bluuebunny/crossref_metadata_2025 huggingface dataset:
Pressure Measurements in Highly Viscous and Elastic Fluids
Authors: Yesilata Bulent , O¨ztekin Alparslan , Neti Sudhakar , Kazakia Jacob
Published: July 2002

Pressure measurements in flows of highly viscous and elastic fluids are of practical importance in polymer processing and rheology systems. Special problems arise during such pressure measurements. High fluid viscosity results in excessive dynamic response time (rise time) of the pressure measuring systems. This is true for systems that consist of manometers as well as pressure transducers attached to the base of a small hole at the wall. We model the dynamic response and examine related disturbing effects. These systematic errors in pressure measurements include hole-pressure effects, instabilities in cavity flow, and the time lag of the disturbance wave. We consider static and dynamic flow systems of a polymer solution (PIB/C14/PB Boger fluid) to study these problems and show that instantaneous pressure measurements in these systems can effectively be performed. [S0098-2202(00)02703-6]
Analyses of Contact Pressure and Stress Amplitude Effects on Fretting Fatigue Life
Authors: Iyer K. , Mall S.
Published: July 2002

Elastic-plastic finite element analyses of a cylinder-on-plate configuration, studied experimentally, were performed to provide an explanation for the decrease in fretting fatigue life with increasing contact pressure. Three values of normal load, namely 1338 N, 2230 N, and 3567 N, and three stress ratios (0.1, 0.5, and 0.7) were considered. Based on a previously determined dependency between contact pressure and friction coefficient, the effect of coefficient of friction was also evaluated. The deformation remained elastic under all conditions examined. Cyclic, interfacial stresses, and slips were analyzed in detail. The amplification of remotely applied cyclic stress in the contact region is shown to provide a rationale for the effect of contact pressure and stress amplitude on life. Comparisons with previous experiments indicate that the local stress range computed from finite element analysis may be sufficient for predicting fretting fatigue life. Further, the results suggest that the slip amplitude and shear traction may be neglected for this purpose.
Transforming Complex Eigenmodes into Real Ones Based on an Appropriation Technique
Authors: Foltete E. , Piranda J.
Published: July 2002

A new method allowing the determination of normal modes corresponding to the complex ones identified on a structure is proposed. It is based on an appropriation technique applied to forced responses computed from the identified eigensolutions. The set of applied forces is optimized with respect to an appropriation quality criterion. The knowledge of both complex and normal modes allows the full generalized damping matrix to be determined. The complex modes can then be recalculated using the normal modes and the full generalized damping matrix which provides a test of validity by comparison with the original complex modes. Simulated and experimental tests demonstrate the efficiency of this new method.
Mechanics of Surface Roughening in Metal Forming Processes
Authors: Wilson William R. D. , Lee Weiming
Published: July 2002

Inspection of 1100-H14 and 5052-0 aluminum alloy surfaces deformed in tension, sheet forming, and rolling with a thick lubricant film indicated that similar mechanisms were involved in the roughening process. The predominant mechanism was associated with the orientation of slip systems in adjacent grains leading to mismatch strains at the grain boundaries. The emergence of slip planes played a lesser role in the roughening process. A roughening model that assumed a spatial hardness variation was developed. Theoretical predictions of the dependence of the Ra surface roughness with bulk strain, based on micro-hardness measurements, show excellent agreement with experiment.
High-Cycle Thermal Fatigue Crack Initiation and Growth Behavior in a Semi-Infinite Plate Model
Authors: Hayashi Makoto
Published: July 2002

At a T-junction in piping system, hot and cold water mixes in a whirl. The vibrating mixing boundary between the hot and cold water causes a temperature fluctuation on the inner surface of the pipe just after the connection point at the T-junction, and this temperature fluctuation yields a cyclic thermal stress near the pipe surface, resulting in crack initiation. In this study, the thermal stress distribution was analyzed for a semi-infinite plate model. The allowable water temperature range for the fatigue crack initiation was determined based on the mechanical fatigue test results. The thermal fatigue crack arrest behavior was analyzed based on the distributions of the stress intensity factor. The arrested crack depth is found to be in proportion to the reciprocal root of the frequency of the temperature fluctuation and is 3.8 mm for the frequency of 1 Hz.
Virus Transmission Through Compromised Synthetic Barriers: Part I—Effect of Unsteady Driving Pressures
Authors: Myers Matthew R. , Das Bigyani
Published: July 2002

Although synthetic membranes such as gloves, condoms, and instrument sheaths are used in environments with highly time-varying stresses, their effectiveness as barriers to virus transmission is almost always tested under static conditions. In this paper it is shown how a previously developed mathematical model can be used to transform information from static barrier tests into predictions for more realistic use conditions. Using a rate constant measured for herpes adsorption to latex in saline, and an oscillatory trans-membrane pressure representative of coitus, the amount of virus transmitted through a hole (2 μm diameter) in a condom is computed. Just beyond the exit orifice of the pore, transport is dominated by the rapidly dissipating viscous jet of virus suspension, which results in an accumulation of viruses roughly 20 pore radii from the barrier surface during each cycle. Due to virus adsorption to the barrier surfaces, the simulations reveal a gradual decrease in virus flow with increasing number of cycles, and thus a slow divergence from predictions based upon steady-state conditions. Still, over the 500 cycles simulated, steady-state predictions approximate the net number of viruses transmitted to within 25 percent error.
Resonance and the Aging Spring
Authors: Lardner T. J.
Published: July 2002

The steady-state response of the classic mass-spring-dashpot model when the spring stiffness decays exponentially with time (an aging spring) and the system is excited by a forcing function whose frequency is equal to the natural frequency of the system with the constant initial stiffness is investigated. The steady-state response is obtained in terms of the dumping and decay constants of the system and exhibits an oscillation about a nonzero value.
Equivalent Thermal Resistance of a Corrugated Contact Boundary
Authors: Wang C. Y.
Published: July 2002

The heat conduction across a corrugated contact boundary between two different materials is solved by perturbations. [S0022-1481(00)00802-1]
Evolution of Si-on-GaAs (001) surface morphology towards self-organized ordered Si structures
Authors: Wang Z. M. , Däweritz L. , Schützendübe P. , Ploog K. H.
Published: July 2002

Scanning tunneling microscopy studies of the restructuring of GaAs (001) surfaces induced by Si deposition have been performed. With increasing Si coverages, different reconstructions are developing. Their interaction with the surface step structures results in a distinct separation into different surface phases with different Si coverages, revealing unique Si distribution patterns. This phenomenon is explained by considering kinetically accessible thermodynamically determined structures.
Postdeposition annealing of pulsed laser deposited CNx films
Authors: González P. , Soto R. , Lusquiños F. , León B. , Pérez-Amor M.
Published: July 2002

A study on the modification of the physicochemical properties of the carbon–nitrogen compounds when submitted to a thermal annealing process is reported. Original films were obtained by ArF laser ablation using organic and inorganic targets in a reactive atmosphere of ammonia or in vacuum conditions. The evolution of the film chemical composition and bonding configuration was followed by controlled thermal effusion, Fourier-transform infrared and energy dispersive x-ray spectroscopies. The thermal energy supplied to the material during the postdeposition annealing of the CNx films promotes the formation of single CN bonds although the film nitrogen concentration decreases by the effusion of hydrogen cyanide, cyanogen, and CN radicals. Additional experiments at different substrate processing temperatures were carried out in order to analyze the role of the temperature on the film properties during the film processing and during postdeposition annealing.
Piezoresistance in Evaporated Nickel Films
Authors: Klokholm E.
Published: July 2002

The electrical resistance of a metal can be altered by the application of an elastic stress. In Ni this effect is generally negative; namely a tensile stress causes a decrease in resistance. The longitudinal gage coefficient γ (defined as the relative change in resistance divided by the relative change in specimen length) is about −20. In evaporated Ni films, the observed γ depends on the sign and the magnitude of film stress. For large tensile stresses, γ at room temperature is small and positive. As the temperature is initially increased γ changes markedly because of the change in stress with temperature. The gage coefficient increases negatively and reaches a maximum of about −10 at about 100 °C, and finally becomes about +3 at temperatures just above the Curie temperature of Ni (360 °C). After annealing at temperatures of 380 °C, the film stress apparently anneals since, as the specimen cools, γ does not follow its initial heating curve. At room temperature after annealing γ=2.7.
X-ray source combined ultrahigh-vacuum scanning tunneling microscopy for elemental analysis
Authors: Hasegawa Y. , Tsuji K. , Nakayama K. , Wagatsuma K. , Sakurai T.
Published: July 2002

An ultrahigh-vacuum scanning tunneling microscope (UHV-STM) combined with an x-ray source has been developed. STM samples were irradiated with an x-ray beam and an x-ray induced photoemission current was detected with the tip. By using the system, apparent height increases due to the x-ray induced current were successfully observed in STM images of Cr/Cu(111), Au/Cu(111), Si(111)7×7, and Si(111)-5×1 Au surfaces. A bias voltage applied to the tip enhances collection of the x-ray induced current and increases the apparent height. The relative height increase of the Au overlayer to the Cu substrate in the STM images of the Au/Cu(111) surface was found to depend on the x-ray irradiation, suggesting that it may be a promising tool for elemental analysis in a STM.
Structural properties of CdS-doped glass nanocrystallites grown by pulsed laser deposition in high vacuum
Authors: Wang H. , Zhu Y. , Ong P. P.
Published: July 2002

By conventional pulsed laser deposition followed by in situ annealing in high vacuum, we have successfully fabricated CdS-doped glass (CDG) nanocrystalline thin films on Si substrates. Photoluminescence (PL) spectra of CDG films show an emission band at about 539 nm (2.30 eV), which is attributed to a new CdO composite formed by the interaction of the CdS nanoparticles and SiO2 in the film. The PL spectrum arising from the CdO band–band transition has a peak intensity which depends only on deposition times and not on the annealing treatment of the film. However, higher annealing temperatures yielded a greater crystalline size of CdO, as is evident from the resulting redshift of the CdO band in the PL spectra. The presence of CdO in the films was further confirmed by both energy dispersive x-ray and x-ray diffraction (XRD) measurements. Its growth in crystalline size with annealing temperature was also confirmed by analysis of the diffraction peak lines in the XRD spectra. Furthermore, XRD measurements also reveal that the crystal direction of the films was greatly determined by the annealing temperature. Finally, transmission electron microscopy pictures reveal the three different nanocrystalline structures of CDG corresponding to the different films produced with different heat treatments.
Thin-walled vacuum chambers of austenitic stainless steel
Authors: Moore Boude C.
Published: July 2002

It is proposed and recommended that vacuum chambers and systems to be built of austenitic stainless steel should be designed for the thinnest walls possible, consistent with structural integrity under atmospheric pressure. The reason for this design goal is to greatly reduce the time, effort, and cost needed to outgas the chambers to reach the desired and specified vacuum level. Of course, this is directly contrary to the universally accepted concern with permeation of atmospheric hydrogen. This permeation has recently been shown to be greatly exaggerated. Atmospheric permeation is at least 100 times less than previously estimated, and is possibly nonexistent. Errors in the previous estimate will be briefly summarized. A proposed outgassing process for hydrogen differs from the accepted process. In this proposal, room temperature outgassing is single sided, occurring only on the vacuum side. The residual concentration distribution of hydrogen in the wall is a quarter sine wave with zero on the vacuum side and peak on the air side. At bake temperatures the distribution becomes uniform, the same as the initial distribution, but at a lower concentration. Subsequent room temperature outgassing follows the same equations as the initial, but with reduced rate and with zero time reset to the end of bake.
Frequency-dependent pulsed direct current magnetron sputtering of titanium oxide films
Authors: Kim J.-Y. , Barnat E. , Rymaszewski E. J. , Lu T.-M.
Published: July 2002

Dramatic dependence of dielectric properties on the pulsing frequency was found for titanium oxide films deposited using the pulsed dc magnetron sputtering technique at room temperature. The frequency range studied was between 50 and 250 kHz by varying the oxygen pressure. A minimum leakage current density of 0.22 μA/cm2 at 0.5 MV/cm electric-field strength for a film with dielectric constant of 26 was achieved for relative oxygen pressure P=60% [P(%)=PO2/(PO2+PAr] and frequency f=200 kHz.
Characterization and modeling of electrical resistivity of sputtered tungsten films
Authors: Ligot J. , Benayoun S. , Hantzpergue J. J.
Published: July 2002

Tungsten (W) thin films were deposited on a polyimide substrate by sputtering deposition in pure argon plasma using a triode discharge system. The properties of these W films were investigated as functions of ions energy, argon pressure and film thickness. The composition and crystallographic and micrographic structures of W films were determined by Rutherford backscattering spectroscopy and x-ray diffraction techniques, respectively. Less than 6 at. % argon and metallic impurities (due to the sputtering chamber configuration) was incorporated into the W films and different volume ratios of tungsten crystallographic phases (Wα and Wβ) were observed in the films. The electrical resistivity of Wα films was interpreted from impurity concentrations and the microstructure with a model based on electron scattering mechanisms at grain boundaries. It was shown that the electron reflectivity of the grain boundaries depends of the size of the grains. In order to evaluate the contribution of Wβ phase on the electrical resistivity of biphase W films, two models were proposed. The model of the averaged effect of the two phases leads to calculations that are in good agreement with experimental results and an intrinsic resistivity of Wβ phase is proposed to be close to 30 μΩ cm.
Nanoscale patterning using self-assembled polymers for semiconductor applications
Authors: Guarini K. W. , Black C. T. , Milkove K. R. , Sandstrom R. L.
Published: July 2002

Thin films of self-organizing diblock copolymers may be suitable for semiconductor applications since they enable patterning of ordered domains with dimensions below photolithographic resolution over wafer-scale areas. We investigate the process window for forming ordered arrays of nanoscale polymer domains in thin films across 8-in.-diam silicon wafers, including the effect of substrate material and surface treatment, annealing conditions, copolymer molecular weight, and film thickness. We also demonstrate pattern transfer of the nanoporous polymer template using both reactive ion etching and metal lift off.
Ionization Gauge Calibration System Using a Porous Plug and Orifice
Authors: Owens Charles L.
Published: July 2002

A calibration facility in which reproducible pressures are conveniently generated for ionization gauge calibration is described. The method uses two conductances in series, both operating in the molecular flow region, to produce low pressures at the test gauge. These low pressures are referenced to higher pressures whose measurement can been accomplished by convenient methods. The test pressure is proportional to the ratio of the two conductances. By using a porous material and a thin plate orifice, the reference pressure is reduced by a factor of approximately one million. A convenient feature of the system is the fact that once the ratio of the conductances has been determined, it can be used for many gases. Experimental results obtained using this method over the range from 10−3 to 10−9 Torr are presented.
Electrostatic Getter-Ion-Pump Design
Authors: Bills Daniel G.
Published: July 2002

The theory and design of a nonmagnetic, multicelled, triode, getter-ion pump capable of attaining pressures of less than 3 × 10−11 Torr and a pumping speed for air of 1700 liter/sec using a 6-in.-diam orifice is described. A quantitative theory is presented for maximizing the ionizing efficiency of electrons trapped in the electrostatic potential of a cylindrical diode. The experimentally verified theory predicts that for optimum results, electrons must be injected in a well-defined range of angular momenta from an injector whose potential is nearly that of the outer cylindrical electrode. The theory also predicts the optimum axial and radial position for injection. In the new pump, each cell consists of an open cylindrical grid within which is a central anode and two electron injectors. All cells are surrounded by a common cathode which also serves as the pump housing. A new-design, large-area, resistance-heated sublimator with pressure-controlled sublimation rate is located on the axis of the cylindrical cathode. Because the ionizing and gettering functions have been effectively separated it has been possible to optimize each function separately.
Theory of Pulsed Molecular-Flow Networks
Authors: Kendall B. R. F. , Pulfrey R. E.
Published: July 2002

A general molecular-flow network theory applicable to volumes interconnected by small orifices or porous membranes is discussed. Parameters which describe the properties of such orifices and membranes are first defined. Basic theory is then extended to cover operation with mixtures of gases having different molecular weights. Characteristics of several networks with pulsed pressure inputs are then derived. It is shown that the mass-dependent resistance to flow of an orifice or porous membrane makes it possible to use certain molecular-flow networks as gas analyzers. Other networks are described which have potential applications in improving gauge response to rapid pressure fluctuations.
Multisource deposition rate control using a mass spectrometer as a sensing element
Authors: Lutz H.
Published: July 2002

A deposition rate controller for a multisource, high-rate, electron-beam evaporation system for simultaneous deposition of two to four materials is described. The system utilizes a quadrupole mass spectrometer as a material selective sensor to monitor the fluxes of the different evaporants, and a dedicated minicomputer serves as a process controller to adjust the deposition sources to maintain the desired rates. The computer can control a variable leak valve instead of one of the evaporation sources to maintain the desired partial pressure of a background gas. Experience gained in using the system is discussed.
X-ray lithography at ∠100 Å linewidths using x-ray masks fabricated by shadowing techniques
Authors: Flanders D. C.
Published: July 2002

A new technique for fabricating high contrast x-ray masks with precisely controlled linewidths of less than 100 Å is described. The technique is based on the deposition at an oblique angle (shadowing) of x-ray absorber material onto relief structures of triangular or square cross section in a polyimide plastic membrane. Precise linewidth control is possible because shadowing angle, absorber thickness,and relief structure can be precisely determined. The smooth and well-controlled triangular cross-section structures required are produced in silicon by anisotropic chemical etching and then transferred to polyimide by molding. The square structures are made by reactive-ion-etching of SiO2 with CHF3 and are transferred to polyimide by molding. Results of a numerical model of carbon K (45 Å) x-ray exposures in PMMA of shadowed triangular profile masks are presented which indicate that linewidth control of ±50 Å should be possible for submicrometer period grating. Scanning electron micrographs of PMMA gratings of 1 μm, 3200 Å and 1968 Å period with linewidths as small as 400 Å are shown. The successful replication of ∠200 Å linewidth patterns in PMMA using the carbon K x-ray and shadowed square cross-section masks is reported.
GaAs metallization: Some problems and trends
Authors: Woodall J. M. , Freeouf J. L.
Published: July 2002

Ohmic and Schottky barrier contacts with desired properties are difficult to form on GaAs devices. This is due mainly to the fact that the position of the Fermi energy is loosely ’’pinned’’ near midgap for GaAs surfaces which are metallized using conventional techniques. Doped alloyed metal ohmic and refractory metal Schottky contacts formed on carefully cleaned surfaces are currently widely used. New contacting techniques including the use of lattice matched heterojunctions, nonalloyed n++ and p++ surfaces, graded band gap structures, and special surface treatment prior to metallization promise to provide both greater flexibility and control for future applications.
Application of ≊100 Å linewidth structures fabricated by shadowing techniques
Authors: Flanders D. C. , White Alice E.
Published: July 2002

A variety of shadowing techniques have been developed for fabricating simple structures with lines and spaces in the 100 Å linewidth regime. In the basic technique, a smooth vertical step with precisely determined depth is produced in a substrate by reactive ion etching. This step is shadowed at a shallow angle by evaporation in order to deposit material on the vertical wall. The substrate is then etched at normal incidence with an ion beam to remove the thin layer of material outside the step. This leaves a thin rectangular line of material at the step. By alternately evaporating different materials and by adding lithography and etching steps, more complex structures can be made. Applications of these structures in wire grating optical polarizers and the use of long thin wires for studying electron localization are described. Optical polarizers with extinction ratios of nearly 200 to 1 have been made. This demonstrates some of the unique capabilities of the shadowing technique since high quality polarizers require large areas of high aspect ratio ≊100 Å linewidth metal lines.
Retention and thermal release of oxygen implanted in graphite
Authors: Wampler W. R. , Brice D. K.
Published: July 2002

The retention of oxygen implanted in graphite at 1.5 and 3 keV was measured as a function of fluence. At fluences less than 1016 O/cm2 the oxygen was all retained, but at higher fluences the retention saturated. Models describing the retention are discussed which include the effects of sputtering and a saturation limit to the local oxygen concentration. Thermal release of oxygen implanted to saturation at room temperature began at 250 °C and was 90% complete by 750 °C.
Characteristics of radio frequency silicon carbide films
Authors: Raveh A. , Inspektor A. , Carmi U. , Avni R.
Published: July 2002

Martensitic stainless-steel plates were coated with silicon carbide (SiC) in a low-pressure inductive rf plasma reactor from a mixture of tetra-methyl-silane and hydrogen in argon. The SiC films were characterized with regard to crystalline structure, homogeneity and morphology using x-ray diffraction (XRL), and optical and electron microscopy techniques, respectively. The film’s structure was identified as hexagonal α-SiC with free carbon embedded in it. Its surface consists of small spherical shapes whose size was found to be related to the structure and surface homogeneity of the film. The hydrogen concentration in the gas feed played an important role in determining the structure (XRD), composition (Auger electron spectroscopy measurements), and density (sink float method) of the SiC films. The microhardness and density were found to be dependent on the total carbon content in the films, with a maximum value, corresponding to SiC films with composition close to stoichiometric.
Theory of H bonding and vibration on close-packed metal surfaces
Authors: Feibelman Peter J. , Hamann D. R.
Published: July 2002

Self-consistent linearized augmented plane-wave calculations for H monolayers adsorbed on Pt(111), Ru(0001), Cu(111), and Cu(1×1)/Ru(0001) thin slabs predict the following: the H-atom equilibrium position on these substrates is generally in the face-centered cubic threefold hollow at a height above the surface where the clean-metal electron density is about 0.015 a.u. The symmetric stretch (SS) frequency lies in the range 130–165 meV, and is about 30% greater than the asymmetric stretch (AS) frequency on the same substrate. These results contradict the mode assignments of Baro et al. [A. M. Baro, H. Ibach, and H. D. Bruchman, Surf. Sci. 88, 384 (1979)] for H/Pt(111) which were based on the observation of weak dipole scattering by the low-lying mode, and of Barteau et al. [M. A. Barteau, J. Q. Broughton, and D. Menzel, Surf. Sci. 133, 443 (1983)] for H/Ru(0001). The pairwise spring model of H–metal vibration invoked by these groups in support of their mode assignments neglects a major component of the H–metal interaction, that between the adsorbed H and the delocalized electrons of a metal surface. It is this interaction which is responsible for the fact that the frequency of the SS vibration is greater than that of the AS.
Ultrahigh vacuum measurements in China
Authors: Hua Z. Y.
Published: July 2002

Research and development on UHV gauges were started in China in 1953. Since then incessant efforts have been devoted to improvements of Bayard–Alpert gauges, suppressor gauges, extractor gauges, deflector gauges, and modulated Bayard–Alpert gauges. Performances of various gauges, from a special gauge with all electrodes degassed by direct resistance heating, to a shielding gauge with no photocurrent effect are briefly reviewed in the present paper. Finally, a method for UHV gauge calibration is suggested and a new quadrupole structure for partial pressure measurement is described.
Scanning tunneling microscopy characterization of the geometric and electronic structure of hydrogen-terminated silicon surfaces
Authors: Kaiser W. J. , Bell L. D. , Hecht M. H. , Grunthaner F. J.
Published: July 2002

Scanning tunneling microscopy (STM) methods are used to characterize hydrogen-terminated Si surfaces prepared by a novel method. The surface preparation method is used to expose the Si–SiO2 interface. STM images directly reveal the topographic structure of the Si–SiO2 interface. The dependence of interface topography on oxide preparation conditions observed by STM is compared to the results of conventional surface characterization methods. Also, the electronic structure of the hydrogen-terminated surface is studied by STM spectroscopy. The near-ideal electronic structure of this surface enables direct tunnel spectroscopy measurements of Schottky barrier phenomena. In addition, this method enables probing of semiconductor subsurface properties by STM.
Interfacial reactions in the Ti/GaAs system
Authors: Kim Ki Bum , Kniffin Margaret , Sinclair Robert , Helms C. R.
Published: July 2002

The reaction between thin Ti films and GaAs, in the temperature range 300–600 °C, was studied using a combination of Auger electron spectroscopy, transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy, and electrical measurements. Titanium starts to react with GaAs at ∼400 °C, producing a layered Ti/TixGa1−x/TiAs/GaAs microstructure. The reaction sequence suggests that Ti diffuses into the GaAs and liberates Ga while forming TiAs. Kinetic studies show that the reaction is diffusion controlled with an activation energy of 1.75±0.05 eV. The reaction products, for fully reacted films, were identified from electron diffraction patterns as a NiP-type TiAs phase and TixGa1−x (hexagonal structure: a=0.569 nm, c=0.932 nm, x=0.35±0.05). Correlation of electrical measurements with TEM results indicates that the formation of TiAs at the interface coincides with an increase in barrier height (0.84 eV) over the as-deposited value (0.72 eV).
Surface analysis with pulsed-laser stimulated field desorption
Authors: Tsong Tien T. , Liou Yung , Liu Jiang
Published: July 2002

Using a pulsed-laser stimulated field desorption time-of-flight spectrometer, known as the pulsed-laser atom probe, surface atoms and atomic layers of one’s choice can be mass analyzed one by one. In addition, it is an ion kinetic energy analyzer with which the binding energy of surface atoms can be measured. We have developed a high-resolution system which measures flight time of each ion with a time resolution of 156 ps. With a flight path of ∼778 cm, this system has a resolution and accuracy of about one to two parts in 105 in mass analysis, ion kinetic energy analysis, and ion reaction rate measurement. This system has been used to study the binding energy of surface atoms in well-defined sites, formation of cluster ions and their magic and critical numbers, compositional variation across the interface of silicon and silicide layer, field induced surface states, field dissociation of compound ions, and other desorption phenomena. We describe here this high-resolution system, how it is calibrated, and also a few of these studies.
Redistribution phenomena in aluminum alloy/titanium thin films
Authors: Slusser George J. , Ryan James G. , Shore Susan E. , Lavoie Mark A. , Sullivan Timothy D.
Published: July 2002

The chemical and structural changes occurring in aluminum alloy/titanium layered metallizations and their implications are discussed. Characterization of Ti/Al–Cu/Si films was performed by secondary ion mass spectrometry (SIMS), Rutherford backscattering spectrometry, and transmission electron microscopy. Silicon and/or copper additions to aluminum produce a retarded reaction rate between aluminum and titanium upon annealing. SIMS measurements of annealed films show titanium diffusion throughout the entire aluminum film. In the absence of either silicon or copper, the titanium content is homogeneous at a level of ∼6×1018 atoms/cm3. Addition of silicon does not prevent titanium diffusion, but reduces the Ti concentration in the bulk of the film while producing a higher concentration in the near-surface region. Copper additions produce a similar, but much less dramatic effect.
Metalorganic chemical vapor deposition growth of Cd1−yZnyTe epitaxial layers on GaAs and GaAs/Si substrates
Authors: Ahlgren W. L. , Johnson S. M. , Smith E. J. , Ruth R. P. , Johnston B. C. , Kalisher M. H. , Cockrum C. A. , James T. W. , Arney D. L. , Ziegler C. K. , Lick W.
Published: July 2002

As a step toward growth of HgCdTe on GaAs and GaAs/Si substrates, Cd1–yZnyTe buffer layers were grown on these substrates. A conventional pyrolytic process at relatively high temperature (441 °C) was used. Epitaxial growth on GaAs was achieved for all alloy compositions, 0≤y≤1. The solid–vapor distribution curve for alloy deposition was determined experimentally for one particular set of deposition parameters, and compared with a thermodynamic model. Deposit uniformity was also studied experimentally and compared with a model incorporating coupled fluid dynamics and mass transport (but not chemical kinetics) with realistic reactor boundary conditions and thermal effects. Epitaxial growth on the GaAs(123) substrates orientation was studied by x-ray techniques. Cd1–yZnyTe epitaxial layers grown on these substrates were tilted with respect to the substrate toward 〈111〉, about a 〈12̄1〉 axis. The degree of tilt depended on the alloy composition y, ranging from 1.7° for y=1 to 3.2° for y=0. These results are consistent with a model of the GaAs(123) surface as a terraced structure consisting of (111) oriented ledges and steps parallel to [12̄1]. The crystal lattice perfection of the epitaxial layers was assessed by x-ray double-crystal rocking curve analysis. The best full width at half-maximum (FWHM) obtained for CdTe layers was 80 arc s, and for ZnTe layers it was 150 arc s. Cd0.96Zn0.04Te layers also grown on GaAs/Si(001) tilted 3.5° toward 〈111〉. Some layers grown on these substrates also had rocking curve FWHM≤100 arc s. Hg0.7Cd0.3Te was grown by liquid phase epitaxy on a CdZnTe/GaAs/Si substrate, and the resulting layer had a rocking curve FWHM of 165 arc s.
Plasma induced gas heating in electron cyclotron resonance sources
Authors: Rossnagel S. M. , Whitehair S. J. , Guarnieri C. R. , Cuomo J. J.
Published: July 2002

Neutral gas density has been measured in both the source and sample regions of an axial electron cyclotron resonance (ECR) plasma device. The measurements involved sampling with a small tube to an external capacitance manometer. The gas density in the central ECR region was found to be strongly dependent on the applied power and to decrease approximately linearly with discharge power. At the maximum applied power of 1250 W, and at an Ar pressure of 0.7 mTorr, the gas density was reduced to 14% of its preplasma value, indicative of significant gas heating and rarefaction. This is equivalent to a gas temperature of 2500 K (0.2 eV), which is consistent with reported Doppler broadening optical emission measurements. At the sample region, approximately 35 cm from the ECR region, the gas density was reduced by gas heating to only 85% of its preplasma value. The electron density was measured in the ECR region by means of a commercial microwave interferometer device. Electron densities, integrated across the width of the chamber, reached ≂2×1012cm−3 at 1250 W and 0.7 mTorr Ar. The ionization fraction at 0.7 mTorr and 1250 W of applied power was 0.31, assuming an average electron density across the chamber. Indications point towards a localization of the plasma in the center of the chamber, which would indicate an ionization fraction of more than 0.50. These results suggest a significant influence of gas temperature and rarefaction on the dynamics of plasma formation and ionization efficiency. In addition, an isotropic, chemical component to many reactive etching systems must be anticipated due to the potentially high gas temperatures in and near the ECR region.
Comparative study of the preparation of negative electron affinity GaAs photocathodes with O2 and with NF3
Authors: Ciccacci Franco , Chiaia Gualtiero
Published: July 2002

We discuss the possibility of replacing oxygen with nitrogen trifluoride in the preparation of stable GaAs negative electron affinity (NEA) photocathodes. The different role of O2 versus NF3 exposure during the activation is examined by means of quantum yield and photocurrent lifetime measurements. Quantum yield results clearly demonstrate that NEA conditions can be attained also with NF3. Measurements performed on the same samples and in the same experimental conditions, show a remarkably different time evolution of the activation process in the two cases. However, as a result of a huge number of activations, no evidence of significantly larger lifetimes for NF3 prepared photocathodes can be deduced.
Optical properties of ion assisted deposited CeO2 films
Authors: Al-Robaee Mansour S. , Krishna M. Ghanashyam , Rao K. Narasimha , Mohan S.
Published: July 2002

Single layer films of CeO2 have been deposited both by conventional electron beam evaporation and ion assisted deposition with oxygen and argon ions. A broad beam Kaufman ion source (3 cm diam) has been used to generate the ions. A systematic study has been made on optical properties such as refractive index, extinction coefficient and inhomogeneity of the films as a function of: (1) oxygen partial pressure in the range 1×10−4 to 1×10−5 mbar. (2) Incidence of oxygen ions with energy in the range 300–700 eV and current density in the range 50–220 μA/cm2. (3) Incidence of mixed argon and oxygen ions of different ratios. The refractive index of the films deposited under the influence of ion bombardment showed higher indices than the conventionally evaporated films. The maximum index obtained with an oxygen ion bombardment was 2.3 at an ion energy of 600 eV and current density of 220 μA/cm2. The bombardment of the films with a mixed argon–oxygen (25% Ar) ion beam of the same energy and current density was found to further increase the refractive index. The extinction coefficient in both cases was negligible.
Direct optical observation of hydrogenation induced damage in GaAs
Authors: Shwe C. , Gal M. , Gross M.
Published: July 2002

Differential reflectance (DR) spectroscopy has been applied to the study of surface damage on GaAs caused by direct exposure to a hydrogen plasma. DR spectra reveal features at photon energies corresponding to the critical points of the GaAs band structure. The observed signal appearing below the GaAs band gap is attributed to defect states created by the hydrogen plasma. Comparison with the DR spectra of samples exposed to an argon plasma suggests that the defect states are caused by ion impact and are independent of the chemical nature of the impinging ions. The density of defect states shows a linear dependence on maximum ion energy.
Ion-beam sputtered diamond-like carbon with densities of 2.9 g/cc
Authors: Cuomo Jerome J. , Doyle James P. , Bruley John , Liu Joyce C.
Published: July 2002

Thin films of carbon have been deposited at temperatures ranging from 77 to 1073 K. It has been found that diamond-like properties of the films change with the deposition temperature and the thermal conductivity of the substrate. Densities as high as 2.9 g/cc with an sp3 bond content >40% have been observed. Substrates that have been investigated include graphite, NaCl, Si, Al2O3, fused quartz, and diamond. Density measurements have been made using Rutherford backscattering spectrometry and electron-energy-loss spectroscopy while hydrogen profiling was conducted using forward recoil spectrometry.
Inchworm controller for fine approach in a scanning tunneling microscope
Authors: Jeon D. , Willis R. F.
Published: July 2002

This article addresses the problem of controlling the smooth approach of a scanning tunneling microscope using a commercial ferroelectric tube or ‘‘inchworm’’ device for both coarse and fine adjustment. A circuit is described for adapting the commercial control electronics such that the tip to sample approach time is less than 10 min with a fine control resolution of better than 1 Å to prevent the tip crashing into the surface.
Diffusion of Si atoms and dimers on Si(100)
Authors: Huang Z.-H. , Allen R. E.
Published: July 2002

Activation energies for diffusion of Si adatoms and dimers on a Si(100) surface are estimated through computer simulations. The potential field is probed by forcing an adatom to move adiabatically, while the surrounding atoms relax. The Stillinger–Weber potential is used. It is found that (1) the diffusion barrier height for an isolated adatom is smaller than that for a dimer; (2) the activation energies are comparable for the two atoms in a dimer to hop together or to separate from each other; (3) the activation energies of an isolated dimer, a dimer sitting next to a dimer chain, and a dimer at the end of a dimer chain are almost identical, despite differences in the binding energies.
Vibrational and rotational excitation in a capacitively coupled 13.56 MHz radio frequency CF4 plasma studied by infrared absorption spectroscopy
Authors: Haverlag M. , de Hoog F. J. , Kroesen G. M. W.
Published: July 2002

Infrared absorption spectroscopy has been used to determine the vibrational and rotational excitation of CF4 in a parallel plate plasma etcher. The vibrational and rotational temperatures Tvib and Trot of the CF4 molecules were extracted from the band structure of the ν3 peak of CF4 around 1283 cm−1, using a double beam Fourier transform spectrometer. Measurements were performed with and without plasma, at 0.12 cm−1 apodized resolution. From the change of the relative (hot) Q-branch intensities the vibrational temperature was estimated. Furthermore the rotational temperature, which is in these conditions likely to be very close to the gas temperature, was estimated from the shape and intensity of the R branch of the ν3 peak. It was established that both Tvib and Trot have values around 400 and 350 K, respectively. It is therefore concluded that under the studied circumstances the influence of the plasma on Tvib is small.
Energy resolved angular distribution of argon ions at the substrate plane of a radio frequency plasma reactor
Authors: Janes Joachim , Huth Christoph
Published: July 2002

The energy resolved angular distributions of argon ions of a 13.56 MHz rf discharge bombarding the powered electrode in a parallel plate reactor are investigated. Argon ions from the plasma are sampled through a small orifice in the powered cathode and are analyzed using a quadrupole mass spectrometer equipped with an energy filter. The angular resolution of the instrument is slightly better than 1°. The process pressure ranges from 5 to 50 mTorr and the rf power is varied to yield dc bias potentials between −100 and −450 V. The measured energy distributions of argon ions extend from 0 eV up to a maximal energy corresponding to the dc bias potential and exhibit significant structures which are explained by the effect of collisions in the sheath combined with rf modulations of the sheath potential. The principle structures in the ion energy distributions are nearly independent from the angle of ion trajectories with respect to the electrode normal. The energy resolved ion angular distributions are investigated in the range between ±3° and show structures which may be resulting from charge exchange collisions and elastic scattering of ions in the sheath. Angular distributions centered around the surface normal are found with angular widths between 1° and 2°. Furthermore, extrema at angles between 1° and 2° are detected for distinct energies and plasma parameters.
Energetic carbon deposition at oblique angles
Authors: Cuomo Jerome J. , Pappas David L. , Lossy Richard , Doyle James P. , Bruley John , Di Bello Gregory W. , Krakow William
Published: July 2002

Carbon is energetically deposited by pulsed laser vaporization, cathodic arc and ion beam sputtering to provide amorphous diamond films with varying degrees of diamondlike quality. Laser and arc films prepared at normal particle incidence are high in sp3 content and electrical resistivity, and exhibit optical behavior comparable to diamond. As the incident angle of the depositing species becomes increasingly oblique, the diamondlike character is progressively degraded. This is verified by decreases in sp3 fraction, resistivity, and optical transmittance. These changes are accompanied by a roughening of the microstructure, but no apparent variation in the transmission electron diffraction pattern. For deposition at the most oblique angles, the development of biaxial stress anisotropy is observed, as the compressive stress measured along the direction of incidence decreases at a greater rate than along the perpendicular direction. The implications of these results on the mechanisms proposed for amorphous diamond formation are discussed.
In situ photoreflectance study of Schottky barrier formation in InP(110)
Authors: Hwang J. S. , Tyan S. L.
Published: July 2002

The effects of using different p-InP(110) surfaces (air exposed, metal covered, and annealed) on the surface Fermi level position are studied by photoreflectance (PR). Measurements are performed on the (110) atomical clean surface under ultrahigh vacuum conditions in a molecular beam epitaxy chamber. The built-in electric field, which is associated with the barrier height, at the surface and/or metal/InP interface is evaluated from the Franz–Keldysh oscillations exhibited in the PR spectra. Schottky barrier heights of 0.21±0.02 eV for an atomically clean surface, 0.47±0.03 eV for an air exposed surface and 0.82±0.05 eV for a surface annealed at 350 °C are found. In addition, the Schottky barrier height for the Ag/p-InP(110) and Au/InP(110) interfaces are found to be almost identical (0.43±0.04 and 0.47±0.03 eV, respectively), while for Al/p-InP(110) the barrier height is 0.60±0.04 eV. Due to the low doping level and possibly thin metal coverage, our values of the barrier height are less than previous photoemission studies.
Orientation of methyl iodide adsorbed on MgO(100): Results from 257-nm photodissociation studies
Authors: Fairbrother D. H. , Trentelman K. A. , Strupp P. G. , Stair P. C. , Weitz Eric
Published: July 2002

Measurements of the angular and polarization dependence of methyl photofragments produced as a result of 257-nm photodissociation of methyl iodide adsorbed on MgO(100) are reported. At submonolayer coverage an adsorbate geometry is proposed where methyl iodide has its molecular axis aligned along the surface normal, iodine being directed towards the surface. This orientation is compatible with other experimental and theoretical data which is discussed.
Magnetic force microscope combined with a scanning electron microscope
Authors: Kikukawa Atsushi , Hosaka Sumio , Honda Yukio , Koyanagi Hajime
Published: July 2002

A magnetic force microscope (MFM) using frequency modulation detection was combined with a scanning electron microscope (SEM). The first goal was to facilitate the selection of the MFM imaging field by positioning the magnetic tip using the SEM. The second goal was to improve the performance of the MFM by operating it in a vacuum. The efficiency of the combined SEM was proved by imaging the particular region (about 3 μm in length) on the sample. The improved features of a MFM operated in a vacuum were demonstrated by comparing images taken in air and in a vacuum. The lateral resolution was improved to 50 nm in a vacuum while it was 100 nm in air, although that resolution could possibly be due to atomic force. The dependence of the MFM image on the tip to sample spacing is discussed also.
Transformer coupled plasma etch technology for the fabrication of subhalf micron structures
Authors: Carter J. B. , Holland J. P. , Peltzer E. , Richardson B. , Bogle E. , Nguyen H. T. , Melaku Y. , Gates D. , Ben-Dor M.
Published: July 2002

A transformer coupled plasma (TCP) source has been integrated into a production tool and characterized for subhalf micron etching of thin films. A planar 13.56 MHz plasma is produced over a wide pressure range of 1–500 mTorr. Langmuir probe measurements below 10 mTorr show ion densities ≳1012 cm−3 and low plasma potentials. These properties are favorable for high etch rates and low damage to device structures. Radio-frequency power is also supplied to the wafer electrode for dc bias control. Separation of the plasma generation and dc bias functions allows the control of microloading effects upon the etch profiles of dense and isolated lines. Performance of the tool is described for the etching of polysilicon and tungsten polycide films on substrates up to 200 mm in size. The evaluated characteristics include etch rate, selectivity, and microloading. The TCP is shown to be an advanced source with the capability for meeting 64 megabit device requirements.