bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Rib Arrangements on Heat Transfer and Flow Behavior in a Rectangular Rib-Roughened Passage: Application to Cooling of Gas Turbine Blade Trailing Edge
Authors: Kiml Robert , Mochizuki Sadanari , Murata Akira
Published: July 2002

Experimentation was conducted to examine the heat transfer and pressure drop characteristics in a rib-roughened rectangular passage with aspect ratio 2:1 for four rib configurations: 90 deg, 75 deg, 60 deg and 45 deg oblique ribs. The ribs were attached to two opposing long side walls instead of short side walls. In this study the oblique ribs were intended to function as secondary flow inducers as well as turbulators to improve the heat transfer of the bottom wall (one of the short side walls). The results revealed that, in order to enhance the heat transfer of the bottom wall, the oblique ribs should be arranged so that the secondary flow along the ribs hits the top wall instead of the bottom wall. Flow visualization test was performed to understand the heat transfer mechanisms. It was confirmed that the heat transfer enhancement at the bottom wall was attributed to the rib-induced secondary flow where the flow along the ribs hit the top wall, turned back and carried cold air from the passage core region towards the bottom wall. The highest average heat transfer was achieved for the 60 deg rib pattern due to the strong rotational momentum of the secondary flow and higher heat transfer enhancement on the rib-roughened walls in comparison to the other three rib patterns.
Thermal Penalty of an Immersed Heat Exchanger in Integral Collector Storage Systems*
Authors: Arora Saurabh , Davidson Jane , Burch Jay , Mantell Susan
Published: July 2002

The use of a heat exchanger in solar water heating systems reduces the overall system efficiency. In this paper, we derive a simple "penalty factor" that gives the fractional reduction in thermal efficiency imposed by a heat exchanger immersed in an isothermal integral collector storage (ICS) system. The penalty factor depends only on the effectiveness of the heat exchanger, the capacitance of the hot water delivered, and the product of the loss coefficient and aperture area of the ICS. This factor allows the designer to select an appropriate heat exchanger without extensive simulation or experiments. Application of the penalty factor for a load-side (or on-demand) heat exchanger, which operates intermittently at varying flow rates, is discussed and illustrated through example.
Forced Oscillations in Combustors With Spray Atomizers
Authors: Zhu M. , Dowling A. P. , Bray K. N. C.
Published: July 2002

Most types of combustion-driven devices experience combustion instabilities. For aeroengine combustors, the frequency of this oscillation is typically in the range 60–120 Hz and is commonly called “rumble.” The rumble oscillations involve coupling between the air and fuel supplies and unsteady flow in the combustor. Essentially pressure fluctuations alter the inlet fuel and air, thereby changing the rate of combustion, which at certain frequencies further enhances the pressure perturbation and so leads to self-excited oscillations. The large residence time of the liquid fuel droplets, at idle and subidle conditions, means that liquid and gaseous phases must both be considered. In the present work, we use a numerical model to investigate the forced unsteady combustion due to specified time-dependent variations in the fuel and air supplies. Harmonic variations in inlet air and fuel flows have been considered and the resulting unsteady combustion calculated. The influence of droplet size distribution has also been investigated. The calculations provide insight into the interaction between atomization, unsteady combustion, and flow oscillations.
Observations on Cutting With 600-MPa Waterjets
Authors: Hashish Mohamed
Published: July 2002

Waterjet technology development for 600-MPa (87-Ksi) operations involves efforts on machining process development, pumps, plumbing, nozzles, and machining systems development. In this paper, data will be presented on cutting with water and abrasive waterjet at these elevated pressures. The effects of waterjet (WJ) and abrasive waterjet (AWJ) parameters on cutting rates of several materials are analyzed. It is observed that the power required for cutting is reduced as the pressure increases. Sheet metal and composites can be cut effectively with waterjets. The quality of the cut surfaces, however, improves by increasing pressure, adding abrasives, and operating at optimal standoff distances.
A Performance-Based Representation for Engineering Design
Authors: Zhu Liang , Kazmer David
Published: July 2002

A design representation is developed to model multi-attribute systems utilizing multi-dimensional clipping and transformation algorithms. Given a linear system characterization, three types of supporting information is generated for the decision maker: (1) a function matrix that describes the performance attributes dependent upon the decision variables; (2) a decision space that corresponds to the feasible decision set that meets performance requirements, and; (3) a performance space that represents the feasible performance region and the Pareto Optimal set. The analytical method developed for solving these feasible spaces is described for a linear system model. A case study is presented to demonstrate how to utilize the representation to locate a feasible solution and proceed to the desired trade-off of multiple attributes. Moreover, the potential incorporations of the representation with other influential design methodologies are discussed.
Normal Indentation of Elastic Half-Space With a Rigid Frictionless Axisymmetric Punch
Authors: Fu G.
Published: July 2002

The contact of a simply connected axisymmetric punch with an elastic half-space is examined. The problem is mathematically formulated by using potential theory and complex variable analysis. The final solution of these equations is obtained by assuming a polynomial punch profile. The conditions for complete contact and incomplete contact are also derived. The solutions give the pressure profile at the punch–elastic half-space interface for any polynomial punch profile, even for noninteger power polynomials, as long as the contact region is simply connected. The results show that some classic solutions in linear elasticity are special cases of the derived solution and determine the range of validity for those solutions.
An Experimental Investigation on the Effect of Vibration on Casting Surface Finish
Authors: Rasgado M. T. Alonso , Davey K.
Published: July 2002

One of the failings of the pressure die casting process is that variable surface quality is a common result. This paper provides evidence that die vibration can be used to polish castings as they form during solidification. Evidence is obtained from experiments performed on a purpose built rig that is designed to be representative of the pressure die casting process. The rig’s design is such that part of the casting face can be subjected to tangential vibration at prespecified frequencies and amplitudes. The castings made are viewed under a microscope and micrographs produced. These combined with Talysurf readings show that die vibration can be used to generate casting surfaces with a quality significantly superior to that of the die. Supporting evidence is also provided by thermocouple readings and the solution of the inverse parabolic heat equation. The expected increase in the interfacial heat transfer coefficient is obtained with improved casting surface quality. Established in the paper is the effect of vibration frequency and amplitude on the Ra value of the casting surface. It is shown that threshold values for frequency and amplitude exist, below which surface improvement is diminished.
Parametrization of Reduced Order MIMO Tracking Prefilters With Optimality Considerations
Authors: Bement Matt , Jayasuriya Suhada
Published: July 2002

A primary disadvantage of using an internal model to achieve multivariable tracking is the high order of the internal model. In situations where it is known that each output is to track only its associated reference input, the internal model formulation results in an overdesign of sorts. A method is presented through which a prefilter may be constructed to achieve asymptotic tracking of only the required reference inputs. It is shown that obtaining the prefilter requires the solution of a polynomial matrix equation. Conditions for existence of a solution to this equation, as well as an algorithm for its construction, are presented. Since existence of a solution implies an infinite number of solutions, the algorithm provides a means of parametrizing all solutions of a given order. Unlike prefilter techniques such as plant inversion, the method presented may be applied to nonminimum phase systems and results in proper, physically realizable systems. Since an infinite number of solutions exist, criteria for defining and obtaining the optimal solution are presented. In fact, it is shown that obtaining the optimal prefilter reduces to solving a set of linear equations. A multivariable system is used to demonstrate the effectiveness of the optimization procedure. In addition, the tracking is shown to be robust with respect to certain structured plant perturbations.
Use of Micropathways to Improve Oxygen Transport in a Hepatic System
Authors: McClelland Randall E. , Coger Robin N.
Published: July 2002

Establishing suitable oxygen transport pathways within bioartificial liver replacement devices continues to be an important engineering challenge. Oxygen delivery is critical since this is one of the nutrients necessary to maintain hepatocyte viability and function. In the current study, the microporosity of a collagen extracellular matrix has been modified to permit both diffusion and convection mass transport. Using fluorescent visualization, the enhancement technique was found to extend the oxygen transport distance from 170 μm to 360 μm. Furthermore, in hepatocyte culture studies, the enhancement technique was observed to yield a sixfold increase in the amount of viable hepatocytes able to be sustained by a single O2 source. Normalized function studies confirm that hepatocyte function was also improved in the enhanced collagen configurations. [S0148-0731(00)00903-1]
Disturbance Rejection With Simultaneous Input-Output Linearization and Decoupling Via Restricted State Feedback
Authors: Tsirikos A. S. , Arvanitis K. G.
Published: July 2002

The disturbance rejection with simultaneous input-output linearization and decoupling problem of nonsquare nonlinear systems via restricted state feedback is investigated in this paper. The problem is treated on the basis of an algebraic approach whose main feature is that it reduces the determination of the admissible state feedback control laws to the solution of an algebraic and a first order partial differential systems of equations. Verifiable necessary and sufficient conditions of algebraic nature based on these systems of equations are established for the solvability of the aforementioned problem. Moreover, an explicit expression for a special admissible restricted state feedback controller is analytically derived. [S0022-0434(00)02101-8]
Effect of Laser Shock Processing (LSP) on the Fatigue Resistance of an Aluminum Alloy
Authors: Yaxin Tang , Yongkang Zhang , Hong Zhang , Chengye Yu
Published: July 2002

The laser shock induced stress wave is described and measured with a polyvinylidene fluoride (PVDF) transducer. A principle for selecting laser parameters is proposed. A small sized laser with a high power is used for Laser Shock Processing (LSP). The fatigue life of the aluminum alloy 2024T62 is greatly improved after LSP. With 95% confidence, the mean fatigue life of LSP specimens is 4.5–9.8 times that of unshocked ones. The fatigue and fracture resistance mechanisms of LSP such as the variation of the surface hardness, the microstructure and the fracture section of specimens before and after LSP are analyzed. [S0094-4289(00)01601-7]
Effect of Plasma Cutting on the Fatigue Resistance of Fe510 D1 Steel
Authors: Chiarelli M. , Lanciotti A. , Sacchi M.
Published: July 2002

The paper describes the results of a research programme, carried out at the Department of Aerospace Engineering of the University of Pisa, for the assessment of the influence of plasma cutting on the physical and mechanical properties of Fe510 D1, a low carbon steel widely used in carpentry. The activity started by observing that several industries rework plasma cut edges, particularly in the case of fatigue structures, in spite of the good quality of the plasma cut edges in a fully automatic process. Obviously, reworking is very expensive and time-consuming. Comparative fatigue tests demonstrated that the fatigue resistance of plasma cut specimens in Fe510 steel was fully comparable to that of milled specimens, as the consequence of the beneficial residual stresses which formed in the plasma cut edges. [S0094-4289(00)02201-5]
Thermal Response of Automotive Hydrocarbon Adsorber Systems
Authors: Koltsakis G. C. , Stamatelos A. M.
Published: July 2002

Modern hydrocarbon adsorbers for gasoline engines are promising candidates for cold start emission control. In this paper, the flow and heat transfer in a typical complex system, comprising a “barrel type” adsorber and two conventional catalysts is studied. A mathematical model is developed and applied for the computation of the flow and pressure distribution, as well as transient heat transfer in the system. The model is aimed at understanding and quantifying the particular thermal response behavior of hydrocarbon adsorber systems. Illustrative results with variable geometric parameters under realistic input conditions are presented. [S0742-4795(00)01701-4]
Synchronous Vortex Shedding (Vortex Pumping) Downstream of a Flat Plate Array
Authors: Guillaume D. W. , LaRue J. C.
Published: July 2002

Flow visualization and statistics, obtained downstream of an array of flat plates, are presented. Flow visualization shows that the mean separation between streaklines for the flow downstream of adjacent channels is negatively correlated. Consistent with this observation, the zero-time cross correlation of the fluctuating velocity between adjacent plates is negative. Vortices shed at the trailing edges of the bounding surfaces that form a channel in the plate array are in-phase, but they are nearly 180 deg out-of-phase with the vortices shed at the trailing edges of the bounding surfaces of adjacent channels. Relative to the mean velocity, the axial velocity on the midplane of the channel increased in the region between each pair of vortices. At downstream positions not near the vortex pair, the velocity on the midplane is relatively decreased. Hence, vortices shed at the trailing edges of the channel surfaces lead to “vortex pumping,” which is consistent with the negative correlation of the fluctuating velocity on the midplanes between adjacent channels. [S0098-2202(00)01701-6]
Evaporation Heat Transfer and Pressure Drop in Horizontal Tubes With Strip-Type Inserts Using Refrigerant 600a
Authors: Hsieh S.-S. , Jang K.-J. , Tsai Y.-C.
Published: July 2002

Results of a study on saturated boiling heat transfer of refrigerant R-600a in horizontal tubes (ID=10.6 mm) with strip-type inserts (longitudinal strip LS with/without perforated holes and cross-strip CS inserts) are reported. Local heat transfer coefficients are measured for a range of heat flux (9.1∼31.2 kW/m2), mass velocity (8.23∼603.3 kg/m2s), and equilibrium mass quality (⩽0.8) and the influences were studied. The data were compared with the performance of the corresponding smooth tubes. Enhancement factors are presented and discussed. Pressure drop measurement was also conducted and it is found that both single-phase and two-phase pressure drops increase with increasing heat flux levels and mass velocities. [S0022-1481(00)00302-9]
Optimization of Proximity Recording Air Bearing Sliders in Magnetic Hard Disk Drives
Authors: O’Hara Matthew A. , Hu Yong , Bogy David B.
Published: July 2002

The object of this paper will be to optimize the contact stiffness (CS) of an existing proximity recording air bearing surface (ABS). The CS is a measure of the slider’s increase in contact force with increase in slider/disk interference. By minimizing this, the amount of force transmitted through the slider at the interface is minimized. This should, in turn, minimize the amount of wear, improving the tribological performance. Comparisons of the pre- and post-optimized slider have been made. In combination with research that demonstrates the ability of the CS parameter to predict tribological behavior (Hu et al., ASME J. Tribol., 120, pp. 272–279) this paper demonstrates the feasibility of numerical optimization of the tribological behavior of proximity recording air bearing sliders. [S0742-4787(00)03201-X]
Purple Membrane by X-ray Photoelectron Spectroscopy
Authors: Brizzolara Robert A. , Boyd Jennifer L. , Thorne Rose E. , Tate Ann E.
Published: July 2002

Purple membrane is a constituent of the cell membrane of Halobacterium halobium. It is of technological interest due to the very fast, efficient electrical response to light of its integral protein, bacteriorhodopsin. Dried films of purple membrane are of importance for the fabrication of devices from this material. In this article, x-ray photoelectron spectroscopy (XPS) spectra of purple membrane fragments dried on SiO2 are presented. To remove excess lipid from the substrate surface, the samples were washed with distilled water subsequent to the purple membrane drying step. The presence of purple membrane fragments on the substrate surface was verified by atomic force microscopy prior to XPS analysis.
Aluminum Foil by XPS
Authors: Rotole John A. , Sherwood Peter M. A.
Published: July 2002

The XPS spectra of argon ion etched aluminum metal were collected with a VSW HA150. This spectrometer is equipped with monochromatic Al Kα x-radiation, a 16 channel multichannel detector, and an electrostatic hemispherical analyzer with a radius of 150 mm providing an instrument with exceptional capabilities. We report the Al 2p core level with resolved 2p1/2 and 2p3/2 spin-orbit split components. The peak to valley separation on the high binding energy side between the spin orbit components was determined to be 0.18 eV and the separation between these components was 0.44 eV. The valence band, survey, and the Al 2s, O 1s, and C 1s core levels are also reported.
Theory for the Energy Distribution of Secondary Electrons
Authors: Amelio G. F.
Published: July 2002

A theory in terms of the Boltzman transport equation is presented for the spectral distribution of excited (hot) electrons in solids. Solutions of the steady-state, field-free equations are obtained by a Green's function technique, which offers the advantage of separating the excitation mechanism from the scattering processes. For purposes of application the question of an electron beam normally striking the planar surfaces of copper and silicon is investigated. Scattering functions representing electron–electron and, most importantly, electron–plasmon interactions are developed from which the necessary Green's functions are derived. Secondary emission spectra are then predicted, using an excitation function based on a perturbation calculation and using an appropriate emission probability formulation. Inclusion of the plasmon scattering contribution leads to agreement with experiment within 10%–20%. Approximate closed-form solutions to the necessary integrals are also offered as well as a more empirical approach to obtaining the electron energy distributions.
Vapor Deposition by Liquid Phase Sputtering
Authors: Krutenat R. C. , Gesick W. R.
Published: July 2002

Liquid binary alloy targets have been sputtered at ion densities of up to 100 W/cm2 providing deposition rates in excess of 10 mils/h in a combined sputtering-evaporation mode. At high power densities a serf-sputtering mode has been demonstrated which allows deposition from 10−7 to 10−2 Torr. Comparison of sputtered deposit compositions of Pb-24 In, Fe-30 V and Fe-32 Ni with theoretical molar ratios predicted on the basis of thermal vaporization shows that alloy fractionation is substantially reduced. The composition of deposits from solid or liquid Pb-24 In targets had nearly the same Pb/In ratio, 5.8 (target ratio = 1.75) although the predicted ratio for thermalized vapor was 1300. For Fe-30 V liquid targets where less than 0.5% vanadium is predicted from thermal vaporization alone, a sputtered deposit containing 10.3% vanadium was found, suggesting that the approximate sputtering/evaporation ratio is 0.3. Liquid phase targets of Fe-32 Ni alloy had average molar ratios of Fe/Ni close to 3 (target ratio was 2.2), whereas the predicted ratio from thermal vaporization was 5.8. There was only a slight increase in Fe/Ni ratio in the self-sputtering mode at 10−6 Torr over that obtained with argon sputtering at 10−3 Torr.
Relations between Structure and the Optical and Electrical Properties of Amorphous Si and Ge Films
Authors: Brodsky M. H.
Published: July 2002

A review of recent structural, electrical, and optical experiments on amorphous Ge and Si films is given. Amorphous Ge and Si have no long-range periodic ordering but do have a short-range order with nearly the same tetrahedral arrangements as the corresponding crystals. SiC and the III–V compounds probably retain a similar structure in the amorphous phase. Electron spin resonance and small-angle diffraction studies on amorphous Ge and Si give indications of a large number of dangling bonds and internal surfaces distributed throughout the volume of the films. Strong correlations exist between the annealing out of the dangling bonds and accompanying decreases in the electrical conductivity, optical absorption, and refractive index. Structural models have been formulated which agree with the data on density, radial distribution function, and dangling bonds. These models indicate what features should be incorporated into the interpretation of the conduction and absorption experiments. Some promising areas of further research are indicated.
Photoconductive PbSe Epitaxial Films
Authors: Schoolar R. B. , Lowney J. R.
Published: July 2002

Photoconductive PbSe films were grown epitaxially on NaCl and KCl substrates. The films had hole concentrations as low as 9×1016 cm−3 and Hall mobilities as high as 15 000 cm2 V−1 sec−1 at 77 K. Nearly strain-free films were prepared by transferring them from alkali-halide substrates to a plastic with almost the same thermal expansion coefficient as PbSe. These films retain high mobilities, are unaffected by moisture, and can be cycled between 300 and 77 K. The plastic-mounted films have a cutoff wavelength of 4.4 μ at 300 K and 6.4 μ at 77 K corresponding to the optical energy gap of bulk PbSe. In contrast, the response of films on NaCl and KCl extends to 8.3 μ at 77 K corresponding to the optical energy gap of highly strained PbSe. The blackbody responsivities of the most sensitive films increase monotonically from 0.2 V/W at 300 K to 4 V/W at 77 K. Response times, measured with a GaAs laser, are 2×10−7 sec, and photoconductive lifetimes calculated from the responsivities are 7×10−7 sec at 77 K. Peak detectivities at 77 K are 8×108 cm Hz12 W−1 and are Johnson-noise-limited at 2 KHz.
Magnetic Bubble Devices
Authors: Bobeck A. H.
Published: July 2002

The properties of cylindrical magnetic “bubble” domains have been extensively described in the literature. Our understanding of bubble technology has now progressed to the point where it is possible to undertake the design and evaluation of specific bubble systems. Bubble domains, cylindrical islands of reverse magnetization, exist in specially prepared single crystal uniaxial magnetic platelets and epitaxial films. These domains are manipulated by localized magnetic fields generated by currents applied to conductors (conductor access) or inplane fields applied to structured permalloy patterns (field access). An important application of bubbles will be in bulk storage. Study of propagation circuits indicates that reasonable field access memory design objectives are (1) in-plane field frequency, 0.1–10 MHz; (2) in-plane field, 10–30 Oe; (3) storage density, 1.5–10  megabits/in.2; (4) bits/chip, 10 000–100 000.
The Preparation of Thin Films of B-1 Structure Superconducting Ternary Compounds
Authors: Gavaler J. R. , Janocko M. A. , Jones C. K.
Published: July 2002

NbN, a binary B-1 structure superconducting compound, has been successfully prepared in thin film form by a high-purity sputtering process [J. R. Gavaler, J. K. Hulm, M. A. Janocko, and C. K. Jones, J. Vac. Sci. Technol. 6, 177 (1969)]. In this paper, we report on the deposition of ternary compounds, based on NbN, using a similar technique. The inclusion of a third element, such as carbon, titanium, or zirconium into the NbN structure was accomplished by sputtering in an argon-nitrogen atmosphere from a two-element target. These targets were made either by hot pressing a powder mixture of the elements into a proper form or by welding together two metal sheets into a single unit. Superconducting transition temperatures of ≳ 17 K have been obtained in both Nb–C–N and Nb–TiN thin films by depositing these films at very high temperatures. However, critical current and field data measured at 4.2 K showed that the use of very high substrate temperatures also caused a deleterious effect on these properties.
Analysis of thin-film structures with nuclear backscattering and x-ray diffraction
Authors: Mayer J. W. , Tu K. N.
Published: July 2002

Backscattering of MeV He4 ions and Seemann-Bohlin x-ray diffraction techniques have been used to study silicide formation on Si and SiO2 covered with evaporated metal films. Backscattering techniques provide information on the composition of thin-film structures as a function of depth. The glancing-angle x-ray technique provides identification of phases and structural information. Examples are given of V on Si and on SiO2 to illustrate the major features of these analysis techniques. We also give a general review of recent studies of silicide formation.
Phenomenology of metal-semiconductor electrical barriers
Authors: McGill T. C.
Published: July 2002

The phenomenological rules governing the values of electrical barriers between metals, and semiconductors or insulators are reviewed. The barrier energies on ionic insulators are shown to vary strongly with metal electronegativity, while in the case of covalent semiconductors, the barrier energies are relatively independent of the metal. The barrier energy from the metal Fermi level to the conduction band of the semiconductor is shown to be approximately two thirds of the semiconductor band gap with certain exceptions. The success of a simple barrier model in accounting for the properties of the barrier are reviewed. The variation of barrier energy with electrical field is reported for Al-SiO2, Al-GaSe, and Al-GaAs and compared with simple theory including image-force lowering and field penetration into the metal. Transport through interfacial barriers is illustrated by discussing transport through metal-GaSe-metal structures and metal-InAs Schottky barriers.
Reconsideration of the seal mechanism in the ConFlat® system
Authors: Kurokouchi Satoshi , Morita Shinsaku , Okabe Masayuki
Published: July 2002

The “capture model” is predicated from the concept that sealing is accomplished by compression arising within a gasket between a knife edge and the retaining counter of a flange. Although it has been the rationale for the ConFlat® metal seal system, the credibility of the existing model has yet to be verified with respect to the seal mechanism, and hence, warrants reconsideration. In the present study, experimental results indicate that complete capture of the gasket is seldom obtained, and that capture is not a key factor in the sealing process. Numerical analyses of stress distribution in tightened gaskets show that capture rarely increases seal pressure, and has little influence on improving sealing reliability in the ConFlat system. Rather, the sealing ability of the ConFlat system seems to depend primarily on intense compressive stress on 20° tapers of the seal surfaces.
Molecular beam epitaxial growth of IV–VI multiple quantum well structures on Si(111) and BaF2(111) and optical studies of epilayer heating
Authors: Wu H. Z. , McCann P. J. , Alkhouli O. , Fang X. M. , McAlister D. , Namjou K. , Dai N. , Chung S. J. , Rappl P. H. O.
Published: July 2002

IV–VI semiconductor multiple quantum well (MQW) structures (PbSe/PbSrSe) were grown on Si(111) and BaF2(111) substrates by molecular beam epitaxy. Structural and optical properties of the MQW structures have been studied using reflection high-energy electron diffraction, high resolution x-ray diffraction (HRXRD), Fourier-transform infrared (FTIR) transmission, and midinfrared photoluminescence (PL). Numerous satellite diffraction peaks and narrow linewidths of the HRXRD rocking curves indicate the high crystalline quality of the structures grown on both Si and BaF2. Longitudinal and oblique valley subband transitions without superposed interference fringes were observed in FTIR differential transmission spectra. Continuous wave midinfrared photoluminescence was also observed from both sets of samples. Comparison of FTIR and PL spectra allows determination of localized epilayer heating in the MQW samples due to optical pumping. For a typical laser pumping power of 9.1 W/cm2 the heating in a MQW layer on Si(111) was 70 °C, while the amount of heating for a MQW layer on lower thermal conductivity BaF2 was 83 °C.
Ion beam aperture-array lithography
Authors: Ruchhoeft Paul , Wolfe J. C. , Bass Robert
Published: July 2002

We explore a new technique, ion beam aperture-array lithography (AAL), for fabricating low cost, large area nanostructure arrays. In this approach, a broad beam of light ions illuminates a stencil mask containing a periodic array of circular apertures. The array of transmitted beamlets is moved over the substrate, thereby printing an array with the same period but arbitrary unit cell. AAL has several advantages over ion beam proximity lithography: (1) the mask pattern density is lower, (2) the unit cell patterns are defined by software, and (3) dose and shape correction can be applied to compensate for system blur. Dose optimization methods are discussed and experimental results with 150 nm apertures presented.
Microstructure and mechanical properties of Zr–Si–N films prepared by rf-reactive sputtering
Authors: Nose M. , Chiou W. A. , Zhou M. , Mae T. , Meshii M.
Published: July 2002

ZrN and ZrSiN films were prepared in an rf sputtering apparatus that has a pair of targets facing each other (referred to as the facing target—type rf sputtering). Films were deposited on silicon wafers without bias application or substrate heating in order to examine only the effect of silicon addition to the transition metal nitride films. The contents of zirconium, nitrogen, and silicon of the films were determined with an electron probe microanalyzer. The transmission electron microscopy studies were carried out in addition to x-ray diffraction. For the high resolution transmission electron microscopy observation, the field emission type transmission electron microscope was used, which provides a point-to-point resolution of 0.1 nm. The samples were observed both parallel and perpendicular to the film surface, which were plane and cross sectional views, respectively. In order to investigate the relationship between the mechanical properties and microstructure of films, the hardness was measured by a nanoindentation system at room temperature. The load was selected to keep the impression depth below 60 nm (not more than 5% of film thickness) so that the influence from the substrate can be neglected. The hardness of the films increases with small Si additions reaching the maximum value of 35 GPa at around 3 at. % Si. The tendency to grow columnar grains was strongest around this composition, while grains became equiaxial above 5 at. % of Si. The films containing 12.8% Si, which showed the lowest hardness of 18 GPa, consist of nanocrystal grains. The presence of ZrN nanocrystals embedded in Si3N4 was not observed in the present study. The hardening mechanism due to the addition of small amounts of Si in ZrN can not be determined at this time. The grain size and residual stress can make minor contributions to the hardening. A possibility of solid solution hardening due to atomistic strain, such as nitrogen atoms at interstitial sites or other point defects is postulated and should be examined further.
Effects of the underlayer substrates on copper chemical vapor deposition
Authors: Lin Cheng-Li , Chen Peng-Sen , Chen Mao-Chieh
Published: July 2002

Copper chemical vapor deposition (Cu CVD) on different substrates, including TiN, Ta, and TaN, was studied with regard to the physical property, nucleation, and adhesion of the deposited Cu films. The Cu film deposited on TiN substrate has a number of favorable properties over the films deposited on Ta and TaN substrates: lower electrical resistivity, lower impurity contamination, and higher (111)-preferred orientation. Moreover, CVD of Cu films on TiN substrate has a shorter incubation time and better film adhesion. From the viewpoint of adhesion, microstructure, and physical properties of the Cu film, we may conclude that TiN is a better underlayer substrate than Ta and TaN for Cu CVD.
Modulation Characteristics of Several Bayard–Alpert Type Gauges
Authors: Lange W. J. , Singleton J. H.
Published: July 2002

Several Bayard–Alpert-type ion gauges were constructed with a modulator electrode. Curves of ion collector current versus modulator potential were obtained for each gauge and as a function of other electrode potentials and electron current. The most striking difference is found to occur between gauges with and without grid endcaps. For gauges with open end grids, the ion collector current is found to exhibit a maximum at a modulator potential 20–30 V below grid potential. Such a modulation characteristic provides the opportunity to utilize the modulation technique for obtaining the true ion current and spurious current without producing gross potential changes within the gauge. This results in a minimum perturbation of electron orbits and reduces pressure changes due to electron desorption and subsequent adsorption on the modulator since the modulator is continuously bombarded by electrons.
Thin Films of Niobium for Cryotron Ground Planes
Authors: Joynson R. E. , Neugebauer C. A. , Rairden J. R.
Published: July 2002

A process is described for the vacuum deposition of thin films of superconductive niobium for use as electrical ground planes in cryoelectric circuitry. High-purity niobium films are deposited onto glass and aluminum substrates by evaporation from a focused electron-beam-heated source.

The deposition process is described in detail, and the influence of substrate temperature on film purities is discussed. A pinhole-free insulation between 1000–3000 Å is formed on the niobium films by anodization, and the surface roughness of the niobium is examined with an electron microscope as a function of oxide thickness. The superconducting properties of the niobium films are described in terms of their critical temperature, lattice parameter, resistance ratio, critical currents of shielded Sn films, and their ability to resist flux trapping.
Atomic and molecular beam scattering from macroscopically rough surfaces
Authors: O'Keefe D. R. , Palmer R. L.
Published: July 2002

The scattering of thermal energy atomic and molecular beams from macroscopically rough surfaces has been found to display scattered flux distributions that are typically skewed towards the incoming, beam i.e., backscattered. Such an observation is consistent with the results reported in the literature describing flow-conductance measurements, which are less than the conductance calculated assuming the Knudsen (diffuse) scattering law. Two types of surfaces were studied in the present work: shot-blasted surfaces and gold-blacked surfaces. Both these surfaces displayed scattered flux distributions of a backscattered nature with only subtle differences noted between the two. The conditions required for backscattering are contrasted with the conditions which appear to be necessary for Knudsen scattering and the possibilities are considered for direct application of these observations to a description of the environment existent in typical vacuum systems.
Two-dimensional ion effects in relativistic diodes
Authors: Poukey J. W.
Published: July 2002

In relativistic diodes, ions are emitted from the anode plasma. The effects and properties of these ions are studied via a two-dimensional particle-simulation code. The space charge of these ions enhances the electron emission, and this additional current (including that of the ions themselves) aids in obtaining superpinched electron beams for use in pellet fusion studies.
Molecular beam study of oxygen and C2 hydrocarbon chemisorption and reactions on Pt(111)
Authors: Palmer Robert L.
Published: July 2002

The chemisorption and reactions of oxygen and the C2 hydrocarbons (acetylene, ethylene, and ethane) on epitaxially grown Pt(111) crystals have been studied using modulated molecular beam techniques. The sticking coefficient of ethylene is observed to be about half that for acetylene, which is near unity on oxygen covered Pt(111) in the temperature range 550–1000 K. For ethane, S<0.05 under these same conditions. The results of this study are in agreement with other studies that show that the adsorption of the C2 hydrocarbons on platinum at elevated temperatures results in a surface acetylenic species. The first step in the oxidation process appears to be the removal of hydrogen atoms from this surface acetylene, either by molecular desorption or by reaction with surface oxygen atoms. Surface carbon then reacts with surface oxygen to form CO which either desorbs or reacts further to form CO2. At high oxygen pressures, the reaction rate is apparently limited by the mobility of surface oxygen atoms which have an activation barrier to diffusion on Pt(111) of about 16 kcal/mole. Some implications of this high surface mobility with regard to the gas–surface oxygen equilibrium are discussed. The observance here of two distinct components in the angular desorption distributions of CO and CO2 is discussed in terms of finer details of the reaction mechanism.
LEED analysis of the principal nonpolar (112̄0) and (101̄0) surfaces of cadmium sulfide
Authors: Chang Shih−Chia , Mark Peter
Published: July 2002

A LEED analysis of the clean (112̄0) and (101̄0) nonpolar surfaces of CdS prepared by an ion bombardment−thermal anneal technique reveals: (1) Only integral−order beams are observed with both surfaces. (2) The measured unit mesh dimensions of the surface lattice agrees, to within experimental error (6%), with unit mesh dimensions computed for the undistorted surface. (3) A structure factor intensity analysis based on the C46v space group successfully predicts the missing order beams observed with the (112̄0) surface and the mirror symmetry relative to the c axis of the beam intensities observed with both surfaces. (4) The best estimate for the inner potential is 10±2 V.
Growth and properties of semi-insulating epitaxial GaAs
Authors: Mattes Brenton L. , Houng Yu-Min , Pearson Gerald L.
Published: July 2002

We have found that in order to grow liquid-phase epitaxial (LPE) semi-insulating gallium–arsenide layers, chromium must be used to form deep energy levels, and the shallow donors and acceptors must be self-compensated. The shallow and deep levels appear to be dependent on impurities that arise from chemical reactions between the growth system components. The reactions can be controlled by systematic bakeouts of the arsenic-saturated gallium melt before each growth. This effect has been dramatically demonstrated in layers grown from melts baked out in the temperature range from 600 ° to 850 °C. For example, layers grown from melts baked out below and above ∠775 °C in a fused quartz–graphite–hydrogen growth system change from an n- to p-type, respectively. The bakeout transition temperature is essentially independent of the growth temperature and the Cr concentration. The resistivity in layers grown from undoped melts increases smoothly through the transition range. However, the resistivity reaches a peak of ∠300 Ω-cm in layers grown from Cr-doped melts baked out at the transition temperature. Electrical and mass spectrographic measurements on layers grown from undoped and Cr-doped melts indicate that electrical and chemical compensation occurs between impurities in the melt and in the layer. Photoluminescence measurements at 77 °K show 1.3 and 0.8 eV emission bands for n- and p-type layers grown from Cr-doped melts, respectively. In the high-resistivity layers, many unidentified deep levels are observed from 0.6 to 1.2 eV that parallel levels found in a Cr-doped, semi-insulating GaAs substrate.
Field dependent internal photoemission probe of the electronic structure of the Si–SiO2 interface
Authors: DiStefano T. H.
Published: July 2002

Details of the electronic bands near the Si–SiO2 interface were examined by the technique of determining the field dependence of the threshold Φ (ε) for internal photoemission. From a measurement of Φ (ε), the conduction band bottom φ (x) in the SiO2 was obtained to within approximately two lattice units of the interface. In calculating the effective potential φ (x), corrections were made for the effects of the photon-induced tunneling and field penetration into the silicon. The Si–SiO2 interfaces were produced by oxidizing 10Ω cm (100) silicon at 1050° C to an SiO2 thickness of 1090 Å. Photoemission thresholds were measured for electric fields up to 7×106 V/cm. The conduction band potential obtained from the threshold measurements shows only a small deviation from a flat band, less than +0.05 eV, up to a point 4 Å from the silicon surface. There is no indication of a large ionic charge or of a greatly reduced SiO2 bandgap to within about two lattice units of the interface.
MOS-gate technology on GaAs and other III–V compounds
Authors: Hartnagel H. L.
Published: July 2002

High-quality native oxides on GaAs, InP, and other compound semiconductors have been grown by an electrolytic process involving glycol and an aqueous solution. A study of the physical processes involved enables one to give the ideal electrolyte properties required for good oxidation. Two important requirements are a reduction in the dissolution rate and the setting up of a cation saturation level near the anode for oxidation to start. Good electrical interface properties can be achieved. First GaAs MOS FET’s have been fabricated using this oxidation. The anodization process is also of value in material studies by employing the hole-concentration dependent oxidation rate for n-type materials.
Determination of electrical surface properties of Si, GaAs, and CdS using acoustic surface wave
Authors: Das P. , Motamedi M. E. , Gilboa H. , Webster R. T.
Published: July 2002

The surface properties of semiconductors can be measured by placing the sample in proximity to a surface acoustic wave delay line and applying a pulsed rf signal to the input. There will be time-dependent changes in the attenuation constant of the delay line, in the acoustoelectric voltage, and changes in the convolution voltage (if the device is a convolver) all due to the varying surface properties of the semiconductor. Further information can be obtained by subjecting the semiconductor to a pulsed dc electric field, or a second large pulsed rf field, and also by exposing the semiconductor to different wavelengths of light and repeating the above experiments. Some of the specific properties which have been determined are: (a) the location of the surface states in the energy band of epitaxial GaAs and CdS, (b) variation of the surface conductivity as a function of surface potential in Si, (c) type of surface carriers and their variation due to illumination, and (d) lifetimes associated with the emission and absorption of carriers in the surface traps. There is no physical contact with the semiconductor surface and the method is simple and sensitive.
Utilization of a subliming solid (arsenic) in rf reactive sputtering
Authors: Berak J. M. , Quinn D. J.
Published: July 2002

Reactive sputtering involving the controlled sublimation of arsenic in a suitable vacuum system has been investigated. The design of the vacuum chamber, pumping system, and arsenic-pressure controller is discussed. A gallium cathode was used to synthesize single-crystal GaAs films by reactive sputtering. Measurements of the growth rate, stoichiometry, and purity are reported. The film growth rate was found to increase with temperature indicating a surface reaction on the substrate. Single-crystal films of Ga1−xAlxAs were also deposited using this process.
Auger depth profiling of Au–AlxGa1−xAs interfaces and LPE AlxGa1−xAs–GaAs heterojunctions
Authors: Garner C. M. , Shen Y. D. , Kim J. S. , Pearson G. L. , Spicer W. E. , Harris J. S. , Edwall D. D. , Sahai R.
Published: July 2002

Ion-milling Auger electron spectroscopy has been used to study the depth profiles at the AlxGa1−xAs–GaAs interface and the Au–AlxGa1−xAs interface. Studies were made of ’’abrupt’’ and intentionally ’’graded’’ growth LPE AlxGa1−xAs–GaAs heterojunctions grown on the (100) face of GaAs. The ’’abrupt’’ growth AlxGa1−xAs–GaAs interfaces were found to be graded with an interface width of 100–130 Å. The depth profiles of two intentionally ’’graded’’ AlxGa1−xAs–GaAs heterojunctions revealed the interface widths to be ∠525 Å and ∠1500 Å for samples produced by a new technique. The studies of the Au–AlxGa1−xAs interface revealed an oxide layer to be present in the interface for samples which had been chemically etched prior to deposition of the Au. This oxide layer was found to be thicker than the native oxide on AlxGa1−xAs which had not been etched.
Depth profiles of sodium and calcium in glasses: A comparison of secondary ion mass analysis and Auger spectrometry
Authors: Malm D. L. , Vasile M. J. , Padden F. J. , Dove D. B. , Pantano C. G.
Published: July 2002

Depth profiles of sodium and calcium in soda-lime glasses have been measured by both Auger electron spectrometry and secondary ion mass spectrometry. Profiles by the two techniques agree closely and can be influenced by experimental conditions. In particular, radiation heating from a charge neutralization filament in the SIMS system is shown to alter the sodium depth profile in specimens which have a surface depletion of sodium.
High-contrast registration marks for electron-beam pattern exposure on (100) silicon
Authors: Iida Y. , Everhart T. E.
Published: July 2002

Secondary-electron signals have been measured from 10-μm-square registration marks as a function of electron-beam energy (10∠30 keV). These marks are anisotropically etched holes in (100) silicon which may or may not be covered with SiO2. The uncovered holes are sharp enough to measure electron-beam diameters less than 100 Å. PMMA coating (4000 Å) on the uncovered registration holes reduces signal contrast at 25 kV, incident beam energy from 0.87 to 0.79, and from 0.78 to 0.76 for the mark covered with a SiO2 layer, where perfect contrast is unity. The signal-transition distance from substrate to hole, ε20%–80%, for the mark with a SiO2 cover is degraded to approximately 0.6 μm. However, it is experimentally possible to register vernier patterns to at least ±0.25 μm accuracy, with SiO2-covered holes used as registration marks.