bluuebunny/crossref_metadata_2025 huggingface dataset:
Topics in vacuum system gas flow applications
Authors: Santeler Donald J.
Published: July 2002

Evacuation to high vacuum utilizes gas flow in the choked, laminar, transition, and free molecular flow ranges. Understanding the gas flow equations applicable in these different ranges frequently explains the physical phenomena which are occurring as evidenced by the following situations. Contaminants are removed from systems and mechanical-pump oil backstreaming is eliminated by using forced gas flow operation in the laminar viscous flow range. The mean free path dependency on pressure explains the independent behavior of condensible gases flowing from the system to a liquid nitrogen trap while pump-generated permanent gases are flowing backward through the trap to the system. The highly directional gas flow which occurs in space simulation chambers can be combined with good high-vacuum technology to obtain improved processing for applications such as molecular beam epitaxy. The current understanding of gas flow in capillaries demonstrates that the large pressure drop where the leak exits into a high-vacuum system results in most leaks being in the viscous flow range. This compromises our understanding of so-called ‘‘air equivalent leakage’’ as well as suggesting new concepts of leak detection. A more fundamental understanding of gas flow also helps to explain the many problems of long time constants in very small leaks and in situations having two leaks in series such as O-ring seals. Finally, understanding the nature of gas flow identifies the relative benefit of contra flow leak detectors versus conventional flow leak detectors as well as turbomolecular pumps versus oil diffusion pumps in leak detectors.
Plane Poiseuille flow: Rigid sphere gas
Authors: Hickey K. A. , Loyalka S. K.
Published: July 2002

Plane Poiseuille flow of a rarefied gas is a problem of fundamental interest in vacuum science and technology. In this paper, this problem is solved as based on the linearized Boltzmann equation, rigid sphere intermolecular force, and diffuse reflection at the planar surfaces. Explicit results for the flow rate and velocity profile are obtained. The flow rates, as obtained by two independent methods, are in good mutual agreement, and provide a reasonably good description of the available experimental data.
Time dependence of the resistance of sputtered carbon films
Authors: Jensen C. L. , Hoffman R. A.
Published: July 2002

The electrical resistance of carbon films sputtered under high Ar pressure and low bias was observed to increase by as much as 200% when the films were exposed to the atmosphere for a period of several days. Substrate temperature and sputtering power had no effect on the time dependence of the resistance. The time dependence of the resistance appears to be related to the formation of a porous structure when films are sputtered under high Ar pressure and low bias. The increase in resistance noted when sputtered carbon films were exposed to air bears some similarity to aging behavior observed for discontinuous metal films. The initial resistivity of the films was dependent on Ar pressure, bias, substrate temperature and power.
Calculation of thickness distribution for ion beam sputter deposition
Authors: Fujiwara Akio
Published: July 2002

A simple analytical formula for thickness calculation which is especially fitted for the ion beam sputtering (IBS) system is derived. An arbitrary sputtering pattern can be treated in this formulation. This treatment, which greatly reduces the calculation time as compared with conventional ones, enables optimization of the IBS system design.
Annealing of polystyrene microcapsules for inertial confinement fusion experiments
Authors: Kobayashi S. , Norimatsu T. , Nakai M. , Tanaka K. A. , Yamanaka T. , Nakai S. , Ito K.
Published: July 2002

An underwater-annealing technique has been developed to recover the original strength of fragile polystyrene (PS) microcapsules fabricated by an emulsion technique. PS microcapsules are heated up to 120 °C in a pressurized chamber prior to the dehydration process. This is done to recover the strength required for the pressure difference across the shell wall during fuel filling for inertial confinement fusion experiments.
Development of a movable quadrupole mass spectrometer for measuring gas density
Authors: Hiroki S. , Abe T. , Obara K. , Murakami Y.
Published: July 2002

A quadrupole mass spectrometer (QMS) with a specially designed analyzing head which was movable in a dynamic vacuum system was fabricated and the performance was tested. The head comprises a collimator and an airtight casing containing a rf tuning and its detection circuit. The rf circuit is tuned by supplying variable frequency of the rf voltage since the resonance frequency depends weakly on environmental temperature. This QMS can be obtain a normal mass spectrum for a mass range 1–50 amu even when the vessel is baked to 150 °C. The measured pressure rise of Ar is 1.08×10−5 Pa at a distance of 125 mm from the effusing nozzle of argon gas with a flow rate of 1.9×10−5 Pa m3 s−1, which is two times as large as the calculated value.
Fluorine field ion source using fluorine–helium gas mixture
Authors: Ochiai Yukinori , Nomura Eiichi , Kojima Yoshikatsu , Matsui Shinji
Published: July 2002

The ionization of fluorine with a field ion source is demonstrated. A fluorine(10%)–helium(90%) gas mixture and a (110) oriented tungsten emitter are used. The ion source is operated at a pressure of 1.5×10−5 Torr and at temperatures between 7 and 80 K using a (110) plane of the emitter. Two current peaks in the I–V characteristics are observed at temperatures over 46 K and one of them is confirmed to correspond to fluorine ion emission, which shows a maximum at 52 K and has an angular current density of 1.5×10−6 A/sr and a brightness of 6×108 A/cm2  sr. The I–V characteristics’ dependency on the crystal planes of the emitter tip such as (111) and (121) are also presented.
Dual-frequency N2 and NH3 plasma modification of polyethylene and polyimide
Authors: Klemberg-Sapieha J. E. , Küttel O. M. , Martinu L. , Wertheimer M. R.
Published: July 2002

Surfaces of polyethylene and polyimide films were treated in NH3 and N2 plasma using ‘‘dual-frequency’’ excitation: The samples were exposed to a microwave (2.45 GHz) glow discharge, while variable radio frequency (13.56 MHz)—induced negative direct current bias voltage values were simultaneously applied. The surface chemical structure was determined by high-resolution x-ray photoelectron spectroscopy. Up to 40 at. % of nitrogen was incorporated onto the sample surface by exposure to a microwave discharge in N2, while systematically lower N uptake was found in NH3 plasma. Nitrogen was found to be bonded predominantly in amine (C–N) groups by NH3 -type plasma, and in imine groups (C=N) by N2 plasma. Surface ‘‘damage’’ of polyimide, including opening of benzene rings and breaking of carbonyl groups, accompanied by the formation of increasing concentrations of chemically reactive receptor sites, has been demonstrated with increasing the energy of bombarding species.
Optimization studies on magnetic field geometry for planar magnetron sputtering targets
Authors: Rao G. Mohan , Mohan S.
Published: July 2002

The present study deals with the design aspects of planar magnetron sputtering targets. A permanent ring magnet with modified pole piece geometry has been used for maximum ionization efficiency. The efficiency of electron containment on the target surface has been evaluated in terms of current at the electrically isolated substrates. The details of the relation between the magnetic field strength and field geometry on the ionization currents and operating pressure have been discussed. The best among the designs studied, when operated at a pressure of 8×10−3 Torr resulted in a deposition rate of about 2000 Å/min at a current density of 4 mA/cm2. The substrate temperature rise was about 20 °C under these conditions. The design details of the magnetrons, experimentation for evaluating the electron containment have been discussed in this article.
Error reduction in monodirectional ion milling
Authors: Carter G. , Nobes M. J. , Katardjiev I. V.
Published: July 2002

When ion milling is employed to change the contours of large area surfaces it is often assumed that the sputtering rate is directly proportional to the sputtering yield for normal ion incidence on to a plane surface. It is shown how this zero order approximation can lead to errors in expected contours and higher order approximations are analyzed to indicate how errors can be reduced by improved choice of sputtering parameters. The behavior of static, broad beam, and dynamic, swept focused beam systems are discussed.
Absence of molecular deuterium dissociation during room-temperature permeation into polystyrene inertially confined fusion target shells
Authors: Honig A. , Alexander N. , Fan Q. , Gram R. Q. , Kim H.
Published: July 2002

Polystyrene microshells filled with deuterium and tritium gas are important target shells for inertially confined fusion (ICF) and are particularly promising for targets containing spin–polarized hydrogens fuels. A currently active approach to the latter uses polarized D in HD, in a method which requires preservation of the high purity of the initially prepared HD (very low specified H2 and D2 concentrations). This would not be possible if dissociation should occur during permeation into the target shells. We have thus tested polystyrene shells using a novel method which employs very pure ortho-D2 as the test gas. An upper limit of 6×10−4 was deduced for the dissociation probability of D2 upon room temperature permeation through an approximately 8 μm wall of polystyrene, clearing the way for use of polystyrene target shells for ICF fusion experiments with spin–polarized hydrogen–isotope fuels.
Leak calibration by the ΔPΔV and pressure difference techniques
Authors: Basford James A.
Published: July 2002

Two techniques for calibrating leaks, one primary and one secondary, are described. The ΔPΔV method, a primary technique, is a modification of the PΔV technique which requires less time, has smaller outgassing error, and allows simultaneous, automated calibrations of several leaks in the range 10−8–10−12 mol s−1. The pressure difference method is a comparison technique in which a mass spectrometer is used to compare the partial pressure of gas collected from the leak being calibrated to a known partial pressure generated by a constant flow. It is useful for calibrations in the 10−12–10−15 mol s−1 range. Both methods have been incorporated in an automated apparatus.
The mechanical properties and microstructure of plasma enhanced chemical vapor deposited silicon nitride thin films
Authors: Taylor J. Ashley
Published: July 2002

Plasma enhanced chemical vapor deposited silicon nitride thin films, possessing a wide range of mechanical and physical properties, were made by changing the flow rate ratios of the various processing gases, NH3/SiH4/N2, while basically keeping the other deposition parameters constant. A set of films with N/Si ratios of 1.0 to 1.5 were produced, all showing compressive stress. The intrinsic compressive stress was found to increase with increasing amounts of N–H bonding. The density and Young’s modulus also increased with increasing amounts of N–H bonding. The values for Young’s modulus, obtained by using a Nano indenter instrument, were mainly dependent upon the film density, and the hardness to modulus ratio was 0.09 for all of the silicon nitride thin films.
Intrinsic stress in sputtered thin films
Authors: Windischmann H.
Published: July 2002

A review of the literature reveals that the intrinsic stress in sputtered thin films can be tensile or compressive depending on the flux and energy of particles striking the film. Stress data indicates that the normalized momentum P*n=γ√ME (where γ is the energetic particle/atom flux ratio, M the mass, and E the energy) may be the appropriate stress scaling factor. The forward sputtering model predicts a √E dependence. An idealized stress–momentum curve is constructed consisting of three regimes:(1) a region of increasing tensile stress at low P*n, due to a porous microstructure, followed by (2) a sharp transition from tensile to compressive stress at intermediate momentum, accompanied by a conversion to zone T-type microstructure and (3) a saturation region at high momentum, due to plastic flow. For any deposition process the sign and magnitude of the stress depends on P*n, which is a function of several deposition parameters. Calculations indicate that stress reversal in sputtered and ion-assisted evaporated films occurs at normalized momentum P*n of about 5–15×10−23 kg m/s/atom (Pn=0.3–1 √eV/atom).
A fuel pellet injector for the microwave tokamak experiment
Authors: Hibbs S. M. , Allen S. L. , Petersen D. E. , Sewall N. R.
Published: July 2002

Unlike other fueling systems for magnetically confined fusion plasmas, a pellet injector can efficiently deliver fuel gas to the plasma core, enhancing plasma confinement. We installed a new pellet injector on the microwave tokamak experiment (MTX, formerly Alcator-C) to provide a plasma with a high core density for experiments both with and without ultrahigh-power microwave heating. Its four-barrel pellet generator is the first to be designed and built at Lawrence Livermore National Laboratory. Based on ‘‘pipe-gun’’ technology developed at Oak Ridge National Laboratory, it incorporates our structural and thermal engineering innovations and a unique control system. The pellet guide section, differential vacuum-pumping stages, and fast-opening propellant valves are reused parts of the Impurity Study Experiment (ISX) pellet injector built by ORNL. We tailored designs of all other systems and components to the MTX. Our injector launches pellets of frozen hydrogen or deuterium into the MTX, either singly or in timed bursts of up to four pellets at velocities of up to 1 000 m/s. Pellet diameters at formation range from 1.02 to 2.08 mm. A diagnostic stage measures pellet velocities and allows us to photograph the pellets’ flight. We are striving to improve the injector’s performance, but its operation is already very consistent and reliable.
Low temperature processing and characterization of metastable anisotype heterojunction-gate strained-layer field-effect transistors
Authors: Lin C. L. , Wieder H. H.
Published: July 2002

A low-temperature, self-aligned processing technology, without source/drain ion implantation and rapid thermal annealing, for strained layer, metastable structures is presented. A peak transconductance of 216 mS/mm is obtained for a 2 μm gate length device. Improved device-to-device uniformity and reproducibility, compared to a high-temperature process, is obtained. Device modeling using the hyperbolic tangent model with only two adjustable parameters shows very good agreement with experimental data.
Sputter-induced changes in permalloy target microstructure
Authors: Chaug Yi-Shung , Williamson D. L.
Published: July 2002

Permalloy films were deposited with an S-gun magnetron rf sputtering unit and permalloy targets. The crystallographic textures of the targets at the beginning and at the end of their lives were determined by x-ray diffraction measurements. Sputter-induced changes in target crystal texture and x-ray linewidths were observed. Mössbauer effect spectra indicated a marked magnetic texture rotation resulting from the magnetron sputtering. Changes in the target microstructure caused by magnetron sputtering were target dependent. These changes were correlated with observed drifts in the deposited permalloy film magnetostriction through target life.
How is the fractal dimension of a thin film top surface connected with the roughness parameters and anisotropy of this surface?
Authors: Varnier F. , Llebaria A. , Rasigni G.
Published: July 2002

It was previously shown how the fractal dimension of thin films top surfaces can be obtained from the surface relief reconstructed by microdensitometer analysis of an electron micrograph of a shadowed replica of the surface. Here is presented a comparative study of roughness, fractal dimension and anisotropy of thin films top surfaces. After a theoretical study devoted to some regular and more or less isotropic surfaces, results are given for several real surfaces and it is shown how the characterization of a rough surface by its fractal dimension yields results about its roughness and anisotropy.
Structural and magnetic properties of ion beam sputtered deposited Cu/Fe multilayers
Authors: Qadri S. B. , Kim C. , Kim K. H. , Lubitz P. , Twigg M.
Published: July 2002

Fe/Cu multilayers have been deposited using the ion assisted/ion beam sputtering technique. X-ray diffraction and selected area transmission electron diffraction show that Fe is in the body-centered-cobic phase. These results were in agreement with extended x-ray absorption fine structure measured at the Fe K edge using synchrotron radiation. Magnetic measurements using vibrating sample magnetometer and ferromagnetic resonance show nominal moment of the Fe, but moderate out of plane anisotropy.
Remarks on the use of photoelectron spectroscopy in high temperature superconductors
Authors: Dayan Moshe
Published: July 2002

It is shown that photoelectron spectroscopy results on high temperature superconductors should not be interpreted in terms of direct characterization of quasiparticles, as has generally been attempted. This limitation, which is due to the secondary electrons produced by inelastic scatterings, exists in angular intergrated and angular resolved experiments. It amounts to an asymmetric broadening of inherent peaks, which occurs even just below the Fermi level. This broadening has been observed in various measurements, including the high energy resolution measurements which have resolved the superconductive gap structure.
Detection of aluminum particles during the chemical vapor deposition of aluminum films using tertiaryamine complexes of alane (AlH3)
Authors: Simmonds Michael G. , Gladfelter Wayne L. , Rao Nagaraja , Szymanski Wladyslaw W. , Ahn Kang-ho , McMurry Peter H.
Published: July 2002

Two methods of analyzing particles were interfaced to a low pressure chemical vapor deposition (CVD) reactor to evaluate whether or not particles were formed in the gas phase during the growth of aluminum films using tertiaryamine complexes of alane. A laser light scattering particle counter was used to detect large (>200 nm) particles in real time and established that the appearance of particles corresponded to the flow of precursor into the CVD reactor. A particle impaction system was used to collect particles (>20 nm) for analysis using analytical electron microscopy and electron diffraction. This established that the particles were crystalline aluminum and that the particle sizes ranged from 20–700 nm. The median size was 85 nm.
Experimental studies of inhomogeneous coatings for optical applications
Authors: Ouellette M. F. , Lang R. V. , Yan K. L. , Bertram R. W. , Owles R. S. , Vincent D.
Published: July 2002

A novel codeposition process has been developed for the fabrication of inhomogeneous optical coatings. These single-layer coatings exhibit composition and refractive index that vary continuously with thickness. Two types of inhomogeneous optical filters for antireflection and narrow band rejection applications, respectively, were experimentally fabricated using different vacuum deposition processes. The antireflection coating, composed of ZrO2 and MgF2, was prepared by electron beam coevaporation. The narrow band rejection filter, made up of SiO2 and TiO2, was codeposited by ion assisted, dual ion beam sputtering technique. The physical, chemical, and microstructural characteristics, as well as optical and environmental properties of these filters were evaluated.
Quantitative surface analysis: Agreeing initial data processing
Authors: Seah M. P.
Published: July 2002

The concept of agreement, its related policy and traceability in quantitative surface analysis are briefly reviewed. Current work from National Physical Laboratory (NPL) is then reviewed to enable laboratories to obtain Auger electron and x-ray photoelectron spectra which agree numerically from laboratory to laboratory and which are then traceable to national standards. This work provides the primary calibration to ensure that the source data are of sufficient validity to enable the use of universal data processing methods, central data banks, and theoretical functions for analysis. The calibrations for Auger electron spectroscopy (AES) and, very recently, for X-ray photoelectron spectroscopy (XPS) indicate, providing certain rules of good instrument operation are followed, that accuracies of 2% to 3% may be obtained for absolute spectral measurements. This opens the way for unifying future general work in these two techniques.
Quantitative microanalysis of oxygen in zirconium by Auger electron spectroscopy
Authors: Betteridge J. S. , Hocking W. H. , Hayward P. J.
Published: July 2002

Calibration curves for quantitative microanalysis of oxygen in zirconium by Auger electron spectroscopy have been derived from studies of well-characterized standards using a PHI 590A SAM. Knowledge of the intensity-energy response function of this instrument assures long-term reproducibility and may permit transfer of the results. Auger electron spectra were recorded in the pulse-counting mode from surfaces that had been thoroughly cleaned by argon-ion sputter etching and therefore incorporate any preferential sputtering effects. Surface recontamination by reactive constituents of the residual gas was determined to be unimportant for short analysis times in clean ultrahigh vacuum. Electron-stimulated desorption of oxygen was found to be significant at high incident electron-beam current densities and was accounted for empirically. Linear calibration curves were obtained using O and Zr peak areas measured above simple tangent backgrounds.
Photoelectron microscopy in the life sciences: Imaging neuron networks
Authors: Mercanti Delio , De Stasio Gelsomina , Ciotti M. Teresa , Capasso C. , Ng W. , Ray-Chaudhuri A. K. , Liang S. H. , Cole R. K. , Guo Z. Y. , Wallace J. , Margaritondo G. , Cerrina F. , Underwood J. , Perera R. , Kortright J.
Published: July 2002

Photoemission techniques like electron spectroscopy for chemical analysis are the leading electronic probes in materials science—but their impact in the life sciences has been minimal. A critical problem is that the lateral resolution in ordinary photoemission does not exceed a few tenths of a millimeter. This space-averaged probe is nearly useless for most of the fundamental problems in biophysics and biochemistry, which deal with microstructures in the submicron range or smaller. This limit is being overcome with photoemission microscopes, such as our scanning instrument maximum. The first scanning photoelectron micrographs of a cellular system with submicron resolution are presented. Minute details of neuron networks are imaged on maximum, thereby opening the way to novel applications of photoemission in the life sciences. The details include individual neurons, axons, dendrites, and synapses, and composite large-area scanning micrographs were routinely produced with a lateral resolution of 0.5 μm.
Effects of sulfur on vapor and liquid H2O adsorption on stainless steel
Authors: Baer D. R. , Lannutti S. M.
Published: July 2002

This paper reports a study of the influence of surface S on the adsorption of water vapor and liquid on an 18% Cr, 8% Ni austenitic stainless steel at room temperature. X-ray photoelectron spectroscopy measurements of the increase of O as a function of water exposure indicate that S inhibits water vapor uptake in direct relation to the amount of S on the surface, up to coverages ≊0.8 monolayer. Higher S coverages did not further inhibit water uptake. In contrast, one monolayer of S on the surface did not significantly alter the thickness or composition of films formed in pure liquid water at 25 °C. Exposure of the S-dosed steel to H2 O water vapor or liquid produced no observable change in the S 2p photopeak.
Temperature optimization in an azimuthally symmetric single-wafer chemical vapor deposition reactor: The low pressure regime
Authors: Kotecki David E. , Barbee Steven G.
Published: July 2002

A finite element model of an azimuthally symmetric single-wafer chemical vapor deposition reactor is combined with experimental design theory to determine the influence of process and design conditions on the temperature distributions within the reactor. In such a reactor, it has been found that temperature nonuniformities as great as 15% can occur at the wafer surface and in the gas phase above the wafer. A two-level Taguchi L16 experimental design matrix is used to evaluate the effect of five reactor design parameters and three process parameters on the temperature distributions. The reactor is operated in the ‘‘low pressure regime,’’ where heat transport between the susceptor and the wafer is by radiation only and heat transport by conduction, convection, and radiation are considered elsewhere in the reactor. Results of the analysis indicate that the susceptor radius and temperature are the dominant parameters controlling within wafer and gas phase temperature uniformity, while the thermal conductivity of the gas strongly effects the radial temperature gradients in the wafer.
Role of ion energy in ion beam oxidation of semiconductors: Experimental study and model
Authors: Vancauwenberghe O. , Herbots N. , Hellman O. C.
Published: July 2002

Ion beam oxidation (IBO) is a low temperature growth technique where a directional low energy (≤1 keV) ion beam introduces the oxygen into the substrate and athermally activates the chemical reaction leading to the oxide growth. In this work, IBO of Si, Ge, Si1−xGex was investigated experimentally as a function of ion energy from 100 eV to 1 keV. The results show a strong dependence of the materials properties such as phase formation, stoichiometry, and thickness upon the ion energy. To investigate the kinetics of IBO and to account for the observed relationship between ion energy and films properties, three models were successively developed taking progressively into account: (1) ion implantation and sputtering (model IS), (2) replacement and relocation events, i.e., ion beam mixing effects (model ISR) and (3) oxygen diffusion (model ISRD). The simulation results show that the model IS based only on implantation and sputtering cannot explain the oxide thickness dependence upon ion energy observed experimentally, but can give qualitative information on the phases formed by IBO. Ion beam mixing effects in the model ISR lead to spatial redistribution of the elements in compound targets and account for the evolution of stoichiometry as a function of depth. Thermal and point defect mediated diffusion of free oxygen and the strong driving force for oxidation must be considered to account for the observed thicknesses, sharp interfaces and kinetics of IBO growth in three stages.
Take-off angle dependent x-ray photoelectron spectroscopy, secondary ion mass spectrometry, and scanning electron microscopy for determining the thickness and composition of passivation layers on technical aluminum foils
Authors: Gunter P. L. J. , Borg H. J. , Niemantsverdriet J. W. , Rheiter H. J. H.
Published: July 2002

Angle dependent x-ray photoelectron spectroscopy, static secondary ion mass spectrometry, and scanning electron microscopy have been used to investigate the effect of a cleaning procedure on the composition, morphology and thickness of passivation layers on technical aluminum foils. The results show that the cleaner, a solution of sodium carbonate, phosphate and surfactants, not only removes undesirable oil contaminations efficiently, but also etches the surface. Because magnesium-rich inclusions are etched at a faster rate than the surrounding aluminum, the foil acquires roughness on the scale of about 100 nm, whereas at the same time the surface composition changes. In particular, small amounts of phosphate are deposited on the surface. All these factors are considered favorable for improved adhesion.
Possible many-body effects in scanning tunneling microscopy of molecular adsorbates
Authors: Mintmire J. W. , Harrison J. A. , Colton R. J. , White C. T.
Published: July 2002

The imaging of nonconducting adsorbates has been reported for a variety of materials using scanning tunneling microscopy. These results are unexpected because of the low densities of states these adsorbates have near the Fermi level. We discuss how screening effects could couple the adsorbate states with the substrate electronic states in the vicinity of the Fermi surface and enhance the local density of states of the adsorbate states near the Fermi level.
High quality YBCO films grown over large areas by pulsed laser deposition
Authors: Greer J. A.
Published: July 2002

High quality films of YBCO have been grown in situ by pulsed laser deposition (PLD) on small samples as well as both 5 cm (2 in.) and 7.6 cm (3 in.) diam (100) LaAlO3 and 5 cm (100) NdGaO3 substrates. Films grown on small LaAlO3 and NdGaO3 substrates display critical temperatures Tc in excess of 89 K while critical current densities Jc of 5 MA/cm2 at 77 K have been obtained. Films grown on 5 cm diam substrates display Tc’s in excess of 89 K, and Jc’s in excess of 2 MA/cm2 at 77 K. Also, a patterned three-piece strip line resonator (1.56 GHz fundamental frequency) fabricated using samples cut from a 5 cm diam LaAlO3 substrate yielded a microwave surface resistance Rs of 700 μΩ at 77 K when scaled to a frequency of 10 GHz. Substrates were radiatively heated without the use of absorbing layers such as nickel or thermally conductive layers such as silver paint or indium, thus making backside film deposition a clean and simple process. YBCO films grown on the backside of small LaAlO3 substrates (previously coated with 5000 Å of YBCO) display Tc’s ≳88 K with no significant degradation in the front side film properties. Furthermore, recent results of backside PLD of YBCO onto three-inch diameter LaAlO3 substrates have yielded films on both surfaces with Tc’s ≳86 K, and Jc’s ≳2 MA/cm2. The novel features of the large area PLD system will be described, and the uniformity for a number of important electrical and physical film properties will be reported.
Gas–plasma interactions in a filtered cathodic arc
Authors: Puchert M. K. , Davis C. A. , McKenzie D. R. , James B. W.
Published: July 2002

The physical interactions between the metal plasma beam of a filtered cathodic arc and noble gases introduced into the beam path are studied. Langmuir probe measurements show that the ion saturation current increases rapidly and nonlinearly with pressure until a cutoff point, after which there is a general decrease with a reproducible fine structure in the form of subsidiary maxima and minima. For helium, the electron density increases exponentially by two orders of magnitude, as the pressure rises from base pressure. Electron collisions are believed to be the dominant cause of gas ionization. A theory is proposed to explain these measurements which predicts under special conditions an exponential increase in ion density. The fine structure may have its origin in the so called ‘‘ionization instabilities.’’ Gas ion currents of up to 2 A have been measured showing that the cathodic arc may be useful as a source of gas ions for assisting film deposition.
Design and evaluation of a primary high-vacuum standard
Authors: Jitschin W. , Jousten K. , Wandrey D.
Published: July 2002

Calibration pressures in the high- and ultrahigh-vacuum range are conveniently generated by the expansion of gas in a continuous flow. The design and the performance of a new continuous (often called dynamic) expansion standard and a partly computer-controlled flowmeter are reported. Pressures are generated from 10−6 to 10−2 Pa with uncertainties (2σ, linear addition of individual uncertainties) between 1% and 4%. A comparison with a static expansion standard was carried out and showed good conformity between the two standards.
X-ray photoemission study of SF6/O2 triode reactive ion etching of polycrystalline silicon, silicon dioxide, and their interface
Authors: Thomas J. H. , Singh B.
Published: July 2002

Surface and interfacial residue films formed on polycrystalline silicon, silicon dioxide, and the interface between polycrystalline silicon on SiO2 by reactive ion etching with SF6/10%O2 at 100 mTorr have been investigated using x-ray photoemission spectroscopy. Reactive ion etching residue films produced in a simple diode reactor and in a triode reactor operated with the electrodes powered in phase and 180° out of phase were compared. In-phase excitation of the triode produced the lowest etch rate of polycrystalline silicon and SiO2 and the highest selectivity. 180° out-of-phase excitation produced the highest etch rates and lowest selectivity. The diode performed in between the triode configurations. Surface residue film thickness and composition on polycrystalline silicon and SiO2 appear rate dependent. Composition and chemistry at the surface and the interface are variations of Si(OF)x. In the case of SiO2, the high etch rate of the 180° out-of-phase excited triode reactor produced a SiF-like species that may be a percursor to the formation of Si(OF)x. The highest etch rate produces the thinnest surface residue film thickness. At the interface, the 180° out-of-phase excited triode produced the most abrupt interface (<150 Å). The diode and 0° in-phase excited triode produced increasingly large interfacial widths that may be interpreted as etch nonuniformities over a 3×3 mm2 analysis area.
Formation of polyhedral voids at surface cusps during growth of epitaxial TiN/NbN superlattice and alloy films
Authors: Hultman L. , Wallenberg L. R. , Shinn M. , Barnett S. A.
Published: July 2002

Epitaxial TiN/NbN(001) superlattice thin films with periods λ between 0 (alloy) and 9.6 nm have been grown by ultrahigh vacuum reactive magnetron sputter deposition on MgO(001) substrates in mixed Ar/N2 discharges. Cross-sectional transmission electron microscopy was used for characterizing layer and defect structure. Coherency strain relaxation close to the film/substrate interface resulted in nonplanar growth with surface cusps and the creation of apparent column boundaries at which TiN and NbN layers curved towards the substrate, but across which the basic lattice was ordered. Also, a fraction of the boundaries were associated with threading defects along the growth direction. The column boundaries and threading defects were decorated by voids that exhibited an orthorhombohedral shape, were elongated in the growth direction, and typically had flat surfaces on {100} planes. The origin of voids is suggested to be through self-shadowing at surface cusps in combination with limited adatom mobility. The voids subsequently attained equilibrium shape as the result of surface and bulk diffusion. The void density varied with λ and the void length in the growth direction was generally an integer number of periods, indicating that the void formation was influenced by the superlattice layers. The formation of limited voids is suggested to be characteristic of thin film growth close to the epitaxial temperature.
An ultrahigh vacuum, magnetron sputtering system for the growth and analysis of nitride superlattices
Authors: Mirkarimi P. B. , Shinn M. , Barnett S. A.
Published: July 2002

An ultrahigh vacuum, magnetron sputtering system designed for the deposition and in situ analysis of nitride superlattices is described. Superlattices are deposited from two sputter sources aimed at a fixed substrate position. The chamber features a sample insertion load lock, a computer-controlled shutter to modulate the sputtered fluxes, a retarding field analyzer for in situ low energy electron diffraction and Auger electron spectroscopy (AES), and substrate heating to >800 °C. Deposition of epitaxial TiN, VN, NbN, and nitride superlattices is described. Deposition rates decreased, and the film nitrogen content increased until stoichiometry was reached, as the N2 partial pressure was increased. The film thickness and composition were uniform to within 10% over the 1.2 cm wide substrates. AES studies of the initial stages of TiN deposition onto VN(100) indicated a layer-by-layer growth mechanism. Single-crystal TiN/NbN(100) and TiN/V0.6Nb0.4N(100) superlattices were grown and found to have flat, sharp interfaces, and exhibited hardness enhancements in excess of 200% over homogeneous alloys of the same composition.
Mass spectrometric study of tetraethoxysilane and tetraethoxysilane–oxygen plasmas in a diode type radio-frequency reactor
Authors: Charles C. , Garcia P. , Grolleau B. , Turban G.
Published: July 2002

Mass spectrometry of tetraethoxysilane (TEOS) vapor, TEOS, and TEOS–O2 radio-frequency plasmas has been investigated in a diode type plasma reactor. The TEOS vapor spectrum shows eight main heavy ions containing silicon and oxygen in a background of many second order ions. When coupling a pure TEOS plasma (13.56 MHz, 50 W, 150 mTorr) the same ions are observed but with variable abundance. For low m/e range (1–50) the variations show that hydrocarbons and alcohols formation is induced by the discharge. When adding a second reactant like oxygen the TEOS dissociation increases. Four ions in the low m/e range show a sensitive variation in the quadrupole mass spectra (QMS) (CO+,CO+2,COH+,COH+2). This corresponds to the formation of stable volatile compounds containing oxygen (CO,CO2,COH2) in the gas phase and on the surface: the oxidation occurring on the surface is associated with a desorption effect which removes carbon atoms from the growing film on the electrodes and walls. The QMS results are related to Fourier transform infrared (FTIR) results of deposited layers on silicon substrate placed on the grounded electrode: for a pure TEOS plasma or a TEOS–He plasma the undecomposed TEOS molecules recondense on the growing film giving a nonadherent gel-like layer when operating at low substrate temperature; characteristic vibration modes of the TEOS molecules (C–H, C=O, Si–O–C) appear in the FTIR spectrum. The intensity of the corresponding peaks decreases to zero when gradually introducing oxygen: the increase of the TEOS dissociation limits the TEOS recondensation on the film; a correlation is established between the surface oxidation and CO, CO2, COH2 desorption and the disappearance of the infrared carbon vibration modes.
1-Bromo-2-chloroethane adsorption on Cu(111)
Authors: Kadodwala M. , Jones Robert G.
Published: July 2002

Low energy electron diffraction, Auger-electron, and ultraviolet photoemission spectroscopies (UPS) and Δφ measurements were used to study the adsorption of 1-bromo-2-chloroethane on Cu(111). Room temperature adsorption led to the formation of a (√3×√3)R30° structure composed of equal parts chlorine and bromine, the remainder of the molecule returning to the gas phase as ethene. Adsorption at 110 K occured molecularly in a layer by layer mode up to the fourth molecular layer. UPS shows that the first monolayer which is in direct contact with the copper, is oriented and probably in one conformation. On warming, the multilayers desorbed leaving a single layer of 1-bromo-2-chloroethane which had already begun to react with the surface. Physisorbed ethene at 173–183 K has been tentatively identified by UPS as one of the products of this low temperature reaction, the others being Clads and Brads. Further heating desorbed the ethene and left a (√3×√3)-Cl/Br surface the same as that formed at room temperature. The molecule was also found to undergo a clean electron stimulated reaction, which led to the two chemisorbed halogens and a gaseous product carrying away the carbon, presumably ethene. The behavior of 1-bromo-2-chloroethane is compared with that of 1,2-dichloroethane on the same surface.
Radio-frequency superconductivity technology: Its sensitivity to surface conditions
Authors: Kneisel P.
Published: July 2002

The application of rf-superconductivity technology in particle accelerator projects has become increasingly evident in recent years. Several accelerator laboratories around the world are presently involved in large scale projects. The reasons for this multitude of activities are a matured technology based on a better understanding of the phenomena encountered in superconducting cavities and the influence of improved material properties, contamination control and quality assurance measures. This article gives an overview of the basis of rf-superconductivity technology by emphasizing the sensitivity of several important surface effects: the residual surface resistance, and the effects of resonant and nonresonant electron loading.
Loss of selectivity during W chemical vapor deposition on Si using the WF6/SiH4 process
Authors: Groenen P. A. C. , Tekcan Ö. F. , Hölscher J. G. A. , Brongersma H. H.
Published: July 2002

The undesired deposition of W on SiO2 during W chemical vapor deposition on Si with the WF6/SiH4 process has been studied by in situ time resolved mass spectrometry. This study shows that for [SiH4]/[WF6]<0.3 loss of selectivity occurs due to an autocatalytic reaction on the SiO2 surface. Based on the observations, a model for the process has been proposed. In this model, the rate limiting step is the formation of Si2H2n from two SiH4 molecules. This reaction requires a nucleation site, probably an impurity in the SiO2 or adjacent metallic areas, and is retarded by WF6. Subsequently, the Si2H2n reacts with WF6 to a W-containing species that will then also act as a nucleation site. When the density of W-containing species approaches monolayer coverage, these species react together with Si2H2n, thus forming areas of metallic W.
Precise property determinations of arsenosilicate glass thin films using infrared spectroscopy
Authors: Niemczyk T. M. , Wangmaneerat B. , Haaland D. M.
Published: July 2002

The combination of infrared spectroscopy and chemometric data analysis has been shown to provide a valuable method for rapid, nondestructive, at-line characterization of film properties for a variety of thin films. We demonstrate the precise determination of As content and film thickness for arsenosilicate glass thin films. Calibrations based on the infrared data yielded standard errors of prediction of 0.10 wt. % and 10 Å for the arsenic content and film thickness, respectively. Further, it is demonstrated that profiling the film properties across the wafer surface can increase the accuracy of the determinations by improving the correspondence of the infrared and reference property measurements. This profiling also provides rapid information about spatial variations of film properties.
Hot electron scattering effects in metal–semiconductor structures and their role in interface transport
Authors: Ludeke R. , Bauer A.
Published: July 2002

The spectroscopy mode of ballistic electron emission microscopy was used to study the thickness dependence of the collector current Ic for 8–90 Å thick Pd films deposited on Si(111) and Si(100) substrates. The observation of similar spectral intensities for the thinnest films on both orientations is attributed to disorder induced scattering at the Pd–Si interface, which is conventionally equivalent to a breakdown of transverse momentum conservation. Fits to a model based on this interpretation give unprecedented agreement over a wide energy range. The attenuation of Ic with film thickness exhibits strong nonexponential behavior for all tip biases studied (≤6 V), which is due to a changing dominance among scattering mechanisms as the film thickness varies. A simple analytical expression, based on a random-walk approach, is derived that allows a unique determination of the energy dependent elastic and inelastic mean free paths of hot electrons in the Pd films.
Aggregation structure and surface properties of immobilized organosilane monolayers prepared by the upward drawing method
Authors: Ge Shouren , Takahara Atsushi , Kajiyama Tisato
Published: July 2002

Octadecyltrichlorosilane [OTS, CH3(CH2)17SiCl3] and [2-(perfluorooctyl)ethyl] trichlorosilane [FOETS, CF3(CF2)7CH2CH2SiCl3] monolayers were prepared on a water surface. The monolayers of OTS and FOETS amphiphiles were polymerized to form a Si–O–Si linkage on the water subphase. The polymerized monolayers were transferred onto a glass plate or silicon wafer surface by the upward drawing method and were covalently bonded to the Si–OH groups of the glass or silicon wafer surface. Electron diffraction patterns revealed that the OTS monolayer was in a crystalline state, while the FOETS monolayer was in an amorphous state at 293 K. The bright field image showed homogeneous molecular aggregation in the OTS and FOETS monolayers. The atomic force microscopic and frictional force microscopic images of the OTS/FOETS mixed monolayers distinctly showed a phase-separated structure. Deposition of the OTS, FOETS, and OTS/FOETS monolayers on the substrate was confirmed by attenuated total reflection Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy. A highly hydrophobic property was observed for OTS, FOETS, and OTS/FOETS monolayer immobilized surfaces. Dynamic contact angle measurements indicated that the surface structure of these monolayers did not show reorganization upon environmental change because of polymerization and the formation of a covalent bond between the monolayer and the substrate surface.
Ultrahigh vacuum and surface science
Authors: Palmberg Paul W.
Published: July 2002

The role of ultrahigh vacuum (UHV) technology in the development of modern surface science is discussed. Surface science progressed slowly prior to about 1960 because of highly specialized skills needed to construct apparatus and carry out experiments. The rapid development of UHV technology, including stainless steel vacuum hardware and ion pumps in the 1960s, made it possible to construct apparatus with relative ease and attracted many capable scientists to the field of surface science. The number of analytical techniques for characterizing surfaces expanded dramatically in a span of less than ten years. The early development of these techniques and their impact on surface science is reviewed.
Synchrotron radiation excited etching of SiC film using reactive species generated by a microwave discharge
Authors: Terakado Shingo , Ogura Masayoshi , Suzuki Shigeo , Tanaka Kenichiro
Published: July 2002

Synchrotron radiation (SR) excited etching of SiC film was studied using a mixture of SF6 and Ar. It was found that only the region irradiated by SR was etched. By introducing a 2.45 GHz microwave discharge as a generator of reactive species, the etch rate of the irradiated region was increased by one order of magnitude while retaining the area selectivity. It was determined that the etching reaction occurred due to a surface photochemical reaction and was promoted by the increase in the number of reactive species affected by means of microwave discharge. From the dependence of the etch rate on the photon energy using monochromatic soft x rays, it was found that the photoabsorption of the sample took part in the etching reaction.
Photoemission study of the growth of the LaF3/Si (111) interface
Authors: Malten C. , Cramm S. , Colbow K. M. , Eberhardt W.
Published: July 2002

Photoemission spectroscopy with synchrotron radiation was used to study the LaF3/Si (111) interface as a function of annealing temperature for LaF3 films. These films range in thickness from 0.7–11 monolayers and have been deposited at room temperature. The La/Si photoemission intensity ratio at surface sensitive and bulk sensitive experimental conditions shows that island formation occurs at 420 °C. The stoichiometry of the LaF3 films is conserved until desorption begins at approximately 580 °C, where fluorine desorbs from the surface completely and lanthanum remains on the silicon substrate. From a line shape analysis of the Si 2p and La 4d core levels it is apparent that the interface is dominated by La–Si bonds. Changes in the surface Fermi level are induced by the penetration of lanthanum into the surface layers of the silicon substrate upon annealing.