bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of Vacancies on Optical Properties of Sic Nanocrystallites
Authors: Plucinski K.J. , Kityk I.V. , Kassiba A. , Charpentier C. 
Published: April 2011

ABSTRACTTo investigate the origin of vacancies in SiC nanopowders, complex theoretical and experimental investigations of SiC nanopowders of different geometry sizes were carried out. Our theoretical approach included ab initio band energy calculations and molecular dynamics simulations with dynamic boundary conditions. Experimental methods included EPR spectra. The significant influence of nanocrystallite and grain sizes on the concentration and type of vacancies is demonstrated. On the other hand, our comparison of experimental data and theoretical simulations show that vacancies influence the optical properties of SiC nanocrystallites.
Finite Element Analysis of 2-D Dielectric Waveguides with Helmholtz Vector Equations and Virtual Exterior Elements
Authors: Zheng Tieyu , Bao Nal-Keng , Chiang Kin-Seng , Chung Po-Sheun 
Published: April 2011

ABSTRACTThis paper reports a finite-element-method formulation, which is based on the Helmholtz vector equations in terms of transverse electrical field components to characterize two-dimensional dielectric waveguides with an arbitrary continuous permittivity profile. A virtual exterior element iteration technique is associated with the finite-element analysis to process the remote boundary condition. This technique achieves both excellent computational efficiency and accuracy when studying the dielectric propagation constants and cutoff frequencies. The spurious-infection-free modal electrical field can be obtained directly. Numerical results of circular optical fibers with the parabolic permitivity profile are presented to show the validity of this technique.
Estimation of The Critical Radius for The Nucleation of the C54 Phase in C49 TiSi2: Role of The Difference in Density
Authors: Migas D.B. , Iannuzzi M. , Miglio Leo , La Via F. , Grimaldi M.G. 
Published: April 2011

AbstractWe discuss the rather scattered measurements of the lattice parameters for C49 TiSi2, which are reported in literature, along with new and accurate X-ray diffraction measurements and ab-initio calculations. Both agree in indicating that the density of the metastable C49 structure cannot be much smaller than the one for the polymorphic C54 phase, as it is commonly reported. We conclude by demonstrating that only in the case of such a smaller difference in density between the two phases, the elastic strain contribution to the nucleation energy of the C54 structure in the C49 matrix can be neglected. The estimation of the critical radius strongly depends on this issue.
Microstructure Evaluation for Time Dependent Nucleation Protocols in KJMA Kinetics
Authors: Pineda Eloi , Crespo Daniel 
Published: April 2011

AbstractThe microstructure developed in a first order phase transformation is obtained using a populational extension of the Kolmogorov, Johnson-Mehl and Avrami (KJMA) model, PKJMA. PKJMA allows one to determine the grain size distribution resulting from nucleation and growth kinetics. PKJMA is grounded on the mean field hypothesis that the free space around the growing grains is randomly distributed, independent of the grain radius. Although this approach is perfectly valid for the case of constant nucleation, a detailed analysis of the model shows that this hypothesis does not hold in the case of time dependent nucleation protocols or pre-existing nuclei. In this work, the PKJMA model has been improved by estimating the average free surface around the grains as a function of their radius and the time elapsed since nucleation. The resulting model gives quantitative determination of the microstructure developed under a variety of nucleation and growth processes: pre-existing nuclei, constant nucleation, and the combination of both mechanisms, constant and radius dependent growth rates. Comparison with Monte Carlo simulations, showing a quantitative agreement will be presented.
Growth, Microstructure and Micro-Raman Studies of Rf Magnetron Sputter Deposited SrBi2Ta2O9 and SrBi2TaNbO9 Films
Authors: Srinivas S. , Jain Menka , Katiyar Ram S. 
Published: April 2011

AbstractA systematic study is undertaken on the effect of growth conditions, on the microstructure and other properties of radio frequency (RF) magnetron sputter deposited SrBi2Ta2O9 (SBT) and SrBi2TaNbO9 (SBTN) films. Polycrystalline SBT and SBTN films were deposited on Si (100), platinized Si, and MgO substrates using stoichiometric targets. Cross sectional scanning electron microscopy reveals the tendency for columnar growth in the films deposited at high substrate temperatures and at high partial pressures of sputtering gas mixtures. AFM studies show that the grain size and the homogeneous surface morphology depends on the post annealing time. XPS studies reveal that oxygen vacancies lie in the Bi2O2 planes. The compositional dependence of the rigid-sublattice mode and the symmetric stretching mode of oxygen octahedrons in the Raman spectra of these materials have been discussed.
Short-Range Order and Nanocrystallization in Amorphous Zr-Ti-Cu-Ni-Al
Authors: Xing L. Q. , Gu Xiaofeng , Lusby T. A. , Melmed A. J. , Hufnagel T. C. 
Published: April 2011

AbstractWe have examined the effect of Ti content on the crystallization kinetics of Zr-based amorphous alloys. In Zr59Ti3Cu20Ni8Al10, annealing above the glass transition temperature produces 50-100 nm crystalline precipitates, as seen in transmission electron microscope images. In contrast, TEM images and diffraction patterns from annealed Zr54.5Ti7.5Cu20Ni8Al10 show no evidence of crystalline phase formation. Structural changes upon annealing do occur in this alloy, however, as revealed by field ion microscopy. The effect of Ti is to favor the formation of clusters of short-range order; this tendency for clustering is apparently the cause of difference in crystallization behavior between the two alloys.
Low Energy Ion Assisted Vapor Deposition
Authors: Zhou X. W. , Wadley H. N. G. 
Published: April 2011

AbstractThe performance of multilayered thin film materials often depends sensitively upon the (physical) roughness and degree of (chemical) mixing at interfaces. Irradiation of a growth surface with an assisting ion beam is often used to modify surface roughness. Molecular dynamics has been used to explore the use of low energy (less than 20 eV) Xe+ and Ar+ assisted deposition of model Ni/Cu/Ni multilayers to control both physical roughness and chemical mixing. The study indicated that under normal ion incidence condition, ion energies as low as 3 eV could effectively flatten the relatively weakly bonded copper surface (and therefore the nickel on copper interface). Higher ion energies (at least 10 eV) were required to flatten the more strongly bonded nickel surface. Chemical intermixing by an exchange mechanism between a surface atom and an underlying atom in an already deposited layer depended upon the binding energy of the already deposited layer. As a result, significant chemical mixing occurred as 9 eV (and above) ions impacted with nickel atoms on an already deposited copper surface. At a given ion incident energy, (the heavier) Xe+ ions resulted in less roughness but more mixing. A modulated ion assistance strategy in which no assisting ion beam was used while depositing the first few monolayers of each new metal layer was found to successfully reduce both interfacial roughness and interlayer mixing.
Controlling the Diamond Film Morphology by Low-Energy Electron Bombardment
Authors: González J. A. , Figuero O. L. , Weiner B. R. , Morell G. 
Published: April 2011

AbstractWe studied the effects of low-energy electron bombardment during diamond growth over the film crystalline quality and morphology. The film growth was monitored via the effective extinction coefficient (k) at 1.96 eV with in situ ellipsometry, in order to determine the developmental stage of the film in real time. Taking advantage of this in situ monitoring, we triggered the electron bombardment over the growing surface at different growth stages and studied the corresponding induced changes in film morphology and crystalline quality. Ex situ Raman spectroscopy and scanning electron microscopy (SEM) were also employed to evaluate the crystalline quality and the morphology of the grown films, respectively. We found that electron bombardment can be used to control the surface morphology of the films (triangular, pyramidal, square, amorphous). The results also indicate that applying the electron bombardment over the diamond film during the whole time of growth is detrimental to its crystalline quality and favors the formation of non-sp3 carbon. However, when the electron bombardment is triggered just after high quality scattered diamond crystallites have formed, the resulting film is of similar quality as those grown without bombardment. Therefore, properly chosen and triggered electron bombardment during diamond growth by chemical vapor deposition (CVD) can be used to control the film morphology while maintaining the film crystalline quality.
Inclined Substrate Deposition by Evaporation of Magnesium Oxide for Coated Conductors
Authors: Bauer Markus , Metzger Ralf , Semerad Robert , Berberich Paul , Kinder Helmut 
Published: April 2011

AbstractBiaxially textured MgO buffer layers were deposited on metal substrates using “inclined substrate deposition” (ISD). The influence of the substrate inclination angle, deposition rate, and film thickness on the texture is shown. Scanning electron microscopy reveals columnar growth. We developed a growth model to explain the texturing. To test this model we have carried out 3D Monte-Carlo simulations. We find that the preferred orientation arises from mutual shadowing of the columns and directional surface diffusion due to their initial momentum.YBa2Cu3O7 (YBCO) films deposited on the ISD buffer layers are highly textured. The ab-planes of the YBCO are tilted with respect to the surface by typically 25° towards the direction of MgO vapor incidence. Therefore, the critical current density jc is anisotropic with up to 8 × 105 MA/cm2 in one direction and 4 × 105 MA/cm2 in the other. For tape coating the MgO deposition direction can be chosen so that the high jc is along the tape.
Flux Mapping and Magnetic Behavior of Grain Boundaries in Nd-Fe-B Magnets
Authors: Volkov V.V. , Zhu Yimei 
Published: April 2011

AbstractAdvanced Fresnel- & Foucault-Lorentz microscopy were applied to analyze magnetic behavior of the grain boundaries in Nd-Fe-B hard magnets. In-situ TEM magnetizing experiments combined with these imaging methods revealed the process of magnetization reversal in polycrystalline sintered and die-upset Nd-Fe-B under various magnetic fields. Fine details of magnetic flux distribution, derived from the magnetic interferograms created by phase-coherent Foucault imaging, provide a quantitative description of the local variation of magnetic flux. Our study suggests that the grain boundaries play an important multi-functional role in the reversal of magnetization, by acting as (a) pinning centers of domain walls, (b) centers of nucleation of reversal domains, and (c) sinks or sources for migrating magnetostatic charges and/or dipoles. They also ensure a smooth transition for irreversible remagnetization in polycrystalline samples.
Investigation of Copper Segregation to the Σ5(310)/[001] Symmetric Tilt Grain Boundary in Aluminum
Authors: Plitzko Jürgen M. , Campbell Geoffrey H. , King Wayne E. , Foiles Stephen M. 
Published: April 2011

AbstractThe Σ5 (31O)/[001] symmetric tilt grain boundary (STGB) in the face centered cubic (FCC) metal aluminum with 1at% copper has been studied. The model grain boundary has been fabricated by ultra-high vacuum diffusion bonding of alloy single crystals. The segregation of the copper has been encouraged by annealing the sample after bonding at 200 °C. TEM samples of this FCCmaterial were prepared with a new low voltage ion mill under very low angles.The atomic structure of the Σ5(310)/[001] STGB for this system was modeled with electronic structure calculations. These theoretical calculations of the interface structure indicate that the Cu atoms segregate to distinct sites at the interface. High resolution electron microscopy (HRTEM) and analytical electron microscopy including electron energy spectroscopic imaging and X-ray energy dispersive spectrometry have been used to explore the segregation to the grain boundary. The HRTEM images and the analytical measurements were performed using different kinds of microscopes, including a Philips CM300 FEG equipped with an imaging energy filter. The amount of the segregated species at the interface was quantified in a preliminary way. To determine the atomic positions of the segregated atoms at the interface, HRTEM coupled with image simulation and a first attempt of a holographic reconstruction from a through-focal series have been used.
Fabrication and Field Emission Properties of Carbon Nanotube Cathodes
Authors: Bower C. , Zhou O. , Zhu W. , Ramirez A. G. , Kochanski G. P. , Jin S. 
Published: April 2011

ABSTRACTA variety of carbon nanotube films have been fabricated and tested as cold cathodes. A spray deposition technique was developed for processing as-grown bulk nanotubes, both single-walled and multi-walled, into films of randomly oriented nanotubes. Films of randomly oriented multi-walled nanotubes were grown using thermal chemical vapor deposition, and arrays of well-aligned multi-walled nanotubes have been fabricated using a microwave plasma enhanced chemical vapor deposition technique. The emission current-voltage (I-V) characteristics of these nanotube cathodes have been measured. Both multi-walled (random and aligned) and single-walled carbon nanotubes exhibit low turn-on fields (∼ 2 V/μm to generate 1 nA) and threshold fields (< 5 V/μm to generate 10 mA/cm2). Significantly, these cathodes were capable of operation at very large current densities (> 1A/cm2), making them candidates for application in a variety of vacuum microelectronic devices.
Aligned Carbon Nanotubes Via Microwave Plasma Enhanced Chemical Vapor Deposition
Authors: Cui H. , Palmer D. , Zhou O. , Stoner B. R. 
Published: April 2011

ABSTRACTAligned multi-wall carbon nanotubes have been grown on silicon substrates by microwave plasma enhanced chemical vapor deposition using methane/ammonia mixtures. The concentration ratio of methane/ammonia in addition to substrate temperature was varied. The morphology, structure and alignment of carbon nanotubes were studied by scanning electron microscopy and transmission electron microscopy. Both concentric hollow and bamboo-type multi-wall carbon nanotubes were observed. Growth rate, size distribution, alignment, morphology, and structure of carbon nanotubes changed with methane/ammonia ratio and growth temperature. Preliminary results on field emission properties are also presented.
Effects of O2 Gas Addition on Diamond-Like Carbon Film Deposition
Authors: Nakamura N. , Itani T. , Chiba H. , Watanabe K. , Kurihara K. 
Published: April 2011

ABSTRACTThe role of 02 gas addition on the deposition of Diamond-like Carbon (DLC) film was studied for hard disk drive (HDD) media application. The influence of 02 gas mixing ratio on DLC film quality was investigated using the dc magnetron sputtering method with a solid graphite target and Ar, CH4 and 02 mixing gases. The 02 mixing ratio was varied between 0% and 50%. Film quality was evaluated using Raman spectroscopy and XPS. When 02 gas mixing ratio increased the peak in Raman spectra shifted gradually to higher wavenumbers and its bandwidth became narrower. This indicates graphite component increased in the DLC film. In addition, the lubricant coverage on oxygen-containing DLC was improved. Because adding oxygen increases the terminations of carbonyl group on DLC surface, this result suggests that the polar surface causes higher affinity for the lubricant
High Reverse Breakdown a-C:H/Si Diodes Manufactured by rf-PECVD
Authors: Paul Shashi , Clough F.J 
Published: April 2011

ABSTRACTThin films of hydrogenated amorphous carbon ( a-C:H ) deposited by radio frequency plasma-enhanced chemical vapour deposition (rf-PECVD) have been studied for various applications. An interesting property of these films is their high breakdown strength ( 107 Vcm−1 ). This property of a-C:H can be exploited in high breakdown heterostructure diodes or as passivation layers and insulator layers in MIS devices. Reports on the applications of a-C:H/Si diodes exist in the literature. Diodes in which the a-C:H films have been deposited by rf-PECVD, have been reported only once. In this article the diodes produced reportedly failed to exhibit reproducible I-V characteristics under high voltage stress. We have investigated the process dependence of structural and electrical properties of rf-PECVD a-C:H films deposited at room temperature from a CH4/Ar gas mixture (at a pressure of 100 mTorr) using a capacitively coupled rf-PECVD. We observe a clear correlation between the dc-self bias and the rectification ratio of a-C:H/Si heterojunction diodes. Optimised diodes show rectification ratios upto 104 and a stable reverse breakdown voltage, typically around 850 V. I-V and C-V measurements show no evidence of hystersis. Scanning Electron Microscopy was carried out to determine the quality of the films deposited. Micro-Raman analysis was used to estimate the ID/IG ratio in the films deposited under different dc-self bias.
UV Raman Studies of Microcrystalline Diamond
Authors: Okada Katsuyuk , Kanda Hisao , Komatsu Shojiro , Matsumoto Seiichiro 
Published: April 2011

ABSTRACTMicrocrystalline diamond films have been prepared in a 13.56 MHz low pressure inductively coupled plasma, in which the pressure of CH4/H2and CH4/CO/H2 plasmas was varied from 45 to 50 mTorr. The bonded structures of the obtained deposits were studied by Raman spectroscopy with 514, 325, and 244 nm excitation wavelength. 514 nm excited Raman spectra exhibit two peaks at ∼1355 cm−1 and ∼1580 cm−1 corresponding to sp2 bonding without CO additive (CH4/H2, plasma). New peaks at ∼1150 cm−1 assigned to sp3-bonded carbon network and at ∼1480 cm−1 appear with CO additive (CH4/CO/H2, plasma). 325 nm excited Raman spectra show a shoulder at ∼1150 cm−1, a clear 1332 cm−1 diamond peak, and the peak at ∼1580 cm−1 is remarkably enhanced. In 244 nm excited Raman scattering, the 1332 cm−1 diamond peak is only enhanced whereas the peak at ∼1580 cm−1 is correspondingly diminished. These features of the Raman spectra imply that the vibrational modes of sp2 sites are resonantly enhanced with 514 nm excitation because the 514 nm (2.4 eV) corresponds to the π-π* transition in sp2-bonded carbon, while the 325 nm (3.8 eV) and 244 nm (5.1 eV) excitations are possibly sufficient to excite the σ state of both sp2- and sp3-bonded carbon
Tensile Properties of Amorphous Diamond Films
Authors: LaVan D.A. , Hohlfelder R.J. , Sullivan J.P. , Friedmann T.A. , Mitchell M. , Ashby C.I.H. 
Published: April 2011

ABSTRACTAmorphous diamond is a new material for surface micromachined microelectromechanical systems (MEMS) and sensors. Its strength and modulus was tested in uniaxial tension by pulling laterally on a specially designed sample with a flat tipped diamond in a nanoindenter. Several sample designs were attempted. Of those, only the single layer specimen with a 1 by 2 μm gage cross section and a fixed end rigidly attached to the substrate was successful. Tensile load was calculated by resolving the measured lateral and normal forces into the applied tensile force and frictional losses. Displacement was corrected for machine compliance using the differential stiffness method. Post-mortem examination of the samples was performed to document the failure mode. The load-displacement data from those samples that failed in the gage section was converted to stress-strain curves using carefully measured gage cross section dimensions. Mean fracture strength was found to be 8.5 ± 1.4 GPa and the modulus was 831 ± 94 GPa. Tensile results are compared to hardness and modulus measurements made using a nanoindenter
Coalescence of C60 Molecules in Fullerite by Intense Femtosecond Laser Pulses: An Ab–Initio Simulation
Authors: Gambirasio A. , Bernasconi M. , Benedek G. , Silvestrelli P. L. 
Published: April 2011

ABSTRACTWe present an ab–initio molecular dynamics study of the modifications induced on fullerite by the irradiation with ultrashort very intense laser pulses. We identified the threshold for the non–thermal cage–opening of the C60 molecules which is the analogue of the laserinduced non–thermal melting observed in semiconductors and graphite. The new phase formed by the non–thermal coalescence of the C60 molecules is fluid–like and mainly formed by small chains of 2–fold coordinated carbon atoms.
Dehydration Time Dependence on Piezoelectric and Mechanical Properties of Bovine Cornea
Authors: Jayasuriya A. C. , Scheinbeim J. I. , Lubkin V. , Bennett G. , Kramer P. 
Published: April 2011

AbstractThe Young's Modulus (E) and piezoelectric coefficient (d31) have been investigated as a function of dehydration time for bovine cornea at room temperature. The piezoelectric and mechanical responses observed were anisotropic for bovine cornea and d31 decreased, while E increased with dehydration. In addition, water molecules appear to increase the crystallinity (of collagen) in the cornea. With dehydration of the cornea, reduction of crystallinity and changes in hydrogen bonding were observed by Fourier Transform Infra Red (FTIR) and Wide Angle X-ray Diffracion (WAXD) measurements.
Novel Polymer Electrets
Authors: Sessler G. M. , Hillenbrand J. 
Published: April 2011

AbstractPermanently charged films with a cellular or porous structure represent a new family of polymer electrets. These materials show piezoelectric properties with high transducer constants. The electromechanical response equations of such films are derived for their operation as sensors and as actuators. Experimental results are also presented for cellular polypropylene. In particular, measurements of the direct and inverse transducer constants, the thermal stability of the charge, and Young's modulus are discussed. Assuming reasonable charge distributions and charge densities, the calculated transducer constants are in good agreement with the measured values. Both the theoretical model and the measurements show the reciprocity of the transducer constants.
Polarization Stability of Amorphous Piezoelectric Polyimides
Authors: Park C. , Ounaies Z. , Su J. , Smith J. G. , Harrison J. S. 
Published: April 2011

AbstractAmorphous polyimides containing polar functional groups have been synthesized and investigated for potential use as high temperature piezoelectric sensors. The thermal stability of the piezoelectric effect of one polyimide was evaluated as a function of various curing and poling conditions under dynamic and static thermal stimuli. First, the polymer samples were thermally cycled under strain by systematically increasing the maximum temperature from 50°C to 200°C while the piezoelectric strain coefficient was being measured. Second, the samples were isothermally aged at an elevated temperature in air, and the isothermal decay of the remanent polarization was measured at room temperature as a function of time. Both conventional and corona poling methods were evaluated. This material exhibited good thermal stability of the piezoelectric properties up to 100°C.