bluuebunny/crossref_metadata_2025 huggingface dataset:
Reduction of False Scattering of the Discrete Ordinates Method
Authors: Li Hong-Shun , Flamant Gilles , Lu Ji-Dong
Published: September 2002

A novel method, the Double Rays Method (DRM), is proposed to capture the discontinuous nature of the radiation intensity, in order to reduce false scattering of the discrete ordinates method (DOM). Numerical tests demonstrate that the DRM successfully removes false scattering in all the two-dimensional test problems discussed in this paper. The effect of false scattering on the computational results in two-dimensional situations is investigated with the DRM. False scattering plays a double role: when the boundary emits radiation in a limited number of directions, or when the irradiation comes from a limited number of directions, it produces a smeared intensity field and radiative heat flux distribution, and thus must be removed. In the case of diffuse boundary, however, false scattering plays a useful role and thus should be retained.
Solutions of Radiative Heat Transfer in Three-Dimensional Inhomogeneous, Scattering Media
Authors: Ruan L. M. , Tan H. P.
Published: September 2002

In the present study, we use the Monte-Carlo (MC) method to simulate radiative heat transfer in three-dimensional inhomogeneous scattering unit cube with black or gray walls. The results show that the averaging method of non-uniform radiative properties in each medium element has influence on the results. One reasonable averaging method has been employed in our model. In mean while, several characters of exchange factor have been employed to estimate the performance of pseudo-random numbers generator and the numerical uncertainty of MC simulation.
Experimental Validation of a Combined Electromagnetic and Thermal Model for a Microwave Heating of Multi-Layered Materials Using a Rectangular Wave Guide
Authors: Rattanadecho P. , Aoki and K. , Akahori M.
Published: September 2002

The heating of multi-layered materials by microwave heating with rectangular wave guide has been investigated numerically and experimentally. The multi-layered materials, which consist of the layer of higher dielectric material (antireflection layer) and lower dielectric material (sample), have the convergent effect of the incident microwave in sample, and it can change the heating pattern in the sample with ease. In this study, the effect of an antireflection layer thickness on the heating process is clarified in detail, considering the interference between incidents and reflected waves in the dielectric materials. Based on a model combining the Maxwell and heat transport equations, the results showed that when a layer of lower dielectric material is attached in front of sample, the microwave energy absorbed and distribution of temperature within the sample are enhanced. The predicted results are in agreement with experimental results for microwave heating of multi-layered materials using a rectangular wave guide.
Modeling of metallic
materials at high strain rates with continuum damage mechanics
Authors: Voyiadjis GZ , Palazotto AN , Gao X-L
Published: September 2002

Damage modeling of metallic materials under high strain rate loading conditions is reviewed. The emphasis is on the modeling efforts based on continuum damage mechanics, although many important references dealing with general aspects of dynamic behavior of materials are also discussed. Relevant issues on the use of continuum damage mechanics and on the damage modeling of composites are addressed as well. This review article deals with 134 references
Optimum Design of Spacecraft Radiators With Longitudinal Rectangular and Triangular Fins
Authors: Krikkis Rizos N. , Razelos Panagiotis
Published: September 2002

In the present study the optimum dimensions of longitudinal rectangular and triangular radiating fins with mutual irradiation are determined. The basic assumptions are one-dimensional heat conduction and gray diffuse surface radiation. The governing equations are formulated by means of dimensionless variables and solved numerically in order to carry out the required minimization procedure. The optimum fin dimensions, thickness and height, are presented in generalized dimensionless form and correlations are provided in order to assist the spacecraft thermal systems designer. The results are analyzed and expressed in explicit correlations. Several diagrams, are also included, that give insight to the operational characteristics of the heat rejection mechanism. Moreover, special attention is given to the error analysis of the numerical methods used, since the accuracy and the reliability of the algorithms employed for the solution of the integro-differential equation is important for the calculation of the heat dissipation at the fin base and its subsequent optimization.
Growth behaviors of low-pressure metalorganic chemical vapor deposition aluminum silicate films deposited with two kinds of silicon sources: Hexamethyldisilazane and tetraethyl orthosilicate
Authors: Kuo Dong-Hau , Chuang Po-Yo
Published: September 2002

Amorphous aluminum silicate films with film thicknesses of 0.5–2.7 μm were prepared on silicon substrates by low-pressure metalorganic chemical vapor deposition. This deposition was conducted using aluminum tri-sec-butoxide as the aluminum source and tetraethyl orthosilicate or hexamethyldisilazane as the silicon source. The choice of different silicon sources is based on their reactivity. The study of growth kinetics is based on the variation of growth rate with deposition temperature and reactant input. These two systems showed big differences in growth kinetics and film composition.
Growth-controlled cubic zirconia microstructure in zirconia–titania nanolaminates
Authors: DeLoach J. D. , Aita C. R. , Loong C.-K.
Published: September 2002

Zirconia microstructure selection (phase and crystallographic orientation) was studied in sputter-deposited multilayer films consisting of nanocrystalline ZrO2 and amorphous TiO2. The goal was to understand the mechanism for ZrO2 microstructure selection as a function of nanolaminate architecture (number of interfaces and ZrO2 and TiO2 layer thickness) in a growth regime of limited surface diffusion. The results show that there are two competing paths that ZrO2 microstructure can follow in a ZrO2–TiO2 nanolaminate. One path depends upon geometric shadowing resulting in the formation of a columnar morphology within a ZrO2 layer. This path leads to cubic (220) growth as an intermediate microstructure, and ultimately to the formation of cubic (200) crystallites spanning several bilayers. In this case, ZrO2 renucleation within a layer is suppressed. The second path depends upon renucleation within a ZrO2 layer, involving first tetragonal (111) formation, and then the transformation of tetragonal (111) to monoclinic(11-1)-(111), consistent with a finite crystal size effect. The establishment and maintenance of a columnar morphology (and hence, the suppression of renucleation events), ultimately leads to cubic (200) growth, and is consistent with a growth-controlled microstructure selection mechanism. This mechanism appears to strongly depend upon the existence and planar quality of the TiO2 growth–restart surfaces.
Ion-enhanced chemical etching of ZrO2 in a chlorine discharge
Authors: Sha Lin , Cho Byeong-Ok , Chang Jane P.
Published: September 2002

Chlorine plasma is found to chemically etch ZrO2 thin films in an electron cyclotron resonance reactor, and the etch rate scaled linearly with the square root of ion energy at high ion energies with a threshold energy between 12–20 eV. The etching rate decreased monotonically with increasing chamber pressures, which corresponds to reduced electron temperatures. Optical emission spectroscopy and quadrupole mass spectrometry were used to identify the reaction etching products. No Zr, O, or ZrCl were detected as etching products, but highly chlorinated zirconium compounds (ZrCl2, ZrCl3, and ZrCl4) and ClO were found to be the dominant etching products. ZrCl3 was the dominant etching products at low ion energies, while ZrCl4 became dominant at higher ion energies. This is consistent with greater momentum transfer and enhanced surface chlorination, as determined by x-ray photoelectron spectroscopy, at increased ion energies. Several ion-enhanced chemical reactions are proposed to contribute to the ZrO2 etching.
Transition layers in metal bilayers produced by pulsed laser deposition in vacuum
Authors: Tselev A. , Gorbunov A. , Pompe W.
Published: September 2002

Main processes which accompany the interaction of energetic particles with the substrate and the growing film in the pulsed laser deposition (PLD) in vacuum are considered. The subplantational film growth mode, which is inherent to PLD, results in the formation of diffuse transition layers (TLs) between the individual materials of the substrate and film. It is argued that thermodynamic forces do not play a significant role in formation of TLs at room temperature by PLD in vacuum, and the resulting concentration profile between the individual materials is determined almost purely by ballistic effects. Up to 10 nm thick TLs in Fe/Al and Ag/Co PLD-produced bilayers have been determined by numerical simulations, semiquantitative analysis and experimentally by means of a quartz thickness monitor. The latter technique has been proposed as an in situ method for determination of TLs between the individual materials with different sputtering yields. The concentration profiles of TLs are featured by a steep slope on the substrate side and an up to 10 nm long tail of the underlying material in the upper layer.
Multiple phase structures of Hf silicide precipitated from Hf silicate: An atomic view
Authors: Lee Jung-Ho , Ichikawa Masakazu
Published: September 2002

Multiple phase structures of crystalline hafnium silicide precipitated from the silicate have been found as a function of temperature (900–1000 °C) by using scanning tunneling microscopy and x-ray photoelectron spectroscopy. At 900 °C, a crystalline silicate structure transforms into a bulklike (1×1) “facetbar” of HfSi2 near the topmost surface, but into a “platelet” around the interface with Si. A Si-depletion zone is found to only form near platelets, not facetbars. Upon further annealing to 1000 °C, facetbars likely transform into platelets, and the atomic structure of a platelet also transforms to a patchlike feature having two equivalent antiphase sites, which are shifted by a half (∼2.3 Å) of the (1×1) unit length along the 〈110〉 directions.
Thermal decomposition pathway and desorption study of isopropanol and tert-butanol on Si(100)
Authors: Kim Jaehyun , Kim Kwansoo , Yong Kijung
Published: September 2002

Thermal decomposition pathway and desorption of isopropanol (IPA) and tert-butanol on Si(100) were studied using temperature programed desorption. Adsorbed alcohols studied were decomposed into atomic hydrogen and alkoxy on the surface. During heating the sample up to 1000 K, acetone, propylene, and hydrogen were desorbed as decomposition products of IPA on Si(100). Desorption pathways of IPA on Si(100) were largely consistent with those on metal surfaces: β-hydride elimination reaction to acetone and C–O scission to propylene. For tert-butanol, which has no β-hydrogen, isobutene and hydrogen were observed as main desorption products.
Optimized oxygen plasma etching of polyimide films for low loss optical waveguides
Authors: Agarwal Navnit , Ponoth Shom , Plawsky Joel , Persans P. D.
Published: September 2002

Sidewall roughness in waveguides is one of the consequences of a reactive ion etch (RIE) step. Sidewall roughness increases scattering losses and can impediment the scaling of waveguide dimensions to on-chip levels. This article presents results from our experiments on the study of optimal RIE conditions to minimize roughness on waveguide sidewalls. Roughness in planar polyimide films was studied for different plasma etch conditions to obtain an understanding of how roughness evolves. Pressure was found to be the dominant factor affecting interface roughness. RIE done at lower pressures was found to increase the roughness on the film surface. We propose that the roughness produced depends on the angle of incidence of the etchant species with respect to the surface the more obliquely the etchant species were incident on the surface, the lower was the roughness produced. Roughness produced on waveguide sidewalls was studied by measuring their propagation loss. For sidewalls, lower pressure RIE resulted in smoother sidewalls. This result was correlated with the previously obtained results for thin film surfaces. Based on our experiments we propose low pressure RIE to minimize sidewall roughness and fabricate low loss optical waveguides.
Annealing behavior of a Cs2O/Cs2O2/GaAs(110) surface studied by electron spectroscopy
Authors: Wu J. X. , Li F. Q. , Zhu J. S. , Ji M. R. , Ma M. S.
Published: September 2002

A Cs2O/Cs2O2 overlayer was prepared by simultaneous oxygen–cesium adsorption on GaAs(110) at room temperature. In situ electron spectroscopy and work function measurements have been used to study the Cs2O/Cs2O2/GaAs surface as a function of annealing temperature. The Cs2O/Cs2O2/GaAs surface exhibits metallic and has a work function value of 0.9 eV. There are Cs–O–Ga, Cs–O–As, As–O, and Ga–O bonds at the interface of Cs2O2/GaAs. Annealing facilitates the interfacial reaction and the minimum of the work function (0.7 eV) was observed after annealing at 540 K. After the decomposition of Cs2O and Cs2O2 at 620 K, the surface dominated by the Cs–O–Ga and Cs–O–As species remains negative electron affinity with a work function value of 1.1 eV. For further annealing, the fast Cs desorption is associated with the decomposition of the Cs–O–Ga and Ca–O–As bonds as well as the evaporations of As2O3 and CsAsO2, forming Ga2O3.
Semiempirical profile simulation of aluminum etching in a Cl2/BCl3 plasma
Authors: Cooperberg D. J. , Vahedi V. , Gottscho R. A.
Published: September 2002

A semiempirical profile simulator to predict topographic evolution during Cl2/BCl3 plasma etching of photoresist patterned Al lines has been developed. Given incident flux distributions, the profile simulator uses a combination of a particle based Monte Carlo algorithm and analytic ray-tracing algorithm for solving feature-scale ion and neutral flux transport, respectively. We use angular and energy distributions for reflected ions that are consistent with experimental observation and molecular dynamic simulations. Etch yields with energy and angular dependence are experimentally determined for physical sputtering and ion-enhanced etching. The spontaneous etch rate of A1 by chlorine and the spontaneous desorption rate of Cl from photoresist are estimated from experimental results. Sticking coefficients for etchant, chlorine, and depositor, CClx, and depositing flux are determined by fitting simulated profiles to experimental data. A semiempirical site-balance model is developed to compute the surface coverage of etchant. The reaction probability of neutrals at surfaces is self-consistently determined from the surface coverage at incident location. Competition between etching and deposition on feature sidewalls is modeled. A shock-tracking method is used to advance the profile using computed etch/deposition rates. Simulation results are presented which demonstrate that facet formation, aspect ratio dependent etching, and critical dimension gain, are captured accurately by the calibrated profile simulator. In addition, the calibrated profile simulator along with results of a 23 design of experiments in which photoresist and Al etch rates were measured on open frame wafers have been used to create a plasma reactor model. The reactor model relates the operational parameters including inductively coupled power, rf bias and gas flow ratio to the flux variables, i.e., Cl flux, ion flux, ion energy, and depositor flux, that are used as inputs to the profile simulator. In this manner, calibration of the profile simulator requires a minimum of high resolution, expensive, patterned wafers. The reactor model so created is shown to be in quantitative agreement with results from the hybrid plasma equipment model (Ref. 1).
Redeposition of etch products on sidewalls during SiO2 etching in a fluorocarbon plasma. I. Effect of particle emission from the bottom surface in a CF4 plasma
Authors: Min Jae-Ho , Hwang Sung-Wook , Lee Gyeo-Re , Moon Sang Heup
Published: September 2002

The effect of etch-product redeposition on sidewall properties during the etching of step-shaped SiO2 patterns in a CF4 plasma was examined using a Faraday cage located in a transformer coupled plasma etcher. Sidewall properties were observed for two cases: with and without particles emitted from the bottom surface in normal contact with the sidewall. Particles sputtered from the bottom surface were redeposited on the sidewall, which contributes to the formation of a passivation layer on the surface of the latter. The passivation layer consisted of silicon oxide, SixOy, and fluorocarbon, CxFy, the latter comprising the major species. Ar plasma experiments confirmed that CxFy or a fluorocarbon polymer must be present on the sidewall in order for the SixOy species to be deposited on the surface. The redeposited particles, which were largely F-deficient fluorocarbon species, as evidenced by x-ray photoelectron spectroscopy analyses, functioned as precursors for fluorocarbon polymerization, resulting in a rough sidewall surface. The chemical etch rates of SiO2 were retarded by the redeposition of particles, which eventually formed a thick layer, eventually covering the bulk SiO2. Auger electron spectroscopy analyses of the sidewall surface affected by the emission from the bottom suggest that the surface consists of three distinct layers: a surface-carbon layer, a redeposition-etch combined layer, and bulk SiO2.
Generating high-efficiency neutral beams by using negative ions in an inductively coupled plasma source
Authors: Samukawa Seiji , Sakamoto Keisuke , Ichiki Katsunori
Published: September 2002

To minimize radiation damage caused by charge buildup or ultraviolet and x-ray photons during etching, we developed a high-performance neutral-beam etching system. The neutral-beam source consists of an inductively coupled plasma (ICP) source and parallel top and bottom carbon plates. The bottom carbon plate has numerous apertures for extracting neutral beams from the plasma. When a direct current (dc) bias is applied to the top and bottom plates, the generated positive or negative ions are accelerated toward the bottom plate. Most of them are then efficiently converted into neutral atoms, either by neutralization in charge-transfer collisions with gas molecules during ion transport and with the aperture sidewalls in the bottom plate, or by recombination with low-energy electrons near the end of the bottom plate. We found that negative ions are more efficiently converted into neutral atoms than positive ions. The neutralization efficiency of negative ions was almost 100%, and the maximum neutral flux density was equivalent to 4.0 mA/cm2. A neutral beam can thus be efficiently produced from the ICP source and apertures in our new neutral-beam source.
Two-directional N2 desorption in thermal dissociation of N2O on Rh(110), Ir(110), and Pd(110) at low temperatures
Authors: Horino H. , Rzeźnicka I. , Kokalj A. , Kobal I. , Ohno Y. , Hiratsuka A. , Matsushima T.
Published: September 2002

Two-directional N2 desorption was found in N2O dissociation on Rh(110), Ir(110), and Pd(110) below 160 K by angle-resolved thermal desorption. N2O(a) is mostly dissociated during heating procedures, emitting N2(g) and leaving O(a). N2 showed four desorption peaks in the temperature range of 110–200 K. One of them commonly showed a cosine distribution, whereas the others sharply collimated off the surface normal in the plane along the [001] direction. The collimation angle was about 70° on Rh(110), 65° on Ir(110), and 43°–50° on Pd(110). A high-energy-atom assisted desorption model was proposed for N2 inclined emission.
Giant polarization in organic heterostructures
Authors: Thurzo Ilja , Kampen Thorsten U. , Zahn Dietrich R. T.
Published: September 2002

Deep levels or polarization effects can influence the charge transport through organic layers. Both effects can be identified by charge deep-level transient spectroscopy (Q-DLTS). Here, deep levels or polarization effects cause the charge transient signal Q(t) to be dependent or independent on the bias voltage, respectively. Q-DLTS, accompanied by feedback charge capacitance (FCM) measurements, has been used in the present work to investigate an organic heterostructure grown on an inorganic semiconductor. GaAs(100) substrates (n=0.34×1018 cm−3) were sulfur passivated by wet chemical etching and additional annealing under ultrahigh vacuum (UHV) conditions. Organic molecular beam deposition was used for the growth of 20 nm of 3,4,9,10-perylenetetracarboxilic dianhydride (PTCDA, Lancaster) and 27 nm of tris-(8-hydroxyquinoline) aluminum (Alq3, Syntec). Silver was evaporated on the Alq3 film through a shadow mask resulting in an array of circular contacts with an area of A=2.1×10−7 m2. The back contact to the GaAs(100) was achieved by an In–Ga alloy resulting in a series resistance of 20 Ω. The electrical characterizations were done at room temperature and in situ in the UHV system. The Q-DLTS measurements show a well resolved maximum in Q(t). The amplitude remains almost constant as a function of the bias voltage, which is a clear indication of a polarization in the organic heterostructure. From the experimental results the permittivity dispersion is determined to 2.37. The permittivity dispersion is independently obtained from FCM measurements. With the experimentally determined excess capacitance ΔC of 90 pF and the thickness of the organic heterostructure the permittivity dispersion is determined to 2.42. The FCM scans show no hysteresis due to the absence of deep levels. The ΔC/C=1 presented here clearly indicates the presence of a giant polarization.
W and WC layers deposition by shielded inductively coupled plasma source
Authors: Colpo P. , Meziani T. , Sauvageot P. , Ceccone G. , Gibson P. N. , Rossi F. , Monge-Cadet P.
Published: September 2002

Tungsten and carbon tungsten films have been deposited by a plasma enhanced chemical vapor deposition (PECVD) technique. The plasma-assisted deposition was performed by inductively coupled plasma source (ICP). A Faraday shield was arranged within the plasma chamber to prevent electrically conductive film deposition on the dielectric chamber wall that would screen the electromagnetic field. External electrical parameters and ion densities of the shielded inductive plasma source are measured and compared to classical ICPs source characteristics. Tungsten deposition has been performed from WF6 diluted in argon and hydrogen. A deposition rate of 5 μm/h was obtained. Hardness measurements show that the tungsten hardness can be increased from 5 to 20 GPA by biasing the substrate. WC films were deposited by adding methane or acetylene to the WF6/H2 mixture. The hardness of the WC films depends strongly on the methane or acetylene flow rate, i.e., on the film carbon content. The WC hardness has been correlated to the crystallographic structure. The first hardness maximum peak corresponds to a solid solution of carbon in the tungsten. Correlation between the deposition parameters, such as the gas composition, dc bias and coating properties has been investigated by means of AES, XRD, and nanoindentation analysis.
Diode laser measurements of CFx species in a low-pressure, high-density plasma reactor
Authors: Littau M. E. , Sowa M. J. , Cecchi J. L.
Published: September 2002

We have developed and used an infrared diode laser absorption spectroscopy diagnostic to measure concentrations of fluorocarbon radicals, including CF, CF2, and CF3, during selective oxide etching with a low-pressure, high-density plasma reactor. The fluorocarbon radicals are the precursors for the etch process, as well as for the protective polymer that provides selectivity to the nonoxidized materials. The ability to measure the radical concentrations is important for developing a reproducible oxide etch process. We utilize wavelength modulation to increase the detection sensitivity for operation at the low pressures used in high-density plasma reactors. We use a N2O reference cell to provide wavelength calibration, facilitating identification of the fluorocarbon absorption lines. The N2O cell also provides actinometric calibration, which allows us to compare measurements under different experimental conditions and at different times. We present measurements in an inductively coupled plasma (ICP) etch tool comparing CFx=1–3 concentrations in CFH3:Ar to those in a C2F6:H2:Ar chemistry. We also present measurements of the rotational temperature of CF2, which is an essential parameter for extracting concentration measurements from the diode laser measurements.
X-ray photoelectron spectroscopy study of two nitrogen-containing polymer surfaces metallized by nickel
Authors: Bébin Philippe , Prud’homme Robert E.
Published: September 2002

The metallization of polyacrylonitrile (PAN), poly(styrene-co-acrylonitrile) (SAN) and polystyrene (PS) by nickel has been investigated by x-ray photoelectron spectroscopy. Even if there is no significant loss of chemical elements during the metallization process, surface degradation is systematically seen by the presence of amorphous carbon at the interfaces. Nickel oxidation is detected by the presence of metal nitride (with PAN and SAN) and its concentration is directly proportional to the initial nitrogen concentration in the substrates. The analysis of metallized polymer surfaces exposed to air indicates that the changes induced at the surface of the polymer by the nickel condensation are irreversible and suggests the presence of a real metal nitride at the interface. The behavior of SAN under metallization is the sum of the behavior of PS and PAN; this copolymer can merely be represented as a mixture of styrene and acrylonitrile repeat units with no particular effect due to their distribution in the macromolecular chain.
Performance characteristics of single-stage disk-type drag pump
Authors: Heo Joong-Sik , Hwang Young-Kyu
Published: September 2002

The direct simulation Monte Carlo (DSMC) method is applied to investigate steady and unsteady flow fields of a single-stage disk-type drag pump. Two different kinds of pumps are considered: the first one is a rotor–rotor combination, and the second one is a rotor–stator combination. Each of rotor and stator has 10 Archimedes’ spiral blades, respectively. In the present DSMC method, the variable hard sphere molecular model with the no time counter technique is employed to simulate the molecular collision kinetics. For simulation of diatomic gas flows, the Borgnakke–Larsen phenomenological model is adopted to redistribute the translational and internal energies. Some experimental works are carried out to verify the numerical results. Good agreement between the numerical results and the experimental data is shown.
Structure and properties of carbon nitride thin films synthesized by nitrogen-ion-beam-assisted pulsed laser ablation
Authors: Chen Z. Y. , Zhao J. P. , Yano T. , Shinozaki T. , Ooie T.
Published: September 2002

Carbon nitride films were deposited by pulsed KrF excimer laser ablation of graphite with assistance of low energy nitrogen-ion-beam bombardment. The nitrogen to carbon ratio, bonding state, microstructure, and surface morphology of the deposited carbon nitride films were characterized by x-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FTIR) spectroscopy, micro-Raman spectroscopy, and atomic force microscopy, respectively. The irradiation effect of the nitrogen ion beam with various ion currents on the synthesis of carbon nitride films was investigated. XPS and FTIR analyses indicate that the bonding state between carbon and nitrogen in the deposited films is influenced by nitrogen irradiation with different ion currents during deposition. The carbon–nitrogen bonding of C–N and C=N is observed in the films. High nitrogen ion current is proposed to promote the desired N–sp3C bonds, i.e., the C3N4 phase. In addition, tribological properties of the carbon nitride films deposited on TiN coated stainless steel substrates were also studied in both dry and oil environments, which exhibits a low friction coefficient compared with hard TiN film.
Structural study on (CH3)2S/Cu(100) by near edge x-ray absorption fine structure and x-ray photoelectron spectroscopy
Authors: Yagi S. , Nakano Y. , Ikenaga E. , Sardar S. A. , Syed J. A. , Soda K. , Hashimoto E. , Tanaka K. , Taniguchi M.
Published: September 2002

We have investigated the (CH3)2S/Cu(100) system using polarization dependent S K-edge near edge x-ray absorption fine structure (NEXAFS) and x-ray photoelectron spectroscopy (XPS) for both S 1s and C 1s electrons. From the XPS results, the (CH3)2S molecule is found to adsorb through the sulfur atom on the Cu(100) surface. There is a little polarization dependence in the S K-edge NEXAFS spectra for submonolayer phase. The orientation angle of the molecular plane is estimated to be 33° from the surface.
Recommended practices for measuring and reporting outgassing data
Authors: Redhead P. A.
Published: September 2002

This document recommends a set of uniform procedures for the reporting of outgassing data. Its intention is to establish a consistent set of units, nomenclature, methods of data presentation, and certain experimental parameters in order that outgassing data from different sources is consistently reported so as to be useful to all. This document was prepared by a subcommittee of the Recommend Practices Committee of the American Vacuum Society and is an updating of a previous Recommended Practice published in 1965.
Effects of bridge pattern on performance of YBaCuO microbolometers
Authors: Laou P. , Phong L. Ngo
Published: September 2002

The effects of bridge pattern on the performance of YBaCuO microbolometers were investigated. For this purpose, Si3N4 bridges with grids and hinges of varying width were created on Si wafers by means of bulk Si micromachining. Semiconducting YBaCuO films were sputter-deposited onto the bridges to form resistive bolometers. In reducing the width of the hinges from 10 to 5 μm, one can enhance the bolometric responsivity by approximately two times at room temperature. Further, a factor of enhancement of as large as three could be achieved on bridges with a grid pattern. The grid pattern also modified the spectral absorbance of the bridges. The enhancement of experimental responsivity was shown to be consistent with the one predicted from changes in thermal conductance, electrical resistance, and optical absorbance of the bolometers.
Helium permeation througha-C:H films deposited on polymeric substrates
Authors: Valentini L. , Bellachioma M. C. , Lozzi L. , Santucci S. , Kenny J. M.
Published: September 2002

The influence of amorphous hydrogenated carbon a-C:H coatings on gas permeation through polymer films was investigated. Hydrogenated amorphous carbon (a-C:H) films were deposited, at room temperature, from a CH4/Ar plasma produced by a radio frequency glow discharge system at 13.56 MHz. Polyether–etherketone (PEEK) and polyetherimide foils with different thicknesses were used as substrates. The permeation of He was measured and the reduction of the permeability coefficient is correlated here to the composition and density of the a-C:H films. The density and film structure of the layers were analyzed using x-ray reflectivity and Raman spectroscopy of films deposited onto silicon reference samples. A less pronounced reduction of the permeability coefficients for hard, dense diamond-like layers is reported with respect to those obtained for soft, polymer-like layers on PEEK substrates. Surprisingly, the barrier efficacy of the coating decreases with an increase in a-C:H film density. This unexpected result is attributed to intrinsic stress and the corresponding formation of microcracks. The effect of nitrogen incorporation, which reduces film permeability, is investigated in terms of the stress relaxation mechanism promoted.
Secondary ion mass spectrometry induced damage adjacent to analysis craters in silicon
Authors: Clark M. H. , Jones K. S. , Stevie F. A.
Published: September 2002

Damage introduced by dynamic secondary ion mass spectrometry (SIMS) depth profiling is studied. A silicon sample with a boron marker layer was depth profiled by dynamic SIMS. After subsequent annealing at 750 °C for 30 min, the SIMS sample was reanalyzed by plan-view transmission electron microscope (PTEM) and SIMS. PTEM images showed the presence of interstitial defects near the original SIMS crater, and SIMS depth profiles of similar regions exhibited boron diffusivity enhancements. Excess interstitials were introduced into the Si surface up to 2 mm from the original 225 μm×225 μm crater. Both PTEM and SIMS results showed that the damage and its effects diminished with an increase in distance from the original crater.
Abnormal room-temperature oxidation of silicon in the presence of copper
Authors: Hinode Kenji , Takeda Ken’ichi , Kondo Seiichi
Published: September 2002

The room-temperature reaction between copper (Cu) and silicon (Si) was investigated. The areas of an Si substrate covered with very thin or island-like Cu oxidized formed thick (>100 nm) oxide (SiO2). The areas covered with thick and nonisland-like Cu film did not. These unoxidized areas transformed into SiO2 when the side surfaces of the sample were exposed to air after sectioning for transmission electron microscope observation. The supply of oxygen was found to control this oxidation process. The presence of a Cu silicide, such as Cu3Si, was found to not necessarily be needed for oxidation. The oxidation rate estimated from observation was about 150 nm/month. Copper atoms were detected at the SiO2/Si interface and identified not as silicides but as body-center-cubic-structured Cu several atom layers thick.
Reactivity of Cu with poly(tetrafluoroethylene) and poly(vinyl chloride): Effect of pre- and post-metallization modification on the metal/polymer interface
Authors: Perry C. C. , Torres J. , Carlo S. R. , Fairbrother D. Howard
Published: September 2002

The reactivity of Cu with poly(tetrafluoroethylene) (PTFE) and poly(vinylchloride) (PVC) during thermal evaporation, as well as the effect of pre- and post-metallization Ar+ ion and x-ray mediated surface modification treatments on the metal/polymer interface, have been studied using in situ x-ray photoelectron spectroscopy (XPS) and ex situ atomic force microscopy (AFM). During thermal evaporation, copper was unreactive on PTFE but reacted with PVC to form CuCl. Pretreatment of PTFE or PVC surfaces by Ar+ ion or x-ray irradiation did not modify the chemical reactivity of the polymer surface during subsequent Cu deposition, although significant morphological changes were observed on PTFE by AFM. In contrast, post-metallization modification of the Cu/PTFE interface by Ar+ ion or x-ray irradiation lead to the production of CuF2, and increased the yield of CuCl in the Cu/PVC system. In either the Cu/PTFE or Cu/PVC systems, the maximum concentration of copper halide formed and dependence upon treatment time was found to be similar for either Ar+ ion or x-ray irradiation post-metallization treatment strategies, suggesting a common reaction mechanism.
Microstructure, chemistry, and tribological performance of MoSx/WSey co-sputtered composites
Authors: Savan A. , Haefke H. , Simmonds M. C. , Constable C. P.
Published: September 2002

Co-sputtered thin films have been deposited from MoS2 and WSe2 targets in order to investigate the relationships between tribological behavior and film microstructure. The stoichiometries of pure films for the sputtering conditions used, were found to be MoS1.6 and WSe1.5 as measured by wavelength dispersive x-ray analysis. The mechanical properties of the composite films were investigated by pin-on-disk wear testing in 50% relative humidity air as a function of WSe2 concentration. X-ray diffraction measurements indicate that the microstructure is strongly affected by the inclusion of WSe2 and there is a strong correlation between microstructure and tribological performance. X-ray and Raman measurements indicate a large increase in the c axis of the MoS2, which may be due to intercalation. X-ray photoelectron spectroscopy measurements show no evidence that either Se or W chemically substitutes into the MoS2 structure.
Chemical structure of ultrathin SiO2 film with nitrogen incorporated by remote nitrogen plasma
Authors: Cho M.-H. , Roh Y. S. , Whang C. N. , Jeong K. , Ko D.-H. , Yoo J. Y. , Lee N. I. , Fujihara K.
Published: September 2002

The nitrided ultrathin SiO2 films using a remote nitrogen plasma source were investigated by high-resolution x-ray photoelectron spectroscopy. At the low nitridation temperature of 500 °C, the nitrogen is effectively incorporated in 15 Å SiO2 film. The chemical shifts of the N 1s peaks show that the quantity of the second-nearest neighbors of oxygen atoms and N–O bonds influences the difference of the peak shift depending on the nitridation temperature and post-annealing in ultrahigh vacuum. The peak intensity changes of the N 1s peak at the different take-off angles indicate that the nitridation dominantly occurs at the interfacial region as the nitridation temperature increases, which suggests that the highly incorporated nitrogen at the surface region can be accomplished even with a low temperature nitridation process using a remote nitrogen plasma source. The defect formation due to the nitrogen incorporation resulted in a negative shift of the capacitance–voltage curve, and the difference is increased as the nitridation temperature is elevated.
High-rate deposition of a-SiNx:H for photovoltaic applications by the expanding thermal plasma
Authors: Kessels W. M. M. , Hong J. , van Assche F. J. H. , Moschner J. D. , Lauinger T. , Soppe W. J. , Weeber A. W. , Schram D. C. , van de Sanden M. C. M.
Published: September 2002

Driven by the need for improvement of the economical competitiveness of photovoltaic energy, the feasibility of high-rate (>1 nm/s) amorphous silicon nitride (a-SiNx:H) deposited by the expanding thermal plasma (ETP) technique has been explored with respect to the application of the a-SiNx:H as functional antireflection coating on crystalline silicon solar cells. First, the deposition rate and the a-SiNx:H film properties, such as refractive index, Si, N, and H atomic density, and hydrogen bonding configurations, have been mapped for various operating conditions. From ellipsometry, elastic recoil detection, and infrared spectroscopy, it has been shown that deposition rates up to 20 nm/s can be reached with a fair film homogeneity and that the refractive index and the N/Si ratio can fully be tuned by the plasma composition while the hydrogen content can be controlled by the substrate temperature. Good antireflection coating performance of the a-SiNx:H has therefore been observed for monocrystalline silicon solar cells. These cells with ETP a-SiNx:H yielded only slightly lower conversion efficiencies than high-quality reference cells due to a much lower degree of surface passivation. This lack of surface passivation has also been shown in a separate study on the surface recombination velocity. Furthermore, it has been tested whether the a-SiNx:H films lead to silicon bulk passivation, which is essential for solar cells based on cheaper, defective silicon stock material such as multicrystalline silicon. It has been proven that bulk passivation of the cells is indeed induced by the high-rate ETP deposited a-SiNx:H after a high-temperature step in which the metal contacts of the cells are processed. These results make the ETP technique an interesting candidate for high-throughput processing of competitive silicon solar cells.
Reactive sputter deposition of tungsten nitride thin films
Authors: Baker Colin C. , Shah S. Ismat
Published: September 2002

Tungsten nitride (WNx) thin films were deposited by reactively sputtering a pure W target in an argon/nitrogen atmosphere. The nitrogen concentration in the growth chamber was varied from 2% to 60%. Film growth and properties were studied as a function of nitrogen concentration in the films. The cathode current and voltage variations during the film growth indicated cathode poisoning when the nitrogen concentration in the chamber was in the range of 2%–5%. This poisoning was accompanied by a reduced film growth rate. However, both the cathode current and deposition rate decrease were small due to the low resistivity and similar sputter yield of the WNx phase formed at the surface of the target and pure W. X-ray photoelectron spectroscopy analyses showed that the films were composed of ∼33 at. % nitrogen when the nitrogen concentration in the chamber was greater than 10%. X-ray diffraction (XRD) analysis confirmed that the films were predominantly W2N with the characteristic (111) peak at 2θ=37.7°. Slight shifts in the (111) peak position were due to excess nitrogen incorporation in interstitial positions, which caused lattice distortions. Postdeposition annealing removed the excess interstitial nitrogen and the XRD peaks shifted closer to the characteristic value.
Plasma enhanced atomic layer deposition of SrTiO3 thin films with Sr(tmhd)2 and Ti(i-OPr)4
Authors: Lee J. H. , Cho Y. J. , Min Y. S. , Kim D. , Rhee S. W.
Published: September 2002

SrTiO 3 (STO) thin films were deposited in the deposition temperature range of 250–350 °C by plasma enhanced atomic layer deposition (PEALD) with Sr(tmhd)2 (tmhd=tetramethyl heptanedionate) and Ti(i-OPr)4 (i-OPr=iso-propoxide) as a precursor. Two precursors were dissolved in tetrahydrofuran, delivered into the vaporizer separately by a newly developed pulse injection method, and the vapor mixture was introduced into the reactor. An argon purge was inserted after the precursor injection and afterward, plasma was generated with the oxygen introduction. Deposition rate was saturated at 0.3–0.4 Å/cycle. Despite the poor volatility of Sr(tmhd)2, SrTiO3 thin films were reproducibly deposited and using plasma activated O2 gas as an oxidant, films could be deposited at low temperature with carbon residue of STO thin films minimized. Step coverage of both SrO and SrTiO3 were above 90% due to the self-limiting growth behavior of atomic layer deposition process.
Temperature dependence of oxide decomposition on titanium surfaces in ultrahigh vacuum
Authors: Mizuno Y. , King F. K. , Yamauchi Y. , Homma T. , Tanaka A. , Takakuwa Y. , Momose T.
Published: September 2002

It is well known that the surface of titanium forms stable oxides of Ti2O, TiO, Ti2O3, Ti3O5, TinO2n−1 (4<n<38) and TiO2 and, as a result, the surface exhibits a high degree of immunity against attack by acids and chlorides. However, titanium is also a very active getter. To characterize the gettering process, we have investigated the temperature dependence of stable oxides on titanium in ultrahigh vacuum (UHV) using Auger electron spectroscopy, quadrupole mass spectrometry (QMS), and x-ray photoelectron spectroscopy (XPS) in the temperature range from room temperature (RT) to 600 °C. The surfaces of titanium specimens were prepared by electropolishing (EP), and a thin titanium oxide layer, principally TiO2, was formed on the surface at RT. On increasing the temperature to above 300 °C, the OKLL Auger intensity began to decrease in a drastic way, while in contrast, the TiLMM Auger intensity was increased. Above 450 °C, no oxygen was detected on the titanium surface in UHV. However, the outgassing rates of H2O, O2, CO, and CO2 from the surface did not show any changes in QMS measurements below 450 °C. This behavior is explained as gettering, which is an enhancement of diffusion of oxygen from the surface into the bulk. To investigate the temperature dependence of the chemical states of titanium oxides on an EP surface, XPS analysis was also performed in the same way in the range of 200–450 °C. The results showed drastic changes of the titanium oxide core XPS levels such that the TiO2 decomposed into suboxides at 180 °C, and even the remaining TiO2 was still decreasing on heating up to 420 °C. The surface oxide composition on titanium is very sensitive to the temperature.
Tribological behavior of alumina doped zinc oxide films grown by pulsed laser deposition
Authors: Prasad S. V. , Nainaparampil J. J. , Zabinski J. S.
Published: September 2002

Zinc oxide, a well-known piezoelectric material, has become the subject of tribological investigations. This research describes the synthesis and tribological evaluation of alumina doped zinc oxide [ZnO(Al2O3]) films grown in vacuum by a pulsed laser deposition (PLD) technique using hot pressed ZnO–5 wt % Al2O3 targets. For comparison, pure ZnO films were grown under identical PLD conditions. The films were characterized by scanning electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction, and x-ray photoelectron spectroscopy. Friction measurements were made using a ball-on-disk tribometer. Nanotribological studies were conducted on wear scars of ZnO and ZnO(Al2O3) films by atomic and lateral force microscopy. Both ZnO and ZnO(Al2O3) films were crystalline, with a strong (002) texture. The friction coefficient of the ZnO(Al2O3) film (μ=0.15) was considerably less than that of the pure ZnO film (μ=0.34). Wear scars on doped ZnO films were relatively smooth and, unlike in the case of pure ZnO films, no cracks were observed. Lateral force microscopy images of wear scars on ZnO(Al2O3) films showed dark contrast regions indicating the presence of a slippery phase. No such phase contrast was observed in the case of pure PLD ZnO film grown in vacuum.
Advantages of laser-acoustical leak testing for construction and operation of low-temperature installations and superconducting experiments
Authors: Herz W.
Published: September 2002

At the Institute of Technical Physics of the Research Center Karlsruhe, superconducting magnets for nuclear fusion applications have been tested in the vacuum tank TOSKA for more than 20 years. A crucial test parameter of the magnet coils (mass up to 120 metric tons) as well as of the peripheral components, such as current leads (up to 80 kA), helium refrigerators (2 kW), and low-temperature transfer lines (length ∼200 m), is their vacuum tightness at operating conditions (minimum temperature ∼2 K, maximum refrigerant pressure 25 bar). Because the final tests at cryotemperature are costly and time consuming, intermediate tests at room temperature have already been performed at the stages of manufacturing, certification, and assembling, and prior to cooldown. So far, these tightness tests have been performed with probe gas helium employing a conventional mass spectrometer leak detector, whereby the smallest detectable leakage is limited by the He partial pressure in the surrounding air. Therefore, a new technique of leak measurement was investigated using the probe gas sulfur hexafluoride SF6, which does not occur in natural air, and which can be sensitively detected by a laser-acoustical leak detector. The obtained experimental results reveal the substantial advantages of the new method with respect to detection sensitivity, testing expenditure, and costs. The results can be transferred to tightness tests in other fields of technology.