bluuebunny/crossref_metadata_2025 huggingface dataset:
An Implicit Scheme for Cascade Flow and Heat Transfer Analysis
Authors: Xu C. , Amano R. S.
Published: July 2002

A new efficient implicit scheme, based on the second-order time and spatial difference algorithm for solving steady flow by using time-marching Navier–Stokes equations, was developed for predicting turbine cascade flows and heat transfer. The difference scheme comprises an explicit part in the intermediate time-step and an implicit part in the local time-step. The viscous flux vectors are decomposed to simplify the flow calculation in the explicit step. The time difference terms are expressed in terms of the viscous dependent terms that appear in the diffusion terms in the form by adding eigenvalues of viscous flux matrices into the time derivation term. In the presently proposed scheme, the two-sweep procedure is used in the implicit step instead of employing a traditional matrix operation to save the computational time. This method has been used to calculate the flow around C3X and VKI cascades. The computed results were compared with experimental data as well as with other published computations. The comparisons for both surface pressure and heat transfer coefficient showed good agreement with the experiments. [S0889-504X(00)01702-5]
Elastic-Plastic Analysis of the PVRC Burst Disk Tests With Comparison to the ASME Code Primary Stress Limits
Authors: Jones D. P. , Holliday J. E.
Published: July 2002

This paper provides a comparison between finite element analysis results and test data from the Pressure Vessel Research Council (PVRC) burst disk program. Testing sponsored by the PVRC over 20 yr ago was done by pressurizing circular flat disks made from three different materials until failure by bursting. The purpose of this reanalysis is to investigate the use of finite element analysis (FEA) to assess the primary stress limits of the ASME Boiler and Pressure Vessel Code (hereafter the Code), and to qualify the use of elastic-plastic (EP-FEA) for limit-load calculations. The three materials tested represent the range of strength and ductility found in modern pressure vessel construction and include a low-strength, high-ductility material, a medium-strength, medium-ductility material, and a high-strength, low-ductility, low-alloy material. Results of elastic and EP-FEA are compared to test data. Stresses from the elastic analyses are linearized for comparison of Code primary stress limits to test results. Elastic-plastic analyses are done using both best-estimate and elastic-perfectly plastic (EPP) stress-strain curves. Both large strain-large displacement (LSLD) and small strain-small displacement (SSSD) assumptions are used with the EP-FEA. Analysis results are compared to test results to evaluate the various analysis methods, models, and assumptions as applied to the bursting of thin disks. The test results show that low-strength, high-ductility materials have a higher burst capacity than do high-strength, low-ductility materials. Linearized elastic FEA stresses and ASME Code primary stress limits provide excessive margins to failure for the burst disks for all three materials. The results of these studies show that LSLD EP-FEA can provide a best-estimate analysis of the disks, but the accuracy depends on the material stress-strain curve. This work concludes that SSSD EPP analysis methods provide a robust and viable alternative to the current elastic linearization method of satisfying the primary stress limits of the Code. [S0094-9930(00)01602-4]
Hydrodynamic Analysis of Direct Steam Generation Solar Collectors
Authors: Odeh S. D. , Behnia M. , Morrison G. L.
Published: July 2002

Direct steam generation collectors are considered with the aim to improve the performance of a parabolic trough collector leading to a reduction of operating costs of solar electric generation systems. In this study a hydrodynamic steady state model is developed and linked with a thermal model to optimize the performance of once-through direct steam generation solar collectors. The hydrodynamic model includes flow pattern classification and a pressure drop model. Flow pattern maps for typical DSG collectors with horizontal and inclined absorber tubes are generated to investigate the variation of flow conditions with radiation level, tube diameter, tube length and flow rate. Two-phase flow frictional pressure drop correlations for the range of operating conditions in a DSG collector are selected from the wide range of published correlations by comparison with experimental data for typical steam-water flow conditions in a DSG collector. Pressure drop is calculated for different operating conditions for both horizontal and inclined solar absorber tubes. Alternative operational strategies are evaluated to achieve optimum performance of a direct steam generation collector at different radiation levels. [S0199-6231(00)00101-5]
Spatial Modulation of Repeated Vibration Modes in Rotationally Periodic Structures
Authors: Kim M. , Moon J. , Wickert J. A.
Published: July 2002

When a structure deviates from axisymmetry because of circumferentially varying model features, significant changes can occur to its natural frequencies and modes, particularly for the doublet modes that have non-zero nodal diameters and repeated natural frequencies in the limit of axisymmetry. Of technical interest are configurations in which inertia, dissipation, stiffness, or domain features are evenly distributed around the structure. Aside from the well-studied phenomenon of eigenvalue splitting, whereby the natural frequencies of certain doublets split into distinct values, modes of the axisymmetric structure that are precisely harmonic become contaminated with certain additional wavenumbers. From analytical, numerical, and experimental perspectives, this paper investigates spatial modulation of the doublet modes, particularly those retaining repeated natural frequencies for which modulation is most acute. In some cases, modulation can be sufficiently severe that a mode shape will “beat” spatially as harmonics with commensurate wavenumbers combine, just as the superposition of time records having nearly equal frequencies leads to classic temporal beating. An algebraic relation and a diagrammatic method are discussed with a view towards predicting the wavenumbers present in modulated eigenfunctions given the number of nodal diameters in the base mode and the number of equally spaced model features. [S0739-3717(00)01501-4]
Nickel Mg K
α XPS Spectra from the Physical Electronics Model 5400 Spectrometer
Authors: Mansour A. N.
Published: July 2002

Nickel by Mg Kα XPS

Nickel spectra were measured with the Physical Electronics Model 5400 x-ray photoelectron spectrometer (XPS) using unmonochromatized Mg Kα x rays and four pass energy settings corresponding to analyzer energy resolutions of 1.34, 0.54, 0.27, and 0.13 eV. The specimen is a high purity (99.95%) 4 μm thick nickel foil that was obtained from the Goodfellow Corporation and was sputter-cleaned by 3 keV Ar ions for 5 min. We present the survey spectrum (binding energy range of 0–1100 eV) measured at an analyzer energy resolution of 1.35 eV. Multiplexes of the Ni 2p (845–895 eV), Ni 3p (55–88 eV), Ni 3s (100–130 eV), Ni 2s (995–1025 eV), valence band region (−5–20 eV), and Ni LVV Auger lines (378–428 eV) were measured at analyzer energy resolutions of 0.54, 0.27, and 0.13 eV.
Zinc Aluminate (ZnAl2O4) by XPS
Authors: Strohmeier Brian R.
Published: July 2002

Zinc aluminate (ZnAl4O4, also known as zinc aluminum oxide) is a material that has applications as a catalyst and catalyst support. This paper presents the XPS spectra of the major Zn, Al, and O photoelectron lines, and the major x-ray induced Zn LMM Auger lines for ZnAl2O4.
Three-dimensional simulation of film microstructure produced by glancing angle deposition
Authors: Smy T. , Vick D. , Brett M. J. , Dew S. K. , Wu A. T. , Sit J. C. , Harris K. D.
Published: July 2002

A novel three-dimensional (3D) ballistic deposition simulator 3D-FILMS has been developed for the modeling of thin film deposition and structure. The simulator features a ballistic transport algorithm to model incident species with angular distributions appropriate to physical vapor deposition systems. Two-tiered data structuring is employed in order to enable the simulator to run using memory resources available to workstations. The simulator has been applied to a unique class of thin films grown by the technique of glancing angle deposition (GLAD). These films exhibit low bulk density due to an internal structure consisting of isolated microcolumns, which can be engineered into a variety of 3D forms. Because of their inherent 3D morphology, created by a combination of complex substrate motion and 3D shadowing, GLAD films represent an ideal test subject for 3D simulation. Scanning electron microscope images of films are presented together with simulation results, which correctly reproduce aspects of column morphology, column growth competition and extinction, and film bulk density.
Particle transport in a parallel-plate semiconductor reactor: Chamber modification and design criterion for enhanced process cleanliness
Authors: Nijhawan Sandeep , McMurry Peter H. , Campbell Stephen A.
Published: July 2002

Convective, diffusive, and thermophoretic particle transport in a parallel-plate semiconductor reactor is investigated. Measurements that illustrate particle transport in the reactor are presented and a Eulerian continuum particle transport formulation is used to quantitatively explain the measurements. Experimental and numerical results show that particles formed in the parallel-plate region are confined in a thin sheath (∼2 cm) between the “hot” wafer and “cold” showerhead inlet. This sheath is located at the point where downward convective transport balances upward transport by thermophoresis. The particle sheath location is independent of particle size but is dependent on gas flow rates and temperature of the wafer and showerhead inlet. In addition, experimental and numerical results show that as particles exit the parallel-plate region, the radial thermophoretic particle transport can produce “ring-like” contaminant deposits on the outer wall of the reactor under certain flow conditions. We propose a simple reactor design modification and an analytic design criterion to avoid particle deposition on the chamber walls.
Search for improved transparent conducting oxides: A fundamental investigation of CdO, Cd2SnO4, and Zn2SnO4
Authors: Coutts T. J. , Young D. L. , Li X. , Mulligan W. P. , Wu X.
Published: July 2002

The bulk of developmental work on transparent conducting oxides (TCOs) has been somewhat empirical. This statement applies both to more familiar materials such as indium tin oxide (ITO) and to less-well-known materials that have emerged in recent years. In this article, we place a greater emphasis on more fundamental research. Our eventual goal is to gain a thorough understanding of these materials, their potential for further improvement, whether or not they suggest new and potentially superior materials, and the way their properties are influenced by structural and other issues. We also hope to provide guidelines to other researchers working in this area. We have investigated films of cadmium oxide (CdO), cadmium stannate (Cd2SnO4 or CTO), and zinc stannate [Zn2SnO4 (ZTO)]. The CdO was prepared by chemical-vapor deposition, whereas the stannates were prepared by rf sputtering. In both cases, Corning 7059 glass substrates were used. However, some depositions were also made onto tin oxide, which had a profound effect on the nucleation of CdO, in particular. It is well known that a high free-carrier mobility is essential for a TCO with near-ideal electro-optical properties. Increasing the free-carrier concentration also increases the free-carrier absorbance but a higher mobility reduces it. We have achieved free-electron mobilities in CdO (Eg∼2.4 eV) of greater than 200 cm2 V−1 s−1, of almost 80 cm2 V−1 s−1 in CTO (Eg∼3.1 eV), but of only 10–15 cm2 V−1 s−1 in ZTO (Eg∼3.6 eV). We have characterized these materials, and will show key data, using techniques as diverse as the Nernst–Ettingshausen effect; Mössbauer, Raman, optical, and near-infrared spectroscopies; atomic-force and high-resolution electron microscopy; and x-ray diffraction. These measurements have enabled us to determine the effective mass of the free carriers and their relaxation time, the probable distributions of cations between octahedral and tetrahedral sites, the role of the deposition parameters on the carrier concentrations, and the nature of the dominant scattering mechanisms. We also consider issues relating to toxicity of cadmium and to reserves of indium. Both are of great significance to prospective large-volume manufacturers of TCO films and must be taken into account by researchers.
Schottky barrier tuning with heterovalent interlayers: Al/Ge/GaAs versus Al/Si/GaAs
Authors: Berthod C. , Binggeli N. , Baldereschi A.
Published: July 2002

Using ab initio calculations, we compare the effects produced on the Al/GaAs(100) Schottky barrier height by Ge and Si interface layers with thickness ranging from 0 to 2 monolayers. The dipole layers, generated by the group-IV atomic substitutions at the interface, increase/decrease the p-type Schottky barrier at the As-/Ga-terminated Al/GaAs(100) junction. Although the trends with Ge and Si interlayers are similar for coverages less than 0.5 monolayers, at higher coverages the Schottky barrier exhibits a stronger nonlinear behavior, and smaller barrier variations, in Al/Ge/GaAs(100) than in Al/Si/GaAs(100). In particular, at a coverage of 2 monolayers, the use of Ge interlayers instead of Si ones reduces by 25% the barrier tunability. These trends are at variance with those predicted by existing macroscopic band-structure models, and our results should help in discriminating between different mechanisms of Schottky barrier tuning.
Charging effects in AlGaN/GaN heterostructures probed using scanning capacitance microscopy
Authors: Smith K. V. , Dang X. Z. , Yu E. T. , Redwing J. M.
Published: July 2002

Charging effects in an AlxGa1−xN/GaN heterostructure field-effect transistor epitaxial layer structure have been studied using scanning capacitance microscopy. Voltages of ⩽6 V applied between an AlxGa1−xN/GaN sample structure and a conducting proximal probe tip are found to create trapped charge in both doped and undoped heterostructures. Scanning capacitance measurements obtained over a wide range of bias voltages allow the charge distribution to be mapped both laterally and in depth with submicron to nanometer scale spatial resolution. Scanning capacitance imaging as a function of bias voltage performed in conjunction with numerical capacitance–voltage simulations suggests that positive charge can be trapped at the AlxGa1−xN surface and within the GaN layer and negative charge can be trapped at or near the AlxGa1−xN/GaN interface.
Interface tuning of the InAs/AlSb heterostructure-based quantum wells
Authors: Ichizli V. M. , Mutamba K. , Droba M. , Sigurdardóttir A. , Hartnagel H. L.
Published: July 2002

This work shows the importance of interface consideration at the barrier sides for quantum well (QW)-based semiconductor structures, on the example of the InAs/AlSb heterostructure. Various interface combinations of AlAs and InSb type have been included in an InAs/AlSb double-barrier resonant-tunneling-diode structure, and the resulting transmission functions have been calculated. A systematic comparison of the resulting structures with each other and also with the traditional case without interface consideration have been made. Clear tendencies and relationships observed in the transmission characteristics of the different structures let the interface tuning emerge as a quality tool for QW-device tayloring.
Atomic structure and composition of the (2×4) reconstruction of InGaP(001)
Authors: Vogt P. , Lüdge K. , Zorn M. , Pristovsek M. , Braun W. , Richter W. , Esser N.
Published: July 2002

In this study scanning tunneling microscopy (STM), soft x-ray photoemission spectroscopy (SXPS), and reflectance anisotropy spectroscopy were used to investigate the microscopic structure of (2×4) reconstructed InGaP(001) surfaces. The samples were grown lattice matched on GaAs(001) by metalorganic vapor phase epitaxy. Immediately after growth the surfaces were passivated by a thick amorphous cap consisting of a P/As double layer and then transferred to ultrahigh vacuum (UHV) analysis chambers either equipped with STM or connected to the BESSY synchrotron radiation source for photoemission experiments. Thermal desorption of the As/P capping layer at 460 °C under UHV conditions leads reproducibly to the formation of a III-rich (2×4) reconstruction, the more P-rich (2×1) could not be obtained. The low energy electron diffraction image shows a clear (2×4) pattern with sharp integer-order and fractional-order spots. STM images show rows along the [1̄10] direction with fourfold separation in the [110] direction, similar to the (2×4) reconstruction of InP(001). SXPS spectra of the In 4d/Ga 3d and P 2p core levels demonstrate that this surface may consist of a mixed-dimer structure analogous to the one found on InP(001) and GaP(001) (2×4). Further annealing of the sample to higher temperatures degrades the surface without producing another reconstruction. The (2×4) reconstruction thus represents the most III-rich (least P-rich) stable surface for InGaP(001).
ZnSe/CdTe/ZnSe heterostructures
Authors: Rubini S. , Bonanni B. , Pelucchi E. , Franciosi A. , Garulli A. , Parisini A. , Zhuang Y. , Bauer G. , Holý V.
Published: July 2002

Epitaxial ZnSe/CdTe/ZnSe heterostructures were successfully fabricated by molecular beam epitaxy on GaAs(001) wafers despite the large in-plane lattice mismatch (14.3%) between the two II–VI materials. X-ray reciprocal space maps and selected area diffraction results indicate single-phase, (111)-oriented growth of CdTe onto the lower ZnSe(001) cladding layer, and single-phase, (111)-oriented growth of the topmost ZnSe layer, with a small inhomogeneous residual strain within the CdTe layer. Cross-sectional transmission electron micrographs reveal a distribution of rotational microtwins within the (111)-oriented layers near each interface. The low-temperature near-band-edge photoluminescence from the CdTe layer is free-exciton related, and exhibits a linewidth of only 5–6 meV.
Some effects of structure and composition on the properties of electron beam vapor deposited coatings for gas turbine superalloys
Authors: Boone D. H. , Strangman T. E. , Wilson L. W.
Published: July 2002

Multi-element overlay coatings applied by electron beam vapor deposition to gas turbine superalloys have been the subject of intensive research and development programs for the past eight years. Such coatings have proven to be superior to diffusion coatings in a number of critical applications primarily because of the ease with which compositional variations can be effected to meet unique protection and mechanical requirements. Overlay coating structural features have been identified (i.e., open columnar structure, vapor source spit marks, flakes and pits), along with present and future methods for their control. Laboratory observations have indicated that in a line-of-sight process, the open columnar structure is the result primarily of shadowing effects and the limited surface diffusion of the depositing atoms. Point defects (spits, flakes, and pits) result from pool behavior and substrate contamination. Methods of minimizing these defects range from in-process controls to post-coating processing. Current development areas for improved processing techniques such as gas randomization and ion plating should result in further improvements and elimination of some present post-coating processing requirements.
IGFET Inverter Circuits made with Electron Lithography
Authors: Pease R. F. W. , Henderson R. C. , Dalton J. V.
Published: July 2002

In IGFET circuitry, it has been predicted that halving the lateral dimensions should bring about approximately a fourfold speed advantage; providing doping levels, vertical dimensions, and applied voltages are constant. We have used electron lithography to make p-channel IGFET inverter circuits with 9- and 4-μ gates and have demonstrated a sixfold improvement in the propagation delay for smaller circuits. The devices were made using a refractory metal and ion implantation as described by Moline et al., and by Boll and Lynch. (IEDM, Washington, 1972). The electron resist (used for all four lithographic stages) was much more sensitive than polymethylmethacrylate.
Electron-Beam Fabrication of Ion Implanted High-Performance FET Circuits
Authors: Fang F. , Hatzakis M. , Ting C. H.
Published: July 2002

This paper describes the design, fabrication and test results of a high-performance IGFET circuit made by combining electron-beam technology for all masking steps and ion implantation for the diffusion steps. The circuit consists of an eleven stage ring oscillator with two FET devices per stage. The enhancement mode device is the switching element and the depletion mode is used as load. The aluminum gate length of the devices is 1 μ and the width is 5 μ. The aluminum metallization, defined with electron-beam exposure of PMMA resist, also serves as a self-aligning mask for the ion implantation of source and drain in the gate region. The average delay per stage was determined by measuring the periodicity of the circuit oscillation and dividing by 22. Test results on several circuits indicate that the average delay per stage is approximately 295 psec.
Processes for multilevel metallization
Authors: Vossen J. L. , Schnable G. L. , Kern W.
Published: July 2002

Film deposition and etching techniques for producing multilevel metallized structures on complex devices are reviewed. Emphasis is placed on process procedures for controlled contouring of topographic features induced during pattern etching, techniques for ensuring coverage by deposited films of topography introduced into the substrate, and dielectric deposition procedures that enhance breakdown strength and minimize pinholes. Broadly, the classes of processes discussed are the following: (i) metallization techniques that reduce susceptibility to electromigration and hillock formation and that ensure step coverage; (ii) dielectric deposition techniques that result in good step coverage, low stress, and low pinhole density; (iii) photolithographic and etching techniques that can taper steps generated in the films and that do not form pinholes.
Metal powder production by vacuum atomization
Authors: Wentzell J. M.
Published: July 2002

The problems inherent in metal atomization have spurred the development of vacuum atomization, a process showing much promise. In this process, the potential energy for atomization can be stored within the molten metal, which increases the efficiency. Also, the higher tap densities of vacuum-atomized powders, as compared with argon-atomized powders, is a distinct advantage. Alloy powders based on Ni, Co, Fe, Cu, Al, and misch metal have all been made successfully by this process. Powder metallurgy will play a significant role in this era of conservation and cost reduction, and vacuum atomization has shown that the unconventional approach may offer the most practical solutions to some of our current problems.
Charge induced pattern distortion in low energy electron beam lithography
Authors: Satyalakshmi K. M. , Olkhovets A. , Metzler M. G. , Harnett C. K. , Tanenbaum D. M. , Craighead H. G.
Published: July 2002

Charge induced pattern distortions in low voltage electron beam lithography in the energy range of 1 to 5 kV were investigated. Pattern distortion on conducting substrates such as silicon was found to be small, while significant pattern placement errors and pattern distortions were observed in the case of electrically insulating substrates caused by charge trapping and deflection of the incident electron beam. The nature and magnitude of pattern distortions were found to be influenced by the incident electron energy, pattern size, electrical conductivity, and secondary electron emission coefficient of the substrate. Theoretical modeling predicts the electron beam deflection to be directly proportional to the trapped surface charge density and inversely proportional to the accelerating voltage.
Characteristics and mechanism of etch process sensitivity to chamber surface condition
Authors: Xu Songlin , Sun Zhiwen , Qian Xueyu , Holland John , Podlesnik Dragan
Published: July 2002

Process variation with chamber surface condition in high density plasma reactors can seriously affect the process performance and productivity of device manufacturing. In this work, the impact of chamber surface coating on polycrystalline-silicon (polysilicon) gate etching with Cl2- and HBr-based plasma has been studied. The dependence of process sensitivity to surface coating on various processing conditions has been characterized and the mechanism of process shift has been analyzed. Based on the experimental results, the root cause of process sensitivity has been attributed to the change of surface recombination rate of free radicals on different chamber surfaces which leads to a variation in reactive neutral density. Under a certain discharge condition, the Cl and Br densities in a clean chamber with anodized aluminum and alumina surfaces are >60% lower than those in a seasoned chamber with silicon oxide deposition, resulting in lower polysilicon and oxide etch rate in the former case. In general, the process sensitivity to chamber surface condition depends on process regime and is higher for those processes where etching is more chemical in nature, such as processes at higher pressure and with Cl2-based chemistry. Processes with higher oxygen concentration and higher source power are also more sensitive due to the accelerating surface oxidation of polysilicon surface in a clean chamber. Approaches to reduce the effect of process sensitivity have been discussed.
Adsorption and reaction of ethene on oxide-supported Pd, Rh, and Ir particles
Authors: Frank Martin , Bäumer Marcus , Kühnemuth Ralf , Freund Hans-Joachim
Published: July 2002

Supported metal clusters and nanoparticles are of fundamental and technical interest, their use in heterogeneous catalysis being of particular importance. Yet on the atomic scale, there is only limited knowledge about the dependence of adsorption behavior and catalytic activity on particle size and morphology. In order to contribute to an understanding of such relationships in the case of hydrocarbon reactivity, we have studied the interaction of ethene with alumina-supported Pd, Rh, and Ir particles. Aggregates ranging in size from a few atoms up to several thousand atoms were prepared by metal vapor deposition onto a planar oxide support under ultrahigh vacuum conditions. The adsorption and dehydrogenation of ethene have been investigated by infrared and photoelectron spectroscopy. The infrared data reveal the formation of both π and di-σ bonded species upon adsorption at 90 K. On Pd, this involves a net charge transfer from the adsorbate to the metal, as shown by infrared spectra of co-adsorbed carbon monoxide. Upon heating to room temperature, the ethene adlayers on Rh and Ir deposits dehydrogenate to ethylidyne. In the case of Pd particles, this process is accompanied by the desorption of a particle-size-dependent fraction of the ethene.
Energy spectra of electrons in a dc glow discharge with a semitransparent anode
Authors: Pletnev Vladimir , Zukotynski Stefan
Published: July 2002

A numerical model for a planar dc discharge with a semitransparent anode positioned between two symmetrical cathodes is developed. The kinetic equation is solved iteratively by means of the direct Monte Carlo method. This approach makes it possible to find stationary particle fluxes and space-charge distributions with controlled precision. The numerical calculations are carried out for hydrogen, in which case the model can be well tested. The role of the semitransparency of the anode is investigated with respect to the formation of a space-charge layer and electron energy spectra. The conditions for a stable self-sustained discharged with a semitransparent anode are discussed. The energy spectra for electrons are found to be very far from equilibrium and to have peaks linked with the peculiarities of the inelastic electron–atom collisions at low energies. The possibility of controlling the electron energy spectra using the transparency of the anode is considered.
Growth of dense SiC films on Si at medium temperatures by pulsed laser deposition
Authors: Craciun Valentin , Lambers Eric , Bassim Nabil D. , Baney Ronald H. , Singh Rajiv K.
Published: July 2002

Thin SiC films were grown on (100) Si substrates by the pulsed laser deposition technique at medium temperatures. The influence of the substrate temperature, from 550 to 700 °C, and of the laser repetition rate upon film composition and optical properties has been investigated. Using a 2.5 J/cm2 laser fluence and a 10 Hz repetition rate, dense and finely crystalline SiC films exhibiting very good optical properties and containing less than 2% oxygen were grown at a substrate temperature of only 700 °C.
Chromium doped ZnO thin films deposited by chemical spray: Chromium effect
Authors: de la L. Olvera M. , Maldonado A. , Matsumoto Y. , Asomoza R. , Melendez-Lira M. , Acosta D. R.
Published: July 2002

The influence of chromium doping on the physical properties of ZnO thin films, deposited by the chemical spray technique, is presented. In particular, we have studied the chemical stability of ZnO:Cr as a function of chromium concentration on the starting solution. Although, according to x-ray diffraction measurements, the Cr incorporation into the films remains below 1 at. % for all the concentrations used, a notorious influence is observed on the etching rate, the crystalline orientation, and the surface morphology. The resistivity of the as-deposited films is of the order of 104 Ω cm. After a vacuum annealing at 400 °C its magnitude decreases at around 103 Ω cm. The films show a high transmittance, about 80% at 550 nm, irrespective of the Cr concentration used in the starting solution.
Electrical characteristics of nitrogen incorporated hydrogenated amorphous carbon
Authors: Magill D. P. , Ogwu A. A. , McLaughlin J. A. , Maguire P. D. , McCullough R. W. , Voulot D. , Gillen D.
Published: July 2002

Nitrogen incorporation into hydrogenated amorphous carbon (a-C:H) films has recently attracted a wide range of interest due to its contribution in reducing film stress and improving field emission properties. In this work we characterize the electrical properties of nitrogen containing a-C:H films. The a-C:H films were prepared by plasma enhanced chemical vapor deposition in an acetylene (C2H2) environment with a range of bias voltages. Nitrogen incorporation was achieved by exposing the films to an atomic nitrogen flux from a rf plasma with up to 40% dissociation and atomic nitrogen fluxes of up to 0.85×1018 atoms s−1. Raman results indicate that the doping process is accompanied by some structural changes seen by the G-band peak shifts. X-ray photoelectron spectroscopy spectra suggest that the dopant levels exceed those previously reported. Capacitance probe and I–V techniques showed a decrease in contact potential difference and density of states for doped films, indicating a rise in the Fermi level.
Contact-pressing metallization
Authors: Khang Dahl-Young , Lee Hong H.
Published: July 2002

Direct contact-pressing metallization is introduced and demonstrated as a method for metallization. In this contact-pressing metallization, a free sheet of metal or a deposited film supported on a polymer-coated carrier wafer is placed on a substrate with contact or via holes and then pressed against the substrate between the platens of a hydraulic press. Plastic deformation caused by high temperature pressing is the mechanism by which the holes are filled. This conceptually simple and yet effective method can be an alternative to other metallization techniques.
Deep plasma etching of piezoelectric PZT with SF6
Authors: Bale M. , Palmer R. E.
Published: July 2002

Reactive ion etching with sulfur hexafluoride (SF6) gas has been employed to create deep structures in bulk samples of the piezoelectric material lead zirconate titanate, Pb(Zr,Ti)O3 (PZT). SF6 is chosen for compatibility with dry etching of silicon with a possibility for production of hybrid silicon-piezoelectric devices. Thick photoresist layers have been used to pattern PZT to a depth of 2 μm at a rate of 120 nm min−1. The use of more durable nickel masks, formed by electroplating through the thick resist, leads to structures greater than 100 μm in height, with an average sidewall angle of ∼72°. The profile of the deep PZT structures is seen to depend on etch duration and the spacing of structures, attributed to the redeposition of mask and etch products, respectively. The addition of nitrogen and argon to the SF6 plasma is shown to produce small improvements in the profiles. By combining gas addition with heating of the substrate PZT etch rates up to 200 nm min−1 have been obtained.
Hands-on tools for nanotechnology
Authors: Seeger A. , Paulson S. , Falvo M. , Helser A. , Taylor R. M. , Superfine R. , Washburn S.
Published: July 2002

We describe some mechanical and electrical measurements on carbon nanotubes. We discuss electron beam lithography techniques to form metal wire contacts to the as-found nanometer structures. Starting from a unique collaborative perspective, we suggest some improved design and alignment methods.
Influence of the elemental composition and crystal structure on the vacuum properties of Ti–Zr–V nonevaporable getter films
Authors: Benvenuti C. , Chiggiato P. , Mongelluzzo A. , Prodromides A. , Ruzinov V. , Scheuerlein C. , Taborelli M. , Lévy F.
Published: July 2002

Nonevaporable thin film getters based on the elements of the fourth and fifth columns of the periodic table were deposited by sputtering. Among the some 20 alloys studied to date, the lowest activation temperature (about 180 °C for a 24 h heating) was found in the Ti–Zr–V system with a well-defined composition range. Characterization of the activation behavior of such Ti–Zr–V films is presented. The evolution of the surface chemical composition during activation is monitored by Auger electron spectroscopy and the functional properties are evaluated by pumping speed measurements. The pumping speed characteristics are quite similar to those already measured for commercially available nonevaporable getter materials, except for the much lower saturation coverage for CO. This inconvenience, which is due to the smooth surface structure of these films, can be counteracted by increasing the roughness of the substrate.
Electron optics using multipole lenses for a low energy electron beam direct writing system
Authors: Yamazaki Yuichiro , Nagano Osamu , Hashimoto Susumu , Ando Atsushi , Sugihara Kazuyoshi , Miyoshi Motosuke , Okumura Katsuya
Published: July 2002

The Coulomb interaction is the dominant factor respecting the electron optical properties, and its dominance is particularly marked in the case of the low energy electron beam direct writing system. To reduce the Coulomb interaction contributions, we propose a concept: the use of a multipole electron optical system providing a nonrotationally symmetric cross section of the electron beam. The system consists of an illumination optics, character projection apertures, an imaging optics providing the electrostatic quadrupole quadruplets and deflectors with the optics length of 100 mm. The optical properties are optimized under the following conditions: main deflection field size of 0.5 mm×1.5 mm, beam convergence angle on the wafer of 1 mrad, shot size of 5 μm square, beam voltage of 5 kV, and reduction ratio of 10. The blur due to the Coulomb interaction is estimated using Monte Carlo simulation with a thin lens approximation. The calculated Coulomb blur can be reduced to less than 60 nm in the x–z plane and 20 nm in the y–z plane, which are small in comparison with the 700 nm blur of the conventional optics, because the round crossover with high charge density does not exist in the beam path of the imaging optics. Moreover, by providing the nonrotationally symmetric illumination optics, the Coulomb blur is further reduced to 20 nm or less when the illumination angle ratio is greater than 10.
Retention of neon in graphite after ion beam implantation or exposures to the scrape-off layer plasma in the TEXTOR tokamak
Authors: Kim Y. M. , Philipps V. , Rubel M. , Vietzke E. , Pospieszczyk A. , Unterberg B. , Jaspers R.
Published: July 2002

The interaction of neon ions with graphite was investigated for targets either irradiated with ion beams (2–10 keV range) or exposed to the scrape-off layer plasma in the TEXTOR tokamak during discharges with neon edge cooling. The emphasis was on the influence of the target temperature (300–1200 K) and the implantation dose on the neon retention and reemission. The influence of deuterium impact on the retention of neon implanted into graphite has also been addressed. In ion beam experiments saturation is observed above a certain ion dose with a saturation level, which decreases with increasing target temperature. The temperature dependence of the thermal desorption corresponds to an apparent binding energy of about 2.06 eV. The retention of neon (CNe/CC) decreases with increasing ion energy with values from 0.55 to 0.15 following irradiation with 2 and 10 keV ions, respectively. The reemission yield during the irradiation increases with target temperature and above 1200 K all impinging ions are reemitted instantaneously. The retention densities measured using the sniffer probe at the TEXTOR tokamak are less than 1% of the total neon fluence and are over one order of magnitude smaller than those observed in ion beam experiments. The results are discussed in terms of different process decisive for ion deposition and release under the two experimental conditions.
Practical approach for modeling extreme ultraviolet lithography mask defects
Authors: Gullikson E. M. , Cerjan C. , Stearns D. G. , Mirkarimi P. B. , Sweeney D. W.
Published: July 2002

An approximate method is proposed to calculate the extreme ultraviolet (EUV) scattering from a defect within a multilayer coating. In this single surface approximation (SSA) the defective multilayer structure is replaced by a single reflecting surface with the shape of the top surface of the multilayer. The range of validity of this approximation has been investigated for Gaussian line defects using two-dimensional finite-difference-time-domain simulations. The SSA is found to be valid for sufficiently low aspect ratio defects such as those expected for the critical defects nucleated by particles on the mask substrate. The critical EUVL defect size is calculated by combining the SSA with a multilayer growth model and aerial image simulations. Another approximate method for calculating the aerial image of an unresolved defect is also discussed. Although the critical substrate defects may be larger than the resolution of higher numerical aperture cameras, the point defect approximation provides a useful framework for understanding the printability of a wide range of defects.
I–V characteristics of thin-film gated photocathodes for electron-beam lithography
Authors: Pei Z. , Berglund C. N.
Published: July 2002

Thin-film photocathodes have been proposed for high-throughput multi-electron-beam lithography applications. In these approaches, arrays of independently modulated sources are achieved by varying the incident light energy reaching each photocathode. For many applications, however, the optical complexity of such a scheme limits the attractiveness of the photocathode approach. To resolve most of these complex concerns, a novel gated photocathode structure had been proposed, which allows each electron beam to be modulated independently and extinguished completely by applying several volts of negative voltage to the gate relative to that to the cathode. In this article we present a study of the detailed I–V characteristics of the thin-film gated photocathode structure. A typical I–V characteristic from any one of ten gated photocathodes fabricated with different geometrical configurations shows three clearly defined regions. In region I, currents are zero when the gate voltage is less than the negative extinction gate voltage. In region II, the cathode and the anode current increase with the gate voltage. The gate current is constant and its magnitude is much smaller than that of the anode current. In region III, all of the currents increase with the gate voltage but more slowly than in region II. The effects of the gate diameter, the insulator layer thickness, and the accelerating field on these parameters have also been examined. A theoretical model has been developed to explain the results. The calculated I–V curves are in good agreement with the experimental curves.
Template-directed vapor–liquid–solid growth of silicon nanowires
Authors: Lew Kok-Keong , Reuther Cordula , Carim Altaf H. , Redwing Joan M. , Martin Benjamin R.
Published: July 2002

The synthesis of Si nanowires in nanoporous anodic alumina membranes was demonstrated using a combination of Au electrodeposition and vapor–liquid–solid growth at 500 °C using SiH4 as the Si source. The average diameter of the nanowires was 200±54 nm which was close to the pore size distribution of the membranes. High-resolution transmission electron microscopy revealed that the nanowires consist of a crystalline Si core, oriented in the 〈100〉 or 〈211〉 growth direction, with a thin (<3 nm) native oxide coating. In this process, Au terminates both ends of the growing wires, resulting in the formation of Au–Si–Au nanowires.
Low turn-on voltage Mo-polycide field emitter arrays applied to field emission flat panel display
Authors: Uh Hyung Soo , Park Sang Sik , Lee Jong Duk
Published: July 2002

As an attempt to develop field emission flat panel displays, gated Mo-polycide field emitter arrays (FEAs) have been designed and successfully fabricated. The field emission display (FED) using these FEAs eliminates the difficulty of achieving well-to-well isolation that is considered as one of the most serious problems of silicon-based FED. The fabricated Mo-polycide FEAs were applied to a 0.7 in. diagonal monochrome FED composed of 25×25 pixels. Each pixel consists of 25×25 tips. At an anode voltage of 200 V dc and a gate voltage of 60 V with duty of 1/3, the anode current of several hundred nanoamperes per pixel was obtained from vacuum-sealed Mo-polycide FEAs. Emission tests in various vacuum environments revealed that the electron emission was reduced as the vacuum was degraded and estimated vacuum inside panel was 1.0×10−6, 1.2×10−5, and 2.9×10−6 Torr at pre-seal-off, post-seal-off, and after getter activation, respectively. Alphabetical characters can be displayed on the FED panel using driver circuits which are able to drive 640×480 pixels. The produced images have demonstrated a luminance of up to 70 cd/m2 at an anode voltage of 200 V and were degraded over time. The degradation of the luminescence seemed to be related with the Coulombic aging and burn-in of the phosphor, which could be indirectly confirmed from the microscopic picture of the FED phosphor screen showing burn-in of the phosphor which was observed on the spots with special brightness.
Optical and Structural Properties of Oxidized Titanium Films
Authors: Arntz Floyd , Chernow Fred
Published: July 2002

This paper is concerned with the properties of evaporated titanium films and their oxides. Thin films of titanium (100 to 500 Å) were evaporated at pressures below 5 × 10−9 Torr and subsequently oxidized. Amorphous quartz and single crystals of alkalai halides and CaF2 were used as substrates. Evaporations were performed at substrate temperatures in a range from 25 ° to 500 °C. The structures of the films were investigated prior to, during, and following oxidation by employing reflection electron diffraction. The uv transmission spectra of the oxidized films were taken after removing them from the vacuum chamber.
Use of a Cooled Quartz Crystal Microbalance to Study the Molecular Flow and Condensation of CO2 in Vacuum
Authors: Baker M. A. , Holland L.
Published: July 2002

The molecular condensation rate and condensation characteristics of a collimated molecular beam of carbon dioxide were determined using a h.f. crystal microbalance. The CO2 molecules were condensed on a quartz vibrator cooled with liquid nitrogen. An analysis was made of the contributions to the total condensation rate of the preferred and randomized gas flows using different crystal positions and orientations. Molecular intensity distribution of the CO2 beam was measured with the quartz vibrator mounted on a probe which traversed the beam. The effect of different angles of beam incidence on the condensation rate was studied by rotating the quartz vibrator in a uniform part of the beam. The results showed deviations from the cosine law after initial condensation at non-normal incidence. The condensation followed the cosine law for thick deposits and this was attributed to incident molecules making several collisions in a porous layer.
Poly(butene-1 sulfone) —A highly sensitive positive resist
Authors: Bowden M. J. , Thompson L. F. , Ballantyne J. P.
Published: July 2002

The positive electron resist poly(butene-1 sulfone) (PBS) has been reported previously. As with other electron resists, sensitivity has been shown to be dependent on a number of processing parameters such as accelerating voltage, developer, developer solvent, and polymer characteristics (namely, molecular weight, molecular weight distribution, etc.). Previous reports have involved resist samples and conditions resulting in sensitivities within the range of 4–6×10−6 C/cm2 at 10 kV. For certain uses, for example, on the Bell Laboratories electron beam exposure system (EBES), a sensitivity of better than 1×10−6 C/cm2 at 10 kV is desired for efficient operation. Recent studies involving samples of varying molecular parameters verify feasibility of sensitivities of 7–8×10−7 C/cm2 at 10 kV for carefully controlled molecular weight and molecular weight distribution. As expected, processing of PBS at this sensitivity requires careful attention to polymer dissolution mechanisms. An ideal developing system should dissolve the irradiated region while hardly swelling the unirradiated region. This requires a developing solvent to be kinetically poor but thermodynamically good. Swelling and loss of resolution can occur when these conditions are not fulfilled.
Deep uv lithography
Authors: Lin Burn Jeng
Published: July 2002

Using deep-uv light ranging from 2000 to 2600 Å, submicrometer patterns in photoresist with height-to-width aspect ratios as high as 15 can be achieved. The well known electron-beam positive resist, polymethyl methacrylate (PMMA), is used as the deep-uv photoresist. Its optical absorption coefficient, dissolution rate, and sensitivity are given in the deep-uv wavelength region. Its absorption coefficient, being a factor of two lower than that of AZ 1350J, makes it suitable for deep penetration of submicrometer-wide beams. The negligible sensitivity at wavelengths longer than 2600 Å eliminates the need for an expensive filter. Both Xe–Hg arc lamps and deuterium spectral lamps have been used to expose the resist. Chrome or aluminum masks on quartz or sapphire substrates were found satisfactory. Chevron patterns of 1.6 μm width and 0.4 μm spacing and Y–I bars of 1.6 μm width and 0.2 μm gaps were printed in 3 μm of PMMA 2041, as well as Y–I bars of 0.5 μm width and 0.25 μm gaps in 1.78 μm of PMMA 2041. The exposure time in both cases was below 10 min.