bluuebunny/crossref_metadata_2025 huggingface dataset:
Ti, TiN, and Ti/TiN thin films prepared by ion beam assisted deposition as diffusion barriers between Cu and Si
Authors: Mu Haicuan , Yu Yuehui , Luo E. Z. , Sundaravel B. , Wong S. P. , Wilson I. H.
Published: July 2002

A comparative study of Ti and TiN [ion beam assisted deposition (IBAD)] films as diffusion barriers for Cu has been done. It is found that amorphous Ti (a-Ti) and TiN (a-TiN) films show better thermal stability than (010) oriented Ti (c-Ti) and (111) oriented TiN (c-TiN) films. Such thermal stability can be attributed to their microstructure lacking grains that are fast diffusion paths compared to the imperfect preferentially oriented films prepared by IBAD. Compared to a 300 Å amorphous TiN layer, a 600 Å c-Ti/a-TiN multilayer shows inferior thermal stability, while improvement resulting from the 600 Å a-Ti/a-TiN multilayer is observed. Reasons for these effects are discussed.
Schottky barrier height and electron affinity of titanium on AlN
Authors: Ward B. L. , Hartman J. D. , Hurt E. H. , Tracy K. M. , Davis R. F. , Nemanich R. J.
Published: July 2002

Approximately 100 or 1000 Å of AlN was deposited on the (0001)Si-face of on-axis n-type 6H–SiC. The surfaces were examined by ultraviolet photoemission spectroscopy (UPS) utilizing the He I α (21.2 eV) and the He II α (40.8 eV) excitation. Experimental difficulties are discussed. Titanium was deposited on the clean surface of in situ grown AlN. The titanium–AlN interface was also characterized with UPS. Two approaches are presented to identify the valence band maximum (VBM) and the electron affinity χ of the clean surface of AlN was found to be either 0 to 1 eV depending upon the position of the valence band edge. The same assumptions were applied to the analysis of the Ti/AlN interface and, for the case of χ=0 eV, the position of the valence band maximum is 3.4 eV below the position of the Fermi level. For the case of χ=1 eV, the position of the valence band maximum is 4.4 eV below the position of the Fermi level. Therefore, the p-type Schottky barrier height of titanium on AlN is measured to be 3.4±0.2 or 4.4±0.2 eV for χ=0 eV and χ=1 eV, respectively. Independent of the selection of the valence band maximum, the observed Schottky barrier differed from that predicted by the Schottky–Mott model by 1.5±0.2 eV.
Roughening of the Si/SiO2 interface during SC1-chemical treatment studied by scanning tunneling microscopy
Authors: Gotoh M. , Sudoh K. , Iwasaki H.
Published: July 2002

The Si/SiO2 interface morphology is observed with subnanometer resolution by an ultrahigh vacuum scanning tunneling microscope (STM). We analyze the roughness of the Si/SiO2 interface for a chemical oxide film formed by a wet chemical process (NH4OH/H2O2/H2O treatment). The oxide film is selectively removed by irradiating a field emission electron beam extracted from a STM tip at a temperature of 300–350 °C. We find that during the chemical process the roughness of the Si/SiO2 interface increases with the treatment time.
Properties and the influences on plasma performance for the film produced by radio frequency boronization
Authors: Li J. , Zhao Y. P. , Gong X. Z. , Wan B. N. , Gu X. M. , Luo J. R. , Zhang S. D. , Li C. F. , Fang Y. C. , Zhen M. , Wang X. M. , Hu J. S. , Li S. F. , Xie J. K. , Wan Y. X.
Published: July 2002

A new boronization technique focusing on the needs of the future large superconducting device has been developed in HT-7 tokamak. The first try on a tokamak gave very promising results. A fine homogeneous and hard a-B/C:H film was produced by a pulse ion cyclotron resonance frequency plasma. The film shows high adhesion, high thickness and longer lifetime. The ratio of B/C is about 3 up to a depth of 280 nm. X-ray photoelectron spectroscopy analysis shows that the B–B, B–C, C–C, C–O, and B–O bonds were formed during the boronization. The oxygen content in the film increases from 15% to 25% after 250 serious discharges, which demonstrated the strong oxygen gettering by the film. Good uniformity of the film in both toroidal and poloidal directions has been obtained by using long antenna on the high field side. The recycling of hydrogen was easily controlled by using helium rf discharge after boronization, and very strong wall pumping was observed. Plasma performance was significantly improved after boronization. A higher density limit and wider operation space were obtained. The strong hard x ray accompanied by high power lower hybrid current drive was suppressed dramatically. This gives direct evidence that the thin boron film serves as a protecting layer against the energetic particles, which is very important for future long-pulse-length discharge. This new technique has been proved to be very effective for conditioning future large magnetic fusion devices.
Role of delocalized nitrogen in determining the local atomic arrangement and mechanical properties of amorphous carbon nitride thin films
Authors: Holloway B. C. , Kraft O. , Shuh D. K. , Nix W. D. , Kelly M. , Pianetta P. , Hagström S.
Published: July 2002

We report the results of a comprehensive study of the mechanical properties and chemical structure of carbon nitride thin films deposited by magnetron sputtering. Nanoindentation measurements show that the films are very elastic. Using a modified Oliver–Pharr method, to account for the elasticity of the films, the reduced elastic modulus was calculated to fall in the range of 35–55 GPa for all films measured. No quantifiable plastic deformation was measured in the tested films, therefore the hardness calculated (6 GPa) can only be assumed to be a lower bound. Fourier transform infrared spectroscopy of the carbon nitride films indicates the presence of large amounts of single and double bonds, and very small amounts of triple bonding, between carbon and nitrogen. Near edge x-ray absorption fine structure data suggests that there are three predominant types of bonds between carbon and nitrogen. This is consistent with the x-ray photoelectron spectroscopy data which shows N(1s) and C(1s) core spectra with multiple, chemically shifted features. The data suggest, but do not confirm, the presence of nitrogen atoms participating in four bonds (three sigma, one pi). A self-consistent argument is presented that links parametric changes in mechanical properties with changes in a proposed film structure based on nitrogen participating in four bonds. This marks a new approach to the interpretation of nitrogen bonding with carbon in the solid state not only for amorphous carbon nitride, but also other systems such as diamond and boron nitride thin films.
Deposition and Detection of Ag and Au Films Below 0.01 Monolayer
Authors: Behrndt Marianne E.
Published: July 2002

The controlled deposition of extremely small amounts of Ag and Au is described. A shutter arrangement was developed which permits the deposition of metals from 10−3 monolayer upwards, in conjunction with a rate-controlled evaporation source. Either continuous or stepwise variation of film thickness was attained. Deposits below about 1 monolayer consisted of particles which were invisible ill the electron microscope. Their presence was detected by subsequent amplification of their size such that a visible deposit was formed. This was accomplished either by physical development, as known in photographic chemistry, or by vacuum deposition of zinc which was nucleated by these particles. The detection sensitivity of the methods is compared.
Depth distribution of Bi+ and Fe+ implanted into polyimide (C22H10N2O5)n
Authors: Wang Ke-Ming , Hu Hui , Lu Fei , Chen Feng , Zhang Jiang-Hua , Liu Xiang-Dong , Liu Ji-Tian , Wu Bo , Huang Mu-Bin
Published: July 2002

Polyimide (C22H10N2O5)n was implanted with Bi+ and Fe+ ions at different energies, doses, and angles. The depth distribution of implanted Bi+ and Fe+ ions in polyimide was measured by Rutherford backscattering. The results show: (1) For the case of 2×1015 Bi+ ions/cm2, the depth distribution was nearly Gaussian for both energies; for the case of 1×1016 Bi+ ions/cm2, diffusion behavior during implantation is observed. (2) For the case of 1×1016 Fe+ions/cm2, the depth distribution was Gaussian for 200 keV, and the depth distributions of the as-implanted Fe+ ions become bimodal and have a split behavior under 0° and 45° for 350 keV. (3) For a regular distribution, the experimental mean-projected range is in good agreement with the calculated value, within less than 6%, the experimental range straggling is larger than the calculated one based on TRIM'98.
The Outgassing of Copper Pinchoffs
Authors: Begeal D. R.
Published: July 2002

This paper describes a study of the outgassing from the pinch-off of copper tubulations. The gas released is approximately 99.5% CO2 and 0.5% O2. The amount of gas varies with the type of copper, its diameter, and the treatment given to the tubulation prior to the pinch-off. The amount of gas can vary from 1×10−6 cm3 (STP) for 0.250 in. o.d., 0.182 in. i.d. OFHC tubulations that have not been cleaned or baked, to 3×10−9 cm3 (STP) for the same tubes that have been chemically cleaned, and then baked on the vacuum system. Refrigeration tubing showed the same initial amount of outgassing, but still outgassed 3×10−8 cm (STP) even after cleaning. With careful treatment, 0.125 in. o.d.×0.080 in. i.d. OFHC tubulations release less than 3×10−10 cm3 (STP) of the CO2–O2 mixture during a pinch-off.
Spiral channel flows in a disk-type drag pump
Authors: Heo Joong-Sik , Hwang Young-Kyu
Published: July 2002

Pumping performance of a disk-type drag pump is studied numerically and experimentally. Molecular transition and slip flows that arise in a spiral channel on the rotating disk are simulated by using molecular and continuum methods. The molecular approach employs the direct simulation Monte Carlo (DSMC) method, and the continuum approach solves the Navier–Stokes (NS) equations. The formulation of second-order slip boundary conditions is utilized in the NS method. Particular attention is paid to matching the DSMC method with the solutions obtained by the NS method in the slip flow regime. In the experimental study, the inlet pressures are measured for various outlet pressures of a test pump. Comparison between the experimental data and the numerical results reveals that the DSMC method provides the more accurate solution of the rarefied channel flow for the range of Knudsen number Kn>0.02 than does the NS method.
Axisymmetrical particle-in-cell/Monte Carlo simulation of narrow gap planar magnetron plasmas. II. Radio frequency-driven discharge
Authors: Kondo Shuji , Nanbu Kenichi
Published: July 2002

An axisymmetrical particle-in-cell/Monte Carlo simulation is performed for modeling radio frequency-driven planar magnetron discharge. The model apparatus has a narrow target-anode gap of 20 mm to make the computational time manageable. This resulted in the current densities which are very low compared to actual experimental results for a wider target-anode gap. The spatial and temporal behaviors of such plasma parameters as plasma density, electric field, and discharge current are examined in detail. The direct current self-bias in the magnetron discharge is first clarified by a numerical simulation. The self-bias arises at the powered electrode due to the axial asymmetry of plasma caused by the magnetic field. The effects of magnetic field strength and secondary electron emission on the plasma parameters and self-bias voltage are also clarified.
Incorporation of polyhedral oligosilsesquioxane in chemically amplified resists to improve their reactive ion etching resistance
Authors: Wu Hengpeng , Hu Yongqi , Gonsalves Kenneth E. , Yacaman Miguel Jose
Published: July 2002

A chemically amplified (CA) methacrylate resist containing polyhedral oligosilsesquioxane (POSS) has been synthesized by AIBN-initiated free radical polymerization. While the polymer of low POSS concentrations showed little improvement in reactive ion etching (RIE) resistance, incorporation of 20.5 wt % of the POSS monomer into methacrylate-based CA resists significantly improved their RIE resistance in the O2 plasma. High-resolution transmission electron microscopy revealed that the RIE resistance improvement was due to the formation of rectangular crystallite-constituting networks of the silica cages uniformly distributed within the polymer matrix.
Interface configuration and metal adhesion in Au-polycarbonate bilayer structure: Influence of Al+27 ion mixing
Authors: Patnaik Archita , Li Changlin , Xie Shuping , Yang Dequan
Published: July 2002

Structural modification at the Au-polycarbonate (PC) interface upon 100 keV Al+27 ion implantation at a dose and beam current density 5×1016 ions cm−2 and 30–50 nA cm−2, respectively, was studied through x-ray photoelectron spectroscopy (XPS) with a Au thickness of 28.2 nm. XPS depth profiling with 3 keV Ar+ ion sputtering at 1 μA revealed the interface to be sharp covering a few monolayers. A substantial Au atomic concentration of ∼5% in the bulk PC indicated the Ar+ ion assisted diffusion of the metal into the bulk. Existence of weak Au→C charge transfer interactions with Au as the electron injector distributing a net charge density at the C=O bond as the primary interaction site was deduced from the appearance of the 282.4 eV C1s feature [H. A. Mizes, K. G. Loh, R. J. D. Miller, S. K. Ahuja, and E. F. Grabowski, Appl. Phys. Lett. 59, 2901 (1991)]. Al+ ion implantation induced interfacial mixing of the substrate C with the Au film in the bilayer target was observed with the evolution of a broad interface of ∼50 nm thickness, accompanied by the formation of Au–Al, Al–O, and Al–O–C bonds along with dominant graphitization of the polymer. Free carbon transport into and through the Au film to the surface resulted in a diffused interface with an abnormally low oxygen concentration throughout. Au–Al bonding was identified in the Au-rich region, and shifted to Al–O bonding in the C-rich region of the polymer, with the Al atomic concentration reaching a maximum of 1.8%. After ion-beam mixing and surface modification by ion bombardment, force curve measurements performed through atomic force microscopy showed a drastic reduction in the interface adhesion values.
Corrosion behaviors of CrNx and (Ti1−xCrx)N coatings produced by ion plating
Authors: Lee Kwang Hee , Park Changhong , Yoon Yeosang , Lee Jung Joong , Jehn Hermann A.
Published: July 2002

The corrosion behavior of CrNx and (Ti1−xCrx)N coatings, produced by reactive ion plating using thermal and electron beam evaporation, was investigated. To deposit the CrNx coatings, Cr was evaporated by resistance heating and CrNx coatings of various N/Cr composition ratios were obtained by altering the NH3 flow rate. For deposition of the (Ti1−xCrx)N coatings, Ti and Cr were evaporated by electron beam and resistant heating, respectively. The Ti and Cr concentrations were controlled by the Ti to Cr evaporation ratio. Electrochemical properties of the coatings were examined with an EG&G 273 A potentiostat in a pH 7, 0.8 M NaCl solution. The corrosion behavior of both CrN and (Ti,Cr)N coatings showed a similar trend to that of pure Cr. At voltages <0.5 V [versus saturated calomel electrode (SCE)], they showed passivity. However, at voltages >0.5 V (versus SCE), the corrosion current increased abruptly with dissolution of Cr–oxide from the surface oxide layer.
Growth and characterization of epitaxial Ge1−xCx thin films on (100)Si
Authors: Li W. , Shah Ismat , Guerin D. , Chen J. G. , Hwu H.
Published: July 2002

Single-phase, single-crystal, epitaxial Ge1−xCx films were deposited on Si(100) substrates with C concentration as high as 9.0 at. %. The film composition was measured by energy dispersive x-ray spectroscopy. The x-ray diffraction analysis, in combination with Vegard's law, shows a different composition than what is obtained by the energy dispersive x-ray spectroscopy, indicating that Ge1−xCx alloys show a positive deviation from Vegard's law. Both the film thickness and the deposition temperature had a strong influence on the structure of the film. At low temperatures, an amorphous film was obtained. The crystalline structure of the films was also strongly dependent on the thickness of the film. Films thicker than 60 nm were polycrystalline. At temperatures higher than 800 °C and for thicknesses around 50 nm, good-quality single-crystal, epitaxial films were obtained. An energetic condensation process was crucial for incorporating such a high C concentration in Ge. Near-edge x-ray absorption fine structure analysis results showed that the majority of C was in the diamond-like state, which was direct evidence that the C is situated on substitutional sites.
Ion kinetic energy control in dual plasma deposition of thin films
Authors: Wang L. P. , Tang B. Y. , Gan K. Y. , Tian X. B. , Chu P. K.
Published: July 2002

Dual plasma deposition based on plasma immersion ion implantation and plasma deposition is a fledgling technique for the fabrication of functional thin films. One of its advantages is the easy adjustment of the ion kinetic energy during the process. It is straightforward to control the ion kinetic energy during the fabrication of conducting thin films on conducting substrates by simply varying the negative dc voltage applied to the targets. However, for the fabrication of insulating thin films or film deposition on insulating substrates, charge accumulation makes it difficult for ions to attain the proper kinetic energy. In these cases, a pulse or ac voltage is commonly employed. In this article, we theoretically investigate the process window in dual plasma deposition with respect to the pulse width and frequency of the applied voltage to avoid electrical breakdown of the film as well as large ion kinetic energy deviation. The model can deal with the deposition of insulating thin films on conducting or insulating substrates.
Effects of photoassisted O2 annealing on the properties of (Ba,Sr)TiO3 thin films
Authors: Chang S. J. , Lee J. S. , Wei M. C. , Chen J. F. , Liu C. H. , Liaw U. H.
Published: July 2002

A photoassisted O2 annealing method is proposed to anneal (Ba0.75Sr0.25)TiO3 thin films grown by rf magnetron sputtering. A deuterium lamp, which emits strong ultraviolet and vacuum ultraviolet light, was used as the light source of our photoassisted O2 annealing system. It was found that we could achieve a leakage current density lower than 3×10−8 A/cm2 at 2 V and a dielectric constant, ε, as high as 158.6 by annealing (Ba0.75Sr0.25)TiO3 thin films in this system at 650 °C for 2 h.
Membrane mask magnification correction: Alternate technique
Authors: Murooka Ken-ichi , Lim Michael H. , Smith Henry I.
Published: July 2002

We describe a method to correct for magnification error in membrane masks by applying extra stress in a pattern calculated by comformal mapping. The calculational results show this method provides less than 3 nm residual error in 5 ppm correction with a square-shaped membrane. We also show this method is easily expandable to the anisotropic case. Furthermore, we point out that this method enables one to obtain a thermal-distortion-free mask.
Residual Argon Partial Pressure Changes due to an Intermittently Operated Bayard–Alpert Ionization Gauge in Ultrahigh Vacuum
Authors: Axler M. Friedman
Published: July 2002

In a sealed ultrahigh-vacuum glass system incorporating a Bayard–Alpert-type ionization gauge at a total pressure of ∼10−10 Torr (obtained with an oil diffusion pump, mechanical fore-pump, and nonrefrigerated trap), it is demonstrated that by turning off the electron accelerating potential (or all gauge potentials) of the ionization gauge, the gas ambient of the system is perturbed by the desorption of Ar from the gauge surfaces. Partial pressure gas measurements are made with an omegatron mass spectrometer. The quantity and rate of Ar desorption is related in a complex way to the previous history of the system. Experimental data for some representative systems are presented.
Cylindrical Geometry Sputtering Apparatus
Authors: Sinclair W. Robert , Peters F. G.
Published: July 2002

A cylindrical geometry sputtering apparatus and associated fixtures have been described which feature ease of construction and use. Because of the high symmetry of the apparatus, films can be deposited simultaneously on different substrates at different temperatures and meaningful comparisons made between results. Films can be deposited onto substrates that are electrically floating, and it is pointed out that this is valuable in reactive sputtering in oxygen as it minimizes damage to sensitive electronic structures which can be caused by anionic bombardment. The planarity of the sputtered films and the rate of deposition are discussed.
Relationships between Pumping Speed, Capture Probability, and Chamber Geometry in a Spherical Cryopumped Vacuum Chamber
Authors: Hood Charles B. , Barnes Carlisle B.
Published: July 2002

A spherical cryopumped chamber with a test object is analyzed to determine the pumping speeds that will be observed with gauges located in various positions. Equations are developed to relate these speeds to chamber geometry and cryopump efficiency. It is shown that with a certain geometry and gauge location, speeds as high as four times the orifice speed, V̄/4, per unit area can be observed with omni-directional gauges, and even higher speeds can be observed with directional gauges.
Cold-Cathode Magnetron Gauge Characteristics
Authors: Bryant Paul J. , Longley William W. , Gosselin Charles M.
Published: July 2002

A description of cold cathode magnetrons operating as gauges has been developed in terms of the conditions for establishing a discharge and the effects of space-charge buildup. Pressure response curves for NRC type 552 (Redhead) and GCA model 1410 (Kreisman) gauges were determined by a conductance-regulated, pressure-ratio method using Bayard–Alpert type gauges for upstream pressure reference. Four characteristics of normal magnetrons operated below cutoff are predicted from the discharge mechanism and correlated with test data: (1) an out-of-strike state characterized by a steady pressure-independent gauge reading (about 5×10−14 Torr) due to leakage current; (2) a minimum pressure threshold for operation, 2.7×10−12 Torr for the NRC 552, 1.7×10−10 Torr for the GCA 1410; (3) a range (below 10−9 Torr) of nonlinear pressure-dependent response moderated by space charge buildup; and (4) a range of near linear response corresponding to the region of nearly saturated space charge.
Warm-Welding of Metals in Ultrahigh Vacuum
Authors: Batzer Thomas H. , Bunshah R. F.
Published: July 2002

Before metal surfaces can be welded, it is necessary to remove the contamination (oxide) layer on the surface and avoid recontamination of the clean surface by its environment prior to the welding operation. Mechanical abrasion is one way of removing the surface oxide layer used in such processes as friction-welding, roll-bonding, and diffusion-bonding. It would be desirable to have a technique for welding at low temperatures (0.1 to 0.4 Tm), with non-distorting, zero-shear type of leading. This paper describes such a process. In a uhv environment (to delay recontamination to very long times), two halves of a tensile specimen are cleaned by argon-ion bombardment, compressed at about 0.8–0.9 yield strength at 0.1 to 0.4 Tm, and held at temperature for finite times. The welded specimen is then tensile-tested in the uhv system to evaluate the process. The variables studied are temperature, time, loading, and the need for ion cleaning on various metals. Successful welds were produced in OFHC copper, Ti, and Be.
Reference-Transfer Method of Vacuum-Gauge Calibration
Authors: Morrison Charles F.
Published: July 2002

A new vacuum-gauge calibration method is described. Tile pressure ratio generated by the molecular flow of gas through two known, fixed, series conductances is applied repeatedly, serially in time, to establish a progression of increasing chamber pressures. A single pressure indication serves as the higher value in one ratio and the lower value in the succeeding ratio, thereby correlating the calibration pressures by a fixed known factor. Calibration pressures can be calculated after one of them is sufficiently high to be measured accurately by a reference system. In one modification, gauges are calibrated on a symmetrical, well-baffled chamber connected directly to the pump by a large conductance, thus significantly reducing the possible interaction between the establishment of new calibration pressures, and the pumping or outgassing of gauges being calibrated. A simple, single-pump apparatus suffices for calibrating from 10−3 Torr to within a decade of the system ultimate pressure. Re-producibility in the order of 2% is achieved in the 10−9 Torr decade.
Scaling Laws for Experimental Determination of Pumpdown Time in the Molecular Flow Range
Authors: Lewin G.
Published: July 2002

The pumpdown time and ultimate pressure of a vacuum system cannot be accurately calculated since the gassing rates of the walls, which are the determining factor, are complex functions of time and pressure. Scaling laws are derived for dimensions of a scaled-down model of a large vacuum system made of the same materials which has the same pressure-time behavior. If a lumped volume of surface area Al is connected to a pump of speed S through a conductance C, the ratio Al(1/C+1/S) must be kept constant. If the conductance C has a gassing wall of area Ad, the ratios Al/C, Ad/C, and C/S have to be preserved. These results are generalized and the scaling laws are given for a system consisting of several lumped volumes with gassing surfaces connected in series through conductances with or without wall gassing. The same ratios apply in systems with local temperature variations if the same relative temperature distribution is maintained in both systems with the only change that the particle conductance C′ and particle speed S′ have to be substituted for C and S. The influence of wall thickness on the gassing rate is also discussed.
Solar-energy materials preparation techniques
Authors: Mattox D. M.
Published: July 2002

The application of materials to the thermal control of structures, photothermal/electrical conversion, and photovoltaic conversion are reviewed. Applications include solar and infrared reflectors, optical filters, transparent conductors, bulk semiconductor materials, semiconductor films, and selective solar absorbers. The use of thin films in many conservation and photothermal applications is presently economical, but the economics of photothermal/electrical and photovoltaic conversion is still being investigated. The means of obtaining selective solar absorbers which have a high solar absorptance and low ir emittance are discussed, and specific data on an electrodeposited black-chrome selective absorber is presented. It is shown that solar–electric generating plants must be constructed at a cost of about $50/m2 to be competitive with other electrical generating plants, and that a meaningful impact on the electrical energy economy will require a fabrication rate of greater than 1.8 × 108 m2 (50 square miles) per year. Present high-volume deposition capabilities are reviewed, and it is shown that for some types of deposition, namely electrodeposition, e-beam vacuum evaporation, and possibly sputter deposition, facilities exist which approach the desired volumes.
Theoretical analysis of the density within an orbiting molecular shield
Authors: Hueser J. E. , Brock F. J.
Published: July 2002

An analytical model based on the kinetic theory of a drifting Maxwellian gas is used to determine the nonequilibrium molecular density distribution within a hemispherical shell open aft with its axis parallel to its velocity. Separate numerical results are presented for the primary and secondary density distribution components due to the drifting Maxwellian gas for speed ratios between 2.5 and 10. An analysis is also made of the density component due to gas desorbed from the wall of the hemisphere, and numerical results are presented for the density distribution. It is shown that the adsorption process may be completely ignored. The results are applicable to orbital trajectories in any planet–atmosphere system and interplanetary transfer trajectories. Application to the earth’s atmosphere is mentioned briefly.
New SEM–Auger microanalyzer with UHV capability
Authors: Ishida T. , Uchiyama M. , Oda Z. , Hashimoto H.
Published: July 2002

The design and performance of a new Auger microanalyzer (EMAS) with the capability of UHV scanning electron microscope (SEM) is described. The incident electron beam is focused by a magnetic lens system, and the spatial resolution is below 0.5 μm for the Auger analysis mode and on the order of 100 Å in the SEM mode. Possible modes of analysis include point analysis, line analysis, and Auger image mapping, in addition to secondary electron and absorbed current imaging. The depth profiling of chemical composition in submicron structures is also provided by use of ion beam etching. An air-locked sample changer is employed to keep the vacuum of the system at 10−7 Pa during specimen loading and unloading. Three examples of applications to microelectronics devices are presented.
Selective gettering of hydrogen in high pressure metal iodide lamps
Authors: Kuus G.
Published: July 2002

One of the main problems in the manufacture of high pressure gas discharge lamps is the elimination of gaseous impurities from their arc tubes. Long degassing processes of all the lamp components are necessary in order to produce lamps with a low ignition voltage and good maintenance of the radiation properties. The investigation described in this article deals with a selective getter place in the arc tube which can replace the long degassing process. The getter consists of a piece of yttrium encapsulated in thin tantalum foil. By this way it is possible to use the gettering action of tantalum and yttrium without having reaction between the metal iodide of the arc tube and yttrium. Yttrium is used because this metal can adsorb a large quantity of hydrogen even at a temperature of 1000°C. Hydrogen forms the main gaseous impurity in the high pressure metal iodide lamp. For this reason the adsorption properties like adsorption rate and capacity of the tantalum–yttrium getter for hydrogen are examined, and the results obtained from lamp experiments are given.
An AES and SIMS study of the co-adsorption of CO2 and O2 on molybdenum
Authors: Dawson P. H.
Published: July 2002

The adsorption of CO2 on polycrystalline molybdenum is blocked even by the partial (aproximately two-thirds) presence of the strongly bound β2 oxygen. Pre-adsorption of CO2 at room temperature does not impede subsequent oxidation. The CO2 adsorption kinetics at room temperature can be explained by a two-site adsorption model with rapid dissociative chemisorption and carbon and oxygen in equivalent sites. On heating the CO2-saturated surface above 900 K, CO is lost from the surface. Interaction of CO2 at 1200 K gives a small buildup of carbon until the surface oxygen concentration increases sufficiently that the loss rate exceeds the deposition rate.
Investigation of rf-sputtered Nd–glass films for integrated optics
Authors: Griffiths G. J. , Khan P. J.
Published: July 2002

The rf sputtering of Nd–glass films from targets containing low dissociation energy oxides has been investigated, and factors affecting optical quality and process time are discussed. These include gas composition and pressure, input power density, substrate temperature, annealing, surface damage, and thermal properties of both host glass and substrate. Several methods for overcoming anion depletion in the films and reducing waveguide losses are evaluated.
Anode behavior in high intensity field emission diodes
Authors: D’Anna E. , Leggieri G. , Luches A. , Nassisi V. , Perrone A. , Perrone M. R.
Published: July 2002

When intense electron beams are used to study plasma–beam interactions or to excite or control high power gas lasers, the field emission diode must have an anode transparent to electrons but thick enough to sustain pressures up to hundreds of psi. We calculated the temperature rises for 18 μm stainless steel anode foils struck by electron beams of 250 and 380 keV, 10 and 16 kA respectively, and 15 ns pulse duration. The temperature rises (291° and 352 °C, respectively) are not sufficient to justify anode breakdown. Beam inhomogeneity and heat induced brittleness of the foil are major causes of anode breakdowns.
Transition metal compound surfaces I: The cubic sodium tungsten bronze (NaxWO3) surface
Authors: Langell M. A. , Bernasek S. L.
Published: July 2002

The two dimensional surface structure and the surface chemical composition of (100) cubic sodium tungsten bronze (NaxWO3) has been investigated using low energy electron diffraction and Auger electron spectroscopy. Single crystals with bulk x values ranging from 0.5 to 0.9 were examined. The (100) surface exhibits the square symmetry of the WO3 lattice, with fractional order features corresponding to ordered sodium row structures which depend on the crystal x value. Auger spectra support covalent bonding models of these materials, in which sodium contributes little to the lattice binding. LEED and Auger results indicate sodium depletion in the surface region. In addition, evidence of a sodium order/disorder transition in the surface region is obtained.
The Si(111)–Pd interface: Spectroscopic evidence of chemical processes at liquid nitrogen temperature
Authors: Abbati I. , Braicovich L. , De Michelis B. , del Pennino U.
Published: July 2002

We present the results of angle integrated photoelectron spectroscopy (hν=21.2 eV) on Si(111)–Pd interfaces. We have found that some intermixing between Si and Pd takes place also when the interface is prepared at liquid nitrogen temperature (LNT). After preparation at LNT the intermixing increases at room temperature (RT). The results are discussed in connection with the interface formation mechanism.
Design for a high temperature, high vacuum evaporation furnace
Authors: West K. W.
Published: July 2002

An evaporation furnace capable of temperatures greater than 1700°C in high vacuum, with temperature monitoring, is described. The assembled furnace can be inserted through a standard 2.75 in. vacuum flange.
Oxygen plasma etching of thick polymer layers
Authors: Goldstein I. S. , Kalk F.
Published: July 2002

Reactive ion etching of thick (≳100 μm) epoxy, polyester, and photoresist layers in oxygen was studied as a function of gas flow, gas pressure, gas purity, and rf power density. Etch rates greater than 2500 Å/min were obtained with low substrate temperatures. The etch was found to be extremely directional so that structures with aspect ratios as large as 30 to 1 were measured. Both the etch geometry and mask material appear to have some effect on this directionality. In addition the etch was found to smooth the etched surface so that surface finishes better than 200 Å were possible.
A new x-ray generator for XPS applications
Authors: Ganschow O. , Steffens P.
Published: July 2002

This paper describes a new x-ray generator for the production of Al Kα or Mg Kα radiation to be used for photoelectron spectroscopy of solid surfaces. The x-ray source is equipped with a stationary anode rated for 1.5 kW loss power (with Al anode) during continuous operation, corresponding to a power density of 12 kW/cm2. Its power supply is based on switching regulators and has a 20 kV, 2 kW stabilized anode voltage supply with 50 ms settling time. Two of these x-ray generators have been operated for three years with different commercial XPS systems. The resulting improvements in performance are shown.
X-ray absorption in characterization of laser fusion targets
Authors: Clement X. , Coudeville A. , Eyharts P. , Perrine J. P. , Rouillard R.
Published: July 2002

Many plastic or metal-coated targets are opaque, so their thickness and thickness uniformity cannot be obtained by optical means. Therefore, we have built and tested a new system based on monochromatic x-ray absorption measurements. This system is also able to perform nondestructive measurements of argon fill pressure in glass microballoons. The x-ray source is a diffraction tube with a chromium target and fine focus (0.4×0.8 mm2). Since monochromatic calculations are involved in this method, we use electronic discrimination to isolate the chromium Kα line (5.4 keV) from the bremsstrahlung spectrum. The detectors are xenon-filled proportional counters. The system is composed of two beams (10 μm in diameter), one used as a reference and the other as the measurement arm. A Pet desk computer is coupled to the experiment. We achieved a precision better than 10% for gold layers in the range of 0.1 to 1 μm, and better than 20% for argon pressures in the range of 5–13 bars.
Mössbauer depth profiling technique for oxidation studies
Authors: Bayreuther G.
Published: July 2002

A Mössbauer depth profiling technique has been developed which provides depth selective information about composition, stoichiometry, chemical nature, and structure of iron oxide films. A depth resolution of 5 Å or better can be obtained. The method is especially useful for very thin oxide layers (<100 Å) where standard methods can give only very limited information. The method uses special thin film samples of metallic iron which contain a thin probe layer of 57 Fe, the rest being depleted of this isotope. Thus, the power of Mössbauer spectroscopy for the identification of iron compounds is combined with a high resolution nondestructive depth profiling technique. The method is applied to study the low temperature oxidation of iron films. By oxidation at 453 K in pure oxygen a nonstoichiometric or noncrystalline oxide is formed.
The determination of electron inelastic mean free path using evaporated films
Authors: Londry F. , Slavin A. J.
Published: July 2002

Monte Carlo simulations of the growth of evaporated films have been carried out under various assumptions affecting the type of growth. The corresponding curves of Auger signal from the film as a function of deposition time have been analyzed to extract values for the electron inelastic mean free path λ. A smoothness parameter C defined as the fraction of the substrate covered after the deposition of 1 monolayer equivalent of atoms, is used to characterize the degree to which growth is layer by layer, i.e., one layer is complete before the next one begins. It has been found that values of λ correct to within 10% can be obtained for values of C as low as 0.85; below C values of 0.85 the results for λ become unreliable. It is shown that film formation may be made essentially layer by layer by a reasonable choice of the deposition flux density and the substrate temperature, provided that the system is one in which atoms can walk off terraces. It is also shown that elastic electron backscattering should not affect these calculations significantly.
Interfacial layers in high-temperature-oxidized NiCrAl
Authors: Larson L. A. , Browning R. , Poppa H. , Smialek J.
Published: July 2002

The oxide and diffusion layers produced in a Ni–14Cr–24Al alloy by oxidation in air at 1180 °C for 25 h have been studied using scanning Auger microscopy and ball cratering for depth profiling. During cooling, following oxidation, the oxide layers formed by this alloy spalled profusely. The remaining oxide was very thin (<100 Å) and was primarily Cr2O3 with a trace of Ni (although other oxides are possible). The underlaying metal substrate exhibited γ/γ′ (Ni/Ni3Al) and β (NiAl) phases; however, there was metallic interfacial layer at the surface. This layer was similar to the bulk γ/γ′ phase, but slightly enriched in Cr and Al. These data are compared to electron microprobe results from a nominally identical alloy. The diffusion layer thickness is modeled with a simple mass balance equation and compared to recent results on the diffusion process in NiCrAl alloys.
Preparation of NbN by reactive magnetron sputtering using Ne and Kr inert diluents
Authors: van Dover R. B. , Bacon D. D. , Sinclair W. Robert
Published: July 2002

Previous studies of the preparation of NbN by reactive sputtering have employed Ar–N2 gas mixtures. We have shown that high-Tc films (Tc=14.2 K) can be prepared on substrates held near room temperature by sputtering a Nb target in a dc s-gun magnetron with that gas mix. This paper reports the results of an investigation of the properties of NbN films sputtered in the same system using alternative inert gas diluents, specifically Ne and Kr. The Tc of these films was found to depend systematically on the N2 partial pressure, total gas pressure, and dc cathode voltage; the maximum transition temperatures obtained using Ne–N2 and Kr–N2 mixtures were 12.8 and 12.7 K, respectively. When Tc is plotted versus ρ a rough general correlation is observed, though data for films sputtered in each inert gas tend to segregate. We conclude empirically that sputtering NbN in an Ar–N2 ambient gives the highest film quality and that using Ne or Kr in place of Ar offers no advantages.
Electron emission from 〈100〉 LaB6 cathodes with large cone angles and flat tips
Authors: Yamabe M. , Furukawa Y. , Inagaki T.
Published: July 2002

This investigation was done to determine the relationship between the arrangement of the crystal faces located at the tip surface of single-crystal 〈100〉 LaB6 cathodes and their emission characteristics from the viewpoint of beam uniformity. The results indicate that as the cone angle of 〈100〉 spherical tip cathodes increases, the angular emission pattern becomes more uniform due to the restriction of the coverage of the crystal faces on the tip and the beam divergence becomes larger. The crystal face appearing on the tip surface is restricted most in flat tip cathodes, and the flat tip cathodes produce a uniformly concentrated angular emission pattern. Because of the strong restriction of the crystal face, the decrease of beam divergence with an increase in emission current is smaller in flat tip cathodes than in spherical tip cathodes. The restriction of the crystal faces appearing on the tip by means of enlarging the cone angle including the flat top is effective in order to obtain uniform electron emission. The brightness of spherical tip cathodes decreases with an increase in the cone angle, while for flat tip cathodes, an increase in the flat surface diameter results in a decrease in brightness.
Helium scattering from (1×1) H–Pt(111)
Authors: Batra Inder P. , Barker J. A. , Auerbach D. J.
Published: July 2002

Lee et al. have recently reported measurements of helium diffraction data for a (1×1) chemisorbed layer of hydrogen on Pt(111) and obtained the corrugation parameters of a hard wall model fit to the data. We have calculated the corrugation parameters using a first principles approach for determining the helium-surface interaction potential. We have performed calculations of helium interaction potential for H in a (1×1) overlayer for fcc and hcp threefold sites and for on top sites at various distances above the Pt(111) surface. By comparing our results with the experimentally determined corrugation we conclude (in agreement with Lee et al.) that H chemisorbs in a threefold site. Furthermore we establish that the vertical height of the H above the top plane of Pt atoms is about 1.0 Å. This corresponds to Pt–H bond length of about 1.9 Å, a value somewhat larger than the Pt–H diatomic bond length of 1.6 Å. Our results compare favorably with the conclusion drawn from vibrational spectroscopy. Our calculated potential is soft with the softness parameter of about 2.6 Å−1. We are unable to distinguish between the fcc and hcp threefold sites on the basis of the corrugation alone, but in combination with the experimental helium diffraction and x-ray data of Lee et al., we confirm their tentative suggestion that the H adsorbs in hcp sites.
A novel method for the determination of the energies of impurity ions bombarding a solid surface exposed to a low pressure plasma
Authors: Gimzewski J. K. , Vepřek S.
Published: July 2002

A technique is presented for the determination of the projected range of metallic ions implanted into a carbon (or silicon) probe from which their impact energy is calculated. The projected range is evaluated from the increase in intensity of a photoelectron or Auger signal from the impurities upon selective chemical etching of the probe by atomic hydrogen. During etching of the substrate the implanted impurities accumulate on the surface resulting in an increase of the signal intensity up to a saturation value. Experimental data is presented for a carbon probe exposed to the scrape-off layer of the TCA tokamak.
Determination of grain boundary impurity effects in polycrystalline silicon
Authors: Kazmerski L. L. , Dick J. R.
Published: July 2002

The relationships between the chemistry and composition of the intergrain regions, and the optoelectronic properties of the grain boundaries are examined. Specifically, two impurity related mechanisms are reported. The first is the segregation of oxygen to the grain boundaries during thermal processing of the materials or devices. The oxygen localization at the boundary directly correlates with the electrical activation of these regions. The second is the passivation of the grain boundaries by incorporation of hydrogen in the intercrystalline regions. The localization of the hydrogen at these defects is demonstrated by SIMS, and the reaction between the hydrogen and the oxygen is indicated.
Studies of initial oxidation of nickel–chromium alloys: Surface annealing by hydrogen ion bombardment
Authors: McIntyre N. S. , Kover L. , Chan T. C.
Published: July 2002

Nickel-18% chromium binary alloy and alloy 600 (77% Ni, 16% Cr, 8% Fe) have been oxidized at 600 °C for periods of several minutes under O2 pressures of <10−6 to 10−4 Torr O2. The polycrystalline surfaces were pretreated by ion bombardment with 5 kV hydrogen ions. The oxide structure developed thereafter is found to be strongly influenced by grain orientation. One major grain orientation produced a chromium-rich surface oxide, while a second orientation gave rise to a surface oxide with a high nickel concentration. On some grain surfaces, a repetitive pattern of nodule oxide growth was observed with a structural pattern which is peculiar to a specific grain orientation. On surfaces remote from H+ bombarded areas, initial surface oxide composition is more governed by local stresses which develop along scratches. It is argued that alloy surface pretreatment with H+ anneals local mechanical stresses and allows substrate crystallographic orientation effects to become important.
A new gross leak calibration for leak detectors
Authors: Scuotto Frank
Published: July 2002

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.