bluuebunny/crossref_metadata_2025 huggingface dataset:
Fracture Probability Integral Applied to Reactor Vessel Life Estimate1
Authors: Chang Shih-Jung
Published: July 2002

The conventional method of fracture probability calculations such as that adopted by the NRC-sponsored PRAISE CODE and the FAVOR CODE developed in this laboratory are both based on Monte Carlo simulation. Heavy computations are required. A new method of fracture probability calculation is developed by direct probability integration. The preliminary version of the development was published in an earlier paper. More detailed development of the method is presented here. The present approach offers simple and expedient method to obtain numerical values of fracture probability. This method can be applied to problems as general as the method of Monte Carlo simulation. This approach also provides a clear physical picture on the meaning of the probability of fracture. Parametric studies are made in this paper to show the variation of the numerical values of the probabilities of fracture as a result of the change of the standard deviation of either fracture toughness or the radiation-induced temperature shift. Also, it is shown numerically that a limiting probability can be obtained if the standard deviation of the fracture toughness approaches zero that implies a deterministic fracture toughness. It confirms the theoretical proof shown in Eq. (11). The limiting probability is the simplistic probability of crack count used by this author where both toughness and temperature shift are assumed to be deterministic values. The general probability of fracture developed here is simply a generalization of the crack count, except the crack count is selected with the appropriate fracture toughness in the toughness distribution. The toughness for the problem considered here is then multiplied by the appropriate temperature shift in the distribution function of the temperature shift. Although the present development is based on linear fracture mechanics assumption and applied to the radiated reactor vessel steel, there is no difficulty in viewing the present development as a general formulation that is capable of handling as many random variables as required by the fracture model. The multiplicity of the integration corresponds to the number of random variables. The probability integral is applied in this paper to calculate the probability of fracture for the high flux isotope reactor (HFIR) vessel that has been weakened due to the radiation embrittlement. The random variables used here are the crack length, the fracture toughness, and the radiation-induced temperature shift that is needed in the parametric representation of the radiated vessel steel.
Measured Performance of Building Integrated Photovoltaic Panels*
Authors: Fanney A. Hunter , Dougherty Brian P. , Davis Mark W.
Published: July 2002

The photovoltaic industry is experiencing rapid growth. Industry analysts project that photovoltaic sales will increase from their current $1.5 billion level to over $27 billion by 2020, representing an average growth rate of 25%. (Cook et. al. 2000)[1]. To date, the vast majority of sales have been for navigational signals, call boxes, telecommunication centers, consumer products, off-grid electrification projects, and small grid-interactive residential rooftop applications. Building integrated photovoltaics, the integration of photovoltaic cells into one or more of the exterior surfaces of the building envelope, represents a small but growing photovoltaic application. In order for building owners, designers, and architects to make informed economic decisions regarding the use of building integrated photovoltaics, accurate predictive tools and performance data are needed. A building integrated photovoltaic test bed has been constructed at the National Institute of Standards and Technology to provide the performance data needed for model validation. The facility incorporates four identical pairs of building integrated photovoltaic panels constructed using single-crystalline, polycrystalline, silicon film, and amorphous silicon photovoltaic cells. One panel of each identical pair is installed with thermal insulation attached to its rear surface. The second paired panel is installed without thermal insulation. This experimental configuration yields results that quantify the effect of elevated cell temperature on the panels’ performance for different cell technologies. This paper presents the first set of experimental results from this facility. Comparisons are made between the electrical performance of the insulated and non-insulated panels for each of the four cell technologies. The monthly and overall conversion efficiencies for each cell technology are presented and the seasonal performance variations discussed. Daily efficiencies are presented for a selected month. Finally, plots of the power output and panel temperatures are presented and discussed for the single-crystalline and amorphous silicon panels.
Construction of Fair Surfaces Over Irregular Meshes
Authors: Westgaard Geir , Nowacki Horst
Published: July 2002

This paper describes the process of constructing a fair, open or closed C1 surface over a given irregular curve mesh. The input to the surface construction consists of point and/or curve data which are individually marked to be interpolated or approximated and are arranged according to an arbitrary irregular curve mesh topology (Fig. 1). The surface constructed from these data will minimize flexibly chosen fairness criteria. The set of available fairness criteria is able to measure surface characteristics related to curvature, variation of curvature, and higher order surface derivatives based on integral functionals of quadratic form derived from the second, third and higher order parametric derivatives of the surface. The choice is based on the desired shape character. The construction of the surface begins with a midpoint refinement decomposition of the irregular mesh into aggregates of patch complexes in which the only remaining type of building block is the quadrilateral Be´zier patch of degrees 4 by 4. The fairing process may be applied regionally or to the entire surface. The fair surface is built up either in a single global step or iteratively in a three stage local process, successively accounting for vertex, edge curve and patch interior continuity and fairness requirements. This surface fairing process will be illustrated by two main examples, a benchmark test performed on a topological cube, resulting in many varieties of fair shapes for a closed body, and a practical application to a ship hull surface for a modern container ship, which is subdivided into several local fairing regions with suitable transition pieces. The examples will demonstrate the capability of the fairing approach of contending with irregular mesh topologies, dealing with multiple regions, applying global and local fairing processes and will illustrate the influence of the choice of criteria upon the character of the resulting shapes.
A Generalized Load-Penetration Relation for Sharp Indenters and the Indentation Size Effect
Authors: Li Z. Y. , Chandrasekar S. , Yang H. T.
Published: July 2002

A dimensional analysis has been made of elastic-plastic indentation of an anisotropic solid, and of a solid showing pressure-sensitive yield behavior. It is found that, P∝δ2, for indentation with sharp, self-similar indenters, where P is the load applied by the indenter and δ is the corresponding distance of penetration of the indenter into the solid. This extends and generalizes a similar result obtained for isotropic solids showing conventional plastic behavior. When a strain-gradient plasticity is incorporated into the material model, then it is found that P is no longer proportional to δ2. Implications of the results for the indentation size-effect and for the determination of stress-strain curves from indentation are discussed.
Hybrid Dish/Stirling Systems: Combustor and Heat Pipe Receiver Development
Authors: Laing Doerte , Pa˚lsson Magnus
Published: July 2002

A hybrid sodium heat pipe receiver has been developed within the project HYHPIRE, funded 50% by the European Commission. The hybrid receiver was designed for the SBP/LCS 10-kWel dish/Stirling system with the SOLO-161 Stirling engine. Design of the heat pipe receiver and combustion system are described in this paper. The system has been tested successfully in all operation modes. Results and experience from the lab tests in combustion-only mode, as well as results from demonstration testing in the dish in solar-only, gas-only, and hybrid mode on the Plataforma Solar de Almeria (PSA) in Spain, are reported.
Effects of Geometry on the Performance of a Downhole Orbital Vibrator
Authors: Reynolds Robert R. , Cole Jack H. , Yuan Zhen
Published: July 2002

The influence of geometry on the pressure field within the confined, water-filled annulus between a central, vibrating cylinder and an outer, rigid enclosure is determined. A two-dimensional model is constructed using the finite element (FE) method and parameters are identified to characterize the eccentricity of the nominal cylinder position, the size of the annulus relative to the inner cylinder and the degree to which the annulus is not circular (i.e., it is elliptic). The FE solution is verified using a closed-form solution for the special case of a concentric cylinder and annulus. It is shown that the system acts as a force multiplier. Analyses of the asymmetrical geometries indicate that while the pressure field on the surface of the cylinder and enclosure can be highly asymmetric, the system is relatively insensitive to minor variations in annulus shape except when the vibrating cylinder is not centrally located within the fluid region or the annulus size itself is small.
Aerosol Transport and Deposition in Sequentially Bifurcating Airways
Authors: Comer J. K. , Kleinstreuer C. , Hyun S. , Kim C. S.
Published: July 2002

Deposition patterns and efficiencies of a dilute suspension of inhaled particles in three-dimensional double bifurcating airway models for both in-plane and 90 deg out-of-plane configurations have been numerically simulated assuming steady, laminar, constant-property air flow with symmetry about the first bifurcation. Particle diameters of 3, 5, and 7 μm were used in the simulation, while the inlet Stokes and Reynolds numbers varied from 0.037 to 0.23 and 500 to 2000, respectively. Comparisons between these results and experimental data based on the same geometric configuration showed good agreement. The overall trend of the particle deposition efficiency, i.e., an exponential increase with Stokes number, was somewhat similar for all bifurcations. However, the deposition efficiency of the first bifurcation was always larger than that of the second bifurcation, while in general the particle efficiency of the out-of-plane configuration was larger than that of the in-plane configuration. The local deposition patterns consistently showed that the majority of the deposition occurred in the carinal region. The distribution pattern in the first bifurcation for both configurations were symmetric about the carina, which was a direct result of the uniaxial flow at the inlet. The deposition patterns about the second carina showed increased asymmetry due to highly nonuniform flow generated by the first bifurcation and were extremely sensitive to bifurcation orientation. Based on the deposition variations between bifurcation levels and orientations, the use of single bifurcation models was determined to be inadequate to resolve the complex fluid–particle interactions that occur in multigenerational airways. [S0148-0731(00)01102-X]
Handbook of Electronic Package Design
Authors: Pecht, Michael , Rafanelli, Anthony J.
Published: July 2002

[S1043-7398(00)01502-4]
Computing Design Rationales by Interpreting Simulations*
Authors: Stahovich Thomas F. , Raghavan Anand
Published: July 2002

We describe an approach for automatically computing a class of design rationales. Our focus is computing the purposes of the geometric features on the parts of a device. This is accomplished by first simulating the device with the feature in question removed and comparing this to a simulation of the nominal device. The differences between the simulations are indicative of the behaviors that the feature ultimately causes. Fundamental principles of mechanics are then used to construct a causal explanation that describes how the feature causes these behaviors. This explanation constitutes one of the rationales for the feature. We have implemented a computer program called ExplainIT that uses this approach to compute rationales and we have tested it on various examples. [S1050-0472(00)01001-1]
Ultrahigh Purity Graphite Electrode by Core Level and Valence Band XPS
Authors: Xie Yaoming , Sherwood Peter M. A.
Published: July 2002

Both core level and valence band XPS spectra were obtained from an ultrahigh purity (UHP) graphite electrode surface. This UHP graphite had a very low oxygen content and an extremely low nitrogen content on its surface. It had a very graphitic structure in both the surface and the bulk as evidenced by XPS and XRD studies. [See Y. Xie and P. M. A. Sherwood, Appl. Spectrosc. 43, 1153 (1989); Chem. Mater. 1, 427 (1989); 2, 293 (1990); Appl. Spectrosc. 44, 797 (1990); Chem. Mater. 3, 164 (1991); Appl. Spectrosc. 44, 1621 (1990); 45, 1158 (1991); Y. Xie, T. Wang, O. Franklin, and P. M. A. Sherwood, ibid. 46, 645 (1992).] Our previously reported work [Y. Xie and P. M. A. Sherwood, Chem. Mater. 1, 427 (1989); 2, 293 (1990); Appl. Spectrosc. 44, 797 (1990); Chem. Mater. 3, 164 (1991); Appl. Spectrosc. 44, 1621 (1990); 45, 1158 (1991); Y. Xie, T. Wang, O. Franklin, and P. M. A. Sherwood, 46, 645 (1992)] showed that XPS valence band spectra were more sensitive to the surface chemical environment than core level spectra, and could be well interpreted by X–α calculations with model compounds. In this work, the valence band spectrum shows that there were two different types of oxygen species on the UHP graphite surface. In separate data records published in Surface Science Spectra, however [see Y. Xie, T. Wang, M. A. Rooke, and P. M. A. Sherwood, Surf. Sci. Spectra 2, 192 (1992)], the valence band spectra showed that only one of the two different oxygen species could be seen on the highly oriented pyrolytic graphite (HOPG) surface, and the other of the two different oxygen species could be seen on the Du Pont E-120 high modulus pitch-based carbon fiber surface. No nitrogen was detected on either the HOPG or the E-120 carbon fiber surface.
How low-energy ions can enhance depositions on low-K dielectrics
Authors: Abramowitz Peter , Kiene Michael , Ho Paul S.
Published: July 2002

Ultrathin titanium nitride layers grown on three different dielectrics were studied to examine how low-energy ions change the chemical composition at and near their interface. Comparisons were made by growing titanium nitride under similar conditions both with (ion-assisted) and without (reactive) nitrogen ions. Although the chemical reactions between the titanium nitride and the three dielectrics under both growth conditions depend on the type of dielectric used, a few general observations were seen. In comparison with the reactively grown samples, all of the ion-assisted growths show a significant increase in the amount of nitride in the titanium nitride layer at and near the titanium nitride/dielectric interface. Moreover, the amount of chemical binding between the titanium nitride and dielectric is increased when low-energy ions are used. Finally, by using angle resolved x-ray photoemission it was determined that the enhancement in the deposition process from low-energy ions occurs without inducing significant intermixing between the titanium nitride layer and the dielectric.
Quantitative theory of scattering in antimonide-based heterostructures with imperfect interfaces
Authors: Shaw M. J. , Corbin E. A. , Kitchin M. R. , Hagon J. P. , Jaros M.
Published: July 2002

We report quantitative calculations of carrier lifetimes in imperfect GaxIn1−xSb/InAs superlattice structures. A microscopic description of imperfections including substitutional anions and interface islands is obtained through a novel strain-dependent empirical pseudopotential calculation. The T matrix of scattering theory is used to take our calculations of scattering lifetimes beyond the Born approximation, including multiple scattering events. Carrier lifetimes are related to the microscopic nature of the defects, their proximity to the interfaces, and the size and shape of interface islands. Anomalous effects due to lattice relaxation are seen to alter hole lifetimes, and their dependence upon position. For isolated isovalent anion defects we predict electron and hole lifetimes as low as 0.2 and 0.8 μs, respectively, for typical defect concentrations.
Scanning capacitance microscopy imaging of silicon metal-oxide-semiconductor field effect transistors
Authors: Kleiman R. N. , O’Malley M. L. , Baumann F. H. , Garno J. P. , Timp G. L.
Published: July 2002

We have studied cross-sectioned n- and p-metal-oxide-semiconductor field effect transistors with gate lengths approaching 60 nm using a scanning capacitance microscope (SCM). In a homogeneous semiconductor, the SCM measures the depletion length, determining the dopant concentration. When imaging a real device there is an interaction between the probe tip and the built-in depletion of the p-n junction. With the help of a device simulator, we can understand the relation between the SCM images and the position of the p-n junction, making the SCM a quantitative tool for junction delineation and direct measurement of the electrical channel length.
Ion-Beam Techniques for Device Fabrication
Authors: Spencer E. G. , Schmidt P. H.
Published: July 2002

Sputtering of solid surfaces by low-energy ion beams can remove materials at a rate useful for machining purposes; the system can be called an ion-milling machine. Milling of solid materials, with minimum change to adjacent materials, is possible by this method. The first part of the paper discusses the parameters involved in ion interactions with solid surfaces. Six different ion-milling techniques and ion sources are next described. Finally, practical procedures obtained with some current problems are given.
An Algorithm for Optimization of Experimental Parameters for Maximum Uniformity of Film Thickness
Authors: Ramprasad B. S. , Radha T. S. , Rao M. Ramakrishna
Published: July 2002

A simple method for evaluating the geometrical parameters yielding maximum uniformity of film thickness on rotating substrates is described. The algorithm is based on numerical integration of the function for relative thickness. It is shown that maximum uniformity is obtained for a normalized source-to-substrate distance ratio of h/δ = 1.37.
Electrical Properties of Evaporated Tellurium Films and TFT's
Authors: Dey S. K.
Published: July 2002

In situ measurement of the resistivity of p-type Tellurium films (thickness≃150 Å) as a function of deposition rate has been made for evaluating their strain sensitivity and incorporation into TFT's. Films deposited at 2 A/sec and subjected to an elongation strain displayed a small strain induced resistivity change which switched from a negative to a positive value as the voltage was increased. For all higher rates, the film showed a consistently positive effect regardless of the applied voltage. The anomalous behavior is ascribed to the conditions affecting the barrier height as the grain boundaries. Exposure to air generally resulted in a marked increase in conductivity. No significant increase in the strain sensitivity was observed in a transistor device using SiO and Al as the insulator and gate electrode respectively although the gate voltage modulation of the drain current was quite normal.
The Use of Ion Beams in Surface Physics Studies
Authors: Carter G.
Published: July 2002

This paper reviews recent progress on the applications of the reflection of ions, the emission of rays by ion bombardment, and the generation of secondary ion species at solid surfaces, for composition and structure analysis. The resolution and sensitivity of the techniques are discussed and the problems of rendering the processes quantitative examined.
Amorphous Thin Films
Authors: Wood C. , Gilbert L. R. , Mueller R. , Garner C. M.
Published: July 2002

The optical and transport properties of the binary amorphous systems Sb-Se, Ge-Se, and Ge-Te, have been investigated as a function of composition. Essentially the whole amorphous phase of each system was prepared in a single evaporation by an elongated substrate coevaporation technique. The optical band gap varied fairly smoothly between the values for amorphous end components. Most films exhibited lnσ vs T−1 relationships. Except for the Sb-Se system, the σ0 values lay in the hopping conductivity range. Those Ge-chalcogenide films showing lnσ vs T−(1/4) hopping conductivity behavior generally converted to a T−1 variation after annealing. The thermal activation energies and thermo-emf measurements showed the Fermi levels to be fixed well away from the band edges in the forbidden gap. Delocalization of states in the gap of α-Ge with increasing chalcogen content was not observed. The results have been interpreted in terms of chemical bonding.
Performance of an Oxide Solid Electrolyte as a Vacuum Oxygen Partial Pressure Gauge
Authors: Mogab C. J.
Published: July 2002

Calcia stabilized zirconia of nominal composition Ca0.15Zr0.85O1.85 has been used as the electrolyte of a galvanic cell for quantitative measurements of oxygen pressure in a vacuum chamber over the range 1–10−7 Torr. The low pressure limit is determined both by permeation of oxygen through the electrolyte and interaction with active residual gases such as CO, H2, and hydrocarbons. The response of the cell to changes in oxygen pressure is dependent on the pressure and independent of the electrolyte temperature over the range 600–800 °C. The rate of approach to a steady-state following step changes in oxygen pressure over the range ≈10−7–10−4 Torr can be represented by the empirical equation (dE/dt)αΔEm, where E is the cell emf, t is time, ΔE is the departure of the emf from the steady-state value, m=1 for step increases in pressure, and m=1.5 for step decreases in pressure. The time constant for relaxation following an increase in pressure has been measured as ≈[8×10−5/PO2(Torr)] sec, where PO2 is the vacuum oxygen pressure.
Hydrogen silsesquioxane/novolak bilayer resist for high aspect ratio nanoscale electron-beam lithography
Authors: van Delft Falco C. M. J. M. , Weterings Jos P. , van Langen-Suurling Anja K. , Romijn Hans
Published: July 2002

A bilayer resist system, consisting of hydrogen silsesquioxane (HSQ) as negative tone electron (e)-beam resist top coat and hard baked novolak resist as bottom coat, has been investigated for its ability to yield high aspect ratio nanoscale structures. For comparison, single layer HSQ (hard mask) has been investigated for its resolution, contrast, and process latitude. In single layer HSQ, dense lines and spaces (1:1) have been resolved down to 20 nm and single lines have been obtained with widths less than 15 nm. Processing conditions which result in higher contrasts in HSQ also result in higher horizontal contrasts, i.e., in poorer process latitudes; this effect has previously been observed for other negative tone e-beam resists as well. In the bilayer combination, HSQ allows nanoscale structures with an aspect ratio exceeding 15 to be etched in hard baked novolak resist. Single lines with 800 nm height and 40 nm width, semidense lines and spaces (1:2) with 155 nm height and 25 nm width, and dense lines and spaces (1:1) with 130 nm height and 40 nm width have been patterned in this bilayer system. Both the single layer HSQ and the HSQ/novolak bilayer system appear to be suitable as e-beam resists for research on nanoscale gates in complementary metal–oxide–semiconductor (CMOS) and other devices.
High-performance membrane mask for electron projection lithography
Authors: Yamashita Hiroshi , Amemiya Isao , Nomura Eiichi , Nakajima Ken , Nozue Hiroshi
Published: July 2002

A high-performance membrane mask for electron projection lithography (EPL) systems is proposed. The design and material selection of the mask described here were carefully executed by considering not only the lithographic performance but also various properties. The mask described in this article consists of a 600-nm-thick diamond-like carbon (DLC) scatter on a DLC membrane 30–60 nm thick. The optimum thicknesses are obtained by calculating angular distributions of the transmitted electrons by our in-house Monte Carlo simulator. It is expected to have an electron transmission of up to 80% and a beam contrast of 100% with an appropriate limiting aperture. A 1-mm-sq membrane of thickness of down to 30 nm could be successfully prepared. The high-performance membrane mask can obtain high resolution and high throughput of the EPL systems simultaneously.
Practical guide to the use of Bayard–Alpert ionization gauges
Authors: Singleton J. H.
Published: July 2002

There are many potential problems in the use of the Bayard–Alpert (BA) gauge and in the interpretation of the data that it provides. This article is a practical guide to its use. Sections in boldface type provide such a guide and are followed in each instance by supplementary, detailed discussion of the rationale behind the guide. The topics addressed include gas pumping, by generation of ions, and by chemical interactions at the electron emitter; the change in gas composition by interaction at the electron emitter; and errors in pressure measurement including Barkhausen–Kurtz oscillations, electron-stimulated desorption, and the x-ray effect. Factors which dictate the specific BA gauge selection, such as the method used for outgas, and the selection of the electron emitter, are discussed.
Structural, morphological, and mechanical properties of plasma deposited hydrogenated amorphous carbon thin films: Ar gas dilution effects
Authors: Valentini L. , Kenny J. M. , Mariotto G. , Tosi P. , Carlotti G. , Socino G. , Lozzi L. , Santucci S.
Published: July 2002

In this article, a thorough investigation of a-C:H films deposited by rf glow discharge from methane–argon mixtures, containing different Ar fractions, onto silicon substrate is presented. The structural, mechanical, and morphological properties of these films were investigated by complementary techniques, such as x-ray reflectivity, Raman spectroscopy, Brillouin light scattering, pin on disk test, and atomic force microscopy. Experimental results are examined to develop a coherent picture of the relationships among deposition parameters, microstructural features, and macroscopic properties. The consistency of the experimental results are checked with a new theoretical physical model that predicts the reaction probability for methyl radicals interacting with the surface of amorphous hydrogenated carbon films.
Epitaxial growth of TiO2 thin films by pulsed laser deposition on GaAs(100) substrates
Authors: Liu Xiaohua , Chen X. Y. , Yin J. , Liu Z. G. , Liu J. M. , Yin X. B. , Chen G. X. , Wang M.
Published: July 2002

Rutile-phase TiO2 thin films have been epitaxially grown on GaAs(100) substrates at 700 °C under 5 Pa oxygen ambient pressure, and at room temperature (30 °C) and 5×10−4 Pa base vacuum by KrF pulsed excimer laser deposition. The [110]-oriented TiO2 films were composed of two types of domains perpendicular to each other in the plane. From atomic force microscopy analysis, the epitaxial films had a surface with roughness less than 7 nm in root-mean-square.
Reactive magnetron sputter-deposition of NbN and (Nb, Ti)N films related to sputtering source characterization and optimization
Authors: Iosad N. N. , Jackson B. D. , Polyakov S. N. , Dmitriev P. N. , Klapwijk T. M.
Published: July 2002

We compare the properties of planar single track balanced and unbalanced sputtering sources by comparing the film properties of NbN and (Nb, Ti)N films sputtered from each source. Our experiments show that reducing the effectiveness of the magnetic trap by changing the magnet configuration is equivalent to reducing the sputtering pressure. We also examine the behavior of the sputtering sources throughout the target lifetime. The balanced sputtering source shows an increase in the magnetic trap effectiveness and a reduction in the heat flux towards the substrate surface as the target becomes grooved (for the fixed applied power and gas pressure), while the unbalanced design shows the opposite behavior. We also show that it is possible to optimize the configuration of the magnetron magnets to produce stable and reproducible (Nb, Ti)N films under the same gas pressure and applied power throughout the target lifetime.
Stable and uniform electron emission from nanostructured carbon films
Authors: Park Kyung Ho , Choi Seungho , Lee Kyung Moon , Lee Soonil , Koh Ken Ha
Published: July 2002

We have systematically studied the electron-emission characteristics of nanostructured carbon films with various amounts of nanoclusters and degrees of nanotube alignment. According to our observation, the dense packing and/or alignment of nanotubes is detrimental to the low-field emission, which we attributed to the electrostatic screening effect. The best emission was observed from the carbon films dominated by nanoclusters; the turn-on field was 1.6 V/μm and the emission-site density was considerably higher than 5×104 site/cm2. The emission from the nanocluster-dominated film was uniform and stable. Raman spectroscopy identified the nanoclusters as crystalline graphite with some structural defects. It is conceivable that the modification of the boning hybridization at the cluster surface resulted in a diamond-like density of states, and that the corresponding small electron affinity was responsible for the excellent emission the from nanoclusters.
Numerical indicator field emission display using carbon nanotubes as emitters
Authors: Kwo Jon-Lian , Yokoyama Meiso , Lee Cheng-Chung , Chuang Feng-Yu , Lin I-Nan
Published: July 2002

A field emission display using carbon nanotubes (CNTs) as emitters is demonstrated. The CNTs, synthesized by arc discharge, were screen printed on glass to serve as the cold cathode. The anode plate, which was indium–tin–oxide coated glass printed with P15 phosphor, was separated from the cathode using 110 μm spacers. The diode structure possesses marvelous field emission properties, including low turn-on voltage (250 V), large emission current density (2.6 mA/cm2 under 450 V) and high brightness (2500 nits). A numerical indicator with 15 pixels, driven by metal–oxide–semiconductor field effect transistors using a gate voltage of 5 V for controlling the on/off of each pixel, illustrates the capability of data addressing.
Polymer pattern formation on SiO2 surfaces using surface monolayer initiated polymerization
Authors: Chen Xiaohua , Tolbert Laren M. , Henderson Clifford L. , Hess Dennis W. , Ruhe Jurgen
Published: July 2002

The use of surface monolayer initiated polymerization, in which initiators are chemically bound to a surface, can generate robust barrier polymers for pattern formation in silicon by reactive ion etching. The combination of poly(vinylarenes) and a new surface initiator based upon a phenylazo initiator provides excellent etch resistance and superior performance.
Analytic expressions of the speed factor for turbomolecular pumps
Authors: Chang Yu-Wen , Jou Rong-Yuan
Published: July 2002

Since Kruger developed the theory for a single stage of a turbomolecular pump in 1960, it has been widely applied to the design and research of turbomolecular pumps for the past 30 years. One of the main ideas in his theory is that the maximum pressure ratio can be expressed as the ratio of the transmission probabilities of the molecules that pass through the blade row upstream to downstream to one of downstream to upstream, and that the maximum speed factor can be expressed as the difference between the above two transmission probabilities. Considering that Kruger's theory was derived under zero flow, we construct a modified expression for the maximum speed factor in this article. In addition, a second approximate expression for the case where the gas flow is between the maximum pressure ratio and maximum speed factor is proposed. The two new expressions are both verified using the direct simulation Monte Carlo method and show a good match.
Fabrication of nanocontacts for molecular devices using nanoimprint lithography
Authors: Austin Michael , Chou Stephen Y.
Published: July 2002

We present a simple process to fabricate gold nanocontacts with a gap as small as sub-10 nm. This method uses a two-step process of nanoimprint lithography (NIL) and electromigration. First, 20 nm wide gold nanowires were fabricated by NIL on a silicon dioxide substrate. Then by passing an electric current through a nanowire, the nanowire is split into two wires with a gap as small as sub-10 nm by electromigration. This fabrication method offers a fast and effective process for producing large numbers of nanocontacts for use in molecular self-assembly, and thus greatly enhances the probability of successful capture of single molecules.
Optoelectronic integration using aligned metal-to-semiconductor bonding
Authors: Giziewicz Wojciech P. , Fonstad Clifton G.
Published: July 2002

A method to monolithically integrate optoelectronic devices with separately fabricated very large scale integrated circuitry has been investigated, and an aligned bonding procedure involving an intermediary metal film has been developed. The optoelectronic device heterostructures are grown epitaxially and patterned on the growth substrate, and then aligned to and bonded into dielectric wells on the target integrated circuit (IC) substrate, an entire wafer at a time. The metal film structure is responsible for the mechanical attachment of the devices to the integrated circuit substrate as well as for the ohmic contact between the parts. Bonding is performed at a low enough temperature to prevent damage to the electronics on the target substrate. Finally, the growth substrate is removed and the heterostructures are processed into optoelectronic devices integrated monolithically with the electronics, leaving a relatively planar optoelectronic integrated circuit. Results will be presented from initial experiments of bonding patterned devices to simple gallium arsenide (GaAs) substrates, and more importantly from recent experiments of bonding devices onto GaAs IC chips from the OPTOCHIP project. The procedure can also be used to integrate III–V devices onto silicon substrates.
Some Properties of the Monopole Mass Spectrometer
Authors: Dawson P. H. , Whetten N. R.
Published: July 2002

Monopole mass spectrometer characteristics have been analyzed by determining ion trajectories under various operating conditions. The trajectories were obtained by numerical integration of the equations of motion. Peak shapes were derived for ions spending 20 rf cycles in the field, for various entrance/exit slit ratios, with ion injection parallel to the instrument axis. Comparison with earlier results shows that resolutions at half-height can be expressed as (n/p)2, where n is the number of cycles an ion spends within the field and p is constant for a given exit slitwidth. Ion injection at an angle to the instrument axis was also considered. Peaks then showed much less spread on the low mass side. For ions entering the field at a fixed angle, the peaks may exhibit a central dip if the exit slitwidth is too small.
Distribution of Material Sputtered from a Disk Electrode
Authors: Schwartz G. C. , Jones R. E. , Maissel L. I.
Published: July 2002

Using the Davidse-Maissel diode sputtering system, the distribution of material deposited in the substrate plane during sputtering is studied as a function of power, sputtering pressure, target-to-collector spacing and electrode shielding. Both rf and dc sputtering are investigated. The target is a cobalt disk surrounded by concentric rings of nickel, iron, and copper; the concentration of each component in the deposit (collected on glass slides) is determined through x-ray fluorescence analysis. A mathematical relationship between the local deposition rate on the substrate and the emission from the source is derived. The proposed model describes the observed distribution as arising from the superposition of two sources: (1) a uniform disk, and (2) a ring of infinitesimal width at the perimeter (both sources emitting with a cosine distribution). The latter phenomenon is due to the fact that the dark space of the glow discharge can wrap around the edge of the electrode.
Activation of filamentary field emitters by growing microneedles of tungsten
Authors: Okuyama Fumio
Published: July 2002

It was attempted to grow microneedles of tungsten on 10-μm-diam tungsten wires for the purpose of preparing emitters of high efficiency for field-ionization mass spectrometry. A large quantity of tungsten needles with dendritic structures was successfully grown by reducing vapor-deposited tungsten oxide with 1–5×10−2 Torr hydrogen while applying a positive potential of 5–6 kV. The needle growth occurred in a critical manner when deposited tungsten oxide attained a temperature of ∠1200 K, and needles obtained were thin enough to easily generate high electric fields of 107–108 V/cm. Testing in a mass spectrometer actually verified that the needles can yield field-ionization mass spectra of satisfactory quality for typical organic substances.
Optical coatings for collection and conservation of solar energy
Authors: Apfel Joseph H.
Published: July 2002

An optical coating applied to a surface can cause radiation incident on the surface to be divided into transmission, reflection, and absorption in a prescribed manner. Thus, coatings affect the control of radiation and enhance the collection, conversion, and conservation of solar energy.
Quantitative AES of stainless-steel samples with computer evaluation
Authors: Färber W.
Published: July 2002

A series of different stainless-steel samples has been investigated. The Auger spectra were evaluated quantitatively using a computer program. This computer program, called AUA, is a least-squares fit program and has stored the spectra of elemental standards and their Auger yields. In the present form the program includes 19 different elements (Si, P, S, Cl, Mo, K, C, Ca, N, Ti, V, Cr, O, Mn, Fe, Co, Ni, Cu, and Al) and is used for the investigation of stainless-steel samples. The structure of the program is explained and a number of examples demonstrates the reliability of the method and the magnitude of the errors. The resulting sample composition is given both in atomic and in weight percent. The expansion to a higher number of elements and thereby the application of the program AUA to other samples is possible.
Electrical properties of the gallium arsenide–insulator interface
Authors: Meiners L. G.
Published: July 2002

Extensive capacitance–voltage (C–V) measurements have been performed on three types of insulators on n-type GaAs: pyrolytically deposited silicon nitride, sputtered silicon nitride, and the oxide produced by anodization. Evaporated aluminum gate contacts and alloyed Au–Ge ohmic contacts were applied and the C–V characteristics of these structures were measured from the quasistatic regime to 150 MHz. Although differences in detail are seen at intermediate frequencies, the data taken at the extreme frequency limits differ very little for the three types of specimens. The quasistatic and high-frequency data are consistent with a model wherein the surface potential with zero applied gate bias is ∠−0.8 V. Application of electric fields of the order of ±106 V/cm at the semiconductor surface results in movement of the surface potential across approximately 1/3 of the band gap. An accumulation layer of surface electrons could not be produced on any of the devices tested.
Chemical vapor deposition of spectrally selective surfaces for high-temperature photothermal conversion
Authors: Seraphin B. O.
Published: July 2002

The surfaces intercepting the incident radiation in photothermal converters must satisfy three requirements. First, they must offer a spectral profile that is properly matched to the solar emission and thermal reradiation properties. Second, they must withstand elevated temperatures without harmful changes of their optoelectronic characteristics. Third, they must operate long enough to make the initial investment a reasonable economic proposition. Multilayer systems deposited by CVD offer attractive features. We report on an absorber–reflector tandem that satisfies all three requairements and is fabricated by a method easily expanded to large-scale economic manufacture. Although CVD technology is well developed for the fabrication of semiconductor devices, efforts to deposit the thin films used in solar energy converters are only in an early stage. A set of characteristic requirements makes it necessary to modify some aspects of existing technology. Attention must be paid to the optical and morphological properties of the deposit, and their dependence on the deposition parameters and the substrate. We discuss the difficulties encountered and describe some preliminary solutions that establish the feasibility of the concept. The silicon absorber can be deposited in satisfactory quality, reducing free-carrier absorption at elevated temperatures to an acceptable level. The layer is protected on either side against diffusion, and mismatches of thermal expansion are neutralized. The highly reflective silver film is stabilized against morphological changes bound to occur under the conditions of the subsequent CVD of the absorber. Recent developments include the CVD of amorphous silicon absorbers of improved temperature stability, and reflector films made of molybdenum. Stacks have been successfully tested at temperatures in excess of 500 °C.
Si(100) surfaces: Atomic and electronic structures
Authors: Chadi D. J.
Published: July 2002

The surface atomic geometries of 2×1 and 4×2 reconstructed Si(100) are determined through energy-minimization calculations. Many possible structural models were tested. The results show the most favorable geometries for both the 2×1 and 4×2 surfaces to be that of asymmetric, partially ionic dimers. The surface atomic coordinates and electronic structures are discussed.
Reactive molecular beam epitaxy of aluminium nitride
Authors: Yoshida S. , Misawa S. , Fujii Y. , Takada S. , Hayakawa H. , Gonda S. , Itoh A.
Published: July 2002

Single-crystal films of AlN have been fabricated on sapphire and silicon substrates by reactive molecular beam epitaxy (MBE) at 1000°–1200°C. The crystal quality of the films was examined by the reflection high-energy electron diffraction technique and the measurement of cathodoluminescence. The results suggest that the epitaxial AlN films prepared by reactive MBE have good quality as compared with bulk single crystal. Nonlinear optical coefficients and the electromechanical coupling constant of surface acoustic waves were also measured. It was shown that the AlN films have unique characteristics and are promising for nonlinear optical and surface acoustic wave devices.
Characteristics of a bakeable ion-cryopumped UHV system
Authors: Michaud M. , Sanche L.
Published: July 2002

This paper describes an UHV system for studying condensed films or free metal surfaces at temperature near 14 K. The system consists of a commercial cryopump, and 80 1/s ion pump, a sorption pump and a 30 l chamber having one square meter of internal surface. The standard nonbakeable components in the cryopump have been modified at the factory. The charcoal is now held in contact with 14 K cryopanel by means of small copper rods and a brass screen; all connections are made by Conflat flanges; and the indium gaskets have been replaced by silver ones. With the exception of the charcoal and the electrical feedthroughs, the system is entirely metallic. A base pressure in the 10−11 Torr range can be reached after a 24 h bakeout period at 250°C. During this period, only the ion pump is operative. Between experiments, the cryopump can be periodically turned off and regenerated by pumping the desorbing gases with the ion pump. The base pressure can be restored 4 h after restarting the cryopump.
Impurities-related memory traps in silicon nitride thin films
Authors: Kapoor V.J. , Bailey R. S. , Smith S. R.
Published: July 2002

Internal photoelectric-effect technique in combination with Auger electron spectroscopy and argon-ion sputtering has been developed for quantitative measurements of impurity and defect-related memory traps in the Si3N4 thin film of a metal–Si3N4–SiO2–Si (MNOS) device. Electrons generated by internal photoemission at the metal electrode under an applied gate bias of −80.0 V and light of energy 4.14 eV were captured by memory traps in the Si3N4 insulator. The resulting trapped electron density of the order of 1.5×1018/cm3 was determined by capacitance-voltage measurements. The chemical depth profiles of nitrogen, silicon, and oxygen throughout the stoichiometric Si3N4 films grown at various NH3 to SiH2Cl2 gas ratios were measured. The amount of oxygen impurity in the film was correlated with variations in the gas ratios and in the trapped electron density. The data suggests an association of trapped electronic charge with some structural defects in addition to oxygen impurity incorporated in the Si3N4 film during the chemical deposition process.
Surface rearrangement of adsorbate-covered Mo(001)
Authors: Semancik S. , Estrup P. J.
Published: July 2002

The changes in surface properties caused by adsorption of carbon monoxide, oxygen, and nitrogen on molybdenum (001) have been studied. The LEED intensities, work functions, and electron-stimulated desorption yields show coverage dependences similar to those for H/Mo(001). To explain the results it is proposed that these adsorbates, like hydrogen, induce a rearrangement of the Mo surface. Due to the substrate distortion, the probability of occupation varies from site to site. The development of (√2×√2) structures observed by LEED can be understood in terms of coupled lattice distortion and occupation probability waves.
Chemical effects in ion scattering spectroscopy
Authors: McCune R. C.
Published: July 2002

The principal use of low-energy ion scattering spectroscopy (ISS) as a surface analytical tool has been the identification of surface layer atoms through binary collision kinematics. In this mode of analysis, the chemical state of the atom is usually not discernible with the data normally obtained. This paper reviews a number of observations which indicate that chemical state information or the nature of local atom arrangements may be inferred from certain aspects of the experimental data. The earliest recognition of chemical state information resulted from study of resonant charge exchange processes for particular ion/atom combinations. By appropriate manipulation of experimental data, it is possible to obtain fingerprint spectra in the inverse velocity domain for various compounds. Recently, two techniques used in this laboratory have been applied to the study of surface atom configurations. In the first, the energy dependence of scatter peak height ratios in ionic compounds is used to infer an atom shielding susceptibility for various cations in oxide matrices. Secondly, a number of peak shift and doublet scattering peaks have been observed in special cases where the surface layer decomposes under bombardment by the probe ion beam.
Novel device structures by molecular beam epitaxy
Authors: Wood C. E. C.
Published: July 2002

This paper briefly reviews a few selected technologically important areas where Molecular Beam Epitaxy has been used to advantage. These include the use of MBE to study and improve ohmic and Schottky metallizations to GaAs and the invention of new types of variable barrier height diodes. The proven potential of MBE grown ternary alloy structures as materials for enhanced microwave and high speed digital devices and the use of selected area epitaxy for state of the art digital integrated circuit elements are also discussed.