bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of the Accommodation Coefficient on Slider Air Bearing Simulation
Authors: Huang Weidong , Bogy David B.
Published: July 2002

In solving the slider air bearing problem, both the Molecular Gas-film Lubrication (MGL) model and the Direct Simulation Monte Carlo (DSMC) model require the accommodation coefficient as input. The accommodation coefficient represents the fraction of the air molecules that interact with solid boundaries in a diffusive manner. In general, the value 1 is used for the accommodation coefficient, which represents a fully diffusive reflection. However, in magnetic hard disk drives, the disk and slider surfaces are becoming ever smoother with different kinds of lubrication on the disk, while the temperature is becoming higher due to the faster spindle speed. Under these conditions the unit value of the accommodation coefficient may no longer be suitable. In order to understand the effect of the accommodation coefficient on the slider’s flying parameters, we used Kang’s new database for the Poiseuille flow rate Qp and Couette flow rate Qc to solve the modified Reynolds equation for two groups of sliders, e.g., negative and positive pressure sliders (“negative” refers to sliders with subambient pressure zones). The results show that, in general, the smaller the accommodation coefficient, the lower the flying height and pitch angle. Positive pressure sliders are more sensitive to the accommodation coefficient than are negative pressure sliders. The typical discrepancy in flying height is around 10%. Also, it is shown that for positive pressure sliders the lower the flying height, the larger the discrepancy percentage. [S0742-4787(00)00402-1]
The Determination of End-Wall Blockage in Axial Compressors: A Comparison Between Various Approaches
Authors: Horlock J. H.
Published: July 2002

The end-wall blockage in axial compressors has been the subject of several investigations over a period of many years. This paper reviews and compares various approaches to determining the blockage, particularly in the “repeating” stage, a stage deeply embedded in the compressor where an equilibrium state is reached, the flow through any one stage repeating in the next. These approaches include: (i) correlations of displacement thickness measured in compressor rigs; (ii) a relationship between outlet blockage and the clearance area, based both on an empirical development of a simple model of the flow through the clearance space and full CFD calculations of the flow; (iii) momentum analysis of the flow through the blockage region, developed from the boundary layer analyses of some years ago, but not now relying on boundary layer concepts. [S0889-504X(00)01502-6]
The V2O5 Surface Phonon Spectrum
Authors: Poelman H. , Fiermans L.
Published: July 2002

V2O5 is a layered semiconducting oxide, which is used as a catalyst for the partial oxidation of hydrocarbons. In view of its catalytic applications, the vibrational properties of the (001) surface were examined by means of HREELS, a technique which is uniquely sensitive to the first layers' characteristics. On a clean single crystal, surface phonons corresponding to IR active vibrational modes are detected. The layered structure of single crystal V2O5 allowed for the creation of a clean (001) surface by UHV cleavage. The loss spectrum was recorded using a SEDRA spectrometer, providing a highly monochromatic, low energy primary electron beam. Hence, with a minimum of surface interference, a detailed loss spectrum with FWHM of 2.87 meV was obtained.
Damage of InP (110) induced by low energy Ar+ and He+ bombardment
Authors: Zhao Q. , Deng Z. W. , Kwok R. W. M. , Lau W. M.
Published: July 2002

Plasma-induced surface damage of a III–V compound semiconductor, a problem associated with many device fabrication processes, is clarified with careful measurements of surface defect density induced by low energy ion bombardment of InP. In the study, n- and p-InP (110) surfaces were prepared by cleavage of InP in ultrahigh vacuum, and then bombarded as a function of ion type (He+ and Ar+), energy (5–100 eV), and fluence (1012–1017 ions/cm2). The dynamic process of surface Fermi level shifting induced by such bombardment was determined by in situ high-resolution x-ray photoelectron spectroscopy, and the data were then converted to information on surface defect formation. It was found that both He+ and Ar+ bombardment with the above conditions moved the Fermi levels of both n- and p-InP (110) surfaces towards 0.95 eV above the valence band maximum of InP. As expected, for the same bombardment energy, Ar+ caused more damage than He+, and for the same ion type, the bombardment induced a surface defect density increasing with both ion energy and fluence. It was also found that the threshold condition for defect formation was a combined function of the impact energy of the incoming ion and the energy released during its neutralization.
Theoretical and experimental investigation of ultrathin oxynitrides and the role of nitrogen at the Si–SiO2 interface
Authors: Demkov A. A. , Liu R. , Zhang Xiaodong , Loechelt Heather
Published: July 2002

We investigate microscopic properties of ultrathin oxynitride gate dielectrics using a combination of first principles electronic structure methods and the attenuated total reflection (ATR) infrared spectroscopy. We use a theoretical structural model based on the Si–SiO2 interface. The quantum molecular dynamics simulations suggest that N accumulates at the interface. We have generated samples with the nitrogen concentrations from 1.69×1014 to 6.78×1014 cm−2. The analysis of nitrogen containing cells indicates a significant structural improvement of the oxide layer and the strain reduction at the interface. We have performed a calculation of the vibrational density of states. The experimental infrared ATR data is in qualitative agreement with the calculation. The valence band offset is estimated with two different theoretical methods. Calculations reveal a close agreement between a reference energy level based method and a direct estimate based on the density of states analysis. For the highest nitrogen concentration considered we find a 0.3 eV increase of the valence band offset due to nitrogen at the interface. The leakage current is studied using the Landauer theory to model the conductance through the gate dielectric.
Ferromagnetic III–V heterostructures
Authors: Ohno H.
Published: July 2002

Properties of the ferromagnetic III–V semiconductor (Ga,Mn)As and heterostructures based on it are reviewed. A model based on hole-mediated ferromagnetic interaction is shown to successfully describe the ferromagnetic transition temperature of (Ga,Mn)As. Spontaneous splitting of resonant tunneling spectra was compared with theory and shown to result from the spin splitting of the valence band. The first demonstration of spin-dependent scattering in magnetic semiconductor trilayers as well as electrical spin injection is also reviewed.
Monte Carlo modeling of electron beam physical vapor deposition of yttrium
Authors: Fan Jing , Boyd Iain D. , Shelton Chris
Published: July 2002

As part of a study on the deposition of superconducting films of YBa2Cu3O7−δ, a three-dimensional electron beam physical vapor deposition process of yttrium in a vacuum chamber is investigated both computationally and experimentally. The numerical analysis employs the direct simulation Monte Carlo (DSMC) method. The experimental studies consist of atomic absorption spectra taken in the evaporated yttrium plume and deposited film thickness profiles. Some important modeling issues such as atomic collision cross sections for metal vapors and hyperfine electronic structure of the atomic absorption spectra are addressed. Film deposition thicknesses on the substrate and atomic absorption spectra given by the DSMC method and experiment are in excellent agreement. Collisions between the atoms are found to have a significant effect on the film growth rate and area of uniform deposition as the evaporation rate of yttrium increases.
Enhanced Superconducting Transition Temperatures in Disordered, Mixed Film Materials
Authors: Guyon E. , Neunier F.
Published: July 2002

Thin superconducting “disordered” films are known to have enhanced thermodynamic critical properties. Various mechanisms can come into play. We have paid particular attention to the possible effect of favorable proximity of polarizable materials in close contact with superconductors. Two types of systems have been studied: (1) mixtures of superconductors and organic polarizable molecules (such as In anthraquinone, where Tc → 4.6K); (2) co-deposited films of superconductors and semimetals or semiconductors (Tc = 6.2K  for  In + 10%  Ge;  6.45K  for  Al + 10% Ge). This effect has to be substrated from the softening of phonon modes due to the existence of a large surface area in such systems. Quantitative information on the two mechanisms is obtained from electron tunneling experiments on the mixtures where the tunneling density of states and phonon spectrum can be analyzed.
Interpretation of Mössbauer Spectra in Thin Iron Films
Authors: Varma M. N. , Hoffman R. W.
Published: July 2002

Mössbauer spectra for films condensed and analyzed in uhv are reported in the thickness range 1–42 Å and from 15–350 K. The main features of the spectra can be explained in terms of superparamagnetic fluctuations of the magnetization within a given crystallite. Films in the thickness range 15–42 Å, have a value of internal magnetic field which is slightly less than the 330 kG observed in bulk iron. As the films approach 12 Å, the hyperfine lines move inwards by about 16% when the temperature is raised from 15 to 350 K, but the lines are still well resolved. Assuming a simple uniaxial anisotropy model the magnetization is stable on a time scale of the Larmor period for particles >90 Å average size and the magnetic hyperfine spectrum collapses to a doublet for particle size <70 Å. We interpret this as arising from the complete collapse of the four excited state levels and the partial decrease of the ground state splitting corresponding to the superparamagnetic fluctuation time being limited by the frequency factor τ0 rather than the volume or temperature. The large separation of the doublet in the 0.4-Å film is explained in terms of an electric field gradient at the iron nuclei due to the glass substrate or some contamination of the substrate.
More Repeatable Moser and Poltz McLeod Gauge
Authors: Miller J. R.
Published: July 2002

Modifications in design and operation are described which increase the repeatability of measurements made with Moser–Poltz McLeod gauges. Larger capillary chambers (≃1-mm diam and height) have been used which when combined with new reading techniques, attention to cathetometer use, awareness of electrostatic charge effects, and vibration, give a repeatability of 0.06 to 0.1 mm (95% confidence level) in reading h1–h2 in the operating equation P=v/(V1–V2)(h1–h2). This compares to the 0.2 to 0.4 mm realized earlier. Possible systematic errors due to heating of the gas by the light source and depression of mercury surfaces in operation when pertinent volumes are usually determined with water (undepressed surfaces) are discussed. Operational photographs, taken through a high-power cathetometer eyepiece, of the light reflected from the mercury surface are presented.
The Development of the Trochoid Vacuum Pump and First Application Experience with This Pump
Authors: Baechler W. G. , Knobloch D.
Published: July 2002

Tests have shown that the circular piston principle, i.e., as in the Wankel motor, is not suitable to construction of a mechanical vacuum pump. Studies of the various possible types of circular piston designs have led finally to the development of the Trochoid pump. This is a pump with a rotating piston in the shape of a hypotrochoid. Pumps were constructed and built with 400 and 630 m3/h pumping speed. The first pumps were tested in the metallurgy, chemical industry, and vacuum meat packing industries. These are now being built on the production line. Larger pumps with pumping speeds up to 2000 m3/h are in design and construction. Features of the trochoid pump are total dynamic balance, extremely low noise level, smaller size than other pumps with the same free air capacity, direct drive, no gears or belts, self-venting, and very large oil capacity.
Improved Turbomolecular Pump
Authors: Osterstrom G. E. , Shapiro A. H.
Published: July 2002

Construction and performance characteristics of a radically new 1600 liter/sec turbomolecular vacuum pump are described. The blade geometry and disk row configuration for the desired pumping speed and pressure ratio were selected from calculations of many models generated in accordance with theory containing no empirical elements. A tenfold improvement in pumping speed over corresponding size machines of a decade ago has been achieved. The new pump also incorporates an integral liquid nitrogen cooled panel with 16 000 liter/sec water vapor pumping capacity.
Pumping Fluid Condensation in Oil Diffusion Pumps
Authors: Hablanian M. H.
Published: July 2002

Condensation conditions of the motive fluid in an oil diffusion pump are considered with particular attention to the backstreaming problem. The backstreaming rate is correlated with the temperature of the “cold caps” surrounding the pump nozzle and it is demonstrated that an upper temperature limit exists near 200 °F where such devices cease to function effectively. The effect of “oleophobic” surfaces on cold caps and baffles is discussed. Conditions existing at the inlet of diffusion pumps and in baffles do not warrant attempts to introduce dropwise condensation. The condensation coefficient of pumping vapor at the temperature of the water cooled wall and with the flow rates used at the top nozzle appears to be very close to unity. The usefulness of creep barriers with modern pumping fluids and trap designs is judged to be questionable.
Surface Studies by Field Ionization Mass Spectrometry
Authors: Beckey H. D. , Röllgen F. W.
Published: July 2002

Surface processes play an important role in vacuum science. The field-ionization (FI) mass spectrometer is a versatile tool for the study of such processes. A review will be given of (1). Experimental techniques of FI mass spectrometry. Different FI-emitter types and their specific applications (metal tips for production of fields up to 5×108 V/cm, sharp metal blades or foils for the study of catalytic reactions on metal surfaces, thin wires covered with organic microneedles for general analytical applications). FI sources with emitter and sample locks. Types of FI mass spectrometers. (2). Growth of organic needles on surfaces in high electric fields (field polymerization”). (3). Mechanisms of surface reactions as studied by the field-impulse desorption technique. (4). Observation and analysis of surfaces by the atom probe field ion microscope of E. W. Müller. (5). Analysis of adsorbed organic molecules by the field desorption technique. The field ionization (FI) mass spectrometer is a versatile tool which can be used for many different studies such as structure elucidation of organic molecules, quantitative analyses of organic mixtures, kinetics of fast ion decomposition reactions, surface reactions, analysis of single surface atoms, and general field ionization phenomena. Only those points will be reviewed here which have some relation to vacuum sicence and technology, i.e., which are concerned with surface phenomena.
Electrical Properties of Sputtered Au/Ta2O5 Cermet Thin Films
Authors: Sashital S. R. , Pakswer S.
Published: July 2002

Thin film cermets of Au/Ta2O5 were deposited by rf co-sputtering, using two different methods, on glass substrates. In the first method a single target of Ta2O5 covered partially with Au was used. The second method utilized tile sputtering of Au, in the form of a mesh placed in the plasma of an rf discharge between the Ta2O5 target and the substrate. The composition of the cermets investigated varied from 11% to 52% by weight Ta2O5. The resistivity varied from 6×10−5 to 32 Ω⋅cm with the corresponding TCR’s from +1700 to −2000 ppm/°C. Resistivities were measured in the temperature range −180-160°C. Plots of logρ vs T−1 for negative TCR films show the occurrence of three different activation energies for the conduction process: a low activation energy for T<133K, intermediate activation energy for 133K<T<∼253K, and a high activation energy for T>253K approximately. Good correlations between resistivity, TCR, activation energy, and composition are observed. Resistivity is seen to correlate well with TCR.
Medium Energy Electron Diffraction
Authors: Moon A. R. , Cowley J. M.
Published: July 2002

In recent years low energy electron diffraction (LEED—electron energy range 10–500 eV), and to a lesser extent reflection high energy electron diffraction (RHEED—energy range 40–100 keV), have played an important role in the investigation of surfaces of solids. Both techniques are however beset with many experimental and theoretical difficulties. Diffraction techniques in the medium energy range (MEED—energy range 1–10 keV) should have theoretical and experimental advantages over both LEED and RHEED. These advantages are discussed and a review is made of the available theoretical methods suitable for this energy range.
Theory of the Inelastic Scattering of Low-Energy Electrons from Crystal Surfaces by One-Phonon Processes
Authors: Roundy V. , Mills D. L.
Published: July 2002

In this paper, we present a theoretical discussion of the form of the differential cross section per unit solid angle, per unit energy shift for the inelastic scattering by one-phonon processes of low-energy electrons from the surface of a semi-infinite crystal. A number of general features of the cross section are discussed, with particular attention to a comparison with the results obtained from the kinematical theory of the scattering process. We have also carried out a series of numerical studies of the dependence of the shape of the energy loss spectrum on momentum transfer for an electron incident on the (100) surface of an fcc crystal. For a general value of the momentum transfer, the energy loss spectrum consists of one or more lines that arise from the scattering off surface modes, and a band that has its origin in scattering produced by bulk modes. The shape of the latter feature, as well as the position of the surface mode peaks, is found to be quite sensitive to the values of the atomic force constants appropriate to the surface layer. It is suggested that the experimental study of the shape of the loss spectrum will provide a powerful means of probing the frequency spectrum of the atomic vibrations near the surface.
Madelung Potential in Surface Reconstruction
Authors: May John W. , Carroll C. E.
Published: July 2002

A reconstructed surface layer on a metal may resemble a two-dimensional ionic crystal. We test this ionic model by estimating the Madelung potential at the sites of foreign anions in mixed layers on nickel. For oxygen on Ni(100), the Madelung potential shifts the electronic energy levels of the ions, and these shifts are consistent with recent experimental data obtained by ion neutralization spectroscopy and photoemission. For sulfur and selenium on Ni(100), reconstruction to form mixed layers is consistent with the data only if the S and Se ions are considerably distorted.
Photoconductivity of InSb after Various Surface Treatments
Authors: Kreutz E. W.
Published: July 2002

Light and x rays change the surface conductivity in n- and p-type InSb single crystals at liquid nitrogen temperature. In order to study the influence of surface parameters, differences in physical characteristics caused by various surface treatments are compared in terms of ambient effects and the ac field effect. Independent of treatment the space charge regions are of p-type, and the energy bands in the surface layer are bent more upwards during irradiation. A combination of different electron excitations from the InSb valence band over the potential barrier into surface states or into vacuum, from the surface states back to the semiconductor or into the vacuum leads to the measured signs of changes in surface conductance. The experimental results give information on the energetic situation and the density of the concerned surface states as well as on the kinetics of the excitation processes.
Changes in Photoelectron Emission from Molybdenum Due to Exposure to Gases
Authors: Clewley J. D. , Crowell A. D. , Juenker D. W.
Published: July 2002

Observations of photoelectron emission from metal surfaces have been used by many investigators to study changes in work function due to exposure to gases. Although changes in the photoemission characteristics not attributable to work function changes have also been observed, there seems to have been little attempt to interpret these changes in terms of electronic changes at the surface. Studies of the changes produced in the surface photoelectric yield of polycrystalline Mo due to exposure to CO, N2, and O2 have been made using vectorial photoeffect methods and interpreted with the aid of a simple Sommerfeld model due to Mitchell which introduces an effective depth of the Fermi sea. Changes in this depth as well as work function changes have been inferred. Exposure to gases increases the work function but decreases the effective depth of the Fermi sea.
Determination of Adsorbate Structures on Metal Surfaces: Alkalis, Rare Gases, and Hydrogen on Tungsten
Authors: Schmidt L. D.
Published: July 2002

The information needed for characterization of adsorbate structures is discussed, and the experimental situation is summarized for three much studied prototype systems: the alkalis, rare gases, and H2 on individual crystal planes of W. While fairly complete pictures of these systems emerge, notable gaps and contradictions remain. The number of distinct states on the surface has not been established for the alkalis and the rare gases on most planes. LEED patterns for Cs and H2 on (100)W have not yet been correlated with amounts and binding states determined by other methods. The alkalis and rare gases are remarkably similar in dipole moment and relative binding energies on different crystal planes. Structures of these systems appear to be determined by substrate geometry, and bonding can be explained reasonably well on the basis of van der Waals and electrostatic forces. For hydrogen the number of states cannot be predicted from substrate geometry alone nor can the relative binding energies be explained from known forces. Still lacking for all of these systems are unequivocal determination of the adsorption sites and the charges on the adsorbates.
Semiconductor Surface States Considered on the Hubbard Model; Correlation with Electron Paramagnetic Resonance Data
Authors: Miller D. J. , Heron D. L. , Haneman D.
Published: July 2002

The occurrence of a strong electron paramagnetic resonance (EPR) signal from clean Si surfaces, and its sensitivity to gas exposures, indicates the presence of a high density of unpaired electrons (about 2×1014 cm−2) in the surface region. Previously this has not been correlated closely with other surface experiments. It is shown that the application of ordinary Hartree-Fock (H-F) band theory to the unpaired electron states leads to serious difficulties in accounting for the EPR results. This problem is considered and shown to result from the inadequate treatment of correlations in H-F theory, which is serious when electron densities lower than in the bulk are encountered. By applying the improved treatment developed by Hubbard for such cases, some difficulties are shown to be removed. One obtains a natural explanation of the two narrow surface state bands deduced by Allen and Gobeli from Si surface photoelectric data. The approach should generally be applicable to all semiconductor surfaces. It is predicted that where two surface state bands are formed by this mechanism, their separation will be of the order of, or greater than, the surface bandwidths.
GaAs Evaporated Thin Film Memory Diodes
Authors: Takahashi Kiyoshi , Moriizumi Toyosaka
Published: July 2002

Memory effects observed on GaAs thin films that were evaporated on tungsten substrates have been studied. If metallic films are evaporated on the GaAs thin films, a polarized memory effect is found between the tungsten substrate and the metallic film. A nonpolarized memory effect is found if a metallic wire point contact is made to the GaAs film. These memory effects were only slightly dependent on counterelectrode, point contact, and substrate materials used and originated from the properties of the GaAs evaporated film itself.
Auger and Other Characteristic Energies in Secondary Electron Spectra from Thin Evaporated Phosphorus Films
Authors: Melles J. J. , Davis L. E. , Levenson L. L.
Published: July 2002

The structure in the silicon and phosphorus Auger electron spectra (AES) for phosphorus evaporated onto a silicon substrate was studied. Similar satellite peaks were observed on the high-energy side of the silicon and phosphorus principal Auger transition. Measurements of the respective energy separations gave values lower than the silicon bulk plasmon energy. A study of the AES of phosphorus on copper did not show any reptition of the copper fine structure in the phosphorus Auger spectrum. Fine structure was observed on the silicon ionization loss peaks and was interpreted in terms of characteristic losses. These losses match those seen for the principal silicon Auger peak in size and energy. Electron binding energies, as determined from the ionization loss spectra, are reported.
Superconducting Properties and Structure of Reactively Sputtered Niobium Carbide Thin Films
Authors: Spitzer Hermann J.
Published: July 2002

Niobium carbide thin films have been sputter deposited in a reactive argon and methane plasma at substrate temperatures of 700 °C. The background pressure prior to sputtering was typically in the low 10−7-Torr range, the total sputtering pressure was maintained at 2×10−3 Torr and the partial pressure ratios of argon and nitrogen were monitored and controlled with a residual gas analyser. Jc–H characteristics were measured by applying a pulsed field and pulsed current method and transition temperatures were determined by recording resistivity versus sample temperature. The structure was studied by x-ray diffraction. Hc2 is about 40 kOe and the highest Tc is 9.6 K. Several carbide phases and their mixtures were observed and have been correlated to the partial pressure ratios of the plasma.
Vacuum System for an Infrared Calibration Facility
Authors: Uhlin John
Published: July 2002

Calibration facilities for large aperture (up to 56 cm diam) infrared radiometers require commeasurable size vacuum chambers with full thermal shrouding and ultraclean pumping systems. Such a facility has been fabricated and will be described in detail. The chamber is 106 cm in diameter and 4.87 m long. It utilizes integral ion pumping for operation in the 10−6 Torr region. Economic considerations and time constraints of the total system program required local fabrication and, therefore, non-proprietary-type flange sealing. The sealing mechanism used was the flat flange with aluminum wire effecting the seal. Included in the discussion is the description of the cryogen distribution system which allows complete constant temperature control of the several shroud structures.
Electron Irradiation Effects on Thin CaF2 Films
Authors: Koch F. A. , Vook R. W.
Published: July 2002

CaF 2 films, 30–1000 Å in average thickness, were formed at 25–380 °C on {001} NaCl under ultrahigh vacuum conditions. Transmission electron diffraction and microscopy showed that these films consisted of many {110} oriented crystallites coexisting with {001} oriented crystallites. It was found that high intensity 50-, 80-, and 100-kV electron beams in the electron microscope altered the structure of these films. The electron beams had a randomizing effect on the CaF2 films. Extra diffraction rings were observed that could not be explained in terms of CaF2 or double diffraction reflections. These extra rings were due to CaO. No diffraction evidence for free Ca metal was obtained. Previous work by Evans suggested that CaF2 decomposes to form free Ca under the action of an electron beam. In the present work it is believed that electron irradiation first produces free Ca metal which then oxidizes to CaO in the relatively high oxygen partial pressure in the electron microscope.
A High-Performance, Low-Cost Digitally Driven SEM System for Materials Studies and Microfabrication
Authors: Pasiecznik John , Frey Jeffrey
Published: July 2002

The design and construction of a low-cost but high-performance digitally driven scanning electron microscope (SEM) system is described. The low cost of the system is achieved by designing the digital drive mechanism around a programmable desk calculator with expanded cassette or disk memory. Precision of beam placement and deflection, uniformity of beam current, and reproducibility of beam location; are achieved by combining the best elements of previously developed analog and digital beam-drive systems. A hybrid analog/digital technique is used to generate lines. Endpoint data for lines are specified digitally and a continuous line is generated between the endpoints at a constant writing speed. This technique results in the generation of lines free of steps, glitches, and transients, can be used for generation of rotated or skewed vectors, and is not limited to rectangular geometry. In order to facilitate high-speed operation, not limited by the relatively low-output cycle time of most small programmable calculators, and to conserve the limited memory capabilities of these machines, a dedicated hardware logic system is used to generate all endpoint data needed to fill in rectangular areas. Upon command, a special subprogram can be called to generate circles or other desired geometries. The system can be scaled in time and hence made compatible with most x–y plotters to allow checking of the exposure program. The interface to the HP9820 and the hardware logic system described can be applied easily to other calculators with similar capabilities. Since its capabilities can be achieved at relatively low cost, this system could be of great use in smaller research establishments in programs involving SEM diagnostics and scanning electron-beam exposure of resists for microfabrication, particularly in the semiconductor device field.
An Automated Electron-Beam Mask Generator
Authors: Friedmann E. B. , Livesay W. R. , Rubiales A. L.
Published: July 2002

An over-all system approach has been undertaken to make electron-beam microfabrication practical in a production environment at throughput rates which make it economically attractive to semiconductor manufacturers. An electron-beam system designed for fabrication of IC masks at final size in one step is described. Novel features include an ultrahigh-speed 16-bit digital deflection system, high-vacuum compatible x–y table and a field-emission source. System features described are single operator performance, multiple methods to input mask designs, high-speed deflection system, and (intelligent) beam logic interface and CAD system. The system is capable of producing 1.0-μ lines with ± 0.2-μ precision over a 0.25×0.25-in. scan field with coverage of 3×3-in. masks using step and repeat techniques. The system also includes an automated load-lock, cryopumped vacuum system and a high-speed 16-bit minicomputer. System parameters such as throughout time, writing speed, and factors affecting these parameters will be discussed.
Investigation of Soft X-Ray Absorption Edge Structure using an Energy Modulated Electron Beam
Authors: Ramachandran K. N. , Cox C. D.
Published: July 2002

The absorption edges of elements can be investigated using an energy-modulated electron beam by plotting the derivative of the total x-ray yield against electron energy, called the appearance potential spectrum. A simple apparatus was built, consisting of a tungsten-electron source and a large-area windowless x-ray detector, located in an ultrahigh-vacuum system. The soft x-ray absorption edge structure of the light elements from beryllium to oxygen and a few heavier elements was obtained. Electron currents in the range of 1 mA were normally needed for most of the experiments, though successful recordings were made at 15 μA. All of these spectra show complex structure which is presumably related to the density distribution of the empty states in the valence band. The L-edge structure of iron and nickel is presented in pure and alloyed forms to demonstrate spectral shifts. Some anomalous structure was also obtained from certain specimens. Because of the low-energy of the probing electrons, the technique is basically a tool for surface analysis, sensitive to light elements. The simplicity of the apparatus makes it possible to adapt it to existing systems for surface studies.
Fabrication of Integrated CMOS Transistors using Electron Lithography and Ion Implantation
Authors: Sopira M. M. , Malmberg P. R. , Meiksin Z. H.
Published: July 2002

Electron lithography and ion implantation have been used in the fabrication of integrated complementary P-channel and N-channel transistors. A digitally controlled single electron beam system, the Electron Micropattern Generator, aligned and exposed the eight mask levels required. The cumulative alignment tolerance was 3 μ. Fabricated devices had channel lengths of 1, 2, and 6 μ, and drain-source breakdown voltages of − 22 and + 12 V for the P- and N-type, respectively. Ion implantation was used to produce self-aligned gate structures by extending the diffused source and drain contact regions to the gate edges. The implantation masks consisted of 3000 Å aluminum and 7700 Å PMM resist. Boron and phosphorus ions were implanted at 50 and 100 keV, respectively at dosages ranging from 1×1014 to 1×1015 ions/cm2. Sintering and annealing operations were performed at 500 °C for 10 min in N2 atmosphere. Sheet resistances ranged from 2700 to 1000 Ω/□ for implanted boron and 700−240 Ω/□ for the phosphorus. Evolving high-density circuits require shallow P-well junctions (≈ 2.7μ) and contact regions (≈ 0.7μ) in N-type 〈100〉 oriented silicon of 0.35 Ω-cm resistivity. Evaluation of the transistors showed enhancement mode operation with VTP=−4.8 V and VTN=+1.4 V using a gate dielectric structure consisting of CVD sandwich layers of 125 Å SiO2 plus 750 Å Si3N4, yielding average surface state density of 6×1011 charges/cm2. Evaluation of diffused and implanted transistors, as well as resistors, will be discussed.
Investigation of the Sensitivity of Ionization-Type Vacuum Gauges
Authors: Holanda Raymond
Published: July 2002

A quantitative analysis of a large and representative sample of available data has been made to determine the best criteria for predicting the relative sensitivities of ionization-type vacuum gauges to different gases. The molecular property of the gas that correlates best with relative sensitivity is the ionization cross section σ (eV). The best σ value to choose according to gauge type is as follows: 1. For high-pressure ionization gauges, a σ evaluated at 23 of the accelerating potential of the gauge is the best choice. 2. For Bayard-Alpert and triode gauges, any of three choices are of approximately equal value. These are 100 eV σ values, maximum σ value for each gas, and a σ evaluated at 23 of the accelerating potential for each gauge. 3. For the Alphatron gauge, σ values in the range 5000–10 000 eV provide the best correlation. 4. For cold cathode ionization gauges, insufficient data were available to come to any conclusions.
A Simple Method of Calculating the Effectiveness of High Temperature Radiation Heat Shields
Authors: Welch Kimo M.
Published: July 2002

A method is given whereby one may graphically determine the radiation heat transfer properties of a number of closely packed radiation shields. The method uses the gray body formula, taking into account variations in total thermal emissivity of the adjacent shields as a function of temperature. Results were used in the construction of a high temperature vacuum furnace. Excellent correlation was found between graphically predicted and calorimetrically measured results.
Generation of Picosecond Pulse Electron Beams
Authors: Ura K. , Morimura N.
Published: July 2002

Picosecond pulse electron beams were generated by means of a transverse-type gate and a buncher. The 20 keV beam was deflected by a 1 GHz symmetrical reentrant cavity and chopped by a slit into several tens picosecond pulses. These pulses were bunched by a 4 GHz reentrant cavity. The pulsed beam was then deflected by the other 1 GHz x–y deflectors and finally reached the screen, where the pulse width was measured by comparing the lengths of two chopped arcs with that of the unchopped full circle. A minimum pulse width of 6 psec was recorded. It was observed that as the deflecting voltage of the transverse gate increases, the pulse width decreases at first, reaches a minimum, and then increases. This can be explained by the longitudinal velocity modulation due to the fringing field of the deflector. When the beam chopped by the transverse gate was injected to the longitudinal gate, the maximum phase compression ratio was less than 5; this is also explained by the above-mentioned effect.
The Beam Optics Design of Pulsed, Large Area Electron-Beam Accelerators in the 150–300 kV Range
Authors: Frutiger W. A. , Uglum J. R. , Quintal B. S. , Nablo S. V.
Published: July 2002

We have modified the design of our commercial “Electrocurtain” electron-beam accelerators to provide for pulsed, medium current-density beams (10–30 mA/cm2) with a total output beam-area in the range of 1000–1500 cm2. Two different approaches to the design of such systems are presented. In the first approach, a cylindrically symmetric geometry is employed, with the cathode extending along the symmetry axis (typically 1-m long). Beam expansion to the desired output area is dominated by the electric fields in the coaxial accelerating gap. For the second approach, several short cathodes span the short dimension of the output window and are evenly spaced along the long dimension of the window. Beam expansion is achieved in a field-free region. In both cases, the beam current is provided by cylindrically divergent Pierce-type diodes fitted with barium-dispenser cathodes. This design allows for grid control of the output current independent of the main accelerating voltage. Computer simulations of the beam flow will be discussed.
Surface structure determination via a transform-deconvolution method
Authors: Landman Uzi , Adams D. L.
Published: July 2002

A fast direct-transform method for the determination of surface structures from low-energy-electron diffraction (LEED) intensity data is presented. Basic principles of a proper transform construction and its applications are discussed and demonstrated. The effects of data truncation is studied and a deconvolution procedure for extraction of accurate structural information from the transform is described. Results of a complete surface structure determination of Ni(100) by application of the method to experimental data are discussed.
Diffraction peaks in secondary-electron energy spectra
Authors: Becker G. E. , Hagstrum H. D.
Published: July 2002

Energy spectra of secondary electrons from the (100) face of a well-ordered Ni crystal display peak in the 100–400-eV range, which cannot be associated with Auger transitions in atoms at the surface. These peaks diminish with increasing temperature at the same rate as the integer-order peaks at the same energy in the I-E characteristic for the (0,0) LEED beam near normal incidence. These peaks are also diminished by any degradation of the crystalline order in the near-surface region of the crystal such as that caused by ion implantation during sputtering or by the presence of surface impurities in a nonordered structure. The. observed properties suggest a diffraction phenomenon, and a discussion is given of possible relationships with other diffraction effects.
Thickness distribution of a metal-alloy from a high-rate electron-beam source
Authors: Erikson E. Darrell
Published: July 2002

The coating thickness distribution from a rod-fed electron-beam source was investigated for three modes of evaporation: (1) high vacuum evaporation, (2) evaporation at a 2–70 mTorr pressure of argon in the substrate chamber (i.e., “pressure plating”), and (3) evaporation at 1–20 mTorr pressure of argon and with 3–7-kV dc bias applied to the substrates (i.e., “ion plating”). The source used a 5.1-cm-diam 304-L stainless steel rod as the evaporant and, at a nominal power of 60 kW, had apparent deposition rates above 25 μ/min at a 32-cm source-to-substrate distance. Experimental results indicate that there is a marked change in the thickness distribution when deposition takes place at increased pressures, with the over-source coating thickness at 70 mTorr being almost five times as thick (2.92 vs 0.66 mm) as those coatings deposited at 4×10−5 Torr. The results also indicate, for high evaporation rate sources, that the thickness distribution is not influenced by the application of a high voltage bias to the substrate during deposition but is influenced by ambient pressures in the region of the substrate.
A bakeable vacuum microbalance for determining metal oxidation kinetics
Authors: Hussey R. J. , Graham M. J. , Cohen M.
Published: July 2002

Details are given of a vacuum microbalance used to study the oxidation of metals at high temperatures over a pressure range of 10−6–760 Torr. The balance is a modified Cahn RG Electrobalance housed inside a stainless steel chamber, which forms part of a bakeable all-metal UHV system. All possible electrical components were taken outside the vacuum system and all internal electrical connections were replaced by spot-welded platinum wire. After bakeout at 100 °C pressures of <5×10−8 Torr were obtained, the outgassing rate from the balance, walls, etc., being ∼8×10−8 Torr·liter·sec−1. Low oxygen pressures were maintained by a Granville-Phillips automatic pressure controller and either a conventional wire-wound resistance furnace or a radiant heating furnace using quartz-iodine lamps was employed to heat the samples. The performance of the balance is illustrated by some results on the oxidation kinetics of iron and nickel at 500 and 700 °C. The total noise level during an experiment was typically about 3 μg.
Electrostatic effects in microbalances. I. General considerations of the effectiveness of a radioactive ionizing source under ambient conditions
Authors: Hawley Robert E. , Williams Colin J.
Published: July 2002

This paper discusses the effectiveness under ambient conditions of an α-emitting polonium 210 source in relieving electrostatic charges of approximately −1000 V caused by friction, and what are believed to be “apparent” static charges of at least −2000 V caused by an induced dipole alignment in a dielectric material. It was noted that charges applied on either the exterior or interior of a specially designed microbalance hangdown glass tube could affect the sample basket and could be efficiently alleviated by the α irradiation. Charges of ∼20 V were found to be sufficient to maintain the sample basket against the wall of the enclosure, while charges of several hundred volts were required for the initial displacement of the sample basket.
The tungsten evaporation limit of hot-cathode ionization gauges
Authors: Angerth B. , Hulek Z.
Published: July 2002

Comparative measurements of pressures in the low 10−12-Torr range with hot-filament total and partial pressure gauges have shown discrepancies which can be partly explained by the influence of tungsten vapor from the hot filament on the total pressure gauge readings (tungsten evaporation limit). The method proposed by Alpert and Buritz, with a slight modification, was used for estimates of the tungsten evaporation limit; i.e., a second filament served as an auxiliary source of evaporated tungsten atoms. Three gauges were tested, one gauge with a buried collector and two modulated Bayard-Alpert gauges. The experiments showed that the tungsten evaporation limits of all three gauges fell in the range (1–2)×10−12 Torr (nitrogen equivalent pressure) with an electron emission of 10 mA. Provided the variation of the gauge sensitivity with the emission is known, it is recommended to operate at reduced emission (e.g., 4 mA), at which level the tungsten limit is substantially lower. Low-work-function emitters, as a means to obtain a low-temperature electron source, were not covered by the present study, which aimed at determining some performance limitations at very low pressures of a large number of existing gauges equipped with tungsten filaments.
An evaporation system for the metallization of bilevel substrates
Authors: Davis R. H. , Deo S. R.
Published: July 2002

An evaporation system has been designed and built to deposit uniform thin-film metallization on both surfaces of a ceramic substrate. The metallization consists of successive thin layers of Ti-Pd-Au which are to be deposited over an area of 9.5×11.5 cm and on the inside of 67 small holes (via holes) distributed over this area. The uniform evaporation over the area and through the holes in a single pump-down cycle is achieved by rotating the substrates biaxially inside the vacuum chamber. All deposition parameters (e.g., substrate, temperature, rate of deposition, deposition thickness, etc.) are automatically controlled since visual checks are inoperative due to shielding requirements. The uniformity of depositions on both the surfaces of the ceramic and around the perimeter of the via holes has been found to be within 3% over a range of thickness between 500 and 4000 Å.
Synchrotron x-ray diffraction and transmission electron microscopy studies of interfacial reaction paths and kinetics during annealing of fully-002-textured Al/TiN bilayers
Authors: Chun J.-S. , Carlsson J. R. A. , Desjardins P. , Bergstrom D. B. , Petrov I. , Greene J. E. , Lavoie C. , Cabral C. , Hultman L.
Published: July 2002

Dense fully-002-textured polycrystalline TiN layers, 110 nm thick with a N/Ti ratio of 1.02±0.03, were grown on SiO2 by ultrahigh vacuum magnetically unbalanced magnetron sputter deposition at Ts=450 °C in pure N2 utilizing high N2+/Ti flux ratios and low energy (EN2+=20 eV) ion irradiation of the growing film. Al overlayers, 160 nm thick and possessing a strong 002 texture inherited from the underlying TiN, were then deposited at Ts=100 °C without breaking vacuum. Synchrotron x-ray diffraction was used to follow interfacial reaction paths and kinetics during postdeposition annealing as a function of time (ta=200–1200 s) and temperature (Ta=500–580 °C). Changes in bilayer microstructure and microchemistry were investigated using transmission electron microscopy (TEM) and scanning TEM to obtain compositional maps of cross-sectional and plan-view specimens by energy dispersive x-ray analysis. The initial bilayer reaction step during annealing involves the formation of a continuous AlN interfacial layer which, due to local epitaxy with the TiN underlayer, grows with the metastable zinc-blende structure up to a thickness x≃3–5 nm, and with the wurtzite structure thereafter. Ti atoms released during AlN formation diffuse into the Al layer leading to supersaturation followed by the nucleation of dispersed regions of tetragonal Al3Ti with inherited 002 preferred orientation. The aluminide domains grow rapidly until they reach the free surface; thereafter growth is two dimensional as Al3Ti grains spread radially. The overall activation energy for Al3Ti formation and growth is 1.8±0.1 eV. In situ synchrotron x-ray diffraction analyses during thermal ramping show that the onset temperature for interfacial reactions was increased by more than 100 °C for fully dense completely 002-textured bilayers compared to 111-textured bilayers deposited by conventional reactive sputter deposition.