bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Effect Of Pore Structure And Cracking On The Permeability Of Concrete
Authors: Bier Thomas A. , Ludirdja Darmawan , Young J. Francis , Berger Richard L. 
Published: March 2011

AbstractPermeability measurements have been conducted for mortars, concrete and hydrated cement pastes. The permeability with water as the penetrating medium has been measured in a low pressure range (˜ 0.5 psi) and at higher pressures up to 400 psi. Samples never exposed to drying and oven dried samples (105 °C) have been investigated. Pore structure of the investigated samples has been characterized using mercury intrusion porosimetry.The results are discussed with regard to changes in structure during the experiment due to progressing hydration and healing of cracks.
The Relationship Between The Porosity And Permeability Of The Surface Layer Of Concrete And The Ingress Of Aggressive Ions
Authors: Crumbie Alison K. , Scrivener Karen L. , Pratt P. L. 
Published: March 2011

AbstractThe durability of concrete is strongly dependent on the distribution of porosity particularly in the surface layers. To study this distribution, concretes at different water to cement ratios were studied by methanol counter diffusion and by analysis of backscattered electron images. The distribution of porosity in the surface was compared with that in the bulk. Samples of the same concrete were imnersed in sodium sulphate solutions while others were left in lime water as a control. The effects of the immersion on the microstructure was studied with backscattered electrons in the SEM.
Influence of Water Cement Ratio and Curing on the Permeability and Structure of Hardened Cement Paste and Concrete
Authors: Gräf Herbert , Setzer Max J. 
Published: March 2011

AbstractCuring affects sincerely the durability of concrete especially in surface regions. This is reflected in the pore structure and in the permeability. In a systematic research the structural changes due to water cement ratio and curing have been studied by mercury porosimetry, by nitrogen adsorption, by oxygen diffusion and by oxygen permeability. Due to these results diffusion and permeability are connected by a power law. Structural changes alter the permeability by four orders of magnitude. The results can be well explained by pore size distribution both for hcp and for concrete. Carbonation and frost action as well as strength and elastic modulus are closely correlated to permeability and therefore to pore structure. For practical application it is possible to give advice for concreting and curing. Service life can be predicted by permeability measurements in an early stage. The results are comparable with Nyames /20/.
Scaling Behavior Of Dynamic Permeability In Porous Media
Authors: Sheng Ping , Zhou Min-Yao , Charlaix E. , Kushnick A. , Stokes J. P. 
Published: March 2011

AbstractWe show that the scaling of the dynamic permeability κ(ω) by its static value κ0 and the frequency ω by a characteristic frequency ω0 particular to the medium results in a dimensionless function , with , which is dominated by the geometry of the throat regions in a porous medium. If the pore cross sectional area S varies slowly near the throat, i.e. dS/dz ≃ 0 where z is the distance normal to the cross section, then is an approximate universal function independent of microstructures. When scaling holds, the dynamic permeability κ(ω) is shown to contain only two pieces of geometric information, and the knowledge of either the low-frequency or the high-frequency asymptotic constants of κ(ω) would enable one to deduce the other missing parameters. In particular, since the high-frequency asymptotic parameters of κ(ω) can be related to the electrical formation factor and the volume-to-surface ratio, the static permeability value κ0 may be directly deduced from such non-permeability measurements.
Microstructure and Porosity of Metakaolin Blended Cements
Authors: Bredy P. , Chabannet M. , Pera J. 
Published: March 2011

AbstractFive compositions with 10% to 50% metakaolin for cement substitution were studied. The rate of hydration was studied from the compressive strength after up to 6 months of curing and from the hydrates formed (DTA-XRD). The metakaolin addition considerably reduced portlandite content in the hydrated cement and contributed to the formation of hydrated gehlenite which is not present in OPC paste. The microstructure study (SEM) shows that pozzolanic cement pastes were less crystallized than plain pastes. Mercury intrusion was used to measure porosity of hydrated cement pastes. The porosity with blended cements was higher than that with OPC, except for 10 and 20% metakaolin substitution. Evolution of the pore size distribution was studied: the pozzolanic pastes enhance small diameters.
Pore Structure of Low Porosity DSP Cement Pastes
Authors: Touse Sara A. , Bier Thomas A. , Knepfler Cheryl A. , Young J. Francis , Berger Richard L. 
Published: March 2011

AbstractThe pore structure of low porosity cement pastes containing varying quantities of silica fume has been examined using mercury intrusion porosimetry (MIP) and nitrogen adsorption (NA) measurements. The water:solid ratio for all DSP pastes studied was 0.18. It was observed that, as for conventional pastes, removal of water by solvent replacement with methanol minimizes changes to the pore structure. Vacuum or oven drying severely reduces specific surface area and obscures important trends.It was found that capillary porosity in excess of 10 nm (100 Å) is essentially absent and that the pore volume measured can be considered an intrinsic part of the binding phase. The influence of silica fume and curing times on pore structure has been measured and the implications of the data will be discussed. Comparisons will be made with conventional cement pastes.
Some Experimental Possibilities With Mercury Intrusion Porosimetry
Authors: Winslow Douglas 
Published: March 2011

AbstractThe importance of knowing the pore size distribution of a material, and the utility of mercury intrusion, are briefly reviewed. Mercury intrusion results can be used to obtain the specific surface of a material. Under the right circumstances, this method has many advantages over vapor sorption, and a mercury intrusion test may be desirable for this reason alone. The procedure and limitations are described. Modern instruments allow for the measurement of mercury extrusion as well as intrusion. This opens the possibility of measuring two pore size distributions. One is reversibly intruded, and the other is not. The use of these sub-distributions in seeking correlations with material properties and behavior is discussed. The applied-pressure/diameter-intruded relationship of the Washburn equation depends upon the surface tension and contact angle. Inter-metallic solutions with mercury as the solvent offer the possibility of reducing the surface tension and/or the contact angle. This allows the use of lower pressures to intrude the same diameter pore, or the intrusion of smaller pores at the same pressure. The practical application of using such solutions is described.
Observation of Oxidation-Enhanced and -Retarded Diffusion of Antimony in Silicon: The Behavior of (111) Wafers
Authors: Tan T. Y. , Ginsberg B. J. 
Published: March 2011

ABSTRACTAn experiment was performed to study the oxidation-enhanced and -retarded diffusion (OED and ORD) of Sb in silicon wafers oxidized in dry O2 at 1160°C. The ORD data of (100) wafers agree well with the prediction of a model assuming that Si self-interstitials (I) and vacancies (V) coexist in thermal equilibrium at high temperatures. An adjustment of the I supersaturation values is needed to bring the ORD/OED data of (111) wafers to fit with the model satisfactorily. This indicates the existence of a mechanism which injects V into (111) wafers in addition to the normal mechanism of I injection due to SiO2 growth.
Improved Meltback Procedures for Liquid-Phase-Epitaxial Growth of Planar and Buried Heterostructures
Authors: Chin B. H. , Chin A. K. , Digiuseppe M. A. , Lourenco I. A. , Camlibel I. 
Published: March 2011

ABSTRACTIn the liquid phase epitaxy on indium phosphide, the substrate,just prior to the growth of the first epitaxial layer, is commonly etched back with an indium melt to remove any thermallydegraded surface and to ensure uniform and consistent wetting.This procedure, however, often produces defects which degrade both planar and buried heterostructure devices. For planar edgeemitters and lasers, the resulting rippled surface morphology degrades device performance by scattering light. For buried heterostructures, the meltback in the regrowth step leads to indium-rich inclusions. The effects of meltback on material quality are presented, and a new multiple meltback procedure which maintains flat surface morphology and eliminates inclusions is described.
Electrically Active Defects in Cid Imaging Arrays Fabricated on Hg0.7 Cd0.3Te
Authors: Schaake H.F. , Lewis A.J. 
Published: March 2011

ABSTRACTCID imaging arrays were fabricated on Hg0.7 Cd0.3Te produced by the solid state recrystallization technique. It was found that the most serious source of dark current was sub-grain boundaries. SEM studies of the microstructure revealed by etching showed that boundaries with a high denisty of dislocations were detectable sources of dark current, while those boundaries with a low density of dislocations, as well as individual dislocations were not. TEM showed that all dislocations were free of precipitates, and most were not dissociated. The sub-grain boundaries were found to arise from misorientation between dendrites which form during the solidification from the melt.
The Structure of a Near Coincidence Σ=5, [001] Twist Boundary in Silicon
Authors: Vaudin Mark , Ast Dieter 
Published: March 2011

ABSTRACTThe dislocation structure of a near coincidence Σ=5 [001]twist boundary in silicon was studied using transmission electron microscopy. Secondary dislocations, with localized cores, were observed in the boundary accommodating a small deviation (<.5°) from perfect coincidence. The O-lattice theory for general low angle boundaries was extended to calculate the expected dislocation content of near coincidence boundaries. Comparison between predictions and observations was used to deduce information on the primary dislocation structure of the boundary.
Ion Irradiation Effects on Pt Contacts To Si with and without Interfacial Chemical Oxide
Authors: Banwell Thomas , Finetti Manuela , Suni Ilkka , Nicolet Marc-A. , Lau S. S. , Scott David M. 
Published: March 2011

ABSTRACTThe electrical properties of ion irradiated metal-semiconductor contacts are investigated. Silicide contacts are fabricated by depositing Pt on chemically clean or slightly oxidized (∼14 Å SiO2) n+-and n-type <111> Si, followed by a Si ion irradiation (1014 − 6×1015 Si/cm2) through the metal-Si interface at various substrate temperatures, and a final thermal annealing in vacuum to form the silicide. Forward I-V measurements are employed for electrical characterization. Metal-Si interaction and substrate damage are measured by MeV ion backscattering and channeling, and interfacial oxygen monitored by nuclear 16O(d,α)14N reaction.Platinum contacts prepared on clean n-type substrates are Schottky diodes with a barrier height øBn = 0.83 eV. After Si irradiation, the forward I(V) is a power law whose form is largely independent of the dose. Subsequent thermal annealing induces silicide formation, but at a reduced rate compared to irradiated samples. The do characteristics is roughly exponential again, but departures from the original Schottky characteristics remain and are largest for the highest Si doses. The effect is attributed to radiation damage in the Si that is not consumed by the silicide reaction.Platinum contacts prepared on chemically oxidized samples behave differently for different substrate materials, although the total amount of interfacial oxygen is always the same. On n+-type samples, the silicide formation at 400°C is laterally uniform for Si doses ≥ 2 × 1014 cm−2, but is nonuniform for all doses (≤ 2 × 1015 Si/cm2) on n-type samples. For n+-type samples at 250°C, a dose of 2 × 1015 Si/cm2 is required to induce (uniform) silicide formation; the kinetics displays a time delay compared with that of clean n+ substrates. On oxidized n-type substrates, the I(V) characteristics of Pt contacts before irradiation is not Schottky-like, but power-law-type. After irradiation, the characteristic is the same as for the clean irradiated samples. Thermal annealing induces only incomplete recovery toward an exponential behavior.These results demonstrate that radiation damage in the unreacted Si remains significant for the electrical behavior of all.These results demonstrate that radiation damage determines the I(V) characteristics of as-irradiated Pt contacts to n-type Si regardless of the presence of an interfacial oxide layer. After annealing at 400°C for 30 min, radiation damage is still significant, but the oxidized samples recover less than the clean ones. The results are attributed to radiation damage in the unreacted Si substrate.
The Nature of Point Defects and their Influence on Diffusion Processes in Silicon at High Temperatures
Authors: GÖsele U. , Tan T.Y. 
Published: March 2011

ABSTRACTThe paper highlights recent progress in understanding the role of vacancies and self-interstitials in self- and impurity diffusion in silicon above about 700°C. How surface oxidation of silicon leads to a perturbation of the pointdefect population is described. An analysis of the resulting oxidationenhanced or -retarded diffusion of group III and group V dopants shows that under thermal equilibrium as well as under oxidation conditions both vacancies and self-interstitials are present. For sufficiently long times vacancies and self-interstitials attain dynamical equilibrium which involves their recombination and spontaneous thermal creation in the bulk of silicon crystals. The existence and the nature of a recombination barrier slowing down the recombination process are discussed in this context. Recent experimental and theoretical results on the diffusion of gold in silicon enable us to determine the selfinterstitial component of silicon self-diffusion and to obtain an estimate of the respective vacancy contribution. The two components turn out to be of the same order of magnitude from 700°C up to the melting point.
Defects, Dislocations and Degradation of Compound Semiconductors
Authors: Johnston W. Dexter 
Published: March 2011

ABSTRACTDiode lasers and/or LEDs fabricated from the Ga1 − xAlxAs/GaAs or In1 −xGaxAsyP1−y alloy system provide the basis for rapidly developing optical communications systems. These devices are operated at very high optical and electrical power densities, and the inevitable less-than-perfect efficiency results in intense local thermal and athermal lattice excitation. This in turn can lead to generation, motion and growth of extended defect structures including dislocation networks, precipitation of impurities, or phase separation.For the AlxGa1−xAs material, a predominant degradation effect is the development of so-called <100> “dark line defects” (DLDs). These have been shown to arise from recombination enhanced climb of threading dislocations giving rise to dipole loops of a primarily interstitial character. A less common form, the <110> DLDs, is associated with slip and typically arises from the strain associated with mechanical damage or careless handling or device processing.The In1−xGaxAsyP 1−y device material affords less energy per recombina ion event by virtue of its smaller band-gaps, but is likely to have more lattice mismatch strain than Ga1−xAlxAs for typical compositions of device interest. Thus slip, <110> DLDs, and precipitates are the commonly observed features of In1−xGaxAsyP1−y degradation.
Laser Annealing of Ion Implanted Semiconductors
Authors: Narayan J. 
Published: March 2011

ABSTRACTPhoton energy from laser beams can be used to rapidly heat and melt localized regions of semiconductors with a high degree of spatial and temporal selectivity. Pulsed lasers have been successfully used to anneal displacement damage and to remove other defects. However, the number density of trapped defects increases with velocity of solidification and finally thin layers turn directly amorphous after laser-melt quenching. Annealing characteristics are found to be a strong function of ion implantation variables, which determine optical properties of materials. By both solid- and liquid-phase crystallization, supersaturated solid solutions can be formed. Residual defects in SPE grown layers primarily consist of dislocation loops. Device applications utilizing these transient thermal processing techniques are reviewed briefly.
The Friction and Wear Behavior of Ion Beam Assisted Nitride Coatings
Authors: Tetreault Thomas G. , Hirvonen J.K. , Parker G. 
Published: March 2011

AbstractThe method of Ion Beam Enhanced Deposition, (IBED), was used to produce hard films of i-BN, i-SixNy and i-TixNy. The friction, hardness, adhesion, and wear behavior of these nitride coatings were examined using a ball-ondisc friction/wear tester. The friction and wear results were sensitive to stoichiometry and the presence of impurities (e.g., hydrogen) in the film as well as the choice of ball material (400C stainless steel or silicon nitride).
Growth of Stoichiometric Bn Films by Pulsed Laser Evaporation
Authors: Murray P. T. , Donley M. S. , McDevitt N. T. 
Published: March 2011

AbstractThe feasibility of growing stoichiometric thin films of BN by pulsed laser evaporation has been investigated. Films grown under high vacuum conditions were N-deficient. This result is consistent with thermodynamic calculations, which indicate that B metal formation, with concomitant N2 desorption, is energetically favored over BN formation. Stoichiometric films were grown in NH3 with substrate temperatures of 400, 500, and 1000ºC. Analysis of films grown under these conditions by grazing incidence x-ray diffraction indicates the films to be highly oriented, hexagonal BN.
Characterization of TiN Films Prepared by ion Beam Assisted Deposition
Authors: Chang Albert L. , Kant R. A. 
Published: March 2011

AbstractOne of the advantages of the ion beam assisted deposition process is its controllability of the processing parameters such as: ion-to-atom arrival ratio and the ion energy. In this study, the effects of the nitrogen ion energy (from 1 KV to 30KV) on the TiN film morphology and microstructures were systematically investigated as a function of ion-to-atom arrival ratios, using TEM, XTEM, SEM, ESCA and other analytical techniques.
Interfacial Chemical Reactions Between MoS2 Lubricants and Bearing Materials
Authors: Zabinski J.S. , Tatarchuk B.J. 
Published: March 2011

AbstractX-ray Photoelectron.pectroscopy (XPS) and Conversion Electron M6ssbauer bpectroscopy (CEMS) were used to examine iron that was deposited on the basal plane of MoS2 single crystals and subjected to vacuum annealing, oxidizing, and reducing environments. Iron either intercalated into the MoS2 structure or formed oriented iron sulfides depending on the level of excess sulfur in the MoS2 structure. CEMS data demonstrated that iron sulfide crystal structures preferentially aligned with respect to theMoS2 basal plane and that alignment, and potentially adhesion, could be variedby appropriate high temperature annealing procedures.
Synthesis and Characterization of MoS2 Thin Films Grown by Pulsed Laser Evaporation
Authors: Donley M. S. , Murray P. T. , McDevitt N. T. 
Published: March 2011

AbstractThe growth and characterization of MoS thin films grown by pulsed laser evaporation is investigated. TOF anafysis of the ions evaporated from an MoS2 target indicates that PLE results primarily in the evaporation of atomic Mo and S species; MoxSy clusters were also detected, but were present at a significantly Iower intensity. TOF velocity analysis indicates an effective plasma temperature of 1500K. Stoichiometric MoS2 films were grown at substrate temperatures between room temperature and 500ºC under the above laser conditions. XPS data is used to develop a Wagner chemical state plot. Analysis of the films by Raman spectroscopy and glancing angle x-ray diffraction indicates the films to be crystalline, hexagonal MoS2, with a tendency for basal plane orientation parallel to the substrate.
A Tribological Study of Mo/Al2O3 in Sliding Contact
Authors: Hong Hyun-Soo , Winer Ward O. 
Published: March 2011

AbstractThis is Part II of a tribological study of metal/ceramic pair in a sliding contact. The tribological behavior of molybdenum against a single crystal A12O3 was investigated at bulk temperatures of 23ºC and 400ºC using a sliding speed of 4 m/s and loads from nine to twenty five Newtons. The role of oxidational wear was confirmed at both temperatures. The linear dependency of wear rate on load was identified at 23ºC tests. At 400ºC, there was a rapid increase of wear rate at a load of about 25 N possibly due to the volatilization of MoO3, which is the limitation of molybdenum oxide as a solid lubricant. However, this study showed that the out-of-contact oxide formation may have prevented the catastrophic oxidation during contact at the real area of contact. It also showed that in-situ formed molybdenum oxide has good lubricating properties (≃ 0.3) and a low wear rate (≃ 10-14 m3/m). Therefore, this molybdenum can be used for a large range of sliding speeds and loads.
The Acoefficient of Friction Between Boron Carbide (B4 C)Surfaces in Air and Ultrahigh Vacuum (UHV)
Authors: DeKoven Benjamin M. , Hagans Patrick L. 
Published: March 2011

AbstractFriction measurements between two contacting B4C surfaces in airand UHV at room temperature using 0.10-0.13N loads are reported. A novel pin (radius=0.005m) on flat device allowing for interchange in UHV is used. The tribological surfaces can be examined using scanning Auger and XPS in the same UHV system. The coefficient of friction for air exposed surfaces is found to vary between air (0.20-0.25) and UHV (1.2-1.8). Stick-slip behavior, indicating strong adhesion, is observed in UHV while only a smooth friction value is measured in air. Air pressures ≥ 100Pa are necessary toreduce the friction from the high value in UHV. The friction between the clean surfaces in UHV initially is 0.8-1.3, but following mechanical conditioning at a higher velocity the friction drops to 0.17-0.25. In situmechanical conditioning is necessary to obtain reproducible friction values for the clean surface. Exposing the clean surfaces to oxygen (103Pa) while conditioning results in an increase in friction (1.0-1.2). Auger line scans through the scar made using the clean surfaces show enhanced B and reduced C. Similar Auger scans for oxygen exposed surfaces indicate that tearing of the oxide layer may be the reason for the high friction. The friction for a clean pin and an in situ nitrogen-implanted flat (10keV, saturation dose) is 0.70-0.80. Film transfer to the pin is observed.