bluuebunny/crossref_metadata_2025 huggingface dataset:
Aerodynamic Analysis of Multistage Turbomachinery Flows in Support of Aerodynamic Design
Authors: Adamczyk John J.
Published: July 2002

This paper summarizes the state of 3D CFD based models of the time-averaged flow field within axial flow multistage turbomachines. Emphasis is placed on models that are compatible with the industrial design environment and those models that offer the potential of providing credible results at both design and off-design operating conditions. The need to develop models free of aerodynamic input from semiempirical design systems is stressed. The accuracy of such models is shown to be dependent upon their ability to account for the unsteady flow environment in multistage turbomachinery. The relevant flow physics associated with some of the unsteady flow processes present in axial flow multistage machinery are presented along with procedures that can be used to account for them in 3D CFD simulations. Sample results are presented for both axial flow compressors and axial flow turbines that help to illustrate the enhanced predictive capabilities afforded by including these procedures in 3D CFD simulations. Finally, suggestions are given for future work on the development of time-averaged flow models. [S0889-504X(00)02002-X]
Comparison of Different Acceleration Techniques and Methods for Periodic Boundary Treatment in Unsteady Turbine Stage Flow Simulations
Authors: von Hoyningen-Huene Martin , Jung Alexander R.
Published: July 2002

This paper studies different acceleration techniques for unsteady flow calculations. The results are compared with a nonaccelerated, fully explicit solution in terms of time-averaged pressure distributions, the unsteady pressure and entropy in the frequency domain, and the skin friction factor. The numerical method solves the unsteady three-dimensional Navier–Stokes equations via an explicit time-stepping procedure. The flow in the first stage of a modern industrial gas turbine is chosen as a test case. After a description of the numerical method used for the simulation, the test case is introduced. The purpose of the comparison of the different numerical algorithms for explicit schemes is to facilitate the decision as to which acceleration technique should be used for calculations with regard to accuracy and computational time. The convergence acceleration methods under consideration are explicit time-stepping with implicit residual averaging, explicit time-consistent multigrid, and implicit dual time stepping. The investigation and comparison of the different acceleration techniques apply to all explicit unsteady flow solvers. This paper also examines the influence of the stage blade count ratio on the flowfield. For this purpose, a simulation with a stage pitch ratio of unity is compared with a calculation using the real ratio of 78:80, which requires a more sophisticated method for periodic boundary condition treatment. This paper should help to decide whether it is crucial from the turbine designer’s point of view to model the real pitch ratio in unsteady flow simulations in turbine stages. [S0889-504X(00)00702-9]
Control of Wave Propagation in Periodic Composite Rods Using Shape Memory Inserts
Authors: Ruzzene M. , Baz A.
Published: July 2002

Longitudinal wave propagation is controlled using shape memory inserts placed periodically along rods. The inserts act as sources of impedance mismatch with tunable characteristics. Such characteristics are attributed to the unique behavior of the shape memory alloy whereby the elastic modulus of the inserts can be varied up to three times as the alloy undergoes a phase transformation from martensite to austenite. With such controllable capability, the inserts can introduce the proper impedance mismatch necessary to impede the wave propagation along the rods. An analytical model is presented to study the attenuation capabilities of the composite rods and to determine the influence of the various design parameters of the inserts that can control the width of the pass and stop-bands. The numerical results demonstrate the potential of shape memory alloys in controlling the dynamics of wave propagation in rods. Furthermore, the obtained results provide a guideline for designing inserts that are capable of filtering out selected excitation frequencies through proper adjustment of the geometry of the inserts as well as their activation strategies. [S0739-3717(00)00102-1]
Single Crystal CuInSe2 Analysis by High Resolution XPS
Authors: Sobol P. E. , Nelson A. J. , Schwerdtfeger C. R. , Stickle W. F. , Moulder J. F.
Published: July 2002

Copper indium selenide (CIS) is a material commonly used in photovoltaic devices. High resolution XPS spectra are obtained from a freshly fractured single crystal CIS sample. Spectra include Cu 2p, In 3d and Se 3d core lines along with valence band and survey spectra.
Sputter Deposited Aluminum Nitride on Si(111)
Authors: Chourasia A. R. , Chopra D. R. , Hatwar T. K.
Published: July 2002

A thin film of aluminum nitride was deposited on Si(111) by reactive rf magnetron sputtering. The sputtering was carried out from a Al target (99.999%purity) in an Ar and N2 atmosphere. The films are analyzed by x-ray photoelectron spectroscopy. The films were also characterized by transmission electron microscopy, transmission electron diffraction and x-ray diffraction.
A Polycrystalline Diamond Film by XPS
Authors: Vasquez Richard P.
Published: July 2002

High resolution XPS measurements of the C 1s, including energy losses and the valence band regions, are presented for a polycrystalline diamond film. These spectra are useful for comparison to the graphite and C60 forms of carbon.
InAs(110) by XPS
Authors: Poirier D. M. , Weaver J. H.
Published: July 2002

XPS spectra were recorded for the InAs(110) surface. For comparison, data were acquired for a sample cleaved in situ (Accession #00107) and for a sample exposed to air for 60 min (Accession #00108). The electronic record includes the In 4d, As 3d, In 3d, As LNN, In MNN, and the valence band region.
Interaction of alcohols with a-CHx films
Authors: Shukla Nisha , Gellman Andrew J.
Published: July 2002

Temperature programed desorption has been used to study the desorption kinetics and desorption energies of a set of alcohols and fluorinated alcohols adsorbed on an a-CHx film. The alcohols serve as models for the hydroxyl end groups of Fomblin Zdol, the lubricant most commonly used with the amorphous carbon overcoats sputtered onto the surfaces of magnetic data storage disks. Temperature programed desorption has been used to measure the desorption energies of the alcohols over a range of coverages and to compare the desorption energies of fluorinated and hydrocarbon alcohols. The desorption energies are all coverage dependent and decrease with increasing alcohol coverage. This is believed to be due to heterogeneity of the a-CHx films surface. In all cases the low coverage desorption energies of the fluorinated alcohols were found to be higher than those of their hydrocarbon counterparts. The implications of this observation are that the interaction of the alcohols is through hydrogen bonding of the hydroxyl groups to the a-CHx films. This conclusion is consistent with that reached in a similar study of the adsorption of alcohols to the surfaces of a-CNx films.
Composition and Structure of Sputtered Films of Ferroelectric Niobates
Authors: Foster N. F.
Published: July 2002

Thin films of several niobate materials have been deposited by dc sputtering onto gold-plated fused-quartz substrates at temperatures up to 600 °C. The sputtering targets were pressed disks made in some cases from the pre-reacted ferroelectric niobate powder and in other cases from a mixture of the appropriate reactants. The structure of the resulting films was examined by x-ray diffraction and the composition by electron microprobe analysis. At sufficiently high substrate temperatures the films all showed well-defined crystal structures, although many of them were nonstoichiometric, being rich in Nb2O5. The loss of the more volatile components was in some cases compensated by increasing the percentage of these components in the target. Some of the films showed piezoelectric activity, but the effective piezoelectric coupling was very low.
Film Deposition by Molecular-Beam Techniques
Authors: Cho A. Y.
Published: July 2002

A review of molecular-beam epitaxy of GaAs and the observation of surface structures with high-energy electron diffraction in an ultrahigh-vacuum system is described. The utilization of these surface structures as growth conditions to produce n- and p-type layers when doped with Sn, Ge, and Mg, and the electrical and optical evaluations of the layers thus grown is also discussed. The molecular-beam epitaxy method may be used to fabricate extremely thin multilayer structures and may play an increasing role in semiconductor technology.
Thickness Distribution and Step Coverage in a New Planetary Substrate Holder Geometry
Authors: Behrndt Klaus H.
Published: July 2002

Thickness distribution and step coverage are calculated for a new planetary substrate holder geometry in which the substrate surface is vertical. Results for the new geometry are compared with those for arrangements presently in use. Substantial improvements can be obtained simultaneously for thickness uniformity, step coverage, and batch size in the new geometry. For example, maximum-to-minimum thickness variation is 0.4% on 10-in. platens in a 24-in. bell jar. Step coverage in the vicinity of 100% can be attained. The batch size with vertical platens may exceed that with horizontal ones by a factor of up to 3 in the same bell jar. Eccentric sources may be used in the new geometry to decrease cusp formation in the vicinity of steps without loss of uniformity of thickness distribution.
Novel alignment system for imprint lithography
Authors: White D. L. , Wood O. R.
Published: July 2002

A novel alignment system for imprint lithography in the deep sub-hundred nanometer realm is proposed. The new system is inherently more precise than the alignment systems used in conventional projection lithography because alignment marks on an imprint mold (the functional equivalent of a photomask in projection lithography) are directly compared to alignment marks on a wafer with no intermediate optics or reference points. If the measured misalignment is so severe that all marks cannot be brought into registration simultaneously by the usual x–y translations and rotations, the mold is deliberately deformed with a system of piezoelectric actuators in such a way that its induced distortions precisely match those on the wafer and all of the alignment marks at each chip site can be pulled into registration simultaneously. Finite-element analysis indicates that using actuators to distort the mold is superior to distorting the wafer.
Multisource optimization of a column for electron lithography
Authors: Mankos M. , Coyle S. , Fernandez A. , Sagle A. , Allen P. , Owens W. , Sullivan J. , Chang T. H. P.
Published: July 2002

The optimization of key parameters determining the performance of a multisource electron column is discussed. A 50 keV multisource test bed incorporating a photocathode and multiple modulated light beams has been developed and tested. The multisource test bed allows for a detailed evaluation of both the photocathode sources and the electron optics for sub-100 nm lithography applications and is designed to reduce electron–electron interactions. Results have been obtained using cesiated GaAs negative electron affinity and gold photocathodes at beam energies varying from 10 to 50 kV, allowing the experimental evaluation of key design parameters.
Study of surface chemical changes and erosion rates for CV-1144-O silicone under electron cyclotron resonance oxygen plasma exposure
Authors: Yan Li , Gao Xiang , Bungay Corey , Woollam John A.
Published: July 2002

CV-1144-O silicone thin films were irradiated in an electron cyclotron resonance oxygen plasma, which is a simulation of the low earth orbital environment. A crude equivalence between this plasma system and the low earth orbital environment was determined by measuring Kapton weight loss in the plasma and comparing to Kapton weight loss in space experiments. Changes in optical properties and erosion rates under ultraviolet light and atomic oxygen radiation were studied using in situ spectroscopic ellipsometry (SE). The erosion rate at the beginning of the plasma exposure was significantly faster than that at later stages. Approximately one third of the total silicone thickness was etched away within 1 h, which according to the equivalence experiment, corresponds to about two months in low earth orbit. The refractive index of silicone in the visible range increased during the exposure, indicating that the film was being densified. Optical constants (both before and after plasma exposure) were determined by ex situ spectroscopic ellipsometry in the ultraviolet–visible–near-infrared (0.7–8.5 eV) and IR (200–7000 cm−1) ranges. Also, SE was used to map thickness and uniformity before and after radiation. Regression fits using Lorentzian and Gaussian oscillators as parametric models for the optical constants were excellent, and the major absorption peaks in the IR region were identified. The before- and after-radiation spectra showed significant decreases in CH3-associated peaks and increases in SiOx-associated peaks.
Ion energy distributions in a pulsed, electron beam-generated plasma
Authors: Walton S. G. , Leonhardt D. , Blackwell D. D. , Fernsler R. F. , Murphy D. P. , Meger R. A.
Published: July 2002

In this work, we investigate the ion flux at a grounded electrode located adjacent to a pulsed, argon plasma generated by a high-energy electron beam. The plasmas, produced in 100 mTorr, are characterized by high plasma densities (>1011 cm−3) and low electron temperatures (<1.5 eV). An energy selective mass spectrometer was used to measure temporally resolved ion kinetic-energy distributions at the electrode surface. In addition, ion energy distributions are presented for various electrode locations. The ion energy distributions correlate well with Langmuir probe measurements of the plasma potential.
Summary of quick disconnect vacuum flanges
Authors: Mapes M.
Published: July 2002

In accelerator environments, especially proton machines, high background radiation necessitates the need for quick disconnect vacuum flanges. The use of quick disconnect vacuum flanges significantly reduces the dose of radiation received by workers when installing or removing vacuum chambers in the accelerator. Over the course of many years there have been many designs used for these flanges at Brookhaven National Laboratory for such machines as the Alternating Gradient Synchrotron (AGS), the AGS Booster, and the Relativistic Heavy Ion Collider. Several different flanges with apertures as large as 14 in. in diameter were also evaluated for use in the Spallation Neutron Source project. A summary of various quick connect flanges as well as some commercially available flanges and the evaluation results are presented.
Scanning spreading resistance microscopy study of a metalorganic chemical vapor deposited grown InP optoelectronic structure
Authors: Dixon-Warren St. J. , Lu R. P. , Ingrey S. , Macquistan D. , Bryskiewicz T. , Smith G. , Bryskiewicz B.
Published: July 2002

Scanning spreading resistance microscopy (SSRM) is a promising new tool for dopant profiling in semiconductor materials. We present the results of a SSRM study of the cross section of a metalorganic chemical vapor deposited grown optoelectronic structure. The SSRM measurements are compared with the secondary ion mass spectrometry (SIMS) and excellent spatial agreement is obtained. However, we find that obtaining quantitative agreement with SIMS is complicated by the differing nonlinear I-V characteristics of n- and p-type InP. The results suggest that obtaining quantitative agreement with SIMS would require calibration of each SSRM probe tip with both n- and p-type materials. The high spatial resolution of the technique is demonstrated by our ability to easily resolve the 17.5 nm quantum well and barrier layer structure of the device. The results suggest that the greatest strength of SSRM will be the delineation of complex buried semiconductor structures.
Trench etch processes for dual damascene patterning of low-k dielectrics
Authors: Jiang P. , Celii F. G. , Dostalik W. W. , Newton K. J. , Sakima H.
Published: July 2002

The use of dual damascene patterning for integration of Cu with low-k dielectric films has introduced new challenges for plasma etch processes. With a via-first dual damascene approach, an important issue for trench etch is defect formation (i.e., oxide ridges) around vias which can degrade device reliability. The use of low-k films as the dielectric material adds additional complexity and more limitation on the etch process parameters. This article discusses the development of etch processes that meet the special requirements for Cu/low-k dual damascene trench etch. All experiments were conducted in a medium-density TEL dipole ring magnet system. The dielectric film used here was an organosilicate glass (OSG). Using C4F8/N2/Ar chemistry, a trade-off was observed between etch rate and oxide ridge formation. The N2:Ar ratio was found to be the key parameter in controlling the severity of the oxide ridges, but eliminating the ridges using the N2:Ar ratio resulted in a low OSG etch rate and poor throughput. However, we found an alternative method which achieves a high OSG etch rate while maintaining critical dimension control and ridge-free conditions. The effect of various process parameters on the OSG etch rate and ridge formation is detailed. A comparison of experimental results against numerical simulations of C4F8-based bulk plasmas with varying gas flow ratios is also reported.
Surface treatment and characterization of PMMA, PHEMA, and PHPMA
Authors: Lim Hyuneui , Lee Yeonhee , Han Seunghee , Cho Jeonghee , Kim Kang-Jin
Published: July 2002

Poly(methylmethacrylate) (PMMA), poly(2-hydroxyethyl methacrylate (PHEMA), and poly(2-hydroxypropyl methacrylate) (PHPMA) were modified to improve the wettability by two techniques: plasma and plasma source ion implantation. The modified surfaces were characterized to investigate the dependence of the modification and hydrophobic recovery on the polymer structure. The differences obtained under optimal experiment conditions among the polymers were interpreted in terms of their polymer structures including the glass transition temperature. The surface free energy, calculated from the contact angle measurements, revealed that its polar component was a dominant factor in improving the wettability. The PSII treatment created more functional groups on the surface and extensively modified the polymer layer than the plasma treatment.
Capacitance sensor with sub-zeptofarad (<10−21 F) sensitivity for scanning capacitance microscopy
Authors: Tran T. , Oliver D. R. , Thomson D. J. , Bridges G. E.
Published: July 2002

In this article we compare several different configurations of capacitance sensors based on a coupled transmission line design. The performance of these designs is compared in a well-defined test fixture. Sensitivities as low as 0.71×10−21 F/√Hz have been measured. Sample loading and parasitic effects are discussed.
Role of low-temperature (200 °C) nitridation in the growth of GaN by plasma-assisted molecular-beam epitaxy
Authors: Namkoong Gon , Doolittle W. Alan , Brown April S. , Losurdo Maria , Capezzuto Pio , Bruno Giovanni
Published: July 2002

The effects of sapphire nitridation temperature on the properties of the GaN epitaxial layers grown by rf plasma-assisted molecular-beam epitaxy were investigated. It is found that a nitridation temperature as low as 200 °C acts as a singular point for producing a homogeneous AlN layer on the sapphire substrate. The optical and structural characteristics of GaN epitaxial layers were dramatically improved by exploiting a 200 °C nitridation temperature. Systematic characterization of the nitrided layer, using spectroscopic ellipsometry and x-ray photoelectron spectroscopy, reveals that the sapphire nitridation chemistry, specifically, AlN vs NO production, depends on the surface temperature. A temperature at 200 °C produces a smooth, uniform AlN layer with 6 Å thickness that is close to the critical thickness of AlN on sapphire substrate. This homogeneous AlN acts as diffusion barrier for oxygen during high-temperature growth, as confirmed with secondary ion mass spectrometry measurement. In contrast, a high-temperature nitridation produces a nonhomogenous AlN layer embedded with NO which provides a source for oxygen diffusion into the subsequent GaN epitaxial layer and induces the degraded GaN epitaxial layer. Therefore, improved GaN quality can be traced back to the chemistry of the nitridation.
Carbide formation on Nb surfaces during high−temperature H irradiation
Authors: Thomas G. J. , Bauer W.
Published: July 2002

We have observed the formation of ’’star−shaped’’ features ∠1−10 μ in size on the surfaces of Nb samples after implantation with 150 keV H at 975−1275 K. Depending on specific conditions of temperature, vacuum, and surface preparation, they are sometimes found only within the implanted region, and sometimes over the entire sample surface. Scanning and transmission electron microscopy, and scanning Auger analysis, indicate that the features are due to the formation of Nb2C precipitates. These results suggest that carbide growth can occur on Nb surfaces at high temperatures under CTR−like vacuum conditions, and that the formation of carbides can be enhanced in a radiation environment. This process can have important consequences on the use of Nb for CTR first wall applications.
Multiple−scattering Xα calculations on Al2O3 and Al2O2N
Authors: Brower K. L.
Published: July 2002

The one−electron energy level structure for single complexes of Al2O3 and Al2O2N are calculated using the multiple−scattering Xα method of Johnson. The results of our calculations on Al2O3 are in qualitative agreement with the band structure calculations of Douglas on α−Al2O3. The results of our calculations on the Al2O2N complex suggest that a nitrogen atom substituting for an oxygen atom in sapphire may act as an electron trap or, under either thermal or photon excitation, as an acceptor center. From our calculations the optical spectrum expected for a neutral Al2O2N complex in sapphire is predicted.
Digitally positioned mechanical stage
Authors: Pasiecznik J. , Reeds J. W.
Published: July 2002

A computer-controlled, servo-driven, vacuum X–Y stage has been built for electron-beam microfabrication. The stage travel is 5×5 cm. Slew speed is 0.75 cm/s. Balance time is less than 1 s for small motions. Repeatability of positioning has been determined to be 0.01 μm. Accuracy is 0.01 μm plus 0.005 μm/cm of stage travel (laser interferometer error). Backlash between the stage and the drive servo motors has been eliminated by utilizing special friction drive ’’lead screws’’ in place of conventional threaded lead screws and Mylar drive belts in place of gears. Bellows seals on the stage drive shafts are equipped with an auxiliary vacuum pump to reduce air pressure loading on the servo drive system. Stage position is sensed by means of a two-axis He–Ne laser interferometer which reflects the sensing laser beams from a precision optical ’’true square’’ mounted on the stage. For each axis, a digital servo stores a 24-bit position command generated by a computer, and compares this desired position with the actual position sensed by the laser interferometer. If the digital position error exceeds 12 bits, a maximum output to the servo motor causes it to move at slewing velocity. When the error is less than 12 bits, a digital-to-analog converter generates an analog signal proportional to the digital errors and feeds it to the servo motor. A zero speed detector circuit and an error tolerance comparator indicate when the stage is stopped within preset accuracy requirements. The tolerance comparator output may also be used to correct the electron beam position if it is desired to begin exposure before the stage has settled. Servo damping is provided by means of tachometer generator coupled to the servo motor.
Quantitative depth profiling analyses of the surface layer in Be–Cu dynodes
Authors: Nakao Fusafumi , Birakawa Masahiro , Yamamoto Terumasa
Published: July 2002

A programmable SIMS instrument was developed and used to perform accurate depth profiling analyses of an activated Be–Cu alloy. The instrument offers information at every 75 Å under typical ion bombarding conditions, 0.3 μA of 8 keV 40Ar+. Analytical results showed that the BeO of 10 wt. % or more is formed on the surface, which is composed of a reasonably homogeneous BeO layer with a thickness of the order of 300 to 500 Å. The BeO spreads out toward the inner layer and reaches 5000 Å or more. The Be concentration on the surface is less than 0.2 wt. %, but at a depth of more than 3000 Å it aapproximates the concentration of the mother body, about 1.9 wt. %.
Variable spot-shaped e-beam lithographic tool
Authors: Weber E. V. , Moore R. D.
Published: July 2002

The EL2 system was developed as a direct wafer writing e beam tool to be used for product and process development. EL2 is a high thruput, high resolution, fully automated tool that utilizes the variable spot shape technique as well as other design innovations. This paper will review the system architecture, design approach, system specifications, and results obtained with this system. The systems utilize a variable spot shaped column with a maximum spot size ranging from 2×2 μm to 4×4 μm adjustable in increments of 0.1 and 0.2 μm, respectively. Gun brightness and column alignment are maintained by a group of servos which maintain proper operating conditions. The spot is positioned via a raster deflection which can be up to 8 mm. A calibration technique is employed to insure deflection accuracy over long time periods. Overlay is achieved by scanning alignment marks in the four corners of fields and processing the backscattered electron signals to determine field adjustments. EL2 is capable of exposing over 10 wafers (2.25 in) per hour with 1.25-μm linewidths and 0.3-μm overlay (30). This is accomplished with 10-μC resist sensitivity and machine availability of about 80%.
Far infrared Faraday rotation in a two-dimensional electron gas
Authors: Piller Herbert
Published: July 2002

The Faraday rotation is a sensitive method for determining the effective mass of the charge carriers in a two-dimensional electron gas. At light frequencies much larger than the cyclotron frequency the Faraday rotation is independent of scattering. Faraday rotation, combined with transport measurements, allows a determination of the populations of the subbands and the subband energy separations in an inversion layer on p-Si (100). A metal-oxide-semiconductor (MOS) system will show an enhancement of the measured Faraday rotation because of multiple internal reflections of the light between the metal and substrate boundaries of the system. Our calculations give a twentyfold enhancement. The resonance Faraday rotation at light frequencies close or equal to the cyclotron frequency permits the determination of scattering parameters.
Video recording of low intensity CEMA images
Authors: Panitz J. A.
Published: July 2002

An assembly of TV components used to observe, record, and display low-light-level visual images is described. The system has been used to analyze static field-ion and transient field-desorption images from a CEMA detector operating in ultrahigh vacuum. (AIP)
Radio-frequency mass selective excitation and resonant ejection of ions in a three-dimensional quadrupole ion trap
Authors: Fulford John Edward , Nhu-Hoa Duong , Hughes Richard James , March Raymond Evans , Bonner Ronald Francis , Wong Gordon John
Published: July 2002

The three−dimensional quadrupole ion store (QUISTOR) has been employed as a reactor for the study of ion/molecule reactions using external mass analysis, and as an ion trap for the study of stored ion dynamics using either external mass or in situ resonant absorption. Excitation of the axial frequency component of ion motion is accomplished by application of small (∠1 V) RF potentials to an end−cap of the QUISTOR. The frequencies at which ion resonance is observed differ from those predicted by theory and are dependent upon trapped ion density. Thus, the frequency shift may be related to both the space charge within the QUISTOR and perturbation of the stability diagram. the simultaneous application of in situ resonance absorption and external mass analysis has been utilized in three separate studies. (1) In ionized argon, Ar+ has been ejected by resonance absorption and the rate constant for the subsequent partial charge reaction of Ar2+ with argon has been determined to be 4.8±1.6×10−12 cm3 molecule−1s−1. (2) In ionized 2−propanol at ∠0.1 Pa and 4 ms after the ionizing pulse, we have found the ambient space charge experienced simultaneously by nine ion species to be sensibly constant. (3) The coupling of precursor to product ions in ion/molecule reactions of the 2−propanol system has been investigated: this particular application closely resembles the double resonance technique in ion cyclotron resonance mass spectrometry.
Problems and prospects of compound semiconductor field-effect transistors
Authors: Wieder H. H.
Published: July 2002

The application of binary, ternary, and quaternary semiconducting III– V compounds for high frequency field-effect transistors (FETs) and microwave integrated circuits (ICs) presents hitherto unavailable options and challenging problems which arise from the inherent bulk and surface properties of these materials and of the interfaces between them and metal or dielectric overlayers. Although the depletion-mode (normally-on) Schottky barrier gate GaAs transistor is the older and, at this stage, more advanced technology, alternative approaches based primarily on insulated gate FETs and other materials such as InP, InxGa1−xAs, and InxGa1−xAsyP1−y have been demonstrated to have important advantages for enhancement type (normally-off) as well as depletion- and inversion-mode insulated gate FETs, a potential high frequency analog of the lower frequency silicon MOS technology. The problems and prospects of such devices and structures as well as those of a variety of Schottky barrier gate and heterojunction gate transistors will be discussed in terms of their surface and interface properties.
Mechanism of oxide film growth on GaAs by plasma anodization
Authors: Yamasaki K. , Sugano T.
Published: July 2002

The transport of oxygen in the oxide during anodization in oxygen plasma has been investigated using isotopic oxygen. The in-depth profiles measured by IMA for samples anodized in 16O2 and 18O2 indicates that oxygen does not move in the oxide. The growth rate K, which is limited by drift of ionic sites in the oxide, is represented by K=K0exp[−(q/kT)(Wi−ZbEox)] and the values of Wi and Zb have been obtained to be 1.5 ± 0.5 eV and 44 ± 16 Å, respectively, from the dependence of the growth rate and the electric field intensity in the oxide, Eox, on the current density and the substrate temperature during anodization. The current efficiency in anodization is independent of the oxidation time and the current density, but it increases with the substrate temperature and the electron temperature of the plasma. By the relationship between the growth rate and the plasma conditions, it has been concluded that oxidants are supplied from the plasma in the form of neutral atoms, and adsorbed oxygen atoms are ionized by electrons.
Trap studies on GaAs–Si3N4 interfaces
Authors: Schuermeyer F. L. , Singh H. P.
Published: July 2002

The dynamic properties of GaAs–Si3N4 interfaces in IGFET structures were studied. It was observed that the charging of the interface states with electrons is very fast and approximately 90% of the interface charge is trapped within 1 ns of charging time. The studies indicated that two processes contribute to the discharge of the surface states. When the active layer is totally depleted, mainly leakage currents from the SI GaAs substrate discharge the surface states. When the active layer is not totally depleted, thermal electron emission from the interface dominates the discharge of surface states. A surface state trap level of 0.71 eV was measured. Furthermore, charging of surface states in an area adjacent to the gate was studied and it was observed that the charging occurs while the transistor is pinched off. Finally, current flow through the Si3N4 film was studied and it was concluded that these currents are too small to account for charging and discharging of interface states.
Electron transmission probabilities through GaAs/strained GaAsP/GaAs(100) heterostructures
Authors: Osbourn G. C.
Published: July 2002

Results of a tight binding calculation of the transmission probabilities of electrons through GaAs/strained GaAsP/GaAs(100) heterostructures are presented. The GaAsP layer thicknesses considered are sufficiently thin that the GaAs/GaAsP lattice mismatch is accommodated by layer strain rather than dislocation generation. For layers with small GaP content, incident electrons in Bloch states near Γ can transport through the alloy in Bloch states that are also near Γ. Transmission probabilities are large and exhibit resonant (total) transmission at GaAsP layer thicknesses determined by the wavevector k of the accessible GaAsP Bloch states. For layers with large GaP content, incident electrons must either ’’tunnel’’ through the GaAsP evanescent states associated with the Γ minimum or undergo phononless intervalley transfer at the interface to the accessible Bloch states near X in GaAsP. For extremely thin GaAsP layer (less than a few lattice constants), the tunneling type process dominates. The phononless intervalley transfer process is found to occur with very small probability except for carrier energies and layer thicknesses corresponding to resonant transmission.
Emission characteristics of single-crystal LaB6 cathodes with 〈100〉 and 〈110〉 orientations
Authors: Furukawa Y. , Yamabe M. , Itoh A. , Inagaki T.
Published: July 2002

To investigate the total emission characteristics of single-crystal LaB6 cathodes, the dependence of brightness and emittance (the product of crossover size and beam divergence) on cathode tip curvature were measured. The smaller the radius of the tip curvature and the lower the tip temperature becomes, the lower the emission current at which angular emission anisotropy due to the lattice structure of LaB6 crystal appears. The emission of 〈110〉 LaB6 cathodes was found to be more affected by lattice structure than that of 〈110〉 LaB6 cathodes. To obtain a uniform distribution beam it is more advantageous to use 〈100〉 LaB6 cathodes than 〈110〉. Uniform angular emission were obtained with a 〈100〉 LaB6 cathode of 100 μm tip radius even at an emission current of 700 μA and a tip temperature of 1500 °C. Under these conditions, the measured brightness and emittance were 3.9×105 A/cm2 sr and 61 μm mrad, respectively.
The composition and structure of oxide films grown on the (110) crystal face of iron
Authors: Langell M. , Somorjai G. A.
Published: July 2002

Epitaxial oxide layers of Fe3O4-like composition and symmetry have grown on Fe(110) crystals exposed to oxygen gas. The epitaxial relationship between the oxide and the Fe(110) substrate is elucidated and the orientation of the oxide film has been explained in terms of the close registry between the Fe(110) and Fe3O4(111) crystal lattices. Both the structure and composition of the iron oxide epitaxies are a function of substrate temperature and oxygen pressure, and oxide formation has been observed over only part of the temperature–pressure range investigated. While oxide surfaces with Fe2O3-like composition have been observed, they are disordered and are only approximately one monolayer in thickness.
An apparatus for microsectioning diffusion samples by sputtering
Authors: Mundy J. N. , Rothman S. J.
Published: July 2002

A new sputtering apparatus for taking thin sections from solid-state diffusion samples is described. New features include the use of a Kaufman-type ion gun, high-yield chamber geometry, and a catcher-foil advance mechanism capable of taking 32 sections without breaking vacuum. The apparatus can also be used as a general laboratory facility for ion milling.
Background subtraction techniques in surface analysis
Authors: Grant J. T.
Published: July 2002

The data acquired from most surface analysis instrumentation are composed of two parts, (a) peaks of interest, and (b) a background. The background is usually regarded as a hindrance to data processing and various techniques have been developed to eliminate or reduce its effects. These methods include linear and integral background subtraction, signal differentiation, dynamic background subtraction, special modulation techniques, and deconvolution. This paper will review methods for background subtraction in secondary ion mass spectroscopy, ion scattering spectroscopy, x-ray photoelectron spectroscopy, and Auger electron spectroscopy.
Preparation and characterization of beryllium coatings
Authors: Dua A. K. , Agarwala R. P. , Desai P. B.
Published: July 2002

The application of low Z coatings on various structurally strong components of a controlled thermonuclear tokamak fusion reactor is expected to reduce the plasma contamination and power loss. With this view, coatings of beryllium have been given on different substrates like (304 and 316) stainless steel, monel-400, molybdenum, copper, and graphite in a specially designed vacuum deposition unit employing physical vapor deposition technique, and its morphology studied as a function of deposition parameters such as substrate temperature, coating thickness, deposition rate, and angle of deposition. It has been characterized using various analytical techniques. Its morphology has been studied with the help of a scanning electron microscope. Coating adherence and hardness have been measured. Results obtained have been analyzed and discussed.
Flame rig testing of thermal barrier coatings and correlation with engine results
Authors: Johner G. , Schweitzer K. K.
Published: July 2002

To minimize detrimental thermal stresses in high-performance aeroengines, attempts are made to protect hot components, e.g., combustion chambers, blades, vanes, etc., with plasma-sprayed zirconia coatings. In the present evaluation, the best coating material is first defined using an appropriate rig test. Two different types of test rig, one simulating mainly thermal fatigue stresses and the other centrifugal stresses, are described in detail. The results obtained in each rig with thermal barrier coatings of different chemical composition are also discussed. For the application of thermal barrier coatings in aeroengines, it is necessary to analyze the main stresses on the component to be coated. The paper uses a turbine vane and a blade as examples. In addition, another flame rig is presented which permits the simulation of stresses very similar to those in jet engines. The results of these tests are compared with the behavior of thermal barrier coatings on turbine blades and vane segments in a production-type engine.
Effect of ion bombardment during deposition on the x-ray microstructure of thin silver films
Authors: Huang T. C. , Lim G. , Parmigiani F. , Kay E.
Published: July 2002

The effect of argon ion bombardment, during deposition on the microstructure of several tens of nanometers thick Ag films, has been studied. The structure of the Ag films was analyzed by x-ray powder diffraction method. Results show that Ar ion bombardment not only influenced the film growth process but had a significant effect on the structure of the resulting films. In comparison to an evaporated thin Ag film, our films showed much less [111] preferred orientation and a lattice expansion normal to the film surface instead of contraction, with compressive rather than tensile surface strain and plane stress. We also observed much smaller grain sizes, and higher twin fault probabilities, microstrains and dislocation densities. These structural parameters varied systematically with the normalized energy En, that is, the energy deposited by incident energetic Ar+ at the film surface per arriving Ag atom; at first rapidly, then leveling off when En≥42% eV/Ag atom. Preferential orientation is believed to be dependent on film thickness as well as on En. Unlike other parameters, twin fault probability increased to a maximum at En=20 eV/Ag atom and then decreased as En increased further due to self-annealing during deposition.
Rotational epitaxy of periodic overlayers
Authors: Doering Dale L.
Published: July 2002

Rotational epitaxy refers to the alignment of a solid overlayer along a specific orientation relative to the substrate. Rotational epitaxy along nonsymmetry orientations represent an important alternative to pseudomorphic strain or misfit dislocations for the accommodation of lattice misfit in epitaxial thin films. In this study, the orientations of possible epitaxial overlayers which are periodic relative to the substrate are examined over a wide range of overlayer and substrate lattice mismatch. Both square and hexagonal lattice structures are considered. By comparing the relative orientation and lattice mismatches of periodic overlayers, sets of related structures are observed. The rules which define the relationships between periodic structures in each set can be demonstrated using geometrical models. The results provide a unique insight into the observations of rotational epitaxy in rare gas layers physisorbed on graphite and alkali metals chemisorbed on metals.
A review of the present state of art in hard coatings grown from the vapor phase
Authors: Sundgren J.-E. , Hentzell H. T. G.
Published: July 2002

Hard-coating materials range from ultrahard materials such as ‘‘diamondlike carbon’’ through refractory compounds to alloys. However, transition-metal carbides and nitrides have achieved by far the highest level of commercial success. Titanium nitride and titanium carbide are the most studied and used. In this paper a review of the hard coating literature is given and includes in addition to nitrides and carbides also oxides, borides, mixed compounds, metals and alloys, and ‘‘diamondlike’’ carbon coatings. Only coatings grown from the vapor phase are discussed. Some considerations involved in selecting coating/substrate combinations as well as basic concepts of hardness and hardness measurements are also given. For example, it is shown that in order to measure the hardness of the coatings correctly the ratio between the film thickness and the depth of the indentation has to exceed a critical value, which depends on the coating/substrate combination. For TiN on steel, the coating thickness has to be a factor of 5 larger than the indentation depth. For all types of hard coatings there is still a lack of knowledge on how nucleation and growth processes are affected by processing parameters and how the resulting film microstructure correlates to physical properties. Based on results presented in the literature, the existing knowledge about relationships between the microstructure and physical properties of hard coatings is discussed. Particular emphasis is placed on the role of microstructural features such as grain boundaries, nonequilibrium structures, impurities, and texture in controlling the film hardness. For example, voids and weak grain boundaries give rise to low film hardnesses whereas dense films with a high defect concentration can have hardnesses far above bulk values. Because the coatings in many cases are grown at high rates, low temperatures, and under the influence of an impinging ion flux, supersaturated solid solutions and entrapment of noble-gas impurities are common features. Such coatings exhibit high stress levels (most commonly of a compressive nature) and high hardness values.
Formation of ceramic thin films by solid-state interface reactions
Authors: Hesse D.
Published: July 2002

The formation of single-crystal Mg2TiO4 films and large-grained, multiply positioned MgTiO3 films by solid-state interface reactions is investigated by transmission electron microscopy, selected area electron diffraction, electron probe microanalysis, Rutherford backscattering spectrometry, and other methods. Stoichiometric single-crystal Mg2TiO4 spinel films grow by a topotaxial reaction between the MgO substrate and a TiO2 vapor. A submicron-marker experiment revealed the cations to be the diffusing species. The films are free of observable lattice defects, except for a network of cation antiphase boundaries. Two new preparation methods are presented that enable edge-on solid–solid reaction interfaces to be investigated by in situ observation in the high-voltage electron microscope. Periodic lines of contrast at the semicoherent Mg2TiO4/MgTiO3 interface are interpreted in terms of dislocations, which probably restack the oxygen sublattice of MgTiO3 to that of spinel. The single-phase MgTiO3 films obtained show a regular eightfold-positioned structure, partly due to grain growth and reorientation processes. Interface strain is assumed to determine whether Mg2TiO4 or MgTiO3 is formed as the final thin-film phase during the solid–solid reaction.
Bulk and surface optical absorption in molybdenum disulfide
Authors: Roxlo C. B. , Chianelli R. R. , Deckman H. W. , Ruppert A. F. , Wong P. P.
Published: July 2002

Optical absorption in crystalline MoS2 has been measured from 0.7 to 3.5 eV using photothermal deflection and transmission spectroscopies. We have determined the indirect band gap in both natural and synthetic material. Photon energies below the band gap show defect absorption which is strongly concentrated at the edge surfaces. These surface defects have the same optical properties in microcrystals and lithographically textured single crystals.
Surface characterization of clean polyimide films by high-resolution electron energy-loss spectroscopy
Authors: Pireaux J. J. , Gregoire C. , Thiry P. A. , Caudano R. , Clarke T. C.
Published: July 2002

The first high-resolution (≂10 meV, full width at half-maximum of the elastic peak) electron energy-loss spectra from surfaces of clean polyimide thin films are presented and discussed. Changes in the polymer surface composition are recorded after heating in vacuo: curing at T≂500 K for 1 h is necessary to desorb water from the surface and recrystallize the polymer material. A dozen vibrational bands are then clearly resolved, most of them being assigned, with the help of infrared data, to phenyl, carbonyl, CN, and COC species. Low-energy bands at 410 and 175 cm−1 are tentatively assigned to collective modes of the almost crystalline material. Electron induced vibrational spectra collected in different geometries or with different electron impact energies show mainly modification of the phenyl vibrational bands; information on surface sites and surface structure is deduced. Finally, electronic transitions between 4 and 10 eV and secondary electron emission are also evidenced.
End-Hall ion source
Authors: Kaufman Harold R. , Robinson Raymond S. , Seddon Richard Ian
Published: July 2002

The end-Hall ion source has been developed for high-current, low-energy ion-beam applications. Beam currents up to 1 A have been obtained at mean ion energies of 30–120 eV, using Ar, Kr, or O2. The end-Hall source should be useful in applications where large currents of low-energy ions are used in conjunction with thin-film deposition to increase adhesion, modify stress, increase density or hardness, produce a preferred orientation, or improve step coverage. It should also be useful for reactive etching. It is suited for use in a production environment because it is simple, mechanically rugged, and reliable.
Electron stimulated desorption from GaAs(100) surface
Authors: Ekwelundu E. C. , Ignatiev A.
Published: July 2002

Measurements of electron stimulated desorption of CO+, CO+2 , C+, and O+ have been carried out for a sputter-cleaned and annealed GaAs(100) surface exposed to CO2, O2, and NO at room temperature. The dependence of the ion yields on the incident electron beam energy from 0 to 200 eV exhibits thresholds at the Ga 3d, 3p, and 3s and As 3d and 3p core level binding energies. The total desorption cross section for the ionic species is ∼10−18 cm2.