bluuebunny/crossref_metadata_2025 huggingface dataset:
Studies of mid-frequency pulsed dc biasing
Authors: Kelly P. J. , Hall R. , O’Brien J. , Bradley J. W. , Henderson P. , Roche G. , Arnell R. D.
Published: July 2002

The application of mid-frequency (100–350 kHz) pulsed dc power at the substrate is a recent development in the magnetron sputtering field. It has been found that, unlike the dc case, if the bias is pulsed in this range, the current drawn at the substrate does not saturate, but continues to increase with increasing bias voltage. In addition, this effect becomes more marked as the pulse frequency is increased. For example, under a particular set of operating conditions, a threefold increase in ion current was observed at a bias voltage of −300 V when the bias was pulsed at 350 kHz, compared to the dc case. This phenomenon is believed to be due to the initiation of a second discharge at the substrate. Pulsing the substrate bias voltage, therefore, offers a novel means of controlling the ion current drawn at the substrate. Clearly, this has significant implications in relation to film growth, sputter cleaning, and substrate preheating processes. Consequently, the variation in ion current with pulse frequency and bias voltage has been studied for an unbalanced magnetron sputtering system. In addition, substrate heating rates, current–voltage wave forms and plasma characteristics have also been investigated. A series of TiO2 and TiN films were then grown under different bias conditions. Analysis of these films showed that the application of pulsed dc power at the substrate can significantly influence film structure and properties. In particular, shifts in crystalline structure and texture were observed.
Performance of the Raith 150 electron-beam lithography system
Authors: Goodberlet James G. , Hastings J. Todd , Smith Henry I.
Published: July 2002

The performance of a Raith 150 electron-beam lithography system is reported. The system’s resolution, stability, intrafield distortion, stitching, and overlay performance are evaluated. Patterning at low- and high-acceleration voltages is compared. The system was used to pattern sub-20 nm features, and the largest intrafield distortion for a 100 μm field was measured to be 15 nm. Pattern-placement accuracy below 35 nm, mean plus twice the standard deviation, was demonstrated.
Microfabricated field emission devices using carbon nanofibers as cathode elements
Authors: Guillorn M. A. , Melechko A. V. , Merkulov V. I. , Ellis E. D. , Simpson M. L. , Lowndes D. H. , Baylor L. R. , Bordonaro G. J.
Published: July 2002

The digital electrostatic electron beam array lithography concept under development at the Oak Ridge National Laboratory proposes performing direct write electron beam lithography with a massively parallel array of electron emitters operating simultaneously within a digitally programmable microfabricated field emitter array (FEA). Recently we have concentrated our research efforts on the field emission (FE) properties of deterministically grown vertically aligned carbon nanofibers (VACNFs). We have measured the FE properties of isolated VACNFs using a moveable current probe and found that they have low FE turn-on fields and can achieve stable emission for extended periods of time in moderate vacuum. In order to use the VACNF in microfabricated FEA devices we have subjected them to a variety of processing phenomenon including reactive ion etching and plasma enhanced chemical vapor deposition, and found them to be quite robust. Using these processes we have fabricated operational gated cathode structures with single VACNFs cathodes. The issues involved in this fabrication process and the performance of these devices are discussed.
Power spectral densities: A multiple technique study of different Si wafer surfaces
Authors: Marx Egon , Malik Igor J. , Strausser Yale E. , Bristow Thomas , Poduje Noel , Stover John C.
Published: July 2002

Power spectral densities (PSDs) were used to characterize a set of surfaces over a wide range of lateral as well as perpendicular dimensions. Twelve 200-mm-diameter Si wafers were prepared and the surface finishes ranged from as-ground wafers to epitaxial wafers. The wafer surfaces were then measured with different methods: atomic force microscopy, angle-resolved light scatter, interferometric microscopy, optical profiling, stylus profiling, and capacitance-based wafer thickness gaging. The data were used to compute one-dimensional PSDs and the curves were plotted as functions of spatial frequencies, comparing results for different samples or for different instruments. The useful frequency range for each method is indicated and differences in the calculated PSD values in the overlapping region of two or more methods are discussed. The method used to convert two-dimensional PSDs to one-dimensional ones is presented.
Initial growth and texture formation during reactive magnetron sputtering of TiN on Si(111)
Authors: Li T. Q. , Noda S. , Tsuji Y. , Ohsawa T. , Komiyama H.
Published: July 2002

The initial growth and texture formation mechanism of titanium nitride (TiN) films were investigated by depositing TiN films on (111) silicon substrates by using reactive magnetron sputtering of a Ti metallic target under a N2/Ar atmosphere, and then analyzing the films in detail by using transmission electron microscopy (TEM) and x-ray diffraction (XRD). Two power sources for the sputtering, dc and rf, were compared. At the initial growth stage, a continuous amorphous film containing randomly oriented nuclei was observed when the film thickness was about 3 nm. The nuclei grew and formed a polycrystalline layer when the film thickness was about 6 nm. As the film grew further, its orientation changed depending on the deposition conditions. For dc sputtering, the appearance of (111) or (200)-preferred orientations depended on the N2 partial pressure, and the intensity of the preferred orientation increased with increasing film thickness. For rf sputtering, however, when the film thickness was small (for instance, about 20 nm), the film showed (200) orientation, independent of the N2 partial pressure, and further growth caused the film to orient to the (111) orientation when the N2 partial pressure was low (about 0.015 Pa). The results indicated that preferred orientation of TiN films is controlled by a competition between kinetic and thermodynamic effects.
Radiation-induced protective carbon coating for extreme ultraviolet optics
Authors: Klebanoff L. E. , Clift W. M. , Malinowski M. E. , Steinhaus C. , Grunow P. , Bajt S.
Published: July 2002

A technique is described that uses radiation and a gas-phase species to produce a protective carbon coating on extreme ultraviolet (EUV) optics. A specific example is given in which a ∼5 Å carbon coating is deposited on EUV Mo/Si optics via coexposure to radiation (EUV photons, electrons) and ethanol vapor. Auger electron spectroscopy, sputter Auger depth profiling, and EUV reflectivity measurements are presented that suggest a carbon coating that is substantially void free and protects the optic from water-induced oxidation at the water partial pressures used in the tests (∼2×10−7 Torr). The coating is also resistant to atmospheric degradation, and to gasification by the combination of electrons and molecular oxygen. The protective coating reduces the relative reflectivity (ΔR/R0) of an optic by ∼0.5%.
Dependence of electrical and optical properties of amorphous SiC:H thin films grown by rf plasma enhanced chemical vapor deposition on annealing temperature
Authors: Park M. G. , Choi W. S. , Hong B. , Kim Y. T. , Yoon D. H.
Published: July 2002

In this article, we investigated the dependence of optical and electrical properties of hydrogenated amorphous silicon carbide (a-SiC:H) films on annealing temperature (Ta) and radio frequency (rf) power. The substrate temperature (Ts) was 250 °C, the rf power was varied from 30 to 400 W, and the range of Ta was from 400 to 600 °C. The a-SiC:H films were deposited by using the plasma enhanced chemical vapor deposition system on Corning 7059 glasses and p-type Si (100) wafers with a SiH4+CH4 gas mixture. The experimental results have shown that the optical bandgap energy (Eg) of the a-SiC:H thin films changed little on the annealing temperature while Eg increased with the rf power. The Raman spectrum of the thin films annealed at high temperatures showed that graphitization of carbon clusters and microcrystalline silicon occurs. The current–voltage characteristics have shown good electrical properties in relation to the annealed films.
Metastable Alloy Films
Authors: Mader S.
Published: July 2002

Metastable alloy films of a number of binary alloy systems with limited terminaI solubilities were prepared by simultaneous vapor deposition of the two components onto a cold substrate. The resulting structures are either crystalline solid solutions (of concentrations higher than the terminal solubility) or amorphous solutions. Several examples for both types of structures are described. The conditions for occurrence of the amorphous structure are found to be a difference of atomic radii of the components in excess of 10% and a sufficiently low substrate temperature. The composition range of the amorphous structure increases with increasing difference of the atomic size of the components. Amorphous structures generally decompose at about 0.3 Tm (where Tm is the average melting temperature), while metastable crystalline structures decompose near 0.45 Tm. Thus, for many of the alloys studied, the metastable structure persisted to room temperature and above.
Angle-of-Incidence and Stress Effects on Rotating and Stationary Substrates
Authors: Behrndt Klaus H.
Published: July 2002

Films deposited at an oblique angle-of-incidence of the vapor stream have frequently been observed to display an anisotropic structure because of preferential growth of the film material in the vapor direction. This phenomenon occurs on stationary substrates while, if the substrate is rotated during film fabrication, the vapor is deposited on all sides of a growing grain or island. If an integration is performed over the varying directions and amounts of the incident vapor, an “integrated incidence vector” can be calculated for planar substrates. Its direction should be that of average growth. It is calculated for which geometrical configuration (diameter and location of the substrate with respect to the source) this vector will be normal to the surface of the substrate, thus eliminating the angle-of-incidence effect. Then, the stress patterns in ZnS films on stationary and rotating substrates are discussed. It is shown that the pattern on stationary substrates is strongly affected by the angle-of-incidence while, on rotating substrates, no indication of incidence effects can be observed.
Cryosorption Pumping of Hydrogen at 20 °K II. Development and Performance of Cryosorption Panels
Authors: Stern S. A. , Hemstreet R. A. , Ruttenbur D. M.
Published: July 2002

The development of cryosorption panels consisting of Molecular Sieve adsorbents bonded to refrigerated aluminum plates is described. The sticking coefficient of hydrogen on a cryosorption panel refrigerated with liquid hydrogen was found to be 0.16 in the high-vacuum range, corresponding to a pumping speed of 6600 liter/sec per ft2 of panel. A higher sticking coefficient, near unity, can be obtained with a more efficient shielding of the adsorbent surface against thermal radiation. The pumping speed decreases markedly when the surface is contaminated with more condensable gases, such as nitrogen. Therefore, the cryosorption panels must also be shielded from condensable contaminants. The panels can be mounted directly inside vacuum chambers, and can be scaled up without difficulty.
Ion Storage in Three-Dimensional, Rotationally Symmetric, Quadrupole Fields. I. Theoretical Treatment
Authors: Dawson P. H. , Whetten N. R.
Published: July 2002

The theoretical basis for the trapping of charged particles in a three-dimensional, rotationally symmetric, quadrupole field is discussed. The authors have constructed both a sensitive mass spectrometer and an ion gauge based on ion storage. This paper presents background material for this work, based on numerically computed solutions to the differential equations of motion. Predictions are obtained concerning ion trajectories, resolution, sensitivity, storage, and peak shape.
Residual Gas Analysis and Leak Detection by Time-of-Flight Measurements on Neutral Metastable Atoms and Molecules
Authors: Crosby David A. , Zorn Jens C.
Published: July 2002

We have designed and built a residual gas analyzer which is sensitive to N2, He, A, Ne, and other molecules which have energetic metastable states. The presence of these gases is revealed by measuring the time of flight of metastable, electrically neutral molecules between a pulsed electron gun and an Auger surface detector. When used as a residual gas analyzer, the present instrument can detect partial pressures of 10−7 Torr or greater; when used as a leak detector with helium tracer gas, the instrument can detect leak rates of 10−5 Torr liters/sec or larger. The sensitivity of the present instrument can be markedly improved with obvious refinements. The metastable time-of-flight analyzer will operate in a 10−4 Torr environment and it has other advantages which may make it a valuable complement to the more conventional methods of leak detection and residual gas analysis.
Auger Electron Spectrometer as a Tool for Surface Analysis (Contamination Monitor)
Authors: Taylor Norman J.
Published: July 2002

The advances in reliable ultrahigh vacuum systems and techniques over the past ten years have made it possible to maintain a solid surface in an environment in which minimum monolayer formation times are of the order of many hours or even days. As a result, increased emphasis is now being placed on the preparation of clean surfaces or surfaces of known composition. Such preparation is necessary prior to the meaningful study of the various properties of the surface, either crystallographic or electronic. The practical applications of such studies may be found, for example, in photoemitters, secondary emitting surfaces, and thermionic emitters. By means of Auger electron analysis it is becoming increasingly possible to determine the composition of surface contaminants. With such knowledge, appropriate cleaning procedures may be employed and their effectiveness monitored. After briefly describing the Auger effect and a practical spectrometer based on electron bombardment induced Auger emission, some experiments on surface treatment and analysis are described. Observations are made on 304 stainless steel, gallium arsenide, and tungsten.
Proximity effect in electron-beam lithography
Authors: Chang T. H. P.
Published: July 2002

A simple technique for the computation of the proximity effect in electron-beam lithography is presented. The calculations give results of the exposure intensity received at any given point in a pattern area using a reciprocity principle. Good agreement between the computed results and experimental data was achieved.
Cross-section profiles of single-scan negative electron-resist lines
Authors: Lin L. H.
Published: July 2002

The profile of a negative electron-resist line resulting from a single-scan exposure to an electron beam can provide much fundamental information in high-resolution lithography. A simple experimental method for determining this profile is presented here. The method is based on the measurements of the beam radius in the resist film and the contrast characteristics of the resist. The resist profile is calculated from the incident beam radius and current, the beam radius at the resist–substrate interface, and the resist contrast and exposure threshold. The calculated results are then compared with measurements taken from cross-section scanning electron micrographs of actual resist lines. Good agreement has been obtained in spite of the simplicity of the described method and approximations involved.
Calculation of deposition rates in diode sputtering systems
Authors: Westwood W. D.
Published: July 2002

The scattering of sputtered atoms by the sputtering gas has been modelled to obtain values for the distances which the atoms travel normal to the sputtering target before their energies are reduced to the thermal energy of the gas. This distance increases with the mass and energy of the sputtered atom and with decreasing gas pressure; for a 5-eV atom of mass 80, it decreases from 42 cm at an argon pressure of 0.1 Pa to 0.44 cm at 10 Pa. For most diode sputtering configurations, the sputtered atoms are thermalized before reaching the substrate and the transport to the substrate is by diffusion. Relative deposition rates for substrates situated behind apertures or masks in these diffusive sputtering situations have been measured and compared with the solid angles subtended at the substrate by the effective aperture. The agreement between relative values is very good. Thus, the solid angle provides a simple measure for determining the effect of a mask on the deposition profiles. Significant changes in rates and profiles are possible. With a 5-cm-square aperture, the rate at the center decreases by 50% as the substrate moves 2 cm away from the aperture plane and there is a 30% variation in rate over the substrate. It is impossible to obtain a sharply defined edge using a mechanical mask.
Kinetics of thermal desorption and thermal conversion of adsorbates: AES studies
Authors: Robertshaw G. , Estrup P. J.
Published: July 2002

A surface analysis technique, called ’’thermal conversion spectroscopy’’ (TCS), has been developed which employs Auger electron spectroscopy (AES) to measure adsorbate coverage as a continuous function of temperature. The technique is expected to be particularly useful in studies of the kinetics of surface processes which involve a conversion from one adsorbate state to another without causing any corresponding change in the gas phase. To evaluate the technique it has been applied to the desorption of CO from a W substrate and a direct comparison has been made with conventional thermal desorption spectrometry (TDS) done with a mass spectrometer. The Auger detection method is found to give the lower signal-to-noise ratio but the resolution is relatively high since complications arising from sample thermal gradients and overall vacuum system response (pumping speed, wall effects, etc.) are absent. By monitoring the carbon Auger spectrum, data analogous to TDS curves have been obtained for the thermally induced decomposition of ethylene on tungsten. Following saturation at room temperature, the TCS curve almost coincides with the TDS curve for H2. When ethylene and oxygen are coadsorbed the decomposition rate is significantly lower. The implications for the conversion mechanism are discussed briefly.
Development of the ERC cold-cathode ion source for use on the PR-30 ion-implantation system
Authors: Bird H. M. B. , Flemming J. P.
Published: July 2002

The ERC cold-cathode ion source has been in routine production use on several PR-30 systems for the past three years. This source has been further developed to improve target current, lifetime, and stability. The ion-optical lens has been changed from circular to elliptical geometry in order to provide an asymmetric beam for entry into the PR-30 analyzing magnet. This measure, as well as the use of higher extraction voltages, provides higher beam currents on the PR-30 target wafers. Beam steering in the nondispersive direction has been provided to correct the effects of minor machine misalignments, further enhancing target current. The discharge chamber has been modified to increase source lifetime. A new gas-feed control system and a new method of oven temperature control have been devised to provide good source and ion beam stability. The source operates with only occasional attention by unskilled personnel, and has been used principally for boron and arsenic implants. Target currents of 1-mA boron and 4-mA arsenic can be obtained routinely. Lifetimes are of the order of 40–80 h, depending on ion species. The source has also been used to provide 5-mA phosphorus, 4-mA argon, 3-mA helium and neon, and 0.3-mA nickel and palladium ion beams.
Reactions of oxygen with ZnO–101̄0-surfaces
Authors: Göpel W.
Published: July 2002

Investigations are reported on the reaction of oxygen with electrostatic neutral ZnO–101̄0-surfaces studied by means of AES, LEED, EPR, thermal desorption spectroscopy, and isotopic exchange as well as changes in the surface conductivity and work function. Geometric and electronic structures of the surface are discussed. Reversible physisorption data are determined in the range of 120–250 K (ϑ<10−1 for P<10−4 Pa), from which adsorption isotherms and isosteric heats of adsorption are derived. Chemisorption is found in the range of 300–650 K (ϑ<2.5×10−4) on crystals with negligible amount of point defects at the surface. The energy of chemisorption and reaction rates can be described quantitatively by electron transfer models. Desorption rates for zinc and oxygen are derived from measurements of instationary crystal sublimation, the latter being strongly dependent on thermodynamically stable concentrations of oxygen vacancies at the surface, which can be determined quantitatively and removed during reactions with oxygen at lower temperatures (T?700 K). Under these conditions a strong influence of oxygen vacancies on sticking coefficients and rates of electron transfer during oxygen exposure is found. The separation of chemisorption processes and reactions with point defects during oxygen interaction enables a deeper understanding of elementary steps during catalysis on ZnO.
Measurement of MIS capacitors with oxygen-doped AlxGa1−xAs insulating layers on GaAs
Authors: Casey H. C. , Cho A. Y. , Lang D. V. , Nicollian E. H.
Published: July 2002

Metal–insulator–semiconducator capacitors were prepared by doping an Al0.5Ga0.5As layer with oxygen to demonstrate a lattice-matched single-crystal insulator–semiconductor heterojunction. Crystal growth was by molecular-beam epitaxy, and measurements were made on n-type GaAs–Al0.5Ga0.5As–Cr/Au MIS capacitors. Both the absence of hysteresis in the C–V measurements and the absence of observable interface traps by deep-level transient spectroscopy (DLTS) suggest a very small semiconductor–insulator interface trap concentration. Measurement of the admittance as a function of temperature at different frequencies permitted the observation of the dominant deep level in the oxygen-doped Al0.5Ga0.5As–GaAs. This level is at 0.64±0.04 eV with a concentration of ∠1×1017 cm−3. Current–voltage measurements show space-charge-limited currents for forward and reverse biases. These initial measurements on Cr/Au–Al0.5Ga0.5As–GaAs MIS capacitors have shown that insulating behavior can be obtained with oxygen-doped AlxGa1−xAs and the properties are sufficiently promising to investigate the MIS device potential of this lattice-matched heteojunction.
Versatile infrared window mounting for ultrahigh vacuum applications
Authors: Hollins P. , Pritchard J.
Published: July 2002

A versatile infrared window mounting for ultrahigh vacuum applications is described. The method allows the use of alkali halides despite their tendency to cleave when stressed. (AIP)
Dielectric function and surface microroughness measurements of InSb by spectroscopic ellipsometry
Authors: Aspnes D. E.
Published: July 2002

Chemomechanical polishing and anodize stripping methods are examined ellipsometrically as means of preparing <100≳ and <110≳ surfaces of InSb. Both methods leave overlayers which are identified optically as microscopically rough bulk material. A 1:1 mixture of HCl:CH3OH is shown to act as a slow chemical polish. Dielectric function data representing the bulk InSb response more accurately from 1.5 to 6.0 eV than those previously obtained by analysis of reflectance spectra are determined from samples chemically polished in HCl:CH3OH.
Plastic coating of microsphere substrates
Authors: Liepins R. , Campbell M. , Clements J. S. , Hammond J. , Fries R. J.
Published: July 2002

Microsphere coating techniques and results are described together with the criteria that must be met for successful production of targets. An overview of the work at Lawrence Livermore Laboratory, the University of Rochester Laboratory for Laser Energetics, KMS Fusion, Inc., Sandia Laboratory, and Rockwell–Rocky Flats Division is presented. A detailed overview of Los Alamos Scientific Laboratory work describes thick coatings, smooth-surface coatings, organometallic, graded-density and graded-Z coatings; as well as difficult to deposit metal-upon-plastic coatings.
A chemical bonding model for the native oxides of the III–V compound semiconductors
Authors: Lucovsky G.
Published: July 2002

This paper presents a chemical bonding model for the local atomic order in the native oxide phases associated with the III–V compound semiconductors. We review XPS studies of surface and bulk oxides formed on GaAs, pointing out that the core shifts measured in these studies serve to distinguish between various oxidation states of the As and Ga atoms, but do not uniquely specify the local atomic geometries. Local atomic order in binary oxide glasses is discussed in terms of a general model which ascribes any qualitative differences in the local bonding of the two cationic species to the differences in their relative electronegativities. This model is then applied to the native oxides of both III–V and II–VI semiconductors, wherein it serves as a framework for a discussion of their local atomic structure. Finally, it is suggested that IR absorption spectroscopy can be an important tool in complementing XPS studies and thereby providing a definitive assignment of local atomic structure in native oxides of compound semiconductors.
Laser-induced order–disorder transition of the (100)InP surface
Authors: Moison J. M. , Bensoussan M.
Published: July 2002

The first investigation of laser-processed (100)InP surfaces is reported. Under irradiation by a pulsed (3 ns) green laser, above a threshold fluence of 0.2 J/cm2, both stoichiometry and structure of the surface are altered: Matter departure from the surface takes place, together with a transition towards a (1×1) LEED pattern which is attributed to a surface formed by (1×1) terraces and a random array of steps. At higher fluences, desorption increases and a fully disordered surface is obtained. A comparison with the results obtained on other semiconductors and implications for future studies are outlined.
Dynamic gas flow during plasma operation in TMX-U
Authors: Pickles W. L. , Calderon M. O. , Carter M. R. , Clower C. A. , Drake R. P. , Hunt A. L. , Lang D. , Simonen T. C. , Turner W. C.
Published: July 2002

Control of the neutral density outside of the plasma radius is essential for proper operation of the various plasma configurations in Lawrence Livermore National Laboratory’s (LLNL) Tandem Mirror Experiment-Upgrade (TMX-U). TMX-U excess-beam, stream-gun, gas-box, and beam-reflux gases are pumped internally in regions defined by 73° Ti-gettered liners and warm Ti-gettered plasma liners. The array of fast and slow ion gauges—a large TMX-U diagnostic—has been used to measure the dynamic pressure in many of the liner-defined regions on three time scales. The natural divertor action, or plasma pump effect, of mirror plasmas has been measured using the ion gauge diagnostics on a fast time scale during operation of TMX-U with ECRH start up. Routine operation of TMX-U is enhanced by the ability to verify the effectiveness of gettering and to locate leaks using pressure data collected on the two slow time scales. A computer code, dynavac 6, which treats TMX-U as a set of conductance-coupled regions with pumping and sources in each region, has been used to successfully model the overall gas dynamics during all phases of TMX-U operation.
Fusion fuel pellet injection with a railgun
Authors: Hawke R. S.
Published: July 2002

Railguns have been nominated as fusion fuel pellet injectors. It appears that a railgun could launch dielectric hydrogen isotope pellets at velocities up to 10 km/s or more at high repetition rates. A railgun consists of two parallel conductors (rails) that carry current to and from an interconnecting link (plasma arc armature). The magnetic field generated by the rail currents accelerates the armature and pellet. In addition to high launch velocity, a railgun offers several potential advantages for pellet injection: (1) pellets can be dielectric, (2) pellets can be fed into the open breech as rapidly as they are launched, (3) current can be controlled to ensure isentropic acceleration, (4) the mass of the propulsive arc is less than the pellet mass, (5) cryogenic and vacuum operation is possible, and (6) the pellet is provided lateral support permitting acceleration stresses in excess of its tensile strength, which results in shorter injectors, acceleration times, and higher repetition rates. The most restrictive limitation on railgun injector operation results from the low strength of the solid hydrogen pellets. An acceleration stress limited to 30 bars would require a launcher length of 3400 times the DT projectile length to achieve 10 km/s; i.e., a 5-mm-long projectile would require a 17-m launcher. A critical area needing investigation is the potentially adverse effect of the high temperature armature on the pellet.
Design of chromel–alumel thermocouple gauges
Authors: Aldao Celso M. , Löffler Daniel G.
Published: July 2002

The operation principle of thermocouple gauges is well known [Ref. 1: D. R. Denison, Methods of Experimental Physics, (Academic, New York, 1979)] but values of the physical parameters needed for the design of these instruments are not readily available in the literature. We have measured the electrical resistivity, thermal conductivity, and emissivity for chromel and alumel wires as functions of temperature. These functions can be used to design thermocouple gauges presenting maximum sensitivity in a particular pressure range or to modify the sensitivity of commercial instruments for a specific application.
The influence of process conditions on the friction and wear of electrodeposited chromium coatings
Authors: Gawne D. T. , Despres N. J.
Published: July 2002

The friction and wear behavior of chromium coatings produced by different process conditions have been investigated under dry sliding conditions. Crack-free deposits give markedly higher friction coefficients and wear rates than heat treated conventional coatings with the same hardness. The high friction coefficient of crack-free chromium is mainly due to the large plastic strains generated in its surface layers during sliding. The chromium coating showed pronounced increases in hardness at low loads which is attributed to enhanced strain hardening in the very small stressed volumes. The conventional and heat treated coatings are strengthened by the same microstructural mechanisms and conform to the Archard wear equation. The crack-free deposits possess distinctly different crystallographic and metallurgical structures and do not obey the same Archard relationship.
Performance of a new ion optics for quasisimultaneous secondary ion, secondary neutral, and residual gas mass spectrometry
Authors: Lipinsky D. , Jede R. , Ganschow O. , Benninghoven A.
Published: July 2002

We have constructed an electron impact postionizing optics for sputtered neutrals which can be used on quadrupole mass filters for combined secondary neutral mass spectrometry (SNMS), positive and negative secondary ion mass spectrometry (SIMS), and residual gas analysis (RGA). In the SNMS mode, residual gas and secondary ion suppression exceeds 106, and the signal-to-background ratio is better than 104. Detection limits better than 30 ppm are shown using primary ion beam (3 keV Ar+) doses of 80 μAs per amu scan. The sensitivity in the SNMS mode exceeds that of SIMS only if the secondary ion fraction of the sputtered particle flux is in the order of 10−5, which is excessively low. As a first application, we have quantitatively determined secondary neutral and ion fluxes as well as oxygen concentrations on oxygen loaded Si(100) surfaces by purely mass spectroscopic experiments.
Halo plasma heating by neutral beam injection in TMX-U
Authors: Hsu W. L. , Bauer W. , Kerst R. A. , Wilson K. L. , Simonen T. C. , Foote J. H. , Pickles W. L.
Published: July 2002

The electron temperature and density of the halo in TMX-U have been measured by Langmuir probes to study the heating of the halo plasma by neutral beam injection. This study is motivated by the recent interest in using a pair of halo recyclers to enhance the halo density and thereby increase halo shielding. In present TMX-U operation, without halo recyclers, a halo density of 2×1012 cm−3 with electron temperature of 20 eV has been measured during the heating phase with neutral beam injection only. A halo power balance model incorporating several heating mechanisms resulting from neutral beam injection is described. The model accurately predicts the measured temperatures. At the halo density range that one expects to achieve with halo recyclers, the model predicts the existing TMX-U neutral beam sources to heat the halo to at least 30 eV.
Theoretical considerations of energetics, dynamics, and structure at interfaces
Authors: Landman Uzi , Barnett R. N. , Cleveland C. L. , Rast R. H.
Published: July 2002

We review several of our recent studies investigating the structure and dynamics of two kinds of interfaces: solid–gas and solid–liquid types. For the former, we examine the energetics of some metal–vacuum interfaces and the dynamics of surface diffusion. Metal–vacuum interfaces are studied in the context of pseudopotential theory where the varied contributions to surface energy can be relatively easily categorized and interpreted while still providing quantitative accuracy. We examine the roles of the Madelung energy, surface dipole layer, Hartree energy, and electron response to the relaxation process. While qualitative behavior such as oscillatory multilayer relaxation can be seen even from the simplest ‘‘electrostatic’’ picture, quantitative predictions require both the complete theory and acknowledgment of the full three dimensionality of the system. Results are shown for the (111), (100), and (110) faces of aluminum. In exploring the dynamics of surface diffusion, we discuss a molecular dynamics (MD) simulation of model systems of lead monomers and dimers on a copper (110) surface (where there is a negligible size mismatch between dimer and substrate) and find that dimer diffusion rates can be two to three times those of the monomer. We show typical time evolutions of relevant dimer properties as well as vibrational densities of states and find that a librational or ‘‘wagging’’ mode of dimer motion acts as a ‘‘door-way state’’ for the diffusive jump and associate the elevation of the diffusion rate with its existence. We again employ MD to study solid–liquid interfaces both in equilibrium and under circumstances of rapid melting and recrystallization such as those found during laser annealing. We examine the (111), (100), and (110) faces of a fcc crystal and display profiles versus depth at various times of such properties as number density, temperature, potential energy, and diffusion constant, as well as growth rates. In particular, the close-packed (111) face enjoys a continuous growth process, uniform across the surface and mediated by an extensive interfacial region of liquid layering over the solid, while on the open, ‘‘rougher’’ (110) face the layering is suppressed and growth proceeds laterally across the exposed face in steps.
Initial reactions and silicide formation of titanium on silicon studied by Raman spectroscopy
Authors: Nemanich R. J. , Fulks R. T. , Stafford B. L. , Vander Plas H. A.
Published: July 2002

Raman spectroscopy is used to study the initial reactions and silicide formation of evaporated and sputtered Ti on Si〈100〉 substrates. The annealings were performed in a vacuum rapid isothermal annealing system or in a UHV chamber. Raman spectra were obtained after various processing stages or in situ in the UHV system. The results indicate that Si interdiffusion precedes the formation of crystalline silicides. It is suggested that the Si is incorporated in the Ti film, possibly leading to a disordered intermixing and also agglomerates near grain boundaries. The formation of the initial phase is limited by nucleation, and the phase exhibits a Raman spectrum distinct from the final phase presumed to be TiSi2 which forms after annealing to greater than 700 °C.
Monte Carlo calculation for structural modifications in ion-assisted thin film deposition due to thermal spikes
Authors: Müller Karl-Heinz
Published: July 2002

The microstructure of an ion-assisted two-dimensional film, grown from the vapor phase, is modeled by a computer simulation. The inert gas ions, impinging during the vapor deposition, are assumed to create thermal spikes slightly below the film surface. The modification of the microstructure due to atomic hopping, which is induced by the quickly expanding temperature pulse of the spike, is studied. It is demonstrated that as the ratio of the current densities of ions to vapor is increased, the porous columnar microstructure of the film becomes destroyed. Instead of long cavities between the parallel columns, large elongated closed voids are formed.
An enhanced electron-stimulated-desorption ion angular distribution method for imaging molecular orientations of adsorbed species
Authors: Dresser M. J. , Alvey M. D. , Yates J. T.
Published: July 2002

A striking improvement has been made in the quality of positive ion angular distribution data obtained in electron-stimulated-desorption ion angular distribution (ESDIAD). The improved method has been used to study configurational changes in chemisorbed CO on Ni(110) which are induced by intermolecular interactions at high coverage. CO molecules adsorbed with normal C–O bond orientations on ridge Ni sites tilt away from the normal by ±19° in directions perpendicular to the ridges for CO coverages above 0.75 CO/Ni. Evidence for the C–O tilting has also been studied as a function of electron energy. This has demonstrated that an O(1s) excitation process leads to intense and sharp O+ ESDIAD beams. The improved ESDIAD method involves the removal of a soft x-ray background signal which originates from electron impact on the metal surface, and is therefore present in all photographic ESDIAD measurements made to date. The angular distribution of the background effect is independent of electron energy and current density. The resultant ‘‘pure ESDIAD’’ patterns show more quantitative details in high and low signal regions than has been seen before.
Rehybridization of CO under the influence of coadsorbed K on Ru(001)
Authors: Weimer J. J. , Wurth W. , Hudeczek E. , Umbach E.
Published: July 2002

The idea of a rehybridization of the C–O bond due to the influence of CO adsorbed K on Ru(001) is reexamined. New results from angle dependent Auger studies are shown to substantiate the conclusion that the CO is perpendicularly adsorbed at high coverages and to support the rehybridization model. Arguments against the proposition that a K–CO complex forms or that a direct K–CO interaction occurs are summarized. Evidence that the bonding of CO at all mixed layer coverages is similar arises from coverage dependent trends. The rehybridization model for CO on K covered Ru(001) presents a picture of the influence of coadsorbed K on transition metals consistent with all of the results to date.
A new machine for metal surface treatment by dynamic mixing using a high current ion source
Authors: Sato T. , Ohata K. , Asahi N. , Ono Y. , Oka Y. , Hashimoto I.
Published: July 2002

A new machine has been made for practical metal surface treatment with simultaneous ion implantation and metal vapor deposition (dynamic mixing) by using a high current ion source. The machine has a bucket-type ion source, electron beam evaporator, water-cooled rotary specimen holder, and film thickness monitor. The ion energy is variable in the region 4–40 kV and the total beam current for nitrogen is over 600 mA. The beam diameter is about 10 cm. The machine has no magnet for mass analysis. The power supply of the ion source has a high voltage, high speed switch for the gate turn-off thyrister to protect and improve the ion source capability by conditioning. The machine was applied to surface treatment of an aluminum alloy at room temperature and improved wear resistance was obtained for the samples.
Influence of process parameter variation on the reflectivity of sputter-deposited W–C multilayer diffraction gratings
Authors: Sager B. , Benson P. , Jahoda K. , Jacobs J. R. , Bloch J. J. , Sanders W. T. , Lagally M. G.
Published: July 2002

Multilayer W–C diffraction gratings with nominal d spacings of 35 Å have been fabricated by magnetron sputter deposition. The peak and integrated reflectivities of these films have been measured with AlKα x rays and compared to theoretical values. The rms surface roughness has been evaluated. The influence of several sputtering-system process parameters on the reflectivities has been investigated.
Quantitative study of the thermal transpiration effect in vacuum gauges
Authors: Jitschin W. , Röhl P.
Published: July 2002

Pressure measurements in the range of low and medium vacuum are conveniently and accurately performed by mechanical instruments which detect pressure-induced deformations. The stability of both calibration and zero setting are considerably improved by operating the transducers at a stabilized elevated temperature. Due to thermal transpiration the temperature difference between transducer and vacuum vessel may cause a pressure difference which depends on the pressure itself, the geometry and surface properties of the interconnection, and also the gas species. In order to determine the vessel pressure, the empirical correction formula of Takaishi and Sensui has proved to be successful. Our accurate measurements reveal for the first time a minor, but systematic failure of this correction procedure. This failure is attributed to an improper application of the formula, i.e., the disregard of the specific surface properties of the interconnection. To overcome this deficiency, we suggest using fitted values for the temperature and diameter which appear in the formula, instead of actual values. By this procedure the systematic deviations are removed, and the Takaishi and Sensui formula allows description of our vessel pressures better than 0.1%.
A photoelectron spectroscopy and photon stimulated desorption study of H2O on Si(100) 2×1
Authors: Larsson C. U. S. , Flodström A. S. , Nyholm R. , Incoccia L. , Senf F.
Published: July 2002

We have studied H2O adsorption on the Si(100) surface using photoelectron spectroscopy to record Si valence bands and Si 2p core level spectra; and photon stimulated desorption to record Si 2p edge total electron yield and H+-ion yield spectra. We assign the valence-band H2O induced peaks at EB=6.3 and 11.2 eV to the Si–OH and to the O–H bonds, respectively. The H2O dosed Si 2p core level spectrum exhibits two H2O induced equal intensity surface peaks with surface core level shifts of +0.25 and +1.00 eV that we assign to surface Si atoms in the Si–H and the Si–OH bonds, respectively. We interpret the features in the Si 2p edge H+-ion yield spectrum as ion desorption from SiO2 at surface defect minority sites. We conclude that H2O adsorbs dissociatively as H and OH radicals on the Si(100) 2×1 surface dimers and that there are defect minority sites on the surface where H2O adsorption causes SiO2 formation.
Outgassing behavior of A6063-EX aluminum alloy and SUS 304 stainless steel
Authors: Chen June-Rong , Lee Chih-Hao , Chen Jyh-Cheng , Hsieh Huan-Lurn , Liu Yuen-Chung
Published: July 2002

The outgassing behavior of A6063-EX aluminum alloy and SUS 304 stainless steel has been studied by means of analyzing the outgassing rate curves and the residual gases in the vacuum system. The results indicate, when the chamber has been filled with moist gas, the major outgassing process is diffusion for the aluminum alloy, but is desorption for the stainless steel. When the filling gas is extremely dry, the outgassing stimulated by the filament of the ionization gauge may become dominant for both the aluminum alloy and the stainless-steel vacuum chambers.
Dense crystalline ZrO2 thin films deposited by pulsed-laser evaporation
Authors: Sankur H. , DeNatale J. , Gunning W. , Nelson J. G.
Published: July 2002

A TEA-CO2 laser was used to evaporate solid targets of ZrO2 at power densities of 0.25 to 1.5×109 W/cm2. The laser-generated plasma contained ions with velocities in the 2–6×106 cm/s range. This ion flux normal to and 7.5 cm away from the solid source was in the range of 0.25 to 2.5×1014/cm2/laser pulse for the above power density range. ZrO2 thin films deposited by this technique were characterized for their optical and structural properties. Under a broad range of laser power densities, these films had bulklike refractive index values, low absorption, and oriented polycrystalline microstructure.
Surface science studies of the water–gas shift reaction on a model Cu(111) catalyst
Authors: Campbell Charles T. , Koel Bruce E. , Daube K. A.
Published: July 2002

The water–gas shift reaction (CO+H2O→CO2+H2) is a step in many industrial processes, including ammonia and hydrogen production, with potential use in coal conversion schemes as well. It is traditionally achieved on copper- or iron-based catalysts. We have studied the kinetics of this reaction at pressures of ∼40 Torr on a Cu(111) single-crystal surface characterized by pre- and post-reaction surface analyses (Auger electron spectroscopy, x-ray photoelectron spectroscopy, low-energy electron diffraction). Specific rates, activation energies, and reaction orders are consistent with measurements on supported Cu catalysts. The results are interpreted in terms of a mechanism whereby the reaction rate is limited by the dissociative adsorption of water. We have also characterized the sulfur poisoning of this catalyst, which appears to occur by a simple site-blocking mechanism, where the reaction ensemble size is small (≤2 Cu atoms). Finally, we have found that Cs addition (from aqueous CsOH) enhances the reaction rate by a factor of 15. The structure of the catalyst surfaces will be discussed. After reaction, the unpromoted Cu surfaces were always completely metallic, and no surface oxygen was observable. This was true even if the Cu was heavily oxidized before reaction. With Cs addition, oxygen was always observable after reaction, and its level was roughly proportional to the Cs concentration, with an oxygen:cesium atomic ratio near unity. The mechanism of Cs promotion is discussed.
The rehybridization of CO with K coadsorption on Ru(001)
Authors: Jennison D. R.
Published: July 2002

The recently observed ‘‘rehybridized’’ CO, produced by coadsorption with (1)/(3) monolayer of potassium on Ru(001), is studied by cluster calculations. The photoemission and Auger spectroscopic results are consistent with the effects produced by the strong electric field in an ionic K–CO local complex in which the σ orbitals are indeed rehybridized and the 1π level is split. The experiments are not consistent with an sp2 hybridized >C–O species or a (CO)2−2 potassium salt. A long-range electric field arising from hypothetically positive potassium also produces electronic changes in the wrong direction to explain the spectra.