bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructure and Chemical Variation in Class F Fly Ash Glass
Authors: Qian J. C. , Lachowski E. E. , Glasser F. P.
Published: June 2019

Fly ash consists of mixtures of crystalline substances in a glassy matrix. This matrix is itself inhomogeneous. The combustion process gives rise to compositional fluctuations typically on a micrometer scale; these fluctuations are preserved in the glass and are gradational. However, high-resolution transmission electron microscopy of Class F ash also reveals the existence of interfaces on a nanometer scale. These arise as a consequence of phase separation. Textures and interfaces typical of spinodal decomposition and possibility also suggestive of classical immiscibility have been observed. It is believed that the occurrence of phase separation resulting in nanometer-scale inhomogeneities will be a feature common to most Class F glasses. The consequences of this complex microstructure to reactivity are not as yet known, but some speculations are presented.
Is the Available Alkalitest a Good Durability Predictor for Fly Ash Concrete Incorporating Reactive Aggregate?
Authors: Smith Robert L.
Published: June 2019

The available alkali test has been used for years as a method for preventing the use of a high-alkali fly ash in concrete containing reactive aggregate. This report presents data on fifteen good-quality Western ashes, both Class C and Class F, that are currently used in readymixed concrete. All fifteen ashes were effective in reducing the expansion due to the alkaliaggregate reaction. The reduction in mortar bar expansion (ASTM C 441) varied from 16% to 81%. Correlation of the percent reduction was made with available alkalies as Na2O, silica content, lime content, sulfur content, and the sum of silica, alumina and iron oxide. Surprisingly, the best correlation to percent reduction was with sulfur and the least was with available alkalies. This data indicates that most, if not all, fly ashes are effective in reducing the alkali aggregate reaction and that the available alkali test is not the best method for predicting the effectiveness of a fly ash in controlling this reaction.
The Permeability of Chloride Ions in Fly Ash-Cement Pastes, Mortars and Concrete
Authors: Malek R. I. A. , Roy D. M.
Published: June 2019

Fly ash-cement pastes are known to develop fine pore structures that may retard the transport of ionic species. The rapid chloride permeability technique for studying the Cl− ion diffusion in hydrated fly ash/cement pastes, mortars and concrete was used. The technique applies an electrical potential across a cylindrical sample and measures the charge passed in a certain period of time. The results obtained on pastes and mortars cured for 28 days were reported previously and contrasted with those of neat cement pastes and mortars. The present paper reports more extensive studies made to examine the chloride permeabilities of pastes and mortars cured for up to 90 days. In addition, the effect of variable fly ash contents was examined. Concrete samples were included in the test scheme and the data were compared with pastes and mortars. Two important factors controlling the test results are discussed: first the mix design and curing conditions; second the experimental conditions during Cl− permeability measurements. In the second factor, the amount and rate of heat build up and the chloride ion concentrations are compared with the current passed. In addition, measuring current versus resistivity are critically discussed in terms of the voltage-current varistic characteristics of cement matrices.
Modification of the Interfacial Zone Between Aggregate and Cement Paste
Authors: Xueqan Wu , Dongxu Li , Xiun Wu , Minshu Tang
Published: June 2019

In order to improve the properties of concrete, the composition and structure of the interfacial zone must be modified. This may be done by pretreating the inert aggregate with special reagents to form a reactive surface, which will then react with the cement paste, resulting in an enhancement of the bond strength between cement paste and aggregate through the combination of the physical, chemical and mechanical interlocking effects. A cylindrical hole was drilled in a limestone cake and the surface of the hole coated with special solutions; cement slurry was then poured into the hole and the specimens were cured in a fog room. The shearing strength was determined to evaluate the effect of the aggregate pretreatment on the bond strength. The mechanical strength, porosity, electric conductivity of the concrete, orientation degree of the Ca(OH)2 and morphology in the interfacial zone were also examined. It was found that the compressive and flexural strengths increased, and the bond strength between aggregate and cement paste also increased; the porosity, average pore size, number of large harmful pores, electric conductivity and the orientation index of the Ca(OH)2 decreased.
Effect of Bond Strength Between Aggregate and Cement Paste on the Mechanical Behaviour of Concrete
Authors: Yuan Chen Zhi , Guo Wang Jian
Published: June 2019

Concrete is a composite material, consisting of hardened cement paste (HCP), aggregate and pores. The interfacial bond between HCP and aggregate is very important in determining some of the properties of concrete, such as the mechanical behaviour and durability. Recently, the microstructure of the transition zones between different aggregates and HCP has been studied and a mechanism for the formation of the transitional zone has been proposed by Maso. The objective of the present work has been to study the relationship between interfacial bond and mechanical behaviour of concrete in the light of both theoretical and experimental research on the microstructure of the interfacial zone.
A Stludy of the Interfacial Region Between Cement Paste and Aggregate in Concrete
Authors: Scrivener Karen L. , Crumbie Alison K. , Pratt P. L.
Published: June 2019

The application of quantitative image analysis to the measurenent of microstructural gradients in the interfacial zone in concrete is described. Some preliminary results are presented and discussed.
The Mechanisms of Reactive Ion Etching Of SiOx (x≤2) with Electron Cyclotron Resonance and Kaufman Ion Sources
Authors: Kant R. A. , Eddy C. R. , Sartwell B. D.
Published: June 2019

The dominant factors governing reactive ion etching of Si, SiO, and SiO2 thin films during bombardment with energetic Ar ions in a Cl atmosphere were investigated. Etch rates were determined in-situ by measuring weight loss as a function of ion fluence for films deposited on a quartz micro-balance. Measurements were made as a function of ion energy and Cl pressure using a Kaufman gun for ion energies from 300 to 1500 eV and an electron cyclotron resonance microwave ion source for ion energies from 50 to 600 eV and for Cl pressures ranging from 0.006 to 0.05 Pa. Results were compared to sputtering in Ar alone. The results indicated that the presence of the C1 enhanced the etch rate for all three materials, with the degree of enhancement being inversely proportional to the oxygen content of the film. It was also discovered that there was an optimum pressure for enhancement of the etching and that at the highest pressures, the etching could actually be suppressed. These results are discussed in terms of physisorbed gas layers, the thickness of which depends on the balance between the flux of energetic particles and the gas flux.
Thin Film Growth of High Tc Superconductors by Microwave Plasma Assisted Reactive Evaporation
Authors: Tukamoto Akira , Hiratani Masahiko , Aida Toshiyuki , Tarutani Yoshinobu , Takagi Kazumasa
Published: June 2019

The oxidizing activity of an oxygen plasma is investigated in terms of the oxygen content of HoBa2Cu3Ox. thin films. The thermodynamically stable region of HoBa2Cu3Ox. and the region where the HoBa2Cu2Ox films are formed are also determined both in molecular oxygen and in an oxygen plasma. The oxidizing activity of an oxygen plasma is equivalent to that of molecular oxygen at three orders of magnitude higher pressure. The oxygen plasma expands the thermodynamic stability limit toward higher temperatures and the oxidizing activity limit toward lower oxygen pressures. In addition, the interfacial reaction between an oxide superconductor and silicon is investigated. The oxygen ions in HoBa2Cu3O film diffuse into Si even at room temperature, probably enhanced by the strong affinity of silicon for oxygen ions.
Energy Distribution of Negative Oxygen Ions Emitted from YBaCuO and Iron Garnet Targets by dc- and rf-Magnetron Sputtering
Authors: Krumme Jens-Peter , Hack Ron A. A. , Raaijmakers Ivo J. M. M.
Published: June 2019

The energy distribution of negative O− species sputtered from an YBaCuO and an iron-garnet target in dc- and rf-magnetron discharges has been analyzed by means of an energy-dispersive mass spectrometer in the range of noble-gas pressures from 0.05 to 4.2 Pa. Evidence is presented that energetic 0- ions originate essentially from two sources: (a) those formed directly by sputtering from the target surface and accelerated across the sheath in the full cathode-potential gradient; and (b) those created by electron attachment to neutral oxygen atoms near the sheath boundary to the plasma and accelerated in the remaining potential gradient of the sheath. On their path through the plasma these energetic O− ions are eventually annihilated by electron stripping and elastic scattering dominating in the pressure × distance regime above ∼0.1 Pa × m. The yield YO- of type-a O− ions increases with decreasing oxygen-vacancy density. Thus, doping of the noble-gas plasma with up to ∼1 vol% oxygen results in enhanced yield of 0- ions, while doping with hydrogen reduces the formation of O− species but gives rise to the creation of OH- ions. Furthermore, YO-increases with increasing ionicity of the oxides constituting the target, like BaO, exhibiting a larger difference in electronegativity between anions and cations. Thus, we find a between 1 and 2 orders of magnitude less yield of O− ions from a GdBiFeGaAl-gamet, as compared to the YBaCuO target, confirming the dissociative behavior of the BaO bond.
CH4 :H2 :Ar rf/ECR Plasma Etching of GaAs and InP
Authors: Law Victor. J. , Ingram S. G. , Jones G. A. C. , Grimwood R. C. , Royal H.
Published: June 2019

A comparative study of CH4 :H2 , and CH4 :H2 :Ar rf-plasma and microwave electron cyclotron resonance (ECR) plasma etching of GaAs and InP is presented. The study is in two parts;

(i) Kinetic studies of GaAs and InP etch rates as a function of the constituent gas flow rates, applied rf and microwave powers, substrate temperature and position. The results indicate that CH4 :H2 :Ar ECR etching of GaAs is 10× more efficient in the utilisation of the CH4 precursor gas than rf-plasmas. However, the absolute etch rates are lower (70 nm min−1 for rf and 25 nm min−1 for rf biassed ECR-plasmas).The effect of etching conditions on InP morphology is also examined.

(ii) The study of electrical “damage” in GaAs/AlGaAs high electron mobility transistor (HEMT) Hall bar structures, was investigated by ECR-plasma etching off the top GaAs capping layer. Results indicate that ECR-plasma etching with an rf-bias between 0V and −30V does not significantly effect the electrical characteristics of such devices at 300K, with some degredation at 1.2 K.
Chemical Precursors for GaAs Etching with low Energy ion Beams: Chlorine adsorption on GaAs(100)
Authors: Jackman Richard B. , Tyrrell Glenn C. , Marshall Duncan , French Catherine L. , Foord John S.
Published: June 2019

This paper addresses the issue of chlorine adsorption on GaAs(100) with respect to the mechanisms of thermal and ion-enhanced etching. The use of halogenated precursors eg. dichloroethane is also discussed in regard to chemically assisted ion beam etching (CAIBE).
Heteroepitaxy of Si/Si1−xGex Grown by Remote Plasma-Enhanced Chemical Vapor Deposition
Authors: Hsu T. , Qian R. , Kinosky D. , Irby J. , Anthony B. , Banerjee S. , Tasch A. , Magee C.
Published: June 2019

Low temperature heteroepitaxial growth of Si1−xGex films with mole fractions “x” ranging from 0.07 to 0.72 on Si(100) has been achieved by Remote Plasma-enhanced Chemical Vapor Deposition (RPCVD) at substrate temperatures of 305°C and 450°C. Reflection High Energy Electron Diffraction (RHEED), Transmission Electron Microscopy (TEM), and Secondary Ion Mass Spectroscopy (SIMS) were employed to characterize the crystallinity, composition and interfacial sharpness. The Si1−xGex films with thickness below the critical layer thickness were confirmed to have excellent crystallinity with defect density below the sensitivity of TEM analysis (105 cm−2). The Ge profile, from SIMS analysis, in a Si/Si0.8Ge0.2/Si/Si0.82Ge0.18 multilayer structure was found to have a transition width of 30Å/decade, which is the resolution limit of SIMS analysis. There is no Ge segregation observed at the Si/Si1−xGex interface. A superlattice structure with 24 pairs of Si(60Å)/Si0.8Ge0.2 (60Å) layers has been successfully grown by RPCVD at 450°C. From cross-sectional TEM analysis, very low defect densities and abrupt Ge transitions were confirmed.
Ion Beam Sputter Deposition Of Ferroelectric Oxide Thin Films
Authors: Graettinger Thomas M. , Auciello O. , Ameen M. S. , Al-Shareef H. N. , Gifford K. , Kingon A. I.
Published: June 2019

Ferroelectric oxide films have been studied for their potential application as integrated optical materials and nonvolatile memories. Electro-optic properties of potassium niobate (KNbO3) thin films have been measured and the results correlated to the microstructures observed. The growth parameters necessary to obtain single phase perovskite lead zirconate titanate (PZT) thin films are discussed. Hysteresis and fatigue measurements of the PZT films were performed to determine their characteristics for potential memory devices.
Preparation Of Bi4Ti3O12 Films by ECR Plasma SpuTtering
Authors: Masumoto Hiroshi , Goto Takashi , Masuda Youichirou , Baba Akira , Hirai Toshio
Published: June 2019

Epitaxially grown films of Bi4Ti3O12 (BIT) were prepared on the substrate of a sapphire single crystal heated at 650°C using a sintered Bi4Ti3O12 target by electron cyclotron resonance (ECR) plasma sputtering. The BIT film of the same composition with the target was obtained under the conditions of microwave power(Mp) higher than 500 W and RF power(Rp) between 300 to 700 W. Increasing Mp or Rp, the deposition rate of the film was increased and the surface of the film became rough. The film exhibiting flat surface, good crystalline orientation and stoichiometric composition was prepared at such the high rate as 3.5 Å/sec under the conditions of Mp=500W and Rp=500W. Dielectric constants(1KHz) of the films deposited on (1120), (1102) and (0001) of sapphire were 93, 121 and 90, respectively, and refractive indexes of each films for the wave length of 632 nm were 2.32, 2.38 and 2.37, respectively.
Molecular Dynamics Simulations of Thin Film Diamond Growth
Authors: Pailthorpe Bernard A. , Knight Peter
Published: June 2019

The growth of synthetic diamond thin films is studied by molecular dynamics computer simulations of low energy carbon atom deposition onto a low temperature diamond (111) surface. A previously reported Stillinger Weber potential, reparameterised for sp3 bonding in carbon using Hartree-Fock calculations for small carbon clusters, is used to model the interatomic interactions. The penetration of 1-100eV neutral carbon atoms into a (111) surface of carbon at 100K and the resultant surface atom rearrangements and induced film stress are studied. For intermediate energies (20-60eV) the incident atoms penetrate beneath the exposed (111) surface and increase the lateral compressive stress in the diamond film. It is suggested that diamond films grow from below the exposed surface in a region of locally high stress and tetrahedral coordination. The predicted radial distribution functions agree reasonably with electron diffraction studies of vacuum arc deposited amorphous diamond.
Oxidation Of AIN-Al2O3 Composite Film Prepared By Microwave Plasma CVD
Authors: someno Yoshihiro , sasaki Makoto , Hirai Toshio
Published: June 2019

Thermal oxidation resistance, in a temperature range of 600 to 1100° C, of AIN-Al2O3 composite, AIN and θ-A12 O3 films has been studied. The films were prepared by microwave plasma CVD using an AlBr3 -H2 -N2 -Ar gas system at a substrate temperature of 430° C. AIN-Al2O3 composite film was found to have good surface stability below an oxidaton temperature of 1100°C and to have the best properties for insulation film.

Key words: microwave plasma CVD, AIN-Al2O3 composite, passivation film, oxidation resistance, AlBr3
Molecular Dynamics Simulations of Ion Beam Mixing
Authors: Mazzone A. M.
Published: June 2019

This work presents a molecular dynamics simulation of the intermixing of a metallic bilayer. The aim of the simulation is to elicit, in a more rigourous manner than in standard theoretical approaches, trends and phenomena taking place during the post-collisional stage of the cascade.
The Influence of Ion Bombardment on the Surface Composition of 70 wt% Cu-30 wt% Zn Alpha-Brass
Authors: Franetovic Vjekoslav
Published: June 2019

The short time ion bombardment during ion milling resulted in a dramatic change in the surface composition of alpha-brass, selectively removing up to 2/3 of the Zn atoms during the first 5 to 10 minutes of ion milling. This differential sputtering occurred at various ion beam energies and at target temperatures as low as −196°C (LN2 temperature). The effect of differential sputtering completely disappeared after ion milling times in excess of three hours. Such a dramatic change in composition could not be attributed either to a difference in sputtering yield or to different ion milling conditions. It was shown that under constant ion milling conditions this differential sputtering depends strongly and only on the condition of the foil surface. The unexpected disappearance of the effect of differential sputtering with time was attributed to stabilization of a characteristic surface topography produced by long time ion bombardment.
Magnetron-Enhanced Reactive-Ion-Etching of Al-1%Si-2%Cu Alloy
Authors: Fu C. Y. , Hsu R. , Malba V.
Published: June 2019

Plasma etching of Al-1%Si-2%Cu presents serious challenges in corrosion, residue, and critical dimension (CD) control in single wafer etchers. One approach is to pattern the metal with oxide mask so chlorine can no longer be trapped in resist and sidewall polymers to cause corrosion. The magnetron-enhanced reactive-ion-etching (MERIE) offers a high degree of ionization at very low pressure, so anisotropic etching with reasonably high etch rate can be achieved even without sidewall protection. This paper summarizes our MERIE process characterization in terms of the effects of SiCl4 flow rate and plasma power on selectivity and CD control using an oxide mask. Typical etching was performed at 1000 watts and 40 sccm SiCl4 with the unthrottled pressure at 4.0 mTorr and a self-induced dc bias of 75 V. A 2-minute NF3 plasma at 250 watts and 100 sccm of NF3 flow served as the passivation step. This metal etch process has been successfully implemented in a doublelayer-metal interconnect technology.
Universal Energy Dependence of Sputtering Yields At Low Ion Energy
Authors: Muri J. , Steinbrüchel Ch.
Published: June 2019

Sputtering yields Y(E)at ion energies E keV are shown to be described by the equation Y(E) = A(En - ) where A, n, and the threshold energy Eth are constants characteristic for a particular projectile/target combination. Examination of a wide variety of systems reveals that n = 0.5 provides an excellent universal representation of a large body of data, including physical sputtering of metals by noble gas ions, selfsputtering of metals, as well as physical and chemical sputtering of Si and SiO2. The above value for n is consistent with a 1/r4 power law atom-atom interaction potential within Sigmund's theory of sputtering. Another conclusion is that the effect of Eth on Y(E) must be taken into account at ion energies as high as 1 keV, not just near the sputtering threshold.
Experimental and Theoretical Investigations on the Interrelation of Charge Exchange Processes and Energy Loss of Particles at Metal Surfaces
Authors: NÄrmann A. , Heiland W. , Monreal R. , Flores F. , Echenique P. M.
Published: June 2019

We present experiments and a theoretical model for the energy loss distribution of specularly reflected particles after slow (2-5 keV) He ions have been impinging on a Ni(110) surface under grazing incidence. The energy spectra of the backscattered particles are asymmetric with the low-energy tail falling off more slowly than the high-energy tail does.

This asymmetry is accounted for by considering charge exchange events during the interaction with the surface. The main neutralization channel for this system is the Auger-neutralization from the conduction band into the He-1s ground state. The transition rate for this process was calculated from first principles. Assuming that the ‘friction coefficient’ for the system particle-surface depends on the charge state of the particle, we calculate the energy lost by a particle during the interaction as a sum of different contributions belonging to different charge states.
ECR Plasma Etching Technology for ULSIs
Authors: Samukawa Seiji
Published: June 2019

A new electron cyclotron resonance (ECR) plasma etching technology has been developed to realize simultaneously high selectivity, high rate and anisotropic etching for phosphorus doped poly-Si and WSix/poly-Si at a low ion energy. In this technology, a substrate is located around the ECR position (875 gauss position) in an ECR plasma. As a result of ECR position etching, under the low pressure of 5 × 10−4 Torr, a high etching rate and an infinite selectivity to SiO2 etching are realized by using C12/O2 and Cl2/O2/SF6 etching gas.
Solid State NMR Studies of the Adsorbed States of Formic Acid on Y Zeolites
Authors: Duncan T. Michael , Vaughan Robert W.
Published: June 2019

Several multiple-pulse double-resonance NMR techniques have been applied to isolate and characterize the spectra of the adsorbed states of formic acid on two Y zeolites. The two surface states, bidentatT3 and ynidentate, possess different motional properties and 13C - H cross-polarization techniques may be used to separate the spectra. The 13C chemical shift anisotropy is founa to iorrelate with the symmetry of the formate species. The H spectrum of the carbonyl hydrogen, selectively observed with the dipolardifference method, indicates that this hydrogen becomes more acidic upon adsorption.
Influence of the Structural Parameters of Polysilicon Films on the Piezoresistive Properties at High Temperature
Authors: Kleimann P. , Semmache B. , Berre M. Le , Barbier. D.
Published: June 2019

Polycrystalline silicon, used as a transducing material in high temperature Silicon On Insulator piezoresistive pressure sensor, is well known to be strongly dependent on the process parameters. Indeed depending on the deposition, doping and annealing conditions, the structural parameters of polysilicon namely grain size and texture may be very different. We use here a complete model of the piezoresistivity in polysilicon including a significant effect at grain boundaries to study the influence of structural parameters on the resistivities, gauge factors and their thermal drifts between room temperature and 200°C. The model validity has been verified experimentally for two types of polysilicon materials (LPCVD at 620°C and LPCVD at 580°C), subsequently B-doped (from 9×1018 to 9×1019 cm−3) and annealed by Rapid Thermal Annealing at 1100°C/20s and 1100°C/40s respectively. A good agreement between theoretical and experimentally determined resistivities and gauge factors at a variable temperature is observed for the two types of polysilicon materials considering different grain sizes with a <110> dominant texture for LPCVD 620°C series and no preferential texture for LPCVD 580°C series.
Effect of Thermoelastic Stress on the Pressure Response of a Composite SiO2/Si Membrane
Authors: Malhaire C. , Berre M. Le , Barbier D.
Published: June 2019

The layout design of membrane-based sensors such as Silicon On Insulator micromachined pressure sensors requires the knowledge of the mechanical behavior of the complete structure as a function of pressure and temperature. Unfortunately, as a result of thermal mismatch, large stresses usually exist in composite SiO2/Si membranes that significantly affect the pressure response of such sensors, We present here an original study on the 3D-FEM modeling (ANSYS) of pre-stressed SiO2/Si membranes submitted to pressure. The model of thermoelastic stress (without any applied pressure) has been first validated by optical profilometry deflection measurements. 2.94 mm width membranes with Si thickness varying from 10.7 to 19.3 μm, as measured by FT-IR, and covered with 1.46 μm thick thermal oxide grown at 1130°C, have been studied. Thermoelastic deflections from I to 25 μm have been measured for decreasing Si thickness in agreement with the simulation. The simulated longitudinal stress relaxation over the oxide varies from 5 to 40 MPa between the membrane center and the frame when decreasing membrane thickness. Under pressure (10 and 100 mbar) and for a 19.3 μm thick composite membrane (0.5 )μm thick oxide), the calculated strains can exceed by 20% that of a bare Si one, due to a lower overall stiffness produced by the oxide compressive stress.
Charge Trapping and Degradation Properties of PZT Thin Films for MEMS
Authors: Kim Hyeon-Seag , Polla D. L. , Campbell S. A.
Published: June 2019

The electrical reliability properties of PZT (54/46) thin films have been measured for the purpose of integrating this material with silicon-based microelectromechanical systems. Ferroelectric thin films of PZT were prepared by metal organic decomposition. The charge trapping and degradation properties of these thin films were studied through device characteristics such as hysteresis loop, leakage current, fatigue, dielectric constant, capacitancevoltage, and loss factor measurements. Several unique experimental results have been found. Different degradation processes were verified through fatigue (bipolar stress), low and high charge injection (unipolar stress), and high field stressing (unipolar stress).
Experimental Analysis of the Process of Anodic Bonding using an Evaporated Glass Layer
Authors: Choi W. B. , Ju B. K. , Lee Y. H. , Haskard M. R. , Jeong S. J. , Lee N. Y. , Sung M. Y. , Oh M. H.
Published: June 2019

A silicon-to-silicon anodic bonding process using a glass layer deposited by electron beam evaporation will be described. Corning #7740 Pyrex glass was used the source material of electron evaporation. From Auger electron spectroscopy (AES), the composition of the deposited glass layer is nearly same as that of the bulk Pyrex glass plate. Wafers are bonded at a temperature as low as 135 °C with an applied voltage as small as 35Vdc, enabling of this technique to be applied to vacuum packaging of microelectronic devices. Experimental results reveal that an evaporated glass layer of more than 1 μ m thick is suitable for anodic bonding. Finally, The role of sodium ions in anodic bonding was also studied by investigating the theoretical bonding mechanism and examining the results of secondary ion mass spectroscopy (SIMS) analysis.
Titanium-Nickel Shape Memory Thin Film Actuators for Micromachined Valves
Authors: Kahn H. , Benard W. L. , Huff M. A. , Heuer A. H.
Published: June 2019

Microelectromechanical valves have been fabricated from silicon wafers using standard bulk micromachining techniques, which utilize thin (2 μm) films of sputter-deposited titaniumnickel as the actuators. The TiNi shape memory alloy actuators are thermally driven by resistive heating, through the passage of an electric current. TiNi diaphragms (8.4 mm wide) are fabricated and tested in a pressure-temperature controlled fixture in order to determine the mechanical properties of the shape memory film. If a silicon island is left attached to the center of the diaphragm, this can act as a “boss” whose movement against an orifice will open and close the valve. The orifice can be etched into a second silicon wafer or machined from another rigid material. Use of mechanical spacers and external bias springs result in a normally-closed or normally-open configuration. Modulations of up to 90 percent have been observed in gas flows of up to 0.6 liter/min. Water flows as high as 5 ml/min. have been modulated by 60 percent.
Selective Electroless Copper Metallisation of Epoxy Substrates
Authors: Campion L. M. , O'reilly M. , Macauley D. J. , Kelly P. V. , Crean G. M.
Published: June 2019

This paper discusses the development of a novel selective electroless copper metallisation route for the plating of epoxy substrates. This has the potential for the development of a more cost effective and environmentally friendly plating process than currently available technologies. The electroless process required that the electrically insulating epoxy substrate was initially activated to catalyse the reduction of the copper (I1) salt which was in solution to a copper (0) deposit. Selective activation was achieved by coating the epoxy substrates with a new proprietary palladium compound and selectively exposing specific areas to 222nm radiation from a KrCI* excimer lamp. It has been shown that only the palladium metal and not the proprietary precursor catalyse the reaction. After selective seeding the patterned epoxy substrates were copper plated in a commercial electroless copper bath. The process conditions and effect of surface preparation on the quality and resolution of the selectively deposited copper patterns are discussed.
Design and Properties of a Thin-Film, Mems-Based Magnetostrictive Magnetometer
Authors: Kistenmacher T. J. , Osiander R. , Ecelberger S. A. , Givens R. B. , Wickenden D. K. , Murphy J. C.
Published: June 2019

The principles of operation of a MEMS-based magnetometer designed on the magnetoelastic effect are described. The active transduction element is a commercial (001) silicon microcantilever sputter coated with an amorphous thin film of the giant magnetostrictive alloy Terfenol-D [(Dy0.7Tb0.3)Fe2]. The easy axis of magnetization of the Terfenol-D film lies in the plane of the microcantilever and along the acicular direction. In addition to the magnetostrictive transducer, basic components include: (a) mechanical resonance of the coated-microcantilever through coupling to an ac magnetic field; and, (b) detection by optical beam deflection of the microcantilever motion utilizing a laser diode source and a position-sensitive detector. The sensitivity of this magnetostrictive magnetometer is currently 1 μT, which is three orders of magnitude better than a magnetometer based on a similar-sized piezoresistive cantilever.
Self-Passivated Copper Gates For Thin Film Silicon Transistors
Authors: Sirringhaus H. , Theiss S.D. , Kahn A. , Wagner S.
Published: June 2019

A solution to the thin film silicon transistor gate metallization problem in active matrix liquid crystal displays is demonstrated in the form of a self-passivation process for copper. Bottom-level copper (Cu) lines are passivated by a self-aligned CrOx encapsulation formed by surface segregation of chromium (Cr) from dilute Cu1-xCrx alloys (x=0.1–2.3) at 400°C. The encapsulation is an efficient barrier for Cu diffusion into the SiNx gate insulator during the plasma deposition and transistor processing, and solves the problems of oxidation and adhesion to the glass substrate. Gate line resistivities are 4.5 to 7.5μΩcm depending on the initial Cr concentration. The performance of self-passivated Cu-gate thin film transistors is comparable to that of transistors with refractory metal gates.
Influence of Boron Diffusion on Ultra-Thin Oxides
Authors: Nigam T. , Depas M. , Heyns M. , Sofielc C. J. , Mapeldoram L.
Published: June 2019

In this paper the effect of different annealing conditions on boron diffusion is studied for 3 nm gate dielectrics. The use of amorphous material instead of polycrystalline material and the influence of nitridation (two-step N2O oxidation) was investigated. A better control on the flatband voltage (VFB) shift was observed for amorphous-Si gate as compared to polycrystalline-Si gate. A reduction in VFB was observed for N2O oxides as compared to pure oxides, but VFB was still above the ideal value for some of the thermal treatments. A significant reduction in QBD is observed for p+ gates as compared to n+ gates. The lowest post-implantation anneal gives the highest QBD for all the different combinations.
Organic Contamination of Silicon Wafer in Clean Room Air and Its Impact to Gate Oxide Integrity
Authors: Imafuku D. , Mizubayashi W. , Miyazaki S. , Hirose M. , Wakayama Y. , Kobayashi S.
Published: June 2019

Organic adsorbates on silicon wafer surfaces exposed to superclean room air were measured to evaluate organic contamination level of silicon wafers stored in a clean bench up to 180min. Such Si wafers were thermally oxidized and the dielectric degradation behavior were systematically investigated. It is found that a carbon contamination level of half a monolayer influences the charge to quasi-breakdown although the degradation mechanism itself remains unchanged.
Replacement of C-V Monitoring with Noncontact Cos Charge Analysis
Authors: Catmull K. B. , Cosway R. G. , Letherer B. A. , Homer G. S.
Published: June 2019

Many semiconductor processing facilities rely heavily on capacitance voltage (CV) analysis for verification of oxidation furnace cleanliness. CV provides an accepted set of electrical test parameters (Vfb, Qm, Tox Dit, etc). that can be used to monitor tube contamination levels during processing. However, two significant drawbacks of the CV technology are a) the need for costly and time-consuming deposition of MOSCAF (Metal Oxide Semiconductor Capacitor) electrodes, and b) the reduction in electrically active contaminants due to the MOSCAP processing sequence. A commercially available noncontacting technology called corona-oxide-semiconductor (COS) analysis is described here which does not require post-oxidation processing, but does measure the fundamental electrical test parameters required for process control and development [2]. The noncontact COS technology is shown to be significantly more responsive to intentionally introduced electrically active contaminants than poly MOSCAP CV. The data indicate that this difference in sensitivity is due to the immediate, processing-free nature of the COS technology.
Space Charge Analysis in Thin SiO2 Films: Local Vs. Uniform Degradation Models
Authors: Kotov A. E.
Published: June 2019

The behavior of small MOS structures (area 3 μm2), subjected to stresses caused by electron injection, demonstrates an obvious non-parallel shift in the tunneling characteristics (NPS effect), measured in the wide current range (3·10-16 -3·10-8 A) from either tunneling interface. This paper describes and compares two different approaches for the NPS effect interpretation: uniform and local degradation models (UDM and LDM). The UDM implies a modification of the oxide tunneling barrier due to area-uniform electron trapping inside the tunneling distance which could lead to the NPS effect [14]. It is shown that any spatial distribution of negative oxide charge is inapplicable to interpret the NPS effect within the framework of the UDM. The second approach uses the assumption of small (area ∼ 10-3 μm2) structure-stable regions (SSR) formed in noncrystalline SiO2 films during thermal growth. Due to the high resistance of SSRs to the degradation - negative charge generation - electron injection is gradually localized in the SSRs, avoiding a screening effect of electron trapping. It is shown that the influence of non-uniformity in the electron injection appears to be more significant, when degraded MOS structure is tested at low voltages (NPS effect).
Effect of Channel Profile Engineering on Hot Carrier Reliability in nMOSFETs with 100 nm Channel Lengths
Authors: Saha Samar K.
Published: June 2019

Hot-carrier effect was studied for different channel doping profiles in nMOSFET devices with effective channel length near 100 nm using a device simulator. The test structures for device simulation were generated using gate oxide thickness of 3 nm. The channel doping profiles used were abrupt- and graded-retrograde types with low surface and high substrate concentrations, and conventional step profiles with high surface and low substrate concentrations. For accurate device simulation, a hydrodynamic model for semiconductors was used to simulate the non-local transport phenomena in the devices. The simulation results indicate that for ultra-short channel devices, the current drivability and the hot-carrier effects depend on the shape of channel doping profiles. For a given supply voltage, the hot-carrier effects in ultra-short channel devices can be controlled by optimizing the channel doping profiles.
Stress-Recovery Transients in Ultra Thin Oxides on Silicon
Authors: Lundgren Per , Jauhiainen Anders , Ragnarsson Lars-Åke
Published: June 2019

The logarithmic current transients observed after electrical stress of 2 nm thick oxides on silicon show no sign of saturation for times up to 1 Ms. These results contradict the hypothesis that the tunneling distance from oxide defects to an interface is the main source of the dispersive relaxation in our case, and this might very well extend to other cases where such relaxation is observed in MOS devices with thicker oxides.
Effects of Adhesion on the Measurement of Thin Film Mechanical Properties by Nanoindentation
Authors: Tsui T. Y. , Ross C. A. , Pharr G. M.
Published: June 2019

Experiments have been performed on soft aluminum films deposited on hard ceramic substrates to explore the influences of interfacial adhesion on mechanical property measurement by nanoindentation. The substrate materials included soda-lime silicate glass, aluminum oxynitride (ALON), and (100) sapphire. Thin films of high purity aluminum were sputtered onto each substrate to a thickness of 500 nm. Because the films were deposited simultaneously, the only major difference in the specimens was the nature of the substrate, which exerts an important influence on film adhesion through interfacial chemistry. Of the substrates examined, aluminum adheres strongly to glass and sapphire, but poorly to ALON. In addition, two different types of aluminum films on sapphire were examined - one with and the other without a 10 nm interlayer of amorphous carbon which significantly reduces film adhesion. Testing revealed important differences in the hardness of the specimens when measured by standard nanoindentation methods. Characterization of the residual hardness impressions by high resolution scanning electron microscopy showed that the hardness differences arise from an influence of interfacial debonding and film delamination on pile-up in the film. Furthermore, when the pile-up is accounted for in contact area determinations, the film hardness is actually independent of the substrate, thus indicating that the hardness differences observed in nanoindentation testing are an artifact of the testing analysis procedure. Results of the experiments are documented and discussed.
Integrated Fiber Optic Sensors For Nondestructive Characterization Of Concrete Structures
Authors: Ansari F.
Published: June 2019

It is possible to monitor the initiation and progress of various mechanical or environmentally induced perturbations in concrete elements by way of fully integrated optical fiber sensors. Geometric adaptability and ease by which optical fibers can be embedded within concrete elements has led to the development of a number of innovative applications for concrete elements. This article is intended for a brief introduction into the theories, principles, and applications of fiber optic sensors as they pertain to applications in concrete.. However, due to the fact that the transduction mechanism in optical fibers is invariant of the materials employed, the principles introduced here also correspond to other structural materials. The only application related differences among various materials pertain to sensitivity and choice of optical fiber sensor types.
A Multiplexed Optical Fiber Sensor System For Distributed Measurement Of Structural Strains
Authors: Ansari F. , Chen Z. , Li Q.
Published: June 2019

Structurally integrated optical fiber sensors form the basis for smart structure technology. Over the past decade a variety of sensor configurations have been developed for measurement of strains and deformations in structures. Strains and deformations alter the refractive index and the geometry of the optical fiber material. These changes perturb the intensity, phase, and polarization of the light-wave propagating along the probing fiber. The optical perturbations are detected for the determination of strain. The research presented here describes the development of a new optical fiber sensor system for measurement of structural strains based on white light interferometry. An optical switch provides for multiplexing of strain signals from various locations in the structure. Redundant Bragg grating type fiber optic sensors as well as strain gauges were employed for comparison and verification of strain signals as measured by the new system. The system provides capability for distributed sensing of strains in large structures.
Monitoring Fatigue Damage In Concrete
Authors: Subramaniam Kolluru V. , Popovics John S. , Shah Surendra P.
Published: June 2019

Rigid airport pavement structures suffer damage from multi-axial high magnitude cyclic stresses resulting from passing heavy aircraft. It is of interest to model the response of plain portland cement concrete to such loading conditions; thus, the sensitive detection and characterization of such damage during the loading process is important. Low strain vibrational resonance frequency measurement offers direct information concerning the global, apparent elastic moduli of the material and preliminary results have shown such measurements are sensitive to the presence of damage in concrete.

The work reported here includes the theoretical foundation and experimental results of a non-destructive technique, based on vibrational resonance measurement. The tests are applied to monitor damage imparted to end-mounted hollow concrete cylinders subjected to monotonic and cyclic torsional (bi-axial) loads. An introduction to the concepts of vibration testing and details of mechanical and vibrational test procedures employed are given first. The most significant vibrational modes, of all of the possible modes setup within the specimen, are identified. The frequency value of these significant modes in the concrete specimen are experimentally obtained throughout a controlled cyclic testing procedure to failure. The behavior of these modes is then monitored during
a controlled cyclic testing procedure to failure. Distinctions between the frequency values of the various excited resonance modes are noted. Moreover, effects of the two damage types (monotonic and cyclic) on the frequency values of the modes are studied. Finally, conclusions concerning the applicability of the vibrational resonance techniques for monitoring imparted damage in these concrete specimens are drawn.
A Possible Basis for Nondestructive Characterization of Ropes of Nylon 6
Authors: Jiang H. , Davis M. K. , Eby R. K. , Arsenovic P.
Published: June 2019

Physical properties and structural parameters have been measured for ropes of nylon 6 as a function of the number of use operations. The fractional content of the α crystal form, sound velocity, birefringence, tensile strength and length all increase systematically and significantly with increasing the number of use operations. The fractional content of the γ crystal form and fiber diameter decrease with use. These trends indicate that the measurement of such properties and structural parameters, especially the length, provide a possible basis for establishing a reliable, rapid, and convenient nondestructive characterization method to predict the remaining service life of nylon 6 ropes.
The Use of Thermoelasticity to Evaluate Stress Redistribution and Notch Sensitivity in Ceramic Matrix Composites
Authors: Mackin T. J. , Roberts M. C.
Published: June 2019

A new generation of relatively ‘ductile’ CMCs is being developed that expands the general utility of structural ceramic composites. These new materials rely on inelastic mechanisms such as interface failure, matrix cracking, fiber failure and fiber pullout to redistribute stress away from locations of stress concentration.1 The combined effect of these mechanisms can be summarized in three macroscopic damage classifications: Class I damage is the development of a single matrix crack bridged by fibers; Class II damage involves the development of multiple cracks in the matrix; and Class III damage involves the development of a shear damage zone. The operative damage mechanism depends upon the composite constituent properties, while the extent of stress redistribution depends upon the damage mechanism. Recent experiments have identified these damage mechanisms and have also quantified the effect of stress redistribution.2,2,4
Short-Time Fourier Transform of Continuous Wave Doppler Signals
Authors: Wooh Shi-Chang , Wei Coach , Clay Arthur
Published: June 2019

A Doppler-based ultrasonic monitoring scheme was introduced to detect discontinuities on the surface of a rapidly moving object. Single-tone, continuous wave (CW) ultrasound was impinged onto the moving surface and the reflected signal was processed by a Short-Time Fourier Transform (STFT) algorithm to identify surface anomalies. By monitoring the peak magnitude of the STFT spectra within a specified window, it was possible to reconstruct a signal representing Doppler frequency shift continuously in the time domain.
Nondestructive Inspection of Thin, Low-Z Samples using Multiplexed Compton Scatter Tomography
Authors: Evans B. L. , Martin J. B. , Burggraf L. W.
Published: June 2019

The viability of a Compton scattering tomography system for nondestructively inspecting thin, low Z samples for corrosion is examined. This technique differs from conventional x-ray backscatter NDI because it does not rely on narrow collimation of source and detectors to examine small volumes in the sample. Instead, photons of a single energy are backscattered from the sample and their scattered energy spectra are measured at multiple detector locations, and these spectra are then used to reconstruct an image of the object. This multiplexed Compton scatter tomography technique interrogates multiple volume elements simultaneously. Thin samples less than 1 cm thick and made of low Z materials are best imaged with gamma rays at or below 100 keV energy. At this energy, Compton line broadening becomes an important resolution limitation. An analytical model has been developed to simulate the signals collected in a demonstration system consisting of an array of planar high-purity germanium detectors. A technique for deconvolving the effects of Compton broadening and detector energy resolution from signals with additive noise is also presented. A filtered backprojection image reconstruction algorithm with similarities to that used in conventional transmission computed tomography is developed. A simulation of a 360–degree inspection gives distortion-free results. In a simulation of a single-sided inspection, a 5 mm × 5 mm corrosion flaw with 50% density is readily identified in 1-cm thick aluminum phantom when the signal to noise ratio in the data exceeds 28.
Emerging Technologies For Nde Of Aging Aircraft Structures
Authors: Green R. E.
Published: June 2019

Several emerging technologies affording new opportunities for the nondestructive evaluation of aging aircraft structures. Among these technologies are ultrasonic attenuation detection of fatigue and corrosion damage; non-contact ultrasound including laser-laser, laser-EMAT, laser-air, and air-air; laser based acoustic emission source identification; full-field double-pulse holographic imaging; non-linear assessment of adhesive bond quality; x-ray diffraction topographic imaging of the quality of nickel based alloy single crystal turbine blades.