bluuebunny/crossref_metadata_2025_split huggingface dataset:
TiO2 Nanowires as a Wide Bandgap Dirac Material: a numerical study of impurity scattering and Anderson disorder
Authors: Penazzi Gabriele , Deák Peter , Aradi Bálint , Wehling Tim , Gagliardi Alessio , Huy Huynh Anh , Yan Binghai , Frauenheim Thomas 
Published: June 2019

ABSTRACTDirac materials are characterized by exceptional mobility, orders of magnitude higher than any semiconductor, due to the massless pseudorelativistic nature of the Dirac fermions. These systems being semimetallic, the lack of a genuine band-gap poses a serious limitation to their possible applications in electronics. We recently demonstrated that thin TiO2 nanowires can exhibit 1D Dirac states similar to metallic carbon nanotubes, with the crucial difference that these states lie inside the conduction band in proximity of a wide band gap. We analyze the robustness of the Dirac states respect to an Anderson disorder model and substitutional impurity and compare to different one dimensional systems. The results suggest that thin anatase TiO2 nanowires can be a promising candidate material for switching devices.
Optical Modeling of Gold nanoparticles (Au NP) for efficiency improvement of a-Si:H photovoltaic cells
Authors: Yu Peiqing , Blondeau Jean-Philippe , Andreazza Caroline , Ntsoenzok Esidor , Roussel Julien , Dutheil Perrine , Thomann Anne Lise , Mustapha Elyaakoubi , Meot Jacque 
Published: June 2019

ABSTRACTThe efficiency of thin-film solar cells using a-Si:H is limited by the decrease in a-Si:H layer optical path length and its poor light absorption at red and NIR wavelengths. Metal NP such as Au have been shown to increase the absorption in the active material and then cell performances, by exhibiting localized surface plasmon (LSP) resonances. Our work’s goal is to understand NP influence in such cells, to perform an optimal structure by increasing the amount of light absorbed within the cell using NP scattering and luminescence. Modeling based on Mie theory is first carried out using bulk Palik data for Au spheres with various diameters and refractive medium indexes. Using modeling parameters, Au layers were deposited on glass and SnO2 substrates respectively by thermal evaporation in vacuum and sputtering, followed by thermal annealing (200 ∼ 500°C) in order to promote the NP growth. MEB pictures show quasispherical Au NP shape with a mean size of 150nm. This diameter range switches extinction of NP in scattering regime. Annealing temperature (T) strongly affects the NP morphology. Surface coverage decreases and sphericity appears to increase with T. UV-Visible spectroscopy displays distinct LSP resonances around 600nm after annealing with a red shift while T increases.
Emission Diversity of ZnO Nanocrystals with Different Growth Temperatures
Authors: Lozada E. Velázquez , Torchynska T. , González G. Camacho 
Published: June 2019

ABSTRACTScanning electronic microscopy (SEM), X ray diffraction (XRD) and photoluminescence (PL) have been applied to the study of structural and optical properties of ZnO nanocrystals prepared by the ultrasonic spray pyrolysis (USP) at different temperatures. The variation of temperatures and times at the growth of ZnO films permits modifying the ZnO phase from the amorphous to crystalline, to change the size of ZnO nanocrystals (NCs), as well as to vary their photoluminescence spectra. The study has revealed three types of PL bands in ZnO NCs: defect related emission, the near-band-edge (NBE) PL, related to the LO phonon replica of free exciton (FE) recombination, and its second-order diffraction peaks. The PL bands, related to the LO phonon replica of FE, and its second-order diffraction in the room temperature Pl spectrum testify on the high quality of ZnO films prepared by the USP technology.
XRD analysis of TRAM composed from [Sb2Te3/GeTe] superlattice film and its switching characteristics
Authors: Ohyanagi T. , Kitamura M. , Kato S. , Araidai M. , Takaura N. , Shiraishi K. 
Published: June 2019

ABSTRACTWe studied GeTe structures in topological switching random access memories (TRAMs) with a [GeTe/Sb2Te3] superlattice by using X-ray diffraction (XRD) analysis. We examined the electrical characteristics of the TRAMs deposited at different temperatures. We found that XRD spectra differed between the films deposited at 200 and 240°C and that the differences corresponded to the differences in the GeTe sequences in the films.
Mechanism of Orientation of Ca(OH)2 Crystals in Interface Layer Between Paste and Aggregate in Systems Containing Silica Fume
Authors: Jia Wang 
Published: June 2019

ABSTRACTFactors such as the type of aggregate, the addition of silica fume, and the roughness of the aggregate surface, which influence the orientation index of Ca(OH)2 crystals in the interface layer, are discussed, based on the experimental results of Maso [3] and the author. Then, a hypothesis about the mechanism of this orientation is proposed, involving the Ca(OH)2 crystal structure and the principles of physical chemistry of surfaces.From this hypothesis, it is suggested that the reduction of the orientation index of Ca(OH)2 crystals when silica fume is added is due to physical aspects other than the large water requirement of silica fume. The same is also true when the aggregate surface is rough.
Interfaces in Fibre Reinforced Cements
Authors: Bentur A. 
Published: June 2019

ABSTRACTThe microstructure of the matrix in the vicinity of the fibre surface is quite different from the microstructure of the bulk paste matrix. This can have an important effect on the processes that take place at the interface, such as crack-fibre interaction and debonding. The present paper describes the special structure of this zone, in monofilament and bundled fibre reinforced cements, and discusses its effects on some characteristics of the mechanical performance of the composites, which cannot be predicted by analytical models assuming a uniform matrix up to the fibre surface. The modification of the microstructure at the interface as a means for improving properties in some composites is described.
Bonding of Fibrillated Polypropylene Fibers to Cementitious Materials
Authors: Rice Edward K. , Vondran Gary L. , Kunbargi Hassan O. 
Published: June 2019

ABSTRACTResults of Scanning Electron Microscope (SEM) and Energy Dispersive X-ray (EDX) studies on the fracture of polypropylene fiber-hydrated cement interface are presented.The fiber reinforced concrete specimens were tested in direct tension. The resulting fracture surfaces were observed, including surface adhesion and mechanical bond between the fibers and the hydrated cement paste.The nature of the fiber fracture was also studied. Mechanical bond was achieved due to the surface and shape of the fibers. Adhesion between the fibers and the cement paste was observed microscopically and confirmed by (EDX) analysis. The nature of the fiber reinforcement was observed at the tensile fracture.
The Role of the Surface of Glass Reinforcement Fibers on Their Physical Properties and Performance in Composites
Authors: Kruger Albert A. 
Published: June 2019

ABSTRACTThe widely held explanation for mechanical failure of silicate and silica glasses rests upon the existence of Griffith-flaw and associated free ion diffusion concepts used to model crack growth. However, this theory has consistently failed to provide complete agreement with the experimental results. This dilemma coupled with the reports of single-valued strengths in fibers cannot be rationalized by the modification of the intrinsic Griffith-flaw distribution to essentially a delta function.It is for these reasons that the field-enhanced ion diffusion model has been introduced. The inclusion of a term for the electrostatic potential in the thin-film solution of Fick's second law has been shown to be consistent with the experimental results. Therefore, the effects on alkali ion migration as a consequence of the local variations in charge density that occur on the solution side of the glass/water interface play a direct role on the chemical corrosion mechanism. Thus chemistry which can modify the surface potential can alter the rate of aging of glass.It has been found that the chemistry which has been used to modify the corrosion behavior of glass fibers can also alter composite properties. These modifications no doubt arise from changes in the interphase region.We report on the effects of treatments on initial fiber strengths, aging resistance, and preliminary results of composite properties (made from our treated fibers).
Cropped Steel Fiber Reinforced Chemically Bonded Ceramic (CBC) Composites
Authors: Wise Sean , Jones Kevan , Herzfeld Claudio , Double David D. 
Published: June 2019

ABSTRACTVery high strength castable chemically bonded ceramic (CBC) materials have been prepared which consist of finely chopped steel fibers and steel aggregate in a silica modified portland cement matrix. This paper examines the effect of metal fiber addition on compressive and flexural strengths. The overall chemistry of the matrix is held constant but the morphological form of silica used and the cure conditions are altered to examine their effect. Compressive strengths in excess of 500 MPa and flexural strengths in excess of 80 MPa can be obtained.It is found that flexural strength increases proportionally with fiber content over the range of 0 to 10% by volume. Compressive strengths are not affected. Use of silica fume in the mixes produces higher strengths at low temperatures than mixes which contain only crystalline silica. High temperature curing/drying (400°C), which produces the highest strengths, produces equivalent properties for formulations with and without silica fume. Higher water/cement ratios are found to reduce compressive strengths but have relatively little effect on the flexural properties.
Fracture Mechanics of Interfaces
Authors: Shah Surendra P. , Jenq Yeou-Shang 
Published: June 2019

ABSTRACTInterfacial bond properties between fibers and matrix are investigated in the present paper. A fiber pull-out test, which is commonly used to study the interfacial bond strength of fiber-matrix system, is analyzed. The bonding between fibers and matrix is assumed to be perfect before the pull-out load is applied. Griffith energy criterion is used to govern the crack propagation at the interfacial region when debonding begins. A constant frictional shear stress, which may be a result of existence of surface roughness at the interface, is assumed to exist at the wake of debonding region. Based on this mechanism, the total pull-out load can be decomposed as: resistance offered by the interfacial bond and resistance offered by the frictional stress. The proposed approach is applicable to any elastic fiber and matrix system, but only the results of steel fibers and reinforcing bar in a cementitious matrix are reported. The proposed model correctly predicts several experimental trends of bond strengths reported by other researchers. Furthermore, theoretical predictions of progressive failure of bond cracks are found to be in good agreement with a holographic interferometry study on a pull-out test.
On the Modelling of Inelastic Interfaces in Fibrous Composites
Authors: Gopalaratnam Vellore S. , Jin-Cheng  
Published: June 2019

ABSTRACTThe classical fiber pull-out problem has been formulated in onedimension with a view to focus on the nonlinear interfacial response. The fiber and the cocentric matrix are assumed to behave elastically. The local interfacial bond-slip characteristic has been idealized to be elastic-linear softening. This greatly simplifies the otherwise implicit governing differential equation of the debonding process. Solutions to the fiber axial force and interfacial shear stress along the embedded length of the fiber have been obtained by applying appropriate boundary and continuity conditions. The stability of the debonding process has been investigated by varying the fundamental characteristics of the fiber-matrix interface, the fiber embedment length and the fiber diameter. The analytical model has been successfully used to predict many of the characteristics experimentally observed in fibrous composites that fail by fiber pull-out.
Interface Behavior in Reinforced Concrete
Authors: Mital S. K. , Mullen R. L. , Huckelbridge A. A. 
Published: June 2019

ABSTRACTThe mechanism of bond transfer between steel and concrete in a reinforced concrete member is studied in the present work. It is seen that the behavior of the interface zone can be represented by a simple generalized Mohr-Coulomb model. It is also seen that the complex relationships between the local bond stress and local slip suggested by other researchers (cubic or higher order polynomials) may be due to the geometry of the specimen and nature of stress distribution along the bar rather than intrinsic interface behavior. Behavior predicted by a generalized Mohr-Coulomb model is compared to predictions and observed behavior previously reported.
Hydration Characteristics and Morphological Features of Concretes from Structures in Australia, England and the United States
Authors: Baweja Daksh , Roper Harold , Cabrera Jose G. , Cook David J. 
Published: June 2019

ABSTRACTScanning electron microscope studies were carried out on concretes obtained from structures in Australia, England and the United States as part of an assessment of their durability performances. The ages of the structures ranged from nine to thirty years. All structures contained fly ash concretes in some sections, and, in a few cases, direct comparison between these concretes and ordinary portland cement (OPC) concretes was possible. Water: cement ratios of the concretes varied from 0.44 to 0.90. The sources of fly ash were identified in each case. The structures chosen had a range of use classifications encompassing building, hydraulic structures, bridge structures, towers and foundations. Deterioration effects of concretes in some structures were more common than in others. Based on observations, conclusions were drawn on the morphological features and hydration characteristics of the concretes.
Initiation and Propagation of Bond Cracks as Detected by Laser Holography and Acoustic Emission
Authors: Maji Arup , Shah S. P. 
Published: June 2019

ABSTRACTInterfaces between hardened portland cement matrix and aggregates are considered relatively weak and a source of microcrack initiation. Based on optical and scanning electron microscopic studies of fractured concrete specimens, researchers have studied the role of interface in the fracture mechanism of cement composites. Acoustic Emission source location technique and laser holography provide noninvasive and nondestructive tools to study microcracking as well as the pertinent displacement field associated with cracking. In this paper, some results obtained using laser holography, speckle methods and acoustic emission source loction measurements for model concrete specimens containing circular aggregate inclusions are described. Effects of diameter of circular inclusions on mode of cracking are reported.
Effect of Aggregate, Cement, and Mineral Admixtures on the Microstructure of the Transition Zone
Authors: Mehta P. K. , Monteiro P. J. M. 
Published: June 2019

ABSTRACTThis paper contains a review of the results from the studies at the University of California at Berkeley on various factors influencing the microstructure of the transition zone in concrete. Two types of aggregate, two different cement, and three mineral admixtures were investigated. Using cement paste-polished aggregate composite specimens cured up to three years, X-ray diffraction, scanning electron microscopy, and microhardness testing techniques were used for characterization of the transition zone.Compared to the transition zone between a quartz aggregate and an ASTM Type I portland cement, transition zones with smaller and less preferentially oriented crystals of calcium hydroxide were obtained when using a Type K expansive cement, or limestone aggregate, or mineral additives, such as condensed silica fume, granulated blast-furnace slag, and fly ash.
The Contribution of the Transition Zone to the Strength of High Quality Silica Fume Concretes
Authors: Bentur A. , Goldman A. , Cohen M. D. 
Published: June 2019

ABSTRACTThe strength of high strength silica fume concretes is usually attributed to the reduction in w/c ratio and the refinement of the pore structure. A study of concretes and pastes, with and without silica fume, suggests that the contribution of the silica fume to strength is also the result of the densification of the transition zone. It is argued here that this influence is as important as the one due to the reduction in w/c ratio. It is suggested that the densification of the transition zone is the result of the effect of the silica fume on the nature of the fresh concrete.
Residual Stress Analysis by Neutron Time-of-Flight at a Reactor Source
Authors: Priesmeyer H.G. , Schröder J. 
Published: June 2019

ABSTRACTNon-destructive neutron diffractometry for stress analysis will be a powerful experimental tool in material science research performed at the GKSS 5 MW reactor FRG-1. Arguments which show the advantages of the time-of-flight method are given and a suitable high-resolution neutron-efficient type of spectrometer is introduced. First results derived from this method are presented.
Molecular Beam Epitaxial Growth and Characterization of InSb and InAsxSb1−x
Authors: Uppal P.N. , Gill D.M. , Herring R. 
Published: June 2019

ABSTRACTLayers of InSb and InAsxSb1-x were grown on GaAs and GaAs on Si substrates and then characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM) to determine the epilayer quality. Hall-effect measurements and photoluminescence (PL) were also performed. Single-crystal XRD indicated that the 5-μm InSb layers grown on GaAs had a peak full width at half maximum (FWHM) of 120 arc sec for the (004) reflection. Planar TEM of a 7-μm-thick InSb layer on GaAs(001) indicated a dislocation density of 2 x 106 cm−2 at the top of the layer. Hall effect measurements of an undoped 3.5-μm-thick InSb on semi-insulating GaAs indicated an electron density of 3.7 x 1016 cm−3 at 300K and a mobility of 45,000 cm2 / V-sec. At 77K these values were 2.7 x 1016 cm−3 and 49,200 cm2 / V-sec, respectively. The composition of the InAsxSb1-x was a function of the growth temperature and the As2/In ratio for both Sb2 and Sb4. The XRD (004) peak FWHM increased with the x value, indicating a deterioration in material quality. This may be caused by alloy segregation in InAsxSb1-x. The peak FWHM rapidly increases from x=0.1 to x=0.3 and then its value drops, indicating that the quality of the layers improved. InSb layers displayed a strong PL whereas the PL for the InAs0.5Sb0.5 layers was very weak. We also grew InSb and InAsxSb1-x layers on GaAs on Si. Optical transmission measurements on InSb indicated that the layers were under tensile stress. We believe this tensile stress could be used to lower the bandgap of InAsxSb1-x layers to provide longer cut-off wavelengths for infrared detectors.
Shallow P+-N Junction Fabrication by Plasma Immersion Ion Implantation
Authors: Pico C. A. , Qian X. Y. , Jones E. , Lieberman M. A. , Cheung N. W. 
Published: June 2019

ABSTRACTPlasma immersion ion implantation (PIII) has been applied to fabricate shallow p-n junction diodes and MOS test structures. BF3 ions created by an electron cyclotron resonance source were implanted into n-type Si(100) at an accelerating voltage of −2 kv. The implant doses ranged from 4 × 1014/cm2 to 4 × 1015/cm2. In some cases, the top layers of the Si(100) substrates were preamorphized by a 3 × 1015/cm2 to 1016/cm2 implant of SiF4 by PIII at −7.2 kV prior to the BF3 implant. The ideality factor exhibited in both non- and preamorphized samples during forward bias is 1.02 to 1.05. Reverse leakages were measured at 30 nA/cm2 at −5V. High frequency capacitance and high field breakdown measurements of the oxide test structures showed no significant damage to the oxide.
Crystalline Orientation Control in Bi-Sr-Ca-Cu-O Thin Films
Authors: Ishizuka Yoshiki , Terashima Yoshiaki , Miura Tadao 
Published: June 2019

ABSTRACTBi-Sr-Ca-Cu-0 thin films were prepared on (110)SrTiO3 by coevaporation with rf oxygen plasma. The non-(00n) crystalline orientations were formed in the Bi2 Sr2Ca2Cu3Oy1 Bi2Sr2 CaCu2Oy2 and Bi2Sr2CuOy3 phases. Furthermore, it was confirmed that the chemical composition and the oxygen plasma condition influenced the crystalline orientation. On the basis of these results, a new idea for the film growth mechanism is proposed.
Plasma Oxidation of Y-Ba-Cu-O Precursor Filaments
Authors: Klein J. D. , Hachey J. P. , Yen A. 
Published: June 2019

ABSTRACTYBa2Cu3O7 filaments produced from a soluble molecular precursor were reacted using low pressure oxygen heat treatments with and without an applied plasma. Filaments reacted at temperatures between 750 and 800°C with the aid of an oxygen plasma were found to have higher transition temperatures than those reacted under similar conditions without a plasma. The highest zero resistance critical temperature, Tc(0) = 91.6 K, was obtained from a filament reacted in a 0.2 Torr oxygen plasma at 800°C. At the lowest reaction plasma temperature of 700°C a Tc(0) of 88.0 K was observed. X-ray diffraction revealed that filaments reacted at an oxygen pressure of 1 atm were nearly tetragonal while those reacted at 0.2 Torr, with or without a plasma, were quite orthorhombic.
GaAs Epitaxial Growth by ECR-MBE
Authors: Kondo Naoto , Nanishi Yasushi , Shibata Tomohiro , Yamamoto Norio , Fujimoto Masatomo 
Published: June 2019

ABSTRACTElectron-cyclotron-resonance plasma-excited molecular beam epitaxy (ECR-MBE) is a new technique for GaAs growth. This paper describes surface cleaning of GaAs and Si substrates at fairly low temperatures using hydrogen plasma, low temperature growth of GaAs on both substrates, and selective area growth of GaAs on both substrates partially covered with a silicon nitride (SiN) mask. The ability to clean and grow at low temperatures-assumed to be a benefit of using energetic particles—should permit us to grow layers on processed GaAs and/or Si substrates. The electrical properties of grown layers are also described. Selective area growth has been successfully carried out with no deposit on the mask or irregular growth at the mask edge. The desorption process introduced by impinging ions is found to play an important role in the selective area growth.
Structural And Compositional Modifications of III–V Ternary and Quaternary Compounds Induced by Ion Bombardment
Authors: di Bona A. , Facchini A. , Valeri S. , Ottaviani G. , Piccirillo A. 
Published: June 2019

ABSTRACTThe effect of low energy (0.5 to 5 keV) Ar+ beams on the surface structure and composition of monocrystalline ternary In0.53Ga0.47As and quaternary In0.70Ga0.30As0.64P0.36 films epitaxially grown by MO-VPE on InP (100) substrate has been investigated. Quantitative Auger electron spectroscopy has been used with the elemental standard method taking into account the electron diffraction effects. For both semiconductors, the outermost surface layer has been found to be Ga and In enriched. In the subsurface region, the Ga enrichment is even larger, at the expense of As and In. In the quaternary film, P is depleted in the surface as well in the subsurface region. Angular Resolved Auger Electron Spectroscopy is applied to the structural study of the sputter-etched surface. The nature and spatial extension of the ion-induced surface damage have been investigated at different energies, and doses of the primary ion beam. Is has been found that the resistance to the amorphization is strongly enhanced in InGaAs with respect to GaAs.