bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimizing the DSSC Fabrication Process using Lean Six Sigma
Authors: Fauss Brian , Munukutla Lakshmi V. , Main Laura , Polesky Gerald , Kannan Arunachalanadar M.
Published: June 2019

Dye sensitized solar cells (DSSCs) belong to an innovative third generation photovoltaic technology, which is demonstrating tremendous potential to become a revolutionary technology due to recent breakthroughs in fabrication cost. A seven-step quality improvement method is implemented to enhance process efficiency and effectiveness of the DSSCs. Lean Manufacturing’s 5S method successfully increased efficiency in all of the processes. Six Sigma’s DMAIC methodology is used to identify and eliminate each of the root causes of defects in the critical titanium dioxide deposition process. These optimizations resulted with the following significant improvements in the production process: 1. fabrication time of the DSSCs is reduced by 54 %; 2. fabrication procedures improved to the extent eliminated all critical defects 3. The yield of good cells increased from 17% to 90%.
Simulation of Galvanostatic Discharge of the LixC6/Liquid Electrolyte/Liy(NiaCobMnc)O2 Cell
Authors: Chandrasekaran Rajeswari , Seong Yeonkyeong , Bae Chulheung , Jung Joosik , Kim Kwangsoo , Cheong Kyeongbeom , Miller Theodore
Published: June 2019

An isothermal, physics-based model was developed in COMSOL multiphysics software to simulate the galvanostatic discharge performance of LixC6/Liquid Electrolyte/ Liy(NiaCobMnc)O2 dual lithium-ion insertion cell at 298 K. Modeling results are compared with experimental data to provide further insight into design and optimization of these cells for advanced electric vehicles.
Development of nanotechnology experimental modules using ferrofluids for high school classrooms
Authors: Chopra Nitin , Shi Wenwu , Peramsetty Nikita R. , Evans Victoria L.
Published: June 2019

Nanotechnology and nanoscience have a strong potential to impact society and the commercial sector. It is critical to introduce this area to high school classrooms as a teaching tool. Here, we report the development of ferrofluid-based experimental modules in a team effort including a high school student and a high school teacher. The basic experimental modules were developed as follows: A) Electric motor-based patterning of magnetic nanoparticles and carbon nanotubes on a silicon wafer. Electromagnetically activated or ‘spiked’-ferrofluid was utilized here. B) Basic concepts of wettability, hydrophobicity, and oleophilicity were demonstrated by combining hydrophobic CNTs, water, and ferrofluids. C) Finally, the utility of ferrofluid-based environmental remediation was demonstrated for oil removal from oil-water mixture and organic dye separation from water-dye mixture. It is envisioned that the integration of the developed experimental modules into high school curriculum will motivate high school students to pursue degrees in science, engineering, and nanotechnology. Thus, this will assist in the development of future workforce in the area of nanotechnology and materials science.
Introducing Raman Spectroscopy of Crystalline Solids in the Undergraduate Curriculum
Authors: Roughani Bahram , Warner David , Ramabadran Uma
Published: June 2019

We describe an experiment designed as an upper level physics laboratory that introduces students to Raman Scattering of electronic materials and research methodology. This experiment is an effective approach in demonstrating the relationship between the Raman intensity of the scattered light from crystals and symmetry dependent Raman selection rules. In our measurements we alter the angle between the crystal axis and the polarization of the incident laser beam by Si (100) sample rotation. The three dimensional plot of the intensity profile versus the theoretical model is used to distinguish differences between various crystal planes of the same electronic sample. This experiment will combine optical analysis with materials aspects of electronic materials.
Education and Dissemination: Lab-to-Market-to-Classroom
Authors: Campo E. M.
Published: June 2019

In this paper, we present a work plan for the dissemination of refreshable, photoactuatable tactile displays to the visually impaired, serving both Lab-to-Market and Lab-to-Classroom initiatives. The work plan is designed in accordance with the logic model, which identifies an overlap amongst classroom, market, and laboratory. This overlap seems to nucleate when a technology in developmental phase is deployed in a classroom with high affinity to such technology. In this scheme, students are stakeholders whom help decide both content and applications to be included in the developing curriculum, and provide technology feedback, effectively leading to increased consumer acceptance. The identified Lab-to-Market-to-Classroom continuum could be the missing link where to nurture sustainable scientific, technological, and curricular development.
Manipulation of interface electronic structure by thin metal oxide films
Authors: Wang Chenggong , Irfan  , Gao Yongli
Published: June 2019

We have investigated the counter intuitive phenomenon of inserting a metal oxide layer to improve hole injection or extraction in organic semiconductor devices using ultraviolet photoemission, x-ray photoemission, and inverse photoemission spectroscopy (UPS, XPS and IPES). We observed that metal oxides, such as MoO3, substantially increase the work function when deposited on indium-tin-oxide (ITO). The increase lifts up the highest occupied molecular orbital (HOMO) of the hole transport layer, therefore reduces the energy barrier between the HOMO and the Fermi level of the anode. The uplift creates an interface band bending region that results in a drift electric field that encourages the collection of holes at the anode. The optimum thickness for the oxide layer is estimated to be 2 nm. We have also investigated the effects of ambient or O2 exposure of MoO3. We observed that while most of the electronic energy levels of the oxide remained largely intact, the work function reduction was significant. This opens a way for optimal energy level alignment by modifying the work function through exposure. Furthermore, we observed that the work function reduction by exposure could be reversed by proper annealing of the sample in vacuum. The investigations therefore point to manipulate the interface electronic structure and charge injection/extraction by thin metal oxide films.
High-Conductivity Solution-Processed Carbon Nanotube Networks as Transparent Electrodes in Organic Solar Cells
Authors: Ostfeld Aminy E. , Fogden Siân , Catheline Amélie , Kim Kee-Chan , Ligsay Kathleen , McFarlane Graham A. , Arias Ana Claudia
Published: June 2019

Solutions of individual, unbroken single-walled carbon nanotubes in organic solvent were fabricated in a reductive dissolution process. Transparent conductive films deposited from these organic inks gave a significantly higher conductivity to absorptivity ratio than those cast from an aqueous dispersion of carbon nanotubes. For example, films from the organic ink have achieved a sheet resistance of 250 Ω/□ with transmittance of 92% at 550 nm wavelength, compared to 76% transmittance for a 250 Ω/□ film from the aqueous dispersion. The promise of these films as transparent electrodes has been demonstrated by their incorporation into organic solar cells with power conversion efficiency of 2.3%, comparable to that of solar cells produced using indium tin oxide transparent electrodes.
Parameter Study on UV-induced Degradation of Dye-sensitized Solar Cells
Authors: Jensen Katrine Flarup , Veurman Welmoed , Brandt Henning , Im Chan , Wilde Jürgen , Hinsch Andreas
Published: June 2019

The present work investigates the UV stability of the dye-sensitized solar cell (DSC) by parametrical investigation of the material influence on UV stability. UV illumination has been observed to cause degradation by slow photocatalysis in the DSC. Photooxidized impurities represent an unwanted side reaction with the redox pair of the electrolyte as the released electron will deplete the triiodide concentration. A study on the DSC cell was carried out with intermediate electrical characterization by cyclic voltammetry (CV) and electrical impedance spectroscopy (EIS) to map the influence of UV illumination as a function of the H2O concentration in the electrolyte, the plate distance and the triiodide concentration. The results show that the H2O content has a detrimental influence on the DSC stability during UV illumination. A higher concentration of triiodide can buffer the reaction with impurities, so that a longer-term stability is achieved. A recovery of triiodide in UV aged cells with either no remaining triiodide or with such a low concentration that the cell current has been diffusionlimited, was seen during CV to -0.75 V under illumination. The reappearance of triiodide was accompanied with a production of hydrogen bubbles, which was related to the H2O content in the electrolyte and the exposure to UV. Our approach can be used to test the purity and the UV stability of various electrolytes.
Effect of Copper Sulfide nanocrystals in a Poly(3-hexylthiophene)/Titania solar cell
Authors: Quintana-Ramírez Priscilla V. , Arenas M. C.
Published: June 2019

Poly(3-hexylthiophene)/Titania (P3HT/TiO2) heterojunction has been widely studied in the field of hybrid solar cells. Usually, organic dyes shift the neat TiO2 absorption edge toward the visible range improving the conversion efficiency or/and the TiO2 surface is modified with ligands in order to increase the electron transport. On the other hand, copper sulfide, non-toxic semiconductor, has been included in bulk organic P3HT based solar cell, increasing the photocurrent density of devices. Therefore, we propose the use of copper sulfide in the hybrid TiO2/P3HT heterojunction to determine its effect in the performance of TiO2/P3HT solar cell. Copper sulfide nanocrystals (CuxS) were synthesized at 230 °C, 240 °C and 260 °C and, they were mixed with P3HT in order to form P3HT:CuxS bulk heterojunctions. Scattered grains and irregular morphology in the final topography of the reference device (P3HT/TiO2 heterojunction) were observed by AFM, while a granular morphology and a few pores like craters were observed in the devices containing P3HT:CuxS bulk heterojunctions. Chalcocite phase (Cu2S) was obtained at 230 and 240°C and, digenite (Cu1.8S) phase at 260°C, both copper sulfide phases are very promising for solar cells. Despite this, poor rectifications in the devices were found in the current-voltage curves of the devices containing copper sulfide nanocrystals in contrast to the P3HT/TiO2 cell (device without nanocrystals), it could be due to the current leakage or recombination process in the copper sulfide/TiO2 interface. It suggests future work in order to improve the devices.
Probing Confinement Effects on Multilayered Ferroelectric Polymer Films Using Second Harmonic Generation
Authors: Jones J. , Zhu L. , Tolk N. , Mu R.
Published: June 2019

Electrical energy storage plays a key role in mobile electronic devices, stationary power systems, and hybrid electrical vehicles. High energy density capacitors based on dielectric polymers are a focus of increasing research effort motivated by the possibility to realize compact and flexible energy storage devices, taking advantage of light weight and facile processability of organic materials. In addition, dielectric polymers enjoy inherent advantages of self-healing mechanism and high breakdown strength, leading to capacitors with great reliability and high energy density. It is the focus of this group to develop a multilayered ferroelectric PVDF system for improved energy storage efficiency. These systems are fabricated using enabling technology in co-extrusion which allows more cost effective and large area device production as opposed to more conventional layer-by-layer techniques. Many efforts have been made by the team to fabricate these micro- and nano-layered systems resulting in much improved device performance. A three-time improvement of capacitive electrical energy density has been demonstrated. The focus of this research is to understand the physics of why these multilayered systems perform better than a single layer by developing a characterization technique using both confocal second harmonic generation (SHG) and electric field induced second harmonic (EFISH) laser spectroscopy. Our results have shown that SHG is a very sensitive, non-destructive and versatile technique that can be used to study the ferroelectric and structural properties of layered systems. When combined with EFISH this technique allows the interrogation of structural and dielectric properties within the individual layers and at the interfaces between the layers. Further, the proposed techniques can be readily employed in-situ which can provide information in real time during sample processing with static and time-resolved spectroscopic measurements.
Competition between Exciplex Formation and Photocarrier Generation in Molecular-Scale Donor-Acceptor Heterojunctions
Authors: Tsutsumi Jun’ya , Yamada Toshikazu , Matsui Hiroyuki , Hasegawa Tatsuo
Published: June 2019

Donor-acceptor mixed-stack charge-transfer (CT) compounds can be regarded as a model system for charge carrier separation in molecular-scale donor-acceptor heterojunctions. Here we investigated fundamental photocarrier generation characteristics in single crystals of a donoracceptor mixed-stack system, phenothiazine-tetracyanoquinodimethane (PTZ-TCNQ). The laser beam-induced current (LBIC) measurement on the crystals allowed the discrimination between the exciton and the photocarrier diffusion on the basis of the observed spatial decay profiles. We found that the photocarriers are directly generated by higher-lying CT band excitation and exhibit extremely long diffusion length reaching more than 10 μm. We discuss the origin of the efficient photocarrier generation in terms of the geminate electron-hole pair formation.
Analytical Model for Heat Transfer in a Finite Region of Organic Phase Change Materials
Authors: Zhu Yejun , Huang Baoling , Wu Jingshen
Published: June 2019

The concept of low carbon, energy saving and sustainable design has been widely accepted all over the world. As a matter of fact, large amount energy is consumed to control the indoor environment to maintain a comfortable ambience for living and working. To increase the energy utilization efficiency, phase change material (PCM), which can store and release heat through phase change, has been recognized as an excellent candidate for green building. Analytical model is of great importance to describe and predict heat transfer with phase change. The classic Stefan problem solution is quite suitable for crystalline materials, which requires the input of certain phase change temperature. However, many PCMs widely used, like paraffin, are semi-crystalline materials, which have a much larger phase changing temperature range compared with small molecule crystalline materials. It is important to appropriately model the phase change of semi-crystalline polymers for the application of PCM. Furthermore, in large spatial scale prediction, widely used semi-infinite plane model is usually quite suitable to explain initial heat transfer. Unfortunately, semi-infinite plane is not the same as real situation. In this paper, by using the temperature at the end of the phase change as the equivalent melting temperature, a heat transfer model for semi-crystalline organic PCM is constructed. Meanwhile, this model concerns the phase change in a limited region. This model can serve as a fast tool to predict the one-dimensional heat transfer with phase change in an explicit form. The model is validated by the results of simulations and experiments reported in the literature.
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

Dirac 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

The 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

Scanning 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

We 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

Factors 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

The 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

Results 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

The 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

Very 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

Interfacial 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

The 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

The 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.
A Novel Experimental Setup to Measure the Changes in Electrical Conductivity of Hydrating Cementitious Materials
Authors: Majling J. , Moses P. , Perez-Pena M. , Roy D. M.
Published: June 2019

One of the alternative ways to fabricate shaped bodies from cementious materials would be to press the loose powder of materials (in steel dies, or isostatically) and to infiltrate them with liquids using the natural capillary forces of porous bodies [1,2].
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

Scanning 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

Interfaces 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

This 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

The 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

Non-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

Layers 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

Plasma 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

Bi-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

YBa2Cu3O7 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

Electron-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

The 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.
Electrical Damage Due to Low Energy Plasma Processing of GaAs Structures
Authors: Zappe Hans P. , Kaufel Gudrun
Published: June 2019

The effect of numerous plasma reative ion etch and physical milling processes on the electrical behavior of GaAs bulk substrates has been investigated by means of electric microwave absorption. It was seen that plasma treatments at quite low energies may significantly affect the electrical quality of the etched semiconductor. Predominantly physical plasma etchants (Ar) were seen to create significant damage at very low energies. Chemical processes (involving Cl or F), while somewhat less pernicious, also gave rise to electrical substrate damage, the effect greater for hydrogenic ambients. Whereas rapid thermal anneal treatments tend to worsen the electrical integrity, some substrates respond positively to long-time high temperature anneal steps.
Deposition Of Aluminium Nitride Film By Ion Beam Enhanced Reactive Magnetron Sputtering
Authors: Huang R. F. , Wen L. S. , Wang H. , Wu J. , Hong R. J.
Published: June 2019

Aluminium nitride film has been synthesized at substrate temperatures lower than 100 °C by using ion beam enhanced reactive magnetron sputtering. The growth rate was much higher than that obtained by usual physical vapor deposition at low substrate temperatures. The stoichiometry of the film was controlled by varying the resultant current of the ion beam used and identified by X-ray diffraction analysis. The optical properties of the film were also studied.
PACVD Fluorinated Silicon Nitride Films Deposited From SiF4/NH3 GAS MIXTURES
Authors: Castro A. , Gasset M. , Gomez-Aleixandre C. , Sanchez O. , Albella J. M.
Published: June 2019

Fluorinated silicon nitride films deposited from SiF4/NH3 gas mixtures by PACVD at two different frequencies have been investigated. At 13.56 MHz, low deposition rate was detected and no appreciable changes were observed when the deposition parameters varied in a wide range. On the contrary, higher deposition rates were achieved when a 35 KHz frequency was applied. These low frequency silicon nitride films showed an increase in the fluorine content In their structure when the SiF4 flow ratio in the gas mixture was increased, as detected by analytical resolution of the IR spectra. In addition, analysis of the plasma emission spectra has been performed in order to explain the effect of the plasma frequency in the deposition process.
Thin Film Growth Using Low-Energy Multi-Ion Beam Deposition System
Authors: Shimizu S. , Sasaki N. , Ogata S. , Tsukakoshi O. , Seki S. , Yamakawa H.
Published: June 2019

A high-current, low-energy multi-ion beam deposition system has been developed for the fabrication of tailored new materials. This system consists of two ion sources, a dual-sector type mass analyzer and a deceleration system. Several ion species can be extracted successively from the two ion sources by switching the mass analyzer selection. Artificially structured materials, especially having a layered structure, can be grown by the fine control of the growth process of each layer. Ar* ion deceleration characteristics of this ion beam deposition system and preliminary results about the epitaxial growth of Ca film on Si(100) are shown.
The Effects of Ion Energy on Carbon and Tungsten Films Fabricated by Direct Ion Beam Deposition and Ion Beam Sputtering Deposition
Authors: Kataoka I. , Ito K. , Hoshi N. , Yonemitsu T. , Etoh K. , Yamada I. , Delaunay Jean-Jacques
Published: June 2019

The x-ray reflectivity and surface morphology of C/W multilayers fabricated by ion beam sputtering (IBS) method was evaluated. Also the surface roughness and amorphous structure of C and W films fabricated by direct ion beam deposition (DIBD) method were evaluated as a function of ion energy. The reflectivity was measured by the C-K line (4.47nm) and STM was used for surface roughness measurement and root-mean-square value of correlation function of the RHEED pattern was used for evaluation of amorphous structure. The reflectivity of C/W multilayer was about 69% of the theoretical one, and micro-columnar structures were observed from STM images. The film structure and surface roughness of DIBD film were changed with the depositing ion energy. The surface roughness of films becomes smaller as the depositing energy becomes higher in the energy range from 20 to 140eV.
Plasma Immersion Surface Modification With Metal Ion Plasma
Authors: I. G.  , Godechot X. , Yu K. M.
Published: June 2019

We describe here a novel technique for surface modification in which a metal plasma is employed and by which various blends of plasma deposition and ion implantation can be obtained. The new technique is a variation of the plasma immersion technique described by Conrad and co-workers. When a substrate is immersed in a metal plasma, the plasma that condenses on the substrate remains there as a film, and when the substrate is then implanted, qualitatively different processes can follow, including ‘conventional’ high energy ion implantation, recoil implantation, ion beam mixing, ion beam assisted deposition, and metallic thin film and multilayer fabrication with or without species mixing. Multiple metal plasma guns can be used with different metal ion species, films can be bonded to the substrate through ion beam mixing at the interface, and multilayer structures can be tailored with graded or abrupt interfaces. We have fabricated several different kinds of modified surface layers in this way.
Selective Copper Plating in Silicon Dioxide Trenches with Metal Plasma Immersion Ion Implantation
Authors: Kiang Meng-Hsiung , Pico Carey A. , Lieberman Michael A. , Cheung Nathan W. , Qian X. Y. , Yu K. M.
Published: June 2019

Selective deposition of copper in SiO2 trenches has been carried out using plasma immersion ion implantation and electroless Cu plating. To form the seed layer for electroless Cu plating on SiO2 , sputtered Pd and Si atoms were partially ionized by the Ar plasma and then deposited at bottoms of SiO2 trenches; Ar ions also assisted the ion beam mixing of the deposited Pd/Si films with the SiO2 substrate. We found a threshold Pd dose of 2–3×1014/cm2 is required to initiate the electroless plating of Cu. By controlling the Pd dose and the tapering angle of the SiO2 trench sidewalls, 1 μm wide Cu filled lines with flat surfaces suitable for planarized multilevel metallization were successfully fabricated.
Argon Plasma Induced Surface Modifications For Resistless Patterning Of Aluminium Films
Authors: Agrawal Neeta , Tarey R. D. , Chopra K. L.
Published: June 2019

Argon plasma exposure has been used to induce surface chemical modification of aluminium thin films, causing a drastic change in etch rate in standard HNO3/CH3COOH/H3PO4 etchant. The inhibition period was found to increase with power and Ar plasma exposure time. Auger electron and x-ray photoelectron spectroscopies have indicated formation of an aluminium fluoride (AlF3) surface layer due to fluorine contamination originating from the residue left in the plasma chamber during CF4 processing. The high etch selectivity between unexposed and argon plasma exposed regions has been exploited as a new technique for resistless patterning of aluminium.
Simulations of Low-Energy Ion/Surface Interaction Effects During Epitaxial Film Growth.
Authors: Kitabatake Makoto , Greene J. E.
Published: June 2019

Molecular dynamics simulations were used to follow low-energy ion/surface interactions including kinetic energy redistribution in the lattice as a function of time, projectile and lattice atom trajectories, and the nature, number, and depth of residual defects. The simulations were carried out using the Tersoff many-body potential for Si. Irradiation events were initiated with 10 and 50 eV Si atoms incident normal to the Si(001)2×l surface at an array of points in the primitive surface unit cell. Ion-induced epitaxial growth was observed due to both Si projectiles and Si lattice atoms coming to rest at epitaxial positions through direct deposition as well as site exchange occurring via diffusional and collisional processes. 36 simulations of 10 eV (50 eV) Si bombardment resulted in an average stopping position of 0.5 Å (1.6 Å) below the surface, 10 (13) epitaxial events, 7 (24) exchange events between the projectile and a lattice atom, and the formation of 15 (63) interstitials and 0 (36) vacancies. The interstitials preferentially diffuse toward the surface and are annealed out over times corresponding to monolayer deposition at typical Si MBE growth temperatures.