bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Temperature Dependent Damping Behavior of Novel Nanocomposites for Structural Materials Applications
Authors: Asmatulu Ramazan , Claus Rick , Mecham Jeff , Inman Dan 
Published: April 2011

ABSTRACTNear nanoscale fine particles including vanadium dioxide (VO2) and zinc oxide (ZnO) were incorporated into matrix materials (tin and polymer adhesives). A number of mechanical damping tests were conducted on the prepared composite materials at frequency ranges of 0 − 2 kHz and over a broad temperature range. The mechanical vibration test results showed that VO2 and ZnO gave significantly higher negative-stiffness (or damping) at approximately 68 °C (155 F) and 29 °C (85 F). For example, approximately 15% and 12% damping values were achieved at first and second resonance frequencies, respectively, which can potentially prevent vibration on the materials. This significant improvement on the damping of the nanocomposite material may be because of the ferroelasticity, viscoelasticity and/or interfacial sliding at those particular temperatures. It was also observed the etching of substrate surfaces improved adhesion and contributed consistent results to vibration testing reproducibility. Thus, it is concluded that nanocomposite existing damping properties can be an important method to achieve large damping responses over a broad temperature range.
Effect of nm-Thin Inorganic Layered Fillers on the Crystallization of Polymer Nanocomposites
Authors: Nakajima H. , Wang Z. M. , Strawhecker K. , Manias E. 
Published: April 2011

ABSTRACTThe crystallization behavior of polymers in nanocomposites with inorganic fillers (montmorillonite layered silicate, MMT) is reviewed. Various different polymers are comparatively discussed [poly(vinyl alcohol) (PVA), polypropylene (PP), syndiotactic-polystyrene (sPS), and poly(ethylene oxide) (PEO)] representing three types of filler/matrix interactions: strong specific interactions (PVA/MMT), weak/negligible interactions (sPS and PP/o-MMT), and “unfavorable” (PEO/MMT). In the case of PVA/MMT, crystallization of PVA is strongly promoted by MMT, also stabilizing a new crystal form not found in bulk PVA. For sPS and PP/o-MMT, crystallization is only moderately affected, exhibiting traces of simple heterogeneous nucleation and mostly bulk-like crystal structures, with very small traces on non-bulk crystals. For PEO, crystallization is impeded near the MMT surfaces, due to coordination of the surface cations to the PEO. In all cases smaller spherulite sizes develop when filler is added, independent of the size of the bulk polymer spherulites, whereas the crystallization temperature changes reflect the strength of the polymer/surface interactions.
Characterization of Strain-Tolerant Ceramic/SAM Bilayer Coatings
Authors: Yang Q. , Salami T. O. , Chitre K. , Oliver S. R. , Cho J. 
Published: April 2011

ABSTRACTCeramic coatings can provide an ideal protection for MEMS (MicroElectroMechanical Systems) structures while imposing a great challenge in processing a prime, reliant coating due to their inherent brittleness and defects formed during processing. In an attempt to compensate for the weakness of the ceramic coating, we have developed a low-temperature solution precursor process to create strain-tolerant, protective bilayer coating consisting of an integrated ceramic-organic hybrid material. The top ceramic coating offers an inert, protective layer whereas the underlying nanometer scale self-assembled organic coating provides compliance for the overlying hard coating. Together, these bilayers minimize mechanical and thermal stresses. In addition, organic self-assembled monolayers(SAM) act as a ‘template’ by forming a proper surface functionality for the subsequent growth of hard ceramic coatings. Molecular level understanding of the microstructure and micromechanics involved in the synthesis and processing of the coating is systematically studied by a variety of characterization techniques such as XRD, AFM, SEM/EDS and nanoindentation. This work is also complemented by numerical simulation to provide a clearer understanding of the stress development in the ceramic coating and its interfacial properties.
Deformation Processes during Indentation of Mesoporous Silica Thin Films
Authors: Klotz M. , Perriot A. , Barthel E. 
Published: April 2011

ABSTRACTNanoindentation was used to probe the mechanical response of mesoporous silica films as a function of processing treatment. A contrasted behaviour appears between low temperature processed films which retain the templating agent and are thus little compressible, and high temperature processed films, which are more condensed and also exhibit high porosity. We suggest that the behaviour of the former is dominated by shear flow, at least above a given threshold, while the latter are characterized by a yield strength in compression as is commonly found in porous materials. The response to indentation allows fast qualitative comparison of mechanical responses: in the present work, we show that a fast UV-O3 treatment results in mechanical properties which are undistinguishable from a much more cumbersome high temperature heat treatment.
Production and Mechanical Properties of Nanocrystalline Intermetallics Based on TiAl3-X
Authors: Calderon H. A. , Aguilar-Virgen J. C. , Cruz-Gandarilla F. , Umemoto M. 
Published: April 2011

ABSTRACTProduction of intermetallic materials in the system TiAl3-X (X = Cr, Mn, Fe) has been achieved by means of mechanical milling and sintering techniques. Spark plasma sintering is used since it reduces time at high temperature and inhibits grain growth. The produced materials have grain sizes in the nano and microscale depending on the material and processing variables. The TiAl3-X alloys are formed mostly by the cubic L12 phase. The average grain size ranges between 30 and 50 nm in the as sintered condition. Aging at elevated temperature has been used to promote grain growth. Compression tests have been performed to evaluate mechanical properties as a function of temperature and grain size. In all cases yield stresses higher that 700 MPa are obtained together with a ductility that depends upon temperature and grain size. No ductility is found for the smallest grains sizes tested (30 nm) at room temperature. Above 673 K, these materials show ductility and additionally they present a quasi superplastic behavior at temperatures higher that 973 K. On the other hand ductility can also be developed in the TiAl3-X alloys by inducing grain growth via annealing. Alloys with grains sizes around 500 nm show high ductility and a large density of microcraks after deformation suggesting that the yield strenght becomes lower than the stress to propagate the cracks. In such materials, a considerably high strength is retained up to 873 K.
Mechanical Properties of Boron Doped Diamond Films Prepared by MPCVD
Authors: Liang Qi , Catledge Shane A. , Vohra Yogesh K. 
Published: April 2011

ABSTRACTA chemical vapor deposition hydrogen/methane/nitrogen feedgas mixture with unconventionally high methane (15% CH4 by volume) normally used to grow ultra-hard and smooth nanostructured diamond films on Ti-6Al-4V alloy substrates was modified to include diborane (10% B2H6 in hydrogen) for boron-doping. The flow rate for B2H6 was varied to investigate its effect on plasma chemistry, film structure, and mechanical properties. It was found that boron in the plasma can easily be incorporated into diamond films and change the lattice parameter and affect film structure as measured by Raman spectroscopy. Grazing angle x-ray diffraction shows a strong dependence of diamond lattice parameter with diborane flow rate and B2H6:CH4 flow rate ratio. Thermal stability of these films was evaluated by heating in an oxygen environment above 700 °C. Nanoindentation measurements show that the films have high hardness close to that of nanostructured diamond. High film hardness and toughness, combined with good thermal stability and low surface roughness indicate great potential as wear resistant coatings able to withstand high temperature oxidizing environments.
Channeling Study of the Damage Induced in Ion-Irradiated Ceramic Oxides
Authors: Thomé Lionel , Gentils Aurélie , Garrido Frédérico , Jagielski Jacek 
Published: April 2011

ABSTRACTThe evaluation of the damage generated in crystalline ceramic oxides placed in a radiative environment is a major challenge in many technological domains. The use of the channeling technique is particularly well adapted to measure the depth distribution of the irradiation-induced disorder and to monitor the damage build-up. This paper describes the methodology used for the study of radiation damage with the channeling technique, presents a new method of analysis of channeling data based on Monte-Carlo simulations and provides recent results concerning the damage induced in ion-bombarded ceramic oxide single crystals in both nuclear (low-energy ion irradiation) and electronic (high-energy ion irradiation) slowing-down regimes.
Surface Modification of γ - Al2O3 nanoparticles by Electron Co-irradiation-induced Graft polymerization of MMA
Authors: Xiang X. , Zu X.T. , Wang Z.G. , Jiang B. 
Published: April 2011

ABSTRACTElectron beam co-irradiation graft polymerization has been carried out up to an absorbed dose of 30 kGy in air at room temperature between methyl methacrylate (MMA) monomer and γ- Al2O3 nanoparticles and micronparticles, respectively. The results showed that the percent graft of nano-Al2O3 and micron-Al2O3 is 6.4% and 0.9%, respectively. In the FT-IR spectra of irradiated nanoparticles, there was a new absorption peak at 1725 cm-1 that was attributed to carbonyl stretching vibration and Al-O-C bonds forming on the surface of nanoparitcle. But in the spectra of micron-Al2O3, the absorption peak at 1725 cm-1 was very weak. X-ray photoelectron spectroscopy (XPS) measurements confirmed the existence of carbonyl. The UV absorption intensities of two γ- Al2O3 powders strengthened after irradiation graft polymerization. These results showed that MMA has been successfully grafted onto nano-Al2O3 surface at the dose of 30 kGy. However, there were few new chemical bonds on micron-Al2O3 surface. It could be deduced that irradiation graft polymerization of γ- Al2O3 nanoparticles was easier than that of micronparticles.
Electron-irradiation-induced Changes of martensitic transformation characteristics in TiNi shape memory alloys
Authors: Zu X. T. , You L.P. , Zhu S. , Wang Z. G. , Wu J. H. , Wang L. M. 
Published: April 2011

ABSTRACTTiNi shape memory alloy samples were irradiated within R-phase by 1.7 MeV electrons with different doses. The martensitic transformation temperatures were measured by Differential Scanning Calorimeter (DSC). The results indicated that the temperature Ms of the onset of R-phase-to-martensite transformation decreased with increasing the dose. The electron irradiation had a slight effect on the other transformation temperatures. The second lifetime of positrons determined by Positron Annihilation Technology were lowered with an increment of the irradiated dose. Relaxation of the elastic stress fields around the Ti3Ni4 precipitates was the cause of the observed change of the transformation characteristics because of the migration and accumulation of electron irradiation-induced point defects.
Atomistic simulations of threshold displacement energies in SiO2
Authors: Mota F. , Caturla M.-J. , Perlado J.M. , Dominguez E. , Kubota A. 
Published: April 2011

ABSTRACTSilica is one of the candidate materials for final focusing mirrors in inertial fusion reactors. This material will be exposed to high neutron irradiation fluxes during operation. Radiation damage results in point defects that can lead to obscuration of this material; that is, degradation of the optical properties of silica. In this paper we present molecular dynamic simulations of defect production in silica glass. Results on the threshold displacement energies due to oxygen Primary Knock-on Atoms (PKA) are reported concluding that a range of energies (20–40 eV) exists in which the defects have a probability to be created. In addition, we determine a range of distances for a PKA to become a stable defect out of its original position. Our present analysis is focused on the formation of Oxygen Deficient Centers (ODC).
Isotope and Dose Effects in Low-Energy H/D Blistering of Silicon: Narrow Operational Window for Ion-Cutting at < 100 nm
Authors: Moutanabbir O. , Terreault B. , Shaffer E. , Ross G. G. 
Published: April 2011

ABSTRACTHydrogen ion blistering has applications in the fabrication of silicon-on-insulator and other devices. Si (001) samples implanted with different fluences of 5 keV H or D ions were rapidly thermal annealed under vacuum. The surface morphology studied by atomic force microscopy revealed that: (1) there is not only a threshold fluence but also a maximum fluence for blistering; and (2) there is a giant isotope effect: The H and D blistering fluence “windows” are (1.5–3.5) × 1016 H cm-2 and (4–8) × 1016 D cm-2 respectively. Due to the higher fluences and higher gas pressure, D blisters are larger (80% surface coverage) than H blisters (60% coverage) and twice as voluminous. Raman spectroscopy and thermal desorption spectrometry suggest that the high fluence blister absence and the giant isotope effect are both connected with an enhancement of the Si–H/D bond stability.
Enhancement effect of photoluminescence in Si nanocrystals by phosphorus implantation
Authors: Kim Joonkon , Woo H.J. , Choi H.W. , Kim G.D. , Hong W. 
Published: April 2011

ABSTRACTDifferent from bulk silicon crystal, nano-sized Si crystalline embedded in dielectric medium is known as an efficient light emitting center. In nano-crystalline Si, excitonic electron-hole pairs are considered to be attributed to radiative recombination. But the defects surrounding crystalline nc-Si suppress light emitting, which works as a non-radiative decay path. Hydrogen is usually utilized in order to encapsulate the dangling bonds in the Si:SiO2 interface, dramatically enhancing luminescence yield from nc-Si embedded in dielectric medium. Unfortunately because hydrogen has higher mobility in the matrix, subsequent thermal processes may reduce the enhancement effect. Thus instead of easily reversible hydrogen, phosphorus was introduced by implantation, and was to have the same effect and to be resistive to thermal treatments. Samples were prepared by 400 keV Si implantation with dose of 1 × 1017 Si /cm2 and by multi-energy P implantation to make relatively uniform P concentration in the region where implanted Si ions are distributed. Precipitation of crystalline silicon was obtained by annealing at 1100°C for 2 hour in pure Ar environment. Experimental data such as enhancement effect of PL yield, decay time, peak shift for the phosphorus implanted nano-crystalline Si are shown, and the possible mechanisms are discussed.
Effects of Surfactants N and Br on Ordering in GaInP
Authors: Chapman D.C. , Howard A.D. , Rieth L. , Wixom R.R. , Stringfellow G.B 
Published: April 2011

ABSTRACTFormation of the CuPt ordered structure during the organometallic vapor phase epitaxial (OMVPE) growth of GaInP has significant effects on the electrical and optical properties, necessitating control of ordering. Formation of the CuPt structure is thermodynamically driven by the surface structure during growth. This has led to the study of the use of surfactants as a way of controlling ordering. To date, these studies have centered on the group V elements isoelectronic with P. Sb and Bi are both larger than P. This leads to less ordering. N, on the other hand, is smaller than P, which makes it potentially interesting. The other disordering mechanism, observed for Te as a surfactant in GaInP, is kinetic. Rapid step propagation leads to a reduction in ordering. This suggests another potentially interesting class of surfactants, the group VII elements, such as Br, that have been reported to increase the step velocity during OMVPE growth. This paper describes the results of the addition of the surfactants N and Br during the OMVPE growth of GaInP. Addition of N (DMHy) results in a clear reduction in order parameter, due to thermodynamic effects. The addition of Br (CBr4) is also observed to systematically decrease the amount of CuPt ordering and is found to correspond to a significant roughening of the surface, which is postulated to be the origin of the reduction in order parameter.
Quadruple-period ordering in MBE GaAsSb alloys
Authors: Batyrev Iskander G. , Norman Andrew G. , Zhang Shengbai , Wei Su-Huai 
Published: April 2011

ABSTRACTExperimental and theoretical studies are reported for a quadruple period ordering found in GaAsSb alloy layers grown by molecular beam epitaxy at high growth temperatures. We propose a growth model that accounts for the observed three-dimensional (3D) ordered structure. It is shown that the already-ordered material in the previously grown layer affects the reconstruction of the growth front with respect to the underlying alloy template resulting in the correct stacking of the individual 2D ordered layers into the observed 3D ordered structure.
1.5 micron InAs quantum dot lasers based on metamorphic InGaAs/GaAs heterostructures.
Authors: Ustinov V.M. , Zhukov A.E. , Kovsh A.R. , Maleev N.A. , Mikhrin S.S. , Vasil'ev A.P. , Nikitina E.V. , Semenova E.S. , Kryzhanovskaya N.V. , Musikhin Yu.G. , Shernyakov Yu.M. , Maximov M.V. , Ledentsov N.N. , Bimberg D. , Alferov Zh.I. 
Published: April 2011

ABSTRACT1.5 micron range emission has been realized using the InAs quantum dots embedded into the metamorphic InGaAs layer containing 20% of InAs grown by MBE on a GaAs substrate. Growth regimes were optimized to reduce significantly the density of dislocations propagating into the active layer from the lattice mismatched interface. 2 mm long InGaAs/InGaAlAs lasers with 10 planes of quantum dots in the active region showed threshold current density about 1.4 kA/cm2 with the external differential efficiency as high as 38%. Lasing wavelength depends on the optical loss being in the 1.44–1.49 micron range at room temperature. On increasing the temperature the wavelength reaches 1.515 micron at 85C while the threshold current characteristic temperature of 55–60K was estimated. High internal quantum efficiency (η>60%)and low internal losses (α=3–4 cm ) were realized. Maximum room temperature output power in pulsed regime as high as 5.5 W for 100 micron wide stripe was demonstrated. Using the same concept 1.3 micron InGaAs/InGaAlAs quantum well lasers were fabricated. The active region contained quantum wells with high (∼40%) indium content which was possible due to the intermediate InGaAs strain relaxation layer. 1 mm stripe lasers showed room temperature threshold current densities about 3.3 kA/cm (λ=1.29 micron) and 400 A/cm2 at 85K. Thus, the use of metamorphic InGaAs layers on GaAs substrate is a very promising approach for increasing the emission wavelength of GaAs based lasers.
Instabilities, Elasticity, and Wetting Effect in Multilayer Heteroepitaxial Growth
Authors: Huang Zhi-Feng , Desai Rashmi C. 
Published: April 2011

ABSTRACTFor multilayer semiconductor films comprising various material layers, the coupling of elastic states in different layers as well as the nonequilibrium nature of the growing process are essential in understanding the surface and interface morphological instability and hence the growth mechanisms of nanostructures in the overall film. We present the theoretical work on the stress-driven instabilities during the heteroepitaxial growth of multilayers, based on the elastic analysis and the continuous nonequilibrium model. We develop a general theory which determines the morphological evolution of surface profile of the multilayer system, and then apply the results to two types of periodic structures that are being actively investigated: alternating tensile/compressive and strained/spacer multilayers. The wetting effect, which arises from the material properties changing across layer-layer interfaces, is incorporated. It exhibits a significant influence of stabilization on film morphology, particularly for the short-period superlattices. Our results are consistent with the experimental observations in AlAs/InAs/InP(001) and Ge/Si(001) multilayer structures.
Hexagonal Lattice Photonic Crystal in Active Metallic Microcavity
Authors: Tam H. L. , Huber R. , Li K. F. , Wong W. H. , Pun Y. B. , So S. K. , Xia J. B. , Cheah K. W. 
Published: April 2011

ABSTRACTA hexagonal lattice photonic crystal was fabricated inside the metallic microcavity. And a thin film of Alq3 was incorporated inside the textured cavity as an active medium. The microcavity is designed such that the modified photonic modes due to the textured structure can couple to the excited electronic states of Alq3. This leads to changes in the emission characteristics of Alq3. From the angle-resolved transmission (ARTR) results, the photonic bandgap was observed at all angles from normal incident to 60°. The presence of surface plasmon (SP) was observed in both TM and TE modes of the transmission. Compare to the bulk Alq3 photoluminescence spectrum, significant modification of the photoluminescence (PL) spectrum was observed in the angle-resolved photoluminescence (ARPL). The photoluminescence spectra showed clear suppression in luminescence intensity for the range inside the photonic bandgap. We use decouple approximation for the standing wave modes and derive the photonic waveguide characteristics for two-dimensional textured metallic microcavities. The theoretical result is in good agreement to the experimental result.
Characterization By Variable Angle Spectroscopic Ellipsometry Of Dielectric Columnar Thin Films Produced By Glancing Angle Deposition
Authors: Gospodyn James , Brett Michael J. , Sit Jeremy C. 
Published: April 2011

ABSTRACTThin films composed of MgF2 and TiO2 were grown by glancing flux incidence, where the physical vapor flux arrives at the substrate between 80° and 90° with respect to substrate normal. The resulting films are composed of slanted columns inclined toward the incoming flux. The films were modeled using the Bruggemann effective medium approximation (EMA) and were found to be biaxial with one of the principal indices of refraction along the direction of the posts. The indices of refraction for MgF2 and TiO2 films were found to be in the range of 1.06 to 1.2 and 1.36 to 1.62, respectively, at a wavelength of 600 nm. The indices of refraction were found to decrease as the deposition angle increased. The film density was also found to be independent of the film thickness for films ranging in thickness from 500 nm to 3400 nm.
Photonic Crystal Tapers for Coupling Large Ridge Waveguides to Photonic Crystal Waveguides
Authors: Ndi Francis C. , Toulouse Jean 
Published: April 2011

ABSTRACTWe present a study of various photonic crystal taper structures each characterized by the taper angle and roughness for coupling light into 2-dimensional photonic crystal waveguides from large ridge waveguides. The photonic crystal waveguide is made of a triangular lattice of holes in a dielectric. The objective is to find a taper structure that offers the best coupling efficiency over a range of widths of the ridge waveguide while leaving a small footprint. We show that such a structure indeed exists and can be further optimized as the width of the ridge waveguide gets even larger leading to more than 90% increase in coupling efficiency in some cases.