bluuebunny/crossref_metadata_2025 huggingface dataset:
Skewed Wake Induction Effects on Thrust Distribution on Small Wind Turbine Rotors
Authors: Chaney Ken , Eggers, Alfred J. , Moriarty Patrick J. , Holley William E.
Published: July 2002

Accurate prediction of both the center of thrust location and the magnitude of the thrust on a rotor disk are critical to satisfactory modeling of the yawing of small wind turbines to large angles to passively control overshoots in power and loads at higher wind speeds. Of the two, the prediction of the center of thrust location upwind of the center of a yawed rotor disk appears to be the most uncertain and potentially in serious error. This error is due to uncertainties in skewed wake effects on the thrust distribution on the disk. Three skewed wake models are examined to better understand the potential sources of error. First is the dynamic inflow model originally developed for helicopters, and second is a modification of this model developed for wind turbines. Third is an earlier cylindrical vortex wake model which pioneered the study of skewed wake effects for helicopters, and which can be generalized for wind turbine applications. It is concluded that this generalized model and the original dynamic inflow model are the most promising for small wind turbine applications, and their predictions of center of thrust and blade root moments are compared for an idealized rotor. The focus is on static equilibrium loads, and note is taken of the potential importance of accounting for expanding wake effects. The basic results of the study are applicable to large as well as small wind turbine rotors.
Application of Differential Transform Method to Heat Conduction in Tapered Fins
Authors: Bert Charles W.
Published: July 2002

This paper analyzes steady-state heat conduction in a triangular-profile fin using a relatively new, exact series method of solution known as the differential transform method. This method converges with only six terms or less for the cases considered. Its advantage is that, unlike many popular methods, it is an exact method and yet it does not require the use of Bessel or other special functions.
Parametric Optimization of Structures Under Combined Base Motion Direct Forces and Static Loading
Authors: Bucher Izhak
Published: July 2002

This paper deals with the optimization of vibrating structures as a mean for minimizing unwanted vibration. Presented in this work is a method for automatic determination of a set of preselected design parameters affecting the geometrical layout or shape of the structure. The parameters are selected to minimize the dynamic response to external forcing or base motion. The presented method adjusts the structural parameters by solving an optimization problem in which the constraints are dictated by engineering considerations. Several constraints are defined so that the static deflection, the stress levels and the total weight of the structure are kept within bounds. The dynamic loading acting upon the structure is described in this work by its power spectral density, with this representation the structure can be tailored to specific operating conditions. The uncertain nature of the excitation is overcome by combining all possible spectra into one PSD encompassing all possible loading patterns. An important feature of the presented method is its numerical efficiency. This feature is essential for any reasonably sized problem as such problems are usually described by thousands of degrees of freedom arising from a finite-element idealization of the structure. In this paper, efficient, closed form expressions, for the cost function and its gradients are derived. Those are computed with a partial set of eigenvectors and eigenvalues thus increasing the efficiency further. Several numerical examples are presented where both shape optimization and the selection of discrete components are illustrated.
Influence of Thermal Effects on Hole Quality in Dry Drilling, Part 2: Thermo-Elastic Effects on Hole Quality
Authors: Kalidas Shiva , Kapoor Shiv G. , DeVor Richard E.
Published: July 2002

A finite element thermo-elastic model is devised to capture the radial errors induced in the workpiece in drilling. The temperature rise in the workpiece modeled in Part 1 of this paper is utilized in obtaining the thermo-elastic deformations in the workpiece at various process conditions. The predicted errors are compared to the average errors measured with the aid of a CMM. The predicted profiles agree well with the experimentally observed tapered hole profiles in the absence of cutting fluids. In the presence of cutting fluids the predicted radial errors only account for 10 percent of the experimentally observed errors.
Open-Loop Nonlinear Vibration Control of Shallow Arches via Perturbation Approach
Authors: Lacarbonara W. , Chin C.-M. , Soper R. R.
Published: July 2002

An open-loop nonlinear control strategy applied to a hinged-hinged shallow arch, subjected to a longitudinal end-displacement with frequency twice the frequency of the second mode (principal parametric resonance), is developed. The control action—a transverse point force at the midspan—is typical of many single-input control systems; the control authority onto part of the system dynamics is high whereas the control authority onto some other part of the system dynamics is zero within the linear regime. However, although the action of the controller is orthogonal, in a linear sense, to the externally excited first antisymmetric mode, beneficial effects are exerted through nonlinear actuator action due to the system structural nonlinearities. The employed mechanism generating the effective nonlinear controller action is a one-half subharmonic resonance (control frequency being twice the frequency of the excited mode). The appropriate form of the control signal and associated phase is suggested by the dynamics at reduced orders, determined by a multiple-scales perturbation analysis directly applied to the integral-partial-differential equations of motion and boundary conditions. For optimal control phase and gain—the latter obtained via a combined analytical and numerical approach with minimization of a suitable cost functional—the parametric resonance is cancelled and the response of the system is reduced by orders of magnitude near resonance. The robustness of the proposed control methodology with respect to phase and frequency variations is also demonstrated.
Distributed-Parameter Modeling for Geometry Control of Manufacturing Processes With Material Deposition
Authors: Doumanidis Charalabos , Skordeli Eleni
Published: July 2002

Recent solid freeform fabrication methods generate 3D solid objects by material deposition in successive layers made of adjacent beads. Besides numerical simulation, this article introduces an analytical model of such material addition, using superposition of unit deposition distributions, composed of elementary spherical primitives consistent with the mass transfer physics. This real-time surface geometry model, with its parameters identified by in-process profile measurements, is used for Smith-prediction of the material shape in the unobservable deposition region. The model offers the basis for a distributed-parameter geometry control scheme to obtain a desired surface topology, by modulating the feed and motion of a moving mass source. The model was experimentally tested on a fused wire deposition welding station, using optical sensing by a scanning laser stripe. Its applications to other rapid prototyping methods are discussed. [S0022-0434(00)02301-7]
Thermal Placement Design for MCM Applications
Authors: Huang Yu-Jung , Fu Shen-Li
Published: July 2002

This paper introduces an algorithm that focuses on the placement of the power dissipating chips for multichip module applications. The main design issue is addressed on the chip placement to achieve uniform thermal distribution. Our approach to the placement problem is based on the modified force-directed placement method. The proposed thermal force-directed placement method is to relate the force equations to the power dissipation values of the individual bare chip. Examples of multichip placement are presented. The finite element simulation results are also investigated and compared with quadrisection placement methods. [S1043-7398(00)01002-1]
Augmentation of Thin Falling-Film Evaporation on Horizontal Tubes Using an Applied Electric Field
Authors: Darabi J. , Ohadi M. M. , Dessiatoun S. V.
Published: July 2002

Heat transfer enhancement of falling-film evaporation on commercially available horizontal tubes using an applied electric field was studied experimentally. The tube surfaces tested included: smooth, 19 fins per inch (19 fpi) low-fin type, and Turbo BIII which is a state-of-the-art commercially available boiling tube. The nominal outside diameters of all the tubes were 19 mm. Experiments were performed with R-134a at a saturation pressure of 550 kPa. Effects of heat flux, film flow rate, applied electric field potential, and heat transfer surface on the heat transfer coefficient were investigated. In addition, the effect of Poloyl-ester oil on the heat transfer coefficients was also investigated. Experiments were conducted for oil concentrations ranging from 0.5 percent to 5 percent on a mass basis. Small concentrations of a poloyl-ester lubricant were found to improve the heat transfer performance, while large concentrations reduced the heat transfer coefficient. [S0022-1481(00)00702-7]
Poly (n-butyl methacrylate) by XPS
Authors: Moulder J. F. , Stickle W. F. , Sobol P. E.
Published: July 2002

XPS measurements are presented for high purity poly (n-butyl methacrylate). The data include the valence band region and the principal core levels.
Interaction of O2 with TiO
x
(x=1.15) by He I UPS
Authors: Henrich V. E.
Published: July 2002

The rocksalt oxide TiOx, with x within about ±20% of 1.0, contains up to 15% of both cation and anion vacancies. This highly defective structure is thus fairly permeable to adsorbates such as oxygen. The Ti2+ cations have a nominally 3d2 electron configuration; as evidenced by the large density-of-states at the Fermi level, TiOx is metallic. However, exposure to even small amounts of O2 completely oxidizes the cations in the near-surface region to Ti4+, to a depth of several lattice constants. This is seen in these spectra by the reduction and ultimate depopulation of the Ti 3d emission band near 1 eV binding energy; after large O2 exposures, the spectra are very similar to those of the insulating oxide TiO2. [See V. E. Henrich, H. J. Zeiger, and T. B. Reed, Phys. Rev. B 17, 4121 (1978).]
Analysis of silicon–oxide–silicon nitride stacks by medium-energy ion scattering
Authors: Landheer D. , Ma P. , Lennard W. N. , Mitchell I. V. , McNorgan C.
Published: July 2002

This article describes medium-energy ion scattering (MEIS) measurements of [N] and [O] profiles using protons incident on nitride–oxide (NO) films produced by oxidizing Si(100) substrates in N2O plasmas and nitride–oxide–nitride stacks formed by depositing silicon nitride on the NO films. Concentrations were obtained from the MEIS spectra using a multiparameter Marquardt–Levenberg fitting procedure. Integral [N] and [O] were separately measured by nuclear reaction analyses and compared to the concentrations obtained from the MEIS profile. The analysis shows that nitrogen diffuses through oxide films during the deposition of silicon nitride by electron–cyclotron resonance chemical-vapor deposition and accumulates at the Si/SiO2 interface.
Kinetics of tip-induced island growth on Si(111) with a scanning tunneling microscope
Authors: Shklyaev Alexander A. , Shibata Motoshi , Ichikawa Masakazu
Published: July 2002

The kinetics of island growth on Si(111) with a scanning tunneling microscope (STM) is measured as a function of the tip–sample bias voltage. Two processes appear to be involved in the island growth in the center of the tip–sample interaction. Field-induced evaporation transfers atoms between the sample and the STM tip, and creates an area of incomplete surface structures with atoms mobile under the electric field. The second process is directional field-induced diffusion which transfers atoms along the surface. We derived a scaling relation for the initial island growth rate, the dipole moments of atoms on the surface, and the tip–sample bias voltage. This scaling relation was used to estimate the values of field–dipole interaction parameters from the kinetic data obtained for the initial island growth rate.
Rutherford Scattering and Channeling: A Useful Combination for Studying Crystal Surfaces
Authors: Davies J. A.
Published: July 2002

Rutherford scattering of energetic (MeV) atomic particles has been used for many years as a simple quantitative tool for analyzing high-mass impurities on the surface of a low-mass substrate. However, recent experiments in single crystal substrates have shown that, by rising a channeled beam, the value of Rutherford scattering as an analytical technique can be enhanced in several ways. For example, (1) the sensitivity is increased sufficiently to detect even low-mass impurities on the surface; (2) the composition of thin oxide or nitride surface layers can be measured directly; (3) the lattice location of the impurity atoms can often be accurately specified; and (4) the amount of lattice distortion in the surface region can be observed. A brief description of the basic principles of channeling and of Rutherford scattering is given, followed by some examples illustrating their combined use in studying the surface region of single crystals.
Spatial Initial Distribution of Ions in an MBAG and the Modulation Factor
Authors: Comsa George
Published: July 2002

The experimental sequence of the values of the modulation factor in a modulated Bayard-Alpert gauge for He, Ne, At, and Kr is explained on ground of the differences in shape of the corresponding ionization cross-section curves. A short discussion concerning the dependence of the modulation factor on electron current and filament-grid spacing is also given.
Analysis of Operational Data of Vacuum Arc and Electroslag Remelting Plant
Authors: Mueller-Aue Hans J.
Published: July 2002

A production plant containing three vacuum arc remelting (VAR) furnaces and one electroslag remelting (ESR) furnace is described. Production of about ten million pounds of a variety of material grades is analyzed by breakdown of the production program by steel grades and ingot size in order to evaluate the economies of the VAR and ESR processes. A realistic annual remelting capacity of the three VAR furnaces is about 11.5 million pounds for a mixed ingot production program with specific requirements of material quality and processing technology, taking into account the factors influencing the possible annual production. A graph illustrating the scattered values of melt rate and power consumption for steel remelted under varying conditions shows that the complexity of the ESR process can lead to very different statements when comparing the VAR and ESR processes. A correct comparison of the advantages and disadvantages of the two remelting processes and an understanding of the economic factors of each process requires a knowledge of the base on which the figures for comparison are determined.
Theory and Practice of Steady-State Evaporation of Alloys
Authors: Dale E. Brock
Published: July 2002

InSb films have been grown by steady-state evaporation, a technique that produces a vapor with the same composition as the starting liquid. Films deposited on glass substrates at room temperature typically have Hall coefficients of 10–50 cm3/C, resistivities of 0.05 and 0.5 Ω cm, and Hall mobilities of the order of 200 cm2/V  sec. X-Ray fluorescence analyses of films deposited on thin plastic substrates at room temperature indicate random departure from stoichiometry of as much as 1%. Comments are made on source design and conditions that may cause deviations from stoichiometry. The theory of steady-state evaporation is briefly discussed.
Superconducting Transition Temperatures of Vapor-Deposited Niobium Nitride
Authors: Oya Gin-ichiro , Onodera Yutaka
Published: July 2002

Thin films of the superconducting compound niobium nitride were deposited at atmospheric pressure on fused silica substrates by reaction of gaseous niobium pentachloride with ammonia and hydrogen gases in a fused silica apparatus. Suitable conditions for the preparation of NbN were found by calculating the free energies of reaction for several possible reactions involving niobium chlorides, ammonia, and hydrogen. Niobium nitride films could be formed at substrate temperature ranging from 900°–1000°C. The deposition rate varied with the reaction conditions from 20 to 1500 Å/sec, and deposits ranged from smooth films of polycrystals in which the individual crystal faces were 20 μ in length. The x-ray diffraction data for the NbN films deposited at 1000°C revealed face-centered cubic structure with cube edge of about 4.358 Å. Niobium nitride films prepared by this method had a wide range of resistivities, temperature coefficients of resistance, and superconducting transition temperatures depending on the deposition conditions. The maximum transition temperature obtained was 15.75 K for the films deposited at 900°C.
Structure and Intrinsic Stress of Platinum Films
Authors: Rottmayer R. E. , Hoffman R. W.
Published: July 2002

The stress in platinum thin films was measured on microscope cover glass, fused quartz, and single-crystal silicon as a function of thickness at temperatures ranging from 100 ° to 600 °C. The stress had a high tensile value (≅1010 dyn/cm2) at 100 °C. It decreased sharply at 300 °C and was very small at 500 ° and 600 °C. A 1-MeV electron microscope was used to study the thicker films. For deposition temperatures of 100 ° and 300 °C and thicknesses below 1300 Å, the structure of the films was columnar with grains 100 Å in lateral extent. In addition, the platinum deposited on silicon above 300 °C showed some preferred orientation and formed Pt-Si compounds. The origin of a large tension in the films was consistent with a grain boundary model. The decrease in stress at 300 °C was ascribed to surface diffusion in the growing film. The low temperature data also correlated well with the flow stress calculations of Chaudhari, Mader, and Freedman.
Superconducting Properties of Annealed Nb–Al–Ge Thin Films
Authors: Janocko M. A. , Gavaler J. R. , Jones C. K.
Published: July 2002

Annealed bulk Nb–Al–Ge possesses the highest superconducting transition temperature presently known (Tc∼20 K). In this paper we report on Tc and on other superconducting properties of annealed Nb–Al–Ge thin films which were prepared by sputtering from a 3Nb⋅0.8Al⋅0.2Ge cathode. Annealing was performed in a high vacuum environment maintained at 10−9Torr or less, for times and temperatures near the optimum conditions for bulk Nb–Al–Ge. Films with Tc's from 12 to 16 K were annealed and in all cases a rise in Tc was observed, with the maximum value obtained thus far being 17.5 K. The current carrying capacity (Jc) values, already substantially higher for unannealed thin films than for the bulk, were raised even further in the annealed samples, indicating that annealing has no detrimental effects on the flux pinning in these films.
Changes in the rf Conductivity of Discontinuous Molybdenum Films Exposed to Oxygen
Authors: Deshpande S. M. , Crowell A. D.
Published: July 2002

The frequency-dependent electrical resistance of discontinuous (i.e., ultrathin, <100-Å thick) metal films can be interpreted in terms of a simple equivalent circuit with frequency independent parameters whose values can be obtained by a computer analysis of the film resistance as a function of frequency in the megahertz range. The equivalent circuit is composed of a resistance Rb, associated with conduction in the film grains, and a resistance Rg in parallel with a capacitance Cg, associated with conduction across intergranular gaps. By observing changes in these quantities for evaporated Mo films exposed to O2 in situ, it has been possible to differentiate between the effects of this gas on the bulk conductivity in the grains from its effects on intergranular conductivity. Upon exposure to O2 at 10−7 to 10−4 Torr and room temperature (∼22°C), Mo films showed a more rapid increase in Rb than Rg during initial stages of chemisorption and oxidation, and vice versa as oxidation proceeded, showing that the changes in conductivity of these films produced by the interaction with gas molecules depends upon the location of the molecules within the film.
A new GaAs, GaP, and GaAsxP1−x vacuum deposition technique using arsine and phosphine gas
Authors: Morris F. J. , Fukui H.
Published: July 2002

A new vacuum deposition process for depositing thin films of GaAs, GaP, and GaAsxP1−x is described. This process is similar to the standard molecular beam technique except that the arsenic and phosphorus are supplied from the decomposition of arsine and phosphine gas. The advantages of this process over the more conventional one-source and two-source molecular beam techniques are that the new gas-source process is more easily controlled and more reproducible and the deposition source materials are essentially inexhaustible, permitting a large number of samples to be coated during a single run. The process has been optimized for depositing polycrystalline films 800–1000-Å thick with sheet resistivities exceeding 1013 Ω/square for use as a resistive sea for silicon-diode-array camera tube targets. Variations in the deposition parameters, such as gallium temperature, the ratio of gallium to arsenic or phosphorus flux incident on the substrates, deposition time, and substrate temperature, were made to determine their effects on the film properties. A standard process was developed which permitted reproducible deposition of films which satisfactorily met the requirements of the camera tube application.
Superconductivity of Transition Metal Thin Films Deposited by Noble Gas Ion Beam Sputtering
Authors: Schmidt P. H.
Published: July 2002

Noble gas ion beam sputtering techniques have been used to prepare thin films of several transition metals. Thin films of Mo, Ti, W, and Zr metals have been found to be superconducting with transition temperatures substantially higher than those observed for the respective bulk metals. Cr thin films have been found to be superconducting for the first time. Ion beam sputtered thin films of Nb, Ru, Ta, and V metals were similarly deposited, resulting in decreases in Tc compared with bulk values. In each case the transition temperatures were seen to depend on the noble gas used for deposition. The highest transition temperatures were obtained for those films deposited with xenon gas. Superconducting transition temperatures are correlated with the kind of gas used for deposition, the apparent particle size, and with changes in the size of the metal lattice.
Crystal Structure of Evaporated MgO Films on Amorphous and Polycrystalline Substrates
Authors: Aboelfotoh M. O.
Published: July 2002

Thin films of MgO were prepared by deposition from the vapor phase on amorphous and pylycrystalline substrates. Transmission and reflection electron diffraction were used to determine the orientation of the crystals in these MgO films. It was found that, on amorphous substrates initially at room temperature, the films possessed a crystal orientation which varied with film thickness. Films thinner than ∼ 500 Å showed a random orientation. As the film thickness was increased above ∼ 500 Å, a [111] preferred orientation was developed with an axis inclined away from the substrate normal and toward the direction of the vapor beam at oblique vapor incidence. At high substrate temperature (∼ 150–300 °C), the films followed the same behavior during growth. This preferred orientation is interpreted as a final growth orientation. On silver films as substrates, initially at room temperature, the same [111] preferred orientation was observed in films ≲ 100 Å thick and with increasing film thickness the orientation persisted. In thick deposits a slight inclination of the orientation axis was also observed at oblique vapor incidence. These results suggest that on Ag substrates the orientation is an initial nucleation orientation and also a final growth orientation.
Structural and Electrical Properties of Evaporated-Amorphous and Vitreous-Amorphous V-VI Compounds
Authors: Ast D. G.
Published: July 2002

It is not widely realized that the structure of evaporated films differs significantly from the structure of vitreous bulk specimens. The atomic arrangement of vitreous specimens retains the short range order of the liquid from which they were prepared, whereas evaporated films are built up by the individual arrival of molecules and hence are inherently more random. The composition of these molecules depends on the composition of the evaporant and the evaporation conditions. Inspection of the radial distribution functions (RDF) of evaporated As2S3, As2Se3, and As2Te3 show consistently the appearance of an additional peak in the RDF of evaporated films. The peak is absent in the vitreous form and disappears when evaporated films are annealed in the vicinity of the glass transition temperature. These structural differences are reflected in the electronic properties of evaporated and vitreous samples.
Behavior of ions in SiO2
Authors: Williams R.
Published: July 2002

Several methods that have been used to inject ions into layers of thermally grown SiO2 are reviewed and compared. We have studied the injection of various ionic species through the free surface of the oxide. A thin layer of a salt containing the desired ion is coated on the surface which is then charged with a corona discharge of the proper polarity. Some positive ions move through the oxide under these conditions while others do not. The determining factor is apparently the ionic radius. The smallest negative ion is F− and this shows some mobility under these conditions, though less than the smaller positive ions.
Higher zones of stability for the quadrupole mass filter
Authors: Dawson P. H.
Published: July 2002

Matrix methods based on phase-space dynamics are used to examine the feasibility of operating a quadrupole mass filter using one of the higher zones of stability. Ion transmission efficiencies are calculated for various modes of operation. By using lower rf, performance may approach that of the conventional mass filter under certain conditions, but instrument apertures are generally somewhat smaller.
Ultrahigh vacuum system for the study of the mechanical and electrical properties of metallic surfaces
Authors: Cuthrell Robert E.
Published: July 2002

A bakeable ultrahigh vacuum system was constructed for the study of the mechanics of deformation, contact resistance, bonding, friction, and high-resolution topography of metallic surfaces in contact. The instrument consists of a work chamber which is isolated from building vibrations and in which metallic samples may be cleaned by sputtering, annealed by electron bombardment, and brought together with precise control of mechanical and environmental variables. Facilities are provided for load and contact resistance measurements. A laser interference fringe microscope, which is mounted in the work chamber, is used for quantitative surface topography determinations and the measurement of load-bearing areas. This system has been used for electrical contact and solid-phase bonding studies.
Schottky barriers and plasmons
Authors: Inkson J. C.
Published: July 2002

The changes in the electron exchange and correlation potential are related to the collective excitation at the interface of a metal semiconductor junction. They are shown to change discontinuously across the band gap, and the possible effects on the barrier formation are discussed. The possibility of surface superconductivity through exciton and plasmon exchange is considered briefly.
A simplified self-consistent model for image force and interface charge in Schottky barriers
Authors: Crowell C. R.
Published: July 2002

Some qualitative features are shown for an electrostatically self-consistent solution, initially without correlation and exchange forces, for the effect of electrons which tunnel from the metal of a Schottky barrier into the energy band gap of the semiconductor. The effect of an incremental electric field in the bulk semiconductor is deduced from a simple analytical treatment. In covalent semiconductors most of the incremental electric field terminates in the semiconductor in a manner almost independent of the nature of the metal, i.e., the effective “metal” electrode exists inside the bulk semiconductor. This is not true for ionic semiconductors. When the “metal” electrode location is used as the origin for the image force, a normal square root of the field dependence of the Schottky image force lowering is predicted at low electric fields and a linear dependence is predicted at high electric fields, both as reported recently by Andrews. The model also predicts the order of magnitude of the very small barrier variation between p- and n-type semiconductors. Interface contamination is predicted to have a very small effect on the barrier height provided the dopant occurs within the range of the tunneling electrons. If the dopant is deeper, however, and converts the semiconductor type, the effective barrier height, charge storage and photosensitivity are radically changed. It is shown that this phenomenon creates effective Schottky barrier configurations that have softer reverse current-voltage characteristics than an uncontaminated barrier. These conclusions are reinforced by measurements on Hf-n-type-Si Schottky barriers.
Novel multibridge-structured piezoelectric microdevice for scanning force microscopy
Authors: Chu J. , Wang Z. , Maeda R. , Kataoka K. , Itoh T. , Suga T.
Published: July 2002

In this article we report the structure and the microfabrication method of a novel micro-scanning force microscopy (SFM) device. It is a lead zirconate titanite (PZT) bimorph structure in the shape of a cantilever supported by bridges. Electric fields applied to the separated sections of the electrodes on the levers can induce lever deflection and actuate the tip in x, y, and z directions. The cantilever can vibrate and sense its own vibration amplitude to detect the surface topography in the cyclic contact SFM mode. In the fabrication process, the sol–gel method is modified for constructing high quality PZT films 3 μm thick. The single bridge device has shown microscopy sensitivity of 0.32 nA/nm in a vertical direction, with actuation sensitivities of 70–80 nm/V in a lateral direction. The multibridged structure has been proven to be effective in elevating the eigenfrequency, which is very important for improving the SPM data rate.
Porous field emission devices based on polyimide membranes using diode and triode configurations
Authors: Mammana V. P. , Fonseca L. R. C. , Filho A. Pavani , Monteiro O. R. , Ramprasad R. , von Allmen P.
Published: July 2002

Residual gas inside field emission displays (FED) is the most important issue related to the device lifetime. Increasing the display area while maintaining the display thickness unchanged results in lifetime decrease, since the pressure gradient is fostered. Therefore, improvement of vacuum properties is a mandatory step towards large area displays. In a prior publication we have demonstrated that porous diamond membranes show good vacuum performance, while requiring low emitter switching voltage. In this work, we continue the porous membrane development by using polyimide as the base material for the membrane. The use of polyimide instead of diamond allows for easier production of large area porous FEDs. In addition, we present results of preliminary field emission experiments showing a direct correlation between the emitted current and the number of pores. This result strongly suggests that the emission sites are located at the pore edges in the polyimide membranes, similar to our observations for diamond membranes. From the theoretical point of view, we propose a new geometry, still based on the use of pores, but including a grid for triode mode operation. Finally, we present electron trajectory simulations that address some of the focusing issues in the proposed device.
Direct measurement of emission current distribution of Spindt-type field emitters
Authors: Xie Chenggang , Hayes Greg , Wei Yi
Published: July 2002

A specially designed Spindt-type emitter array is used to study field emission characteristics of the Spindt-type field emitter. Each pixel in the array contains only one tip, is independently addressable, and is spaced 110 μm from the adjacent pixels. The pixels are electrically and optically distinguishable from each other. The emission current distribution of 2560 field emitters in an array is directly measured as a function of gate voltage. The ratio of maximum current to minimum current is as high as 100:1. There are two peaks observed in the current distribution. The position of the high current peak is strongly dependent on the gate voltage, while the position of the low current peak is less sensitive to the gate voltage. The variations in beam size and beam position of individual field emitters are also measured. These variations within individual emitters are partly responsible for large beam size observed in field emission displays with pixels containing hundreds of emitters. Change in the current distribution of individual emitters was recorded as the emitters were aging. Statistically, the emitters operating at high current age faster than those at low current.
Development of the quadrupole mass spectrometer with the Bessel–Box type energy analyzer: Function of the energy analyzer in the partial pressure measurements
Authors: Takahashi N. , Hayashi T. , Akimichi H. , Tuzi Y.
Published: July 2002

The quadrupole mass spectrometer (QMS) with the Bessel–Box type energy analyzer has been developed. The analyzer is placed between the ionizer and the quadrupole mass filter for the separation of the gas phase ions and the electron stimulated desorption (ESD) ions produced in the ionizer according to their kinetic energies. Three important results for the improvement of the accuracy of partial pressure measurements have been obtained by the QMS. First, the elimination of ESD ions gives the simple mass spectra of gas phase ions for the accurate analysis of the spectra. Second, the signal intensity profiles of the peaks of parent ions and the fragment ions with same mass to charge ratio (M/e) in the mass spectra are obtained and are discussed in relation to the mechanism of ion formation. Third, the sensitivity of the QMS for the very small amount of impurities in the gases of higher pressure (high vacuum region) is also improved down to a few tens of parts per billion of the total pressure due to the reduction of background noise. The noise is much reduced by the geometrical structure of the energy analyzer which prevents the ion collector, a secondary electron multiplier, from the irradiations of vacuum ultraviolet photons and soft x rays generated in the ionizer.
Recent progress in the characterization of electron emission from solid-state field-controlled emitters
Authors: Binh Vu Thien , Semet V. , Dupin J. P. , Guillot D.
Published: July 2002

The solid-state field-controlled emitter (SSE) structure is an ultrathin large gap semiconductor (UTSC) layer on a metallic surface. Quantum calculations show that the electron emissions from the SSE cold cathodes result from a serial two-step mechanism: first is the injection into the UTSC of a large concentration of electrons through the Schottky junction with the consequence of a significant lowering of the emission barrier, followed by the emission of the electrons from the UTSC surface, a current modulated by the applied voltage. The determination of the current densities versus the applied field from the experimental total current versus applied voltage data, measured for the SSE planar cathodes, used results obtained with electron optics numerical simulations of the field distributions across the planar area in front of a hemispherical probe. Discussions about this methodology are presented. This allows a comparison between the experimental results and the theoretical predictions. The specific behavior of the SSE cathodes was highlighted as well as the role of the different parameters (temperature, thickness,) in the control of the electron emission from these novel flat cold cathodes.
Metalorganic chemical vapor deposition Pb(Zr,Ti)O3 and selected lower electrode structures as a pathway to integrated piezoelectric microelectromechanical systems
Authors: Chen Ing-Shin , Roeder Jeffrey F. , Kim Dong-Joo , Maria Jon-Paul , Kingon Angus I.
Published: July 2002

The actuation mechanism is an important aspect of many micromachined devices. Electrostatic actuation has been the prevailing actuation method due to its relative ease in implementation using conventional silicon microfabrication techniques. Other mechanisms are becoming more accessible to micromachine designs as new materials are introduced into the microfabrication process. Recent progress in nonvolatile memory has led to successful incorporation of Pb(Zr,Ti)O3 (PZT) thin films into microelectronic devices. The present work expands on this area and investigates PZT thin films and electrode/barrier combinations for applications in micromachined devices. Incorporation of PZT thin films into silicon micromachined devices requires electrode systems and deposition techniques that are compatible with silicon microfabrication. In this study, Ir/IrOx and Ir/(Ti,Al)N lower electrode systems were developed to suppress diffusion of reactive species (e.g., Pb) into silicon-based microelectromechanical system devices and to enhance PZT film adhesion. Piezoelectric PZT thin films from 0.3 to 1 μm thick were prepared on silicon wafers with these electrode structures by metalorganic chemical vapor deposition. Hysteresis loops of longitudinal piezoelectric coefficient (d33) were measured by dual-beam interferometry and used to characterize piezoelectric activity in these films. The effective d33 exhibited an apparent dependence on film thickness. d33 values up to 70 pm/V were obtained for 1 μm films, while thinner films exhibited lower d33 values between 54 and 60 pm/V. The dielectric loss (tan δ) was below 2% for most films irrespective of their thickness.
Balancing the etching and passivation in time-multiplexed deep dry etching of silicon
Authors: Blauw M. A. , Zijlstra T. , van der Drift E.
Published: July 2002

For the Bosch deep silicon dry etch process with SF6–C4F8 a quantitative approach is developed. Essential plasma surface interactions and the transport properties of ions and radicals in high aspect ratio structures are unravelled. Balancing the interactions during etching and passivation pulses is essential for maximal profile control. In the anisotropic regime the etch rate is aspect ratio dependent largely due to depletion of fluorine radicals and with some involvement of passivation polymer redeposition. The anisotropic process tends to stop at a limiting aspect ratio because of improper removal of polymer passivation at the trench bottom. Both higher ion flux and ion energy are found to be crucial to push the Bosch process to higher achievable aspect ratios. Practical process implications are discussed. In situ ellipsometry shows that the polymer passivation step is a complex process with an ion induced component. More efficient removal of the passivation layer at the trench bottom by adjusting the plasma chemistry could further improve the Bosch plasma etch process.
CH
4
-based dry etching of high Q InP microdisks
Authors: Choi Seung June , Djordjev Kostadin , Choi Sang Jun , Dapkus P. Daniel
Published: July 2002

CH 4 -based InP dry etching techniques have been investigated by using electron cyclotron resonance etching and reactive ion etching (RIE) methods to obtain microdisk and ring structures having smooth, vertical sidewalls, and specular etched surfaces. The RIE method is chosen for the device etch process owing to the higher perfection of the surfaces generated by this process. Excess CH4 introduced in the InP RIE process was found to generate excessive polymers and resulted in sloped, rough sidewalls. A multistep RIE process involving a high-pressure (75 mTorr) condition, followed by a lower pressure (15 mTorr) etching to the completion of the structure was developed that leads to very smooth sidewalls. This process was successfully utilized in the fabrication of vertically coupled microdisk resonators.
Proximity exposure effect analysis using the phenomenon of resist debris formation in electron beam lithography
Authors: Deshmukh P. R.
Published: July 2002

The phenomenon of resist debris (RD) formation is shown to be a useful method for proximity exposure (PE) effect analysis in electron beam lithography. Some simulation results and corresponding experimental results discussed in this article on RD formation over the electron beam exposed pattern areas before and after PE effect correction reveal certain unique features associated with the method. These unique features of the method have direct relevance with the electron beam exposure parameters assumed in the simulation work, their implementation during the experiments, pattern shape-spacing fidelity, and also the correction scheme used for the PE effect correction.
Comparative study on alloy cluster formation in Co-Al and Co-Pt systems
Authors: Konno Toyohiko J. , Yamamuro Saeki , Sumiyama Kenji
Published: July 2002

The formation of alloy clusters using a plasma-gas-aggregation technique is described for Co-Al and Co-Pt systems. This method employs two separate elemental sputtering sources and a growth chamber. Metallic vapors generated were cooled rapidly in an Ar atmosphere, and grown into alloy clusters. The composition of the clusters was controlled by adjusting the ratio of the applied sputtering power. We found that B2-CoAl clusters of about 12 nm in diameter were formed for a composition range wider than that predicted by the Co-Al phase diagram, and that high-temperature fcc-CoPt clusters were formed in the Co-Pt system. These findings suggest the nonequilibrium nature of the cluster formation. The size distribution of the clusters is highly monodispersive and does not follow commonly observed log-normal distribution. These results were discussed from the viewpoint of simple gas dynamics. We concluded that monomer absorption with discrete residence time is the dominant mechanism for monodispersive alloy cluster formation, and that the contrasting thermodynamical features between the Co-Al and Co-Pt systems are at the cause of the observed difference in average cluster size.
Secondary Electron Emission of Vacuum-Cleaved Solids
Authors: Whetten N. R.
Published: July 2002

Recent work on the secondary electron emission properties of solids with less than 1/100 of a monolayer of adsorbed gas on the surface is reviewed. The solids were cleaved in a high vacuum so that secondary emission measurements could be completed in a time that was short compared to the monolayer adsorption time. The solids include graphite, NaCl, KCl, NaBr, KBr, and KI. The gases released from the alkali halides at the moment of cleavage were analyzed with a partial pressure analyzer.
Ferromagnetic and Structural Properties of Nearly Perfect Thin Nickel Platelets
Authors: De Blois R. W.
Published: July 2002

Nearly perfect, single-crystal thin platelets of nickel and nickel alloy are readily grown non-epitaxially by the reduction of the halide. Thicknesses range from about 500 Å to over 105 Å; areas extend to over 1 mm2. Etching in HCl reveals dislocation densities generally either of zero or of 103–104 cm−2. Ferromagnetic domain studies with the platelets have yielded the following results: (1) 180 ° walls with mixed NéelBloch character may coexist with Bloch walls in both nickel and NiCo platelets at least 7000 Å thick. The presence of a geometrically required crosstie spot establishes the partially Néel-wall character. (2) one may precisely determine the applied field required to drive out a nucleus of reverse magnetization from the corner of a platelet by noting the form of the returning domain structure. (3) the 180 ° wall in a rectangular Ni-Co platelet with a simple closure pattern forms the arc of a circle in an applied field; i.e., there is a uniform effective pressure acting along its length. (4) Topological restraints are largely responsible for hysteresis in nickel platelets several thousand angstroms thick. In small driving fields Ni-Co rectangular platelets may have virtually no hysteresis or coercive force (Hc<0.01 Oe). In large fields there is hysteresis from irreversible topological changes, but there may still be no coercive force. (5) Near the transitional thickness for crosstie walls the platelets show both coercive forces of several tenths of an oersted and an after-effect. The ferromagnetic resonance experiments of Rodbell with nickel platelets are also briefly mentioned.
Increase of Residual Background Gases During Ultrahigh-Vacuum Mass Spectroscopic Analysis
Authors: Rozgonyi G. A.
Published: July 2002

It has been observed that anomalously high residual background-gas pressures will occur in an ultrahigh-vacuum mass spectrometer exposed to increasing argon pressure. The gases have been identified as hydrogen, helium, neon, carbon monoxide, methane, and ethane. The vacuum system is bakeable, with sputter-ion and cryogenic sorption pumps. Vacua of less than 1×10−10 Torr are routinely obtained. A mechanism is described to account for the appearance of the above gases based on the vacuum-system components. The gases either evolve from the sputter-ion pump or are inefficiently pumped by it. These gases migrate through the system and are adsorbed on the various internal surfaces when the pressure is below 10−9 Torr. They are subsequently desorbed by argon bombardment, most likely in the vicinity of the total- and partial-pressure gauges, as the argon pressure is increased. In a static system, the residual gases will increase to as ranch as 1% of the argon pressure. In a dynamic system, the gases are still observed, but at lower concentrations.
Electronic Structure of Clean Metallic Interfaces
Authors: Duke C. B.
Published: July 2002

A review of the theory of clean metallic interfaces is presented. First, the contributions to the potential at a metallic interface due to bulk electron–electron, bulk electron–ion, and surface interactions, are illustrated for a metal–vacuum interface. We then review the description of this potential by phenomenological models and by dynamical models. Its description by a particular dynamical model, the local-density approximation for an electron fluid in an average positive background, is developed and compared with earlier models. The model is extended to describe bimetallic interfaces. Its major prediction is that the redistribution of charge at a bimetallic or metal semiconductor junction relative to the isolated metal–vacuum interfaces of its components causes substantial modifications of the potential at the interface. This effect suffices to describe the systematics of metal–semiconductor contacts without introducing surface states.