bluuebunny/crossref_metadata_2025 huggingface dataset:
Forming Limit Analysis of Sheet Metals Based on a Generalized Deformation Theory
Authors: Chow C. L. , Jie M. , Hu S. J.
Published: July 2003

This paper presents the development of a generalized method to predict forming limits of sheet metals. The vertex theory, which was developed by Sto¨ren and Rice (1975) and recently simplified by Zhu, Weinmann and Chandra (2001), is employed in the analysis to characterize the localized necking (or localized bifurcation) mechanism in elastoplastic materials. The plastic anisotropy of materials is considered. A generalized deformation theory of plasticity is proposed. The theory considers Hosford’s high-order yield criterion (1979), Hill’s quadratic yield criterion and the von Mises yield criterion. For the von Mises yield criterion, the generalized deformation theory reduces to the conventional deformation theory of plasticity, i.e., the J2-theory. Under proportional loading condition, the direction of localized band is known to vary with the loading path at the negative strain ratio region or the left hand side (LHS) of forming limit diagrams (FLDs). On the other hand, the localized band is assumed to be always perpendicular to the major strain at the positive strain ratio region or the right hand side (RHS) of FLDs. Analytical expressions for critical tangential modulus are derived for both LHS and RHS of FLDs. For a given strain hardening rule, the limit strains can be calculated and consequently the FLD is determined. Especially, when assuming power-law strain hardening, the limit strains can be explicitly given on both sides of FLD. Whatever form of a yield criterion is adopted, the LHS of the FLD always coincides with that given by Hill’s zero-extension criterion. However, at the RHS of FLD, the forming limit depends largely on the order of a chosen yield function. Typically, a higher order yield function leads to a lower limit strain. The theoretical result of this study is compared with those reported by earlier researchers for Al 2028 and Al 6111-T4 (Grafand Hosford, 1993; Chow et al., 1997).
Kinetics of Diffusional Phase Transformation in Multicomponent Elastic-Plastic Materials
Authors: Fischer F. D. , Simha N. K. , Svoboda J.
Published: July 2003

The goal of this paper is to derive a micromechanics framework to study the kinetics of transformation due to interface migration in elastic-plastic materials. Both coherent and incoherent interfaces as well as interstitial and substitutional atomic diffusion are considered, and diffusional transformations are contrasted with martensitic ones. Assuming the same dissipation for the rearrangement of all substitutional components and no dissipation due to diffusion in an interface in the case of a multicomponent diffusional transformation, we show that the chemical driving force of the interface motion is represented by the jump in the chemical potential of the lattice forming constituent. Next, the mechanical driving force is shown to have the same form for both coherent and frictionless (sliding) interfaces in an elastic-plastic material. Using micromechanics arguments we show that the dissipation and consequently the average mechanical driving force at the interface due to transformation in a microregion can be estimated in terms of the bulk fields. By combining the chemical and mechanical parts, we obtain the kinetic equation for the volume fraction of the transformed phase due to a multicomponent diffusional transformation. Finally, the communication between individual microregions and the macroscale is expressed by proper parameters and initial as well as boundary conditions. This concept can be implemented into standard frameworks of computational mechanics.
Investigation Into Cumulative Damage Rules to Predict Fretting Fatigue Life of Ti-6Al-4V Under Two-Level Block Loading Condition1
Authors: Jin O. , Lee H. , Mall S.
Published: July 2003

The effects of variable amplitude loading on fretting fatigue behavior of titanium alloy, Ti-6Al-4V were examined. Fretting fatigue tests were carried out under constant stress amplitude and three different two-level block loading conditions: high-low (Hi-Lo), low-high (Lo-Hi), and repeated block of high and low stress amplitudes. The damage fractions and fretting fatigue lives were estimated by linear and non-linear cumulative damage rules. Damage curve analysis (DCA) and double linear damage rule (DLDR) were capable to account for the loading order effects in Hi-Lo and Lo-Hi loadings. In addition, the predictions by DCA and DLDR were better than that by linear damage rule (LDR). Besides its simplicity of implementation, LDR was also capable of estimating failure lives reasonably well. Repeated two-level block loading resulted in shorter lives and lower fretting fatigue limit compared to those under constant amplitude loading. The degree of reduction in fretting fatigue lives and fatigue strength depended on the ratio of cycles at lower stress amplitude to that at higher stress amplitude. Fracture surface of specimens subjected to Hi-Lo and repeated block loading showed the clear evidence of change in stress amplitude of applied load. Especially, the repeated two-level block loading resulted in characteristic markers which reflected change in crack growth rates corresponding to different stress amplitudes.
Effects of starting material of aluminum doped zinc oxide underlayer on the electric properties of palladium doped silver film
Authors: Oyama T. , Maekawa M. , Yanagisawa T.
Published: July 2003

Crystallographic and electric properties of a palladium doped silver (Ag–Pd) layer formed on an aluminum doped zinc oxide (AZO) film in the multilayer system of Ag–Pd(10.5 nm)/AZO(42 nm)/glass were investigated. All of the films in this study were deposited by dc magnetron sputtering. Two kinds of sputtering targets, aluminum doped zinc metal (AZ) and AZO, were used for the deposition of AZO films. The AZ target was sputtered in an oxygen or carbon dioxide atmosphere whereas the AZO target was sputtered in an argon or argon/oxygen atmosphere. The Ag–Pd layers were deposited under the fixed sputtering condition. From x-ray diffraction patterns it was found that the most developed Ag(111) peak appeared in the case of the Ag–Pd film on the AZO layer deposited from the AZ metal target with oxygen. Atomic force microscope observation revealed that the smallest surface roughness was obtained in this case. Electrical resistivity of the Ag–Pd layer changed by up to 17% depending on deposition conditions and the target materials of the underlayer. The Ag–Pd film deposited on the AZO layer from the AZ target in an oxygen atmosphere also showed the lowest resistivity of 7.1×10−6 Ω cm. The smallest refractive index of Ag–Pd film was shown by the same sample from an analysis using spectroscopic ellipsometry (SE). Deposition of a thin metal (Zn–Al) overlayer on Ag–Pd/AZO/glass increased the overall resistivity of the multilayer. This may imply the diffusion of zinc atoms into the Ag–Pd layer, however, the resistivity recovery was observed after some storage time, which suggests the effect of an electron scattering at the surface.
Electronic structure of SixSn(1−x)/Si(111)-(3×3)R30° phases
Authors: Lobo J. , Tejeda A. , Mugarza A. , Michel E. G.
Published: July 2003

We report on an investigation on the electronic band structure of the SixSn(1−x)/Si(111)-(3×3)R30° phases using angle-resolved photoemission. This reconstruction is observed in the coverage range between 0.15 and 0.40 ML. We investigated its surface states bands as a function of coverage. While there is no structural indication of a (3×3) ordering at low temperature, several features typical of the (3×3) phase are found in the valence band. We present also an analysis on the influence of the Si intermixing in the surface state properties.
Vacuum chamber with distributed titanium sublimation pumping for the G-line wiggler at Cornell High Energy Synchrotron Source
Authors: Li Y. , He Y. , Mistry N. B.
Published: July 2003

This article describes a 3-m-long vacuum chamber for the new wiggler magnet at the Cornell Electron Storage Ring (CESR) for the synchrotron light beam line of the Cornell High Energy Synchrotron Source (CHESS). Copper was chosen as the main chamber material for its good electric and thermal conductivities. Proper mechanical design and welding procedure were implemented to meet very tight tolerances to ensure adequate vertical aperture for the stored beams in CESR while allowing the required small wiggler gap. Distributed titanium sublimation pumping is incorporated along the 3 m length of the chamber to provide sufficient pumping speed and capacity for CESR and CHESS operations. The chamber pumping performance was evaluated prior to installation. Linear distributed pumping speeds at the beam line of ∼720 l/s/m for N2 and CO and ∼4000 l/s/m for H2 were measured. The measured pumping capacities for N2, CO and H2 are ∼1.0, ∼2.0 and ∼77 Torr l, respectively, for each titanium sublimation cycle. Measurements also showed that CO molecules adsorb on the N2 and H2 saturated titanium films with virtually the same initial sticking coefficient as on a fresh titanium film. Analyses indicated very different CO adsorption mechanisms between the N2 and H2 saturated titanium films. While the replacement of surface H2 by CO was observed, little desorption of nitrogen was measured. Operational experience showed excellent vacuum pumping performance over two years after the chamber installation.
Interfacial interactions of polymer coatings with oxide-free phosphate films on metal surfaces
Authors: Wang Yuqing , Sherwood Peter M. A.
Published: July 2003

A method for producing thin oxide-free phosphate films using an easier process than those previously reported is described. The process is carried out under ambient conditions using aqueous phosphoric acid. The chemistry of the phosphated surface prepared by the process and the interaction of this surface with a thin film of polyvinyl alcohol (PVA) are examined with the purpose of evaluating the potential of this film to serve as an adhesion promoting layer. The surface chemical changes are monitored by core and valence band x-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy, with the resultant spectra compared to those from band structure calculations. Valance band photoemission interpreted by band structure calculations can be used to study the interfaces involved, and proves to be a very effective tool for conclusively identifying the surface species present. The process for forming oxide-free phosphate films forms the same surface chemistry as previously reported for other processes. PVA is found to strongly interact with the oxide-free phosphate film on aluminum metal illustrating the potential of such films as adhesion promoters.
Surface analytical characterization of SiO2 gradient membrane coatings on gas sensor microarrays
Authors: Bruns M. , Frietsch M. , Nold E. , Trouillet V. , Baumann H. , White R. , Wright A.
Published: July 2003

Ion beam assisted deposition is applied to cover a gas sensor microarray of an electronic nose with an ultrathin gas-permeable SiO2 membrane varying in thickness across the array. Auger electron spectroscopy sputter depth profiles and non-Rutherford backscattering spectroscopy were used to study the uniformity of the deposition and the subsequent annealing step. The combination of spectroscopic ellipsometry for the freshly prepared membranes and line scans derived from Auger and angle resolved x-ray photoelectron spectroscopy, respectively, for the baked membrane is presented as a powerful quantification method for the determination of the desired SiO2 membrane thickness profiles.
X-ray photoelectron spectroscopy study of the first stages of ZnO growth and nanostructure dependence of the effects of polarization at ZnO/SiO2 and ZnO/Al2O3 interfaces
Authors: Martin-Concepción A. I. , Yubero F. , Espinós J. P. , González-Elipe A. R. , Tougaard S.
Published: July 2003

A critical characteristic of nanoparticles and, in general, of nanomaterials, is the overweighing importance of the surface and interface layers relative to the bulk because of the small size of the aggregates (in three dimensions) or thickness of the layers (in the case of two dimensions) that constitute the nanomaterial. This article reports the characterization of interface layers of ZnO/MOx (MOx: Al2O3 and SiO2) using x-ray photoelectron spectroscopy (XPS). Careful experiments consisting of the deposition of ZnO material on SiO2 and Al2O3 substrates have been performed. Several samples were produced and characterized in situ. The nanostructure of the first stages of growth of the ZnO deposited was determined by Tougaard peak-shape analysis of several photoelectron peaks in both the substrate and overlayer and the growth mechanisms determined were found to be consistent. Thus, the actual nanostructure of the growing ZnO films was carefully determined. In addition, the chemical interaction at the ZnO/MOx interface was monitored by following the variation of the Auger parameter of the Zn atoms as the amount of ZnO deposited was increased. Thus, changes of the Auger parameter of the Zn atoms were correlated with the actual nanostructures formed by the ZnO deposits. From this information, a model is presented that accounts for changes in the electronic parameters determined by XPS as a result of bonding and polarization interaction at the interface.
Origin of crystalline quality deterioration in epitaxial growth of CeO2 layers on Si substrates
Authors: Inoue Tomoyasu , Sakamoto Naomichi , Horikawa Akihiro , Takakura Hirofumi , Takahashi Kosei , Ohashi Masayuki , Shida Shigenari
Published: July 2003

CeO 2 layers with various degrees of crystallinity are characterized to get insight into the origin of the deterioration of epitaxial layers on Si substrates. The surface morphology of CeO2 layers is studied using atomic force microscopy and is correlated with the crystallinity of the layer determined by reflection high-energy electron diffraction. It is clearly observed that the surface morphology changes according to the crystallinity of the CeO2 layers. Single crystalline CeO2(110) layers with good crystallinity have a nanometer-scale periodically corrugated surface structure, which consists of (111) facets. As the crystalline quality of the CeO2 layers becomes worse, the number of irregularly shaped hillocks and tetrahedral hillocks increases and corresponds to distorted (110) grains and (111)-oriented polycrystalline grains, respectively. It is found that the crystalline quality is not uniform; different regions of crystallinity are distributed from place to place and the ratio of their population changes according to the degree of crystalline quality. Direct observation of irregularly shaped hillocks is carried out using cross-sectional lattice images from high resolution transmission electron microscopy. These features are discussed to understand the origin of the irregularly shaped hillocks in terms of the surface properties of the substrates at the early stage of growth.
Profile coatings and their applications
Authors: Liu Chian , Conley R. , Assoufid L. , Macrander A. T. , Ice G. E. , Tischler J. Z. , Zhang K.
Published: July 2003

We report a method of profile coating to achieve a certain selected thickness profile of a thin film coating using dc magnetron sputtering. In profile coatings, the substrate is passed over a contoured mask at a constant speed to obtain a desired profile along the direction perpendicular to the substrate-moving direction. The shape of the contour depends on the desired profile and the thickness distribution directly above the gun at the substrate level. Si wafers of 4 in. diameter were coated through a 100×152 mm2 aperture on the top of the shield can. The thickness distribution was then obtained using a spectroscopic ellipsometer with computer-controlled X-Y stages. A model has been developed to fit the measured thickness distribution. The relative thickness weightings are then obtained at every point 1 mm apart for the entire open area of the aperture. When the substrate is moving across the shield can during depositions, the film thickness is directly proportional to the length of the opening on the can along the moving direction. By equating the summation of relative weighting to the required relative thickness at the same position, the length of the opening at that position can be determined. By repeating the same process for the whole length of the required profile, a contour can be obtained for a desired thickness profile. The contoured mask is then placed very close (∼1 mm) to the substrate level on the shield-can opening. The number of passes and the moving speed of the substrate are determined according to the required thickness and the growth rate calibration. This method of profile coating has been applied to coat laterally graded W/C multilayers. It has also been applied to coat Au on a cylindrical mirror to obtain an elliptical mirror for x-ray focusing applications. Test results for these applications will be presented.
In situ studies of the amorphous to microcrystalline transition of hot-wire chemical vapor deposition Si:H films using real-time spectroscopic ellipsometry
Authors: Levi D. H. , Nelson B. P. , Perkins J. D. , Moutinho H. R.
Published: July 2003

In situ real-time spectroscopic ellipsometry (RTSE) provides detailed information on the evolution of the structural and optical properties of Si:H films during growth [Collins et al., Appl. Surf. Sci. 154-155, 217 (2000)]. We have used in situ RTSE to characterize the morphology and crystallinity of hot-wire chemical vapor deposition (HWCVD) Si:H films grown on native-oxide covered crystal silicon substrates as a function of substrate temperature Ts, hydrogen dilution R=[H2/SiH4], and film thickness db. Transitions from one mode of film growth to another are correlated with abrupt changes in the magnitude of the surface roughness during film growth. The degree of crystallinity of the film can be determined from the shape of the dielectric spectrum. We have studied the growth parameter space consisting of R from 0 to 14, Ts of 250 and 500 °C, and db from 0 to 1 μm. We have mapped out the crystallinity versus R, Ts, and db based on our analysis of the RTSE data. The transition between a-Si:H and μc-Si:H for growth on crystalline silicon substrates is near the R=3 to R=4 dividing line and is also a strong function of film thickness. Initial coalescence of purely μc-Si:H material does not occur until R⩾10. These results have been corroborated using Raman scattering and atomic force microscopy to characterize the crystallinity and surface morphology of the films.
Thermal stability of thin Ti films on Al single crystal surfaces
Authors: Ramana C. V. , Choi Bum Sik , Smith R. J. , Hutchinson R. , Stuk S. P. , Park Byoung Suk , Saleh Adli A. , Jeon Dong Ryul
Published: July 2003

Chemical roughness and alloy formation at metallic interfaces can significantly degrade the performance of multilayer thin film magnetic device structures. We have investigated the use of Ti interlayers, one or two atoms thick, to stabilize the interface for ordered growth of Fe films on Al(100), a system characterized by considerable interdiffusion at room temperature. The practicality of the interlayer concept is strongly coupled to the stability of the interlayer at elevated temperatures. In this investigation we have characterized the structure of thin Ti layers on Al single crystal surfaces as a function of temperature using Rutherford backscattering and channeling and low-energy ion scattering. The Ti layers are shown to be stable up to temperatures of about 675 K, at which point diffusion of Ti into the Al lattice occurs. Channeling measurements show that the Ti atoms sit on Al lattice sites as substitutional impurities. The stability of the Ti film appears to increase with the packing density of the Al surface, being slightly more stable for the close-packed Al(111) surface, and diffusing into the more open Al(110) surface at a lower temperature.
Quantitative x-ray photoelectron spectroscopy: Simple algorithm to determine the amount of atoms in the outermost few nanometers
Authors: Tougaard Sven
Published: July 2003

It is well known that due to inelastic electron scattering, the measured x-ray photoelectron spectroscopy peak intensity depends strongly on the in-depth atom distribution. Quantification based only on the peak intensity can therefore give large errors. The problem was basically solved by developing algorithms for the detailed analysis of the energy distribution of emitted electrons. These algorithms have been extensively tested experimentally and found to be able to determine the depth distribution of atoms with nanometer resolution. Practical application of these algorithms has increased after ready-to-use software packages were made available and they are now being used in laboratories worldwide. These software packages are easy to use but they need operator interaction. They are not well suited for automatic data processing and there is an additional need for simplified quantification strategies that can be automated. In this article we report on a very simple algorithm. It is a slightly more accurate version of our previous algorithm. The algorithm gives the amount of atoms within the outermost three inelastic mean free paths and it also gives a rough estimate for the in-depth distribution. An experimental example of its application is also presented.
Measuring vacuum ultraviolet radiation-induced damage
Authors: Lauer J. L. , Shohet J. L. , Hansen R. W.
Published: July 2003

During plasma processing of semiconductors, ultraviolet (UV) and vacuum ultraviolet (VUV) radiation are present, but their effects can be difficult to separate from those due to charged particles incident on the wafer. The contribution of VUV photon irradiation to gate-oxide damage, and damage to dielectric materials in general, was examined using two measurement techniques that can predict the possibility of damage. They are (1) surface potential measurements and (2) electrically erasable read-only memory transistors (CHARM-2 wafers). To isolate the radiation effects, unpatterned oxide-coated wafers and CHARM-2 wafers were exposed to VUV synchrotron radiation. VUV exposure of dielectrics and conductors results in an accumulation of positive charge due to photoemission. As a result, it can become difficult to distinguish the photoemitted from the plasma-deposited charge. In addition, it was determined that the UV monitors on CHARM-2 wafers did not respond to VUV radiation.
Environment, health, and safety performance plays a vital role in sustaining the growth of the semiconductor industry
Authors: Miller Coleen , Worth Walter
Published: July 2003

Rapid technology advances and rapid growth have historically been the basis for the success of the semiconductor industry. Over the last 25 years the industry has enjoyed a growth rate (∼15%) which far exceeds the growth rate of the U.S. economy overall (3%–4%). To ensure that this rapid growth rate can be sustained into the future, it is important that the industry makes efficient use of natural resources, minimizes any impact on the environment, and ensures the protection of its workers and the communities in which it operates. It has been repeatedly shown that resource efficiency is linked to lower operating costs and better environmental performance. International SEMATECH’s Environment, Safety and Health (ESH) division is engaged in several projects that are aimed at enabling continued, sustainable growth for the industry. These include energy and water conservation, perfluorocompound (PFC) emissions reduction as well as early ESH assessment of the multitude of new chemicals and materials being considered for 157 nm photolithography, low-k dielectrics, and advanced gate stacks. The timely assessment of any potential ESH impacts associated with these materials is essential to ensure that they are used in a safe and environmentally sound manner through cost-efficient ESH solutions and controls. This paper will describe the approach and results of International SEMATECH’s efforts in the areas of resource conservation, PFC emissions reduction, and early identification of potential ESH impacts associated with the next generation semiconductor chemicals and materials.
Study of damage reduction of (Ba0.6,Sr0.4)TiO3 thin films etched in Ar/CF4 plasmas
Authors: Kang Pil-Seung , Kim Kyoung-Tae , Kim Dong-Pyo , Kim Chang-Il
Published: July 2003

A barium strontium titannate (BST) thin films were etched in CF4/Ar using inductively coupled plasma. The high etch rate obtained at a CF4(20%)/Ar(80%) and the etch rate in pure argon was twice as high as that in pure CF4. This indicated that BST etching is a sputter-dominated process. It is impossible to avoid plasma-induced damage by energetic particles in the plasma and the contamination of nonvolatile etch products. The plasma damage was evaluated in terms of leakage current density, residues on the etched sample, and the change in roughness. After the BST thin films were exposed in the plasma, the leakage current density and roughness increased. In addition, there are appeared a nonvolatile etch products and the x-ray diffraction (XRD) (110) and (111) intensities are decreased and broaden. After annealing at 600 °C in O2 ambient for 10 min, the leakage current density, roughness, and nonvolatile etch products were reduced and the XRD (110) and (111) intensities increased. From these results, the attribution of the recovery of plasma induced damage by annealing process is owing to the desorption of metal fluorides at high temperature.
Chemical bonding of perfluoropolyether with carbon underlying layer induced by visible laser light
Authors: Zhu Lei , Zhang J. , Liew T. , Ye K. D.
Published: July 2003

We investigated the chemical bonding of perfluoropolyether lubricant molecules with carbon overcoat surface by irradiating with a visible pulsed laser light. A Nd:yttrium–aluminum–garnet laser with a wavelength of 532 nm was used to irradiate the lubricant film (1–2 nm) on carbon overcoat surface in ambient environment. The bonding formed was characterized at the molecular level using the time-of-flight secondary ion mass spectroscopy. We found that with increasing laser fluence, the ion yield of the end group CF2CH2OH of the lubricant decreases which can be an indication of chemical bond formation of the end group with the active sites of the carbon underlying layer. X-ray photoelectron spectroscopy reveals more lubricant on the laser-irradiated area than the surrounding nonirradiated area after washing off nonbonded lubricant by solvent Vertrel XF, which has little effect on bonded lubricant. Furthermore, we propose a method to quantify the bonding/nonbonding ratio of lubricant by considering the end-group intensity versus its neighboring fluorocarbon fragments.
Comparison between Monte Carlo and analytical calculation of the conductance of cylindrical and conical tubes
Authors: Gómez-Goñi J. , Lobo P. J.
Published: July 2003

The accurate calculation of transmission probabilities of ducts in the molecular flow regime has become a need of vacuum standards on the ultrahigh vacuum region. The usual approach is to simulate a molecular flow of molecules with a Monte Carlo method, because of the difficulties that arise trying to find a solution of the Clausing integral equation in a system of a given geometry. As modern computers increase their speed, the accuracy of Monte Carlo methods is getting higher. It is therefore important to compare simulation results with data obtained by other methods to check that pseudorandom numbers generated are uniformly distributed and not correlated. We have applied both a Monte Carlo method and numerical methods to solve the Clausing integral equation for cylindrical and conical tubes. Both Monte Carlo and numerical methods are consistent within estimated uncertainties. In the case of conical ducts, we obtain values which agree very well with values found in the literature and with uncertainties several orders of magnitude smaller. In the case of cylinders, very accurate transmission probabilities are obtained solving numerically the Clausing integral equation. Comparing with other values found in the literature using a variational method, our values are near the upper bound and quite far away from the lower bound.
Coadsorption of CO and hydrogen on the Zn-terminated surface of ZnO: A molecular beam study
Authors: Kunat M. , Burghaus U.
Published: July 2003

Presented are simultaneously detected adsorption probability and He atom reflectivity measurements, respectively, of CO adsorbed on a hydrogen precovered Zn-ZnO surface. The results obtained are consistent with a simple site blocking mechanism as demonstrated by Monte Carlo simulations.
Cell adhesion and spreading on polymer surfaces micropatterned by ion beams
Authors: Satriano C. , Carnazza S. , Licciardello A. , Guglielmino S. , Marletta G.
Published: July 2003

The cell adhesion and spreading behavior on surfaces of poly(ethyleneterephtalate) and poly(hydroxymethylsiloxane) micropatterned by focused 15 keV Ga+ beams has been studied. It has been found that while no modification in the cell adhesion process could be observed for unirradiated and irradiated areas on the patterned surfaces, in the case of polyhydroxymethylsiloxane the cell adhesion process is basically confined within the irradiated areas and a clear dependence of the cell ordering on the lateral size of the irradiated areas is observed. The results are discussed in terms of the specific spatially resolved chemical modification induced by Ga+ irradiation onto the two different polymers. Thus, the irradiation-induced modification of composition, functional groups concentration, surface free energy, and nanoscale morphology have been studied by means of x-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry, contact angle, and atomic force microscopy. The cell adhesion and spreading behavior was found to nicely correlate with the increase of the acid-base component γAB of the surface free energy and more particularly with the dramatic increase of the Lewis basic electron-donor term.
High-temperature fiber matrices: Electrospinning and rare-earth modification
Authors: Kataphinan W. , Teye-Mensah R. , Evans E. A. , Ramsier R. D. , Reneker D. H. , Smith D. J.
Published: July 2003

We demonstrate the production of nonwoven mats of high-temperature organic and inorganic fibers by electrospinning. Specifically, glass/ceramic (tetraethylorthosilicate–SiO) and fire-blanket (polydiphenoxyphosphazene–PDPP) precursors are electrospun, and the resulting fibers are characterized by scanning electron microscopy, thermogravimetric analysis, and infrared (IR) spectroscopy. We find that the SiO fibers are smaller in diameter and more uniform than the PDPP fibers, and stable to higher temperatures. We also coat these fiber systems with several rare-earth nitrates, and find that these coatings can be used to selectively modify the near-IR spectra of the fibers. This work extends the use of electrospinning into two new classes of materials, and demonstrates that we can subsequently modify the optical properties of the electrospun fibers.
High-rate deposition of abrasion resistant coatings using a dual-source expanding thermal plasma reactor
Authors: Schaepkens M. , Selezneva S. , Moeleker P. , Iacovangelo C. D.
Published: July 2003

A unique high-rate plasma deposition process has been developed to generate abrasion resistant coatings on polymeric substrates. The process relies on the integration of a plurality of individual expanding thermal plasma sources into a multisource setup. In this work, we will discuss the effects of various hardware and process parameters on the performance of a dual-source system that has been used to apply abrasion resistant coatings to polycarbonate substrates. It will be shown that a properly engineered dual-source system can generate transparent organosilicon-based coatings that provide uniform glasslike abrasion resistance across a 30 cm width on substrates that are laterally translated past the dual-source array.
Effects of carbon-containing gases on the field-emission current of multiwalled carbon-nanotube arrays
Authors: Sheng L. M. , Liu P. , Liu Y. M. , Qian L. , Huang Y. S. , Liu L. , Fan S. S.
Published: July 2003

Field emission from carbon nanotubes can be affected by common carbon- containing residual gases in vacuum systems. In this article, we will show the effects of CO, CO2, CH4, and C2H4 gases on the field-emission currents of patterned multiwalled carbon-nanotube arrays prepared by chemical vapor deposition. Exposure to CO and CO2 at 10−5 Pa can reduce the emission current from 22% to 49%, depending on the specific partial pressure and exposure time. Such a reduction can be fully recovered by continuous emission under a high vacuum of 10−6 Pa. Exposure to CH4, and C2H4 can increase the current, but the current stability is poor, and after the exposure, the current did not recover.
Energetic deposition of niobium thin film by ecr-plasma
Authors: Wu G. , Phillips H. L. , Sundelin R. M.
Published: July 2003

An electron cyclotron resonance (ECR)-plasma reactor has been built to do energetic ion deposition of refractory metals in vacuum. The system uses an E-beam gun to create refractory metal flux. The neutral metal flux feeds into a microwave resonator and forms pure metal plasma created by electron cyclotron resonance. The metal ions are extracted to a biased substrate for direct deposition. A retarding field energy analyzer is developed and used to measure the kinetic energy of metal ions at the substrate location. A high-quality niobium thin film is obtained through this deposition system. The niobium film exhibits an excellent superconducting transition. The niobium ion energy distribution has been measured. The niobium ion at the substrate location has a median kinetic energy of 64 eV with an energy spread of 20 eV under certain plasma conditions.
Effect of sputtering pressure on residual stress in Ni films using energy-dispersive x-ray diffraction
Authors: Alfonso J. A. , Greaves E. D. , Lavelle B. , Sajo-Bohus L.
Published: July 2003

A procedure for determining the residual stress in thin films using energy dispersive x-ray diffraction was investigated. The effect of the sputtering pressure on the residual stress in dc magnetron sputtered Ni films was studied in greater detail using this approach. The behavior reported suggested the possibility of controlling or influencing the sign and/or magnitude of the residual stress. In addition, the stress variation with increasing negative bias voltage is also presented. In the range studied, between −15 and −150 V, residual stress is always tensile.
Effects of Si addition on the microstructural evolution and hardness of Ti–Al–Si–N films prepared by the hybrid system of arc ion plating and sputtering techniques
Authors: Park In-Wook , Choi Sung Ryong , Lee Mi-Hye , Kim Kwang Ho
Published: July 2003

Ti–Al–Si–N films were deposited on WC–Co substrates by the hybrid coating system of arc ion plating method for Ti–Al sources and dc magnetron sputtering technique for Si incorporation. The synthesized Ti–Al–Si–N films were revealed as composites of solid-solution (Ti,Al,Si)N crystallites and amorphous Si3N4 by instrumental analyses such as x-ray diffraction, high-resolution transmission electron microscopy, and x-ray photoelectron spectroscopy. The Si addition in Ti–Al–N films affected the refinement and uniform distribution of crystallites by percolation phenomenon of amorphous silicon nitride similar to that of the Si effect in TiN film. The solubility limit of Si in the Ti0.76Al0.24N crystal is believed to be about 6 at. %. No free Si was observed due to the very high ionization rate of nitrogen gas in the arc plasma. As the Si content increased up to about 9 at. %, the hardness of Ti–Al–N film steeply increased from 30 GPa to about 50 GPa. Ti–Al–Si–N films having the maximum hardness showed the nanocomposite microstructure consisting of fine (Ti,Al,Si)N crystallites, about 8 nm in size, dispersed uniformly in the amorphous Si3N4 matrix.
Super-smooth indium–tin oxide thin films by negative sputter ion beam technology
Authors: Sohn M. H. , Kim D. , Kim S. J. , Paik N. W. , Gupta S.
Published: July 2003

An ionized physical vapor deposition, negative sputter ion beam (NSIB) technology, is described for the deposition of super-smooth indium–tin oxide (ITO) thin films with highly transparent and conductive properties at near-room temperature deposition. A negatively charged sputter ion beam is produced by retrofitting an ITO magnetron sputtering cathode with a cesium vapor injector capable of releasing controlled amounts of cesium vapor into the plasma during deposition. Using this highly energetic deposition process, ITO thin films have been obtained at near-room temperature (less than 50 °C) with super-smooth surface (<1 nm rms), resistivity of 4×10−4 Ω cm, and transmittance higher than 85% (at wavelength 550 nm) on polycarbonate substrates.
Present status of the KEK B-factory vacuum system
Authors: Suetsugu Y. , Kanazawa K. , Kato S. , Hisamatsu H. , Shimamoto M. , Shirai M.
Published: July 2003

The KEK B-Factory (KEKB) is a two-ring electron-positron collider with asymmetric energies to quest the CP violation. The design beam currents are 1.1 A and 2.6 A for 8.0 GeV electron and 3.5 GeV positron ring, respectively. Most of beam chambers are made of oxygen free copper for its ability to withstand the intense heat load and to shield effectively the radiation from the high beam currents. The pumping scheme is a combination of the nonevaporable getter pumps and auxiliary sputter ion pumps. Special care is taken of the inside of beam chambers to avoid excitation of higher-order modes (HOM). The commissioning of KEKB started in December 1998. The vacuum system has been operating almost satisfactorily. The average pressure of about 3×10−7 Pa is achieved now for both rings at the beam current of about 1 A. The coefficient of photon-stimulated gas desorption has been decreasing steadily to less than 1×10−6 molecules photon−1 at the integrated linear photon density of about 7×1025 photons m−1. The presence of high-current bunched beams in the ultrahigh vacuum creates several problems particular to the accelerator vacuum system. A nonlinear dependence of pressure on beam current is observed in the low-energy ring due to the electron multipactoring. The intense HOM sometimes causes hardware troubles especially for the movable masks. Based on the experiences so far, a discussion of upgrading the KEKB vacuum system has just started aiming for a higher luminosity machine.
Barium–strontium–titanate etching characteristics in chlorinated discharges
Authors: Stafford Luc , Margot Joëlle , Langlois Olivier , Chaker Mohamed
Published: July 2003

The etching characteristics of barium–strontium–titanate (BST) were investigated using a high-density plasma sustained by surface waves at 190 MHz in Ar/Cl2 gas mixtures. The etch rate was examined as a function of both the total gas pressure and the Cl2 fraction in Ar/Cl2 using a wafer temperature of 10 °C. The results were correlated to positive ion density and plasma composition obtained from Langmuir probes and mass spectrometry. The BST etch rate was found to increase linearly with the positive ion density and to decrease with increasing chlorine atom concentration. This result indicates that for the temperature conditions used, the interaction between chlorine and BST yields compounds having a volatility that is lower than the original material. As a consequence, the contribution of neutral atomic Cl atoms to the etch mechanism is detrimental, thereby reducing the etch rate. As the wafer temperature increases, the role of chemistry in the etching process is enhanced.
Plasma-enhanced chemical vapor deposition of SiO2 from a Si(CH3)3Cl precursor and mixtures Ar/O2 as plasma gas
Authors: Barranco A. , Cotrino J. , Yubero F. , Girardeau T. , Camelio S. , Clerc C. , Gonzalez-Elipe A. R.
Published: July 2003

Silicon dioxide thin films have been prepared at room temperature by remote plasma-enhanced chemical vapor deposition in a downstream reactor by using Si(CH3)3Cl as a volatile precursor and a microwave electron cyclotron resonance external source. Experiments are done at constant pressure by changing the relative amount of Ar species R in the plasma gas. The aim was to obtain thin films with low density and, therefore, low refractive index. Characterization of the species of the plasma is carried out by optical emission spectroscopy. The changes of the plasma conditions are correlated with the growing rate and microstructure of the films, the latter determined by atomic force microscopy and infrared spectroscopy. It is found that the growing rate of the films decreases and their roughness increases as R increases. The optical properties of SiO2 thin films are analyzed by optical ellipsometry. A decrease in the refractive index is found for the films grown with high values of R. The possible routes for activation of the precursor and the formation of the SiO2 thin films are discussed.
Pulsed laser ultrahigh vacuum deposited silicon in the presence of excess cesium and oxygen studied with x-ray photoelectron spectroscopy and atomic force microscopy
Authors: Choo Cheow-Keong , Tanaka Katsumi , Suzuki Hiroaki , Saotome Nobuyuki , Ichida Kouji
Published: July 2003

Si/Cs/O clusters were prepared in an ultrahigh vacuum system with pulsed laser ablation of Si in the presence of Cs vapor and molecular oxygen. The effects of an O2 ambient, the pressure, and the deposition sequence of Cs and O2 on the oxidation state of cesium oxides and silicon oxides, as well as on the formation of Si/Cs/O clusters, were studied with x-ray photoelectron spectroscopy and atomic force microscopy (AFM). Oxygen 1s spectra were deconvoluted to cesium oxide(s) at around 530.5 eV and silicon oxide(s) at 532.3 eV. From the low binding energy side to the high binding energy side, Si 2p spectra were assigned to negatively charged Si clusters (94 and 96 eV), silicon suboxide (102 eV), SiO2 (104 eV), and Si/Cs/O clusters (106 eV), respectively. The high binding energy species was explained by the formation of Si(CsO1+x)n clusters. Surface morphologies were influenced by the oxidation state of cesium oxides and their amount. The work function decrease as much as 0.5±0.1 eV was measured with ex situ AFM.
Comparison of the stability of hot and cold cathode ionization gauges
Authors: Li Detian , Jousten Karl
Published: July 2003

When ionization gauges are used as reference or secondary standards, their stabilities are the most important features. Generally, only hot cathode gauges are used as reference or secondary standards in calibration services. Some traditional reasons preventing the use of cold cathode gauges are the presence of discontinuities in the current versus pressure characteristic, the ignition delay at very low pressures, and the poor stability especially under contaminating vacuum environments. Though current inverted magnetron designs are believed to avoid some of these problems, at least under clean conditions, no “hard facts” have been published to support this claim. Here, we present the experimental results of calibrations of three hot cathode gauges and two inverted magnetrons against a primary high-vacuum standard over the range 10−7 to 10−3 Pa with gases of N2, Ar, He, and H2, respectively. During a continuous observation period of 72 h at a constant pressure of about 1×10−4 Pa, hot cathode gauges showed better stabilities than inverted magnetrons in N2, Ar, and He, but all gauges behaved similarly in H2. Repeated calibrations over a period of about 6 months showed that all gauges had similar long-term stabilities in N2, Ar, and He. For H2, however, the stability of inverted magnetrons was better than that of hot cathode gauges. For different gases, the discontinuities of inverted magnetrons occurred at different pressures, making their calibrations more elaborate.
Feature profile evolution in high-density plasma etching of silicon with Cl2
Authors: Jin Weidong , Sawin Herbert H.
Published: July 2003

A Monte Carlo based profile simulator was constructed that incorporated the dominant reaction mechanisms of surface chlorination under simultaneous neutral and ion bombardment, surface etching, and ion reflection. The profile simulation is based on the kinetics model developed from beam studies that measured the ion energy, ion and neutral fluxes and ion angular dependencies of Cl+ ion-enhanced etching with Cl. The profile evolution of patterned samples with oxide hard mask etched in an inductively coupled plasma etcher were simulated. The mechanisms of undercutting and microtrenching forming were discussed. Ions scattered from the neighboring hardmask were primarily responsible for the undercutting, while ions reflected from bowed feature sidewalls were primarily responsible for the microtrenching. The profile evolutions under different processing conditions were compared with experimental results and some etching artifacts were characterized and discussed. The neutral-to-ion ratio was found to influence the surface chlorination significantly, thus causing variation of profile evolution. Higher ion energy would give more ideal profiles due to increased ion directionality. However, higher ion energy also increased the etching rate and reduced the chlorination at the bottom of the feature. The reduced chlorination of the feature bottom relative to the sidewall increases the ratio of lateral etching to vertical etching, and decreases the etching anisotropy. The influence of SiCl2 deposition and mask angle on feature profile evolution were also investigated.
Stability of carbon subatomic films on metal surface against bombardment by low-energy gas ions
Authors: Babaev V. P. , Suvorov A. L. , Zaluzhny A. G. , Dev’jatko Ju. N. , Lazarev N. E. , Zaluzhny A. A.
Published: July 2003

The original techniques of measurement and analysis of parameters of low-frequency fluctuations of field-emission current of metal–film systems developed earlier have been used in this work to measure sputtering coefficients of carbon films (coverage from 1 to 4 monolayers) on Fe, Nb, Ta, and U. Directly measured values were amplitudes of abnormal fluctuations of field-emission current ΔIn caused by hits of individual bombarding ions at the film. Calculations of sputtering coefficients Yf have been carried out using analytical expressions of the theoretical model developed. Sputtering coefficients of carbon films by ions H+ and He+ with energy in the range of 2.0–10.0 keV have been measured. Energy dependencies Yf for fixed θ of each type of ion have been determined. Besides, for certain fixed energy values Ei of each ion type dependency, Yf versus θ has been determined (where θ is the quantity of monolayers). Measured values Yf, in all cases, are significantly higher than that of bulk carbon. Having used another original technique combining ion-field microscopy and precision measurements of current and/or light characteristics of local areas of ion-field images, energy thresholds Eth of the beginning of sputtering of carbon films on metal surfaces have been determined. Energy distributions Yf for various θ in the near-threshold energy region have been measured.