bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure and corrosion properties of PVD Cr–N coatings
Authors: Liu C. , Bi Q. , Ziegele H. , Leyland A. , Matthews A.
Published: July 2002

PVD Cr–N coatings produced by physical vapor deposition (PVD) are increasingly used for mechanical and tribological applications in various industrial sectors. These coatings are particularly attractive for their excellent corrosion resistance, which further enhances the lifetime and service quality of coated components. PVD Cr–N coated steels in an aqueous solution are usually corroded by galvanic attack via through-coating “permeable” defects (e.g., pores). Therefore, the corrosion performance of Cr–N coated steel is determined by a number of variables of the coating properties and corrosive environment. These variables include: (i) surface continuity and uniformity; (ii) through-coating porosity; (iii) film density and chemical stability; (iv) growth stresses; (v) interfacial and intermediate layers; (vi) coating thickness; (vii) coating composition; and (viii) substrate properties. In this article, PVD Cr–N coatings were prepared, by electron-beam PVD and sputter deposition, with different compositions, thicknesses, and surface roughnesses, by changing the N2 flow rate, applying multilayering techniques and changing the substrate finish prior to coating. The microstructure of such coatings is investigated by various analytical techniques such as glancing angle x-ray diffraction and scanning electron microscopy, which are also correlated with the corrosion performance of the coated steel. Both dc polarization and ac impedance spectroscopy were employed to investigate the corrosion resistance of Cr–N coated steel in a 0.5N NaCl solution. It has been found that the N2 flow rate during reactive deposition strongly determines the microstructure of Cr–N coatings (due to the changing nitrogen content in the film) and can thus affect the corrosion resistance of coated systems. The surface finish of the steel substrate also affects the uniformity and coverage of PVD coatings; grooves and inclusions on the original substrate can raise the susceptibility of coated systems to crevice corrosion. Increased coating thickness can also greatly reduce the incidence of through-coating porosity such that the improvement in corrosion performance of thicker Cr–N coatings is significant.
Density of Thin Evaporated Aluminum Films
Authors: Hartman Thomas E.
Published: July 2002

The mass per unit area of evaporated aluminum films was measured with a piezoelectric quartz crystal microbalance. The thickness of the films was measured by multiple beam interferometry. The density of the films was determined from the sensitivity of the microbalance for a set of aluminum films ranging in thickness from a few hundred to a few thousand angstroms. The sensitivity of the microbalance was determined for a set of AT-cut quartz crystals ranging in fundamental frequency from 2 to 10 Mc/sec. The density of the thinner films is less than the thicker films but rapidly approaches a value of 2.61±0.03 g/cm3 for films in excess of 500 Å. This value is about 3% less than the value of 2.70 g/cm3 for bulk aluminum. The aluminum films were evaporated in a pressure of 2×10−6 Torr with normal incidence on unheated glass and quartz substrates. The low density of the films cannot be explained on the basis of oxide formation in the residual atmosphere. The most likely explanation is that the films are porous which is partially confirmed by surface replication transmission electron micrographs.
Mechanism of silicon etching by a CF4 plasma
Authors: Mauer J. L. , Logan J. S. , Zielinski L. B. , Schwartz G. C.
Published: July 2002

The mechanisms for the reactive ion etching of silicon by CF4 plasma are investigated. A model is proposed whereby silicon is etched by chemical reaction with free fluorine to produce a volatile species, and also by physical sputtering. The chemical etching is shown to be enhanced by ion bombardment of the reacting surface. This etching process, together with a model for cracking CF4 in the plasma, is evaluated by comparison to actual etch rates. Experimentally, the silicon etch rate is observed to decrease with increasing silicon area, by what is called the loading effect. The functional form of the loading effect, as predicted by the model, is fitted to experimental loading curves. The contributions of the various etching components are separated, to yield empirical values for the enhancement of the chemical reaction by physical sputtering.
Surface activities of Mg in Al alloys
Authors: Sun T. S. , Chen J. M. , Viswanadham R. K. , Green J. A. S.
Published: July 2002

The loss of Mg from Mg-containing Al alloys during heat treatments is a well-known metallurgical problem. Recent studies revealed that regardless of whether the loss of Mg is via formation of MgO in air or via evaporation of Mg in vacuum, the kinetics is primarily controlled by a surface reaction and is described by the relation dC/dt=−M (C−C∞) where C is the Mg concentration in the specimen, and M and C∞ are temperature-dependent constants. However, the specimens used in these studies contained air-formed oxide, and their surface conditions were not characterized. In order to understand the detailed mechanisms, it is necessary to study the surface activity of Mg from well-characterized specimens, using surface sensitive tools. We have studied the loss of Mg from high-purity Mg-containing Al alloys using AES and XPS. The results show that the kinetics of Mg loss from an oxide-covered surface is actually controlled by the diffusion of Mg in the oxide, and that the loss of Mg in vacuum from an oxide-free surface is primarily limited by bulk diffusion. Furthermore, the results also show that the oxidation of a clean surface of these alloys is self-limiting, as in the case of pur Al metal; however, the reaction of Mg with oxygen persists beyond that of Al, resulting in an enrichment of MgO in the oxide layer. Results of other related issues, such as the reduction of Al2O3 by Mg, are also presented.
Sputtering of single and multiple component materials
Authors: Sigmund Peter
Published: July 2002

This article summarizes the basic assumptions underlying conventional sputtering theory and their implications. An attempt will be made to specify those areas where existing theory appears to be confirmed as well as other areas where considerable uncertainties prevail. Specific comments concern the significance of spike phenomena as opposed to linear collision cascades, sputtering of compounds, recoil implantation, and atomic mixing.
Outgassing characteristics of TiC and TiB2 coated graphite
Authors: Craig J. H.
Published: July 2002

Two coatings to minimize high-Z contaminant release in plasma devices are TiB2 and TiC chemically vapor deposited on Poco graphite. Total outgassing rate and mass spectra measurements have been conducted on the materials at room temperature, 100°C and 250°C.(AIP)
XPS measurement of GaAs–AlAs heterojunction band discontinuities: Growth sequence dependence
Authors: Waldrop J. R. , Kowalczyk S. P. , Grant R. W. , Kraut E. A. , Miller D. L.
Published: July 2002

We report the direct measurement, by x-ray photoemission spectroscopy, of the valence-band discontinuity, ΔEv, for two types of abrupt GaAs–AlAs (110) heterojunctions grown by molecular beam epitaxy: (i) those formed by growth of GaAs on AlAs, and (ii) those grown in the reverse sequence, AlAs on GaAs. The ΔEv at GaAs–AlAs interfaces is, on average, 0.25 eV larger than at AlAs–GaAs interfaces. The ΔEv for GaAs–AlAs heterojunctions was found to average 0.4 eV; the corresponding ΔEv for AlAs–GaAs heterojunctions averaged 0.15 eV. The 0.25 eV difference in average ΔEv value that we observe for the two types of interface demonstrates that the energy-band discontinuities depend on growth sequence in the GaAs–AlAs heterojunction system.
Surface diffusion activation energy determination using ion beam microtexturing
Authors: Rossnagel S. M. , Robinson R. S.
Published: July 2002

The activation energy for impurity atom (adatom) surface diffusion can be determined from the temperature dependence of the spacing of sputter cones. These cones are formed on the surface during sputtering while simultaneously adding impurities. The impurities form clusters by means of surface diffusion, and these clusters in turn initiate cone formation. Values are given for the surface diffusion activation energies for various materials on polycrystalline Cu, Al, Pb, Au, and Ni. The values for different impurity species on each of these substrates are approximately independent of impurity species within the experimental uncertainty, suggesting the absence of strong chemical bonding effects on the diffusion.
Metal shell technology based upon hollow jet instability
Authors: Kendall J. M. , Lee M. C. , Wang T. G.
Published: July 2002

Spherical shells of submillimeter size are sought as ICF targets. Such shells must be dimensionally precise, smooth, of high strength, and composed of a high atomic number material. We describe a technology for the production of shells based upon the hydrodynamic instability of an annular jet of molten metal. We have produced shells in the 0.7–2.0 mm size range using tin as a test material. Specimens exhibit good sphericity, fair concentricity, and excellent finish over most of the surface. Work involving a gold–lead–antimony alloy is in progress. Droplets of this are amorphous and possess superior surface finish. The flow of tin models that of the alloy well; experiments on both metals show that the technique holds considerable promise.
Magnetic field enhanced reactive ion etching of polyimide
Authors: Yeh J. T. C. , Grebe K. R. , Palmer M. J.
Published: July 2002

Magnetic field enhanced reactive ion etching of polyimide was investigated using a planar magnetron discharge. Etch studies were conducted with various gas composition, power, and pressure conditions. Etch rates of fully cured polyimide up to 2.5 μm/min were achieved in an oxygen plasma at 6.65 Pa with cathode voltage of about −200 V. The etching nonuniformity caused by localized magnetic field was found to be pressure dependent. Relative motion between the substrates and the magnet assembly improved the uniformity. Patterning of polyimide was achieved by using both erodible and nonerodible masks.
Magnetron sputtering sources for ferromagnetic material
Authors: Window B. , Sharples F.
Published: July 2002

Magnetically enhanced sputtering configurations suited to the dc sputter deposition of ferromagnetic materials at a high rate are discussed. The characteristics of two different types of sources are described and compared with those of a conventional planar magnetron of similar size and construction.
A technique for comparing Auger electron spectroscopy signals from different spectrometers using common materials
Authors: Baer D. R. , Thomas M. T.
Published: July 2002

A simple procedure is outlined to obtain relative sensitivity curves that allow data collected on one Auger electron spectrometer to be related to data collected on a different spectrometer or to a standard data set. Data collected on three CMA systems demonstrate that dN/dE peak-to-peak amplitude ratios for pure elements can vary considerably but in a systematic manner for different systems. Such differences can be produced by variations in system design, by specimen or electron gun alignment, spectrometer contamination or other problems. However, if the differences in relative sensitivity are considered in the data analysis, data sets from different systems can be interrelated with reasonable accuracy.
Imaging properties and energy aberrations of a double-pass cylindrical-mirror electron energy analyzer
Authors: Erickson N. E. , Powell C. J.
Published: July 2002

The imaging properties and energy aberrations of a commercial double-pass cylindrical-mirror analyzer have been characterized using an extension of the method recently reported by Seah and Mathieu. The electron beam from the coaxial electron gun was rastered across a test surface and the intensity of either elastically scattered electrons or of electrons at other selected energies was stored in a computer as a function of beam position on the specimen and other experimental parameters. The intensity data were later plotted to provide an ‘‘image’’ of the detected intensity. Images of this type are presented for electron energies of 100, 500, and 1000 eV and for the application of small offset voltages (typically between −1 and +5 V) between the analyzer and the gun cathode with the instrument operated in conditions appropriate for XPS or AES. Small offset voltages (<1.5 V) lead to significant changes in image shapes while larger offset voltages (≳5 V) lead to image shapes similar to those for the elastic peak but with 20%–40% increased widths. Deflection of the incident beam by up to 2 mm from the axis caused variations of up to ±0.15 eV in the measured positions of the elastic peak. Our observations can be interpreted qualitatively in terms of the known relationship between detected signal and combinations of position of electron emission from the specimen, angle of emission, and electron energy. The images obtained with elastically and inelastically scattered electrons provide a convenient and quantitative means of assessing instrument performance and of defining the specimen area being analyzed for the particular combination of instrument operating conditions and the energy width of AES or XPS features from the specimen.
Prospects for printing very large scale integrated circuits with masked ion beam lithography
Authors: Randall J. N.
Published: July 2002

Ions hold a number of advantages over UV photons, x-ray photons, and electrons when used for high resolution printing. Masked ion beam lithography (MIBL) has demonstrated many of the requirements of a very large scale integrated (VLSI) lithographic tool. Some of the different approaches to MIBL and their advantages will be discussed.
Strain effects in Hg1−xCdxTe (x∼0.2) photovoltaic arrays
Authors: Weiss Eliezer , Mainzer Nili
Published: July 2002

The effect of stress and strain on the performance of Hg1−xCdxTe (x∼0.2) photovoltaic arrays was studied both in the dark and under illumination. Stress, external as well as internal, affects the current–voltage characteristic of the photodiode. The combined action of illumination and strain yields an anomalous response to light absorption in the device. A model is conceived wherein the photodiode and guard ring are treated as a metal-insulator semiconductor field effect transistor (MISFET). Stress developed in the vicinity of small contact windows causes n-type damage, which brings about a forward bias in the device. The effect of strain on the reverse current of the photodiode is explained by a change in the n-channel conductivity of the MISFET. This change is caused by charges which are due either to a piezoelectric effect or n-type damage. Using this model observed phenomena in Hg1−xCdxTe photovoltaic arrays are explained, as due to internal stresses originating from wafer deformation.
Stresses in multilayer combinations of sputter deposited coatings of Ni, Ti, TiC+Ni, and TiB2+Ni on carbon steel substrates
Authors: Chambers D. L. , Taylor K. A. , Wan C. T. , Susi G. T.
Published: July 2002

When hostile abrasive conditions are encountered, surface protection in the form of hard erosion resistant coatings is required. TiC+Ni and TiB2+Ni coatings with combinations of Ni and Ti interfacial coatings were deposited on carbon steel substrates by magnetically enhanced dc sputtering. Thicknesses of the erosion resistant coatings ranged from 8.0 to 12.0 μm and the thicknesses of the interfacial coatings ranged from 2.5 to 9.0 μm. The relationship between erosion resistance and stresses in the coatings were evaluated. Stress measurements were obtained using the bending beam method where stress is determined from the measured deflection of a cantilevered composite material type beam formed by the coating–substrate combination using the equivalent stiffness (EI) method to determine intrinsic, thermal, and shear stress components. Erosion resistance was measured by bombarding the surface of the TiC+Ni and TiB2+Ni coatings with a high-velocity flow of hard alumina particles.
Scanning tunneling microscopy studies of Pd–Sn catalyzed electroless Cu deposited on pyrolytic graphite
Authors: Siperko L. M.
Published: July 2002

Pyrolytic graphite (PG) has been found to be a suitable substrate for adsorption of a Pd–Sn catalyst commonly used as an initiator for deposition of electroless Cu on printed circuit boards. Adsorption on the basal (0001) plane is minimal and results in a highly ordered array of subnanometer catalytic clusters influenced by the substrate order. Significant adsorption, however, takes place at defects, boundaries, and edge planes, resulting in large clusters and patterns that follow the nanometer scale topography of the PG surface. Subjecting a seeded substrate to electroless Cu deposition for 30 sec results in a copper layer, which may be detected by both scanning tunneling microscopy (STM) and square wave voltammetry. STM indicates that the initial copper deposit, which also assumes order on a subnanometer scale, plates uniformly over the seed, resulting in large clusters that accumulate at significant seed adsorption sites.
Low temperature, low pressure CdZnS films produced by metalorganic chemical vapor deposition
Authors: Smith Patricia B.
Published: July 2002

CdxZn(1−x)S thin films were deposited on (100) Si at low temperature and low pressure from the reaction of dimethylzinc, dimethylcadmium, and hydrogen sulfide. A possible application of mixed metal-sulfide films as novel insulators in metal–insulator–semiconductor structures in HgCdTe-based infrared devices provides the motivation for studying the physical properties of the CdZnS films. The films were produced over a 25 to 125 °C range of deposition temperature, and deposition pressure less than 1 Torr. No carrier or diluent gases were used. The polycrystalline films have been characterized by x-ray photoelectron spectroscopy (XPS), scanning electron microscopy, Rutherford backscattering spectroscopy (RBS), and x-ray diffraction. Films with cadmium fractions of zero to 0.75 have been produced and characterized. The growth rate ranges from 4 to 145 Å/s. XPS indicates 1%–2 at. % oxygen contamination in the films, and about 3 at. % carbon within the bulk of the films. The cadmium mole fraction was determined by RBS and XPS. Film stress was determined by measurement of wafer bow, using x-ray diffraction.
Measurement of the surface dynamics of RbCl(001) via high resolution He atom scattering
Authors: Bishop G. G. , Duan J. , Gillman E. S. , Safron S. A. , Skofronick J. G.
Published: July 2002

High resolution He atom scattering experiments have been carried out on the cleaved RbCl(001) surface in the 〈100〉 direction. For most of the experiments reported here the incident He atom wave vector ki was ∼8 Å−1 (corresponding to incident energy Ei≊33 meV) and the target temperature was ∼190 K. Both the Rayleigh wave and a surface optical mode lying in the gap between the bulk acoustic and optical bands (the S2 mode) were observed. The measured surface dispersion branches are compared with model calculations of surface dispersion for both a relaxed and an unrelaxed RbCl(001) surface. The calculated Rayleigh mode dispersion is very nearly the same in both models and agrees well with the experimental results. The experimental optical mode data appear to fit the calculations only in part for each model. A comparison of the RbCl results with previously measured KBr surface dispersion curves shows that their dynamics are largely the same, but with significant differences for part of the S2 mode close to the zone center and for the crossing resonance.
Radio frequency plasma jet applied to coating of internal walls of narrow tubes
Authors: Bárdoš L. , Berg S. , Baránková H.
Published: July 2002

A novel method for deposition of thin films onto internal walls of narrow tubes is described. The method is based on sputtering and/or evaporation of the end of a nozzle in a radio frequency plasma jet system (RPJ). A Ti nozzle of 5 mm outer and 2 mm inner diameter, respectively, was used for TiNx film deposition onto Si substrate inserts fixed on the internal wall of a steel tube of 8 mm bore. The axial distribution of the film thickness along 20–50 mm of deposited area was measured. An effect of separation of macroparticles was found in the RPJ. This enabled the growth of high quality films on the tube walls at rf power levels exceeding 100 W.
Implant-damage isolation of InP and InGaAsP
Authors: Akano U. G. , Mitchell I. V. , Shepherd F. R. , Miner C. J. , Rousina R.
Published: July 2002

The creation of high resistivity layers by ion implantation of doped InP and InGaAsP epilayers, and the potential of the implant-isolation technique for the fabrication of InP-based ridge waveguide lasers, have been investigated. InP and InGaAsP samples, doped with 5×1017 cm−3 Si or Zn, were implanted with multiple-energy 4He or 16O. Ridge waveguide lasers, with ∼0.7 μm dielectric masks to protect the ridge, were implanted with 18O ions. In all cases, the implantation beam flux was maintained at 0.01 μA cm−2. Following 30 s rapid thermal annealing (RTA) in the temperature range 350–750 °C, the sheet resistivities of the InP and InGaAsP samples were determined using either a contactless eddy current or Hall effect measurements. The results show that in both InP and InGaAsP high resistivity layers (∼105 Ω/⧠) are produced by He or O implantation. The thermal stability of the implant-induced isolation depends on the material, the doping type, and the ion dose. High sheet resistivity, stable against 30 s RTA, can be maintained for temperatures up to 550 °C, sufficient for device processing. For samples implanted to calculated (trim) defect concentrations of ∼4×1021 cm−3, p- to n-type conductivity conversion was observed for both InP and InGaAsP.
The effect of the presheath on the ion angular distribution at the wafer surface
Authors: Zheng Jie , Brinkmann Ralf P. , McVittie James P.
Published: July 2002

Knowledge of the ion angular distribution at the wafer plane in an etching plasma is critical for the modeling of the etched profiles. Previously this distribution was thought to be mainly influenced by the magnitude of the sheath voltage and by the collisions which ions encountered in the sheath. This work shows that the acceleration and collisions which the ions experience in the presheath region are also important in determining the ion angular distribution and in shaping the final etching profile.
Measurement of the gas temperature in fluorocarbon radio frequency discharges using infrared absorption spectroscopy
Authors: Haverlag M. , Stoffels E. , Stoffels W. W. , Kroesen G. M. W. , de Hoog F. J.
Published: July 2002

The translational gas temperature was measured in 13.56 MHz radio-frequency (rf) discharges in CF4 and CHF3. Infrared absorption spectra of CF4 and CF2 were recorded using a tunable diode laser and the gas temperature was deduced from the linewidths of the absorption lines of these molecules. It is shown that linewidth measurements yield a simple and direct method to determine the gas temperature, with an accuracy up to ∼10 K. The results obtained in CF4 and CHF3 plasmas indicate that the translational temperatures of all particles investigated in these plasmas are, at most, 50 K above the room temperature. The temperature increases with increasing gas pressure and rf power, but it is independent of the flow rate. This is attributed to an increased heating rate of the gas. Moreover, it was found that the temperature rise is significantly smaller in CHF3 than in CF4, under the same plasma conditions. This can be attributed to a higher power dissipation by chemical conversion of the parent gas in a CHF3 discharge, as compared with a CF4  plasma.
Blackening of argon/mercury cold cathode discharge lamps
Authors: Thielen M. , Wassermann E. F.
Published: July 2002

We report about the physical and chemical origin of the quick loss of intensity of certain argon/mercury cold cathode illumination tubes, especially those manually coated with luminous powder using the European powder technology. The reason is the disintegration of the phosphoric acid binder, which leads to the release of water vapor in the operating plasma tube. Subsequently formed mercury–water complexes lower the intensity of the UV emission of the Hg discharge in the 250 nm range, because the complexes decay radiationless into the ground state, thus, reducing the brightness of the fluorescent powder in the visible range substantially. If shut off, the respective tubes show a turn in color of the luminous powder coating from white to a light brown. We also found that the released water vapor causes heavy sputtering of the activated hollow-cathode-type nickel electrodes. Possible reasons for this are discussed, too.
Structure and chemical composition of fluorinated SiO2 films deposited using SiF4/O2 plasmas
Authors: Han Sang M. , Aydil Eray S.
Published: July 2002

Attenuated total reflection Fourier transform infrared spectroscopy and spectroscopic ellipsometry were employed for chemical and structural analysis of fluorinated SiO2 deposited in SiF4 and O2 plasmas. Isotopic substitution of 16O2 with 18O2 in the feed gas mixture was used to determine whether F is bonded to Si or O atoms in the film. Isotopic substitution experiments revealed that infrared active SiO–F stretching mode in SiO2 matrix appears at 1372 cm-1 but only when the SiF4-to-O2 ratio of the feed gas mixture is reduced below 0.1. The SiOF species in fluorinated SiO2 result from insertion of O into SiF bonds, which have been already incorporated into the film. Deposition experiments using 16O2 and 18O2 also helped identify silicon mono- and di-fluorides (O3SiF and O2SiF2), which were most abundant in fluorinated SiO2. The stretching mode of O3Si–F appears at 950 cm-1, whereas the antisymmetric and symmetric stretching modes of O2Si–F2 appear at 990 cm-1 and 920 cm-1, respectively. The concentration of silicon fluorides increase monotonically with increasing SiF4-to-O2 ratio. The increase in silicon fluoride concentration causes the Si–O–Si phonon peaks to blueshift and narrow by relaxing the Si–O–Si bond angle and by decreasing the film density. Narrowing of the SiO2 phonon at 1080 cm-1 is due to SiOSi bond angle relaxation and not due to a more homogenous and ordered fluorinated SiO2 structure than unfluorinated SiO2 as suggested in previous reports. This bond angle relaxation and density reduction are accompanied by a decrease in the refractive index. Although the low refractive index signals low dielectric constant, the chemical susceptibility of SiF to O2 and H2O limits the maximum allowable silicon fluoride concentration in SiOF films to approximately 11 at. %.
Surface reaction of CF2 radicals for fluorocarbon film formation in SiO2/Si selective etching process
Authors: Inayoshi Muneto , Ito Masafumi , Hori Masaru , Goto Toshio , Hiramatsu Mineo
Published: July 2002

The surface reaction of CF2 radicals on Si and fluorocarbon films was investigated in electron cyclotron resonance (ECR) Ar and H2/Ar downstream plasmas employing CF2 radical injection technique. The effects of Ar+ ions, Ar* metastable species and radiation from plasmas on the fluorocarbon film formation were evaluated in ECR Ar downstream plasma with CF2 radical injection. As a result, CF2 radicals with assistance of Ar+ ion bombardment were found to play an important role in the fluorocarbon film formation. The adsorptive reactions of CF2 radicals on the fluorocarbon film surface with and without Ar and H2/Ar plasma exposures were successfully investigated by in situ Fourier transform infrared reflection absorption spectroscopy and in situ x-ray photoelectron spectroscopy. It was found that the formation of fluorocarbon film in the plasma proceeded through the adsorptive reaction of CF2 radicals at a high probability on the active sites formed by the bombardment of Ar+ ions on the fluorocarbon film surface.
Use of the quartz crystal microbalance to measure the mass of submonolayer deposits: Measuring the stoichiometry of surface oxides
Authors: Narine S. S. , Slavin A. J.
Published: July 2002

This article describes a high-resolution quartz crystal microbalance (QCM) with a reproducibility of 0.2 Hz at 6 MHz, provided the frequency is always measured at the same temperature of the microbalance to within 0.1 °C. This enables the microbalance to measure a change in mass equivalent to about 0.1 monolayer of oxygen atoms. Due to its high mass sensitivity, the QCM can be used for absolute measurements of the stoichiometry of ultrathin oxide films. An absolute measure of the stoichiometry of ultrathin metal oxides is difficult to obtain by other means. In this technique, one measures the frequency shift after the deposition of about one monolayer of the metal film onto the gold electrode of the quartz crystal, in ultrahigh vacuum. The deposited film is then oxidized to completion in a low pressure of oxygen gas, and the frequency shift measured again, at the same temperature as before. The ratio of the frequency shifts and the atomic masses gives the oxide stoichiometry. Following the complete oxidation of submonolayer amounts of Sb on the polycrystalline gold electrode of the QCM, the ratio of oxygen to antimony atoms was measured to be unity. However, it is suggested that the stoichiometry of the oxide formed may be SbAuO rather than SbO, since the latter does not satisfy valency considerations. The accuracy of the microbalance measurements has been checked using an inductively coupled-plasma mass spectrometer, which can easily measure, ex situ, the mass of a monolayer deposit with an accuracy of a few percent.
Langmuir probe studies of a transformer-coupled plasma, aluminum etcher
Authors: Malyshev M. V. , Donnelly V. M. , Kornblit A. , Ciampa N. A. , Colonell J. I. , Lee J. T. C.
Published: July 2002

Spatially resolved positive ion densities (ni+), electron densities (ne), electron temperatures (Te), plasma potentials (Vp), and floating potentials (Vf) were measured with a scanning Langmuir probe (PMT FastProbe) in Cl2 and BCl3/Cl2, inductively coupled plasmas (Lam Research Alliance, transformer-coupled plasma (TCP) metal etcher with a high-flow chamber). Time-resolved ion saturation current was measured during etching of Al/TiN metal stacks. Device damage during the metal stack etching was also studied. Positive ion densities increase nearly linearly with power for all of the gases. The maximum plasma density in the reactor is independent of pressure. The density profiles in the plane of the wafer are peaked above the center of the wafer at low pressure and off center at high pressure. Peaking off center is enhanced for smaller height-to-radius ratio chamber configurations, varied by changing the TCP window–wafer chuck gap. The ni+ uniformity across the wafer depends weakly on power, more strongly on feed gases and radio frequency bias, and most strongly on pressure and the TCP window–wafer gap. Within experimental error, Te is uniform across the reactor at most pressures with a slight fall off beyond the wafer edge. At the lowest pressure, Te dips slightly in the center of the reactor. Addition of 28% BCl3 to a Cl2 plasma causes a 20% decrease in Te due to a decrease in the effective ionization potential of the gas. A small, grounded aluminum electrode was inserted into the plasma to eliminate perturbations from the Langmuir probe on the plasma, caused by charging and discharging of the insulating walls of the reactor. Such perturbations make apparent Te, Vf, and Vp, values too high, and at least partly explain why Te’s measured with the Langmuir probe were higher than those obtained from optical emission spectroscopy.
Planar laser-induced fluorescence of CF2 in O2/CF4 and O2/C2F6 chamber-cleaning plasmas: Spatial uniformity and comparison to electrical measurements
Authors: Steffens Kristen L. , Sobolewski Mark A.
Published: July 2002

Planar laser-induced fluorescence (PLIF) measurements were made to determine two-dimensional spatial maps of CF2 density as an indicator of chemical uniformity in 92% CF4/O2 and 50% C2F6/O2 chamber-cleaning plasmas at pressures between 13.3 Pa (100 mTorr) and 133.3 Pa (1000 mTorr). Measurements were also made of broadband optical emission and of discharge current, voltage and power. All measurements were made in a Gaseous Electronics Conference Reference Cell, a capacitively coupled, parallel-plate platform designed to facilitate comparison of results among laboratories. The CF2 PLIF and emission results were found to correlate with discharge current and voltage measurements. Together, these optical and electrical measurements provide insight into the optimization of chamber-cleaning processes and reactors, suggest new methods of monitoring plasma uniformity, and identify important spatial effects which should be included in computer simulations.
Design and characterization of high capacity nonevaporable getter pumps embedded inside the interaction regions of DAΦNE
Authors: Giannantonio Roberto , Manini Paolo , Mazza Francesco , Dominoni Danilo , Clozza Alberto , Zanin Lucio
Published: July 2002

The DAΦNE Φ-factory is a twin-ring 510 MeV e+e- collider facility under commissioning at INFN-LNF in Frascati. With a stored beam current of 5.3 A, a mean pressure of 1.3×10−9 mbar is required in each ring. For the KLOE interaction region, where a mean pressure of the order of 1.3×10−10 mbar is required, an embedded nonevaporable getter (NEG) pump with a CapaciTorr®-type structure was chosen mainly because of the unavailability of room for the installation of lumped pumps and to take maximum advantage of the sorption capability of the NEG pump for CO in the UHV operating conditions of the machine. A NEG pumping system of the kind discussed in this article seemed to be particularly suitable for the KLOE experiment, where limited servicing and high reliability is required. In this article we report on the design and characterization of both the first pump prototype, fitted with St-172 NEG alloy and the final pump version, where St-185 NEG alloy was used.
Temperature dependence of structure and electrical properties of germanium–antimony–tellurium thin film
Authors: González-Hernández J. , Prokhorov E. , Vorobiev Yu.
Published: July 2002

The interest in the study of Ge:Sb:Te thin films is due to their use as optical and electrical memory materials. Both of these applications are based on the structural change from the amorphous to the crystalline state. Thus, understanding of the mechanism of crystallization in this material is important from basic and technological points of view. In this work we have studied the kinetics of the crystallization of Ge:Sb:Te films prepared by thermal evaporation. For that, in situ resistance and capacitance measurements during heating were used. The transformation kinetics from the amorphous to the crystalline state were analyzed using the Kissinger model, from which the activation energy of the crystallization process is obtained. Using x-ray diffraction, Raman spectroscopy and optical microscope measurements, we have observed that during heating at different heating rates, crystallization of the film is accompanied by the segregation of micrometric inclusions formed by amorphous tissue, perhaps some segregated impurities and crystalline tellurium particles. The number and size of these inclusions depend on the heating rate. From our measurements we found that the capacitance measurements is a sensitive method by which to analyze the crystallization process in thin films. It provides additional information not obtained using other methods.
Al2O3 as an antireflection coating for InP/InGaAsP LEDs
Authors: Chin A. K. , Zydzik G. , Singh S. , Van Uitert L. G. , Minneci G.
Published: July 2002

Front-emitting InP/InGaAsP LEDs are presently used for optical communications. They operate at 1.3 μm, the wavelength at which dispersion is minimum for silica fibers. In this paper, we discuss the use of an electron-beam-deposited Al2O3 antireflection coating to increase the coupled power from a 1.3-μm InP/InGaAsP LED and thereby increase the transmission distance as well. Al2O3 is chosen since its index of refraction (n∼1.77) is very close to the optimum value of n=1.79 for a single layer AR coating on InP at λ=1.3 μm. Additionally, the Al2O3 coefficient of thermal expansion (α∼5.6×10−6/K) nearly matches that of InP (α∼4.5×10−6/K). A factor of 1.31 ± 0.08 increase in power, butt-coupled into an FT3 fiber, was obtained after coating 1.3-μm InP/InGaAsP LEDs with a 1850-Å-thick Al2O3 film. Furthermore, the Al2O3 coating process is simple and produces AR coatings which compare favorably with optimum hydrogen containing silicon nitride films.
Electronic properties of the reconstructed Si(111) 7×7 surface
Authors: Chang Yia-Chung
Published: July 2002

Electronic properties of the Si(111)-7×7 surface have been examined in several structure models, including the Lander’s vacancy, Cardillo’s triangular trough, and McRae’s island models. The surface–atom resolved local density of states for these models are calculated in a realistic tight-binding scheme by the Green’s function method. For McRae’s model, the effect due to the dimerization of the second-layer edge atoms surrounding the island is also included. The comparison of our theoretical results with the experimental measurements for the electron density of states indicates that McRae’s island model is a better candidate for the Si(111)-7×7 surface than the other models under examination.
Plasma-processed positive and negative resist behavior of obliquely deposited amorphous P–Se films
Authors: Gupta P. K. , Kumar Ajay , Malhotra L. K. , Chopra K. L.
Published: July 2002

Thin films of amorphous phosphorus decaselenide (P4Se10) have been explored for lithographic applications. Depending on the substrate temperature during plasma etching in CF4 gas, either positive or negative resist behavior is observed. The effects of substrate temperature and exposure time on etching characteristics are discussed. Contrast values of 2.5 and 2.9 for positive and negative resist, respectively, have been obtained.
Photocathodic deposition of gold alloys for Ohmic contacts to III–V materials
Authors: Kelly J. J. , Rikken J. M. G. , Jacobs J. W. M. , Valster A.
Published: July 2002

Gold–zinc and gold–cadmium alloy layers, suitable for Ohmic contact formation, have been deposited photoelectrochemically on p-type III–V materials. It is shown that, while the nucleation of the plating process is greatly facilitated by illumination of the electrode, further growth of the alloy can proceed in the dark. Impedance measurements were used to investigate the influence of metal deposition on the potential distribution at the electrode interface. Contact properties of annealed gold–zinc layers on GaAs and InP are given. Auger electron spectroscopy measurements were used to study the surface chemistry during annealing. By choosing conditions to ensure maximum selectivity between illuminated and nonilluminated areas of the electrode, it is possible to write directly patterns of a desired composition and thickness using either a focused laser beam or mask projection.
Approaches to deep ultraviolet photolithography utilizing acid hardened resin photoresist systems
Authors: Thackeray James W. , Orsula George W. , Bohland John F. , McCullough Andrew W.
Published: July 2002

This paper describes continuing efforts in the development of acid hardened resin (AHR) resist systems for use in deep UV photolithography. The paper is composed of two sections. The first section deals with further evaluation of a conventional negative-tone deep-UV resist, XP-8843. A study of delay time between exposure and postexposure bake was carried out over a 62 min period. In particular, the linewidth versus exposure curve was generated at 2, 32, and 62 min delay times. Representative SEM cross sections at each time interval were also compared. The authors conclude that no significant time effect is evident, indicative that acid diffusion does not play a role in the 62 min time frame. The effect of defocus on sidewall angle has been evaluated over a 1.8 μ focal range as well. The sidewall angle varied from 85° to 89° reentrant over the entire focal range. Finally, results for XP-8843 at 1.4 μ coating thickness are shown. The second section introduces the silylated AHR (SAHR) process, whereby a highly absorbing resist, such as SAL601-ER7, is treated with hexamethyldisilazane. The exposed, crosslinked areas show virtually no reactivity with HMDS, and the unexposed areas incorporate 8.0% silicon in the film. In this manner, subsequent dry etching leads to a positive tone image.
Application of rate equation modeling to molecular-beam epitaxy
Authors: Kariotis R. , Lagally M. G.
Published: July 2002

A rate equation model describing molecular-beam epitaxy is presented. This consists of a set of equations that govern the population of islands of varying sizes and heights above the substrate. There is one equation for the time rate of change of the number of islands of each possible size at the jth level above the substrate. The application of the method is made to determine interface width as a function of temperature, deposition rate, and binding energies. This width is essentially the number of incomplete layers (coverage different from either 0 or 1) at any given instant, and is a useful measure of the extent to which the system has made the transition from a layer-by-layer to a rough growth mode.
Comparative study of a regular protein layer by scanning tunneling microscopy and transmission electron microscopy
Authors: Amrein M. , Wang Z. , Guckenberger R.
Published: July 2002

Scanning tunneling microscopy (STM) imaging has been performed on the HPI layer (hexagonally packed intermediate layer), freeze-dried and coated with Pt–Ir–C. The HPI layer is a highly corrugated regular protein monolayer, found outermost in the cell wall of the bacterium Deinococcus radiodurans. The average structure of each of the two surface aspects of HPI layer has been determined from STM data using correlation averaging. The signal-to-noise ratio of the raw data obtained from STM of the HPI layer is in the range of 1.5 to 2, values much higher than those usually encountered in data obtained by transmission electron microscopy (TEM). In order to discuss reliability and accuracy of STM imaging, the reliefs obtained by STM are compared to reconstructed reliefs derived from TEM micrographs of freeze-dried and metal-coated specimens.
Scanning tunneling microscopy of DNA: Atom-resolved imaging, general observations and possible contrast mechanism
Authors: Youngquist M. G. , Driscoll R. J. , Coley T. R. , Goddard W. A. , Baldeschwieler J. D.
Published: July 2002

We have shown that it is possible to image DNA with atomic resolution using scanning tunneling microscopy (STM), [R. J. Driscoll, M. G. Youngquist, and J. D. Baldeschwieler, Nature 346, 294 (1990)]. Here we describe that data together with our general observations on STM of DNA in ultrahigh vacuum. We also suggest a possible contrast mechanism for DNA imaging by STM based on wave function orthogonality requirements between a molecule and its substrate. Topographic images are presented which resolve atomic features in addition to the double helical structure and nucleotide pairs of the DNA molecule. Comparisons of experimental STM profiles and modeled contours of the van der Waals surface of A-DNA show excellent correlation. Successive scans show that the imaging is nondestructive and reproducible. For this study, double-stranded DNA was deposited on highly oriented pyrolitic graphite without coating, shadowing, or chemical modification.
High-resolution reactive ion etching and damage effects in the Si/GexSi1−x system
Authors: Cheung R. , Zijlstra T. , van der Drift E. , Geerligs L. J. , Verbruggen A. H. , Werner K. , Radelaar S.
Published: July 2002

The reactive ion etching characteristics of epitaxial GexSi1−x(x≤0.25) alloys in SF6/O2/He and SiCl4/Cl2/He plasmas have been studied. A high-resolution patterning process for Ge0.25Si0.75 using SiCl4/Cl2/He as a dry etch gas mixture has been developed. The etch rate and etch profile of Ge0.25Si0.75 are found to be strongly influenced by the substrate temperature and the oxygen content in the SF6/O2/He gas mixture. Conductance measurements of dry etched narrow wires in a Si/Ge0.2Si0.8 two-dimensional hole gas at 4.2 K reveal less sidewall damage for gas mixture SiCl4/Cl2 compared with SF6/O2/He, SiCl4/Cl2/He, and SF6/O2. Scattering in the conducting wires is studied using weak localization theory.
Mica etch pits as a height calibration source for atomic force microscopy
Authors: Nagahara L. A. , Hashimoto K. , Fujishima A. , Snowden-Ifft D. , Price P. B.
Published: July 2002

We describe a simple technique for creating etch pits in muscovite mica substrates for calibration purposes in atomic force microscopy (AFM). The etch pits are produced by wet etching the mica substrates in concentrated hydrofluoric acid and are formed with specific geometry. Along the long axis of the etch pits, steps of approximately 2 nm are observed which correspond to the molecular planes of mica. These steps bifurcate into 1 nm steps along the short axis. It is these 1- and 2-nm-high steps that permit height calibration.
Review of secondary ion mass spectrometry characterization of contamination associated with ion implantation
Authors: Stevie F. A. , Wilson R. G. , Simons D. S. , Current M. I. , Zalm P. C.
Published: July 2002

Contamination associated with ion implantation is reviewed with an emphasis on secondary ion mass spectrometry (SIMS) characterization. Specific examples are provided using SIMS as a tool to detect and resolve contaminant problems. This study of contamination is organized according to the path of the ion beam through an ion implanter, starting with the source and continuing to the end station. The source material, ion source components, and vacuum system can produce contaminant mass interferences that may not be eliminated by mass filtration in the implanter. A table of possible mass interferences is provided. The mass resolution of the implanter may be insufficient to remove adjacent masses and therefore may permit additional contaminants in the mass-analyzed ion beam. Charge exchange and molecular ion dissociation due to poor vacuum can occur at several locations in the implanter, especially after mass separation but before final acceleration. Detailed examples of BF2 dissociation are presented. Collisions of the ion beam with end station components result in low energy deposition of contaminants that can be driven into the target by the ion implanting beam. The fluence of the species of interest can be in error. Examples of multiple contaminant sources are also provided.
Molecular beam epitaxy of InAs and its interaction with a GaAs overlayer on vicinal GaAs (001) substrates
Authors: Lin X. W. , Liliental-Weber Z. , Washburn J. , Weber E. R. , Sasaki A. , Wakahara A. , Nabetani Y.
Published: July 2002

GaAs/InAs/GaAs heterostructures were grown by molecular beam epitaxy on vicinal GaAs (001) substrates. Effects of substrate misorientation on the early stage of InAs epitaxy, as well as the interaction between InAs and a GaAs overlayer, were studied by transmission and scanning electron microscopies and by photoluminescence measurements. The formation of InAs islands were observed after a few monolayer InAs deposition. Two major results were obtained in this study: (a) Upon deposition of a crystalline GaAs overlayer, InAs islands undergo a novel type of morphological transition, i.e., from disk-shaped to ring-shaped ones. (b) Substrate misorientation results in anisotropic effects on InAs island formation. In comparison with on-axis or [110] tilted samples, substrate misorientation toward [11̄0] by up to 5° leads not only to reduction in InAs island density by a factor of 2, but also to the formation of InAs quantum dots. These results were found to be consistent with photoluminescence experiments.