suction pressure or deformation in laminar shear flow revealed that the malaria parasitePlasmodium (P.) falciparumcould result in significant stiffening of infected human red blood cells (RBCs). In this paper, we present optical tweezers studies of progressive changes to nonlinear mechanical response of infected RBCs at different developmental stages ofP. falciparum.From early ring stage to late trophozoite and schizont stages, up to an order of magnitude increase in shear modulus was found under controlled mechanical loading by combining experiments with three-dimensional computational simulations. These results provide novel approaches to study changes in mechanical deformability in the advanced stages of parasite development in the erythrocyte, and suggest a significantly greater stiffening of the red blood cell due toP. falciparuminvasion than that considered from previous studies.
Nanomechanics and Chemistry of Caries-Like Lesions in Dental Enamel
Authors: Dickinson Michelle E. , Mann Adrian B.
Published: April 2011

Dental enamel lesions are formed by the demineralisation of dental enamel due to dietary and bacterial factors which lower the local pH. If progression of this demineralisation continues the enamel structure eventually fails giving rise to a cavity (carie). Fortunately, in the earliest stages this process is reversible and if the pH of the environment increases, ions such as calcium, phosphate and fluoride can diffuse back into the enamel to give an arrested lesion. Hence, the tooth's structural integrity is preserved. The use of artificially produced enamel caries allows the study of lesion formation under conditions of highly controlled demineralisation. This provides a fundamental insight into the process of caries formation in enamel. In this study human premolars have been treated with a lactic acid solution to create artificial “caries-like” lesions in the enamel on the buccal side of the teeth. In the test samples the lesions penetrated around 100 μm into the enamel structure, accounting for approximately one tenth of the thickness of the enamel. Cross sections through the lesion were characterized with nanoindentation, electron probe micro-analysis and time of flight secondary ion mass spectrometry. From the data obtained maps of both mechanical and chemical properties were plotted across the entire width of the lesions. The results show that the lesions have a significantly reduced hardness and elastic modulus in comparison to sound enamel. These changes in mechanical properties were found to correlate with a loss of calcium and phosphate from the structure. There was also evidence of a stronger, less demineralised layer of enamel close to the lesion's surface. This surface zone is suggestive of remineralisation within the lesion which is of importance with regards to preventing the lesion developing into a carie.
Biodegradable Poly[bis(ethyl alanato)phosphazene] - Poly(lactide-co-glycolide) Blends: Miscibility and Osteocompatibility Evaluations
Authors: Nair Lakshmi S. , Bender Jared D. , Singh Anurima , Sethuraman Swaminathan , Greish Yaser E. , Brown Paul W. , Allcock Harry R. , Laurencin Cato T.
Published: April 2011

We have previously demonstrated that blending biodegradable glycine co-substituted polyphosphazenes with poly(lactide-co-glycolide) (PLAGA) results in novel biomaterials with versatile properties. The study showed that the degradation rate of polyphosphazene/PLAGA blends can be effectively controlled by varying the blend composition while at the same time the degradation products of polyphosphazenes effectively neutralized the acidic degradation products of PLAGA. In the present study, novel blends of hydrophobic, biodegradable polyphosphazene, poly[bis(ethyl alanato) phosphazene] (PNEA) and PLAGA (LA: GA; 85:15) were developed as candidates for bone tissue engineering applications. Two different blend compositions were developed by blending PNEA and PLAGA having weight ratios of 25:75 (Blend-1) and 50:50 (Blend-2) by the mutual solvent technique using dichloromethane as the solvent. The miscibility of the blends was determined using differential scanning calorimetry (DSC), fourier transform-infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). Surface analysis of the blends by SEM revealed a smooth uniform surface for Blend-1, whereas Blend-2 showed evidence of phase separation. PNEA is not completely miscible with PLAGA, as evidenced from DSC and FT-IR measurements. The osteocompatibilities of Blend-1 and Blend-2 were compared to those of parent polymers by following the adhesion and proliferation of primary rat osteoblast cells on two dimensional (2-D) polymer and blend films over a 21 day period in culture. Blend films showed significantly higher cell numbers on the surface compared to PLAGA and PNEA films.
Rheology and Biocompatibility of Poly(lactide)-poly(ethylene oxide)-poly(lactide) Hydrogels
Authors: Agrawal Sarvesh K. , Chin Kyuong S. , Sanabria-Delong Naomi , Aamer Khaled A. , Sardinha Heidi , Tew Gregory N. , Roberts Susan C. , Bhatia Surita R.
Published: April 2011

We report rheological data on hydrogels formed from triblock copolymers of poly(L-lactide) (PLLA) and poly(ethylene oxide) (PEO). We are able to create gels with elastic moduli greater than 10,000 Pa, which is an order of magnitude higher than previously achieved with related physically associated gels of similar chemistry. Moreover, the value of the elastic modulus strongly depends on PLLA block length, offering a mechanism to control the mechanical properties as desired for particular applications. Additionally, we have developed protocols for using these materials for cell encapsulation and present preliminary cell viability studies for encapsulated human liver cells (HepG2 cell line). Our results have implications for the design of new materials for soft tissue engineering, where native tissues have moduli in the kPa range.
Fabrication of Micro-Optical Devices by Holographic Interference of High Photosensitive Inorganic-Organic Hybrid Materials (Photo-HYBIRMER)
Authors: Kang Dong Jun , Kim Jin-Ki , Bae Byeong-Soo
Published: April 2011

Sol-gel derived photosensitive inorganic-organic hybrid materials (Photo-HYBRIMER) containing a large quantity of photoactive molecules exhibit the large changes in both refractive index (over 10-2) and volume (over 30%) on UV exposure. The materials could be used for direct fabrication of micro-optical devices using holographic interference. With the change of the beam number for holographic interference (1-beam, 2-beam, 3-beam and 4-beam interference), various typed micro-optical devices (Fresnel-type lens, 1D- and 2D-typed diffraction gratings) could be easily fabricated. Importantly, the fabricated micro-optical devices exhibited the very homogeneous surface structures and good optical performance.
An efficient top-emitting electroluminescent device on metal-laminated plastic substrate
Authors: Tan L. W. , Hao X. T. , Ong K. S. , Li Y. Q. , Zhu F. R.
Published: April 2011

An efficient flexible top-emitting organic light-emitting device (OLED) was fabricated on an aluminum-laminated polyethylene terephthalate substrate. A spin-coated light-emitting polymer layer was sandwiched between a silver anode and a multi-layered semitransparent cathode. The performance of polymer OLEDs was analyzed and compared with that of the devices having a conventional structure. An optical microcavity formed in the device enables to tune the emission color by varying the thickness of the active polymer layer. The OLEDs having a 110-nm-thick active polymer layer exhibited superior electroluminescence performance, with a turn-on voltage of 2.5V and a luminance efficiency of 4.56 cd/A at an operating voltage of 10V.
Prototyping of three-dimensional photonic crystal structures using electron-beam lithography
Authors: Subramania G. , Rivera J. M.
Published: April 2011

We demonstrate the fabrication of a three-dimensional woodpile photonic crystal in the near-infrared regime using a layer-by-layer approach involving electron-beam lithography and spin-on-glass planarization. Using this approach we have shown that we can make structures with lattice spacings as small as 550 nm with silicon as well as gold thus allowing for fabrication of photonic crystals with omnidirectional gap in the visible and near-IR. As a proof of concept we performed optical reflectivity and transmission measurements on a silicon structure which reveal peaks and valleys expected for a photonic band gap structure. The approach described here can be scaled down to smaller lattice constants (down to ∼400 nm) and can also be used with a variety of materials (dielectric and metallic) thus enabling rapid prototyping full three-dimensional photonic bandgap based photonic devices in the visible.
Writing Laser Power Dependence of Second Harmonic Generation in an Optically Poled Azo-dye/polymer Film
Authors: Wang C. H. , Tai Oliver Y.-H. , Wang Yuxiao
Published: April 2011

The time and power dependence of the optical poling process of an azo chromophore in the PMMA matrix at room temperature is investigated. A model previously proposed is used to account for the writing process of the optical poling of the chromophore/PMMA system. Theoretical predictions of the growth rate and the plateau SHG intensity are found to be in good agreement with the experimental result.
Phosphorescence Quantum Efficiency and Intermolecular Interaction of Iridium(III) Complexes in Co-Deposited Films with Organic Semiconducting Hosts
Authors: Kawamura Yuichiro , Goushi Kenichi , Brooks Jason , Brown Julie J. , Sasabe Hiroyuki , Adachi Chihaya
Published: April 2011

We accurately measured the absolute photoluminescence (PL) quantum efficiency (ηPL) of organic solid-state thin films by using an integrating sphere. We measured the ηPL of conventional organic materials used in organic light emitting diodes, such as a tris (8-quinolionolato)aluminum(III) complex (Alq3), and a phosphorescent 1.5mol%-fac-tris(2-phenylpyridyl)iridium(III):4, 4'-bis(carbazol-9-yl)-2, 2'-biphenyl [Ir(ppy)3:CBP] co-deposited film. Alq3 and Ir(ppy)3:CBP showed a ηPL = 20 ± 1% and 97 ± 2%, which corresponded well to external electroluminescence efficiency using these materials. We also measured red emitting bis[2-(2'-benzothienyl)pyridinato-N, C3'] (acetylacetonato) iridium(III) [Btp2Ir(acac)] with CBP, and the blue complex, bis[(4, 6-difluorophenyl)pyridinato-N, C2](picolinato)iridium(III) [FIrpic], with m-bis(N -carbazolyl)benzene. The maximum ηPL values for Btp2Ir(acac), and FIrpic were 51±1% (at 1.4mol%), and 99±1% (1.2mol%), respectively. These results suggest that the ηEL of red phosphorescent OLEDs using Btp2Ir(acac) as the dopant can be as high as 10%, and blue devices using FIrpic can reach the theoretical limit of 20%.
Synthesis of Dendridic NLO Chromophores for the Improvement of Order in Electro-optics
Authors: Sinness Jessica , Clot Olivier , Hammond Scott R. , Bhatambrekar Nishant , Rommel Harrison L. , Robinson Bruce , Jen Alex K-Y. , Dalton Larry
Published: April 2011

Previous research in organic electro-optics has shown dramatic increases in the hyperpolarizablity of NLO chromophores. However, this large microscopic activity has not been translated to the macroscopic domain. The polymeric electro-optic (E-O) materials continue to lack the high noncentrosymmetric order of the poled chromophores within the matrix necessary for high E-O response (r33). This deficiency of order represents one major obstacle that must be overcome before E-O device commercialization can be achieved. This lack of order is partially due to the large dipole moments of high μβ chromophores, which cause the chromophores to align in a centrosymmetric fashion through intermolecular electrostatic interactions. However, quantum calculations show that when the aspect ratio between the width and length of the chromophore system is adjusted to be greater than 1.4:1 by adding bulky side groups around the center of the chromophore, it would prevent side on pairing of the chromophores. This would cause a decrease in the large areas of centrosymmetric aggregation and thus allow for easier poling of the system. Here we report the synthesis of a nanoscale NLO architecture in which dendritic moieties have been incorporated around the center of the chromophore to give a three dimensional structure in order to achieve the 1.4:1 aspect ratio and maximize the macroscopic order of the system.
Optical Switching Devices Using Redox Polymer Nanosheet
Authors: Matsui Jun , Abe Kenichi , Mitsuishi Masaya , Aoki Atsushi , Miyashita Tokuji
Published: April 2011

Optical switching devices, which control the current direction by light stimuli, were constructed using redox polymer nanosheet assemblies. Two kind of nanosheet-photodiode, which can operate by different light irradiation wavelength were assembled in a series so that each current direction becomes opposite. In the nanosheet photodiodes, one photodiode contains ruthenium complex as a sensitizer and the other contains anthracene. When 460 nm light was irradiated to the nanosheet assemblies, only the photodiode containing the ruthenium complex becomes active and an anodic photocurrent was observed. On the other hand, when 390 nm light was irradiated to the photodiode assemblies, only the photodiode containing the anthracene chromophore becomes active and a cathodic photocurrent was observed. This means that we can control the photocurrent direction by 460 nm and 390 nm irradiation as input signals.
Influence of Halides on the Luminescence of Oxide/Anthracene/Polymer Nanocomposites
Authors: Szabó Dorothée V. , Reuter Heike , Schlabach Sabine , Lellig Christoph , Vollath Dieter
Published: April 2011

Nanocomposites made of an oxide core of a wide band gap insulator, a lumophore monolayer of anthracene and an outer protecting layer of PMMA are studied regarding their luminescence properties and the influence of halides stemming either from the precursor used for synthesis or from the lumophore itself. Halide-free nanocomposites exhibit luminescence spectra resembling to that of anthracene with some significant differences concerning the intensity ratio and an additional peak at 420 nm. Nanocomposites made from chlorides show excimer-like spectra with broad maxima. In microanalysis residual chlorine can be detected. Chlorine-free oxide kernels, coated with 9, 10 dichloroanthracene exhibit luminescence spectra resembling to a superposition of the pure lumophores 9 chloro- and 9, 10 dichloroanthracene. It can be shown that the origin of the halide strongly influences, but does not quench the luminescence spectra of the powders. Suspensions of the chlorine containing nanocomposites in ethanol exhibit modified anthracene like spectra. This is a strong indication for dechlorination by proton-transfer in ethanol. Suspensions of the same material in water lead to spectra showing a superposition of exci-mer spectrum and modified anthracene spectrum. Here a partial dechlorination occurs.
Self-assembled oligonucleotide semiconductor conjugated to GaN nanostructures for biophotonic applications
Authors: Neogi A. , Li J. , Sarkar A. , Neogi P. B. , Gorman B. , Golding T. , Morkoc H.
Published: April 2011

We investigate the optical properties of a new class of wide-bandgap semiconductor based biomaterial system. We have synthesized a guanosine derivative with a strong dipole moment, which self-assemble in ∼ 50 –100 nm confined pits to form a ribbon like semiconductor structure (SAGC). SAGC were successfully self-assembled on GaN/AlN QD matrix and the luminescence from GaN QDs can be resonantly transferred to the SAGC molecules resulting in a significant enhancement in emission from the guanine molecules. We also propose the design of ultraviolet-visible photonic bandgap structures based on hybrid SAGC-GaN photonic crystal.
Supernatant Controlled Synthesis of Monodispersed Zinc Sulfide Spheres and Multimers
Authors: Song Yanning , Liddell Chekesha M.
Published: April 2011

Uniform zinc sulfide spheres and multimers ranging in size from ∼ 90 nm to 1.0 micron were produced in large quantities by adding varying amount of supernatant in a secondary nucleation process. The particle morphology was investigated using scanning and transmission electron microscopy. Smaller particles exhibited increased surface roughness in the nitrate system. Characterization by x-ray and electron diffraction showed that the particles were built up from nanocrystallites. The relationship between the particle size, porosity, and refractive index was studied by modeling UV-Vis spectra using the Mie scattering method. Monodispersed zinc sulfide spheres and multimers in the size range from 100 nm to 600 nm can be used as high refractive index building blocks for photonic crystals with band gaps covering the entire visible spectrum as well as portions of the near-IR and UV regions.
Photoluminescence-structure relationships in ormosils for integrated optical devices
Authors: Sá Ferreira Rute , Molina Celso , Dahmouche Karim , Ribeiro Sidney , Gonçalves Rogéria R. , Bermudez Verónica de Zea , Carlos Luís Dias
Published: April 2011

Planar waveguides with low losses in the infrared (from 0.6–1.1 dB/cm) were prepared with sol-gel derived poly(oxyethylene)/siloxane hybrid doped with zirconium(IV) n-propoxide (ZPO) and methacryloxypropyltrimethoxysilane (MAPTMS). The doped nanohybrids were characterized by small angle X-ray scattering, 29Si nuclear magnetic resonance and photoluminescence spectroscopy and compared with the undoped hybrid material. The results indicate an effective interaction between the zirconium particles and the siliceous nanodomains.
Hierarchical Porous Silicas for Chromatographic Applications Obtained by Pseudomorphic Synthesis
Authors: Galarneau Anne , Iapichella Julien , Petitto Carolina , Renzo Francesco Di , Fajula François
Published: April 2011

Pseudomorphic transformation of pre-shaped silica beads into MCM-41 and MCM-48 is introduced as a new versatile procedure to independently control and finely tune the textural characteristics of advanced high-performance chromatographic supports at nano- and micrometer scale. The reaction takes place in the intergranular porosity of the parent silica-gel particle which acts as a nanoreactor. Because the resulting hybrid mesophase is metastable in its synthesis medium, the kinetics of each of the elementary steps – diffusion of hydroxide and surfactant, dissolution of parent silica, self-assembly, condensation of the new silica network-must be precisely controlled. In the paper examples are given of the preparation of discrete homodisperse spherical particles of MCM-41 and MCM-48, with pore sizes in the range 4 to 9 nm, form different silica sources.
Study of Relationship between Morphology and Mechanical Properties of SiO2-Polyacrylate Hybrid Nanocomposite
Authors: Kao Yi-Hsiao , Su Wei-Fang , Lin K. C.
Published: April 2011

The atomic force microscopic technique is utilized to study the spatial distribution of silica nanoparticles embedded in poly(tetraethylene glycol diacrylate) matrix. The cast samples of these hybrid materials show distinct mechanical property change as the weight ratio (SiO2/polyacrylate) reaches 40%. The morphological observation from spin-coated films on silicon substrates shows pronounced nanoparticle network formation correlated to the elasticity transition. The percolating particles reduce the local strain field, i.e. inhibit the deformation of the stratum, and cause the dramatic increase in the Young's modulus. Our experimental result is consistent with recent theoretical prediction [1].
Structure of Nanocomposite films of CdS nanoparticles in a polymer matrix
Authors: Luccio Tiziana Di , Nickel Bert , Antolini Francesco , Pentimalli Marzia , Tapfer Leander
Published: April 2011

A thiolate precursor was dispersed in a polymer solution and a precursor/polymer film was obtained by casting. Thermal annealing of the precursor/polymer film leads to the formation of a nanocomposite of nanometer-sized CdS dispersed in the polymer (thermolytic process). Different polymers were used as matrix material; in particular we employed a cyclo-olefin copolymer for its good optical properties and extremely low water absorption. After annealing with a temperature between 230 and 250°C in vacuum (pressure of about 6×10−3 mbar) the CdS nanoparticles are found to be crystalline with a diameter of about 2nm in size. The nanoparticle size can be increased up to 15nm by annealing at higher temperatures (300°C). The details of the structural properties of the nanocomposite films have been investigated by small and wide angle x-ray scattering (SAXS and WAXS, respectively). A simple dependence of the nanoparticle dimensions on the annealing temperature was found. Furthermore, SAXS measurements indicate that the separation between the nanoparticles compares with their diameter.
Octadecylphosphonic Acid Self-Assembled Monolayers as Lubricant Coatings Stable in Alkaline Media
Authors: Soullier J. , Tordjeman P. , Mutin P. H.
Published: April 2011

The formation of octadecylphosphonic acid self-assembled monolayers (SAMs) on titanium deposited by cathodic sputtering on planar substrates has been studied by water contact angle measurements and Atomic Force Microscopy (AFM). Dense monolayers were obtained after one week of reaction. Tribological experiments indicated that these monolayers had good lubricating properties, which were maintained after immersion in a 1 M NaOH solution at 65 °C for up to 100 min. The stability in alkaline media of octadecylphosphonic acid SAMs on titanium was ascribed to the high chemical stability of Ti-O-P interfacial bonds.
Er3+-doped Polyether/siloxane Hybrid Materials for Optoelectronics
Authors: Nunes S. C. , de Zea Bermudez V. , Sá Ferreira R. A. , Carlos L. D. , Morales E. , Marques P. V. S.
Published: April 2011

The sol-gel method was employed to obtain poly(oxyethylene) (POE)/siloxane hybrids (di-ureasils) doped with erbium triflate (Er(CF3SO3)3). The host hybrid matrix employed is composed of a siliceous framework to which short POE chains are covalently bonded through urea linkages (-NH(C(=O)NH-). Xerogels with ∞ > n ≥ 5 (where n, salt composition, is the molar ratio of OCH2CH2 moieties per Er ion) were analyzed. Samples with n ≥ 20 are amorphous. Those with n > 20 are thermally stable up to about 325 °C. In the di-ureasils proposed, the Er ions are active at room temperature (RT). Concentration effects on the quenching of the 1.53 mm emission intensity (excited at 488 nm) are negligible.
“Abrasion Resistant Coatings with Ultraviolet Absorption, via sol-gel dipping method.“
Authors: Arfsten Naiming , Alvarez Manuel A.
Published: April 2011

Multi-cpoxy functional - glycidyl ether is used as a cross-linking epoxy compound between modified 22'44'-tetrahydroxybenzophenone and silicone molecules. The adduct reaction products, as effective abrasion resistant coatings and yet reactive in the sol gel process, are formulated into the colloidal based polysiloxane resin as an essential part of the solution for dip coating sheets. Such coatings incorporate ultraviolet radiation selection or absorbing compounds with superb chemical stability and mechanical strength for coatings on substrates such as glass. The hardness of these coatings was measured at 6H following ASTM (D-3363) film hardness by pencil test. The resulting coatings were exposed to ultraviolet (UV-A) radiation during a time greater than 600 hours. The exposed samples still maintain excellent absorption in the UV range.
Two-Dimensional Crystalline Lattice Templating: A New Method for the Preparation of Polymer-Covered Metal and Alloyed Metal Nanorods by a Redox Process.
Authors: Pavel Alexandru C. , Romanovicz Dwight K. , Yacaman Miguel J. , McDevitt John T.
Published: April 2011

We demonstrate in this paper that two-dimensional (2-D) layered ceramics, materials that are highly anisotropic in terms of structure and properties can be used to induce the formation of polymer-covered metal nanorods. The procedure took advantage of the intrinsic planar, layered ordering of the metal cations suitable to be reduced and can be further used to engineer one-dimensional (1-D) metal alloy nanostructures by appropriate doping of the initial layered ceramic lattice with suitable cationic species. The procedure involved the formation in an intermediate step of a polymer-layered ceramic nanocomposite, highly porous to the diffusion of the reducing agent. Two structurally similar layered bismuthates, Bi2Sr2CaCu2O8+δand Bi6Sr2CaO12were used as the precursor layered ceramics and the redox-active metal cations were Cu2+and Bi3+.
Monolithic O/I-Hybrids with Hierarchically Ordered Meso- and Macropores
Authors: Nakanishi Kazuki , Kobayashi Yuki , Amatani Tomohiko , Hirao Kazuyuki , Kodaira Tetsuya
Published: April 2011

Organic-Inorganic hybrid gels with hierarchical well-defined macropores and supramolecularly templated mesopores with long-range orders have been synthesized in the systems of bridged poly(silsesquioxane) systems. Nonionic surfactants such as poly(ethyleneglycol)-poly(propyleneglycol)- poly(ethyleneglycol) triblock copolymers, EOPOEOs, were found to be effective both in inducing the phase separation to give macroporous morphology and in templating the mesopores with narrow size distribution. The number of methylene units in the bridge, changed from 1 to 6 in the present experiments, affected both the phase separation tendency and template strength. In the system containing 1, 2-bis(trimethoxysilyl)ethane, 2D-hexagonal arrangement of mesopores have been prepared in the gel skeleton comprising the well-defined continuous macroporous network with an aid of micelle-stabilizing agent.