bluuebunny/crossref_metadata_2025 huggingface dataset:
Assessment of Molten Carbonate Fuel Cell Models and Integration With Gas and Steam Cycles
Authors: Massardo A. F. , Bosio B.
Published: July 2002

The aim of this work is to investigate the performance of molten carbonate fuel cells (MCFCs), with external sensible heat reformer and gas turbine/steam turbine (GT/ST) combined cycles. The analysis of these MCFC-GT/ST combined cycles has been carried out using the thermo economic modular program (TEMP) modified to allow MCFC, external sensible heat reformer, and catalytic burner performance to be carefully taken into account. The code has been verified through the use of a detailed MCFC model and of the data available for an existing MCFC unit. The thermodynamic and exergy analysis of a number of MCFC combined cycles is presented and discussed, taking into account the influence of technological constraints, also evaluated with the sophisticated model, and the influence of the post-combustion of the fuel directly in the external catalytic burner. The results are presented and discussed in depth.
An Analysis of the Effect of Lower Extremity Strength on Impact Severity During a Backward Fall
Authors: Sandler Reuben , Robinovitch Stephen
Published: July 2002

At least 280,000 hip fractures occur annually in the U.S., at an estimated cost of $9 billion. While over 90 percent of these are caused by falls, only about 2 percent of all falls result in hip fracture. Evidence suggests that the most important determinants of hip fracture risk during a fall are the body’s impact velocity and configuration. Accordingly, protective responses for reducing impact velocity, and the likelihood for direct impact to the hip, strongly influence fracture risk. One method for reducing the body’s impact velocity and kinetic energy during a fall is to absorb energy in the lower extremity muscles during descent, as occurs during sitting and squatting. In the present study, we employed a series of inverted pendulum models to determine: (a) the theoretical effect of this mechanism on impact severity during a backward fall, and (b) the effect on impact severity of age-related declines (or exercise-induced enhancements) in lower extremity strength. Compared to the case of a fall with zero energy absorption in the lower extremity joints, best-case falls (which involved 81 percent activation of ankle and hip muscles, but only 23 percent activation of knees muscles) involved 79 percent attenuation (from 352 J to 74 J) in the body’s vertical kinetic energy at impact KEv, and 48 percent attenuation (from 3.22 to 1.68 m/s) in the downward velocity of the pelvis at impact vv. Among the mechanisms responsible for this were: (1) eccentric contraction of lower extremity muscles during descent, which resulted in up to 150 J of energy absorption; (2) impact with the trunk in an upright configuration, which reduced the change in potential energy associated with the fall by 100 J; and (3) knee extension during the final stage of descent, which “transferred” up to 90 J of impact energy into horizontal (as opposed to vertical) kinetic energy. Declines in joint strength reduced the effectiveness of mechanisms (1) and (3), and thereby increased impact severity. However, even with reductions of 80 percent in available torques, KEv was attenuated by 50 percent. This indicates the importance of both technique and strength in reducing impact severity. These results provide motivation for attempts to reduce elderly individuals’ risk for fall-related injury through the combination of instruction in safe falling techniques and exercises that enhance lower extremity strength.
A Kinetic Investigation of the Role of Changes in the Composition of
Natural Gas in Engine Applications
Authors: Khalil E. B. , Karim G. A.
Published: July 2002

The influence of variations in the composition of natural gas on the ignition and combustion processes in engines is investigated. Particular attention is given to changes in the relatively small concentrations of high molar mass alkanes that may be present in the fuel. A detailed chemical kinetic scheme for the oxidation of the higher hydrocarbon components of up to n-heptane was used to investigate analytically the combustion reactions of different fuel mixtures under constant volume adiabatic conditions with initial states that are similar to those during the ignition delay of a typical internal combustion engine. These comprehensive simulation calculations require much computing capacity and time that would preclude their incorporation in full simulation models of engine processes. A simplification is introduced based on replacing artificially the small concentrations of any higher hydrocarbons that may be present in the natural gas by a kinetically equivalent amount of propane in the fuel mixture. This is done such that the resulting equivalent fuel has the same ignition delay as the original fuel under constant volume engine T.D.C. conditions. This “propane equivalent” concept was used in full engine simulation models while employing a relatively short scheme of 150 steps for the oxidation of fuel mixtures of propane, ethane, and methane in air.
Sensitivity Analysis and Optimization of Undamped Rotor Critical
Speeds to Supports Stiffness
Authors: Huang Shyh-Chin , Lin Chin-Ann
Published: July 2002

This paper introduced a new approach that employed the assumed-modes method and the receptance method, to the sensitivity analysis and the optimization of rotor-bearing systems. First, the frequency equation in terms of receptances was derived. The natural frequencies and the critical speeds for a typical rotor system were then illustrated. Beginning with the receptance equation, the authors, for the first time, derived a sensitivity matrix and employed it into an optimization process. The topographical method in conjunction with the variable metric method followed for the optimal solution. In the solution process, the sensitivity matrix provided important information for search direction. Examples of critical speeds adjustment via supports change in an optimal sense were illustrated. Numerical results showed that the approach was very efficient and the solutions were very accurate. This approach, in addition, provided such valuable information as which supports dominated specific critical speeds. The developed approach proved to be very helpful to rotor engineers in both rotor modification and rotor design.
Performance Analysis of Cavitating Flow in Centrifugal Pumps Using Multiphase CFD
Authors: Medvitz Richard B. , Kunz Robert F. , Boger David A. , Lindau Jules W. , Yocum Adam M. , Pauley Laura L.
Published: July 2002

A multi-phase CFD method is used to analyze centrifugal pump performance under developed cavitating conditions. The differential model employed is the homogeneous two-phase Reynolds-Averaged-Navier-Stokes equations, wherein mixture momentum and volume continuity equations are solved along with vapor volume fraction continuity. Mass transfer modeling is provided for the phase change associated with sheet cavitation. Using quasi-3D (Q3D) analysis, steady and time-dependent analyses were performed across a wide range of flow coefficients and cavitation numbers. Characteristic performance trends associated with off-design flow and blade cavitation are observed. The rapid drop in head coefficient at low cavitation numbers (breakdown) is captured for all flow coefficients. Local flow field solution plots elucidate the principal physical mechanisms associated with the onset of breakdown.
The Foundation of the Sommerfeld Transformation
Authors: Maday Clarence J.
Published: July 2002

The analysis of the one-dimensional journal bearing leads to an interesting integral that is continuous but has an analytic singularity involving the inverse tangent at π/2. This difficulty was resolved by a clever and non-intuitive transformation attributed to Sommerfeld. In this technical brief we show that the transformation has its origin in the geometry of the ellipse and Kepler’s equation that is based upon his observations of the planets in the Solar system. The derivation of the transformation is a problem or exercise in Sommerfeld’s monograph, Mechanics. The transformation is the relation between the two angles that characterize the ellipse, the closed orbit of a body in a central inverse square force field. The angle measured about the focus is the true anomaly (angle) and the angle measured about the center is the eccentric anomaly (angle). We establish the analogy between the orbital radius in terms of the eccentric anomaly and the film thickness of the journal bearing in terms of its central angle.
Noninvasive Measurement of Time-Varying Three-Dimensional Relative Pressure Fields Within the Human Heart
Authors: Ebbers T. , Wigstro¨m L. , Bolger A. F. , Wranne B. , Karlsson M.
Published: July 2002

Understanding cardiac blood flow patterns is important in the assessment of cardiovascular function. Three-dimensional flow and relative pressure fields within the human left ventricle are demonstrated by combining velocity measurements with computational fluid mechanics methods. The velocity field throughout the left atrium and ventricle of a normal human heart is measured using time-resolved three-dimensional phase-contrast MRI. Subsequently, the time-resolved three-dimensional relative pressure is calculated from this velocity field using the pressure Poisson equation. Noninvasive simultaneous assessment of cardiac pressure and flow phenomena is an important new tool for studying cardiac fluid dynamics.
Interaction Between a Semi-Infinite Crack and a Screw Dislocation in a Piezoelectric Material
Authors: Lee Kang Yong , Lee Won Gyu , Pak Y. Eugene
Published: July 2002

The interaction between a semi-infinite crack and a screw dislocation under antiplane mechanical and in-plane electrical loading in a linear piezoelectric material is studied in the framework of linear elasticity theory. A straight dislocation with the Burgers vector normal to the isotropic basal plane near a semi-infinite crack tip is considered. In addition to having a discontinuous electric potential across the slip plane, the dislocation is subjected to a line-force and a line-charge at the core. The explicit solution for the model is derived by means of complex variable and conformal mapping methods. The classical 1/r singularity is observed for the stress, electric displacement, and electric field at the crack tip. The force on a screw dislocation due to the existence of a semi-infinite crack subjected to external electromechanical loads is calculated. Also, the effect of the screw dislocation with the line-force and line-charge at the core on the crack-tip fields is observed through the field intensity factors and the crack extension force. [S0021-8936(00)01501-4]
Fracture Static Mechanisms on Fatigue Crack Propagation in Microalloyed Forging Steels
Authors: Linaza M. A. , Rodriguez-Ibabe J. M.
Published: July 2002

The influence of static mechanisms on fatigue crack propagation in Ti and Ti-V microalloyed steels is considered. Small inclusions originate void nucleation. In contrast, TiN coarse particles contribute to the formation of bursts of cleavage in the fatigue zone. Taking into account the microstructural characteristics of the matrix that surrounds the particle, the microcrack can be confined within the particle or propagate along the matrix forming a cleavage burst. The influence on macroscopic crack propagation of both types of static micromechanisms is considered. [S0094-4289(00)00902-6]
High-Temperature Properties of SiC-Si3N4 Particle Composites
Authors: Woetting G. , Caspers B. , Gugel E. , Westerheide R.
Published: July 2002

Due to promising results in literature, SiC-Si3N4 particle composites in the range 0–100 percent SiC were evaluated. Focusing on high-temperature properties, mainly Y2O3 was used as sintering additive. Consolidation occurred primarily by hot-pressing, sintering tests were performed for comparison. Besides short-term properties like strength, toughness etc., long-term properties like creep and oxidation behavior were determined. Results as a function of SiC-content and microstructure were discussed with respect to materials’ performance at high temperatures and possibilities of their production on a technical scale. [S0742-4795(00)00201-5]
Nonequilibrium Entropy Production Under the Effect of the Dual-Phase-Lag Heat Conduction Model
Authors: Al-Nimr M. A. , Naji M. , Arbaci V. S.
Published: July 2002

In the present work, the nonequilibrium entropy production under the effect of the dual-phase-lag heat conduction model is investigated. It is shown that the entropy production cannot be described using the classical form of the equilibrium entropy production where using this form leads to a violation for the thermodynamics second law. The effect of the phase-lags in temperature and in heat flux on the nonequilibrium entropy production is investigated. Also, the difference between the equilibrium and the nonequilibrium temperatures under the effect of the dual-phase-lag heat conduction model is studied. [S0022-1481(00)01502-4]
Discretizors and Interpolators for Five-Axis CNC Machines
Authors: Sarma Radha , Rao Aarthi
Published: July 2002

Discretization and interpolation of curves are two frequently adopted practices when machining complex curves using computer numerically controlled (CNC) machines. Both practices stem from the need to sample curves at discrete time intervals corresponding to the sampling period of the CNC machine. This paper proposes new techniques for discretization and interpolation that account for the change of tool orientations in five-axis machining. First, the method for discretization proposed in this paper is based on sampling the curves such that specified contour, feedrate, and orientation errors are not exceeded. Second, the interpolator proposed in this paper will be able to avoid excessive angular speeds arising from sampling the curves based on the feedrate alone. [S1087-1357(00)01401-5]
Investigation of a Special 6-6 Parallel Platform for Contour Milling
Authors: Abbasi W. A. , Ridgeway S. C. , Adsit P. D. , Crane C. D. , Duffy J.
Published: July 2002

Recently, companies have been experimenting with parallel-mechanism based approaches for milling machines. This research presents an investigation into the development of a special 6-6 parallel mechanism for application to contour milling. The idea behind this approach is that existing non-CNC milling equipment can be augmented to increase its capability at a lower cost than purchasing traditional 5-axis machining centers. This paper presents the phase of research associated with developing a parametric kinestatic design methodology for a special 6-6 parallel mechanism (Kinestatic Platform, KP). This methodology was applied to the design specifications associated with 5-axis contour milling. The resulting kinestatic design’s dynamics were evaluated to determine the actuation requirements of each connector. A prototype connector was built to allow the evaluation of actuator response under simulated loading conditions. Joint stiffness and control strategy were of primary concern in evaluating the performance of the prototype connector. The parametric kinestatic design and control strategy results are presented. Several observations are evidenced from the research. Joint deflection is an obvious critical issue and the most difficult to quantify. A scheme is proposed detailing the concept of using a separate metrology frame to overcome difficulties associated with accurate connector length determination. [S1087-1357(00)70101-8]
Surface structures and growth kinetics of InGaN(0001) grown by molecular beam epitaxy
Authors: Chen Huajie , Feenstra R. M. , Northrup J. E. , Zywietz T. , Neugebauer J. , Greve D. W.
Published: July 2002

The surface structures and growth kinetics of InGaN(0001) are studied. It is well known that during molecular beam epitaxy GaN surfaces undergo a smooth to rough transition when the growth condition is switched from Ga rich to N rich. It is found here that indium atoms have only a small effect on this transition when deposited on GaN(0001̄), but when deposited on GaN(0001) the indium acts as a surfactant and greatly extends the regime of smooth growth. Near the smooth/rough transition of InGaN(0001) growth, a bright ∛×∛ reconstruction is observed at growth temperature. The formation kinetics of this reconstruction are studied in detail. Scanning tunneling microscopy and total energy computations are used to study the structure of InGaN(0001) surfaces under metal rich conditions. Indium is found to occupy the top two atomic layers of the crystal; its incorporation in the second layer produces significant strain, leading to the formation of small pits on the surface and increased indium concentration inside and around the pits.
Application of Auger Electron Spectroscopy to Reactor Materials Research
Authors: Clausing R. E.
Published: July 2002

The analysis of minute quantities of material on a surface is frequently essential in understanding the behavior of materials relative to the systems of which they are a part. Auger electron spectroscopy offers a unique method for studying the first few atomic layers of a surface. The elemental composition of the surface can be determined provided that the surface is dominated by only a few elements. Also, in favorable circumstances, information on the oxidation state of the surface elements may be obtained. In reactor systems thin films of fission fragments and/or corrosion products may be important not only from the standpoint of the usual materials problems of corrosion or mechanical properties, but also for reasons related to neutron economy, fission-product control, maintenance, and the removal of afterheat due to radioactive decay when a reactor is shut down. Auger analysis is being used to determine the elemental composition of thin film deposits on graphite from the Oak Ridge National Laboratory Molten-Salt Reactor Experiment. This paper considers four main problem areas related to the application of Auger electron spectroscopy to nuclear reactor materials. First, the materials to be studied are radioactive which makes handling them hazardous. While this may necessitate special shielding and safety precautions, it is primarily an inconvenience and except in cases involving unusually intense beta emission the radioactivity of the sample need not interfere with the measurement of Auger spectra. Second, the relative merits of using a retarding potential electron energy analyzer as opposed to cylindrical or spherical sector electron spectrometers are discussed. The retarding potential electron energy analyzers are physically simpler and more readily available, but the spectrometers have important advantages in resolution, in sensitivity, and in discriminating against beta radiation, as well as the background of secondary electrons. Third, the problems encountered during the analysis of the spectra are illustrated. In fission product analysis, chemical shifts, and the overlap of Auger spectra of elements (especially those adjacent to each other in the fourth and higher periods) can become bothersome. If a large number of elements are present on the same surface, the large width of the most prominent Auger peaks is a very significant complicating factor. Fourth, extreme care must be taken to ensure that the surface examined is not contaminated or altered to an unknown extent during sample acquisition or preparation. If contamination cannot be avoided, cleaning techniques which do not destroy the surface of interest must be devised. Thermal treatments, electron bombardment, ion bombardment, or chemical means may be helpful depending on circumstances.
Aluminum Ion Plating of Uranium–Molybdenum Alloy Fast-Burst Reactor Elements
Authors: Bell R. T.
Published: July 2002

Ion plating of thin (<0.002 in.) aluminum coatings on fast-burst reactor parts fabricated from uranium–10% molybdenum alloy was evaluated as a method of protecting the alloy from oxidation and as a means of containing the fission products. A number of core rings were plated with nickel while other rings were ion-plated with aluminum so that a comparison between the two coatings could be made. During the ion plating of aluminum and subsequent heat treatment, certain uranium–aluminum intermetallic compounds (UAl2, UAl3, and UAl4) were formed. During the process of testing to destruction, these rings encountered fissions in excess of 1017 and temperatures in excess of 700°C during which the nickel plating spalled severely while the aluminum and the uranium–aluminum intermetallics remained adherent to the alloy.
New Applications of Electron-Beam Melting and Casting Techniques
Authors: Stephan H. , Dietrich W.
Published: July 2002

The advantages of electron-beam melting and casting compared to vacuum arc casting techniques will be discussed. The relations between fluidity, superheat, mold material, and mold temperature will be demonstrated using cast stars. Essential mechanical and chemical properties of cast rod samples will also be discussed. Process data of an electron-beam investment casting furnace such as beam power, casting production, and attainable superheat will be correlated. Results of a newly developed pelletizing process for titanium-scrap recycling and the purification of tungsten carbide particles illustrating the influence of pellet shape, gas content, and pellet weight will be discussed and compared to another, but different, recycling process for scrap consolidation by electron-beam melting. Use of the electron-beam continuous flow melting process for the production of long and thin titanium and steel castings will be demonstrated. The possibility of using scrap as starting material will be illustrated and compared with other types of starting stock.
Power Supplies for Electroslag Furnaces: A Preliminary Comparison
Authors: Roberts R. J.
Published: July 2002

This paper reviews the relative merits of the five main types of power supplies that can be used for electroslag melting. These are: ac single-phase line frequency, ac three-phase line frequency, dc electrode positive, dc electrode negative, and ac low frequency. The comparisons are based mainly on operating experience with furnaces producing industrial-sized ingots [over 12 in. (30.5 cm) in diameter] in a wide variety of ferrous and nickel-based alloys. The power supplies are compared on the basis of the following 14 industrially important indices: power cost per ton, power supply capital cost, electrode costs, total furnace capital cost, melt setup cost, desulphurization in ferrous alloys, molten metal pool depth, absence of inherent stirring, applicability to slab melting, molten slag starting, melt mode flexibility, supply line balance, supply line flicker, and power supply reliability. In general, the survey shows each of the possible melt modes their advantages, disadvantages, and the fact that none of them can be recommended as a universal solution for all applications. It is, however, apparent from the comparisons that ac single-phase line frequency has the broadest potential application.
Morphology of Nuclei and Epitaxial Behavior of Au and Ag on MgO
Authors: Sato H. , Shinozaki S.
Published: July 2002

Direct and continuous observation of epitaxy of fcc metals on MgO substrates in an electron microscope reveals that the shapes of nuclei at the initial stage of deposition are closely related to the characteristics of the later epitaxial growth. In order to obtain consistent results, MgO substrates are cleaved in situ at the specimen holder at the deposition temperature (300 °∼500 °C) and the metals are evaporated immediately thereafter. The nuclei are clearly found to have characteristic shapes depending on the orientations. For Au, they are square pyramids for nuclei of (100) orientation and triangular pyramids for those of (111) orientation. The application of Wulff’s law to the shapes of these nuclei yields the relative magnitude of the interfacial interaction and the surface energy. The sensitive dependence of the epitaxial characteristics on the shapes of nuclei thus indicates the important contribution of the interfacial interaction to epitaxial behavior.
Preparation and Superconducting Properties of Thin Films of Some Binary Transition Metal Alloy Systems
Authors: Spitzer Hermann J.
Published: July 2002

Thin films with thickness in the order of 3000 Å of Nb–Ti and Nb–Ta alloys have been prepared by dc cosputtering onto fused quartz at 700 °C at deposition rates of approximately 100 Å/min. As a function of composition, Jc–H characteristics were measured using pulsed transverse fields and pulsed currents and Tc’s by monitoring the electrical resistance with temperature. Critical current densities, at comparable fields, are substantially higher than results reported earlier on these alloy systems. Also, the critical temperatures of these films were as high or higher than those of bulk material. The superior superconducting properties are attributed to the application of high substrate temperatures and the metallurgical processes involved therewith, especially the formation of β-phase solid solutions.
Cone Formation on Metal Targets during Sputtering
Authors: Wehner G. K. , Hajicek D. J.
Published: July 2002

When a Cu surface is sputtered by ion bombardment under the condition that Mo atoms arrive at the Cu surface during sputtering an unexpected phenomenon can arise: the surface of the Cu target becomes covered with microscopic cones. The cone density increases with increasing flux density of arriving Mo atoms. When the cones are closely spaced they give the target a velvet-like black appearance. The result of dense cone coverage are a lower sputtering yield and a more oblique ejection of sputtered material. The cone tops seem to consist of Mo nuclei which are constantly replenished via surface migration and protect the underlying Cu from being sputtered.
Ion Source for Magnetic Mass Spectrometer to be Used in Space
Authors: Brubaker W. M. , Burnham D. , Perkins G. D.
Published: July 2002

A special ion source is being developed for use with a double-focusing, tandem-sector, magnetic mass spectrometer intended for possible use in conjunction with a gas chromatograph on a mission to Mars. The combination of the requirements for scanning a wide mass range and using a high- and a low-energy ionizing electron beam creates unusual demands on the stabilization (in space) of the electron beam. The demand for a spare filament further complicates the design. A proposed solution to these constraints is found through the use of an unusually strong magnetic field to collimate the beam. The design of the source and its operating characteristics are discussed.
Titanium Sublimators Used in Conjunction with Diffusion Pumps
Authors: Johnson Gordon E.
Published: July 2002

A titanium sublimator has been installed in a conventional liquid-nitrogen baffle to enhance system pumping speed for active gases. Although initially designed to augment turbomolecular systems, the sublimator also improves performance of diffusion-pumped systems. Using the sublimator, a nominal 6-in. diffusion-pumped system produces baseplate pumping speeds in excess of 1400 liter/sec at pressures below 1×10−6 Torr. Ultimate pressures are typically improved by a factor of 2. The titanium condensing surface, which is constructed of aluminum to maintain uniform cryogenic temperatures, provides varying condensation rates to improve throughput at higher pressures.
Ultrahigh Vacuum Joints Using Compression and Welded Sealing of Aluminum to Beryllium
Authors: Parsons Richard E.
Published: July 2002

A 1-in.-diam beryllium window of a thickness not to exceed 0.005 in. was developed.The window was electrically conductive to its mount and supported atmospheric pressure on one side while maintaining a low helium leak rate. An ultrahigh vacuum and pressure seal was built utilizing a beryllium to stainless-steel joint. A leak-tight configuration was maintained at 150-psi pressure and 200 °C. A beryllium 0.0005-in.-thick vacuum barrier 0.875-in. diam was developed to operate at 200 °C and to hold a differential pressure of 10−3 Torr. The seal was accomplished by containing the beryllium foil in a nested gasket and clamping this “sandwich” in a modified commerical seal configuration.
MilliTorr Pumpdown Anomaly Relationships with Large Pipe Chamber Design Tradeoffs
Authors: Schalla Clarence A.
Published: July 2002

Pumpdown predictability of large pipe-type vacuum chambers is improved through design tradeoff reevaluation based on checkout anomaly analysis. Truncated-cone pipe chambers up to 2000 ft long and 200 000 ft3 in volume, which served as underground nuclear effects testbeds, were analyzed. Inconsistencies in evacuations to a base pressure of 1 mTorr are identified with the sorbing time variable of the chamber wall and experiment support materials. Variations in pressure levels along the pipe chambers are shown related to configuration factors and to design tradeoffs on allowable inleakage from concrete shrouding, sand stemming, and tunnel atmospheres. Cascading graphs innovated for tradeoffs include two recently derived flow conductance equations.
Surface Structures Formed during the Interaction of Sulphur Compounds with the (111) Face of Nickel
Authors: Edmonds T. , McCarroll J. J. , Pitkethly R. C.
Published: July 2002

The interaction of hydrogen sulphide, n-propyl mercaptan, and dimethyl disulphide with the (111) and (100) faces of nickel has been studied by LEED at temperatures up to 700 K. During interaction and subsequent annealing, in vacuo below 10−9 Torr at temperatures up to 1200 K, series of diffraction patterns were observed. Four of the patterns on (111) have been attributed to coincidence nets arising from structures which involve rearrangement and reorientation to (100) type layers. The patterns are described and the interpretations discussed.
Environmental Effects on the Surface Energy of Phyllosilicate Minerals
Authors: Gutshall Paul L. , Phillips James M. , Bryant Paul J. , Cole George M.
Published: July 2002

The phyllosilicate minerals are ideal materials for a study of cohesion between molecularly smooth surfaces. The lamellar structure of these materials allows the surface energy to be measured experimentally by a cleavage process. The surface energy of synthetic phlogopite has been measured in vacuum, air, oxygen, ammonia, carbon monoxide, and water. No reduction in the surface energy was observed in an oxygen environment. However, water vapor, air, carbon monoxide, and ammonia environments reduced the surface energy of phlogopite. Results of this study support a model which explains how selected environments may result in a reduction in the observed surface energy of silicate minerals.
Consideration of L-Shell Ionization Cross Sections in Auger Electron Spectroscopy
Authors: DuCharme A. R. , Gerlach R. L.
Published: July 2002

Classical and quantum mechanical approaches to the LII,III-shell ionizations of isolated atoms by electron impact have been studied. Both descriptions are compared with new total ionization cross sections deduced from the LMM Auger spectra of chemisorbed monolayers. The LII,III-shell total ionization cross sections of S, Cl, Ti, and Cu adsorbed on metal surfaces are reasonably predicted by both theories at higher energies. A model for secondary excitation was recently developed to isolate the one-event cross section information. Calculations which include this effect lead to improved agreement between the experimental total ionization cross sections and those predicted by the single-event ionization theories.
The Adsorption and Decomposition of CO on Pt(111)
Authors: Martinez J. M. , Hudson J. B.
Published: July 2002

A cylindrical mirror electron energy analzyer has been used to study the adsorption and decomposition of CO on an initially clean Pt(111) surface. The observed rate of adsorption and fractional surface coverage as a function of CO exposure are identical to those observed previously in this laboratory by flash filament adsorption technique. This result provides an absolute calibration of the Auger spectrometry system for carbon and oxygen. Beam-induced decomposition of CO was observed at high incident fluxes. The surface oxygen coverage decreased exponentially to zero during electron bombardment, while surface carbon decreased and then levelled off at a finite value. CO adsorption studies on this carbon contaminated surface showed decreasing CO adsorption rate and decreasing saturation coverage with increasing carbon contamination. The adsorption rate approached zero at high carbon concentration.
Nanoscale patterning of self-assembled monolayers with electrons
Authors: Gölzhäuser A. , Geyer W. , Stadler V. , Eck W. , Grunze M. , Edinger K. , Weimann Th. , Hinze P.
Published: July 2002

We show the fabrication of gold nanostructures using self-assembled monolayers of aliphatic and aromatic thiols as positive and negative electron beam resists. We applied a simple and versatile proximity printing technique using focused ion beam structured stencil masks and low energy (300 eV) electrons. We also used conventional e-beam lithography with a beam energy of 2.5 keV and doses from 3500 to 80 000 μC/cm2. Gold patterns were generated by wet etching in KCN/KOH and characterized by atomic force microscopy and scanning electron microscopy. The width of the finest lines is ∼20 nm; their edge definition is limited by the isotropic etching process in the polycrystalline gold.
Carbon deposition by electron beam cracking of hydrocarbons on Ta2Zn3O8 thin film phosphors
Authors: Kondoleon Caroline A. , Rack Philip , Lambers Eric , Holloway Paul
Published: July 2002

The cathodoluminescence (CL) brightness from thin film Ta2Zn3O8 has been studied as a function of vacuum and electron dose. The thin films were prepared by sputtered deposition followed by rapid thermal annealing at 1100 °C for 1 min. Under bombardment by 2 keV electrons, the films produce a blue luminescence with a dominant wavelength of 386 nm. These films were exposed to residual vacuum gas dominated by H2 and H2O at pressures ranging from 10−8 to 10−6 Torr with <10% loss in CL brightness for an electron dose of 23 C/cm2. However, when hydrocarbons from colloidal graphite “paint” raised the base pressure of the vacuum from 2×10−7 to 9×10−7 Torr, the CL brightness was degraded to 5% of its original value after ≈4 h at 2.7×10−4 A/cm2 (corresponding to a dose of 3.9 C/cm2). Degradation stopped when the electron beam was off or could not strike the surface. Auger analysis showed a 1000-Å-thick layer of carbon from electron beam cracked hydrocarbons. The effect of electron beam cracked carbon was concluded to be absorption of luminescent photons. The hydrocarbon contaminants were removed by long term baking of the vacuum system.
Growth of low-defect density In0.25Ga0.75As on GaAs by molecular beam epitaxy
Authors: Pickrell G. W. , Chang K. L. , Epple J. H. , Cheng K. Y. , Hsieh K. C.
Published: July 2002

The growth parameters of In0.25Ga0.75As grown on GaAs by molecular beam epitaxy were investigated. Low substrate temperatures coupled with lower growth rates and low arsenic overpressures were explored and the corresponding threading dislocation densities were determined using transmission electron microscopy. Threading dislocation densities in layers much thicker than the critical thickness were found to be as low as 1×107 cm−2 using optimal growth conditions. In addition, the critical thickness of the ternary alloy was estimated. The evolution of the misfit dislocations and threading dislocations was also examined as a function of epilayer thickness.
Field emission from ultrathin coatings of AlN on Mo emitters
Authors: Kang D. , Zhirnov V. V. , Sanwald R. C. , Hren J. J. , Cuomo J. J.
Published: July 2002

Experiments characterizing both the physics of emission and the performance of Mo tips coated with ultrathin film of AlN were conducted. Ultrathin films of AlN with thicknesses ranging from 7 to 21 nm in 1.5 nm increments were deposited onto Mo tips by magnetron sputtering. In situ field emission measurements were performed after each deposition step. Tip radius, thickness, and morphology of AlN coating were characterized with the transmission electron microscopy. The effect of the thickness of AlN on emission was determined using a Fowler–Nordheim analysis. Various surface treatment effects were studied and measurements of maximum current and emission stability were performed, e.g., maximum current from a single Mo tip with 15 nm of AlN coating was 52 μA.
Fabrication and electrical characterization of high aspect ratio silicon field emitter arrays
Authors: Rangelow I. W. , Biehl St.
Published: July 2002

Micromachined high aspect ratio field emitter areas have been realized to obtain stabile and uniform emission current. Dry etching based on gas chopping method was used to etch the 42-μm-high ultra-sharp emitter tips in single-crystal silicon. Diamond-like carbon (DLC) films of 25–100 nm thickness were deposited from hydrocarbon precursor gas on the Si tips applying inductively coupled plasma enhanced chemical vapor deposition (ICPECVD) technique. Partial stabilization of emission current versus time due to oxygen or nitrogen plasma treatment could be related to surface passivation and/or formation of stable DLC/nanolayer on the emitter surface. It has been shown that DLC-coated emitters provide a comparable good long-term emission stability—the emission current did almost not decrease during a 46 h operation cycle. Summarizing we can say that high aspect ratio field emitter areas seem to have favorable field emission properties in respect to long-term stability.
Fabrication of gated niobium nitride field emitter array
Authors: Gotoh Y. , Kashiwagi Y. , Nagao M. , Kondo T. , Tsuji H. , Ishikawa J.
Published: July 2002

We have fabricated a gated niobium nitride field emitter by the transfer mold method. A silicon mold was fabricated by anisotropical etching, followed by oxidation of the mold and deposition of niobium nitride. Niobium nitride thin films were prepared by ion-beam-assisted deposition. After attaching the sample to a glass substrate, the silicon mold was removed by mechanical and wet etching. A molybdenum thin film was then deposited by electron-beam evaporation. Formation of a gate aperture and an insulating silicon dioxide layer were performed by wet etching of only the apex, with other regions being protected by a photoresist layer. An electron emission test of the fabricated emitter array was performed in a high vacuum. We confirmed electron emission of up to 0.1 μA at the emitter–gate voltage of 30 V.
Surface analysis of (NH4)2Sx-treated InGaN using x-ray photoelectron spectroscopy
Authors: Lin Yow-Jon , Lee Ching-Ting
Published: July 2002

We present the surface analysis of (NH4)2Sx-treated InGaN using x-ray photoelectron spectroscopy. The native oxide and organic contamination on the InGaN surface can be removed by (NH4)2Sx surface treatment. However, the hydroxyl species present on the InGaN surface cannot be removed. Because Ga–S and In–S bonds were formed and N–S bonds were not observed, we deduce that the sulfur atoms would occupy the nitrogen-related vacancies and bond with the Ga and In atoms. The clean surface and surface state reduction caused from the (NH4)2Sx surface treatment would be useful for the formation of ohmic and Schottky contacts between the metal and InGaN layers.
Video analysis of inclusion induced macroparticle emission from aluminum sputtering targets
Authors: Wickersham C. E. , Poole J. E. , Fan J. S. , Zhu L.
Published: July 2002

Molten metal macroparticles emitted from the surface of aluminum sputtering targets during arcing events is an important source of particulate contamination in sputtering. We used high-speed video analysis of arcing from sputtering targets purposefully doped with aluminum oxide inclusions to determine the velocity, trajectory, and relative size of the emitted macroparticles. The results of these analyses show that the molten droplets of aluminum are emitted from the target with velocities ranging from 5 to over 500 m/s. Ejection angles for the observed macroparticles were concentrated at angles of around 30° from the target plane. We also found that only certain arcing events generated video detectable macroparticle emission (∼18% of the arc events). Macroparticle size and velocity did not appear to be related. An estimate of macroparticle temperature based upon the sensitivity of the charge coupled device camera and the observed lack of macroparticle cooling yields an aluminum macroparticle temperature between 1750 and 4000 K. One cathode arc spot was observed on the target surface and the decay in intensity of this spot was used to estimate the cathode arc spot temperature. The cooling rate of a cathode arc spot on the target surface indicated that the arc spot cools by radiation and diffusion and has an initial temperature of 3000 K. This value is consistent with the macroparticle-estimated temperature of 3000±1000 K.
Study of the surface reactivity of optical fibers under aging conditions by flexural resonance
Authors: Mertens Johann , Finot Eric , Bourillot Eric , Fabre Arnaud , Goudonnet Jean Pierre
Published: July 2002

This article reports an original technique for measuring the flexural resonance response of optical fibers of around 1 mm in length considered as atomic force microscope cantilevers. This technique was found particularly suitable for precisely investigating the effect of aging of optical fibers due to external factors such as temperature, action of hydrogen, or ionic aggressive solutions. Compared to the corresponding atomic force microscopy images, the measurement of the resonance frequency shift leads to the determination of two factors characteristic of the surface reactivity of the fiber: first, the decrease in frequency that can be considered in terms of mass loading, and second both the frequency increase and the loss in Q factor resulting from the variation of the Young modulus and the internal friction of the fiber.
Physical understanding of moisture induced degradation of nanoporous aluminum oxide thin films
Authors: Nahar R. K.
Published: July 2002

The effect of moisture on the dielectric properties of porous aluminum oxide thin films is studied. It is observed that the capacitance of Au-porous Al2O3–Al structure gradually changes with time particularly when exposed at higher moisture content. This instability and degradation in the properties of nanoporous aluminum oxide thin films is explained by incorporating the effect of lateral moisture diffusion in the pore wall. The seepage of moisture results in a virtual pore widening. The mechanism is illustrated. A model is proposed to explain the effect of moisture on dielectric degradation and on the capacitance characteristics.
Electrostatic mask protection for extreme ultraviolet lithography
Authors: Moors Roel , Heerens Gert-Jan
Published: July 2002

Protection of the mask against particle contamination is one of the challenges of extreme ultraviolet lithography. In this article a solution using electrostatic fields is introduced. By choosing a nonuniform electrical field both charged and neutral particles can be prevented from moving towards the mask. Experimental results showing the feasibility of the electrostatic mask protection are presented.
Nucleation and film growth during copper chemical vapor deposition using the precursor Cu(TMVS)(hfac)
Authors: Yang Daewon , Hong Jongwon , Richards David F. , Cale Timothy S.
Published: July 2002

This article describes a study of chemical vapor deposition (CVD) copper thin films deposited on TaNx substrates using Cu(TMVS)(hfac) as a precursor. We have characterized the deposition rate, resistivity, surface roughness, and reflectivity of the films as functions of substrate temperature, precursor and carrier gas flow rates, and the presence or absence of water vapor as a coreactant. We have also examined the nucleation process for these films as functions of substrate temperature and the presence or absence of water vapor. We observed an activation energy for nucleation of 39 kcal/mol and an activation energy for film growth of 14 kcal/mol. Introducing water vapor during nucleation reduces the activation energy for nucleation to 6.1 kcal/mol. We found that water vapor helps to reduce the incubation time and activation energy of the nucleation stage and enhances nuclei formation, uniformity, and adhesion. In our reactor, the highest quality films were obtained using a process protocol for Cu CVD in which small amounts of water vapor were introduced before or during the initial stage of deposition at 473 K substrate temperature.
Sensitivity of x-ray photoconductors: Charge trapping and absorption-limited universal sensitivity curves
Authors: Zahangir Kabir M. , Kasap S. O.
Published: July 2002

Direct conversion flat panel x-ray sensors that are currently under development are based on stabilized a-Se (a-Se alloyed with a small percentage of As and doped with Cl in the ppm amount). There are also other potential x-ray photoconductors such as PbO, PbI2, HgI2, CdTe, etc. Indeed, good x-ray images have been reported from PbI2, HgI2, and CdTe based x-ray sensors. The present article considers the x-ray sensitivity of photoconductors in terms of the following combined effects: (i) Absorption of x-rays, controlled by the linear attenuation coefficient α(E) and energy absorption coefficient αen(E), both x-ray photon energy E dependent. (ii) Electric field F and x-ray photon energy dependent ionization of the medium, that is, in terms of the electron and hole creation energy W±(E,F). (iii) The transport and trapping of charges across the photoconductor as they drift to the collecting electrodes. (iv) The electron and hole pairs are generated with an exponentially decaying distribution across the thickness of the photoconductor. We analytically solve the continuity equation by considering the drift of electrons and holes in the presence of deep traps. We derive an expression for the amount of collected charge per unit incident radiation, defined as the x-ray sensitivity S, in terms of W±, α, αen, and the normalized parameters: normalized attenuation depth and electron and hole schubwegs per unit thickness. We obtain two- and three-dimensional universal sensitivity curves that allow x-ray sensitivity of any potential x-ray photoconductor material to be determined from the normalized parameters.
Approximate Calculation of Expansion of Gas from Nozzles into High Vacuum
Authors: Nöller H. G.
Published: July 2002

The exact calculation of the density of a steady-state gas flow by means of the Boltzmann function generally leads to great mathematical difficulties, in the case of an expanding gas passing from the viscous flow region into the molecular flow region. An approximate solution can be found by replacing the actually continuous transition from viscous to molecular flow with a suitably defined discontinuity surface. Molecules that leave the viscous region through this surface continue to fly in straight lines with their respective velocities. By adopting this conception, the density at each point of the molecular-flow region can be found by integration. The general procedure is specialized for the case of the two-dimensional flow and can be applied to the supersonic flow around a corner in vacuum.
15-kJ L
C generator: Low inductance device for a 100-GW pulsed electron accelerator
Authors: Harris N. W. , Milde H. I.
Published: July 2002

The design and construction of a 15-kJ LC generator is described. This type of generator is used for its low inductance compared with more conventional Marx generators. The generator described consists of 20 capacitors rated at 80 kV, 5 reversing switches, and 1 extra-high-voltage transfer switch. The generator was built as a primary store for a high current, high power (300 kA, 100 GW) field-emission electron-beam generator.