bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanisms of Single-Wall Carbon Nanotube Growth by the Laser Vaporization Technique: In Situ Imaging and Spectroscopy
Authors: Geohegan D. B. , Puretzky A. A. , Fan X. , Guillorn M. A. , Simpson M. L. , Merkulov V. I. , Pennycook S. J. 
Published: April 2011

ABSTRACTSingle-wall carbon nanotubes are formed by Nd:YAG laser vaporization of a graphite/(1 at. % Ni, 1 at. % Co) target into flowing argon (500 Torr) within a quartz tube furnace (1000 °C). Here, this process is investigated for the first time with time-resolved laser-induced luminescence imaging and spectroscopy of Co atoms, C2 and C3 molecules, and clusters. These measurements under actual synthesis conditions show that the plume of vaporized material is segregated and confined within a vortex ring which maintains a ˜1 cm3 volume for several seconds. Using time-resolved spectroscopy and spectroscopic imaging, the time for conversion of atomic and molecular species to clusters was measured for both carbon (200 μs) and cobalt (2 ms). This rapid conversion of carbon to nanoparticles, combined with transmission electron microscopy analysis of the collected deposits, indicate that nanotube growth occurs during several seconds of time from a feedstock of mixed nanoparticles in the gas-suspended plume. Using these in situ diagnostics to adjust the time spent by the plume within the high-temperature zone, single-walled nanotubes of controlled length were grown at an estimated rate of 0.2 μm/s.
Elastic Constants of Diamond-Like Carbon Films by Surface Brillouin Scattering
Authors: Ferrari A.C. , Robertson J. , Pastorelli R. , Beghi M.G. , Bottani C.E. 
Published: April 2011

ABSTRACTThe elastic constants of thin Diamond-Like Carbon (DLC) films supply important information, but their measurement is difficult. Standard nanoindentation does not directly measure the elastic constants and has strong limitations particularly in the case of hard thin films on softer substrates, such as tetrahedral amorphous carbon on Si. Surface acoustic waves provide a better mean to investigate elastic properties. Surface Brillouin scattering (SBS) intrinsically probes acoustic waves of the wavelength which is appropriate to test the properties of films in the tens to hundreds of nanometers thickness range. SBS can be used to derive all the isotropic elastic constants of hard-on-soft and soft-on-hard amorphous carbon films of different kinds, with thickness down to less than 10 nm. The results help to resolve the previous uncertainties in mechanical data. The Young's modulus of tetrahedral amorphous carbon (ta-C) turns out to be lower than that of diamond, while the moduli of hydrogenated ta-C (ta-C:H) are considerably lower than those of ta-C because of the weakening effect of C-H bonding.
Observation of Blue Emission from ECR-CVD Deposited Amorphous Hydrogenated Silicon Carbide
Authors: Rusli J. Cui , Yoon S. F. , Yu M. B. , Chew K. , Ahn J. , Zhang Q. 
Published: April 2011

ABSTRACTAmorphous hydrogenated silicon carbide (a-Sil-xCx:H) thin films have been deposited by the electron cyclotron resonance chemical vapor deposition (ECR-CVD) technique at different microwave powers from 100W to 1000W. The films were characterized in terms of their optical absorption and photoluminescence (PL). Their optical band gap E04 ranged from 3.06eV to 3.54eV and when excited at 363.8nm from an Ar+ ion laser, the PL peak emission energy Epl, was found to range from 2.44eV to 2.79eV, corresponding to green to blue emission. The effects of excitation energy Eex, on Epl, and FWHM of the PL spectra were also investigated. A linear relation between the FWHM and Urbach tail width E0was noted, suggesting that the PL bandwidth is mainly contributed by static disorder. The blue emission observed in these a-S1-x-Cx:H films is promising for their applications in large area flat panel displays.
Structure, Properties, and Applications of Single Crystalline Films of Vinylidene Fluoride and Trifluoroethylene Copolymers
Authors: Ohigashi H. 
Published: April 2011

AbstractThe single crystalline (SC) film of copolymer of vinylidene fluoride and trifluoroethylene is a highly crystallized; highly double-oriented, and optically transparent ferroelectric film, which can be prepared by annealing a uniaxially drawn film in the paraelectric phase with its ends being clamped and its surfaces free. The SC film is composed of endlessly extended chain crystals whose c-axis aligns along the stretching direction almost perfectly and the polar b-axis is oriented ±π/6 off the film normal. It does not contain lamellar crystals nor amorphous phase. Owing to such unique structure, the SC film exhibits the ferroelectricity and related properties inherent to the crystal more clearly than the films composed of lamellar crystals. In this paper, we present the results of our recent studies on the SC films: (1) the structure and morphology studied by POM and X-ray diffiractions; (2) the ferroelectric, piezoelectric, and mechanical properties in the ferroelectric phase; (3) molecular chain motions in the paraelectric phase as revealed by dielectric, X-ray diffraction and shear mechanical studies; and (4) applications to shear ultrasonic transducers. The followings are the main results to be emphasized: (A) the Young's modulus in the direction along the stretching axis is much larger (120 GPa at 10K) than that of LC films (15 GPa); (B) the SC film is the most effective piezoelectric polymer film among piezoelectric polymers; (C) the SC film in the paraelectric phase is a liquid crystal of ID-liquid and 2D-solid, and each chain molecule of TGTG' conformation undergoes rotational and flip-flop motions independently of neighboring chains in a highly regular hexagonal crystal lattice, which leads to anomalous dielectric behaviors in the paraelectric phase; (D) SC film transducers for shear ultrasonic waves are effectively usable for NDE.
Effects of Sample Processing and High-Energy Electron Irradiation Conditions on the Structural and Transitional Properties of P(VDF-TrFE) Copolymer Films
Authors: Bharti Vivek , Cheng Z.-Y , Xu H. S. , Shanthi G. , Xu T.-B. , Mai T. , Zhang Q. M. 
Published: April 2011

AbstractRecently it has been demonstrated that using a high electron energy irradiation, the electromechanical properties of polyvinylidene fluoride - trifluoroethylene, P(VDF-TrFE) copolymers can be improved significantly for example; high electric field induced strain (∼ 4.5%) with high elastic energy density, high dielectric constant (∼ 65 with loss less than at 1kHz), high piezoelectric coefficient (∼ 350 pm/V ) and high electro-mechanical coupling coefficient (∼0.45). It was found, depending on sample processing and electron irradiation conditions these properties can be controlled. In this talk we will present the experimental data on the effect of processing and irradiation conditions on structural and transitional behavior of copolymers. These structural information coupled with the electro-mechanical properties will be presented in order to show the possibilities for further improvement.
Analysis of Ferroelectric Switching Process in VDF/Trfe Copolymers
Authors: Kano Kenji , Kodama Hidekazu , Takahashi Yoshiyuki , Furukawa Takeo 
Published: April 2011

AbstractThe ferroelectric switching curve of vinylidene fluoride / trifluoroethylene copolymer exhibits a characteristic time evolution consisting of two processes; an initial gradual increase in proportion to t0 5 followed by a rapid increase according to an exponential function with particularly large exponent 6. Such a switching curve was analyzed by means of computer simulation based on a modified nucleation-growth mechanism. It was found that the initial gradual increase is attributed to generation of considerably large nuclei that grow according to a random-walk scheme. Once such nuclei gain a critical size, they start to grow automatically either one or two dimensionally. The time required to generate critical nuclei serves as an incubation time for the later growth process to result in the large exponent.
Grain Boundary Structure and Sliding of Alumina Bicrystals
Authors: Ikuhara Y. , Watanabe T. , Yarnamoto T. , Saito T. , Yoshida H. , Sakuma T. 
Published: April 2011

AbstractAlumina bicrystals were fabricated by a hot joining technique at 1500°C in air to obtain ten kinds of [0001] symmetric tilt grain boundaries which included small angle, CSL and high angle grain boundaries. Their grain boundary structures were investigated by high-resolution electron microscopy (HREM), and the respective grain boundary energies were systematically measured by a thermal grooving technique. It was found that grain boundary energy strongly depended on the grain boundary characters, e.g., there were large energy cusps at low Σ CSL grain boundaries. But, main part of grain boundary energy is likely to be due to the strain energy around the grain boundary, and the contribution of atomic configuration is not so large. Small angle grain boundaries were consisted of an array of partial dislocation with Burgers vector of 1/3[1100] to form the stacking faults between the dislocations. The behavior of grain boundary sliding was also investigated for typical grain boundaries by high-temperature creep test at 1400°C. As the result, the occurrence of grain boundary sliding was found to depend on the grain boundary atomic structure.
Flow Stress and Elongation of Superplastic Deformation in La55Al25Ni20 Metallic Glass
Authors: Kawamura Y. , Inoue A. 
Published: April 2011

AbstractWe have investigated the flow stress and elongation of superplastic deformation in a La55Al25Ni20 (at%) metallic glass that has a wide supercooled liquid region of 72 K before crystallization. The superplasticity that appeared in the supercooled liquid region was generated by the Newtonian viscous flow that exhibits the m value of unity. The elongation to failure was restricted by the transition of the Newtonian flow to non-Newtonian one and the crystallization during deformation. We succeeded in establishing the constitutive formulation of the flow stress in the supercooled liquid region. Its formulation was expressed very well by a stretched exponential function σflow=Dε exp(H*/RT) [1-exp(E/{ε exp(H**/RT)}0.82)]. Formulations describing the elongation to failure in constant-strain-rate and constant-crosshead velocity tests were, moreover, established. It was found from the simulation that the maximum elongation in the constant-strain-rate test reached more than 106% which was two orders of magnitude larger than that in the constant-crosshead-velocity test.
Analysis of Cavitation in a Near-γ Titanium Aluminide During High-Temperature/Superplastic Deformation
Authors: Lombard Carl M. , Ghosh Amit K. , Semiatin S. Lee 
Published: April 2011

AbstractThe superplastic flow behavior of a near-γ titanium aluminide (Ti-45.5Al-2Cr-2Nb) is determined under uniaxial tension in as-rolled or rolled-and-heat treated conditions (1177°C/4 hr or 1238°C/2 hr). Cavitation characteristics, including cavity growth rates, are established via isothermal, constant strain rate tests conducted at 10−4 to 10−2 s−1 and temperatures between 900°C and 1200°C. Differences in cavitation as a function of initial structure, strain, strain rate and temperature are noted. Cavity growth is found to be largely plasticity controlled. Experimental growth rates are compared with equations that predict rates as a function of strain rate sensitivity. Although the equations assume no coalescence and no nucleation of new cavities, which are experimentally observed, they are useful in predicting actual growth rates.
Stress-Induced Martensite in NiTi Corrugated Films
Authors: Wuttig Manfred , Slutsker J. S. , Mori Kiyotaka , Li Jiang 
Published: April 2011

AbstractFilms deposited on corrugated surfaces develop non-uniform stresses when cooled from the deposition temperature. A disclination model shows that the stresses have rhombohedral and tetragonal components which can preferentially stress induce the martensite variants. The deflection of NiTi/Si bimorphs caused by the formation of martensite should thus be different if the NiTi/Si interface is corrugated or not. Experimental results confirm this expectation.
Energy Absorption and Damping in Magnetostrictive Composites
Authors: Mcknight G. P. , Carman G. P. 
Published: April 2011

AbstractThe mechanical energy absorption characteristics of several polymer matrix Terfenol-D composites were evaluated experimentally. Magnetostrictive composites absorb energy through domain level processes that couple mechanical and magnetic energies. The testing consisted of mechanically cycling the materials at different stress amplitudes (combined compression and tension) at a single frequency. Results indicate that the magnetostrictive composites exhibit a unique combination of high damping properties in conjunction with a relatively high modulus. The measured tan delta values for the materials are functionally dependent upon the stress amplitude. In general, as the stress amplitude increased, the damping or energy absorbed during one cycle decreased. Results also indicate that damping is directionally dependent (i.e. anisotropic) and that bias magnetic fields decrease the energy absorption. The volume fraction of the composites did not play a significant role in the magnitude of damping. This effect may be related to the inherent pre-stress imparted on the particle by the resin during cure.
Dielectric Properties of Highly Oriented Lead Zirconium Titanate Thin Films Prepared by Reactive RF-Sputtering
Authors: Kalpat S. , Du X. , Abothu I.R. , Akiba A. , Goto H. , McKnistry S. Trolier , Uchino K. 
Published: April 2011

AbstractHighly (100) and (111) oriented lead zirconium titanate (PZT) thin films have been grown by using reactive rf-sputtering. PZT thin films with rhombohedral composition have been grown in different orientations using selective rapid thermal annealing cycles. The polarization versus electric field curves and the resistivity of the films were measured using a standardized RT66A ferroelectric test system. The dielectric constant and the loss were determined using an impedence analyzer. The PZT(100) oriented films showed larger dielectric constant and loss than the PZT(111) films. The PZT(100) films possessed sharper square-like hysteresis loops compared to the PZT(111) films, as expected from our phenomenological calculations.
Shape Memory Alloys–Their Challenge to Contribute to Smart Structures
Authors: Boller C. 
Published: April 2011

AbstractShape memory alloys (SMA) have generated a lot of new ideas in engineering. Application is however so far limited to clamps and springs. With respect to smart structures sensing as well as control has to be included. While sensing looks to be relatively feasible control is the big challenge. This paper describes some aerospace related smart structures ideas using SMAs and discusses the challenges which need to be solved before these ideas have can be realised.
A Novel Integrated MEMS Process Using Fluorocarbon Films Deposited With a Deep Reactive Ion Etching (DRIE) Tool
Authors: Ayón A. A. , Chen D.-Z , Khanna R. , Braff R. , Sawin H. H. , Schmidt M. A. 
Published: April 2011

AbstractFluorocarbon films are useful as antistiction films for suspended structure and also for electrical isolation purposes. Furthermore, due to their low dielectric constant and ease of deposition they are useful for VLSI manufacturing applications. Thus, in the interest of building a complete database for these plasma generated fluorocarbon films, we report a designed experiment with a 4-variable matrix to fully characterize deposited films using C4F8 as the feed gas in a high density inductively coupled plasma tool. We also demonstrate the in-situ microfabrication of electrostatic actuators that exhibit the corresponding passivation film for electrical isolation. The utilization of these films as a masking material for MEMS applications and in triple nested mask arrangements is also demonstrated.
Temperature-Dependent Coefficient of Thermal Expansion of Silicon Nitride Films Used in Microelectromechanical Systems
Authors: Bargmann Melissa , Kumpel Amy , Tada Haruna , Nieva Patricia , Zavracky Paul , Miaoulis Loannis N. , Wong Peter Y. 
Published: April 2011

AbstractMicroelectromechanical systems (MEMS) have potential application in high temperature environments such as in thermal processing of microelectronics. The MEMS designs require an accurate knowledge of the temperature dependent thermomechanical properties of the materials. Techniques used at room temperature often cannot be used for high-temperature property measurements. MEMS test structures have been developed in conjunction with a novel imaging apparatus designed to measure either the modulus of elasticity or thermal expansion coefficient of thin films at high temperatures. The MEMS test structure is the common bi-layered cantilever beam which undergoes thermally induced deflection at high temperatures. An individual cantilever beam on the order of 100 νm long can be viewed up to approximately 800°C. With image analysis, the curvature of the beam can be determined; and then the difference in coefficient of thermal expansion between the two layers can be determined using numerical modeling. The results of studying silicon nitride films on silicon oxide are presented for a range of temperatures.
Porous Silicon as a Sacrificial Material for Microstructures Fabrication
Authors: Morel M. , Berre M. Le , Lysenko V. , Delhomme G. , Dittmar A. , Barbier D. 
Published: April 2011

AbstractPorous silicon (PS) is generated by electrochemical etching in hydrofluoric acid (HF). Recently porous silicon has been applied to micromachining and micro-devices as an alternate material, this material being used as a sacrificial layer. This technology competes with conventional techniques like surface and bulk micromachining regarding its speed, simplicity and reduced costs. A wide range of microstructures and free-standing structures can be fabricated with a large freedom of design in relation to the isotropic behavior of the etching. A sacrificial layer may be realized fast over varying thickness (PS formation rate 45 μm/h compared to silicon bulk micromachining rate 20 μm/h for KOH etching).This contribution is devoted to the materials aspects of patterning and processing: we will show how basic microstructures (trenches, polysilicon cantilevers, polysilicon free-standing membranes) may be fabricated using a very simple process based on a single photolithography. The important points are the choice of the mask, porous silicon properties as a function of its formation parameters and the choice of the solution removing the sacrificial layer. The morphology and porosity of the porous silicon layers are indeed mainly determined by the electrolyte composition and by the current density for a given substrate type. Optimized conditions (HF 15% and 80 mA/cm2) lead us to an appropriate porous silicon. Finally the applicability of this technology for various microsensors will be underlined.
The Etch Rate Variations of p+ Silicon Wafers in Aqueous KOH Solutions as a Function of Processing Conditions
Authors: Kilpinen P. , Haimi E. , Lindroos V.K. 
Published: April 2011

AbstractThe etching behaviour of highly boron doped (20 - 25 mω-cm) silicon wafers in aqueous KOH solutions were investigated in the present study. The etch rate of (100) crystal plane and the fastest etch plane projections (31X) and (41X), where X can be 0,1,2…, were measured as a function of processing conditions. The experimental temperatures of solutions were 65 - 75°C and the concentrations 5 - 40 wt-% KOH. The maximum etch rate of (100) crystal plane was measured to locate between 10 - 15 wt-% KOH and the maximum etch rates of fastest etch plane projections were measured to locate between 0 - 10 wt-% KOH in the whole temperature range. In lower concentrations (5 - 20 wt-% KOH) the fastest etch plane projection was determined to be (31X) crystal plane projection. In higher concentrations (25 - 40 wt-% KOH) it was determined to be (41X) crystal plane projection. The results of the present study indicate that there are differences between etch reactions of different etch planes. The difference may be connected to transferring electrons. This could explain why the different etch planes have the position of etch rate maximums as a function of KOH concentration in different places. Furthermore, this could also explain why fastest etch planes are sensitive to experimental conditions.
Structure-Property Relations in Sol-Coated PMN Ceramics: Microscopy, Dielectric and Electromechanical Response
Authors: Sehirlioglu A. , Pilgrim S.M. 
Published: April 2011

AbstractSome of the most promising materials for electrostrictive response are Pb(Mg1/3, Nb2/3)O3 (PMN) - ceramics; however, the properties of a given composition are only optimum in a limited range of temperatures. In a previous study, it was found that sol coating of PMN particles modified and improved the electromechanical and/or dielectric properties of the resulting product--doubling induced strain in some cases. Understanding the origin of these changes will help to produce an optimized PMN ceramic for a given application from a single source powder. This work concentrates on the Ti and Zn coatings which gave superior properties within the concentration matrix. The relation between the structure and the enhanced electrostrictive behavior is studied. Structural characterization is done by XRD, TEM and SEM.Electrical measurements of dielectric constant, loss, polarization and strain, the property determinations needed to complete the structure-property suite.
Design, Synthesis and Characterization of Precursors for Chemical Vapor Deposition of Oxide-Based Electronic Materials
Authors: Just Oliver , Obi-Johnson Betitie , Matthews Jason , Levermore Dianne , Jones Tony , Rees William S. 
Published: April 2011

AbstractFerroelectric and other high dielectric constant metal oxides currently are sought-after for a variety of applications in the electronics industry. To meet the demand of preparation of these interesting materials in a manner compatible with traditional silicon-based fabrication procedures, chemical vapor deposition routes are desired for film growth. Compounds displaying high vapor phase stability are necessary as precursors for these applications. Additionally, in general, it is preferred to utilize compounds in a liquid state, due to the more rapid re-establishment of equilibrium at a liquid-vapor interface, compared to that present at a solid-vapor interface. This combination of desired molecular properties, in turn, presents a great challenge to the coordination chemist. Several of the metals of interest for these uses reside in groups 2–5. Common design features are emerging for the ligands best suited for attachment to these metals for subsequent utilization in the deposition of metal oxides. In order to achieve coordinative saturation of the relatively high ionic radii exhibited by most of these elements, multidentate, monoanionic ligands are relied upon. In the past, most often, homoleptic ligand sets have been employed, thereby reducing the chance for ligand scrambling to occur during the growth process. Such disproportionation processes have been credited, in previous work, with the observation of a temporal decay in vapor pressure of heteroleptic compounds. In some interesting new developments, it has been found that heteroleptic compounds possess sufficient vapor phase integrity to permit their evaluation as CVD precursors. These, and related, results are presented herein.