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Nov 1987

Volume 5, Issue 6, pp. 3287-3454


Characterization of diamondlike carbon films and their application as overcoats on thin‐film media for magnetic recording

Hsiao‐chu Tsai and D. B. Bogy

J. Vac. Sci. Technol. A 5, 3287 (1987); http://dx.doi.org/10.1116/1.574188 (26 pages) | Cited 151 times

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This paper reviews and analyzes the literature on thin carbon layers with emphasis on their use as protective overcoats for thin‐film magnetic media. We discuss carbon as a material, its preparation as a thin film, and review and evaluate various techniques for characterizing its thin‐film properties.
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68.55.-a Thin film structure and morphology
73.61.Ng Insulators
78.66.-w Optical properties of specific thin films
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.

Vibration isolation for scanning tunneling microscopy

M. Okano, K. Kajimura, S. Wakiyama, F. Sakai, W. Mizutani, and M. Ono

J. Vac. Sci. Technol. A 5, 3313 (1987); http://dx.doi.org/10.1116/1.574189 (8 pages) | Cited 25 times

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Vibration isolation technology for scanning tunneling microscopy (STM) to suppress the external mechanical perturbation down to a subatomic scale is described. The system is simplified into two subsystems, a tunneling assembly and a supporting table. Each of them has its own mechanical eigenfrequency. The principle of the isolation exists in making the two eigenfrequencies very different from each other. A theory of isolation developed is based on a model of multiply coupled oscillators with damping. Experimental results of the isolation characteristics for the two types of isolators constructed, one consisting of two‐stage coil springs and the other of multiply stacked metal plates with rubber pieces among them, are well explained by the theory. STM images of graphite are obtained by using these isolators combined with various tunneling assemblies. Thereby the basis for design of the isolators is clarified.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
07.10.-h Mechanical instruments and equipment
07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination

A photoelectron spectroscopy and photon stimulated desorption study of H2O on Si(100) 2×1

C. U. S. Larsson, A. S. Flodström, R. Nyholm, L. Incoccia, and F. Senf

J. Vac. Sci. Technol. A 5, 3321 (1987); http://dx.doi.org/10.1116/1.574190 (4 pages) | Cited 14 times

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We have studied H2O adsorption on the Si(100) surface using photoelectron spectroscopy to record Si valence bands and Si 2p core level spectra; and photon stimulated desorption to record Si 2p edge total electron yield and H+‐ion yield spectra. We assign the valence‐band H2O induced peaks at EB=6.3 and 11.2 eV to the Si–OH and to the O–H bonds, respectively. The H2O dosed Si 2p core level spectrum exhibits two H2O induced equal intensity surface peaks with surface core level shifts of +0.25 and +1.00 eV that we assign to surface Si atoms in the Si–H and the Si–OH bonds, respectively. We interpret the features in the Si 2p edge H+‐ion yield spectrum as ion desorption from SiO2 at surface defect minority sites. We conclude that H2O adsorbs dissociatively as H and OH radicals on the Si(100) 2×1 surface dimers and that there are defect minority sites on the surface where H2O adsorption causes SiO2 formation.
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
73.20.Hb Impurity and defect levels; energy states of adsorbed species
81.65.-b Surface treatments

Aluminum/polyimide interface formation: An x‐ray photoelectron spectroscopy study of selective chemical bonding

Lj. Atanasoska, Steven G. Anderson, H. M. Meyer, Zhangda Lin, and J. H. Weaver

J. Vac. Sci. Technol. A 5, 3325 (1987); http://dx.doi.org/10.1116/1.574191 (9 pages) | Cited 11 times

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High‐resolution x‐ray photoelectron spectroscopy has been used to study the formation of the aluminum/polyimide (Al/PI) interface at room temperature. Aluminum films up to 80 Å thick were vapor deposited onto cured polyimide in situ. Our results show that Al is chemically active for coverages below ∼20 Å. Preferential aluminum bonding with PI occurs at carbonyl sites, as evidenced by the rapid attenuation of the carbonyl C 1s core level photoemission intensity. In the initial reaction stage (1–2 Å), Al preferentially occupies planar imide rings. These adatoms transfer charge to carbonyl carbon atoms via oxygen and this resonance hybrid state of C–O–Al weakens, but does not break, carbonyl bonds. With increasing Al coverage, the formation of strong Al–O bonds is observed and is attributed to a C–O–Al complex compound. Metallic Al is observed at a nominal coverage of 2 to 5 Å. The Al/PI interface exhibits the attenuation behavior characteristic of cluster growth through both reacted and unreacted regions. Annealing the 80‐Å Al/PI interface at 300 °C results in extended reaction with less selective chemical interaction of Al with PI.
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68.35.Fx Diffusion; interface formation
66.30.Ny Chemical interdiffusion; diffusion barriers
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
79.60.Jv Interfaces; heterostructures; nanostructures

An in situ fracture stage for x‐ray photoelectron spectroscopy and Auger electron spectroscopy studies of internal surfaces in polycrystalline materials

P. Brüesch, W. Foditsch, and F. Stucki

J. Vac. Sci. Technol. A 5, 3334 (1987); http://dx.doi.org/10.1116/1.574192 (6 pages)

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An in situ fracture state for x‐ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy studies of internal surfaces in polycrystalline materials is described. The system offers the possibility to study both surfaces produced as a result of a fracture, allowing the comparison of physical and compositional features of one surface with those of its conjugate. The notched sample can be cooled to liquid‐nitrogen temperature prior to fraction. By using an electron collimator only photoelectrons from the fractured surface but not from the notch area are observed. The method is illustrated by XPS measurements obtained from fractured surfaces of an AlMgSiPb alloy (transgranular fracture), a Bi‐doped ZnO varistor (intergranular fracture), and polypropylene containing an antioxidant (interspherulitic fracture). The main motivation which led to the development of this fracture stage lies in the possibility to correlate the microstructure and microchemistry of internal surfaces with the relevant macroscopic properties of polycrystalline materials.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
62.20.M- Structural failure of materials
68.37.-d Microscopy of surfaces, interfaces, and thin films

X‐ray photoelectron spectroscopy study of the Ni/Si oxide/Si interface

T. R. Dillingham, A. R. Chourasia, D. R. Chopra, S. R. Martin, K. L. Peterson, C. Z. Hu, and B. Gnade

J. Vac. Sci. Technol. A 5, 3340 (1987); http://dx.doi.org/10.1116/1.574193 (6 pages) | Cited 3 times

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The electronic structure of the Ni/Si oxide/Si interface has been investigated using x‐ray photoelectron spectroscopy. This interface represents a more realistic situation encountered in semiconductor device processing technology. Approximately 35 Å of high‐purity Ni was sputter deposited on 〈111〉Si (covered with a thin native oxide layer) at room temperature. A sputter profiling technique was employed to determine the composition and reactivity as a function of depth. The measurements show considerable reactivity at the Ni/Si oxide/Si interface, even at room temperature. The Ni 2p3/2 peak exhibits a gradual shift to higher binding energy which indicates that the overlayer cannot be regarded as a single unique nickel silicide phase. The large positive shift of the Ni 2p3/2 and the small shift of the corresponding Si 2p peak suggest that ionicity plays a nominal role in the Ni–Si chemical bond. The valence‐band spectra show a dominant 3d‐derived feature which gradually shifts to higher binding energy. The observed shifts in the Ni levels are attributed to the change in the electronic configuration of Ni in going from Ni‐rich silicide to Si‐rich silicide. A study of the composition as a function of depth shows that the Ni/Si oxide/Si interface is not sharply defined due to the interdiffusion of Ni and Si. Thus, the interface is identified as a graded transition region with composition ranging from Ni‐rich to Si‐rich silicide.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
79.60.Jv Interfaces; heterostructures; nanostructures
68.35.Dv Composition, segregation; defects and impurities

A new photon counter for inverse photoemission

P. M. G. Allen, P. J. Dobson, and P. R. Webber

J. Vac. Sci. Technol. A 5, 3346 (1987); http://dx.doi.org/10.1116/1.574194 (5 pages) | Cited 4 times

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Data are presented obtained from a new design of high‐resolution (70 meV) and high‐sensitivity, fixed isochromat detector for use in inverse photoemission whose peak quantum efficiency is 20% at an energy of 10.08 eV. The detector design is of the Geiger type with a novel combination of a CaF2 window and CS2 vapor fill. The performance of this detector is compared with others currently being used. It is suggested that this design could provide an inexpensive viable alternative for high‐resolution spectroscopy systems. Inverse photoemission spectra obtained from a CuNi(111) surface in ultrahigh vacuum are presented.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Kinetics of surface reactions of CF3 radicals

Robert M. Robertson, Michel J. Rossi, and David M. Golden

J. Vac. Sci. Technol. A 5, 3351 (1987); http://dx.doi.org/10.1116/1.574195 (8 pages) | Cited 4 times

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The kinetics of reactions of CF3 radicals on various substrate materials has been studied in a gold‐coated, stainless‐steel, very‐low‐pressure photolysis (VLPΦ) cell as a function of temperature and radical concentration. The substrate materials were gold, stainless steel, copper, copper oxide, and silica. The CF3 radicals were generated from CF3I by IR‐multiphoton decomposition. The reaction products observed with a mass spectrometer included HF, CO, CO2, COF2, SiF4, and C2F6. Rate constants were obtained as a function of temperature. CF3 reacted most rapidly on copper oxide surfaces; the other metal surfaces were less reactive, and the silica surfaces were least reactive. Previous studies from this laboratory that had reported the reaction of CF3 on fused silica are reinterpreted as reactions of CF3 on the stainless‐steel heater assembly.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Room‐temperature formation and oxidation properties of the Cr/Si(111) interface

P. Wetzel, C. Pirri, J. C. Peruchetti, D. Bolmont, and G. Gewinner

J. Vac. Sci. Technol. A 5, 3359 (1987); http://dx.doi.org/10.1116/1.574196 (7 pages) | Cited 2 times

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The structural and electronic properties of the Cr/Si(111) interface formed at room temperature (RT) are investigated by low‐energy electron diffraction, x‐ray photoelectron spectroscopy and angle resolved ultraviolet photoemission spectroscopy, and work function measurements. The data indicate strong reactive behavior in agreement with a previous study by Franciosi et al. The data show intermixing up to ∼25 monolayer (ML) Cr coverage with an overlayer stoichiometry evolving gradually from Si rich to Cr rich phases with increasing Cr coverage. The reacted phases are metastable and definitely different from any known bulk silicide. Above ∼30‐ML Cr coverage, polycrystalline bulk Cr metal is formed. Further insight into the nature of the intermixed layer comes from oxidation studies of the interface as a function of Cr coverage. A progressive shift of the oxidized Cr 3d, Cr 2p3/2, and Si 2p lines with Cr coverage in the 0–25 ML range implies different oxidation states for Si and Cr species at various steps of the interface formation, and in turn, indicates a composition gradient normal to the surface. The data also demonstrate that above ∼2‐ML Cr coverage the oxygen uptake of the interface is up to 10 times faster than for definite silicides such as CrSi or CrSi2. The enhanced interface reactivity of the metallic RT grown Si–Cr phases apparently originates in their unique metastable bulk and surface composition and structure.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
73.40.Ns Metal-nonmetal contacts
81.65.-b Surface treatments

Surface instability of platinum modified aluminide coatings during 1100 °C cyclic testing

P. Deb, D. H. Boone, and T. F. Manley

J. Vac. Sci. Technol. A 5, 3366 (1987); http://dx.doi.org/10.1116/1.574197 (7 pages) | Cited 4 times

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Platinum additions to aluminide coatings have been reported to be beneficial in both hot corrosion and oxidation environments. The data, however, are somewhat limited and strongly dependent upon structure and test conditions. Therefore, a study of the effects of surface structure under 1100 °C cyclic oxidation conditions of the platinum modified and the unmodified aluminide coatings on the IN‐738 substrate was initiated. During the early stages of this evaluation surface upheavals on the order of 50 μm, often called ‘‘rumpling,’’ were observed for both systems. The degree of rumpling was greater in the platinum modified coatings but was observed to a significant extent with the unmodified coatings as well. The amount of rumpling observed during cyclic testing can be attributed to a number of possible effects including (i) coefficient of thermal expansion mismatch, (ii) thermal gradient across the coated specimen, and (iii) coating mechanical properties. An effect of coating thickness is also observed although it must be noted that for diffusion‐type coatings such as the Pt–Al system, coatings with different thicknesses have different compositions. Therefore, the resulting performance of the coating is a complex interplay of the above‐mentioned variables. Excellent Al2O3 adherence is seen for all the platinum modified aluminides tested, even on the highly convoluted surfaces. The role of rumpling in the high temperature protectively is not known but should be given more consideration as a potential high‐temperature degradation mechanism of these coatings.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.65.-b Surface treatments
81.40.-z Treatment of materials and its effects on microstructure, nanostructure, and properties

Stress measurement in sputtered copper films on flexible polyimide substrates

Alan Entenberg, Vern Lindberg, Kurtis Fletcher, Andrew Gatesman, and Ronald S. Horwath

J. Vac. Sci. Technol. A 5, 3373 (1987); http://dx.doi.org/10.1116/1.574198 (5 pages) | Cited 5 times

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We have investigated the dependence of internal stress on argon pressure for 0.25‐μm copper films sputtered onto a 1‐mil(25‐μm)‐thick polyimide substrate. A dc planar magnetron was used to deposit the copper at a rate of 2 Å/s onto the flexible substrate which was held flat by top and bottom edges. The stress was estimated directly from the resulting radius of curvature of the relaxed film and substrate. The critical argon pressure at which a transition from compression to tension occurs was found to be about 2.5 mTorr. In addition, the dependencies of film morphology, resistivity, and optical reflectance on argon pressure were studied. The critical pressures at which resistivity starts to rise and reflectance begins to decrease are very close to the stress transition pressure. In general, the data are consistent with the dependencies of physical properties on pressure observed for other sputtered metals.
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68.60.Bs Mechanical and acoustical properties
78.66.Bz Metals and metallic alloys
73.61.At Metal and metallic alloys
68.55.-a Thin film structure and morphology

Chemical vapor deposition of zinc phosphide thin films

E. Papazoglou and T. W. F. Russell

J. Vac. Sci. Technol. A 5, 3378 (1987); http://dx.doi.org/10.1116/1.574199 (5 pages)

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The design and analysis of a laboratory scale system for the chemical vapor deposition of thin zinc phosphide films is reported. The deposited films, on mica or glass substrates, were uniform, continuous, and of low electrical resistivity (400–1000 Ω cm). The reactor was made of nonporous graphite (H‐490) and was operated at 1 atm using elemental zinc and phosphine. Model equations describing the evaporation of zinc, the cracking of phosphine, and the deposition reaction have been developed. The evaporation rate of zinc is a function of its temperature and the helium flow rate above its surface. The film growth is controlled by the surface reaction between adsorbed zinc and phosphorus. A Langmuir–Hinschelwood expression for the reaction rate agrees well with the experimental data over a range of substrate temperatures and reactant concentrations.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.61.Cw Elemental semiconductors
73.61.Jc Amorphous semiconductors; glasses
73.61.Le Other inorganic semiconductors

Control of the surface composition of isothermal vapor phase epitaxial mercury cadmium telluride

J. G. Fleming and D. A. Stevenson

J. Vac. Sci. Technol. A 5, 3383 (1987); http://dx.doi.org/10.1116/1.574200 (3 pages)

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A method is described for controlling the surface composition of mercury cadmium telluride during isothermal vapor phase epitaxy of mercury cadmium telluride. The method employs a three‐phase solid–liquid–vapor source in equilibrium with the desired composition. The thermodynamic and kinetic basis of the method is outlined.
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68.35.Dv Composition, segregation; defects and impurities
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.Nq Composition and phase identification

Kinetic theory of laser photochemical deposition

C. Julian Chen

J. Vac. Sci. Technol. A 5, 3386 (1987); http://dx.doi.org/10.1116/1.574201 (13 pages) | Cited 5 times

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A kinetic theory of laser photochemical deposition is developed, which includes the following parts: (1) an analytic formalism for the deposition profile due to gas phase decomposition, (2) a theorem which relates the ballistic case and the diffusion‐dominated case, (3) a detailed account of adsorbed phase photodeposition, and (4) six dimensionless quantities to characterize various deposition processes. The theory is used to analyze and gain insights to a number of recent photodeposition experiments.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.50.-m Photochemistry
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

A spectroellipsometric investigation of the effect of argon partial pressure on sputtered palladium films

Brian T. Sullivan and R. R. Parsons

J. Vac. Sci. Technol. A 5, 3399 (1987); http://dx.doi.org/10.1116/1.574202 (9 pages) | Cited 3 times

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The microstructure of palladium thin films prepared by dc planar magnetron sputtering at low deposition temperatures was investigated as a function of the argon partial pressure. The films were characterized by spectroellipsometry, electron microscopy, and x‐ray diffraction. Below a transition pressure Pt≂15 mTorr, the films consisted of densely packed grains, corresponding to the zone T region in Thornton’s structure zone model. Above this transition pressure the films developed into a more voided columnar structure, characteristic of a zone 1 region. A microstructural analysis of the spectroellipsometric data indicated a general trend to increased porosity and microroughness of the films with higher argon pressures. Furthermore, the effective medium theory of Sen, Scala, and Cohen (SSC), relevant for a random coated‐particle microstructure where the grains are optically isolated from each other, was required to describe the films prepared with argon pressures above Pt. The zone 1 region was therefore best described optically as a random coated‐particle microstructure where the microroughness and porosity varied with the argon pressure. Spectroellipsometry, which is sensitive to the film microstructure, was able to identify the zone T/zone 1 transition through the changes in the pseudodielectric function of the Pd films. Electron microscopy confirmed that for the thin films prepared at argon pressures higher than Pt, the grains became isolated by void boundaries, thus further supporting the random coated‐particle basis of the SSC theory.
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68.55.-a Thin film structure and morphology

Nucleation of body‐centered‐cubic tantalum films with a thin niobium underlayer

D. W. Face and D. E. Prober

J. Vac. Sci. Technol. A 5, 3408 (1987); http://dx.doi.org/10.1116/1.574203 (4 pages) | Cited 15 times

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We discuss the structural and electrical properties of high‐quality Ta films prepared by ion beam sputter deposition. The Ta films grow in two different crystal structures, body‐centered‐cubic (bcc) or tetragonal (β‐Ta), depending on the substrate preparation and sputtering conditions. Ta films deposited on a thin (>0.3 nm) Nb underlayer grow in the bcc crystal structure with properties approaching those of clean bulk polycrystalline material. The bcc‐Ta films have a superconducting transition temperature of 4.3 K and a low‐temperature (10 K) resistivity ρ∼6 μΩ cm. Ta films deposited without a Nb underlayer on Si substrates always grow in the tetragonal (β‐Ta) structure. The β‐Ta films do not superconduct above 1 K and have a high resistivity ρ∼150 μΩ cm. X‐ray diffraction and transmission electron microscope studies of both Ta structures are presented. Both bcc‐Ta and β‐Ta films are deposited on room‐temperature substrates. This allows either type of film to be easily patterned by standard photoresist liftoff methods.
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68.55.-a Thin film structure and morphology
73.61.At Metal and metallic alloys
74.78.-w Superconducting films and low-dimensional structures
81.15.Cd Deposition by sputtering

Distribution of copper deposited inside holes by sputtering

A. N. Pargellis

J. Vac. Sci. Technol. A 5, 3412 (1987); http://dx.doi.org/10.1116/1.574204 (5 pages)

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Both cost considerations and environmental concerns have prompted the search for alternative methods to electroless copper deposition on the walls of vias (holes used for interconnecting different levels of circuitry in printed wiring boards). One attractive possibility is sputter deposition (a dry metallization process) of copper onto hole walls. This requires a knowledge of deposit thickness as a function of depth into the hole. Experimental results are presented for the variation with depth in the thickness of copper deposited onto the walls of circular holes by sputtering. For large distances into holes oriented perpendicularly to the sputter source, the thickness of the deposit decreases with depth as (D/L)3, where D is the hole diameter, L is the distance into the hole, and L/D>2. The experimental results agree with the calculated values obtained by using Lambert’s law, where the emitted flux is integrated over the magnetron area from which the sputtered copper can travel to a particular region on the hole wall. The data are used to predict the deposit thickness as a function of depth into through holes which have been subjected to sputtered copper from both sides. For a deposit thickness on the outer planar surface of 25 000 Å, and holes with aspect ratios A of 1, 2, 3, 5, and 10, the predicted deposit thickness on the hole walls at the midplane are 13 600, 8400, 4400, 1200, and 160 Å, respectively.
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81.15.Cd Deposition by sputtering
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Fabrication of polyvinyl alcohol coated polystyrene shells

Alan K. Burnham, John Z. Grens, and Eben M. Lilley

J. Vac. Sci. Technol. A 5, 3417 (1987); http://dx.doi.org/10.1116/1.574205 (5 pages) | Cited 7 times

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Glass shells have been used traditionally as the deuterium–tritium fuel container for direct‐drive laser fusion experiments because of their convenience and availability, but lower‐Z fuel containers have superior implosion characteristics and diagnostic possibilities. Unfortunately, polymers such as polystyrene (PS) that produce shells easily have very high permeabilities so require cryogenics to retain fuel, and impermeable polymers such as polyvinyl alcohol (PVA) are difficult to make into high‐quality shells. We have developed improved methods of making PS shells with diameters from 0.2 to 0.7 mm and coating them with a 3‐μm layer of PVA to obtain the advantages of both. Both the PS shells and the PVA coating are made in drop towers using gas‐stripped nozzles. Details of the procedures and product quality are discussed.
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28.52.-s Fusion reactors
52.58.-c Other confinement methods

Outgassing behavior of A6063‐EX aluminum alloy and SUS 304 stainless steel

June‐Rong Chen, Chih‐Hao Lee, Jyh‐Cheng Chen, Huan‐Lurn Hsieh, and Yuen‐Chung Liu

J. Vac. Sci. Technol. A 5, 3422 (1987); http://dx.doi.org/10.1116/1.574206 (3 pages) | Cited 2 times

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The outgassing behavior of A6063‐EX aluminum alloy and SUS 304 stainless steel has been studied by means of analyzing the outgassing rate curves and the residual gases in the vacuum system. The results indicate, when the chamber has been filled with moist gas, the major outgassing process is diffusion for the aluminum alloy, but is desorption for the stainless steel. When the filling gas is extremely dry, the outgassing stimulated by the filament of the ionization gauge may become dominant for both the aluminum alloy and the stainless‐steel vacuum chambers.
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
66.30.J- Diffusion of impurities
07.30.Kf Vacuum chambers, auxiliary apparatus, and materials

Outgassing tests on thick plasma‐sprayed TiC coatings for fusion applications

B. Terreault, C. Boucher, P. L. Andrew, A. A. Haasz, C. Brunet, and S. Dallaire

J. Vac. Sci. Technol. A 5, 3425 (1987); http://dx.doi.org/10.1116/1.574207 (5 pages)

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TiC coatings of 300‐μm thickness produced by plasma spraying have been tested for their outgassing properties from room temperature to 1000 °C, to assess their suitability as high‐heat/particle flux protective surfaces in tokamaks. The coatings were found to contain the following approximate amounts of gas (in mol %): H2, 0.9; H2O, 0.7; CO, 0.05; Ar, 0.01; CO2, 0.03, and lesser amounts of N2 and hydrocarbons. The experimental uncertainties are estimated to be ±25%. Whereas argon outgasses totally at room temperature and water vapor mostly below 100 °C, the other gases require much higher temperatures. This material, baked only at ≤100 °C, would be acceptable with respect to the base vacuum of a tokamak; however high‐temperature baking is recommended from the viewpoint of recycling and impurity control.
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
28.52.-s Fusion reactors
52.55.Fa Tokamaks, spherical tokamaks

Poisonous gas effects on the emission of oxide‐coated cathodes

S. Itoh, M. Yokoyama, and K. Morimoto

J. Vac. Sci. Technol. A 5, 3430 (1987); http://dx.doi.org/10.1116/1.574208 (6 pages) | Cited 3 times

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A study of the influence of various gases on the emission of oxide‐coated cathodes is described. Particularly selected were SO2 and NO2, which are closely related to air pollution, and Cl2 gases. For comparison purposes, the poisonous effects of N2, CO2, H2O, O2, CO, H2, and Ar, which are the main components of natural atmosphere, were also examined. To study the influences of gases on the emission of oxide‐coated cathodes and on oxide materials in more detail, the poisoned state of the contaminated cathode was analyzed using secondary electron microscopy and Auger electron spectroscopy. The influence of contaminated gases on the emission of the cathode in the carbonate state prior to activation was also studied.
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79.40.+z Thermionic emission
81.40.-z Treatment of materials and its effects on microstructure, nanostructure, and properties

Fragmentation spectra and appearance potentials of vacuum pump fluids determined by electron impact mass spectrometry

E. D’Anna, G. Leggieri, A. Luches, and A. Perrone

J. Vac. Sci. Technol. A 5, 3436 (1987); http://dx.doi.org/10.1116/1.574209 (6 pages)

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Three different vacuum pump fluid (Fomblin Y‐VAC 18/8, Santovac 5, and DC 704) vapors were subjected to electron bombardment at energies from 10 to 90 eV. The fragmentation spectra were recorded with a quadrupole mass spectrometer. The appearance potentials of the most abundant fragments were determined. The experimental results show very good stability of the Fomblin vapors under electron bombardment.
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07.30.Cy Vacuum pumps
07.30.Kf Vacuum chambers, auxiliary apparatus, and materials
79.20.Kz Other electron-impact emission phenomena

Gettering in cryogenic applications

C. Boffito, B. Ferrario, L. Rosai, and F. Doni

J. Vac. Sci. Technol. A 5, 3442 (1987); http://dx.doi.org/10.1116/1.574850 (4 pages)

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Metallic cryogenic Dewars and pipes, used for storage and transportation of cold fluids such as liquid N2 or He, usually have a vacuum jacket as a thermal insulator. In this case, vacuum has to be maintained in a range of 10−1 Pa or lower. Nonevaporable getters are often used for this purpose. They are particularly useful for sorbing H2 which is released by the warmer walls or by the multilayer insulation; H2 is neither cryocondensed by the cold surfaces nor sorbed by the molecular sieves which may be used to physisorb other gaseous species. The working temperature of the getters may range from room temperature down to the cryogenic fluid temperature. The getter material here considered, and which appears to be adequate for these applications, is the Zr–V–Fe nonevaporable getter alloy. Its sorption characteristics (particularly for H2) are studied both at room temperature and in a cryogenic fluid environment. The behavior of a gettered Dewar jacket is finally studied and discussed.
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07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
07.30.Kf Vacuum chambers, auxiliary apparatus, and materials

Design studies of distributed ion pumps

T. S. Chou

J. Vac. Sci. Technol. A 5, 3446 (1987); http://dx.doi.org/10.1116/1.574851 (7 pages)

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To upgrade the existing vacuum system, a new type of diode distributed ion pump (DIP) has been tested and developed for the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory. The new pumps consist of two titanium cathodes as before, but have five parallel 304 stainless‐steel plates with 16‐mm‐diam holes to replace the 11‐mm‐diam cylinders of the old ‘‘egg crate’’ anode structure. They have pumping speeds for nitrogen of several tens of liters per seconds per meter at 10−9 Torr as is required by the NSLS for good lifetime operation. We first survey previous work on DIP and then present the results of our study on new pumps with different cell sizes and two different anode materials (aluminum and stainless steel). The pumping characteristics of the new pumps are much superior to the old types with respect to ultimate pressure and easier conditioning.
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07.30.Cy Vacuum pumps

A secondary screen discharge for modification of sputtered films

K. L. Westra, R. P. W. Lawson, and M. J. Brett

J. Vac. Sci. Technol. A 5, 3453 (1987); http://dx.doi.org/10.1116/1.574852 (2 pages)

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81.15.Cd Deposition by sputtering
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.65.-b Surface treatments
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