bluuebunny/crossref_metadata_2025 huggingface dataset:
Stabilization of Buoyancy-Driven Unstable Vortex Flow in Mixed
Convection of Air in a Rectangular Duct by Tapering Its Top Plate
Authors: Tseng W. S. , Lin W. L. , Yin C. P. , Lin C. L. , Lin T. F.
Published: July 2002

Stabilization of the buoyancy-driven unstable mixed convective vortex air flow in a bottom heated rectangular duct by tapering its top plate is investigated experimentally. Specifically, the duct is tapered so that its aspect ratio at the duct inlet is 4 and gradually raised to 12 at the exit of the duct. In the study the secondary flow in the duct is visualized and the steady and transient thermal characteristics of the flow are examined by measuring the spanwise distributions of the time-average temperature. The effects of the Reynolds and Grashof numbers on the vortex flow structure are studied in detail. Moreover, the spanwise-averaged Nusselt numbers for the horizontal rectangular and tapering ducts are also measured and compared. Furthermore, the time records of the air temperature are obtained to further detect the temporal stability of the flow. Over the ranges of the Re and Gr investigated for 5⩽Re⩽102 and 1.0×104⩽Gr⩽1.7×105, the vortex flow induced in the rectangular duct exhibits temporal transition from a steady laminar to time periodic and then to chaotic state at increasing buoyancy-to-inertia ratio. Substantial change in the spatial structure of the vortex flow is also noted to accompany this temporal transition. The results for the tapering duct indicate that more vortex rolls can be induced due to the increase in the aspect ratio of the duct with the axial distance. But the vortex rolls are weaker and are completely stabilized by the tapering of the top plate. [S0022-1481(00)70301-X]
Numerical Study of Vortex/Flame Interaction in Actively Forced Confined Non-Premixed Jets
Authors: Anderson K. R. , Mahalingam S.
Published: July 2002

Numerical simulations of coplanar reacting jets subjected to near wall confinement have been performed. The primary conclusion is that for a fixed level of heat release, the mechanism of baroclinic vorticity production increases with more severe wall confinement. [S0022-1481(00)00602-2]
RCC Characteristics of Planar/Spherical Three Degree-of-Freedom Parallel Mechanisms With Joint Compliances
Authors: Kim Whee-kuk , Yi Byung-Ju , Cho Whang
Published: July 2002

A three degree-of-freedom (DOF) planar parallel manipulator has been extensively studied as the fundamental example of parallel manipulators. In this work, we explicitly show that this mechanism possesses a completely decoupled compliance characteristic at the object space, which is the important operational requirement for a RCC device. As the first condition to have a RCC point, this mechanism should maintain symmetric configurations. As the second condition, the same magnitude of revolute joint compliance should be symmetrically placed at the same joint location of each chain. We also investigate the compliance characteristics of a spherical 3 DOF mechanism which has a similar kinematic structure to the planar mechanism through simulation. It turns out that the spherical mechanism also has a RCC point at the intersection point of all nine joint axes in its symmetric configuration. Further, more general output compliance model is derived for those mechanisms with redundant joint compliances. It is expected that these two parallel mechanisms not only can be used as excellent 3 DOF RCC devices, but also can be integrated into the design of a new six DOF RCC device. [S1050-0472(00)01101-6]
Crossable Surfaces of Robotic Manipulators With Joint Limits
Authors: Abdel-Malek Karim , Yeh Harn-Jou
Published: July 2002

A broadly applicable formulation for determining the crossability of singular surfaces and curves in the workspace of serial robotic manipulators is presented. Singular surfaces and curves are analytically determined using nullspace rank-deficiency criteria of the mechanism’s constraint position Jacobian. Imposed joint limits in terms of inequality constraints are taken into account in the formulation. Directions of admissible normal movements on a surface or curve are established from the analysis of the normal curvature of singular surfaces. The normal curvature of a parametric surface used in this formulation, is determined from the first and second fundamental forms adapted from differential geometry. Definiteness properties of a quadratic form developed from the acceleration analysis determine admissible normal movements. For singular surfaces resulting from active joint constraints, definiteness properties are not enough and supplementary criteria are necessary. Two additional criteria are derived. This paper is a complete treatment of the problem of determining whether a singular surface/curve in the workspace is crossable. Planar and spatial numerical examples are presented to illustrate the formulation. [S1050-0472(00)01301-5]
A Contribution on Quasi-Static Mooring Line Damping
Authors: Bauduin Christian , Naciri Mamoun
Published: July 2002

Since the pioneering work of Huse (1986, “Influence of Mooring Line Damping Upon Rig Motions,” Proc., 18th OTC Conference), it is well known that mooring lines may account for a large fraction of the overall damping present in a moored floating structure. This paper is concerned with the mooring line damping induced by the low-frequency, quasi-static, horizontal motion of the mooring line fairlead. The main advantage of the quasi-static approach is that it is much faster than the more accurate finite element methods, and, secondly, that it does not require any finite element modeling skills. A new formulation is proposed and is compared to the results of Liu et al. (1998, “Improvement on Huse’s Model for Estimating Mooring Cable-Induced Damping,” Proc., 17th OMAE Conference), as well as to time domain results obtained with FLEXRISER. The improvement with respect to the previous quasi-static methods is quite notable and our results are closer to FLEXRISER predictions. Finally, quasi-static results are compared to mooring line damping values measured during model tests for full mooring systems. The agreement between the two is very encouraging and suggests that the simpler quasi-static approach may, in some circumstances, be a valuable substitute for the more complex and time-consuming numerical tools. [S0892-7219(00)00102-3]
A Mathematical Transform to Analyze Part Surface Quality in Manufacturing
Authors: Tumer Irem Y. , Wood Kristin L. , Busch-Vishniac Ilene J.
Published: July 2002

The status of fault patterns on part surfaces can provide valuable information about the condition of a manufacturing system. Accurate detection of the part surface condition in manufacturing ensures the fault-free manufacturing of high-quality parts, as well as helping in the accurate design/redesign of machine components and manufacturing parameters. To address this problem, we introduce an alternative mathematical transform that has the potential to detect faults in manufacturing machines by decomposing signals into individual components. Specifically, the paper focuses on the decomposition of numerically generated data using the Karhunen-Loe`ve transform to study a variety of signals from manufacturing. The potential utility of the proposed technique is then discussed in the context of understanding a manufacturing process under constant development. [S1087-1357(00)01801-3]
An Analysis of a Near-Surface Crack Branching Under a Rigid Indenter
Authors: Mukai David J.
Published: July 2002

A near surface branching subsurface crack under a rigid cylindrical indenter is analyzed by a complex variable 2-D elasticity formulation. This analysis focuses on the mode II stress intensity factors (SIF) of a straight crack vs. the mode I SIF of a branched crack. The contact portion of the analysis is limited to a Hertzian contact under simple Coulomb friction. The effects of crack depth and length are examined and it is found that for small indenter footprints, as a crack grows parallel to the surface, conditions favor mode I branching toward the surface. [S0742-4787(00)00401-X]
Wear Tests and Pull-Off Force Measurements of Single Asperities by Using Parallel Leaf Springs Installed on an Atomic Force Microscope
Authors: Ando Yasuhisa
Published: July 2002

At the micro-scale level, the adhesion force dominates the friction force when the normal load approaches zero. For determining the effects of micro wear on the adhesion (pull-off) force, the wear-induced changes in surface topography of asperities and the pull-off force between the asperities and leaf springs were determined. First, single asperities were formed on a single-crystal gold plate and the asperities were rubbed with a silicon leaf spring attached to an AFM (atomic force microscope). A focused ion beam (FIB) system was used to form gold pyramid-shaped asperities on the surface of a single crystal gold plate. The FIB was also used to create the two types of single crystal silicon leaf springs tested here; single and parallel. The single leaf spring was created by flattening the probe-head of a commercially available AFM cantilever for AC mode. The parallel leaf spring was created by removing the central portion of a single-crystal silicon beam (25 μm×50 μm×300 μm). For the single leaf spring, the pull-off force no longer increased when the sliding distance exceeded 5 mm at a load of more than 200 nN. On the other hand, for the parallel leaf spring, the pull-off force increased monotonically with sliding distance, showing a more rapid increase at the higher normal load. The worn area of the asperity peak (measured by using an ordinary AFM probe) was proportional to the pull-off force. The wear volume per unit distance (i.e., wear rate) was estimated from the change in pull-off force, and was found to increase monotonically with the external load. There was no effect of adhesion force on the wear volume. [S0742-4787(00)01102-4]
Bolt Thread and Head Fillet Stress Concentration Factors
Authors: Lehnhoff Terry F. , Bunyard Bradley A.
Published: July 2002

Linear finite element analysis (FEA) was performed to determine stress concentration factors for the threads and the bolt head fillet in a bolted connection. The FEA models consisted of axisymmetric representations of a bolt and two circular steel plates each 20 mm in thickness. The bolts studied were 8, 12, 16, 20, and 24-mm-dia grade 10.9 metric bolts with the standard M thread profile. The threads were modeled at both the minimum and maximum allowable depths. The fillet between the bolt shank and bolt head connection was modeled at its minimum radius. Each bolt was loaded to its proof strength. A comparison is made to stress concentration factors typically used in bolted connection design. Stress concentration factors in the head fillet were 3.18, 3.23, 3.63, 3.58, and 3.90 for the 8, 12, 16, 20, and 24-mm bolts, respectively. Thread stress concentration factors were highest in the first engaged thread and decreased in each successive thread moving toward the end of the bolt. Stress concentration factors for the shallow thread models ranged from 1.17 to 4.33, 0.87 to 4.32, 0.83 to 4.67, 0.87 to 4.77, and 0.82 to 4.82 for the 8, 12, 16, 20, and 24-mm bolts, respectively. Likewise, stress concentration factors for the deep thread models ranged from 1.18 to 4.80, 0.88 to 4.80, 0.78 to 5.12, 0.83 to 5.17, and 0.82 to 5.22 for the 8, 12, 16, 20, and 24-mm bolts, respectively. [S0094-9930(00)01402-5]
Flaw Stability in Mild Steel Tanks in the Upper-Shelf Ductile Range—Part I: Mechanical Properties
Authors: Sindelar Robert L. , Lam Poh-Sang , Caskey, George R. , Woo Leta Y.
Published: July 2002

Mechanical properties of 1950’s vintage, A285 Grade B carbon steels have been compiled for elastic-plastic fracture mechanics analysis of storage tanks (Lam and Sindelar, 2000). The properties are from standard Charpy V-notch (CVN), 0.4T planform compact tension (C(T)), and tensile (T) specimens machined from archival steel from large water piping. The piping and storage tanks were constructed in the 1950s from semi-killed, hot-rolled carbon steel plate specified as A285 Grade B. Evaluation of potential aging mechanisms at both service conditions shows no loss in fracture resistance of the steel in either case. Site and literature data show that the A285, Grade B steel, at and above approximately 70°F (21°C), is in the upper transition to upper shelf region for absorbed energy and is not subject to cleavage cracking or a brittle fracture mode. Furthermore, the tank sidewalls are 1/2 or 5/8-in. (12.7 or 15.875 mm) thick, and therefore, the J-resistance JR curve that characterizes material resistance to stable crack extension under elastic-plastic deformation best defines the material fracture toughness. The JR, curves for several heats of A285, Grade B steel tested at 40°F (4.4°C), a temperature near the average ductile-to-brittle (DBTT) transition temperature (CVN at 15 ft-lb or 20.3 J), are presented. This data is applicable to evaluate flaw stability of the storage tanks that are operated above 70°F (21°C) since, even at 40°F (4.4°C), crack advance is observed to proceed by ductile tearing. [S0094-9930(00)00402-9]
LaAlO3(100) by XPS
Authors: Vasquez Richard P.
Published: July 2002

XPS core level and valence band measurements are presented for a twinned LaAlO3(100) crystal.
Zinc Germanium Phosphide by XPS
Authors: Kuhn W. Kevin
Published: July 2002

High quality single crystal ZnGeP2 has been analyzed by x-ray photoelectron spectroscopy. This material is one of a group of pseudo-III–V compounds that crystallize in a tetragonal chalcopyrite structure and have been shown to have very promising nonlinear optical properties. The spectra presented here include survey and high resolution scans of the photoemission peaks, the Zn and Ge Auger transitions, and the valence band of the compound.
Comparison Spectra of (111) Textured CeO2 Thin Films by XPS
Authors: Pfau A. , Schierbaum K. D. , Göpel W.
Published: July 2002

CeO2 is a large band gap insulator (Eg = 6 eV) and oxygen ion conductor, which is of particular interest as a promoter oxide in three way catalytic converters for automotive exhaust gas purification and as a solid electrolyte in high temperature solid oxide fuel cells. Theoretical work on the photoemission of CeO2 and its lower oxides (Ce2O3 and intermediate phases) has mainly focused on an understanding of the complicated Ce 3d spectra. Of great practical interest is the evaluation of the oxygen stoichiometries from a detailed Ce 3d peak shape analysis. Except for the Ce 3d signals, only very little work has been published on the photoemission of CeO2. In this work photoemission spectra of in situ prepared, stoichiometric (111)-oriented CeO2 thin films (thickness: 40 nm) on clean, sputtered Pt-foil substrates are presented. Instabilities in the energy scale, spectral broadening due to inhomogeneous charging and reduction induced by electron bombardment are circumvented by the use of the conduction Pt substrates. Spectra are recorded at room temperature and sample charging occurs during XPS analysis. The Ce 3d spectra exhibit the typical Ce4+ signals of CeO2. Ce3+ associated emission is beyond the detection limit. The O 1s spectra show only one sharp peak due to lattice oxygen. Higher binding energy shoulders which might be expected in the presence of hydroxyls, carbonates or defect oxygen are not present. The latter are frequently discussed in work concerning high surface area powders relevant for catalysis. The valence band spectrum presented is consistent with literature data and shows at its low binding energy side the oxygen 2p-dominated valence band. Within the detection limit of valence band XPS Ce 4f associated emission is not detected in the valence band. This corresponds to Ce ions being in the +IV oxidation state. In order to fully characterize the photoemission spectra of CeO2 and to provide a full data set for comparison to more complex cerium-based materials, all minor photoemission peaks (Ce 4d, Ce 4p, Ce 5s, Ce 5p, O 2s) and x-ray excited Auger spectra of the O KLL and the Ce MNN lines have been recorded.
Core Level and Valence Band Spectra of Pb3O4 by XPS
Authors: Rondon Sonia , Sherwood Peter M. A.
Published: July 2002

Core and valence band XPS spectra were obtained from a commercial Pb3O4 specimen provided by Aldrich Chem. Co. The XPS data were collected with a VSW HA150 spectrometer equipped with a monochromatic Al Kα x-ray source and a multichannel detector. This report includes the Pb 4f, Pb 5d, Pb 4d, O 1s, C 1s, and valence band photoemission peaks. The XPS analysis showed the presence of small amounts of adventitious carbon, adsorbed water, and hydroxide on the surface of the sample. When collected with achromic radiation the valence band region of PbO2 is overlapped by the MgKα3,4 satellites associated with the relatively intense Pb 5d and O 2s peaks. The use of monochromatic x-radiation allowed one to collect a high resolution valence band spectrum without the interference of these satellite features. This is of particular interest in the study of lead oxides because their XPS valence band spectra present features that can be used successfully to distinguish the different oxide forms.
Vanadium Pentoxide Thin Films by XPS
Authors: Barreca Davide , Rizzi Gian Andrea , Tondello Eugenio
Published: July 2002

Vanadium pentoxide thin films were grown on Al2O3 substrates by chemical vapor deposition and on glass substrates by plasma-enhanced chemical vapor deposition. While the films deposited on Al2O3 are polycrystalline, those grown on glass substrates show a strong (001) preferential orientation and are nanostructured. X-ray photoelectron spectroscopy measurements of the principal core levels for the surface of V2O5 films are reported.
Si etching rate calculation for low pressure high density plasma source using Cl2 gas
Authors: Lee Young D. , Chang H. Y. , Chang C. S.
Published: July 2002

Based on a simplified Cl2 plasma Si etching mechanism, we calculate the Si etching rate with a comprehensive analysis of the effect of ion bombardment. With its flux distribution, the bombarding ions are regarded as the sum of independent monoenergetic beams (SIMB) approach. The Si etching rate is examined over the radio-frequency (rf) frequency (νrf) range from 1 to 20 MHz (0.1νpi≲νrf≲2νpi, where νpi is the ion plasma frequency) under the typical low pressure high density plasma condition. To consolidate the SIMB approach, the etching rate is compared with the result from the monoenergetic single ion beam approach. The difference in the Si etching rate between the two approaches is notable at a low rf frequency range. The effect of threshold energy on the Si etching mechanism is also investigated. We conclude that under a low rf frequency, for a precise etching property examination, the effect of the bombarding ions should be investigated through the SIMB approach.
Fabrication of micro and submicro Y–Ba–Cu–O particles by excimer laser processing
Authors: Luo G. P. , Chen C. L. , Chen S. Y. , Shen J. , Wang Y. S. , Sun Y. Y. , Chu C. W. , Liou Y. , Ming N. B.
Published: July 2002

We have investigated the crystallization of amorphous Y–Ba–Cu–O films with pulsed laser irradiation. The Y–Ba–Cu–O films were prepared on Si (001) substrates by pulsed laser deposition at room temperature. The microstructure and surface morphology of the films during the crystallization process were studied by x-ray diffraction and scanning electron microscopy. Micro or submicro Y–Ba–Cu–O crystalline particles can be obtained with variant laser pulses and energy densities. The particles have half-spherical or even spherical shapes on the film surfaces, and the saturated particle sizes were found to be determined by the film thickness.
Aligned silicon carbide nanocrystals at the SiO2/Si interface by C implantation into SiO2 matrices
Authors: Chen Chang-Ming , Liu Xinquan , Li Zhifeng , Yu Guoqin , Zhu Dezhan , Hu Jun , Li Minqian , Lu Wei
Published: July 2002

In this article, we report a specific feature for the distribution of silicon carbide nanocrystals formed by C implantation into SiO2 followed by thermal annealing. Cross-sectional transmission electron microscopy shows that silicon carbide nanocrystals (islands) are buried in the Si wafer at the SiO2/Si interface in a rectangular array (∼40×10 nm in dimension) and with a spacing of ∼20 nm. High-resolution transmission electron microscopy examination shows that silicon carbide nanocrystals are epitaxial on the Si wafer and are absent in the SiO2 matrix. Photoluminescence peaked at 580 nm is observed for samples annealed at 1100 °C under 514 nm excitation, which is thought to arise from the embedded silicon carbide nanocrystals.
Depth-resolved spectroscopy of interface defects in AlGaN/GaN heterostructure field effect transistors device structures
Authors: Young A. P. , Bae J. , Brillson L. J. , Murphy M. J. , Schaff W. J.
Published: July 2002

We report depth-resolved low energy electron excited nanometer spectroscopy from AlGaN/GaN heterostructure field effect transistors structures with AlGaN thicknesses as thin as 20 nm. By varying the voltage of a low energy electron beam in ultrahigh vacuum, we can determine whether defect induced luminescence is being emitted from the GaN buffer layer, the interfacial region where the two-dimensional electron gas (2DEG) resides, and the AlGaN barrier layer. By increasing the GaN buffer thickness, known to enhance the electron concentration of the 2DEG by reducing the dislocation density in the active region, we observed an enhancement in AlGaN luminescence, and a 20% reduction in the full width at half maximum of the near band edge peak. When a similar structure with no 2DEG is measured, we find a factor of 8 increase in midgap yellow luminescence relative to the GaN buffer emission. Taken together, these findings indicate that differences in buffer layer thickness and electrical quality can affect not only dislocation density and point defect densities, but also the optical properties of the AlGaN barrier layer and its 2DEG interface.
Photoemission results on intralayer insertion at III-V/III-V junctions: A critical appraisal of the different interpretations
Authors: Moreno M. , Alonso M. , Höricke M. , Hey R. , Horn K. , Sacedón J. L. , Ploog K. H.
Published: July 2002

Several researchers have proposed that band discontinuities at semiconductor heterojunctions may be “tuned” by inserting very thin layers of foreign atoms at the interface which are thought to induce an “interface dipole.” Modifications of the apparent valence-band offset, as measured by photoelectron spectroscopy (PES), have been indeed observed upon Si insertion at GaAs–AlAs interfaces, and they have been generally interpreted as real band-offset changes. However, there is an alternative explanation of the photoemission results in terms of band-bending effects. Here, we present results of PES experiments designed to test the two opposing interpretations. We have examined the effect of Si insertion at polar (100) and nonpolar (110) interfaces, and we have studied the insertion of Si (n-type) and Be (p-type) intralayers. Similar results are obtained for polar and nonpolar interfaces, and effects of opposite sign are observed for Si and Be intralayers. These results can be readily interpreted in terms of a band-bending profile modification upon Si or Be insertion. Additional PES experiments performed at different substrate temperatures have allowed us to test the proposed band profiles. From the surface photovoltage effects induced at low temperature, we obtain evidence for sample band bending which is consistent with the room-temperature band profiles proposed. Hence, our results can be completely understood within a “band-bending interpretation,” calling into question the interpretation in terms of a “band-offset tuning effect.”
Third Row Transition Metals by X-ray Photoelectron Spectroscopy
Authors: Engelhard Mark , Baer Don
Published: July 2002

XPS spectra have been obtained from 11 metals in the third row of transition elements using a Quantum 2000 Scanning ESCA Microprobe. The metals analyzed include La, Hf, Ta, W, Re, Ir, Pt, Au, Tl, Pb, and Bi. Each sample was Ar+ ion etched before XPS analysis to remove surface contamination and/or oxide. The spectra include standard survey scans and high-energy resolution scans of the photoelectron peaks, as well as selected x-ray induced Auger peaks. Each spectrum was collected using a 100 μm diameter monochromatic Al Kα x-ray beam scanned over a 1.5 mm × 0.2 mm area of each sample. Survey scans were collected using a 58.7 eV pass energy, while high energy resolution scans were collected using a 23.5 eV pass energy.
An anomalous erosion of a rectangular magnetron system
Authors: Shidoji Eiji , Nemoto Masaharu , Nomura Takuji
Published: July 2002

Monte Carlo simulations were performed to examine the dc magnetron discharge that creates anomalous erosion at the boundary of the curved and straight sections of a rectangular magnetron. In order to examine the cause of anomalous erosion, we performed a series of simulations describing the strong and weak field regions without the curved section. The erosion profiles were calculated under differing magnetic field distributions. We found that anomalous erosion occurs under a magnetic field of more than 200 G. We also found that the cause of anomalous erosion is the weak magnetic field at the curved section as compared to that at the straight section. We confirmed that anomalous erosion does not occur in the case of a rectangular magnetron having a uniform magnetic field. In order to avoid anomalous erosion, the uniformity of the magnetic field has to be within 10% where the vertical component of the magnetic field at the target surface is zero.
Gas Discharge Cleaning of Vacuum Surfaces
Authors: Govier R. P. , McCracken G. M.
Published: July 2002

The efficiency of glow discharges in He, Ne, and Ar for the removal of H2O, CO, and CO2 from the surface of vacuum systems has been demonstrated. However, re-emission of the rare gas and of hydrogen atoms trapped in the surface during the discharge cause the total outgassing rate not to be significantly reduced. In general, as the pressure of the discharge increases, the efficiency of cleaning decreases, and this has been correlated with a decrease in the number of energetic ions hitting the surfaces.
Combined Low-Energy Electron Diffraction and Auger Electron Spectroscopy Studies of Si, Ge, GaAs, and InSb Surfaces
Authors: Grant J. T. , Haas T. W.
Published: July 2002

In the absence of surface impurities detectable by Auger electron spectroscopy, several semiconductor surfaces studied showed surface rearrangement using low-energy electron diffraction. The structures observed are Si{111}2×1 and 7×7, Ge{111}2×1 and 2×8, GaAs{111}2×2, InSb{111}2×2, InSb {111¯} 3×3, and InSb{112}1×1. The Auger electron spectra for some of these surfaces are also presented.
Study of the Competitive Diffusion at 525 °C of Nitrogen and Oxygen in Sputtered β-Tantalum Films
Authors: Croset M. , Velasco G.
Published: July 2002

Thin β-tantalum films, from 200 Å to 1 μ thick, deposited on silicon by diode sputtering in argon at 10−2 Torr, were treated at 525 °C in nitrogen containing well-defined quantities of oxygen and water traces in the parts per million range. The composition of the films, the nitrogen and oxygen incorporation kinetics, were studied by the observation of the nuclear reactions O(d,p) 16O*17 and N(d,α) 14C12 and by ion microprobe mass spectrometry. These experiments enabled us to establish the following points: (i) The predominant initial step of the process corresponds to a rapid (some minutes) nitrogen filling of the film with an almost uniform depth distribution up to an N/Ta ratio of 0.16. (ii) In a competitive process, a simultaneous incorporation of oxygen takes place and imposes the out diffusion of the nitrogen. (iii) Surface oxide film interference colors appear only after the nitrogen removal.
Ion Bombardment Induced Surface Damage in Tungsten and Molybdenum Single Crystals
Authors: Bellina J. J. , Farnsworth H. E.
Published: July 2002

The clean, annealed W(110) and Mo(110) surfaces were bombarded by 1013-1015 noble-gas ions having kinetic energies between 100 and 1000 eV. The degradation of intense peaks in the major beams was observed with a rapid-scan, Faraday collector system. The dependence of the rate of degradation on ion mass and energy and target mass was determined to depend on the energy transferred in two-body, linear, hard-sphere collision. Comparison with sputtering yields and thermal desorption of embedded ions indicated when knock-on lattice distortion rather than direct sputtering or ion embedding probably caused the intensity degradation.
Physics of Ion Plating and Ion Beam Deposition
Authors: Aisenberg S. , Chabot R. W.
Published: July 2002

A review of some dominant mechanisms in ion plating is made. Factors influencing throwing power and film quality are discussed and the damaging effects of a high ambient gas background are considered with a view toward minimizing the harmful effects of contaminant gas background. The physical mechanisms involved in an ion beam deposition process [S. Aisenberg and R. Chabot, J. Appl. Phys. 42, 2953 (1972)] are examined. The effects of chamber pressure, electrical bias arrangements, and the introduction of a coevaporant source are discussed with regard to deposition rate, ultimate film quality, and throwing power of the system.
Electroluminescent Displays
Authors: Vecht A.
Published: July 2002

A review is made of the electroluminescent panels that have been prepared using activated zinc sulfide. The materials control at all stages of preparation is stressed. The characteristics of ac, continuous dc and pulsed dc operation cells are compared. Improved maintenance in dc electroluminescent displays is shown in panels prepared from manganese activated zinc sulfide, coated with a conducting layer of copper sulfide. Other activator systems in zinc sulfide are described and possible new host lattices discussed. Red electroluminescence from manganese activated barium zinc sulfide is described.
Analysis of an Ar–O2–N2 discharge for tantalum sputtering
Authors: Westwood W. D.
Published: July 2002

Both optical-emission spectroscopy and mass spectrometry have been used to investigate the species present in an Ar–O2–N2 glow discharge when tantalum is being sputtered. Special attention has been focused on the conditions under which a decrease in film resistivity is produced by an appropriate N2 flow. The addition of oxygen caused a significant increase in the nitrogen emission but no oxygen emission was observed. The oxygen is gettered more efficiently by the tantalum than is nitrogen so that more nitrogen reaches the center of the discharge when O2 is added. For the same flowrates of N2 and O2, the N2 signal measured by the differentially-pumped mass spectrometer is about 100 times the O2 signal. The changes observed in the electrical and structural properties of the films as the O2 flow was increased are consistent with an increase in nitrogen concentration in the films. When the N2 flow was adjusted to give a resistivity of 100 μΩ cm in the absence of O2, ρ increased to 250 μΩ cm with increasing O2 flow but the films retained the bcc structure. In the absence of N2, the resistivity was independent of O2 flows below a critical level. No evidence for the formation of an oxide of nitrogen was obtained.
Patterning performance of EB-X3 x-ray mask writer
Authors: Ohki Shigehisa , Watanabe Toshifumi , Takeda Yuji , Morosawa Tetsuo , Saito Kenichi , Kunioka Tatsuya , Kato Junichi , Shimizu Akira , Matsuda Tadahito , Tsuboi Shinji , Aoyama Hajime , Watanabe Hiroshi , Nakayama Yoshinori
Published: July 2002

An intensive study of the patterning performance of the EB-X3 revealed that the placement accuracy of a written image was degraded by the thermal effect originating from the temperature difference between the stage and the palette. An optimal writing procedure consisting of two temperature stabilization steps was developed. This procedure enables the EB-X3 to attain an image placement accuracy of better than 10 nm (3σ). A critical dimension control of 7.4 nm (3σ) has been confirmed over a 25-mm-square field.
Overlay compatibility between two synchroton radiation steppers
Authors: Fukuda Makoto , Suzuki Masanori , Haga Tsuneyuki , Morita Hirofumi , Aoyama Hajime , Mitsui Souichirou , Taguchi Takao , Matsui Yasuji
Published: July 2002

A total overlay accuracy of less than 35 nm was obtained with two synchrotron radiation (SR) x-ray steppers developed by NTT and ASET. This value includes the pattern placement errors of two masks, errors due to the wafer etching process, and errors of two steppers that arise in exposure. The error factors affecting the overlay compatibility among SR x-ray steppers were analyzed using double-exposure experiments. The results show that the overlay error induced by the difference in runout between the two steppers was negligibly small and that the magnification change from shot to shot was caused by gap setting variations between the two steppers. These results demonstrate that a SR x-ray stepper can provide sufficient overlay compatibility for the 100 nm technical node and beyond.
Performance of a compact beamline with high brightness for x-ray lithography
Authors: Hirose Sayumi , Miyatake Tsutomu , Li Xuan , Toyota Eijiro , Hirose Masaoki , Fujii Kiyoshi , Suzuki Katsumi
Published: July 2002

We have developed a short beamline with high brightness for x-ray lithography. The beamline contains a single, a scanning toroidal mirror and a vacuum-protection system with an acoustic delay line. The practical exposure intensity on a wafer was approximately 50 mW/cm2 at stored electron current of 500 mA. Dose uniformity of ±2.8% was achieved in a 26 mm×26 mm exposure area by optimizing the scan speed. Minimum resolution of 80 nm was obtained with a 15 μm gap. The optimum dose for TDUR-N908 (Tokyo Ohka) was 1300 mA s, which corresponds to exposure time of 2.6 s when the stored electron current is 500 mA. Since the sensitivity of TDUR-N908 is 110 mJ/cm2, the beam intensity in our beamline is estimated to be 43 mW/cm2. By reducing the exposure field, a beam intensity of more than 50 mW/cm2 can be achieved.
Vacuum ultraviolet spectra of fluorocompounds for 157 nm lithography
Authors: Toriumi Minoru , Satou Isao , Itani Toshiro
Published: July 2002

The optical characteristics in the vacuum ultraviolet region were studied using the molecular orbital method. A model molecule, p-ethylphenol, was used to represent poly(p-hydroxystyrene), and its spectrum was calculated by the semiempirical molecular orbital calculations. The theoretical results were compared with the experimental ones. The wavelengths of the absorption peaks showed good agreement in both results, though the intensities of the absorption did not agree. The fluorination of p-ethylphenol was investigated and it was found that the increase in the number of fluorine atoms became more transparent in the compound. The cause was explained by two factors. One was the redshift of the π–π* electronic transition of the aromatic molecules, of which the oscillator strength did not depend upon the fluorination number. The other was the decrease in the oscillator strength of the peak at 157 nm, of which the wavelength did not significantly shift.
Characterization of extreme ultraviolet lithography mask defects from extreme ultraviolet far-field scattering patterns
Authors: Yi Moonsuk , Jeong Seongtae , Rekawa Seno , Bokor Jeffrey
Published: July 2002

We present far-field scattering patterns from programmed phase and opaque defects on extreme ultraviolet lithography mask blanks. Distinct diffraction fringes were observed for both defect types, with fringe spacing dependent on the defect size. Phase defects and opaque defects were found to show clear differences in scattering properties that can be utilized to classify defects.
New concept for high-throughput multielectron beam direct write system
Authors: Muraki Masato , Gotoh Susumu
Published: July 2002

A new multielectron-beam optical system with correction lens array (CLA) is proposed. The CLA is arranged between an electron source and reduction optics. The CLA can generate plural intermediate images of the electron source as a multisource, and moreover can compensate field curvature and distortion of the reduction optics. The proposed system was designed and optimized through simulations. The specifications are field size of 250 μm square, convergence beam angle of 10 mrad, 64×64 beams, individual beam size of φ25 nm, accelerating voltage of 50 kV, and demagnification ratio of 50. The practical resolution for various resist processes is estimated considering the Coulomb interaction effect, and the throughput is simulated. The proposed system offers the possibility of “maskless” electron beam lithography with throughput in excess of 50 wafers/h (8 in.) for the International Technology Roadmap for Semiconductors (ITRS) 100 nm and 70 nm nodes at 3 μC/cm2 resist sensitivity.
Reticle’s contribution to critical dimension control and overlay in extreme-ultraviolet lithography
Authors: Meiling H. , Benschop J. P. H. , Loopstra E. , van der Werf J. E. , Leenders M. H. A.
Published: July 2002

In order to design an exposure tool for extreme-ultraviolet (EUV) lithography that adheres to technology roadmap requirements, we translated overall system performance requirements to system design specifications by setting up detailed error budgets for critical dimension (CD) control and overlay. In this article we concentrate on the EUV reticle contributions, including surface flatness, hydrocarbon contamination, multilayer d-spacing variations, and mounting in the writer and exposure tool. It is determined that in order to meet the CD-control budget, the reticle multilayer d-spacing variation must be limited to 0.25%, whereas the thickness variation of the hydrocarbon growth should be less than 1.5 nm. The overlay budget requires that the reticle flatness within the site area must be better than ±25 nm, both on the patterned side and on the back side. Also, the chuck of the exposure tool must be flat within ±25 nm. To avoid in-plane pattern distortion, the flatness of the chuck in the e-beam writer must be identical to that of the chuck in the exposure tool, and hence also must be flat within ±25 nm.
Correction of the field curvature in SCALPEL projection systems
Authors: Xiu K. , Gibson J. M.
Published: July 2002

The field curvature and axial chromatic aberration, 2 of 13 aberrations in an electron optical system, make the major contributions to the image blur of a SCALPEL projector. We first give a simple yet quantitative evaluation of the point spread function from the field curvature and chromatic aberration and show the merit of keeping a comparatively low field curvature. Then we describe two ways to reduce the field curvature in an electron projection system. One is to use an immersion magnetic doublet with a constant field along most of the optical column with opposite signs at two ends which are connected by a sharp field transition region. The other way is to use space charge foils. By putting a space charge foil with homogeneously distributed space charge density on either the object or image plane, we show the field curvature can be eliminated in principle without affecting any other aberrations.
Resolution limit of negative tone chemically amplified resist used for hybrid lithography: Influence of the molecular weight
Authors: Pain L. , Higgins C. , Scarfoglière B. , Tedesco S. , Dal’Zotto B. , Gourgon C. , Ribeiro M. , Kusumoto T. , Suetsugu M. , Hanawa R.
Published: July 2002

The objective of this article was to study the resolution limits of different negative tone chemically amplified resists from both commercial and experimental formulations. Process optimization has been done on all samples and this work underlines the importance of the choice of bake temperature to push resists to their ultimate resolution. Furthermore, the influence of several compounds, such as the polymer matrix blend, molecular weight, and photoacid compound, is detailed to determine the influence of each parameter on the final formulation performance.
Highly accurate x-ray masks with 100-nm-class high-density device patterns
Authors: Uchiyama Shingo , Shimada Masaru , Tsuchizawa Tai , Ohkubo Takashi , Oda Masatoshi , Yoshihara Hideo
Published: July 2002

We investigated the relationship between pattern size and the distortion due to absorber etching using two types of Ta absorber—one deposited by electron cyclotron resonance (ECR) and another deposited by radio frequency sputtering—with and without a Ru layer underneath. From the comparison of the results, it was confirmed that the combination of ECR Ta and a Ru intermediate layer can dramatically reduce the distortion due to absorber etching even when 80 nm wide patterns are delineated. This structure has been successfully applied to the fabrication of x-ray masks for five layers of a 100-nm-test element group (TEG) and two layers of a 1-Gbit-class dynamic random access memory. The image placement accuracy of a set of masks for five layers of a 100 nm TEG was better than 22 nm.
Technology and performance of the Canon XRA-1000 production x-ray stepper
Authors: Mizusawa Nobutoshi , Uda Kouji , Tanaka Yutaka , Ohta Hirohisa , Watanabe Yutaka
Published: July 2002

In order to introduce next generation lithography (NGL) into practical use, developing a production-worthy exposure tool is as important as developing a proof-of-concept system and mask technology. The progress of the exposure tool can be used as a measure of the status of each NGL choice. Canon has been focusing on the development of a proximity x-ray lithography (PXL) system for volume production use since the start of development. This has included development of magnification correction, development of a high-seed wafer stage, improvement of illumination intensity, extension of process latitude in the alignment system design, and development of an accurate environment control system. For example, we introduced a new method, using mechanical deformation of the mask, for magnification correction. We also developed a new wafer stage based on a field proven-high-speed wafer stage from our current optical lithography systems. A stepping time (including settling time) of less than 400 ms for a 50 mm step in a low-pressure helium environment was achieved. These achievements have been integrated into our volume production tool: the XRA-1000 x-ray stepper. The XRA-1000 has been installed in ASET and it will be used as the means for other process module development. Its results will demonstrate that PXL technology is the most practical NGL technology for volume production.
Chemical interaction and adhesion characteristics at the interface of metals (Cu, Ta) and low-k cyclohexane-based plasma polymer (CHexPP) films
Authors: Kim K. J. , Kim K. S. , Lee N.-E. , Choi J. , Jung D.
Published: July 2002

Chemical interaction and adhesion characteristics between metals (Cu, Ta) and low-k plasma-treated cyclohexane-based plasma polymer (CHexPP) films were studied. In order to generate new functional groups that may contribute to the improvement of adhesion between metal and plasma polymer, we performed O2, N2, and H2/He mixture plasma treatment on the surfaces of CHexPP films. Chemical interactions at the interface between metals (Cu, Ta) and plasma-treated CHexPP films were analyzed by x-ray photoelectron spectroscopy. The effect of plasma treatment and thermal annealing on the adhesion characteristics was measured by a tape test and scratch test. The formation of new binding states on the surface of plasma-treated CHexPP films improved adhesion characteristics between metals and CHexPP films. Thermal annealing improves the adhesion property of Cu/CHexPP films, but degrades the adhesion property of Ta/CHexPP films.
Study of exchange anisotropy for Ni80Fe20/Fe60Mn40 (111) epitaxial films
Authors: Liu Congxiao , Du Jianhua , Barnard J. A. , Mankey G. J.
Published: July 2002

Ni 80 Fe 20 / Fe 60 Mn 40 (111) epitaxial films grown on Si(110) buffered by Cu were studied systematically by varying the individual layer thicknesses with emphasis on the detailed structure evolution and its influence on the magnetic properties. The Cu buffer layer induced epitaxial face-centered-cubic (111) growth. Film crystallinity improved as the Cu buffer layer thickness t increased, evidenced from the full width of half maximum of 3.3° for t=1 nm and 1.1° for t=100 nm. Film surface roughness increased from 0.56 to 1.1 nm with increasing Cu buffer layer thickness. The exchange bias field was around 90 Oe when the Cu buffer layer film thickness was less than 10 nm, higher than the 70 Oe for films with thicker Cu buffer layers. Reversible measurements of the exchange coupling strength were ∼70 Oe larger than the loop shift for films with Cu buffer layer thickness greater than 10 nm. For these films the coercivity was larger than 30 Oe. A magnetic force microscope showed a magnetization ripple pattern with a characteristic length of ∼2 μm, indicating a strong stray field. The angular dependence of exchange bias field for epitaxial films was quite different from that of polycrystalline films.
Measurements of photon stimulated desorption from thick and thin oxide of KEKB collider copper beam chambers and a stainless steel beam chamber
Authors: Foerster C. L. , Lanni C. , Kanazawa K.
Published: July 2002

Photon stimulated desorption (PSD) from KEKB factory copper chambers was measured at the National Synchrotron Light Source (NSLS), located at the Brookhaven Laboratory. The KEKB is an asymmetrical collider recently constructed in Ibaraki, Japan. The collider utilizes two UHV ring chambers, one for a 3.5 GeV positron beam and the other for an 8 GeV electron beam, for B-meson studies. Two each, 1 m long, 94 mm inner diameter, chemically deoxidized copper beam chambers with conflat end flanges, were provided by KEKB to the NSLS, for measurement of PSD. PSD and specular reflection were measured on NSLS VUV ring beamline U9a. It has been reported that a high temperature air bake on large stainless steel vacuum systems reduces the need for a vacuum bake. To determine the effect of surface oxide, following the initial PSD measurement, the chambers were chemically cleaned and then oxidized in air for a week at 150 °C. PSD was remeasured after the air bake. A similar process and measurement was performed on a stainless steel beam chamber, with the exception of oxidation at 450 °C. After the chambers were installed on beamline U9a, they were exposed to a minimum of 1023 photons direct from the source having a critical energy of 595 eV, striking at an incident angle of 100 mrad. The major PSD yields for hydrogen, carbon monoxide, carbon dioxide, methane, and water vapor are reported as a function of accumulated photon flux, incident surface oxide, and chamber preparation. The results are compared with other PSD measurements on NSLS beamlines and those of other laboratory publications for copper and stainless steel.
Field emisison from GaN on Si substrate
Authors: Czarczyński W. , Kieszkowski P. , Łasisz St. , Paszkiewicz R. , Tłaczała M. , Znamirowski Z. , Z̈ołnierz E.
Published: July 2002

This article presents some investigation results of GaN hexagonal crystals deposited on Si pyramids as field emitters. GaN is considered to be an interesting material for field emission cathodes due to its stability. This exceptional stability makes emitter shaping difficult work. Si is easily formed but GaN grown on Si substrate forms small, separate grains. The formation of such single crystals on Si pyramids may be an easy way for field emitter array formation. The obtained results show that this approach may be useful in practical application. There are some indications that the overheating of emitter tips may lead to decomposition of GaN and to release of metallic Ga.