bluuebunny/crossref_metadata_2025 huggingface dataset:
Dislocation Motion in Crystals With a High Peierls Relief: A Unified Model Incorporating the Lattice Friction and Localized Obstacles
Authors: Dour G. , Estrin Y.
Published: July 2002

The combined effect of the lattice friction and localized obstacles on the individual dislocation velocity is considered. First the two effects are considered separately. The velocity of an individual dislocation is described by the Hirth-Lothe equation for the case of lattice friction and by a power law for the case of localized obstacles. The power law is modified to introduce a static waiting time: the time a dislocation has to wait in its equilibrium configuration at an obstacle until it breaks away by virtue of thermal activation. As a next step, a combination of the two mechanisms is described. A dynamic waiting time is introduced: it corresponds to a situation when a dislocation overcomes the obstacle before it reaches the equilibrium configuration. The model provides a good description of the effects when they are independent, and also gives an interpolation of the two regimes. A simulation for a model material is proposed to illustrate the transition between the two regimes. This unified model is tested against experimental data for in-situ deformation of monocrystalline germanium in a transmission electron microscope. The purpose is to determine an equivalent power law exponent in a regime of plastic flow that does not follow a proper power law. The resolution is not complete because the strength of the localized obstacles is not known. However, the results are promising and allow a discussion relating to the strength of localized obstacles.
Surfactant Transport Over Airway Liquid Lining of Nonuniform Depth
Authors: Williams H. A. R. , Jensen O. E.
Published: July 2002

Numerous effects (e.g., airway wall buckling, gravity, airway curvature, capillary instabilities) give rise to nonuniformities in the depth of the liquid lining of peripheral lung airways. The effects of such thickness variations on the unsteady spreading of a surfactant monolayer along an airway are explored theoretically here. Flow-induced film deformations are shown to have only a modest influence on spreading rates, motivating the use of a simplified model in which the liquid-lining depth is prescribed and the monolayer concentration satisfies a spatially inhomogeneous nonlinear diffusion equation. Two generic situations are considered: spreading along a continuous annular liquid lining of nonuniform depth, and spreading along a rivulet that wets the airway wall with zero contact angle. In both cases, transverse averaging at large times yields a one-dimensional approximation of axial spreading that is valid for the majority of the monolayer. However, a localized monolayer remains persistently two dimensional in a region at its leading edge having axial length scales comparable to the length scale of transverse depth variation. It is also shown how the transverse spreading of a monolayer may be arrested as it approaches a static contact line at the edge of a rivulet. Implications for Surfactant Replacement Therapy are discussed. [S0148-0731(00)00202-8]
Application of Practical Observer to Semi-Active Suspensions
Authors: Nakai H. , Oosaku S. , Motozono Y.
Published: July 2002

This paper presents the development of gain-scheduled observers for semi-active suspensions. The states of the semi-active suspensions must be accurately obtained because the accuracy directly affects system performances such as ride comfort. Nonlinearity in the absorber of the semi-active suspensions is a difficult problem for estimating the accurate states using conventional linear observer theories. To solve this problem, we have designed a new gain-scheduled observer by introducing two improvements. The validity of this nonlinear observer was confirmed by simulations and experiments. The results indicate that the present observer can accurately estimate the suspension stroke velocity using the vertical acceleration sensor on the sprung mass. [S0022-0434(00)02302-9]
On the Nonuniform Deformation of the Cylinder Compression Test
Authors: Chen Fuh-Kuo , Chen Cheng-Jun
Published: July 2002

A theoretical model based on Hill’s general method is developed in the present study to calculate the flow stress in a cylindrical specimen under axial compression in the presence of friction at the die-specimen interface. Unlike most of the published methods which studied the incipient barreling only, the proposed theoretical model takes the barreled shape of the deforming specimen into account. In order to construct the stress-strain curve, the mean effective strain of the barreled specimen was also calculated on the basis of an assumed velocity field. As the present study shows, the proposed theoretical model provides good results, both in magnitude and in trend, for the prediction of flow stresses in the barreled specimen during the compression test. [S0094-4289(00)00602-2]
Inelastic Anisotropy of Inconel 718: Experiments and Mathematical Representation
Authors: Iyer Saiganesh K. , Lissenden Cliff J.
Published: July 2002

A generalized threshold function for viscoplastic materials, which can also serve as a yield function in rate-independent plasticity, is suggested for materials that exhibit a strength differential and/or a permanent volume change. The motivation for this type of a threshold function is that experiments, at both 25 and 650°C, on the nickel-based alloy Inconel 718 indicate that higher stresses occur in compression than in tension. Similar results have been obtained for martensitic steels and other metallic alloys at 25°C. A general approach for determining the inelastic flow dependence on each of the three stress invariants (I1,J2, and J3) is to follow stress paths where only one invariant is changing. Two classical experiments that do this are hydrostatic pressure and pure torsion, however many others are possible. Unfortunately, these stress paths generally require three-dimensional stress states, which are difficult to obtain in the laboratory. Thus, for experimental expediency, tests involving axial-torsional loading of thin-walled tubes can be used to determine the significance of the first and third stress invariants, I1 and J3, respectively. [S0094-4289(00)01303-7]
The Numerical and Experimental Study of Non-Premixed Combustion Flames in Regenerative Furnaces
Authors: Zhang C. , Ishii T. , Hino Y. , Sugiyama S.
Published: July 2002

A numerical procedure is presented to predict the turbulent non-premixed combustion flames in regenerative furnaces. A moment closure method with the assumed β probability density function (PDF) for the mixture fraction is used in the present work. The procedure is applied to an experimental regenerative slab reheat furnace developed in NKK to demonstrate its predictive capability. The predictions are compared with the experimental data. The comparison is favorable. [S0022-1481(00)01302-5]
Numerical Simulation of Heat Transfer in a Transitional Boundary Layer With Passing Wakes
Authors: Wu X. , Durbin P. A.
Published: July 2002

Direct numerical simulation (DNS) has been used to investigate heat transfer and provide thermal statistics in a transitional flow in which turbulent wakes traversing the inlet periodically are swept downstream across a constant-temperature flat-plate. The same heat transfer problem was also computed using unsteady Reynolds-averaged Navier-Stokes (RANS) method with the v2-f turbulence model. During transition, the instantaneous Stanton number field exhibits spotlike structure, which in turn results in a strong streamwise modulation in the phase-averaged Stanton number distribution. At molecular Prandtl number Pr=0.7, the Reynolds analogy factor decreases in the transitional region but remains nearly constant afterwards. After the completion of transition, mean and second-order temperature statistics are in good agreement with previous experimental data from slightly heated turbulent flat-plate boundary layers. Throughout the transitional and turbulent regions the turbulent Prandtl number increases sharply as the wall is asymptotically approached. DNS results at a higher wake passing frequency are also presented to illustrate the effect of freestream turbulence. Unsteady RANS predictions of the time- and phase-averaged Stanton numbers as well as the enthalpy thickness are in reasonable agreement with the DNS. [S0022-1481(00)02002-8]
Flyability Failures Due to Organic Siloxanes at the Head/Disk Interface
Authors: Raman Vedantham , Gillis Donald , Wolter Reinhard
Published: July 2002

With the trend toward lower flying heights and increasing storage capacity in the magnetic recording industry, the role of contamination and methods to counteract its deleterious effects are expected to become important. One area where the role of contaminants is expected to increasingly affect reliability is long term flyability. This is because volatile and semi-volatile materials in the drive can alter the flying characteristics of the slider during operation because of chemistry at the interface. In this paper, we describe the flyability performance of a head-disk interface system using full body capacitance measurements as a monitor of interface reliability. The principal features observed in flyability tests employing two sources of siloxanes, a model organic compound octamethylcyclotetrasiloxane as well as outgassing from an exposed adhesive tape with a release liner, are described. The deleterious effects of siloxane outgassing that lead to changes in the flying characteristics of the slider and subsequent interface failure are described for disks lubricated with Fomblin Z-dol. Chemical identification of the accumulated material on the slider following flyability testing is described. Strikingly different performance is observed for disks lubricated with the cyclic phosphazene X-1P which shows significantly improved flyability performance. Possible mechanisms that lead to the formation of silica at the head-disk interface for Z-dol based disks and reasons for their absence for an X-1P interface are discussed. [S0742-4787(00)01202-9]
An Inverse Analysis for Steady-State Elastohydrodynamic Lubrication of One-Layered Journal Bearings
Authors: Elsharkawy Abdallah A. , Guedouar Lotfi H.
Published: July 2002

This paper presents a solution to an inverse problem for the elastohydrodynamic lubrication of one-layered journal bearings. Eccentricity ratio, viscosity of the lubricant at atmospheric pressure, pressure-viscosity coefficient, and bulk modulus of the lubricant are the parameters to be estimated from a given pressure distribution. The Least-squares optimization technique is used to solve the proposed inverse problem. Results are presented only for infinite-width journal bearings. The results showed that the proposed inverse algorithm is efficient and accurate. [S0742-4787(00)00703-7]
KBr Crystal: Cleaved in Air
Authors: Crist B. Vincent
Published: July 2002

A crystal of infrared-grade potassium bromide (KBr) was cleaved in air using a clean single-edged razor blade. The crystal was adhered to double-sided adhesive tape and analyzed by XPS at an angle that maximizes the information associated with subsurface bulk. The crystal's dimensions were 3 mm × 3 mm × 10 mm (w × h × l), and only the freshly exposed surface was analyzed. A mesh made of nickel wire was placed about 1 mm above the surface of the sample to flatten the electric fields on the sample.
Lead Zirconate–Lead Titanate (PbZrO3–PbTiO3) Thin Film Prepared by the Sol-gel Process by XPS
Authors: Bozack Michael J.
Published: July 2002

An XPS spectrum of the lead zirconate titanate ferroelectric thin film PbZrO3–PbTiO3 (PZT) is presented. The film was prepared by the sol-gel process on a sputtered Pt substrate. PZT is currently under investigation for nonvolatile ferroelectric memory applications requiring polarization reversal.
Structural and mechanical characterization of fluorinated amorphous-carbon films deposited by plasma decomposition of CF4–CH4 gas mixtures
Authors: Jacobsohn L. G. , Franceschini D. F. , Maia da Costa M. E. H. , Freire F. L.
Published: July 2002

Fluorinated amorphous-carbon films (a-C:F:H) were deposited by low-power rf capacitively coupled plasma-enhanced chemical-vapor deposition using CH4–CF4 gas mixtures. Different series of films were deposited, changing one parameter at a time: the CF4 partial pressure from 0% to 100%, the self-bias voltage from −50 to −700 V, and the total deposition pressure from 5 to 15 Pa. The composition was determined by ion-beam analysis (IBA): Rutherford backscattering spectrometry, elastic recoil detection analysis, and nuclear reaction analysis. The atomic density of the films was evaluated by combining the IBA results with the thickness value measured by stylus profilometry. Film structure was investigated by infrared transmission and Raman scattering spectroscopies. The internal stress and Vickers hardness were also measured. For a fixed self-bias, the increase of the CF4 partial pressure leads to a higher fluorine incorporation and the decrease of both hardness and internal stress. The film microstructure changes from diamond-like to a polymer-like structure. The fluorine incorporation also increases with the self-bias, and fluorine-poor polymer-like films are deposited at low-bias voltage. Fluorine incorporation occurs at the expense of the hydrogen content in both cases, i.e., increasing the CF4 partial pressure or the self-bias. Finally, the role of ion bombardment during film growth on the mechanical and structure properties of the films is discussed.
Simulations of a two-junction system with non-Ohmic tunnel junctions for high- and low-impedance environments
Authors: Nakashima H. , Uozumi K.
Published: July 2002

To find the energy-dependent tunnel rates we describe the effective potential energies of an electron tunneling through an ultrasmall capacitor in a two-junction system for the limits of high- and low-impedance environments. Using these effective potential energies, the current–voltage characteristics of the two-junction system are demonstrated.
Stability of boron and phosphorus implanted tungsten silicide structures at high temperatures
Authors: Bashir R. , Hebert F.
Published: July 2002

We report on the stability of sputter-deposited tungsten silicide (WSi2.6) films that were implanted with boron or phosphorus and annealed at high temperatures using rapid thermal annealing. Depending on process conditions, some films were found to be unstable, resulting in peeling and lifting from the substrate. The regime of stability was experimentally determined and found to be a function of the implant dose, species, and anneal temperature. Films implanted with boron were found to be more stable than those implanted with phosphorus. With the appropriate choice of dopant dose, anneal temperature, and capping layer type, the film stacks were found to be stable upon subsequent furnace annealing steps at 900 °C.
Preparation of C60-doped silica aerogels and the study of photoluminescence properties
Authors: Zhou Bin , Wang Jue , Zhao Li , Shen Jun , Deng Zhongsheng , Li Yufen
Published: July 2002

The preparation of C60-doped silica aerogels by the sol-gel process is described in this article. Fourier transfer infrared spectra, time-of-flight mass spectroscopy, and transmission electron microscopy showed that C60 was incorporated into silica aerogels, and the C60 structure was retained in the preparation process. The C60-doped silica aerogels emitted intense visible light (2.10 eV) under Ar+ laser (488 nm) excitation at room temperature, and the photoluminescence peak was “blueshifted” when compared with C60’s. The blueshift is explained based on a quantum confinement effect.
In situ reflectance-difference spectroscopy of doped CdTe and ZnTe grown by molecular beam epitaxy
Authors: Balderas-Navarro R. E. , Hingerl K. , Hilber W. , Stifter D. , Bonanni A. , Sitter H.
Published: July 2002

We have used reflectance-difference (RD) spectroscopy (UV-visible energy range) during the growth and doping process of CdTe(001) and ZnTe(001) layers by molecular beam epitaxy (MBE). The MBE chamber is equipped with an electron cyclotron resonance cell to generate N plasma and a ZnCl2 effusion cell for the p- and n-type doping, respectively. After the first stages of the growth and prior doping, different spectral features were found as we changed from Cd or Zn to Te stabilized conditions due to surface anisotropy. However, as the doping of the growing layer further increased, the RD spectra of both surfaces showed resonances around E1 and E1+Δ1 interband transitions due to the linear electro optic (LEO) effect. Although RD spectra exhibit similar line shapes dominated by surface transitions, differences due to the LEO can be isolated. Different Fermi level pinning mechanisms are proposed for both materials because the RD measurements of the LEO strongly depend on surface termination.
Microstructure of Cu film sputter deposited on TiN
Authors: Furuya Akira , Ohshita Yoshio , Ogura Atsuhi
Published: July 2002

The correlation between the microstructure of Cu films and the deposition conditions of the sputtering method was investigated to obtain larger grain size and higher (111) texture. Cu film was deposited on SiO2 and TiN by varying substrate temperature, Ar gas pressure, and rf power. It is found that the texture of the Cu film has very little dependence on the deposition conditions. The Cu grains are more oriented to (111) on a TiN substrate than on a SiO2 substrate, and the (111) ratio of the Cu films on the TiN substrate increases as the (111) ratio of the TiN film is increased. The maximum increase in grain size was tenfold by reducing the Ar pressure from 3 to 1 mTorr, fivefold by increasing the deposition temperature from room temperature to 300 °C, and twofold by increasing the sputtering power from 1.1 to 4.4 W/cm2. Thus, it is revealed that the lowering of Ar gas pressure is the dominant factor for enlarging the grain size. An increase in the energy of Cu particles brought about by reducing the Ar gas pressure is discussed as one of the factors contributing to the increase in the grain size.
Study of aniline on a Si(111)7×7 surface by scanning tunneling microscopy
Authors: Tomimoto H. , Sumii R. , Shirota N. , Yagi S. , Taniguchi M. , Sekitani T. , Tanaka K.
Published: July 2002

The adsorption of aniline on a Si(111)7×7 surface was examined by scanning tunneling microscopy (STM). In the STM images at negative sample bias, aniline molecules were observed as bright ring-like features. We have found that aniline molecules adsorb on the center adatom site, with its amino group oriented to the rest atom site. The differences in reactivity of the various sites on the Si(111)7×7 surface to aniline were observed. The center adatom site is more reactive than the corner adatom site. With increasing aniline exposure, an aniline chain was observed. From the STM images obtained at various sample biases, this aniline chain is seen to have different electronic structure from an aniline molecule singly adsorbed on the Si(111)7×7 surface. This suggests that aniline molecules are associated with each other on the Si(111)7×7 surface.
Fractality aspects during agglomeration of solid-phase-epitaxy Co–silicide thin films
Authors: Palasantzas G. , De Hosson J. Th. M.
Published: July 2002

Morphology changes of thin CoSi2 films close to the agglomeration threshold have been investigated by in situ scanning tunneling microscopy. Films prior to agglomeration reveal a strong morphology anisotropy where depending on direction the roughness correlation g(r) changes from logarithmic [g(r)∼ln r] to power law [g(r)∼r2c with c≈0.78] at short lateral length scales (r⩽30 nm). Such an anisotropy reflects the complex nature of diffusion process associated with the original anisotropic substrate surface and the formation of pinhole networks. Annealing above the agglomeration threshold (>600 °C), the pinhole network becomes connected breaking the CoSi2 film into aggregates with a two-dimensional fractal dimension D≈1.66 which is close to predictions of diffusion limited aggregation within the mean field theory prediction D=(d2+1)/(d+1) for d=2, and invasion percolation models.
Design of compression shrink-fit ceramic—steel wear ring assembly for chemical mechanical planarization
Authors: Lougher Wayne , Vondra Lawrence
Published: July 2002

Ceramic–metal joining techniques have traditionally been concerned with topics such as interfacial reactions between glass/ceramic, wetting, graded seals, active metal braze reactions, residual tensile stresses, atom migration, temperature and atmospheric effects, etc. These reactions are complex and require substantial trial and error and analytical techniques to develop the proper interfaces for reliable bonding. In contrast, we have developed a simple shrink-fit ceramic/metal join for use as a new ceramic wafer retaining ring in chemical mechanical planarization. The join relies on thermal coefficient of expansion mismatch between the metal and the ceramic. The join requires no other materials such as braze or metallization and can be performed with one heating cycle in a low temperature oven. In addition, the join is reversible with reheating. This article details design considerations for developing this bond. In addition, stress analysis results using finite element analysis are presented and discussed.
Growth of Thin Iron Films on Gold and Rocksalt Substrates at 80 K
Authors: Wassermann E. F. , Sander W.
Published: July 2002

Gold layers, approximately 1000 Å thick, have been evaporated in ultrahigh vacuum onto air-cleaved rocksalt substrates, held at 80 K. Immediately following the gold evaporation thin iron films have been deposited on top of the gold layers. Part of the iron was also evaporated directly onto the rocksalt. All the layers have been covered with a carbon film at low temperature. Nucleation and growth of the iron layers on top of the Au films have been studied after dissolving the Au quantitatively away. For iron layers of equal thickness the differences in film topology have been investigated. For the same stage of growth these differences can be explained by taking the various binding energies between overgrowth and substrate into account. The results can be used to explain relations between the evaporation sequence and changes in the critical temperature of superconductor-normal metal packages in the proximity effect.
Energy Characteristics of Ions Transmitted by a Quadrupole Mass Filter
Authors: Evans Bert E. , Supple Rodney W.
Published: July 2002

An idealized model of the quadrupole electric field predicts that ions leaving the exit aperture of a mass filter can have transverse energy as high as 0.7 Vac, and axial energy equal to that of the incoming ions. A retarding field measurement using a cylindrically symmetric collector has shown that the total energy of transmitted ions is much lower than expected, and has a narrow distribution around the incident ion energy. The energy distribution has been determined for several ions to mass 264 and is found to be mass-dependent. The low energy of emergence and narrow energy distribution indicate possible utility in vacuum applications where a mass-resolved and directed ion beam is required. Improved ion optical design data are available for applications requiring the use of a mass-resolved beam, for instance in detector remote from filter.
Vacuum and Gettering Problems in Electron Tubes and Lamps of Both Filament and Discharge Types
Authors: della Porta P.
Published: July 2002

In this review the problems caused by residual gases in electron tubes and of unwanted gases in filament and discharge lamps are described and discussed with reference to construction and production techniques. A summary of the various sources of residual gases in electron tubes is accompanied by a conceptual description of the use of getters to overcome the undesirable effects of these gases. The basic differences between barium and nonevaporable getters are outlined. Attention is paid to the harmful effects of unwanted gases in incandescent and high- and low-pressure discharge lamps with emphasis on the gas problems in fluorescent tubes. The appropriate gettering technique for each category of lamp is indicated and this includes the description of a new combined getter and mercury dispenser for fluorescent lamps. Finally, the basic differences between analysis of gases in evacuated electron tubes and gas-filled lamps are briefly compared.
The Current Status of the VOD/LD–VAC Process
Authors: Fleischer Hans J.
Published: July 2002

Presented by C. W. Finkl

A. Finkl and Sons Company, subsidiary Republic Steel Company

The vacuum decarburization of high chromium heats called VOD in North America and LD–VAC in the rest of the world has revolutionized the melting practice of stainless steel. Since production trials started at the end of the last decade, a world production capacity of 1 720 000 tons annually has been built or is under construction. This paper deals with the latest design of the Vacuum Decarburizing Unit, and of the basic-lined slide gate ladles. It sequentially describes operating procedures giving time, chemistry, and temperatures related to the separate steps of the process. Multicombinations of melting and vacuum decarburizing facilities are explained along with cost and furnace time savings. Equipment descriptions cover cost and type of ladle refractories, vacuum pumping curve, inherent fume control, and end-point determination. Latest metallurgical developments and short cycle desulfurization in direct combination with decarburization outside the premelting furnace are also discussed, as is the advantage of vacuum ladle degassing in the VOD/LD–VAC unit.
Application Possibilities of Atomic Resonance Absorption Spectroscopy in Vacuum Metallurgy
Authors: Fazekas E. I. , Mezey M. , Bunshah R. F.
Published: July 2002

Many of the processes in vacuum metallurgy involve the presence of one of the constituents in the vapor phase at pressures less than 1 atm, often less than 10−3 Torr. Recently, it has been shown that atomic resonance absorption spectroscopy can be used to detect very low partial pressures. Therefore, the possibility is open to use this technique to study and/or control various vacuum metallurgical processes. This paper considers briefly the theoretical background, demonstrates the application of the principle, and discusses the possible applications in vacuum metallurgy.
An Experimental System for a Study of the Kinetics of Heterogeneous Nucleation of Metals on Singal Crystal Mica Substrates
Authors: Elliot A. Grant
Published: July 2002

An ultrahigh vacuum LEED system has been modified for carrying out step kinetic nucleation studies. A substrate heating oven giving accurate, reproducible (±5 °C) surface temperatures, a condensate evaporation oven, a water-cooled quartz crystal microbalance, and a silicon monoxide evaporation source are described. Operating conditions and procedures leading to the attainment of number densities of nuclei reproducible to within a factor of two and nucleation rates accurate to within ±30% are discussed.
Appearance Potential Study of the Band Structure of Transition Metals on Transition Metal Surfaces
Authors: Houston J. E. , Park Robert L.
Published: July 2002

Soft x-ray appearance potential spectra have been obtained for dilute coverages of transition metals on transition metal surfaces. The appearance potential spectrum of a given core level is the differential excitation probability as a function of sample potential. For transition metals this produces a strong positive threshold peak whose width is related to the unfilled portion of the d band. The titanium-nickel system is of particular interest since, in their pure form, titanium and nickel have nearly empty and nearly filled 3d bands respectively. In preliminary studies of this system, we find the 2p32 peak of nickel in dilute concentration on a titanium surface to be identical to the titanium 2p32 peak obtained from dilute coverages of titanium on a nickel surface. The width of these peaks is intermediate between the clean Ti and Ni values. This result, which suggests a common band model for an alloy of stoichiometry near that of TiNi, is contrasted with recent experimental and theoretical studies of dilute transition metal alloys.
Tunneling from Cambridge Surface States
Authors: Gadzuk J. W.
Published: July 2002

Solids with electron band structures given by a simple analytic function of wavenumber (E∼k2 for free electron bands; E∼k for tightbinding bands) possess localized electron states at their surfaces which are easily treated within the complex k vector formalism developed especially by Heine and collaborators. These surface states, which will be called Cambridge surface states, can occur not only in energy gaps caused by Bragg reflections at Brillouin zone faces but also in spin-orbit split gaps and hybridization gaps within the zone. In this work a theory of tunneling and field emission of electrons from such surface states is developed. The field emission energy distribution from d-band metal surface states is calculated using Harrison’s d-band pseudopotential theory, and the results are favorably compared with experimental data. Since the existence conditions for Cambridge surface states depend crucially upon the boundary conditions at the surface, the act of measurement via a tunneling process can sufficiently alter the boundary conditions that “surface states” are either created or destroyed by “looking” at them. In particular the strong coupling ion neutralization tunneling experiments of Hagstrum are very susceptible to this effect.
Observations of Sputtered Thin Film Growth
Authors: Sherman Dudley M. , Maa J. S. , Hutchinson Thos. E.
Published: July 2002

A commercial TEM has been modified to permit the observation of the early growth behavior of ion beam-sputtered thin films inside the microscope. The growth of silver on evaporated carbon substrates has been studied in detail, but the occurrence of so-called abnormal islands (large platelike particles) has prohibited meaningful quantitative analysis of the early growth processes. Reproducible silver deposits void of any, abnormal island growth have, however, been obtained on muscovite mica and graphite. The qualitative features of the nucleation and early growth of sputter-deposited silver films are similar to those of evaporated films, and to date no dependency of early growth parameters upon deposition method has been found. Silicon and niobium have also been sputtered onto graphite substrates inside the microscope, and preliminary results of early growth studies are given.
Tunneling Studies of the Formation of Intermetallic Compounds in Gold–Lead Films
Authors: Hebard A. F.
Published: July 2002

The possibility of forming the gold–lead intermetallic compounds Au2Pb, AuPb2 and AuPb3 in tunnel structures using thin films of aluminum, aluminum oxide, lead, and finally gold is being studied. The room temperature diffusion of gold into lead films with thickness in the range 1000–3600 Å is found to be rapid, with indications of compound formation taking place within a few hours. Variation of the thickness ratio of the lead and gold films is used to preferentially form a given intermetallic. Each intermetallic is characterized by its transition temperature Tc, energy gap Δo, and by a unique phonon spectrum which is reflected in the derivatives of the tunneling characteristics.
Ultrathin Multiply Connected Rhenium Films
Authors: Lewis R. T.
Published: July 2002

An extensive (> 10 μ) multiply connected ultrathin (∼2 nm) rhenium metal film can be formed on the internal surfaces of porous high area aluminas and silicas by simple chemical means, ac susceptibility measurements have been made on such samples in applied static magnetic fields at temperatures below the superconducting transition of the rhenium film. The results can be interpreted using a model of hollow thin-walled cylinders in which the cylinder diameter is a measure of the extent of multiply connectedness and the wall thickness is a measure of the film thickness. The susceptibility is observed to decrease much more rapidly with increasing ac measuring field than with increasing applied static field. It is assumed that the decrease with ac field is inversely proportional to the cylinder diameter, and the decrease with static field is inversely proportional to the wall thickness. Using this model, estimates from the susceptibility measurements are found to be consistent with independent estimates of the film thickness from x-ray diffraction line broadening and of the extent of multiply connectedness from the decrease in signal after grinding and screening the sample.
Representation of Focal Properties of the Equal-Diameter Two-Tube Electrostatic Lens for Computer Calculations
Authors: Galejs A. , Kuyatt C. E.
Published: July 2002

Previous calculations have given accurate first-order focal properties for the two-tube electrostatic lens at discrete voltage ratios. For computer optimization, calculations involving systems of two-tube lenses, one must be able to calculate the focal properties continuously over some arbitrary range of voltage ratios. Hence the data must be displayed in a continuous manner, and a method of interpolation is needed which yields functions having a high degree of smoothness. Special care must be taken to describe the lens behavior correctly near zero strength or for the voltage ratio approaching unity. A satisfactory solution to this problem has been achieved using cubic splines. The resulting functions of the focal properties are continuous and have continuous first and second derivatives. The total beam behavior, and hence the system design, is determined by the transfer matrix which is obtained from the focal properties. To achieve sufficient accuracy in the lens calculations over the entire range of required focal properties, the region near zero lens strength had to be treated separately.
The role of Coster-Kronig transitions in the ionization of surface atoms
Authors: DuCharme A. R. , Gerlach R. L.
Published: July 2002

Since Coster-Kronig transitions for isolated atoms are often characterized by higher transition rates than other types of Auger emission, it is important to consider the quantitative effect of these transitions on the Auger electron spectroscopy of solid surfaces. We find that cross sections for the electron impact ionization of L and M shells of surface atoms are augmented by core electron vacancy production due to Coster-Kronig transitions. In the case of L2,3 shell ionization of adsorbed Cl, and L1 contribution is calculated to be about 17% of the total cross section for incident electron energies which exceed four times the L2,3 ionization energy. The M1 and M2,3 ionizations account for about 25% of the total M4,5 ionization cross section for Ba when the energies of the incident electrons exceed the subshell ionization thresholds. Calculated cross sections exhibit good agreement with experimental values for the above elements when the effects of Coster-Kronig transitions are included. It is also shown that Coster-Kronig yields may be determined by combining measured secondary electron currents corresponding to respective subshell ionizations with calculated cross sections.
Study of current leakage in InAs p–i–n photodetectors
Authors: Lin Ray-Ming , Tang Shiang-Feng , Kuan C. H.
Published: July 2002

The current leakages of InAs photodiodes have been systematically studied by adding undoped layers having thicknesses of 0, 0.30, and 0.72 μm between the p–n junction. At reverse bias V=−0.5 V, the dark currents of the InAs p–i–n diodes with undoped layer thicknesses of 0, 0.30, and 0.72 μm are about 5×10−6, 7×10−8, and 1×10−10 A, respectively, at 77 K. The leakage current of the InAs p–n diode was successfully reduced by adding 0.72-μm-thick undoped layer between the p–n junction.
Dual tunneling-unit scanning tunneling microscope for practical length measurement based on reference scales
Authors: Zhang Haijun , Wu Lan , Huang Feng , Cheng Shuwen
Published: July 2002

A new setup of dual tunneling-unit scanning tunneling microscope (DTU STM) has been developed that can realize simultaneous calibration between test sample images and standard reference scales. The crystalline lattices and periodic grating features are employed as such scales for practical length measurements, respectively, in the nanometer and the micron orders. The DTU STM consists of a reference unit and a test unit horizontally set in parallel to eliminate Abbe’s errors. Their probe tips are attached to one single XY scanner on the same surface, while the reference and test sample holders are open. As the tips scan over the sample surfaces, two images with the same lateral size are simultaneously acquired. Line lengths in the test image could be measured by counting the number of crystalline lattices or grating patterns in the reference side. Two vertical impact drive mechanisms were applied to coarsely positioned samples in the Z direction. Another two impact drive mechanisms were employed to the horizontal drive sample holders as to automatically position the samples in the lateral plane. We present a brief discussion about the concept and setup of the DTU STM. Some comparison results using crystalline lattices and grating patterns, respectively, as reference scales for length calibration are provided. Experiments show a satisfactory matching between the two tunneling units when covering a wide scan range from 5 nm to 10 μm. With its new setup, the DTU STM is confirmed to be a more accurate device for practical length measurement even when measuring comparatively large and heavy samples.
Oxygen plasma induced degradation in InGaAs/InP heterostructures
Authors: Driad R. , McKinnon W. R. , McAlister S. P.
Published: July 2002

The effects of oxygen plasma conditions on the performance of InGaAs/InP heterostructure bipolar transistors (HBTs) have been studied by comparing the HBT’s characteristics, such as current gain and breakdown voltage, before and after treatment. The base–emitter junction characteristics of InGaAs/InP HBTs were unaffected by oxygen plasma treatments, for exposure periods of up to 10 min and rf powers <200 W. Higher rf powers degrade the current gain. In contrast, the base–collector junction was degraded even for short periods and low rf powers; the base–collector leakage current increased and the breakdown voltage decreased. Further reduction of the current gain was observed when dielectric films were deposited by plasma-enhanced chemical vapor deposition on oxygen treated devices. The dielectric film does not reduce the gain of devices that were not treated by oxygen plasma.
Development and qualification of a vacuum pumping system for metalorganic vapor phase epitaxy copper precursors
Authors: Davis R. P. , Abreu R. A.
Published: July 2002

Semiconductor devices incorporating copper interconnects are set to revolutionize the performance and functionality of integrated circuits. Copper interconnects enable faster and more reliable circuitry at sub-0.25 μm dimensions with lower resistivity and excellent resistance to electromigration. Numerous methodologies exist whereby copper can be deposited, with chemical vapor deposition (CVD) being one such technique. A vacuum pumping system that effectively and efficiently handles the process byproducts from the CVD precursor Cu(hfac)(TMVS) has been developed and qualified. It is shown that a standard dry pump used in conjunction with additional apparatus in the vacuum system results in the safe handling of process byproducts. The performance of each component of the vacuum system has been individually qualified and the abatement performance of the overall system shows >99% destruction efficiency of process effluent.
How to make polyvinylphenol inhibitable by diazonaphthoquinone sulfonates
Authors: Yan Zhenglin , Yeh Tung-Feng , He Xiaohua , Reiser Arnost , Schadt Frank L. , Fincher Curtis R.
Published: July 2002

There is interest in phenolic resins that are transparent at 248 nm and the dissolution of which in alkaline aqueous developers can be inhibited by diazonaphthoquinone sulfonic acid derivatives, the standard photoactive compounds (PACs) of novolak resists. Poly(4-hydroxystyrene), i.e., poly(vinylphenol), has the requisite optical properties, but its dissolution is not very effectively inhibited by standard PACs. We have now found that poly(4-hydroxystyrene) can be made more inhibitable by increasing the acidity of its OH groups and, at the same time, lowering the concentration of the acidic OH groups in the resin.
Effect of chamber pressure and atmosphere on the microstructure and nanomechanical properties of amorphous carbon films prepared by pulsed laser deposition
Authors: Wei Q. , Sankar J. , Sharma A. K. , Yamagata Y. , Narayan J.
Published: July 2002

We have investigated the effect of chamber pressure and atmosphere on the microstructure and nanomechanical properties of amorphous carbon thin films prepared by pulsed laser deposition. The amorphous carbon films were deposited in various atmospheres such as nitrogen and argon at different chamber pressures. We used Raman spectroscopy to study the bonding characteristics of the deposited amorphous carbon films. Atomic force microscopy and optical microscopy were utilized to observe the surface conditions and the microstructures of the deposited films. Nanoindentation measurements were carried out on various samples prepared under different conditions to study the effect of chamber pressure and atmosphere on the elastic modulus and nanohardness of the films. It was found that reduced vacuum leads to formation of amorphous carbon films with reduced elastic modulus and nanohardness. Amorphous carbon films prepared under higher chamber pressures exhibit an increased density of particulates and significantly roughened surface. The results were understood in combination with the optical emission and electrostatic measurements of the laser plasma plume. It was found that the presence of atmosphere decreases the leading edge ionic energies of the species in the laser plasma plume and increases the thermalization of the laser plasma due to an increased possibility of collision.
Lithography using ultrathin resist films
Authors: Pike Christopher , Bell Scott , Lyons Chris , Plat Marina , Levinson Harry , Okoroanyanwu Uzodinma
Published: July 2002

The industry trend toward higher numerical apertures and lower k1 factors is severely constraining the manufacturing process margin for current and future lithography technologies. Ultrathin resist (UTR) films and other thin layer imaging techniques offer the promise of improved process margin as compared to conventional single layer resist schemes. In this study, an UTR over hard mask process was used to pattern the transistor gates of a high performance microprocessor using 248 nm lithography while focusing on four key areas of concern for UTR films: resist film defectivity, response of thin resist to device topography, quality of pattern transfer on device wafers, and device yield comparable to a baseline process. The intrinsic defectivity of resist films as thin as 65 nm is found to be no greater than that of a >500 nm resist film on flat silicon wafers. No pinhole defects are observed during scanning electronic microscopy review of defects on as-coated UTR films. As expected, the UTR process is sensitive to device topography, but the effects are manageable for the conditions used here. Robust pattern transfer with defect levels comparable to the baseline single layer resist process is demonstrated using UTR films as thin as 150 nm and a hardmask. Finally, device yield data confirms that the UTR process is as manufacturable as a conventional single layer resist process.
Growth of InAsN/InGaAs(P) quantum wells on InP by gas source molecular beam epitaxy
Authors: Wang Jyh-Shyang , Lin Hao-Hsiung , Song Li-Wei , Chen Guan-Ru
Published: July 2002

The growth of InAsN/InGaAs(P) quantum wells (QWs) on InP substrates by gas-source molecular-beam epitaxy and a rf plasma nitrogen source is reported for the first time. The double crystal x-ray diffraction satellite peaks of the InAsN/InGaAsP multiple quantum well (MQW) samples are sharper than those of the pure InAs/InGaAsP MQW samples, showing that a flatter heterointerface is achieved due to the smaller lattice mismatch. However, broadening of the satellite peaks and degradation of the photoluminescence (PL) intensity due to the increase of the nitrogen composition in these InAsN/InGaAsP MQWs suggest the existence of defects introduced by the small diameter nitrogen atoms located on arsenic sites. The PL result also shows that the peak energy decreases as the nitrogen composition increases. The estimated transition energy shrinkage coefficient is −31 meV/at. % nitrogen. The largest nitrogen composition obtained in this study is 5.9%, and its 10 K PL peak wavelength is ∼2.6 μm (480 meV). The effects of growth temperature on nitrogen composition and PL intensity are also discussed.
Influence of deposition method and dielectric layer on structure and electrical properties of Mn discontinuous films
Authors: Biegański P. , Dobierzewska-Mozrzymas E. , Wójcik J. , Pieciul E.
Published: July 2002

Two groups of Mn films with different mass thicknesses were obtained on quartz-glass substrates under vacuum conditions (p=10−4 Pa). The films of the first group were thermally evaporated, and the films of the second were obtained by electron gun evaporation. After deposition, the temperature dependencies of the resistance were measured in vacuo in situ for both groups, and the activation energies of the resistance were determined. The results of structural examinations (electron diffraction patterns and microstructures) are also presented. The electrical properties, structure, and content of the thermally evaporated Mn films are distinctly different from those of the films obtained using electron gun evaporation. The films of the second group reach higher resistance and activation energies of resistance values. Indexed electron diffraction patterns show a higher content of MnO in the films of this group. It has been found that the resistance increases with time and that the grains consist of α-Mn, β-Mn, and MnO. The appearance of MnO content with high resistivity (ρ∼1017–1019 Ω m) causes a significant increase in resistance. In order to protect from oxidation, after deposition the Mn films were covered with dielectric MgF2 layers.
Prototype optoelectronic device for generating signals from dc to 10 GHz by resonant laser-assisted field emission
Authors: Hagmann M. J. , Brugat M. , Rodriguez M. , Candal A. , Moros W. E. , Roque A. J. , Mackie W. A.
Published: July 2002

Simulations show the radiation from a laser can increase field emission current by resonant photoexcitation of the electrons, and photomixing could cause oscillations of the emitted current at frequencies from dc to over 100 THz. However, earlier prototypes were limited to operation from dc to 1 MHz because of inefficient coupling of the load to the apex of the emitting tip where the signals are generated. In the new prototype the zirconium carbide tip and the anode are mounted on an 8 mm length of parallel wire transmission line. This is a one-port device, so that external to the tube, the transmission line is connected to the dc bias supply via a rf choke, and to the load via a blocking capacitor and a passive element impedance matching network. Because of the small dimensions and the large value of the beam impedance, the prototype acts as a lumped current source from dc to 10 GHz. In initial testing, a pulsed laser diode is used as the radiation source with a spectrum analyzer as the load. We describe the dc current–voltage characteristics of the prototype and the techniques used to obtain subnanosecond optical pulses in order to determine the frequency response of the new prototype.