bluuebunny/crossref_metadata_2025 huggingface dataset:
In-line sputtering parameters for magnetic recording films
Authors: Johanson Robert G. , Carruthers William G.
Published: July 2002

A process has been developed to produce sputtered longitudinal magnetic recording films, using in-line sputtering systems. Coercivities can be varied from 650 to 1000 Oe, with squareness of 0.85 to 0.90. Modulation is <10%. Although disks produced with these films are in generally accepted parametric performance ranges, no attempt has been made to optimize the films for a particular head/disk/drive combination. The effects of varying the sputtering parameters are discussed.
Surface structure and composition profile of sputter-ion pump cathode and anode
Authors: Audi M. , Pierini M.
Published: July 2002

The composition profile of cathodes and of anode film of sputter-ion pumps previously operated with different gases has been analyzed. Such analysis has been performed using SEM, Auger, and x-ray photoelectron spectroscopy (XPS) techniques. The results give information about the depth of ions implanted into the cathode and the chemical composition of the anodic film. This information is the basis for a full understanding of pumping mechanism of sputter-ion pumps.
Central gas analysis laboratory with remote sampling
Authors: Ellefson R. E. , Morgan F. E. , Anderson B. E.
Published: July 2002

A computerized central analytical facility is described which remotely samples from 70 process points and analyzes the gas samples by mass spectrometry and other analytical techniques. Samples are transported through a capillary by pressure gradient to a vacuum manifold and ultimately to the inlet system of either of two mass spectrometers. Process pressures vary from 400 to 2500 Torr which assures viscous, nonseparative flow within the capillaries, the capillary whose inside diameters range from 0.03 to 0.05 cm. An exhaust-gas recovery system to retain valuable tritium from samples is also described. The sampling manifold and inlet systems are fabricated from high vacuum components and tubing that is polished on interior surfaces. All valves can be computer controlled or manually operated from a central control console. Valve actuation is verified by process changes. The gas is analyzed by a computer-controlled, magnetic-sector mass spectrometer, the results archived in another computer and the approved results sent to the requestor via a data network.
Advanced turnkey computer controlled thermal vacuum facility
Authors: Cary Ronald W.
Published: July 2002

The state-of-the-art has been advanced by CBI Na-Con, Inc. (CBI) in the completion of a turnkey contract, providing a computer controlled high vacuum thermal facility at Rockwell International. The chamber is the first designed and constructed for production-line-type testing of satellites. Four computers networked together provide complete control of the vacuum process, data acquisition, and history logging. A truncated side hinged door provides easy access into the chamber without bridges or lifts and a structural, LN2 cooled flat floor provides a 25 ft W×30 ft L work space. The aluminum shrouds inside provide temperatures of less than 90 K with a 40 kW concentrated heat load. The chamber is also designed so that it can be expanded to twice its present volume to accommodate a solar simulator. The unique features of this facility, including the computer integration of vacuum process equipment, specialized instrumentation and data acquisition equipment is discussed in this paper.
Characterization of the Tokamak Fusion Test Reactor plasma edge by Langmuir–calorimeter probes
Authors: Kilpatrick S. J. , Manos D. M. , Budny R. V. , Stangeby P. C. , Ritter R. S. , Young K. M.
Published: July 2002

Two combination Langmuir–calorimeter probes were operated on the Tokamak Fusion Test Reactor (TFTR) midplane to measure plasma properties of the scrape-off layer. Two different calorimeter elements were used: 0.5×3×8 mm Ta plates or 6.4 mm diameter graphite rods fitted with thermocouples. Separate graphite rods served as Langmuir elements. This paper presents Langmuir probe measurements of the radial profiles of edge density and electron temperature, and calorimeter measurements of heat flux. The variation of these quantities in certain operational regimes are presented, including dependence on Ohmic and neutral beam heating, compression and free expansion, plasma major and minor radii, plasma current, and line integral density with and without Cr gettering.
Operation of cold-cathode magnetron gauges in high magnetic fields
Authors: Thomas S. R. , Goerz D. A. , Pickles W. L.
Published: July 2002

The Mirror Fusion Test Facility (MFTF-B), under construction at LLNL, requires measurement of the neutral gas density in high magnetic fields near the plasma at several axial regions. This background gas pressure (BGP) diagnostic will help us understand the role of background neutrals in particle and power balance, particularly in the maintenance of the cold halo plasma that shields the hot core plasma from the returning neutrals. The BGP consists of several cold-cathode, magnetron-type gauges stripped of their permanent magnets, and utilizes the MFTF-B ambient B-field in strengths of 5–25 kG. Similar gauges have operated in TMX-U in B-fields up to 3 kG. To determine how well the gauges will perform, we assembled a test stand which operated magnetron gauges in an external, uniform magnetic field of up to 30 kG, over a pressure range of 10−8–10−5 Torr, at several cathode voltages. This paper describes the test stand and presents the results of the tests.
Process modeling for submicron complementary metal-oxide-semiconductor very large scale integrated circuits
Authors: Krusius J. P.
Published: July 2002

The issues arising in process modeling of submicron complementary metal-oxide semiconductor (CMOS) very large scale integrated circuits (VLSI) are examined for technologies with minimum feature sizes as small as 1/4 μm. The current process models, simulation methods, and existing process simulators are reviewed. Feature size reduction by a factor of about 5, increase of the dimensionality from one/two to two/three, enchanced process step coupling, new nonequilibrium processing methods, and the lack of multidimensional characterization methods are identified as the most important issues for process modeling. Two complementary paths for the evolution of process modeling are suggested.
Elimination of methane from the outer bulb of low-pressure sodium lamps
Authors: Kroontje W. , de Maagt B. J. , van Rijswick M. H. J. , Sprengers L.
Published: July 2002

The presence of methane in the outer bulb of low-pressure sodium lamps causes undesirable heat losses by conduction through the gas. Methane is formed by the reaction of water vapor or hydrogen gas with traces of carbon in the barium flash getter present in the outer bulb. Elimination of methane has proved to be possible by using a chemical cracking device consisting of, e.g., a supported platinum catalyst. Methane conversion occurs permanently throughout the complete lamp life. After 10 000 h in service the gas pressure is below 10−5 mbar and is only made up of argon and helium.
Preparation of amorphous electrochromic tungsten oxide and molybdenum oxide by plasma enhanced chemical vapor deposition
Authors: Tracy C. E. , Benson D. K.
Published: July 2002

Preliminary experiments have been performed to probe the feasibility of using plasma enhanced chemical vapor deposition (PE–CVD) to prepare electrochromic thin films of tungsten oxide and molybdenum oxide by plasma reaction of WF6, W(CO)6, and Mo(CO)6 with oxygen. Thin films produced in a 300 W, electrodeless, radio-frequency (rf), capacitive discharge were found to be electrochromic when tested with either liquid or solid electrolytes. Optical spectroscopy was performed on two electrochromic coatings after Li+ ion insertion from a propylene carbonate liquid electrolyte. Broad absorption peaks at ∼900 nm for WO3 and 600 nm for MoO3 were observed. Optical results for PE–CVD MoO3 films differ from those reported for evaporated MoO3 films which have an absorption peak at ∼800 nm. The shorter wavelength absorption in the PE–CVD MoO3 films offers the potential for fabricating electrochromic devices with higher contrast ratios and less color change. Optical emission spectroscopy, Auger, and x-ray diffraction analyses indicate these thin film deposits to be predominantly amorphous tungsten and molybdenum oxides.
Hydrogen–oxygen interrelations on a niobium surface
Authors: Shamir N. , Atzmony U. , Schultz J. A. , Mintz M. H.
Published: July 2002

Combined time-of-flight spectrometry of direct surface recoil (TOF-DR) and Auger electron spectroscopy (AES) measurements were utilized to study hydrogen–oxygen interrelations on a polycrystalline niobium surface. It was found that oxygen is energetically favored in the surface region with a hydrogen-rich layer located closely beneath it. Such a double-layered structure is obtained either when the niobium sample is heated in vacuum, or when a sputter-cleaned surface is exposed at room temperature to oxygen. The migration of oxygen atoms from the bulk to the surface and the formation of a surface oxygen enriched region prevents the desorption of H2 even at elevated temperatures. Exposing a sputter-cleaned hydrogen-rich surface to oxygen at room temperature, results in its rapid accumulation replacing topmost hydrogen atoms. A monolayer oxygen coverage is obtained at about 20 L. Subsequent exposures result in accommodation of oxygen in the subsurface region.
Atomic structure of GaAs(100)-(2×1) and (2×4) reconstructed surfaces
Authors: Chadi D. J.
Published: July 2002

Structural models for the Ga (or Al)-rich GaAs(100)-(2×1) surface and for the As-rich (2×4) surface are examined by tight-binding based total-energy calculations. The most stable (2×1) surface contains 1/2 monolayer of Ga vacancies which make the surface nonmetallic and nonpolar. For the (2×4) surface, unit cells containing various combinations of As2 dimers, missing dimers, and Ga vacancies were considered. The most likely surface structure contains three As2 dimers per unit cell. Two such structures, nearly degenerate in energy, are possible. The calculated surface electronic structures agree with photoemission data to within ±0.3 eV. The c(2×8) and (2×4) structures are closely related and both are expected to occur at the surface.
Vibrational excitation of physisorbed CO2 on a Ag(111) surface
Authors: Sakurai M. , Okano T. , Tuzi Y.
Published: July 2002

Vibrational excitations of CO2 molecules physisorbed on Ag(111) at 40 K were measured by high-resolution electron energy-loss spectroscopy (EELS). Measurements of EELS were performed at an incident electron energy of 1.5 to 30 eV for exposures of CO2 ranging from 0.5 to 5 L. Vibrational energies of three fundamental vibrational modes coincided with the values for CO2 molecules in the gas phase within ±3 meV. Resonance excitation of the symmetric stretch mode was observed at incident electron energies of 1.5 to 3 and 9 eV. The excitations of (n00) and (n10) progressions were significant at the incident energy of 2 eV, which is related to a 3.8-eV resonance known for electron–molecule collision in the gas phase.
Chemical state profiles from secondary ion energy distributions
Authors: Solomon J. S.
Published: July 2002

The chemical state of surface atoms affects the yield and energy distribution of secondary ions generated during a secondary ion mass spectroscopy (SIMS) profile analysis. However, because the bonding contributions to secondary ion energies tend to be very subtle, extraction and application of this information from SIMS profile data is rarely attempted. In this work, the mathematical technique of factor analysis was applied to secondary ion energy distribution curves recorded while sputter profiling layered structures. Where real chemical differences were present, the factor analysis solution yielded concentration profiles of the chemical components present.
Scanning tunneling microscopy study of the Re(0001) surface passivated by one-half a monolayer of sulfur in an atmospheric environment
Authors: Marchon B. , Ogletree D. F. , Salmeron M. , Siekhaus W.
Published: July 2002

The Re(0001) surface can be passivated by the adsorption of 50% of a monolayer of sulfur. The structure is ordered as shown by a 2((3)1/2×(3)1/2)R30° low-energy electron diffraction pattern. Exposure to air does not modify the surface composition nor the structure. We have obtained STM images of this surface in an atmospheric environment. Large and atomically flat domains have been observed, together with areas composed of multiple steps of various heights. Images of the local barrier height show a significant decrease near the steps, as expected. Higher resolution images recorded in this mode exhibit atomiclike features which are tentatively assigned to sulfur atoms. Short-range order with distances of the order of the superlattice parameter could be detected. No long-range order, however, has been observed.
Scanning tunneling microscopy imaging of microbridges under scanning electron microscopy control
Authors: Anders M. , Thaer M. , Mück M. , Heiden C.
Published: July 2002

A scanning tunneling microscope (STM) capable of three-dimensional coarse positioning has been developed for the purpose of examining and reexamining specific locations on a specimen surface. The STM is operated inside a scanning electron microscope in order to guide the tip to the area of interest on the specimen. The recording time for large-area STM images could be reduced by using a new scanning technique, which increased the maximum useful scanning speed to roughly 6 μm/s. Silicon wafer fragments were used as tips to improve large-area imaging in the STM. The shape of a thin-film microbridge was examined and then reexamined with a different tip. Characteristic STM image features are observed in both recordings. We conclude that they correspond to the true specimen profile.
Structural, ferroelectric, and pyroelectric properties of highly c-axis oriented Pb1−xCaxTiO3 thin film grown by radio-frequency magnetron sputtering
Authors: Yamaka Eiso , Watanabe Hirohito , Kimura Hideki , Kanaya Hiroyuki , Ohkuma Haruo
Published: July 2002

Thin films of ferroelectric Pb1−xCaxTiO3 (x=0.0–0.4) were formed on MgO, Pt/MgO, SrTiO3, and Pt/SrTiO3 substrates by rf magnetron sputtering. Characterization of the films by x-ray diffraction, x-ray precession, scanning electron microscopy, and electron probe microanalysis showed them to be epitaxially grown with their c-axis oriented perpendicular to the substrate. The decrease in the Curie temperature Tc and the increase in the pyroelectric coefficient dPs/dT with an increase in Ca doping were successfully explained by assuming that the Ca ions occupied Pb ion sites. Pyroelectric infrared detectors using Pb0.7Ca0.3TiO3 thin-film elements gave better performance than the detectors using PbTiO3 ceramic elements. The internal bias field EB and fixed polarization PB were observed to be a function of both the Ca content and temperature in ferroelectric hysteresis curves as well as in hysteresis curves of the dielectric constant as a function of the applied electric field. These phenomena were explained by the difference in thermal behavior between the sputtered films and the substrates at temperatures below Tc.
Surface extended x-ray absorption fine structure study of surface BaO layers on tungsten surfaces
Authors: Shih A. , Hor C. , Mueller D. , Marrian C. R. K. , Elam W. T. , Wolf P. , Kirkland J. P. , Neiser R. A.
Published: July 2002

Surface extended x-ray absorption fine structure (EXAFS) of near-monolayer BaO films on polycrystalline W surfaces has been measured above Ba L3 edge (≊5247 eV), with a total electron yield technique in an UHV system. Bond lengths and coordination numbers of the first two atom shells around the barium adatoms were analyzed using the ratio technique. We found that the first two strong features in the Fourier transform of the EXAFS spectra were from about three oxygen atoms and about six barium atoms, while no feature was observed attributable to the tungsten substrate atoms. A substantial Ba–O bond length contraction was observed for the surface BaO species, which is ∼2.3 Å, in contrast to the 2.76-Å bulk BaO value. An adsorption structural model is proposed.
Cryogenic sample manipulator for multipurpose sample analysis
Authors: Chia Victor K. F. , Veirs D. Kirk , Rosenblatt Gerd M.
Published: July 2002

A cryogenic sample manipulator for ultrahigh vacuum studies of surfaces by Raman spectroscopy of physisorbed gasses is described. The development of a cryogenic off−axis sample manipulator that can be cooled to 15 K and allows the sample to be placed at any distance desired from the rotational axis is reported in this paper. (AIP)
A process for improved Al(Cu) reactive ion etching
Authors: Hu C.-K. , Canney B. , Pearson D. J. , Small M. B.
Published: July 2002

The standard reactive ion etching (RIE) process for etching Al and its alloys in a single-wafer tool is basically a high-pressure (>100 mTorr), multistep etching process. A significant modification to this process is reported which incorporates the standard high-pressure Al(Cu) etch followed by a low-pressure overetch step. The etch gases used for Al(Cu) etching are a mixture of (BCl3/Cl2/CHCl3/N2). At pressures <100 mTorr, the cathode dc self-bias voltage is increased, enhancing the ion bombardment energy and hence directionality normal to the substrate. Then the component of etching by ion assisted or reactively sputtered etching increases relative to the reactive component, increasing the ability to remove Cu-rich residues. The low-pressure overetch step also exhibits a factor of 2 smaller etch bias than the standard process. This is estimated to be 0.05 μm/image in RIE of 1-μm-thick Al(Cu) films. We have demonstrated that lowering the pressure of the overetch step, hence increasing the ion energies but keeping the same reactive species, offers a more effective clearing process. Combining this clearing process with the overetch does not increase the total time required for the process. Using this process, 1.5-μm-thick metal lines of Ti/A1(2.5% Cu)/Si 0.6 μm wide were obtained with vertical sidewalls.
Energy transfer in the inelastic molecule–surface scattering
Authors: Shen Xueying
Published: July 2002

Vibrational (V)–rotational (R)–translational (T) energy transfer in the inelastic scattering processes of a diatomic molecule–stationary surface system has been investigated by three different theoretical approaches. The V–T–R energy distribution in the gas–surface collision is studied by quasiclassical trajectory calculations employing a modified semiempirical London–Eyring–Polanyi–Sato potential. The mechanism of vibrational and rotational excitation of the projectile molecule is examined. A quantum-mechanical bound state calculation and a close-coupling calculation are carried out to obtain the internal transition probabilities of the gas molecule. In the case of a rigid surface, there is no energy exchange between the gas molecule and the phononless surface; however, the molecule can still transfer energy from internal states into translational motion relative to the surface. The nondissipative V–T–R energy transfer plays a significant role in the molecule–surface interaction. The results also show that vibrational mediation is an important factor in selective adsorption, especially for the higher molecular incident (translational) energies. From the close-coupling calculation, we reach the conclusion that it is essential to include the vibrational degree of freedom of the projectile in order to describe the resonance scattering phenomena.
Steady-state rate of decomposition of formaldehyde on Ru(001)
Authors: Sun Y.-K. , Chan C.-Y. , Weinberg W. H.
Published: July 2002

The steady-state, absolute rate of decomposition of formaldehyde on the Ru(001) surface has been measured as a function of surface temperature from 310 to 750 K and for reactant pressures between 9.7×10−8 and 1.6×10−6 Torr. The only observed reaction products were carbon monoxide and hydrogen. Postreaction Auger spectroscopic analysis revealed a clean surface. Two distinct kinetic regimes are observed. At relatively low surface temperatures (and/or high formaldehyde pressures), the rate is zero order in formaldehyde pressure with an apparent activation energy of 23±0.5 kcal/mol and an apparent preexponential factor of 4×1011 s−1. The rate becomes flux limited and first order in formaldehyde pressure with an apparent activation energy of zero at relatively high surface temperatures (and/or low formaldehyde pressures). Perdeutero-formaldehyde decomposes on Ru(00l) with the same kinetic parameters as HCHO. The lack of a kinetic isotope effect indicates that C–H bond cleavage is not the rate-limiting step under these experimental conditions. In the low-temperature regime, the surface is saturated with CO, and the rate is CO desorption limited. Dissociative chemisorption of formaldehyde is irreversible since no isotopic exchange products were observed by reacting a mixture of HCHO and D2 with a molar ratio of 1:4 at a total pressure of 1×10−6 Torr.
The interaction of oxygen molecules with amorphous Ge, Ge:H, and some Ge:C:H alloys
Authors: Shinar R. , Entringer A. G. , Shinar J. , Wu H.-S. , Shanks H. R.
Published: July 2002

The interaction of oxygen molecules with Ar+ sputter-etched (amorphized) Ge(100) and rf sputter-deposited amorphous germanium carbides (a-Ge1−xCx:H), 0≤x≤0.5, was investigated using Auger measurements and core-level, valence-band, and high-resolution electron energy-loss spectroscopies (EELS). A film covered with native oxide was also studied. Samples were exposed to oxygen following surface cleaning by Ar+ etching. This procedure, as previously reported, preferentially removed hydrogen bonded to Ge in a-Ge:H and a-Ge1−xCx:H films. High-resolution EELS indicated dissociative chemisorption of oxygen on Ge in all Ar+-etched samples used in this study. The oxygen appears to be bonded to Ge mainly in an isolated bridge form (+1 oxidation state) at the early stages of oxidation. Even when the surface was pre-exposed to 104-L O2, subsequent exposure to hydrogen atoms indicated the existence of a high density of bonds available for hydrogen bonding, contrary to observations at Ge(111). Under these conditions the Ge–H stretch loss split into two features separated by ∼8 meV. Possible bonding configurations, including oxygen bridging between the first and second layers, are discussed. Valence-band EEL spectra exhibited a single oxygen induced loss at an energy loss similar to that observed for single crystals of Ge. Core-level shifts due to oxidation were not observed as was the case for room-temperature adsorption on single crystals. In addition, no change in the Ge(MVV) Auger line shape was induced by oxygen chemisorption, in contrast to previously observed hydrogen related changes. These results are compared to those reported for single crystals of Ge.
Imaging of biomolecules with the scanning tunneling microscope: Problems and prospects
Authors: Salmeron M. , Beebe T. , Odriozola J. , Wilson T. , Ogletree D. F. , Siekhaus W.
Published: July 2002

The capabilities of the scanning tunneling microscope as a tool to study the morphology and structure of adsorbed biomolecules are reviewed in view of recent experimental results. Problems such as electrical conductivity of the biomolecules, fixation to the substrate and identification are analyzed in detail. In particular, the role of tip–surface interaction giving rise to repulsive forces is illustrated. It is concluded that fixation rather than conductivity is the major obstacle to the use of the STM for biological imaging.
Long-scan imaging by scanning tunneling microscopy
Authors: Cantú Rigoberto García , Garnica Miguel A. Huerta
Published: July 2002

Results are presented of long scan imaging obtained with a scanning tunneling microscope designed to cover a measuring volume of up to 40×40×25 μm3. 316-L austenitic steel and Vickers hardness indentation images are shown. A modulation technique is discussed which improves long scan operation and also identifies if the tip is touching slightly. It is shown that, even in this case, it is possible to achieve high repetition of long scan imaging.
Magnetron sputtered boron films and Ti/B multilayer structures
Authors: Makowiecki D. M. , Jankowski A. F. , McKernan M. A. , Foreman R. J.
Published: July 2002

Boron and Ti/B films have been magnetron sputter deposited and characterized using x-ray diffraction, Auger-depth profiling, and electron microscopy. The amorphous boron films contain no morphological growth features, unlike those characteristically found in thin films prepared by various plasma vapor deposition processes. The use of a high-density boron sputter target prepared by hot isostatic pressing was a major factor in controlling the deposition process. Consequently, the radio frequency sputter deposited boron proves feasible for ultrathin band pass filters as well as the low Z element in high Z/low Z mirrors which enhance reflectivity from grazing to normal incidence.
Stabilization techniques for spinning rotor gage residual drag
Authors: Choi Suk-Ho , Dittmann Sharrill , Tilford Charles R.
Published: July 2002

The pressure-independent residual drag on a spinning ball requires an offset correction for the accurate use of a spinning rotor vacuum gage (SRG) at low pressures. Instabilities in the residual drag (RD) can cause significant errors in low-pressure SRG measurements. The instabilities usually occur as discontinuous shifts when a ball is levitated by the magnetic suspension, or as continuous changes as the ball slows down. The discontinuous shifts in residual drag have been found to be caused by changes in the orientation of the ball’s magnetic moment, induced by the suspension field or the inductive drive circuit. Premagnetizing the ball in a strong field has stabilized the orientation of the magnetic moment and the RD value. The continuous changes are caused by competition between magnetic and inertial forces, which result in a frequency-dependent orientation of the rotational axis of the ball. Etching a spot on the ball alters its shape and defines an inertial axis. Magnetizing the ball in a preferred direction with respect to this axis minimizes both the residual drag and its frequency dependence.
The effect of lateral interactions on the thermal desorption of N2 from Ni(100)
Authors: Varma Shikha , Dowben P. A.
Published: July 2002

We have investigated the desorption of N2 from Ni(100) using thermal desorption spectroscopy (TDS). A modified Polanyi–Wigner equation has been used to obtain the desorption energy and the preexponential factor, both of which depend on the coverage of the adsorbate. We show that there is a large lateral interaction among the adlayer molecules when N2 goes down as ordered c(2×2) on Ni. In addition, the overlayer ordering, in the thermal desorption process, is observed to affect the thermal desorption spectra.
Depth profiling of polymer thin films by infrared spectroscopy
Authors: McClure D. J. , Ouderkirk A. J. , Hill J. B. , Dunn D. S.
Published: July 2002

Infrared spectroscopy has been combined with oxygen sputter etching to produce a technique for determining depth profiles of the chemical and physical structure of organic thin films. This is achieved by measuring the infrared reflection-absorption spectrum of the organic film, supported on a metallized substrate, as the film is sputter etched in an rf oxygen plasma. The thickness of the damaged layer produced on the film as a result of this etching is small, 2–5 nm, and comes to equilibrium very quickly. Subtraction of appropriate spectra then allows the determination of the infrared absorption spectra of thin sections (10–20 nm thick) throughout the depth of 100–200-nm-thick films. Results will be presented on infrared depth profiling to characterize the interpenetration of thin films of oligomers and polymers and to measure the nature, extent, and depth of laser surface modification of polymers.
Effective thermionic work function measurements of zirconium carbide using a computer-processed image of a thermionic projection microscope pattern
Authors: Mackie William A. , Hinrichs Clarence H. , Cohen Ira M. , Alin John S. , Schnitzler Don T. , Carleson Pete , Ginn Robert , Krueger Peter , Vetter Catharine G. , Davis Paul R.
Published: July 2002

We report on a unique experimental method to determine thermionic work functions of major crystal planes of single crystal zirconium carbide. Applications for transition metal carbides could include cathodes for advanced thermionic energy conversion, radiation immune microcircuitry, β-SiC substrates or high current density field emission cathodes. The primary emphasis of this paper is the analytical method used, that of computer processing a digitized image. ZrC single crystal specimens were prepared by floating zone arc refinement from sintered stock, yielding an average bulk stoichiometry of C/Zr=0.92. A 0.075 cm hemispherical cathode was prepared and mounted in a thermionic projection microscope (TPM) tube. The imaged patterns of thermally emitted electrons taken at various extraction voltages were digitized and computer analyzed to yield currents and corresponding emitting areas for major crystallographic planes. These data were taken at pyrometrically measured temperatures in the range 1700<T<2200 K. Schottky plots were then used to determine effective thermionic work functions as a function of crystallographic direction and temperature. Work function ordering for various crystal planes is reported through the TPM image processing method. Comparisons are made with effective thermionic and absolute (FERP) work function methods. To support the TPM image processing method, clean tungsten surfaces were examined and results are listed with accepted values.
A variable temperature x-ray photoelectron spectroscopic study of the surface conversion of diethylaluminum azide to AlN
Authors: Schulze R. K. , Boyd D. C. , Evans J. F. , Gladfelter W. L.
Published: July 2002

Variable temperature x-ray photoelectron spectroscopy was used to study the thermal reaction of condensed thin films of diethylaluminum azide, yielding AlN. This precursor has been shown to be a useful chemical vapor deposition (CVD) reagent for the preparation of AlN thin films by a thermally assisted CVD process. Reaction progress was monitored easily with x-ray photoelectron spectroscopy (XPS) due to the chemical uniqueness and thus the spectral uniqueness of the various functionalities in the molecule. The results are consistent with a mechanism proposed in other studies. They indicate commencement of the surface reaction at about 300 °C and formation of AlN at temperatures above 500 °C. Activation of the diethylaluminum azide by various means causes the elimination of molecular nitrogen concomitant with the formation of an intermediate which is suggested to be a nitrene radical. This intermediate is found to have a high desorption energy, and, its subsequent reaction to yield AlN is confined to the surface.
Photoconductive characterization of ZnxCd1−xTe (0≤x≤0.25) single crystal alloys
Authors: López-Cruz Elías , González-Hernández J. , Allred D. D. , Allred W. P.
Published: July 2002

Large grain polycrystalline and single crystals of ZnxCd1−xTe grown by a modified Bridgman method were studied using the photoluminescence and photoconductivity techniques. The temperature dependence of the band gap, as determined by photoluminescence, follows the Varshni equation for measuring temperature in the range of 15–290 K. One of the fitted parameters, the Debye temperature, monotonically decreases with the increase of the atomic zinc concentrations. A a close correlation between the photoluminescence and photoconductivity measurements is also found. Samples in which the photoluminescence spectra exhibit emission bands associated to cadmium vacancies and other structural defects, show a photoresponse curve which includes, in addition to the intrinsic band, another broad band at lower energies. Using the ionization energies of the defect related bands in the photoluminescence spectra we have identified the second band in the photoresponse curve due to the photoexcitation of trapped carriers at levels related with the structural defects.
Synchrotron radiation photoemission study of the formation of the Ag/GaSb(110) interface
Authors: Mao D. , Soonckindt L. , Kahn A. , Terrasi A. , Margaritondo G.
Published: July 2002

We have studied the chemistry and electronic properties of the Ag/GaSb(110) interface formed at room and low temperature with high resolution core level photoemission spectroscopy. The Ga 3d and Sb 4d core level spectra are deconvolved into bulk, surface, and reacted components. The relative changes in intensities of these components as a function of Ag coverage at room temperature (RT) and low temperature (LT) are studied in terms of interface morphology and chemistry. At LT, the Ga 3d and Sb 4d surface components disappear with about one monolayer of Ag coverage, confirming the two dimensional Ag growth. At RT, on the other hand, the surface components persist up to coverages of several monolayers, indicating a Volmer–Weber growth mode. At higher coverages, both the Ga 3d and the Sb 4d spectra are dominated by reacted components with lower binding energy. The intensity of the Ga 3d core level decays faster as a function of Ag coverage than that of Sb 4d, indicating out diffusion of Sb. Out diffusion is reduced at 80 K. Band bending at the GaSb surface is extracted from the shift of the bulk components. The final position of EF is found to be within 50 meV of the valence band maximum, in good agreement with previous ultraviolet photoemission results.
Overlayer morphology and metallicity: Formation of In/GaSb(110) barriers at room and low temperature
Authors: Lü Z. M. , Mao D. , Soonckindt L. , Kahn A.
Published: July 2002

The morphology and band bending at In/GaSb(110) interfaces formed at room and low temperature are investigated. No disruption of the semiconductor surface is detected. Clustering, which completely dominates the interface at room temperature, is strongly reduced at 35 K. Band bending measurements show that the formation of the Schottky barrier is well described by a model of adsorbate-induced states at low coverage. Pinning of the Fermi level correlates with the metallization of the In layer.
Growth structure of excited oxygen on GaAs(111) surfaces
Authors: Alonso M. , Soria F. , González M. L.
Published: July 2002

The electron-stimulated oxidation of perfect and facetted GaAs(111) 2×2-Ga surfaces has been studied up to 3 nm, by quantitative Auger analysis. After a top oxygen layer has been adsorbed, oxidation progresses by a layer-by-layer mechanism with separate Ga and As oxide phases. On perfect surfaces, one-third of each As monolayer remains embedded in the Ga2O3 formed, indicating that the oxidation proceeds by an ordered breaking of the As bonded to Ga. However, on facetted surfaces all of the oxidized As atoms are desorbed from the surface and only Ga2O3 is detected. Therefore, the formation of As oxides depends on the surface structure, but never these As oxides are buried at the Ga2O3/GaAs interface as it was suggested before.
A hybrid resonance ionization and secondary ionization mass spectrometer
Authors: Downey S. W. , Hozack R. S.
Published: July 2002

Initial results from a hybrid resonance ionization and secondary ionization mass spectrometer (RIMS/SIMS) instrument are presented. Advantages and disadvantages of both techniques are discussed. RIMS performed with pulsed lasers produces ions more efficiently than SIMS, but with a cost of reduced duty cycle. As a result, SIMS may be more sensitive than RIMS in certain instances. RIMS is shown to reduce background, matrix-based mass interferences by its selective atomic photoionization process. Matrix ions from Si are discriminated against using RIMS in the detection of Co. The RIMS detection limit for Co in Si is determined to be 1×1018 cm−3 (20 ppm) for depth profiling applications without pulse counting techniques commonly used in SIMS. Improvements in this figure of merit are possible.
Metalorganic gas control system for gas source molecular beam epitaxy
Authors: Ishikawa Hideaki , Ando Hideyasu , Kondo Kazuhiro , Sandhu Adarsh , Miyauchi Eizo , Fujii Toshio , Hiyamizu Satoshi
Published: July 2002

We have developed a new method to precisely control the small mass flow of low vapor pressure gases without a carrier gas in gas source molecular beam epitaxy. Group III metalorganic gases (TEA1, TEIn, and TEGa) were controlled by measuring the pressure difference at the flow element and giving feedback to the control valve. The beam pressure of source gases monitored at the growth position in a molecular beam epitaxy growth chamber had good linearity with the pressure difference at both sides of the flow element. The beam pressure was controlled with a maximum deviation of 2% for over 1 h of operation. The response of the beam pressure to changes in flow rate was quick with neither overshoot nor undershoot. The beam pressure could be reduced to 1/5 of its initial value in less than 5 s and then restored in less than 3 s. The source gases could be switched on and off abruptly. The rise time to 90% of the saturated beam pressure was less than 1 s and fall time to 10% of the saturated beam pressure was between 2 and 4 s.
Epitaxial growth of transition metal dichalcogenides on cleaved faces of mica
Authors: Ueno Keiji , Saiki Koichiro , Shimada Toshihiro , Koma Atsushi
Published: July 2002

We have grown ultrathin films of layered transition metal dichalcogenides (MoSe2,NbSe2) heteroepitaxially on cleaved faces of mica (muscovite). This is the first success in the heteroepitaxial growth between highly heterogeneous layered materials having different crystal structures and lattice constants that differ by as much as 58%. The lattice matching condition is greatly loosened in those cases because the growth proceeds with weak van der Waals forces between the substrate and the grown layer. This opens a new way to fabricate a heterostructure composed of many kinds of layered materials having various physical and chemical properties.
Improved performance from a new rotation and heating stage design for molecular-beam epitaxy
Authors: Kubiak R. A. , Stonestreet P. , Newstead S. M. , Parker E. H. C. , Whall T. , Naylor T.
Published: July 2002

The performance of a substrate heater/manipulator designed to address reliability and vacuum quality issues is discussed. The manipulator employs a novel, hollow magnetic feedthrough which is directly coupled to the substrate cradle, thus eliminating a gear train between the two. The need for only two in vacuo bearings enhances reliability, with a total of 5×106 rotations accumulated to date without degradation in performance. Negligible increases in residual gas species, most notably CO, are found with either rotation (a severe problem with previous designs employing gear trains) or heating.
A reactive coevaporation system for i
n s
i
t
u, epitaxial YBa2Cu3O7−x thin film deposition
Authors: Chan Siu-Wai , Sampere S. M. , Farrow L. A. , Barner J. B. , Rogers C. T. , Wilkens B. J. , Chase E. W.
Published: July 2002

A new ultrahigh vacuum system has been specially designed and built to deposit high temperature superconducting thin films over a large area with great uniformity in both thickness and composition. The sources are in close proximity and a large distance (460 mm) separates the substrate holder and the sources. We will describe the design and the capabilities of the system including the design rationale. We have prepared in situ YBa2Cu3O7−x films to demonstrate the feasibility of the system. As configured, the reactive coevaporation system can deposit up to 35 mm diam YBa2Cu3O7−x films. Evaporant uniformity is expected up to 60 mm diam with the present limit in area set by the heater size, the size of the appropriate substrates, and the difficulty in attachment of substrates to the holder with uniform thermal contact. Films are prepared by coevaporation of yttrium, barium, and copper from three different evaporation sources with the substrate holder temperature measured at 680 °C in a PO2=5×10−4 Torr ambient. Because the substrate holder is 460 mm above the sources, debris from the sources cannot travel upward and stick to the film surface. Films less than 250 nm thick on (001) SrTiO3 and (001) LaAlO3 exhibit a sharp transition width (ΔT=0.5 K) and Tc(R=0)=90 K by resistivity measurements. In addition, alternating-current (ac) magnetic susceptibility characterization shows sharp transitions (<1 K) at a slightly lower temperature implying that the induced screening current is uniform over the area of the detection coil. These films are structurally very close to single crystals as characterized by both x-ray diffraction and Raman scattering.
Photostimulated evaporation of SiO2 and Si3N4 films by synchrotron radiation and its application for low-temperature cleaning of Si surfaces
Authors: Akazawa H. , Takahashi J. , Utsumi Y. , Kawashima I. , Urisu T.
Published: July 2002

SiO2 and Si3N4 films are shown to be removable by vacuum ultraviolet light irradiation with synchrotron radiation (SR) in an ultrahigh vacuum. The dependence of the photostimulated evaporation rate on substrate temperature shows that the reaction is induced by an electronic mechanism. Polycrystalline Si and crystal Si are unaffected by SR irradiation. By applying this reaction to the thin native oxide film grown during a wet pretreatment, Si surfaces can be cleaned at temperatures as low as 650 °C. Si(100)-2×1 and Si(111)-7×7 structures are observed by reflection high-energy electron diffraction after a few hours irradiation. Two-dimensional epitaxial growth by gas-source molecular-beam epitaxy with Si2H6 occurs selectively on the SR-irradiated region of a Si(100) surface, indicating cleanliness and flatness of the irradiated area.
Self-pulsing emission of a liquid metal ion source
Authors: Werner F. , Gnaser H. , Scholtes J. , Oechsner H.
Published: July 2002

Needle-type liquid metal ion sources are found to exhibit self-sustained, pulsed emission for very smooth emitter surfaces and/or incomplete wetting. A distinct dependence on extraction voltage is found both for the length and height of individual pulses as well as for the interval between pulses. These observations are explained by an insufficient flow of liquid along the shank of the needle. Therefore, the emitting cone collapses and rebuilds only after some time delay necessary for the liquid to flow to the apex. The experimental results are described by a hydrodynamic model that incorporates liquid flow impedance. Liquid film thicknesses, as derived from these results, are found to be ≤1000 Å for self-pulsing emitters. This figure is in agreement with Auger electron spectroscopy sputter depth profiles of those emitters.
Ion extraction from microwave plasma excited by ordinary and extraordinary waves and applications to the sputtering deposition
Authors: Matsuoka Morito , Ono Ken’ichi
Published: July 2002

The right hand circularly polarized waves propagating along the magnetic flux are the most useful for producing overdense plasma. Microwaves channeled perpendicular to the magnetic flux are also efficient for some applications, including conductive-film preparations by sputtering and chemical vapor deposition (CVD) processes. In this study, the plasma excitation by means of the ordinary and extraordinary microwaves have been investigated for conductive film deposition. These waves effectively generate plasma with an approximately cut off density in a low-gas-pressure atmosphere. Ion streams with 4 mA/cm2 current density are extracted from the plasma excited by the extraordinary microwaves under a pressure below 0.02 Pa. These waves are used for the sputtering deposition of conductive films, including iron-nitride films with giant magnetization and Mo films.
Etching behavior of an epoxy film in O2/CF4 plasmas
Authors: Emmi F. , Egitto F. D. , Matienzo L. J.
Published: July 2002

Epoxy polymers are commonly used in microelectronic packaging for printed circuit board fabrication. Exposure to plasma environments occurs during processing for purposes such as drill smear removal, surface modification, and decapsulation. In this investigation, epoxy films made from a brominated diglycidyl ether of bisphenol-A, containing aliphatic and aromatic segments, were etched in a radio-frequency plasma using a planar diode configuration. Etching rates were measured at various compositions of O2 and CF4 in the gas feed. Surface composition of etched and nonetched films were compared using x-ray photoelectron spectroscopy. Comparison of etching behavior and fluorine surface coverage is made with polymers, which are either aliphatic or aromatic. Maxima in etching rates for polyimide, epoxy, and polyethylene films occurred at 22.5%, 35%, and 37.5% CF4 in O2, respectively. Fluorine atom surface coverage was 10%, 20%, and 2%, respectively, under these conditions. It is proposed that the low affinity for fluorine atoms of the aliphatic moieties in the epoxy drives the O2/CF4 gas feed mixture, which yields maximum etching rates toward higher CF4 concentrations, similar to observations made for fully saturated polymers like polyethylene. As a consequence, the aromatic epoxy segments become more heavily fluorinated as occurs for highly aromatic polymers, like polyimide, in fluorine-rich plasmas.
Ion-beam deposition of Ag/Fe multilayers and their structural and magnetic properties
Authors: Qadri S. B. , Kim C. , Twigg M. , Lubitz P. , Rubinstein M.
Published: July 2002

Ag/Fe multilayers of Ag and Fe have been synthesized using ion assisted ion-beam deposition technique. Low angle peaks and well-defined satellite peaks at high angle were recorded indicating the periodic structure and the sharpness of the interface. Read photograph and selected area electron diffraction show that Fe is in bcc structure in Ag/Fe multilayers. Magnetic moment of the Ag/Fe film is comparable to bcc Fe.
Effect of post-deposition annealing on structure and chemistry of the TiN film/steel substrate interfaces
Authors: Erdemir A. , Cheng C. C.
Published: July 2002

This study deals with solid-state phase transformations occurring at interfaces between a TiN film and an AISI M50 steel substrate during postdeposition annealing at 500 and 1000 °C. Cross-sectional transmission electron microscopy (XTEM) was used to investigate the nature of phase transformations at these interfaces. The TiN films were ion plated onto M50 steel with an initial Ti underlayer at 100 °C. XTEM and electron energy loss spectroscopy of the interfaces indicated that the ion-plated Ti underlayers transformed into a TiC phase during annealing at 500 °C and into a Ti(C,N) phase during annealing at 1000 °C. In addition, the density of defects within grains was significantly reduced during annealing and the grains themselves became larger.
Blockage of chemisorption of oxygen on Ni by monolayer coverage of Ne
Authors: Jiang Li-Feng , Glover R. E.
Published: July 2002

Increases in the work function of the (111) surface of Ni caused by small exposures of oxygen gas cooled to 77 K are found to be the same with the Ni crystal at 77 and 5.4 K. There seems to be only one adsorption type, chemisorption. The experiments show, however, that the behavior at the lower temperature is radically changed by preadsorption of small quantities of even a weekly bound adsorbate. Deposition at 5.4 K of monolayer amounts of Ne before deposition of oxygen almost completely blocks oxygen chemisorption until the temperature is raised to the 8.7–12 K range where mass spectrometer measurements show that Ne desorbs.