bluuebunny/crossref_metadata_2025 huggingface dataset:
Stability Analysis of One-Dimensional Steady Cavitating Nozzle Flows With Bubble Size Distribution
Authors: Wang Yi-Chun
Published: July 2002

A continuum bubbly mixture model coupled to the Rayleigh-Plesset equation for the bubble dynamics is employed to study one-dimensional steady bubbly cavitating flows through a converging-diverging nozzle. A distribution of nuclei sizes is specified upstream of the nozzle, and the upstream cavitation number and nozzle contraction are chosen so that cavitation occurs in the flow. The computational results show very strong interactions between cavitating bubbles and the flow. The bubble size distribution may have significant effects on the flow; it is shown that it reduces the level of fluctuations and therefore reduces the “cavitation loss” compared to a monodisperse distribution. Another interesting interaction effect is that flashing instability occurs as the flow reaches a critical state downstream of the nozzle. A stability analysis is proposed to predict the critical flow variables. Excellent agreement is obtained between the analytical and numerical results for flows of both equal bubble size and multiple bubble sizes. [S0098-2202(00)00702-1]
Analysis and Validation of One-Dimensional Models for Gaseous Flows in Micro-Channels
Authors: Sun Hongwei , Faghri Mohammad
Published: July 2002

The paper presents three one-dimensional models to simulate gaseous flows in micro-channels. These include no-slip flow, simple fully-developed, and locally fully-developed models. It is shown that the locally fully-developed model provides a more accurate prediction when both rarefaction and gas acceleration need to be considered in micro-flows. Furthermore, the effects of rarefaction and gas acceleration on the locally dimensionless pressure ratio are specified on the basis of the three models. The validation of these models is accomplished by comparison with the experimental results. [S0098-2202(00)02502-5]
Experimentally Based Study on the Effect of Initial Grain Size for Characterization of the Grain Coarsening Phenomenon During Hot Rolling of a Medium Carbon Steel
Authors: Neishi Yutaka , Akiyama Masayoshi , Kuroda Kouichi
Published: July 2002

Laboratory experiments using a hot deformation simulator were carried out to clarify the effect of initial grain size on the grain coarsening phenomenon in hot metal working with light reduction. As an example of medium carbon steel, AISI1045 was adopted and specimens of various grain sizes were prepared by changing the thermo-mechanical histories. They were subjected to a hot deformation testing by the simulator. The threshold grain size to cause the grain coarsening phenomenon was then determined and a criterion was presented to ensure a fine grain after hot rolling. The validity of the new criterion was checked through hot rolling of bars by a prototype mill in a laboratory. [S1087-1357(00)00801-7]
Studies in Direct Tooling Using Stereolithography
Authors: Li Yun , Gargiulo Edward P. , Keefe Michael
Published: July 2002

Rapid prototyping (RP) technologies are valuable for reducing product development cycle times by creating physical models for visual inspection and form-fit studies directly from a 3-D database. However, if the part is meant for volume production, tooling will be necessary. Tool development and fabrication using conventional techniques and materials is time consuming and expensive. Therefore, it is risky to commit to production tooling in the initial stages of product development. Low volume prototyping is highly desirable but requires a small number of parts (hundreds) to be produced quickly and economically. To meet this need, this paper studies direct tooling using the RP technology of stereolithography (SL) to produce photopolymer tools. Without modifications to improve thermal response, SL molds will not be able to produce production-quality parts. This experimental study quantifies the thermal characteristics of an SL mold for a simple part geometry. Several modifications that affect thermal properties are then studied and both thermal response and part quality are quantified. The data indicate that although it is possible to change the thermal response of an SL mold and obtain reasonable parts, the ability to duplicate traditional mold characteristics (and thus simulate part production before committing to high-volume tooling) is probably not practical. Similar results were achieved when using a more realistic final-part geometry on a production mold machine. Although mold process simulation using SL molds could provide useful design guidance for traditional high-volume part production, this work suggests that these SL molds can be used for low-volume part production. By reducing mold fabrication time and costs, low-volume part production could become cost-effective using traditional high-volume manufacturing techniques. [S1087-1357(00)00702-4]
Prediction of Materials Damage History From Stress Corrosion Cracking in Boiling Water Reactors
Authors: Balachov Iouri , Macdonald Digby , Stellwag Bernhard , Henzel Norbert , Kilian Renate
Published: July 2002

Over the past decade, we have developed deterministic models for predicting materials damage due to stress corrosion cracking (SCC) in boiling water reactor (BWR) primary coolant circuits. These steady-state models have been applied to fixed state points of reactor operation to yield electrochemical corrosion potential (ECP) and crack growth rate (CGR) predictions. However, damage is cumulative, so that prediction of the extent of damage at any given time must integrate crack growth rate over the history of the plant. In this paper, we describe the use of the REMAIN code to predict the accumulated damage functions for major components in the coolant circuit of a typical BWR that employs internal coolant pumps. As an example, the effect of relatively small amounts of hydrogen added to the feedwater (e.g., 0.5 ppm) on the development of damage from a 0.197-in. (0.5-cm) intergranular crack located at the exit of an internal pump was analyzed. It is predicted that hydrogen additions to the feedwater will effectively suppress further growth of the crack. We also report the first predictions of the accumulation of damage from SCC for a variable power operating cycle. We predict that the benefits of hydrogen water chemistry (HWC), as indicated by the behavior of a single crack under constant environmental conditions, are significantly muted by changes in reactor power. [S0094-9930(00)01301-9]
Measuring Rotational Degrees of Freedom Using a Laser Doppler Vibrometer
Authors: Ratcliffe M. J. , Lieven N. A. J.
Published: July 2002

Many model updating and dynamic coupling techniques require the response of a structure to be defined at all degrees of freedom. Standard experimental techniques do not routinely allow the measurement of rotational DoFs. Also time constraints do not permit measurement over a dense grid. A laser system has been developed which enables rotations to be extracted by a simple plane-fitting technique, which is described in this paper. A finite element model-based parametric study is presented, which has shown that the performance of the technique is dependent on the amount of corruption present on translation data. A semi-empirical technique is developed, using second derivatives to exacerbate temporarily the noise corruption, which quantifies accurately the equivalent Gaussian noise on the response data. An experimental study is also presented which shows the considerable promise of these procedures. Finally, a brief description of a model updating case study is presented for illustrative purposes. Terminology: In order to avoid a verbose sentence construction, the coordinate at which it is desired to measure the rotational frequency response functions (FRFs) is hereafter referred to as the rotation point. In addition, the distance between the measured translation FRFs and the rotation point is referred to as the measurement radius. [S0739-3717(00)00401-3]
Stability and Stability Degree of a Cracked Flexible Rotor Supported on Journal Bearings
Authors: Meng G. , Gasch R.
Published: July 2002

This paper investigates the stability and the stability degree of a cracked flexible rotor supported on different kinds of journal bearings. It is found that no matter what kinds of bearings are used, the unstable zones caused by rotor crack locate always within the speed ratio of 2/N1−ΔKξ /4<Ω<2/N when gravity parameter Wg>1.0; and locate always within the speed ratio of 2Ωα/N1−ΔKξ /4<Ω<2Ωα/N when Wg<0.1, where ΔKξ is the crack stiffness ratio, N=1,2,3,4,5,… and Ωα=1+1/2α1/2. When 0.1<Wg<1.0, there is a region where no unstable zones caused by rotor crack exist. Outside the crack ridge zones, the rotor crack has almost no influence on the system’s stability and stability degree; while within the crack ridge zones, the stability and the stability degree depend both on the crack and the system’s parameters. In some cases, the system may still be stable even though the crack is very large. For small gravity parameter Wg<0.1, the mass ratio α has a large influence on the position of the unstable region, but its influence on the stability degree is small. The influence of fixed Sommerfeld number So on the stability degree of the cracked rotor is small, although So has a large influence on the stability degree of the uncracked rotor. [S0739-3717(00)70502-2]
Characterization of an Activated Alumina Claus Catalyst by XPS
Authors: Strohmeier Brian R.
Published: July 2002

In this study, the surface composition of a fresh, commercial, alumina Claus catalyst (Alcoa S-100) was examined by x-ray photoelectron spectroscopy (XPS). This article presents the main XPS core lines and the valence band spectra obtained for the Claus catalyst. The electronic record includes the Al 2p, Al 2s, O 1s, O 2p, C 1s, and valence band spectra.
Observation of Electrical Conductivity During XPS Analysis of Organic Oils
Authors: Beamson G. , Clark D. T. , Hayes N. W. , Law D. S-L.
Published: July 2002

Under the conditions of x-ray photoelectron spectra (XPS) analysis organic liquids appear to behave as electrical conductors. Here we report x-ray photoelectron spectra for pentaphenylether and pentaphenyltrimethyltrisiloxane oils at room temperature. These materials are commercially available as diffusion pump fluids (Santovac 5 and DC705, respectively). Their room temperature vapor pressures are ∼2 × 10−8 Pa and they can be studied by XPS without hazard to the spectrometer vacuum system. Both materials were investigated as relatively thick liquid films (∼10 μm, as determined by weighing) on a piece of silicon wafer. A solid organic film of this thickness would be expected to be an XPS insulator. The oil films on silicon required no external charge compensation and gave high resolution C 1s spectra with the first component of the envelope very close to 285 eV binding energy. Measured binding energies closely followed a bias voltage applied to the silicon wafer. Oil films thicker than 10 μm behaved as XPS insulators. Insulating behavior was also observed on cooling the samples by passing liquid nitrogen through the spectrometer manipulator during analysis. The explanation of these phenomena is not yet clear but the apparent electrical conductivity allows XPS study of low vapor pressure organic liquids in a straightforward way, without charging effects.
Introduction to Surface Spectra of Oxides II
Authors: Baer D. R. , Henrich V. E. , Gassman P. , Franchy R. , Ibach H. , Margaritondo G.
Published: July 2002

This issue of Surface Science Spectra (SSS) is the second of two special issues dedicated to oxide surfaces. The Introduction contains a summary table listing all the submissions in both issues. Ultraviolet photoelectron spectroscopy (UPS), x-ray photoelectron spectroscopy (XPS), x-ray photoelectron diffraction (XPD), and high-resolution electron energy-loss spectroscopy (HREELS) for a wide range of oxides are included. Because HREELS (a vibrational electron energy loss spectroscopy) and XPD are new to SSS, a short introduction to these methods is provided.
Photopolymerized C60 Film by XPS
Authors: Nakao Aiko , Onoe Jun , Takeuchi Kazuo
Published: July 2002

We present here the changes in the valence band and the C 1s core peak and its shake-up satellite of a C60 film upon photopolymerization using x-ray photoelectron spectroscopy. It was found that the intensity of the C 1s shake-up satellite of the phototransformed C60 film decreased with increasing irradiation time of 500 W mercury lamp (0 to 200 h). On the other hand, the valence band spectra of the C60 film was almost unchanged even after 200 h of irradiation, compared with that of pristine C60 film.
Preparation of low-reflectivity aluminum film using direct current magnetron sputtering in Ar/O2 and Ar/N2 atmospheres
Authors: Kamoshida Kazuyoshi
Published: July 2002

Low-reflectivity aluminum films were prepared using a dc magnetron sputtering system under high Ar/O2 and Ar/N2 gas pressures. At a wavelength of 436 nm, pure Al films deposited at 4.0 Pa (30 mTorr) in Ar–1.0 vol. % O2 and Ar–1.0 vol. % N2 atmospheres show a specular reflectivity of 0.06 and a diffuse reflectivity of 0.10. The low reflectivity is ascribable to the formation of columnar structures of several hundred angstroms with open boundaries. Microvoids formed between columnar crystallites are thought to absorb the incident light. The low-reflectivity Al film coatings will probably make it possible to eliminate the effect of reflection in photolithography.
Electron temperature, density, and metastable-atom density of argon electron–cyclotron-resonance plasma discharged by 7.0, 8.0, and 9.4 GHz microwaves
Authors: Kawai Y. , Kano K. , Suzuki T. , Akatsuka H. , Fujii Y.
Published: July 2002

The characteristics of argon plasma discharged by electron–cyclotron resonance (ECR) with the microwave frequencies of 7.0, 8.0, and 9.4 GHz are investigated in the pressure range of 0.013–0.13 Pa, where the magnetic field was adjusted to keep the ECR point at the same position. The input power of the microwave was set at 10 and 50 W. Plasma densities and the electron temperatures were found to be almost independent of the microwave frequency at low pressure. The dependence of the electron density on the microwave frequencies becomes apparent in the higher-pressure range above 0.080 Pa. In the case that the discharge power is 50 W, the plasma operated using 9.4 GHz microwave showed the highest electron density and the plasma operated using 7.0 GHz had the lowest electron density. Metastable-atom densities were estimated by using a collisional radiative model. The mestable-atom densities, ∼1017 m−3, are lower than the electron density ∼1018 m−3 at the discharge power of 50 W, whereas these densities were comparable at the discharge power of 10 W.
Direct measurement of density-of-states effective mass and scattering parameter in transparent conducting oxides using second-order transport phenomena
Authors: Young D. L. , Coutts T. J. , Kaydanov V. I. , Gilmore A. S. , Mulligan W. P.
Published: July 2002

The Boltzmann transport equation can be solved to give analytical solutions to the resistivity, Hall, Seebeck, and Nernst coefficients. These solutions may be solved simultaneously to give the density-of-states effective mass (md*), the Fermi energy relative to either the conduction or valence band, and a scattering parameter that is related to a relaxation time and the Fermi energy. The Nernst coefficient is essential for determining the scattering parameter and, thereby, the effective scattering mechanism(s). We constructed equipment to measure these four transport coefficients simultaneously over a temperature range of 30–350 K for thin, semiconducting films deposited on insulating substrates. We measured these coefficients for rf magnetron-sputtered zinc oxide, both doped and undoped, with aluminum with carrier concentrations in the range of 1×1019–5×1020 cm−3. The (md*) was not constant over this carrier concentration range: varying from 0.3 to 0.48 me, leading us to conclude that zinc oxide has a nonparabolic conduction band. Conductivity effective mass values for zinc oxide matched our md* values, revealing a single valley, nearly spherical, constant energy surface for zinc oxide. The measured scattering parameter changed from close to zero to 1.5 as the carrier concentrations increased. The scattering parameter, Seebeck coefficient, and mobility versus temperature data support neutral impurity scattering in the undoped material and ionized impurity scattering in the Al-doped ZnO. The transport theory also allows an extrapolation for an md* value at the bottom of the conduction band, which was found to be 0.27 me.
Patterning of tantalum pentoxide, a high epsilon material, by inductively coupled plasma etching
Authors: Jonsson L. B. , Westlinder J. , Engelmark F. , Hedlund C. , Du J. , Smith U. , Blom H.-O.
Published: July 2002

Integrated capacitors can easily cover a major part of the total chip area which may seriously affect the cost to produce the chip. By using a high epsilon material as the dielectric material, in the capacitor, the size can be reduced significantly. One very promising candidate is tantalum pentoxide (Ta2O5) which has a dielectric constant of about 25. This should be compared to silicon nitride which has a dielectric constant of 8. In order to make integrated capacitors the tantalum pentoxide must be patterned. Results of a study on etching of tantalum pentoxide, silicon dioxide, and polysilicon with a high density plasma, using an inductively coupled plasma source, are presented and compared to results obtained by means of reactive ion etching. The gas used, CHF3, implies a polymerizing chemistry and the deposition of a fluorocarbon layer is shown to play an important role in the etch process. The fluorocarbon deposition onto the substrate surface is not only affected by the temperature of the substrate itself but also by the temperature of all surfaces that are exposed to the plasma. The process parameters with the strongest influence on the process have been found to be pressure and substrate bias voltage.
Comparison of In0.33Al0.67As/In0.34Ga0.66As on GaAs metamorphic high electron mobility transistors grown by molecular beam epitaxy with normal and inverse step on linear graded buffer layers
Authors: Cordier Y. , Chauveau J.-M. , Ferre D. , Dipersio J.
Published: July 2002

Metamorphic high electron mobility transistors with 33% indium content have been grown on GaAs by molecular beam epitaxy. Linear graded InAlAs buffer layers were used to relax the mismatch strain between the InAlAs/InGaAs heterostructure and the GaAs substrate. The thickness of the graded buffer is shown to influence strain relaxation (tilt and residual strain), surface roughness, and Hall mobility. Furthermore insertion of an inverse step at the end of the grade by a finite reduction of the indium concentration reduces the residual strain and provides similar surface roughness with improved Hall mobility in the InGaAs channel.
Chemisorption Surface Titration and Surface Reconstruction of Alloys
Authors: Sachtler W. M. H.
Published: July 2002

Field ion microscopy revealed that chemisorption of CO and N2 on W induces surface reconstruction even at 78 K. Photoelectron emission from Ru films shows that CO wipes out memory of presintering: films of different initial work function yield equal final work function. Several alloy films equilibrated below 300 °C possess concentration gradients between surface and interior. By chemisorbing H2 or CO on CuNi, AgPd or AuPt the atoms of the VIIIb elements are counted. For RuPt the characteristic work function increase due to CO permits an estimation of the Ru content of the surface. CO adsorption on AuPt and AgPd causes drastic surface reconstruction, the surfaces becoming enriched with the element forming the stronger bonds with CO.
Fundamentals of Ion Plating
Authors: Mattox D. M.
Published: July 2002

The term ion plating is applied to atomistic film deposition processes in which the substrate is subjected to a flux of high energy ions sufficient to cause appreciable sputtering before and during film formation. From the standpoint of adhesion, the principal benefits obtained from ion plating are (1) ability to sputter clean the surface and maintain it “clean” until the film begins to form; (2) provide a high energy flux to the substrate surface giving a high surface temperature without necessitating bulk heating, thus enhancing diffusion, chemical reaction, etc.; and (3) alter the surface and interfacial structure by introducing high defect concentrations, physically mixing the film and substrate material, and influencing the nucleation and growth of the depositing film. Ion plating is particularly effective in obtaining good adhesion in some systems where conventional deposition techniques give poor results. Another effect found in the ion plating process is the very great “throwing power” of the depositing film material. In this paper the fundamental concepts of ion plating are reviewed along with a discussion of problems peculiar to this deposition process. Several representative applications will be described.
Superconductivity and Metastable Phases in Thin Films
Authors: Buckel Werner
Published: July 2002

Results on quenched condensed films of Bi, Sb, Sb+noble metals, Ge, Ge+noble metals, and Sn+Cu are discussed in order to demonstrate the importance of the short-range order for the properties of such films. Two kinds of amorphous films can be clearly distinguished: (a) crystallinelike and (b) liquidlike amorphous films. This classification is important for materials which are partially covalently bonded. The results also show that an interesting relation exists between metastable phases in quenched condensed films and high pressure modifications of the same material.
Nitridation of thermal SiO2 films by radio-frequency plasma assisted electron cyclotron resonance: Effect of plasma modes and process parameters
Authors: Raveh A. , Brewer J. , Irene E. A.
Published: July 2002

Dual-frequency plasma using electron cyclotron resonance (ECR) and radio-frequency (rf) discharges was used for the nitridation of silicon dioxide (SiO2) films, which were grown by conventional thermal oxidation. Nitridation was performed under ion densities less than 1011 ions/cm3 and substrate temperatures of 300±20  °C. The effects of plasma mode (ECR/dc, ECR/rf, ECR, and rf) and the principal process variables (N2 pressure, ECR power, rf applied voltage, and nitridation time) on formation and growth of the nitrided layer were studied by spectroscopic ellipsometry, Auger electron spectroscopy, and atomic force microscopy. It was observed that the nitrided films were composed of an upper layer of silicon oxynitride (SiOxNy) and an inner layer of SiO2. The plasma mode, N2 pressure, and rf bias affected the reactions and concentration of particles in the gas phase, and therefore impacted growth of the nitrided layer. Plasma parameters and plasma modes were optimized to produce a dense upper nitride layer, while minimizing the effect on the inner SiO2 layer, with the goal of preserving the electronic integrity of the Si–SiO2 interface.
Mechanism of ultralow outgassing rates in pure copper and chromium–copper alloy vacuum chambers: Reexamination by the pressure-rise method
Authors: Watanabe Fumio
Published: July 2002

Mechanisms influencing the ultimate outgassing rate of hydrogen from a metal chamber into a vacuum have been clarified by results from a reexamination using the pressure-rise method. The condition of the oxide surface of the metal plays a central role in determining the ultimate outgassing rate. Measurements were made for three materials, oxygen-free high-conductivity (pure) copper, chromium(0.6%)–copper(99.4%) alloy, and stainless steel 304, and are compared with previously published work by the throughput method. In the case of pure copper, the ultimate outgassing rate is dependent on in situ bakeout temperature. When the bakeout temperature is at least 250 °C, the oxide film on the copper surface is completely deoxidized and the ultimate outgassing rate is determined only by the concentration of hydrogen remaining in the bulk. As a result, this pure copper requires over a week in vacuum to attain its ultimate outgassing rate. In the case of chromium–copper alloy, however, the bulk content of hydrogen is mostly degassed during prebakeout at 400 °C, because the surface is not yet covered by a Cr2O3 film and the major copper–oxide film on the surface is easily deoxidized at this prebakeout temperature. During the prebakeout, Cr atoms in the alloy are out-diffused to the surface. The out-diffused Cr atoms on the surface are then oxidized to Cr2O3 when the chamber is subsequently exposed to atmospheric air. Because hydrogen permeation of a Cr2O3 film is over an order of magnitude lower than that for the bulk alloy, the film limits both out-diffusion of hydrogen from the bulk and hydrogen solution into the bulk through permeation when the surface is exposed to atmospheric air. Thus the outgassing rate of the CrCu chamber does not change with changes in bakeout temperature. The key to attaining ultralow outgassing rates in a pure copper chamber is in situ bakeout with extended, continued pumping; but the key for a CrCu alloy chamber is simply prebakeout. By this we can obtain an ultralow outgassing rate at the 10−12 Pa m/s (hydrogen equivalent) level. On the other hand, in the case of stainless steel, the surface is immediately covered by a mixed Cr2O3+Fe2O3 film after the initial electropolishing step, because the content of Cr in stainless steel is over an order of magnitude higher than in the CrCu used. Therefore hydrogen in the bulk is not effectively degassed during 400 °C prebakeout and in situ bakeout. The outgassing rate from the stainless steel chamber was over an order of magnitude higher than from the pure copper and CrCu alloy chambers.
Chemistry and aging of organosiloxane and fluorocarbon films grown from hyperthermal polyatomic ions
Authors: Hanley Luke , Fuoco Erick , Wijesundara Muthu B. J. , Beck Alison J. , Brookes Pat N. , Short Robert D.
Published: July 2002

Polyatomic ions can be used to deposit thin films, modify the phases of interfaces, dope trace elements into interface regions, impact specific chemical functionalities to a surface, and create micron- and nanometer-scale interface structures. This article demonstrates the broad flexibility over the modified surface properties allowed by variation of the incident ion chemical structure and kinetic energy. Organosiloxane (OS) films are deposited here on Al from mass-selected 15–100 eV Si2O(CH3)5+ ions. Monochromatic x-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry are used to determine the OS film chemistry. The OS films vary from essentially organic (lightly cross-linked network) at 15 eV deposition to a more inorganic (highly cross-linked “silica like”) at 100 eV. XPS is also used to examine the aging of fluorocarbon films deposited on polystyrene by 25–100 eV CF3+ and C3F5+ ions. These films undergo only minor changes during aging, forming only a few percent oxygen on the surface. Surface restructuring and other processes are also observed in these fluorocarbon films during aging for up to 8 weeks.
Low energy O2+ and N2+ beam-induced profile broadening effects in Si
Authors: Deenapanray Prakash N. K. , Petravic Mladen
Published: July 2002

The angular dependence of the profile broadening of Na, Li, and F during secondary ion mass spectrometry depth profiling was investigated in either n- or p-type Si using 10 keV O2+ or N2+ bombardment. The electric field-induced segregation of Na and Li at the SiO2/Si interface increased exponentially for O2+ bombardment below ∼27°, whereas a N2+ beam provided better depth resolution. The N2+ beam-induced profile broadening of Li was higher in the low resistivity n-type Si than in the high resistivity p-type Si for bombardment conditions producing a nitride layer at the surface. This behavior was characteristic of the field-induced segregation of Li at the SiNy/Si interface. Profiling below the critical angle for oxide formation resulted in the antisegregation of F into the SiO2 layer and gave sharper profiles. The decay length of F decreased exponentially with the surface charging of the SiO2 layer. By contrast, broader profiles were obtained under N2+ bombardment for the same impact angles.
Wear of ultrathin carbon overcoat characterized by microwear scan and Auger electron spectroscopy
Authors: Wu Tsai-Wei , Deline Vaughn , Scharf Thomas W. , Yen Bing K. , Barnard John A.
Published: July 2002

A new methodology was developed to characterize the tribological performance of ultrathin carbon coatings by the microwear scan and Auger electron spectroscopy. With the magnetic recording application in mind, two 5-nm-thick carbon coatings were deposited on magnetic disks for the study. In a microwear scan process, there were two competing mechanisms that lead to the carbon coating failure—the coating wearoff and the coating structural damage mechanisms. The coating wearoff was a continuous process and always active, whereas the coating structural damage appeared more in a disruptive manner as the applied normal load approached a critical level. The term coating wear rate, defined as the coating thickness reduction per unit applied normal load, was adopted in this microwear scan test. Two simulation models based on carbon (272 eV) and cobalt (775 eV) Auger electron signals, respectively, were developed to calculate the carbon residual thickness inside the wear track. Because of the difference in signal intensities, the coating residual thickness acquired from the carbon Auger electron signal turned out to be much more robust and reproducible than the cobalt signal. Based on these results, a tribological characteristic chart, which contained both the coating wear rate and critical load parameters, is proposed to offer a better understanding and ranking capability towards the tribological performance of ultrathin coating systems.
Effects of gas pressure and substrate temperature on the etching of parylene-N using a remote microwave oxygen plasma
Authors: Callahan Russell R. A. , Raupp Gregory B. , Beaudoin Stephen P.
Published: July 2002

The effects of temperature and pressure on the rate of etching of parylene-N in a downstream oxygen plasma created with a microwave source have been determined. Etch rate increases with increasing substrate temperature, with an apparent activation energy of 6.6–8.0 kcal/mol over the 373–523 K temperature range. The etch rate goes through a maximum between 0.6 and 0.8 Torr as pressure is increased from 0.4 to 1.0 Torr. The observed maxima are more pronounced as substrate temperature increases. Analyses of x-ray photoelectron spectra for unetched and etched films reveal that exposure to the plasma afterglow decreases the relative amount of aromatic carbon and creates carboxylic acid groups in the film. Residual gas analysis of the reactor effluent during etching indicates that the only volatile etch products are H2O, CO2, and CO. Likely reactions that may lead to the formation of the observed etch products are presented and discussed.
Exposure characteristics and three-dimensional profiling of SU8C resist using electron beam lithography
Authors: Wong W. H. , Pun E. Y. B.
Published: July 2002

The properties of a new type of chemically amplified resist, SU8C, are evaluated for electron beam lithography. This resist is a modification of the ultraviolet sensitive negative epoxy SU8. Experimental results show that the sensitivity of SU8C is one of the highest among the different kinds of commercially available resists. At 50 keV energy exposure, the saturation dosage of SU8C is ∼3.8 μC/cm2 while that of PMMA is ∼500 μC/cm2. This implies that SU8C resist is suitable for large area exposure. The contrast γ can also be adjusted to near unity by adjusting the postannealing time, and this is essential for multilevel profiling. 16 level steps have been exposed in one electron beam exposure by changing the clock frequency in sequence, and a vertical profile resolution of 20 nm has been achieved. Lines as narrow as 100 nm have been produced, showing that the resist has high resolution down to the nanoscale. Hardness measurements have also been carried out, and SU8C is an order of magnitude harder than epoxy and PMMA. SU8C resist has high refractive index, high resolution, high sensitivity, and large hardness, making it suitable for microscale binary optics fabrication. To demonstrate the suitability of SU8C resist in microscale optical device fabrication, an array of Fresnel lenses has been designed and demonstrated.
Microscopic field emission investigation of nanodiamond and AlN coated Si tips
Authors: Günther B. , Göhl A. , Müller G. , Givargizov E. , Zadorozhnaya L. , Stepanova A. , Spitsyn B. , Blaut-Bachev A. N. , Seleznev B. , Suetin N.
Published: July 2002

We have investigated the suitability of nanodiamond (ND) and AlN coated Si tip arrays for cold cathodes by means of a field emission scanning microscope combined with scanning electron microscopy. The ND coated tips required an average extraction voltage U(10 nA) of 360 V for 10 μm electrode distance and yielded stable emission up to currents of 10–50 μA. The rather nonuniform emission distribution of the arrays (80 V<U(10 nA)<1800 V) was correlated with the varying morphology of the ND tips. Field-enhancing nanoprotrusions were observed at the apex of the strongest emitters. The AlN coated tips showed strong activation effects at emission currents below 10 nA or after annealing at 250 °C resulting in an average U(10 nA) of 410 V, improved lateral emission uniformity (150 V<U(10 nA)<600 V), and stable currents up to 1–10 μA. Direct high current processing of such emitters led to a partial destruction of the apex. Different field emission mechanism will be discussed for ND and AlN coatings.
Synthesis of BNx–SiNy composite films by multisource plasma chemical vapor deposition
Authors: Nonogaki Ryozo , Yamada Suzuya , Ibukiyama Masahiro , Wada Tetsuya
Published: July 2002

BN x – SiN y composite films were deposited by a multisource plasma chemical vapor deposition (PCVD). Two plasma generators, A and B, were implemented. BF3 and NH3 gases introduced to plasma generator A were separately decomposed by two rf electrodes, respectively. SiH4 and NH3 gases were also separately decomposed in the plasma generator B. Widely spread sheet-like plasma generated by a dc arc plasma gun above the substrate and under a magnetic field also excited the gas in front of the substrate. By this CVD system, the composition of the BNx–SiNy films can be controlled, and the BNx–SiNy films with several atomic percent of silicon are found to have higher hardness and higher electrical resistivity than BNx film.
Mechanically controllable break junctions with quasi-planar electrodes
Authors: Kolesnychenko O. Y. , Jurdik E. , Shklyarevskii O. I. , van Kempen H.
Published: July 2002

Mechanically controllable break junctions with nearly flat (at a lateral scale of ≃10 nm) electrodes and a greatly reduced number of surface defects were fabricated using a gentle procedure of surface modification. The modification process occurs at extremely close separations between the electrodes (≃1.5–2 Å) where high electric fields and surface temperatures can be achieved at relatively low bias voltages. Experimental details, a possible physical mechanism and applications of the proposed technique are discussed.
Approach to the characterization of through-oxide boron implantation by secondary ion mass spectrometry
Authors: Jiang Z. X. , Backer S. , Lee J. J. , Wu L. Y. , Guenther T. , Sieloff D. , Choi P. , Foisy M. , Alkemade P. F. A.
Published: July 2002

Secondary ion mass spectrometry analysis of through-oxide ion implantation in silicon often exhibits strong matrix effects across the SiO2/Si interface. In this study we explored the analytical conditions that required minimal correction for the variation in the relative sensitivity factors and the sputtering rates across the interface. We found that an O2+ beam at 1 keV and 46° provided an equal sputtering erosion rate for SiO2 and Si. Under these sputtering conditions, the SiO2 surface remained smooth, but Si became rough ∼50 nm below the SiO2/Si interface. A complete depth profile of B implantation through oxide was obtained by utilizing the 1 keV 46° O2+ beam in SiO2 and across the SiO2/Si interface and a 1 keV 60° O2+ beam deeper in the Si substrate. The data exhibited an apparent drop in the concentration of the implanted B at the SiO2/Si interface which was attributed to a phase transition in the matrix from amorphous to crystalline. In addition, analyses of an ion-beam synthesized oxide (5 keV O2+ at normal incidence) confirmed the occurrence of outdiffusion of B in the altered layer. Also, the results indicated preferential sputtering of B at the surface.
A new look at the steel cord–rubber adhesive interphase by chemical depth profiling
Authors: Hammer G. E.
Published: July 2002

The adhesive interphase formed between brass plated steel cord and sulfur crosslinked rubber is known to be a complex layer of metal oxides, sulfides, and rubber. Hostile aging of this system produces changes in the structure, morphology, thickness, and mechanical properties of this layer. In a previous publication it has been shown that the overall thickness of the sulfide layer as measured by depth profiling with Auger electron spectroscopy could be used to characterize the degradation of the adhesive bond [G. E. Hammer et al., J. Vac. Sci. Technol. A 12, 2388 (1994)]. In this work multivariate statistical analysis of the sulfur Auger electron spectra was used to produce chemical depth profiles of the individual copper and zinc sulfide layers. These chemical depth profiles give new insight into the adhesion degradation mechanism on the nanometer scale. Particularly, the percentage of copper sulfide in the layer was found to be an accurate predictor of adhesion degradation.
Initial surface reactions between Cl2 molecules and the GaAs (001) 2×4 surface
Authors: Tanaka Yu , Ozeki Masashi
Published: July 2002

Initial reactions for Cl2 molecules at the GaAs(001)-(2×4) surface have been investigated by using a supersonic molecular-beam scattering technique. Results with a high corrugation GaAs(001)-(2×4) surface indicate a complex, dynamical behavior of Cl2 molecules interacting with the surface. A fine chemisorption probability measurement at an incident translational energy of 0.12 eV suggests an extremely fast dissociative chemisorption process with an initial probability of ∼93%. Angular distributions measured for scattered Cl2 molecules at 0.06, 0.12, and 1.45 eV strongly indicate three channels of behavior: inelastic direct scattering, trapping/desorption, and multiple scattering. In particular, the multiple scattering channel arises from the corrugation of the surface.
Ordering and surface state reduction of GaAs (100) by low energy S+ bombardment
Authors: Zhao Q. , Kwok R. W. M. , Lau W. M.
Published: July 2002

S +   ions with well-controlled kinetic energy were used to bombard n- and p-type GaAs (100) surfaces. 50 eV S+ bombardment formed a maximum of 1.5 monolayers of sulfide on a GaAs (100) surface and did not change the nonordered surface to an ordered surface. After the bombardment, the surface Fermi levels for both sulfur ion-bombarded n- and p-type samples were moved towards the midgap. After the samples were further annealed at 400 °C, the surface Fermi level of n- and p-type samples gave a separation larger than that of the samples after the UV/O3 and HF treatment. A sharp (1×1) low-energy electron diffraction pattern was observed and the sulfide coverage was about one monolayer. Under such well-controlled conditions, effective surface passivation by reducing surface states and formation of an ordered surface structure can be achieved.
Effect of buffer-layer engineering on the polarity of GaN films
Authors: Sumiya M. , Yoshimura K. , Ogusu N. , Fuke S. , Mizuno K. , Yoshimoto M. , Koinuma H. , Romano L. T.
Published: July 2002

A combination of coaxial impact ion scattering spectroscopy (CAICISS) and cross-sectional transmission electron microscopy (XTEM) was used to evaluate GaN films grown by metalorganic chemical vapor deposition. The polarity of the surface and the bulk of the buffer layers and high temperature layers could be evaluated with CAICISS and XTEM, respectively. Several buffer layers were grown and annealed at various temperatures on nitrided sapphire substrates prior to deposition of the high temperature (HT) layer. Most of the surfaces of the as-deposited buffer layers were found to have Ga (0001) (+c) polarity. However, after annealing, the N (0001̄) (−c) polarity was exposed due to evaporation of the film. This resulted in HT layers containing columnar and dome-shaped inversion domain with N (0001̄) (−c) polarity. The ratio of +c to −c polarity on the surface of the buffer layers was found by CAICISS to vary with the annealing time. It was found that the polarity of HT GaN films and the buffer layers was consistent using both CAICISS and XTEM.
Gas heating and throw distance for the sputter deposition of aluminum and tungsten
Authors: Drüsedau Tilo P.
Published: July 2002

The throw distance of Al and W atoms was determined (A) by investigating the pressure-dependent deposition rate and applying the Keller–Simmons one-dimensional model. The power density at the target as a parameter was varied over more than one order of magnitude. Whereas the values determined for Al are not influenced by power, the values for tungsten strongly increase with power. This effect is related to strong gas density reduction related to gas heating for W sputtering, which reduces the probability of collisions between sputtered atoms and the gas. The gas heating was experimentally determined by simultaneous measurements of the pressure in the sputtering chamber and at the end of a tubular probe inserted into the hot plasma region. For tungsten, a strong heating and related gas density reduction was found. An analytical expression describing the spatially resolved temperature profile in a sputtering discharge is developed by means of the Keller–Simmons formulas. The influence of various process parameters on gas heating can be easily studied by the model. There is good agreement between the model calculations with the experiments performed as well as with Monte Carlo simulations and experimental findings from the literature. Forward simulations by the model result in a power-independent throw distance (B) for both elements, which are in agreement with the values (A) resulting from the pressure-dependent deposition rate. Existing differences are explained by the rough assumptions of the model, which is critically discussed.
Influence of standing-wave electric field pattern on the laser damage resistance of HfO2 thin films
Authors: Protopapa M. L. , Alvisi M. , De Tomasi F. , Di Giulio M. , Perrone M. R. , Scaglione S.
Published: July 2002

The standing-wave electric field pattern that forms inside an optical coating as a consequence of laser irradiation is one of the factors influencing the coating laser-induced damage threshold. The influence of the standing-wave electric field profile on the damage resistance to ultraviolet radiation of hafnium dioxide (HfO2) thin films was investigated in this work. To this end, HfO2 thin films of different thicknesses deposited by the electron beam evaporation technique at the same deposition conditions were analyzed. Laser damage thresholds of the samples were measured at 308 nm (XeCl laser) by the photoacoustic beam deflection technique and microscopic inspections. The dependence of the laser damage threshold on the standing-wave electric field pattern was analyzed.
Carbon nanotube films grown by laser-assisted chemical vapor deposition
Authors: Rohmund F. , Morjan R.-E. , Ledoux G. , Huisken F. , Alexandrescu R.
Published: July 2002

Films of pure high-quality multiwall carbon nanotubes are grown by laser-assisted thermal chemical vapor deposition in a cold wall reactor. A CO2 laser is used to locally heat a substrate on which nanotubes are grown, employing the catalytic activity of iron nanoparticles. Two kinds of experiments are reported: In a two-step mode, catalytic iron particles and solid carbon are deposited separately, leading to the formation of homogeneous films of nonaligned pure multiwall nanotubes (MWNTs). The role of gas phase heating was investigated by the addition of a sensitizing molecule that absorbs the laser radiation. It is found that large-volume gas phase heating is not needed for the synthesis of high-quality nanotube films. Focused laser radiation allows growth of locally defined nanotube films. In a second set of experiments, iron and carbon are deposited simultaneously. Films of vertically aligned MWNTs of extremely high packing density were produced in this mode under very lean hydrocarbon supply conditions.
Microstructure of xenon−implanted silicon
Authors: Mader S. , Tu K. N.
Published: July 2002

Si implanted with 1014, 1015, and 5×1015 ions/cm2 of 80 KeV Xe ions was examined by electron microscopy and nuclear backscattering. Implantation created amorphous Si, which, after annealing at 700°C, transformed into single crystal material for doses ?1015/cm2 and into a heavily twinned material for the higher dose. Under suitable conditions, such implants can be used as diffusion markers in the study of surface reactions.
Tritium depth profiling by neutron time−of−flight
Authors: Davis J. C. , Anderson J. D.
Published: July 2002

A method has been developed to measure the depth profile of tritium implanted or absorbed in materials. The sample is bombarded with a pulsed proton beam. Neutron energies from T (p,n) reactions occurring in the target are measured by time−of−flight over a 10.8−m flight path. From the neutron energy the proton energy and, thus, the tritium depth in the target may be inferred. The measurements were initiated to determine the depletion of tritium absorbed in titanium layers. These layers had served as targets on a 400−keV T (d,n) neutron generator. A depth resolution of 0.4 mg/cm2 of titanium (0.9 μ) was obtained. Unlike proton backscattering methods, the technique can be used with thick samples. We estimate that a sensitivity of 0.1 at.% tritium in host materials can be obtained. Extension of the method to deuterium depth profiling is possible with the use of the D (d,n) reaction.
Sputtered metal silicide solar selective absorbing surfaces
Authors: Harding G. L.
Published: July 2002

A range of metal silicide interference filters has been prepared on various metal substrates and aged in vacuum at elevated temperatures. These show promise as high-temperature stable selective surfaces for solar energy phototheral conversion. Solar absorptances 75%–80% and emittances of about 2% can be obtained at room temperature for homogeneous metal silicide films on bulk copper. Higher absorptances are obtained using sputtered copper, bulk stainless steel, or evaporated nickel substrates. Emittances of homogeneous metal silicide films on bulk copper increase to about 5% at 500°C. The solar absorptance of an iron silicide on copper surface was temperature independent up to 500°C. Absorptances greater than 90% can be obtained for multilayer metal silicide films on copper. The emittances of these films are somewhat higher than for homogeneous films.
Measurement of plasma discharge characteristics for sputtering applications
Authors: Eser E. , Ogilvie R. E. , Taylor K. A.
Published: July 2002

Plasma and characteristics of rf and dc discharges for sputtering were measured by a cylindrical-type electrostatic probe. Space potentional, floating potential, electron temperature, and plasma density were monitored as a function of discharge voltage, substrate bias, and probe position within the chamber. A description of the probe and supporting circuit used to plot the current–voltage characteristic is given. The electrostatic probe was shown to be a useful tool for characterizing sputtering process and with suitable system calibration, can be used to enhance repeatability of the sputtering process.