bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Simulation of Bubble Merger Process on a Single Nucleation Site During Pool Nucleate Boiling
Authors: Son G. , Ramanujapu N. , Dhir V. K.
Published: July 2002

A bubble merger process on a single nucleation site has been investigated by numerically solving the equations governing conservation of mass, momentum and energy in the vapor and liquid phases. The vapor-liquid interface is captured by a level set method which can easily handle breaking and merging of the interface. The level set method is modified to include the effects of phase change at the interface and contact angle at the wall. Also, the evaporative heat flux from the thin liquid film that forms underneath a growing bubble attached to the wall is incorporated in the analysis. Based on the numerical simulations, the effect of bubble merger on vapor removal rate, flow field and heat transfer has been quantified. The bubble merger pattern predicted numerically has been found to compare well with the experimental observations.
Molecular Dynamics Simulation of Heat Transfer and Phase Change During Laser Material Interaction
Authors: Wang Xinwei , Xu Xianfan
Published: July 2002

In this work, heat transfer and phase change of an argon crystal irradiated by a picosecond pulsed laser are investigated using molecular dynamics simulations. The result reveals no clear interface when phase change occurs, but a transition region where the crystal structure and the liquid structure co-exist. Superheating is observed during the melting and vaporizing processes. The solid-liquid interface is found to move with a velocity of hundreds of meters per second, and the vapor is ejected from the surface with a vapor front velocity of hundreds of meters per second.
Effects of Taper Variation on Conical Threaded Connections Load Distribution
Authors: Baragetti, Ph.D. S.
Published: July 2002

Threaded connections are used in a lot of mechanical and civil engineering applications and, nowadays, are perhaps the most developed and economical way to join two elements made of any kind of material. It is well known that when a bolt is screwed into a threaded hole, the first threads engaged bear more than half of the axial load induced by the make-up torque. This overload in correspondence with the first threads engaged, together with the steep stress gradient induced by the notch effect at the thread root, is the cause of dramatic fatigue failures. Moreover, it is on the first threads engaged, because of the presence of high contact loads on the flanks of the threads, that galling can arise and promote surface damage if the threaded connection has to be screwed and unscrewed many times. The object of this paper is to propose a numerical finite element procedure, confirmed by means of full-scale experimental tests, which makes it possible to quantify the effects induced by varying the taper of rotary shouldered connections (RSCs), in terms of stress state, loads carried by the threads and pressure on the thread flanks. RSCs are conical threaded connections used in the oil industry and the aim of the procedure is to provide the designer with a useful tool able to minimize the dangerous effects of galling and overload.
The Spherical Surface Symmetrical Equal Dividing Angular Quadrature
Scheme for Discrete Ordinates Method
Authors: Li Ben-Wen , Chen Hai-Geng , Zhou Jun-Hu , Cao Xin-Yu , Cen Ke-Fa
Published: July 2002

A new angular quadrature scheme named Spherical surface Symmetrical equal Dividing (abbreviated to SSDN) is presented. The evaluations of double moments by SSDN and other traditional quadrature sets show that the new SSDN is able to provide good accuracy and compete well with others (as for example the SN and LSN method). Radiative predictions in a black-walled rectangular enclosure containing absorbing-emitting medium indicate that, compared with SN,LSN,TN, and SRAPN, the SSDN can give higher accuracy than SN under some order numbers N. Numerical experiments demonstrate the computational economy of SSDN for some cases.
Thermal Analysis of Severe Channel Damage Caused by a Stagnation Channel Break in a PHWR
Authors: Mukhopadhyay D. , Majumdar P. , Behera G. , Gupta S. K. , Raj V. Venkat
Published: July 2002

The reactor channel of the horizontal core of pressurized heavy water reactors experiences very low sustained flow during loss of coolant accident (LOCA) at the reactor inlet feeders caused by certain breaks known as critical channel breaks. In this type of accident the reactor trip is delayed causing a gross mismatch of the heat generation and heat removal in the channel, thus leading to rapid temperature rise in the affected channel. A study has been carried out to identify the phenomena and the break size leading to such a situation. Severe fuel damage is predicted in the channel.
Humidity-Induced Dimensional Changes in Cotton-Phenolic Ball-Bearing Retainers
Authors: Bertrand P. A. , Sinsheimer J. D.
Published: July 2002

The sensitivity of clean and oil-impregnated cotton-phenolic retainers to atmospheric humidity has been measured. The cleaning procedure used here, and vacuum oil-impregnation did not change the dimensions of the retainers. Absorption of water caused the diameter of the retainers to increase by 0.2 to 0.4 percent, depending on the humidity. Oil impregnation of the retainers retarded, but did not stop, the absorption of water. Oil was displaced from the impregnated retainers by water; one-third to one-half of the oil was removed, depending on the atmospheric humidity.
The Stretching and Slipping of Belts and Fibers on Pulleys
Authors: Bechtel S. E. , Vohra S. , Jacob K. I. , Carlson C. D.
Published: July 2002

We derive the equations of motion for an extensible belt on a pulley in which all effects of inertia, including (for the first time) acceleration due to stretching, are retained in the momentum balance. These equations are also valid for fibers and films on rollers undergoing cold draw. We apply our equations to the problem of torque transmission by a belt between two pulleys, and compare the resulting solution to solutions in which centrifugal acceleration is included but stretching acceleration is neglected (the common engineering practice), and the solution in which both centrifugal and stretching accelerations are neglected. We find that ignoring both centrifugal and stretching accelerations results in an overprediction of the maximum moment that can be transmitted, and, for a given transmitted moment, underprediction of the slip angles on the driving and driven pulleys and overprediction of belt strain rates and normal and frictional forces from the pulley on the belt in the slip zones. The common engineering practice of including the effects of centrifugal acceleration but neglecting stretching acceleration also results in errors, for example underpredicting the maximum moment that can be transmitted, overpredicting the slip angles, and underpredicting belt strain rates and normal and frictional forces on the driving pulley. The percentage error increases as the ratios of belt stiffness to centrifugal acceleration or initial belt tension decrease. [S0021-8936(00)01401-X]
Tipping the Cylinder Block of an Axial-Piston Swash-Plate Type Hydrostatic Machine
Authors: Manring Noah D.
Published: July 2002

Tipping the cylinder block within an axial-piston swash-plate type hydrostatic machine is a phenomenon that results in a momentary and sometimes permanent failure of the machine since the fluid communication between the cylinder block and the valve plate is instantaneously lost. The efforts of this research are to identify the physical contributors of this phenomenon and to specify certain design guidelines that may be used to prevent the failure of cylinder block tipping. This research begins with the mechanical analysis of the machine and presents a tipping criterion based upon the centroidal location of the force reaction between the cylinder block and the valve plate. This analysis is followed by the derivation of the effective pressurized area within a single piston bore and the cylinder block balance is defined based upon this result. Using standard control volume analysis, the pressure within a single piston bore is examined and it is shown that an approximate pressure profile may be used in place of the more complex representation for this same quantity. Based upon the approximate pressure profile a design criterion is presented which ensures that the pressures within the system never cause the cylinder block to tip. Furthermore, if this criterion is satisfied, it is shown that the worst tipping conditions exist when the system pressures are zero and therefore a criterion governing the design of the cylinder block spring is presented based upon the inertial forces that contribute to the tipping failure. [S0022-0434(00)00901-1]
Over-Temperature Forecasts on Electronic Packages Through a Transient R–C Model
Authors: Lwo Ben-Je , Tseng Kun-Fu , Kao Ching-Hsing , Lu Luke Su
Published: July 2002

Based on experimental data, a simple R–C (thermal resistance–heat capacitance) model with software precaution strategies are proposed in this paper to predict the steady-state temperature of the circuit in an electronic packaging in real time. Further developments on the new methodology lead to real time monitoring if input power and/or the environment are changing during operations. It is concluded that the new methodologies, which make the over-temperature prediction much more reliable, efficient, sensible, and faster, can be easily employed for over-temperature protection designs on electronic packaging. [S1043-7398(00)00301-7]
Discussion: “Internal Bearing Chamber Wall Heat Transfer as a Function of Operating Conditions and Chamber Geometry” [ASME J. Eng. Gas Turbines Power, 122, No. 2, pp. 314–320]1
Authors: Mirzamoghadam A. V.
Published: July 2002

[S0742-4795(00)03102-1]
Control-Volume Finite Element Analysis of Phase Change During Direct Chill Casting
Authors: Pu X.
Published: July 2002

A fully implicit control-volume finite element method is used to analyze the phase change during DC casting of aluminum alloy. The mathematical model is based on the integral form of the enthalpy equation. A Eulerian-Lagrangian transformation, together with a deforming grid technique, is introduced to efficiently track the evolution of the physical domain. The temperature distribution predicted by the numerical model is in good agreement with that measured in previous experiments. [S0022-1481(00)00502-8]
Analysis of Poly(Ethylene Terephthalate) (PET) by XPS
Authors: Doren Aurora , Genet Michel J. , Rouxhet Paul G.
Published: July 2002

Poly(ethylene terephthalate) is used in numerous industrial applications. Successful medical applications are in the area of cardiovascular surgery. Its chemical functionality makes it propitious to grafting biochemical compounds; surface modification by plasma treatment may also be used to improve biocompatibility and modify wetting properties. The analyzed specimen was a commercial film (Mylar A). The main C 1s region was decomposed into three main components which were clearly identified on the recorded spectrum: 284.8, 286.4, and 288.8 eV attributed, respectively, to carbon only bound to carbon and hydrogen [C_—(C,H)], carbon making a single bond with oxygen [C_—O] and carbon of ester [C_OO]. Satellite peaks were found at 291.3, 293.5, and 295.8 eV. The molar ratios C_—(C,H):C_—O:C_OO were 3:0.92:0.91 excluding the satellite peaks, to be compared with the expected values of 3:1:1. The O 1s peak showed two partially resolved components at 531.6 [O_=C—O] and 533.3 eV [O=C—O_] with a satellite at 538.2 eV. The O:C ratio was 27.8:72.2, to be compared with the expected values of 28.6:71.4. The FWHM of the main C 1s components was in the range of 0.90 to 1.23 eV depending on the component and the mode of decomposition; the FWHM of O 1s components was about 1.40 eV.
Low TCR Kanthal Resistive Films for Hybrid IC's
Authors: Dhere N. G. , Sarma G. H. , Parikh N. R.
Published: July 2002

Investigations were carried out regarding the feasibility of Kanthal resistive films in hybrid integrated circuits. The technique for deposition was conventional evaporation from a multistrand tungsten filament onto substrates at 325 °C, in vacua better than 1×10−5 Torr. The filament source life was found to be long because of the absence of nickel in the alloy. The adhesion of films to glass and ceramic substrates and the compatibility with Al, Au thin films and thick-film Ag compositions used for conductors, were found to be good. Better substrate cleaning procedures and faster deposition rates resulted in lower TCR-value films. Fast evaporation of fresh charge invariably resulted in low TCR-value films. On the other hand the evaporation of the portion of the charge still remaining on the filament after the first evaporation resulted in high TCR-value films. To get low TCR-value films of given sheet resistances using fast evaporation and without the evaporation of the entire charge it was necessary to optimize the Kanthal charge on the filament. Low TCR films (∼10 ppm) were obtained in the range of sheet resistance 20 Ω/sq–250 Ω/sq. Because of simple evaporation technique, excellent adhesion to substrates, compatibility with conductor films, and low TCR values in a wide range of resistivities, Kanthal has been recommended for hybrid IC's.
Structure of Germanium Films Evaporated onto Clean NaCl Substrates
Authors: Shimaoka G. , Chang S. C.
Published: July 2002

Germanium films, 30–300 Å in thickness, evaporated onto vacuum-cleaved and air-cleaved NaCl substrates held at 25 °–500 °C in ultrahigh vacuum at various deposition rates, 0.1–20 Å/sec, have been investigated by reflection electron diffraction and transmission electron microscopy. It was found that structure and epitaxy of films were markedly influenced by substrate surface conditions and deposition rate as well as substrate temperature. Decoration of imperfections of the substrate surface was obtained with germanium (30–100 Å in thickness) deposited at relatively slow rate (0.1–2 Å/sec). Amorphous to crystalline transition temperature was also influenced by deposition rate. Epitaxial orientation of films: (001)Ge//(001)NaCl and [100]Ge//[100]NaCl, was observed on vacuum-cleaved substrate at 250 °C at the slow deposition rate. Good epitaxial films could be prepared at 400 °–500 °C, although the films included microtwins with the twinning planes of {111} in part. However, films on air-cleaved substrates at 400 °–500 °C showed always polycrystalline structure. Epitaxy and structure of films were also influenced considerably by an electron-beam irradiation applied to the substrate during evaporation.
Hydrogen Pumping by Sputter-Ion Pumps and Getter Pumps
Authors: Singleton J. H.
Published: July 2002

Hydrogen pumping speeds in sputter-ion pumps are particularly dependent upon operating conditions. At high pressures of hydrogen, maximum speeds are obtained with the gas diffusing rapidly into the cathodes, but since the diffusion is sensitive to surface contamination, relatively low partial pressures of gases such as nitrogen can greatly reduce the speed. High hydrogen loads can cause serious cathode deformation by titanium hydride formation and, if high cathode temperatures develop, the reversible desorption of hydrogen can stall the pump. At lower pressures cathode surface contamination becomes of greater importance and the hydrogen pumping speed declines drastically. Because hydrogen is a dominant gas at the ultimate of a metal system, it is necessary to combine either a sublimation or a getter pump with the sputter-ion pump in order to maintain efficient pumping. The influence of hydrogen diffusion rates on the pumping capabilities of titanium and other sputter-cathode and getter materials is reviewed.
Casting of metallic filament and fiber
Authors: Maringer Robert E. , Mobley Carroll E.
Published: July 2002

The production of metallic fiber and filament directly from the melt has been practiced for some years. However, the application of these techniques has been limited due to materials-compatibility problems. Two new fiber-casting methods have been developed: Crucible Melt Extraction and Pendant Drop Melt Extraction. Both methods involve bringing the edge of a rotating disk into contact with a source of molten metal. Molten metal solidifies on the periphery of the disk, adheres there for a short time as it is removed from the melt source, and is then spontaneously released from the disk in the form of solid fiber. Both methods significantly reduce the technical difficulties heretofore associated with fiber casting and are amenable to operation in air, inert atmosphere, or vacuum. Metals as diverse as tin and niobium have been fiberized successfully.
Experimental study of the influence of nanoparticle generation on the electrical characteristics of argon–silane capacitive radio-frequency plasmas
Authors: Shen Zhe , Kortshagen Uwe
Published: July 2002

The nonintrusive detection of particle contamination problems is of great interest to plasma processing in the manufacture of semiconductors. We have studied the influence of particle generation in argon–silane capacitive plasmas on the electrical discharge properties which can be nonintrusively measured with a current–voltage sensor. The Fourier components of the rf current and voltage and the respective phase angles between these signals have been studied up to the fifth harmonic of the 13.56 MHz rf power. We show that in particular higher harmonics are much more sensitive to the appearance of particles than the signals at the fundamental frequency or the second harmonic. It appears that the observation of higher harmonics is capable of providing early indication of particle growth in capacitive rf discharges.
Adhesion of Metals in the Space Environment
Authors: Winslow P. M. , McIntyre D. V.
Published: July 2002

Studies have been made of the parameters of time, pressure, and temperature that influence adhesion of structural metals in vacuum. The objective was to provide spacecraft designers with engineering data to ensure separation of instrument capsules and other components from spacecraft in the space environment. These studies were conducted at an environmental pressure of 5×10−9 Torr over a temperature range of 25 °C (77 °F) to 500 °C (932 °F) and at compressive stresses within the elastic limits of the materials. Surface finishes and cleanliness of the test specimens simulated spacecraft hardware. Loading was applied by both static and dynamic modes and the adhesive forces were measured. Data are presented showing the extent of adhesion of a wide variety of materials under these conditions. With static loading, no adhesion occurred except at elevated temperatures. With dynamic loading, adhesion occurred at lower temperatures and lower compressive loads than under static conditions.
Intrinsic Stress in Evaporated Metal Films
Authors: Klokholm E.
Published: July 2002

Recently the author proposed a model for the origin of the observed intrinsic tensile stresses in thin metal films. The model predicts a large stress S relatively independent of thickness, in films when the ratio of the melting to the substrate (absolute) temperatures, Tm/Ts, exceeds 4. Conversely, S will be small when Tm/Ts, is smaller than 4 and should decrease with increasing film thickness. The stress has been measured in Al, Cu, and Ni films as a function of Tm/Ts and the data obtained verifys the above predictions. For Tm/Ts much larger than 4, S in Al films is 2×109 dyn/cm2; in Cu, 7×109 dyn/cm2; and in Ni, 9×109 dyn/cm2. As Tm/Ts becomes less than 4 the stress in each case is small, and decreases with increasing film thickness.
Electrolytic decomposition and photodecomposition of compound semiconductors in contact with electrolytes
Authors: Gerischer Heinz
Published: July 2002

Electrons and holes affect the bond strength of surface atoms. Therefore, in most systems their surface concentration controls the rate of electrolytic decomposition reactions. The thermodynamics of such reactions are characterized by their redox potentials which are equivalent to the Fermi energies of electrons or holes. It is shown that the energy positions of the redox Fermi levels for decomposition with respect to the position of the band edges and the Fermi levels of competing redox reactions, give an immediate indication for the susceptibility of a semiconductor to electrolytic decomposition. This concept is especially useful for the discussion of photodecomposition where the electronic free energy can be described by individual quasi-Fermi levels for electrons and holes. Data are given for the semiconductors ZnO, TiO2, Cu2O, CdS, MoS2, GaP, and GaAs. A model for bond breaking by holes at a kink site of a compound semiconductor is discussed to demonstrate what role the surface bond character plays for the height of activation barriers and how kinetics modify the thermodynamic conclusions on stability.
Surface segregation in the Ag–Au and Pt–Cu systems
Authors: Kelley M. J. , Swartzfager D. G. , Sundaram V. S.
Published: July 2002

Several models have been proposed to predict the direction and extent of surface segregation in binary metal alloys. Auger electron spectroscopy (AES) has proven useful to study these systems qualitatively, but the results of AES have proven difficult to quantify. Ion scattering spectroscopy (ISS) offers an alternative having true first-monolayer sensitivity. ISS was used to study surface segregation in the Ag–Au and Pt–Cu systems. Results are compared with previous findings and model predictions.
The dependence of H2O adsorption and reaction on the structure of the carbon substrate
Authors: Kelemen S. R. , Freund H. , Mims C. A.
Published: July 2002

We have examined the interaction of H2O vapor with three structurally different carbon surfaces. The edge and basal surface of crystalline graphite as well as a ‘‘paracrystalline’’ glassy carbon were characterized with LEED, UPS, and AES. Structural characterization by LEED showed the typical ‘‘ring’’ pattern for the basal surface; the edge surface showed evidence of structural order distinct from the basal plane and the glassy carbon showed only diffuse scattering. UPS from the glassy carbon and edge graphite surfaces showed increases in emission within 2 eV of EF relative to the basal plane. This is associated with the presence of less saturated surface valence structure. Exposure to H2O vapor at 30 °C produced saturation oxygen coverage after 10−2 Torr s on the glassy carbon and after 10−1 Torr s on the edge surface. Adsorption on the basal surface saturated at lower coverages and the residual adsorption activity is attributed to surface irregularities. UPS of the glassy carbon and edge graphite surfaces provided evidence for the dissociative adsorption of water. The adsorbed oxygen species produced are strongly held and desorbed as CO between 650–800 °C. Our results show that the edge surface of graphite and less ordered carbon surfaces are active for H2O dissociation.
Ion–surface interactions during thin film deposition
Authors: Takagi T.
Published: July 2002

The interactions of ion beams with surfaces are strongly dependent on the incident kinetic energy and the amount of ionic charge. Fundamental effects of ion bombardment by atomic and cluster ion beams have been elucidated in terms of kinetic energy of the ion beams. These fundamental effects include enhancement of adatom migration, desorption of physically absorbed atoms, displacement of the surface atoms, sputtering, shallow ion implantation, and trapping of impinging atoms. The importance of low energy ion beams for film formation is shown by taking into account the binding energies of the atoms in a solid. Emphasis has been placed on interactions of ionized cluster beams (ICB) during film formation because ICB offers unique capabilities for deposition due to the properties of the clusters and also to characteristic low energy ion beam transport over a range from thermal energy to a few hundred eV.
Origin of 1/f noise observed in Hg0.7Cd0.3Te variable area photodiode arrays
Authors: Chung H. K. , Rosenberg M. A. , Zimmermann P. H.
Published: July 2002

The origin of 1/f noise in Hg0.7Cd0.3Te photodiodes is investigated with variable area n+–p junction photodiode arrays. From the geometrical dependences, it is found that both G–R current and 1/f noise in these diodes originate dominantly at the surface depletion region. Also, the 1/f noise power is found to be proportional to the reverse bias voltage for 0.01<VR<0.1 V.
Excess (1/f ) noise in Hg0.7Cd0.3Te p-n junctions
Authors: Bajaj J. , Williams G. M. , Sheng N. H. , Hinnrichs M. , Cheung D. T. , Rode J. P. , Tennant W. E.
Published: July 2002

We report on 1/f noise in reverse-biased LPE Hg0.7Cd0.3Te p-n junctions. These studies have emphasized temperatures where the saturation current is limited by diffusion of minority carriers. The 1/f noise is found to originate from an area source, and varies linearly with reverse bias voltage (V) for ‖qV/kT‖<1 and sublinearly for −qV/kT>1. It is also found to have a temperature dependence similar to that of the intrinsic carrier concentration. No increase in noise is observed as a result of induced photocurrent. We conclude that the noise originates in the depletion region in the bulk.
Unbalanced magnetron ion-assisted deposition and property modification of thin films
Authors: Savvides N. , Window B.
Published: July 2002

Unbalanced magnetron (UM-gun) sputtering sources with the unique characteristic of a high deposition rate and concomitant high ion flux represent an exciting new development in ion-assisted deposition of thin films. We have used a UM-gun capable of producing ion current densities up to 5 mA cm−2 (ion flux 3×1016 cm−2 s−1) when operated at a power of 500 W to produce a variety of thin films of amorphous and crystalline materials by varying both the bombarding ion energy in the range 2–100 eV and the ion/atom arrival rate ratio in the range 0.4–10. The great flexibility and usefulness of UM-guns is demonstrated with examples which include (a) hard diamondlike a-C films prepared under very low ion energy (13–16 eV) bombardment which possess a metastable bonding configuration consisting of a mixture of tetrahedral and trigonal coordination that varies with ion energy, (b) hard and wear-resistant TiN films whose electrical and optical properties change dramatically with ion bombardment, and (c) Ni/Cr alloy films showing ion-induced structural modifications.
Surface segregation in binary alloys
Authors: Vahalia Uresh , Dowben Peter , Miller Allen
Published: July 2002

A semiempirical calculation is outlined that allows analysis of experimental results for the apparent surface concentration of binary alloys, obtained by x-ray photoelectron spectroscopy, (XPS). A segregation profile giving the enrichment of the segregating element at and near the surface is obtained from the analysis. Using previously published data for Cu17 Ni83(100) and Cu17 Ni83(111), it is shown that copper segregation is not restricted to the first few layers, but instead extends significantly into the selvedge (near-surface) region. This occurrence is not explainable by the use of present ideal solution models. An extended ideal solution model is presented, in which the bond strengths vary gradually from top-layer values to bulk values. This model is consistent with the observed penetration of copper enrichment into the selvedge. The parameters describing the gradual change of bond strengths are determined via comparison of the results of the model with XPS data.
Influence of geometric factors of the substrate on hydrophilic surface modification of polyurethane sponges by plasma treatment
Authors: Cho D. L. , Yasuda H.
Published: July 2002

The surface modification by plasma treatment occurs by consecutive processes of excitation of gas(es) and deexcitation of excited species. The deexcitation occurs primarily at the surface yielding chemical modification of the surface (nonpolymer-forming plasmas) or deposition of material (polymer-forming plasma) on the substrate surface. Because of this sequence, geometric factors of the substrate in relation to the surrounding plasma phase have crucial influence on the effectiveness of plasma treatments. Simple mathematical models were developed to illustrate the effect of geometric factors involved in plasma treatments, and experimental results obtained with porous polyurethane sponges in various sizes were examined by the mathematical models for both plasma treatments by O2, H2O, and NH3 and plasma polymerization of acrylic acid.
Surface disorder induced Kikuchi features in reflection high-energy electron diffraction patterns of static and growing GaAs(001) films
Authors: Larsen P. K. , Meyer-Ehmsen G. , Bölger B. , Hoeven A.-J.
Published: July 2002

Reflection high-energy electron diffraction (RHEED) investigations have been carried out on reconstructed GaAs(001)-2×4 surfaces under static conditions and during growth by molecular-beam epitaxy. Intensity modulation of streaks in the RHEED patterns is strongly enhanced during growth and high-intensity regions are found at angular positions corresponding to intersections of Kikuchi lines and streaks. The features are explained by a model assuming forward diffuse scattering in the surface layer due to long-range disorder followed by Kikuchi-type diffraction in the bulk.
III–V strained layer supperlattices for long-wavelength detector applications: Recent progress
Authors: Osbourn G. C. , Dawson L. R. , Biefeld R. M. , Zipperian T. E. , Fritz I. J. , Doyle B. L.
Published: July 2002

Recent results of research on III–V InAsSb strained-layer superlattices are reviewed. Successful growth of microcrack-free InSb/InAsSb strained-layer superlatties has been achievedf by both molecular-beam epitaxy and metal–organic chemical vapor deposition techniques. The results provide encouraging indications that these III–V materials have superior structural stability to that of the Hg-rich HgCdTe alloys.
Effects of microstructure and nonstoichiometry on electrical properties of vanadium dioxide films
Authors: Kusano Eiji , Theil Jeremy A.
Published: July 2002

Voided growth structures of sputter-deposited films affect strongly their optical and electrical properties. Vanadium dioxide is an interesting material to study effects of film microstructure and nonstoichiometry on electrical properties because its phase transition makes it possible to investigate electrical behavior both in a semiconducting phase and in a metallic phase. We have deposited vanadium oxide films with different vanadium/oxygen ratios for substrate temperatures between 250 and 550 °C by dc reactive magnetron sputtering. The resistivity ratios between a semiconducting phase and a metallic phase are limited to 103 order by voided boundaries and oxygen vacancies. The voided boundaries are defined by columnar structure and agglomerated grain growth. The results emphasize the necessity of a combination of deposition to obtain the film with a favorable structure and postdeposition annealing to control the film stoichiometry.
Synthesis and structure of ion-beam sputtered multilayer Fe/Ni films
Authors: Kim C. , Qadri S. B. , Yu H. Y. , Kim K. H. , Maruyama B. , Edelstein A. S.
Published: July 2002

Multilayers of Fe/Ni with equal thickness of Fe and Ni layers have been deposited on Si and glass substrates using ion-beam sputtering with composition modulation wavelength λ ranging from 20 to 160 Å. X-ray diffraction scans using Cu Kα radiation were made to look for the satellite peaks that are the signature of coherent multilayers. Satellite peaks were observed only when argon ion-assisted deposition was used in preparing the multilayers. Read photographs using Fe Kα radiation show that the films are highly textured. All the diffraction rings in the Read photograph can be identified to a single face-centered-cubic (fcc) lattice for λ≤36 Å. For higher wavelengths, rings corresponding to body-centered-cubic (bcc) Fe were observed in the Read photographs. Extended x-ray absorption fine structure (EXAFS) measurements taken above the Fe K edge indicate that the Fe in the Fe/Ni multilayers are in fcc and bcc phases for wavelengths of 27.6 and 120 Å, respectively. The average lattice parameter shows an enhancement with decreasing wavelength that is proportional to 1/λ for 26.4≤λ≤52.0 Å.
Control of ion energy and flux in a dual radio frequency excitation magnetron sputtering discharge
Authors: Löwe Hans-Dirk , Goto Haruhiro H. , Ohmi Tadahiro
Published: July 2002

Mean ion energy and ion flux have been investigated in a low-pressure, radio frequency (rf) magnetron discharge (dual rf excitation plasma) as function of substrate rf power and frequency, plasma excitation rf power and process pressure. Electrical and Langmuir probe measurements were used to determine the self-bias of the electrodes and time-averaged plasma parameter, respectively. The energy and flux of ions bombarding the substrate surface can be accurately controlled in the low-energy range (<50 eV) without affecting the state of the discharge by applying an appropriate rf bias power and frequency to the substrate electrode. A simplified sheath model is used to verify the experimentally obtained linear relationship between substrate rf power and self-bias of the electrode. The ion flux to both electrodes as well as the mean ion energy to the plasma excitation electrode are controlled by the plasma excitation rf power. The increase in process pressure from 5 to 40 mTorr reduces the ion flux to the substrate without changing the mean ion energy. The plasma parameters and their spatial distribution are strongly affected by the magnetic field, which also determines the ion energy flux distribution on the substrate surface.
GaAs surface oxidation and deoxidation using electron cyclotron resonance oxygen and hydrogen plasmas
Authors: Lu Z. , Schmidt M. T. , Osgood R. M. , Holber W. M. , Podlesnik D. V.
Published: July 2002

We have used x-ray photoelectron spectroscopy to investigate electron cyclotron resonance oxygen plasma oxidation and hydrogen plasma deoxidation of GaAs surfaces. Experimental evidence shows that ECR oxidation at room temperature forms a stoichiometric oxide layer that is primarily composed of As2O5 and Ga2O3. A hydrogen plasma is shown to clean GaAs surfaces and recover surface order, even at room temperature. Sample heating (200–300 °C) expedites the removal of Ga2O3 and improves surface order. In addition, no significant differences in oxidation and deoxidation were observed for sample biasing, either positively or negatively.
Thermal oxidation of TiN studied by means of soft x-ray absorption spectroscopy
Authors: Soriano L. , Abbate M. , Fuggle J. C. , Prieto P. , Jiménez C. , Sanz J. M. , Galán L. , Hofmann S.
Published: July 2002

The oxidation of TiN in an oxygen flow at temperatures in the range 300–500 °C has been studied by means of soft x-ray absorption spectroscopy. The analysis of the experimental results indicates that O progressively displaces N to form TiO2. The process appears to be controlled by the temperature dependence of the oxygen diffusion. Some oxidation is observed to take place even at room temperature. No evidence of oxynitride formation was found in thermally oxidized TiN, instead complete phase separation is observed. The interface between TiO2 and TiN seems to be very abrupt. The appearance of a sharp absorption peak in the N 1s spectrum of TiN is believed to be due to nitrogen atoms which are displaced during the oxidation process and remain unbounded within the TiO2 matrix. For temperatures above 400 °C, this peak disappears as the interstitial N atoms migrate to the surface and desorb.
Ionized magnetron sputter deposition of amorphous carbon nitride thin films
Authors: Li D. , Lopez S. , Chung Y. W. , Wong M. S. , Sproul W. D.
Published: July 2002

Carbon nitride thin films were prepared using an ionized magnetron sputtering system. An inductively coupled rf plasma was generated in the region between the sputtering source (high purity graphite) and the substrate table. An argon–nitrogen mixture was used as the sputtering gas. Sputtered atoms which pass through the radio frequency (rf) plasma may be ionized, and the degree of ionization depends on several processing variables, such as the gas total pressure, reactive gas partial pressure, and applied rf power. Pulsed substrate bias voltage was varied up to −500 V. Chemical bonding and composition of the deposited films were studied by infrared and Auger electron spectroscopy, respectively. An ultramicroindentation system was used to measure the hardness. Nitrogen was found to be bonded to carbon in various configurations. The dependence of the nitrogen-to-carbon ratio and film hardness on the deposition conditions was studied. Under optimum conditions, films with nitrogen-to-carbon ratio ∼0.3–0.4 and hardness up to 16–17 GPa were made. These values are similar to those obtained without the rf plasma. There is no correlation between the film hardness and the nitrogen-to-carbon ratio.
Strain imaging analysis of Si using Raman microscopy
Authors: Ajito K. , Sukamto J. P. H. , Nagahara L. A. , Hashimoto K. , Fujishima A.
Published: July 2002

We present two-dimensional strain image mapping of the SiO2/Si interface on an Al/SiO2 patterned Si wafer using a modified Raman microscope. A positive shift in the Si Raman peak by approximately 1.0 cm−1, corresponding to 2.49×108 Pa compressive strain, was observed along particular edges between the Al/SiO2 patterned features and bare Si substrate. In addition to strain mapping, surface disorder in the Si wafer was also detected with this technique.
Oxidation of gold by ultraviolet light and ozone at 25 °C
Authors: King David E.
Published: July 2002

Gold surfaces have been found to be hydrophilic only after exhaustive preparation and with the ultimate care in sample preparation and treatment. The use of a combination of ultraviolet (UV) light and ozone has been described as a viable method of producing a clean, hydrophilic, gold surface. We have found that gold surfaces, which have been either stored in the laboratory after vacuum deposition or purchased as high purity standards, are oxidized by a combination of UV light and ozone generated from a mercury lamp. The samples were characterized with x-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS) prior to and after exposure to UV/ozone in a stainless steel box in laboratory air. After the cleaning process gold surfaces were found by XPS to contain less carbon and to be enriched in oxygen. The O 1s on the cleaned surface, which was not present on the untreated surface, consisted of two peaks that are attributed to gold oxide and hydroxyl. The oxide layer was found to be 17±4 Å thick by variable angle XPS depth profiling with an initial stoichiometry of Au2O3. The oxide was found to be stable to extended exposure to UHV and water and ethanol rinses. ISS compositional depth profiles confirmed the oxide layer thickness and that the hydrated surface layer is removed in the initial sputtering of the oxidized gold. Implications of these results related to the mechanism of self-assembly of thiols on gold are discussed.
Surface studies of model supported catalysts: NO adsorption on Rh/CeO2(001)
Authors: Overbury S. H. , Huntley D. R. , Mullins D. R. , Ailey K. S. , Radulovic P. V.
Published: July 2002

The adsorption and reaction of NO on a model catalyst composed of Rh supported on ceria has been studied. CeO2 films were grown epitaxially by laser ablation onto SrTiO3(001) substrates. X-ray diffraction and transmission electron microscopy indicate the films are single crystalline with (001) orientation. Comparison of experimental and computer simulated ion scattering distributions indicate that an annealed CeO2 surface is well ordered and is composed of both O and Ce terminated domains. Exposures to CO and H2 at various temperatures had little or no effect upon the ceria. Photoemission from the Ce 4d levels exhibits complex features that differ between a sputtered and a fully oxidized surface. NO does not adsorb on the Rh free, fully oxidized surface, but does adsorb upon a sputter reduced surface. The thermally induced conversion from molecular NO to atomic N was measured by both N 1s photoemission and x-ray absorption as a function of Rh coverage to determine substrate effects on Rh surface chemistry. Rh deposited on sputtered ceria is more active for NO decomposition and yields higher N2 desorption temperatures than does Rh on the fully oxidized support.
Kinetics of F atoms and fluorocarbon radicals studied by threshold ionization mass spectrometry in a microwave CF4 plasma
Authors: Tserepi A. , Schwarzenbach W. , Derouard J. , Sadeghi N.
Published: July 2002

The absolute concentration of fluorine atoms (F), a parameter of great importance for the characterization and modeling of etching plasmas, was measured by means of threshold ionization mass spectrometry in a CF4 microwave plasma (p=15–100 mTorr). The kinetics of these atoms and those of CF2 and CF3 radicals were studied by pulsing the plasma and time-resolved detection of these radicals with mass spectrometer. Sticking coefficients of F atoms on the different surrounding surfaces were estimated, as a function of the discharge parameters and the nature of the surfaces interacting with the plasma. It was found that the sticking of F atoms on hexatriacontane polymer surface is highly activated by the plasma generated ions and/or ultraviolet radiations.
Twinned epitaxial layers formed on Si(111)√3×√3-B
Authors: Hibino H. , Sumitomo K. , Ogino T.
Published: July 2002

We investigate the growth process of twinned epitaxial Si layers on Si(111)√3×√3-B and their thermal stability. In the initial growth stages, twinned two-bilayer-high (2-BL-high) and untwinned BL-high islands are formed, and at higher surface B concentration, there are more twinned 2BL islands than untwinned BL islands. Domain boundaries of the √3×√3 reconstruction act as preferential island nucleation sites, especially for untwinned BL islands. Therefore, to grow epitaxial layers twinned with the already-grown twinned layers, post-growth anneal is essential to increase the surface B concentration and to reduce the domain boundary density. On the other hand, the temperature at which twinned layers are transformed into untwinned layers strongly depends on the thickness. We demonstrate the possibility of growing superlattices of layers that have twinned and untwinned orientations with the substrate (polytypes) by precisely controlling the growth and post-growth anneal parameters.
Self-consistent particle simulation of radio-frequency CF4 discharge with implementation of all ion–neutral reactive collisions
Authors: Denpoh Kazuki , Nanbu Kenichi
Published: July 2002

The structures of the CF4 radio-frequency discharge between parallel electrodes are clarified by the use of the particle-in-cell/Monte Carlo method. The simulation is performed based on the most reliable collision data, i.e., detailed cross-section data for electron–CF4 collision, measured rate for positive–negative ion recombination, and the newly developed ion–CF4 collision model for endothermic reactions. Reactive collisions between positive ions (especially CF3+) and CF4 molecules are found to be important. The major loss process of negative ions is the recombination with positive ions. It is also found that the discharge sustaining mechanism is the ionization, not the electron detachment from negative ions.
Characterization of silicon oxynitride thin films by x-ray photoelectron spectroscopy
Authors: Shallenberger J. R. , Cole D. A. , Novak S. W.
Published: July 2002

There has been a considerable effort in the past decade to incorporate nitrogen into SiO2 in order to improve the electrical properties of ultrathin (2–10 nm) gate oxides. Process conditions affect the nitrogen concentration, coordination, and depth distribution which, in turn, affect the electrical properties. X-ray photoelectron spectroscopy (XPS) is particularly well suited to obtaining the nitrogen coordination and, to a lesser extent, the nitrogen concentration in thin oxynitride films. To date, at least four different nitrogen coordinations have been reported in the XPS literature, all having the general formula: N(–SixOyHz), where x+y+z=3 and x⩽3, y⩽1, z⩽2. In this article we review the XPS literature and report on a fifth nitrogen coordination, (O)2=N–Si, with a nitrogen 1s binding energy of 402.8±0.1 eV. Next nearest neighbor oxygen atoms shifted the N(–Si)3 peak roughly 0.1 eV per oxygen atom. We also discuss results from a novel approach of determining the nitrogen areal density by XPS, the accuracy of which is dependent on the depth distribution of nitrogen. Secondary ion mass spectrometry is used to determine the depth N distribution, while nuclear reaction analysis is used to check the N concentration measured by XPS.
Improved light stability of colored SiO2 coatings containing organic and metalorganic dye molecules
Authors: Dı́az-Flores L. L. , Pérez-Bueno J. J. , Ramı́rez-Bon R. , Espinoza-Beltrán F. J. , Vorobiev Y. V. , González-Hernández J.
Published: July 2002

Organic and metalorganic dyes have been incorporated into SiO2 coatings using the sol-gel method. It is found that the coatings prepared from sol-gel starting solutions, which were subjected to a ball milling process, have improved light stability. Using optical absorption, atomic force microscopy and microluminescence measurements, it is found that the ball milling process of the starting solutions not only produces better dye dispersion, but there are also some indications that it produces a structure with fewer and smaller pores. These results are in agreement with previous studies, which indicate that the photostability of dyes in metal oxide matrices can be improved when the dye is better dispersed and trapped in more rigid cages.
Stability of hydrogen in silicon nitride films deposited by low-pressure and plasma enhanced chemical vapor deposition techniques
Authors: Xie Joseph Z. , Murarka Shyam P. , Guo Xin S. , Lanford William A.
Published: July 2002

Hydrogen concentration depth profiles in silicon nitride films deposited by low-pressure chemical vapor deposition (LPCVD) and plasma enhanced chemical vapor deposition (PECVD) techniques were studied. Quantitative hydrogen profiling was carried out using the resonant nuclear reaction 15N+1H→12C+4He+γ ray. Hydrogen concentration in as-deposited LPCVD silicon nitride films was ∼2.5×1021 atoms/cm3 and was stable even after a furnace anneal at 450 °C in 3% H2/Ar for 30 min or a rapid thermal anneal at 1000 °C in oxygen for 30 s. These nitride films thus appear to be good hydrogen diffusion barriers. In contrast, hydrogen concentration in as-deposited PECVD silicon nitride films was ∼1.75×1022 atoms/cm3 and dropped to ∼7.5×1021 atoms/cm3 after rapid thermal annealing at 1000 °C in oxygen for 30 s. During high-temperature anneals, the hydrogen diffused from PECVD silicon nitride film into the underlying SiO2 layer. A comparison of the hydrogen concentration in these deposited oxides under the nitrides with those previously reported for as-deposited, but uncovered, SiO2 films points out that the observed threshold voltage shifts in nitride covered metal–oxide semiconductor capacitors are related to the loss of hydrogen from the silicon oxide during vacuum processing for nitride deposition and to the subsequent diffusion in SiO2 from the PECVD nitride films.
Free molecular transport and deposition in cylindrical features
Authors: Cale T. S. , Raupp G. B.
Published: July 2002

A Clausing-like integral equation is derived which applies to both low pressure chemical vapor deposition (CVD) and physical vapor deposition (PVD) in cylindrical contact holes; i.e., over the full range of sticking coefficient (0–1). A steady state assumption is implicit in the formulation. In the absence of film deposition, the flux to the surface is spatially uniform. Analytical expressions are presented for the initial deposition profiles for PVD (unity sticking coefficient). Numerical inversions of the integral equations provide initial deposition profiles for CVD (low sticking coefficients). Initial deposition profiles exhibit poor uniformity in PVD and high uniformity in CVD, in agreement with empirical evidence. The results provide a test for proposed Monte Carlo simulations which are based on the same assumptions.