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Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films

Issue 5 • Date Sep 1986

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Displaying Results 1 - 25 of 27
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • A review of the present state of art in hard coatings grown from the vapor phase

    Page(s): 2259 - 2279
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    Hard‐coating materials range from ultrahard materials such as ‘‘diamondlike carbon’’ through refractory compounds to alloys. However, transition‐metal carbides and nitrides have achieved by far the highest level of commercial success. Titanium nitride and titanium carbide are the most studied and used. In this paper a review of the hard coating literature is given and includes in addition to nitrides and carbides also oxides, borides, mixed compounds, metals and alloys, and ‘‘diamondlike’’ carbon coatings. Only coatings grown from the vapor phase are discussed. Some considerations involved in selecting coating/substrate combinations as well as basic concepts of hardness and hardness measurements are also given. For example, it is shown that in order to measure the hardness of the coatings correctly the ratio between the film thickness and the depth of the indentation has to exceed a critical value, which depends on the coating/substrate combination. For TiN on steel, the coating thickness has to be a factor of 5 larger than the indentation depth. For all types of hard coatings there is still a lack of knowledge on how nucleation and growth processes are affected by processing parameters and how the resulting film microstructure correlates to physical properties. Based on results presented in the literature, the existing knowledge about relationships between the microstructure and physical properties of hard coatings is discussed. Particular emphasis is placed on the role of microstructural features such as grain boundaries, nonequilibrium structures, impurities, and texture in controlling the film hardness. For example, voids and weak grain boundaries give rise to low film hardnesses whereas dense films with a high defect concentration can have hardnesses far above bulk values. Because the coatings in many cases are grown at high rates, low temperatures, and under the influence of an imp- - inging ion flux, supersaturated solid solutions and entrapment of noble‐gas impurities are common features. Such coatings exhibit high stress levels (most commonly of a compressive nature) and high hardness values. View full abstract»

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  • Investigation on the low pressure limit of the Bayard–Alpert gauge

    Page(s): 2280 - 2283
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    To extend the pressure measurement capability of a Bayard–Alpert (BA) gauge, several commercial BA gauges are modified. To study the position dependence of filament on gauge sensitivity, hair‐pin filaments instead of commercial helical filaments were used. The characteristics of the modified gauge, which included the variation of the gauge sensitivity on the applied voltage and the position of the filament, are reported. To monitor the normal and the reverse x‐ray photocurrents, the gauge was inserted into a fixed size tube of 304 LN stainless steel. The validity of the self‐modulation was confirmed. A sensitivity of 60 Torr-1 and an x‐ray limit of 2.7×10-13 Torr (N2 equivalent) was obtained. View full abstract»

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  • A simple ionization gauge for use in a magnetic field

    Page(s): 2284 - 2286
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    A simple ionization gauge is described which can be used to measure fast pressure changes in a weak plasma environment in a magnetic field. The gauge has a conventional triode structure and hence can be readily constructed using commercial components. The gauge tested is, however, much less sensitive than a standard Bayard–Alpert gauge. The gauge is, however, relatively insensitive to an applied magnetic field of up to 5 kG, and will tolerate a large variation in the direction of the magnetic field. View full abstract»

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  • A new gross leak calibration for leak detectors

    Page(s): 2287 - 2292
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    The basic mechanisms of gas flow through leaks are described. Since many variables affect the sensitivity of a helium mass spectrometer leak detector, it is necessary that both fine leak (10-9 Pa m3/s) and gross leak (10-4 Pa m3/s) calibrations be performed (1 Pa m3/s=9.87 atm cc/s at 0 °C). Reference leaks are used to provide known rates of leakage which can be used to adjust leak detector sensitivity and ensure that specified maximum rates of allowable leakage can be detected reliably. Leakage from artificial leaks is used to calibrate the leak detector scales and in combination with unknown leakage from test objects or systems, permits quantitative measurement of leakage rates. Until recently none of the gross calibration standards available were acceptable. A precision gross leak calibrator has been designed that delivers gas into the leak detector at an absolute known rate. This simple device is convenient to use, has good repeatability, and a recalibration interval of three years. View full abstract»

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  • Elimination of methane from the outer bulb of low‐pressure sodium lamps

    Page(s): 2293 - 2296
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    The presence of methane in the outer bulb of low‐pressure sodium lamps causes undesirable heat losses by conduction through the gas. Methane is formed by the reaction of water vapor or hydrogen gas with traces of carbon in the barium flash getter present in the outer bulb. Elimination of methane has proved to be possible by using a chemical cracking device consisting of, e.g., a supported platinum catalyst. Methane conversion occurs permanently throughout the complete lamp life. After 10 000 h in service the gas pressure is below 10-5 mbar and is only made up of argon and helium. View full abstract»

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  • Experiments on eliminating spherical aberration in electron guns using aspherical mesh lenses

    Page(s): 2297 - 2306
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    Experiments on electron lenses incorporating aspherical meshes are described. Two guns with adjustable position of the aspherical mesh were constructed. In the first, the gap between the mesh and the focus electrode was variable; in the second, the gap was fixed and the mesh could be positioned relative to this gap. It was possible to change the spherical aberration from the usually positive value to zero or even to a negative value. This was verified by calculations. Spot size reductions by a factor of 3 were observed at the highest currents around 5 mA. The minimum spot sizes were obtained for a negative spherical aberration of the lens, which compensates the positive aberration of the object. View full abstract»

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  • Influence of geometric factors of the substrate on hydrophilic surface modification of polyurethane sponges by plasma treatment

    Page(s): 2307 - 2316
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    The surface modification by plasma treatment occurs by consecutive processes of excitation of gas(es) and deexcitation of excited species. The deexcitation occurs primarily at the surface yielding chemical modification of the surface (nonpolymer‐forming plasmas) or deposition of material (polymer‐forming plasma) on the substrate surface. Because of this sequence, geometric factors of the substrate in relation to the surrounding plasma phase have crucial influence on the effectiveness of plasma treatments. Simple mathematical models were developed to illustrate the effect of geometric factors involved in plasma treatments, and experimental results obtained with porous polyurethane sponges in various sizes were examined by the mathematical models for both plasma treatments by O2, H2O, and NH3 and plasma polymerization of acrylic acid. View full abstract»

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  • An automated method for high dynamic range secondary ion image depth profiling

    Page(s): 2317 - 2322
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    A variable parameter mode of digital image acquisition was developed for secondary ion image depth profiling (IDP). The new method substantially extends the dynamic range of the IDP technique by automatically optimizing the detector gain and acquisition time for each individual image. Postacquisition processing of IDP’s allows generation of local area depth profiles (LADP’s) from areas ranging in size from 1 μm2 to the entire image field. Detection limits of LADP’s using the entire image field are within a factor of 2–3 of those obtained using conventional pulse‐counting electron multiplier detection. The lowest detectable signal is limited by camera noise to approximately ten secondary ions per second. A LADP from a 1 μm2 area with a dynamic range of four orders of magnitude was achieved using the variable parameter mode. View full abstract»

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  • X‐ray photoelectron spectroscopy observations of argon‐ion bombardment effects on phase separated structures such as SiNx alloys or Si/Si3N4 interfaces

    Page(s): 2323 - 2327
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    SiNx layers have been prepared in an ultrahigh vacuum (UHV) system by reactive electron beam evaporation of Si under NH3 ambient. In situ x‐ray photoelectron spectroscopy (XPS) measurements show that films formed in this way consist essentially of a Si/Si3N4 mixture on a microscopic scale with the Si and Si3N4 clusters embedded in a subnitride compound. Upon mild Ar‐ion bombardment (ion energy ∼1 keV), the analysis of the Si 2p core level lines for various stoichiometries reveals enhanced subnitride local atomic arrangements. This demonstrates the growth, by atomic redistribution, of the intermediate domains connecting the Si‐rich and nitride domains. With increasing ion energy it is found that the phase separation progressively disappears and finally, within the probed depth, the whole film may be thought of as an homogeneous random bonding alloy. A similar behavior observed on a planar Si/Si3N4 interface, probably explains, for the main part, the diffuse nature of the interface observed in sputter profiling experiments. Evidence for preferential nitrogen sputtering as well as modifications of the XPS valence band upon ion bombardment is presented: Thus ion etching of initially heterogeneous structures results in drastic changes in film composition and structure. The present finding may account for a more homogeneous growth in plasma deposited films where ion bombardment is used during the growth. View full abstract»

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  • Intrinsic interface states and defect states for Si/NiSi2(111)

    Page(s): 2328 - 2330
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    The intrinsic interface states and the states associated with interfacial vacancies have been calculated for the type A Si/NiSi2(111) interface. A prominent band of intrinsic interface states is predicted near and below the Si valence band maximum, Ev, dispersing downward from an energy in the Si band gap to an energy about 1 eV below Ev. This band should be observable in photoemission experiments. Our calculation for the interfacial Si vacancy on the NiSi2 side of the interface yields a level, a few tenths of an electron volt above the valence band edge, that can explain observed Schottky barriers at Si/NiSi2(111) interfaces. View full abstract»

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  • Effect of annealing on the structural and electronic properties of Au covered Si(111) surfaces

    Page(s): 2331 - 2335
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    Low energy electron diffraction (LEED), Auger electron spectroscopy (AES), and photoemission yield spectroscopy (PYS) measurements are performed on a set of cleaved (111)silicon surfaces covered with a gold layer from 0 to 5 ML and vacuum annealed from 400 to 700 °C. The results show that the two dimensional Si–Au alloy which forms upon room temperature deposition transforms upon annealing into an ordered structure a few angstroms thick with the Si atoms in an outward position. This new intermixed layer covers uniformly both the crystalline Si substrate and the Au islands which form on the substrate only when gold in excess of the surface alloy composition has been deposited. View full abstract»

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  • (7×7) and (5×5) superstructures of Ge‐covered Si(111) surfaces studied by angle‐resolved electron‐energy‐loss spectroscopy

    Page(s): 2336 - 2342
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    Using angle‐resolved electron‐energy‐loss spectroscopy (AREELS), (7×7) and (5×5) surface structures of the ultrathin Ge films on Si(111)(7×7) surfaces are investigated. At a coverage of 1.5 monolayers (ML) of Ge, the Si(7×7)–Ge surface appears. On this surface a loss peak due to surface states of Ge dangling bonds appear at 1.15 eV (Δk=0 Å-1) and the one due to Si dangling bonds disappears, but the loss peaks due to the Si–Si backbonds are still observed. When the (5×5) surface structure develops at a coverage of 2 ML, the remaining loss peaks due to the Si–Si backbonds disappear and loss peaks due to Ge–Ge backbond surface states at 9 and 14 eV. We propose structural models of the Si(7×7)–Ge and Si(5×5)–Ge surfaces based on the structural models on the clean Si(7×7) surface [Takayanagi et al., J. Vac. Sci. Technol. A 3, 1502 (1985)]. View full abstract»

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  • The effect of inert gas plasma exposure on the surface structure of hydrogenated amorphous silicon (a‐Si:H)

    Page(s): 2343 - 2349
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    In situ ellipsometry experiments have been used to study the modification of hydrogenated amorphous silicon (a‐Si:H) surfaces exposed to He and Ar plasmas at room temperature in an asymmetric capacitively coupled radio‐frequency (rf) glow discharge reactor. Such a system provides an informative way of studying the microstructural changes caused by ion bombardment at two different accelerating potentials. A photon energy of 3.5 eV is used as a probe in the ellipsometry experiment in order to maximize sensitivity to changes in the volume density of Si–Si bonds near the sample surface. As expected, significant differences are observed between the effects of exposure at the anode and the cathode owing to the greater potential difference between the cathode and the plasma. When the a‐Si:H is exposed to a 0.3 W/cm2 He plasma at the cathode (∼–30 V dc bias), a surface layer with a low density of Si–Si bonds is formed, reaching a thickness of ∼35 Å after 30 min. For a fixed time interval and plasma power, the thickness of the low density layer caused by the He plasma is about 2–3 times greater than that caused by Ar. The surface layer is readily consumed by oxidation and its properties are attributed to the presence of microvoids ≲50 Å in size. For samples exposed to a 0.3 W/cm2 He plasma at the anode (grounded), no significant damage is detected. In this case the effect of the plasma is to remove a very thin oxide overlayer. Thus, ellipsometry experiments are effective in determining plasma operating conditions which result in improved surfaces while minimizing roughness layers and damage. View full abstract»

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  • Transparent carbon films: Comparison of properties between ion‐ and plasma‐deposition processes

    Page(s): 2350 - 2355
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    Optical, electrical, and mechanical measurements were made on transparent carbon films prepared by two different techniques: Ion sputtering of graphite with argon ion co‐bombardment and rf plasma decomposition of hydrocarbon compounds. A comparison between the properties of films deposited by each technique is presented. The films deposited by the plasma process were more transparent, had a lower refractive index, and showed less mechanical stress than the sputtered films. They were softer and electrically less stable than the ion‐sputtered films. Both processes produced films having very low charge density and high resistivity. The simplicity of the plasma process and the ability to cover larger areas makes it the preferred process for the protective coating of optical surfaces on a production basis. View full abstract»

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  • Properties of thin antimultipactor TiN and Cr2O3 coatings for klystron windows

    Page(s): 2356 - 2363
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    Low secondary electron emission yield (1–1.3), low radio‐frequency (rf) loss films are of interest as coatings for alumina ceramic high power klystron windows. Very thin (15–50 Å) Ti and TiN layers have been previously used with success in klystron tubes operating at lower power levels (≪35 MW peak power) and short (2.5 μs) pulses but are subject to property changes during air exposure, tube bakeout (550 °C for up to 10 days) and in situ electron bombardment. Higher power tubes (≥50 MW) with longer (5 μs) pulse lengths require coatings that remain stable under these more rigorous conditions in order to avoid multipactoring and window failure due to overheating. Air‐oxidized Cr films offer an alternative to TiN. This work shows that they have the required resistivity for low rf loss, combined with stability in the secondary electron emission (SEE) yield under bakeout and electron bombardment. SEE, AES, XPS, ELS, oxidation, bakeout, and electron bombardment results are presented for Cr and TiN layers deposited by sputtering onto high density alumina substrates. The surface of TiN oxidized to a 9 Å thick TiO2 layer which, under bakeout to 550 °C in vacuum, thinned to 6 Å. This extreme layer thinness resulted in a significant drop in the SEE yield which, unfortunately, was reversible upon reoxidation. The oxidized layer on Cr was 17 Å of Cr2O3 which thinned to 13 Å upon bakeout. This thicker oxide layer produced a stable SEE yield which, although not as low as oxidized TiN, is sufficient to prevent electron multipactor. Windows covered by air‐oxidized Cr films are at least as good, under tube processing conditions, as the best TiN‐coated windows. View full abstract»

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  • Magnetoresistance effect of Ni–Fe film formed by ion beam sputtering

    Page(s): 2364 - 2368
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    This paper reports the result of experimentally investigating the magnetoresistance effect in Ni–Fe films formed by ion beam sputtering (IBS). Although IBS‐formed Ni–Fe film has a well‐defined uniaxial magnetic anisotropy and high permeability, its magnetoresistance effect is smaller than that of film formed by radio‐frequency (rf) sputtering. This small magnetoresistance effect was found to be caused by an increase in film resistivity rather than by a decrease in magnetoresistivity. The increase in resistivity cannot be explained merely by impurity concentration; it is also due to defects produced by Ar+ ion bombardment and the impingement of particles with relatively high energies. When the substrate temperature was higher than 220 °C, the resistivity became smaller as the substrate temperature was increased because of both having larger crystal grains and recovery of defects. View full abstract»

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  • Growth of microprojections arising from sputter etching of Cu–Ag sandwich

    Page(s): 2369 - 2372
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    It is demonstrated that the sputter etching of a Cu–Ag sandwich using a focused Ar+‐ion beam creates a crater covered with densely distributed microprojections, offering a crater‐edge profile poor in resolution. The projections grew in a variety of shapes, ranging from a rod to a wide‐angle cone, and their number density reached ∼109/cm2. The dimensions of the projections were also not uniform, increasing discernibly with depth. It is believed that an enhanced surface mobility of Cu and Ag atoms during the sputtering played a role in growing the projections. View full abstract»

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  • Anomalous structures in thin In–Ge films

    Page(s): 2373 - 2376
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    We present structural studies of coevaporated thin In–Ge films. At high thicknesses they show random percolation structure. At low thicknesses no sharp percolation threshold is observed. Annealing induces the appearance of orientational clusters which span to a length scale of ∼300 times the crystallite size. Their fractal dimension was found to be 1.65±0.1. View full abstract»

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  • Preparation of amorphous electrochromic tungsten oxide and molybdenum oxide by plasma enhanced chemical vapor deposition

    Page(s): 2377 - 2383
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    Preliminary experiments have been performed to probe the feasibility of using plasma enhanced chemical vapor deposition (PE–CVD) to prepare electrochromic thin films of tungsten oxide and molybdenum oxide by plasma reaction of WF6, W(CO)6, and Mo(CO)6 with oxygen. Thin films produced in a 300 W, electrodeless, radio‐frequency (rf), capacitive discharge were found to be electrochromic when tested with either liquid or solid electrolytes. Optical spectroscopy was performed on two electrochromic coatings after Li+ ion insertion from a propylene carbonate liquid electrolyte. Broad absorption peaks at ∼900 nm for WO3 and 600 nm for MoO3 were observed. Optical results for PE–CVD MoO3 films differ from those reported for evaporated MoO3 films which have an absorption peak at ∼800 nm. The shorter wavelength absorption in the PE–CVD MoO3 films offers the potential for fabricating electrochromic devices with higher contrast ratios and less color change. Optical emission spectroscopy, Auger, and x‐ray diffraction analyses indicate these thin film deposits to be predominantly amorphous tungsten and molybdenum oxides. View full abstract»

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  • A note on flow rate and leak rate units

    Page(s): 2384 - 2385
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    The confusion in the literature and in the laboratory surrounding the terminology and units of gas flow rates, particularly as applied to calibrated leak artifacts, has prompted this discussion of leak rate units. Special attention is paid to conflicting usages of the term ‘‘throughput,’’ and how this frequently leads to the loss of crucial information about the gas temperature and hence the true gas flow rate. The advantages of expressing leak rates in ‘‘mol/s,’’ avoiding the complications of both the explicit mention of temperature in the unit and the need for agreement on ‘‘standard’’ temperature and pressure, are also discussed. View full abstract»

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  • Evolution of protrusions during sputtering from composite Ag–Si targets

    Page(s): 2388 - 2390
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    In this paper we describe studies on the effects of the sputtering pressure and power on shape and size of microscopic protrusions formed on a target consisting of a small Ag plate placed on a Si wafer. The influence of the target topography change during sputtering on the composition of the sputter‐deposited film was investigated. It was found that the Ag concentration of the deposited films was considerably reduced with the growth of the target surface protrusion on Ag plates. This is considered to be attributable to the prevention of sputtered atoms from escaping from the target by surface protrusions. View full abstract»

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Aims & Scope

The Journal of Vacuum Science and Technology A is devoted to reports of original research, review articles, and Critical Review articles.

Full Aims & Scope

Meet Our Editors

Editor
G. Lucovsky
North Carolina State University