bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and morphology of various carbides in the Ta–C system
Authors: Grossklauss W. , Bunshah R. F.
Published: July 2002

Tantalum carbides, i.e., TaC and Ta2C, were readily synthesized by evaporating elemental Ta in the presence of acetylene gas. A high-rate physical-vapor-deposition technique employing the activated-reactive-evaporation process was used. The C/Ta ratio of the TaC deposits was found to increase with increasing C2H2 partial pressure. The hardness of the TaC was 2482 kg/mm2 KHN, which is comparable to the literature values, while the hardness of Ta2C was twice that previously reported. It was found that the morphology changed markedly with deposition temperature.
Auger electron spectroscopy of a stable germanium oxide
Authors: Wang K. L. , Joshi A.
Published: July 2002

A stable germanium oxide is formed by depositing a SiO2 film, by chemical vapor deposition (CVD), on a germanium substrate and annealing in oxygen. Auger electron spectra for this stable germanium oxide are presented. The chemical shifts and the new transitions due to oxidation are shown for some major peaks, e.g., for transitions M45N23N23 the energy shifted from 22.5 to 18 eV, and for L1L3M45 from 106 to 101.5 eV. The energy shifts and new transitions in Auger peaks of a thermally oxidized sample are used to establish the presence of germanium oxide in between the SiO2 and Ge due to the oxidation annealings. The profiles of forming gas-annealed and argon-annealed samples are shown to contain very little oxidized Ge. The reduction of interface state density of Ge metal–insulator–semiconductor (MIS) structures when annealed in O is probably due to the oxidation of Ge (and reduction of dissolved hydrogen) which reduces the defects originally present in the interface region following SiO2 deposition.
Effect of the gas–surface interaction on thermal transpiration
Authors: Dadyburjor Dady B. , Sandler Stanley I.
Published: July 2002

The soft-cube model for the scattering of gas atoms from solid surfaces is used, together with the dusty gas theory for flow-through capillary tubes and porous media, to predict the thermal transpiration exponent for a number of gas–solid pairs.
Auger analysis of InSb ir detector arrays
Authors: Chan William S. , Wan Jarm T.
Published: July 2002

Auger and depth-profile analyses were performed on a series of InSb infrared (ir) detector arrays with the view of detecting interfacial contaminants and elucidating their causes which resulted from faults in the processing of the arrays. Three areas in the processing sequence were identified in which the localization of interfacial contaminants and misapplication of materials had occurred with serious consequential effects on array performance and yield. These were wafer diffusion, deposition of SiO, and anodization of the InSb surface. Localized buildup of cadmium dopant during diffusion caused poor junction formation and potential nucleating sites for peeling of contacts. Poor SiO deposition producing uneven and nonstoichiometic SiO layers caused poor device performance. The anodization process was a potential source of introduction of copper contaminant. Carbon contaminant was found to occur at all interfaces of suspected arrays, and if its concentration was greater than 10 at.%, the array performance was seriously affected. The AES technique proved most useful in providing quality-control checks in the array processing sequence.
Ionization-stimulated annealing effects on displacement damage in magnesium oxide
Authors: Krefft G. B.
Published: July 2002

The effects of ion bombardment into MgO were investigated by measuring resulting volume changes with a cantilever beam technique and by monitoring the F band absorption induced in the uv region of the spectrum. Single crystals of MgO were bombarded near 〈100〉 with 500-keV argon, which resulted in an expansion of the implanted near-surface layer due to the ion-induced lattice damage. Under subsequent 100-keV proton irradiation, however, a large fraction of this expansion is relieved since the material compacts. This seems to indicate that defects with different charge states are produced in MgO by heavy-ion bombardment and that electronic processes account for the volume changes observed during subsequent irradiation with the primarily ionizing radiation from the 100-keV H+ implantation. Identical behavior was found earlier for the highly ionic Al2O3 while no such effect was observed in the predominantly covalent SiO2. The present results thus corroborate our model of the existence of defects with different charge states in ionic materials. This behavior of MgO and Al2O3 is of considerable interest since both materials are candidates for first-wall application in CTR environments.
Long Duration Exposure Facility−A unique mode of Shuttle utilization
Authors: Kinard William H.
Published: July 2002

The Long Duration Exposure Facility (LDEF) is a Shuttle-transported, reusable, essentially passive facility with accommodations for a wide variety of experiments which require a free-flying carrier for exposure in space. Specifically, the LDEF is tailored to provide low-cost accomodations for experiments which have modest requirements for electrical power and data systems, and for experiments which benefit from postflight laboratory investigations with the retrieved experiment hardware. Each experiment for LDEF will be totally self-contained in a tray. As the interface with the facility has been minimized, the LDEF experimenters will be freed from many of the requirements which have complicated development of space experiments in the past.
Semiconductor surface physics research in the Space Shuttle orbit
Authors: Lindau I. , Spicer W. E.
Published: July 2002

The prospects for surface physics research on semiconductors with the Space Shuttle are summarized. The effect of residual gases and solar radiation outside the Shuttle on the semiconductor-surface electronic properties are assessed.
Self-consistent background gas density calculation in a multichambered neutral beam line
Authors: Jong Raynard A.
Published: July 2002

A model for calculating the self-consistent background gas density in a multichamber beam-line system is described. This model is applied to the design of the experiment chamber/beam-line vacuum system for the laser-initiated target experiment at the United Technologies Research Center.
Chemical characterization of WC–Co composite materials by AES and ISS (1) Processing
Authors: Tongson L. L. , Biggers J. V. , Bind J. M. , Dayton G. O. , Knox B. E.
Published: July 2002

Technological innovations in the processing of WC–Co composite materials were developed recently in this laboratory. The cobalt binder is precipitated from solution onto WC grains initially. The application of low-energy ion scattering spectrometry (ISS) and Auger electron spectrometry (AES) in optimizing processing modes is discussed. A method is presented for comparing the initial distribution of the binder in the starting materials by correlating the surface compositions determined by ISS and AES with bulk measurements determined by x-ray fluorescence.
Surface analysis of WC–Co composite materials (2) Quantitative Auger electron spectrometry
Authors: Tongson L. L. , Biggers J. V. , Dayton G. O. , Bind J. M. , Knox B. E.
Published: July 2002

The unique sensitivity of Auger electron spectrometry (AES) to combined carbon has been exploited in measuring the surface compositions of hot-pressed, conventionally sintered and mixed powders of WC–Co composite materials. AES sensitivity factors for tungsten and carbon (in WC) relative to cobalt were determined. The concentrations of the major elements in hot-pressed samples measured with AES using the relative sensitivity method were compared to those obtained independently by electron microprobe (EMP) and x-ray fluorescence (XRF) techniques. Corollary studies using ion scattering spectrometry (ISS) showed the absence of (1) matrix effects in the AES measurements, (2) preferential sputtering during ion bombardment, and (3) deposition of the easier-to-sputter component (cobalt) onto WC.
Deflection distortion in scanning electron-beam systems
Authors: Chang T. H. P. , Viswanathan R.
Published: July 2002

A simple method for the measurement of deflection distortions in a scanning electron-beam system using a ’’Stripe Scan’’ technique is described. This technique allows real-time measurements to be performed at high accuracy. Results obtained by this technique have been compared to those obtained by a laser interferometer measuring system and good agreements have been achieved. The effects on distortion of various factors in VSI, a vector scan electron-beam lithographic system, have been evaluated and the results will be described.
Design of a variable-aperture projection and scanning system for electron beam
Authors: Goto Eiichi , Soma Takashi , Idesawa Masanori
Published: July 2002

Results of design calculations of a variable-aperture projection and scanning exposure system is presented. Use is made of newly developed aberration formulas for the focus deflection system, which can handle systems consisting of a set of focus and deflection coils with superimposed fields and of deflection coils arranged in rotated angular positions, taking into account the finiteness of the object. The aberration of less than 0.2 μm and the incident angle less than 1 mrad with the normal, at the corners of a 5×5 mm deflection field, is expected for the 25 μm (maximum) square and 3 mrad semi-angle probe, in the linear MOL deflector, with object to image distange of 100 mm, consisting of only an axially symmetric lens and five linear deflectors without dynamic corrections.
Design of a medium-power x-ray-lithography system
Authors: Hughes Gregory P.
Published: July 2002

A medium-power x-ray-lithography system has been developed. The system includes an inexpensive stationary water-cooled x-ray source and a modified Cobilt aligner system. The exposure system is capable of printing 1-μm lines with an edge accuity of 2000 Å over a 5-cm-diam wafer. The alignment is compatable with this tolerance of line definition. The x-ray source uses a defocused electron beam on a water-cooled anode. For cooling purposes the anode is a thin copper plate with an evaporated aluminum film. The 10-kV electron beam creates a ∠1-cm-diam x-ray source able to handle more than 1 kW of power without detrimental effects on the aluminum film. The system uses an electrostatic shield to prevent over heating a 25-μm-thick beryllium vacuum window by stray electron bambardment. The x rays pass through the beryllium window into a helium atmosphere where they expose the wafer through the x-ray mask. The wafer is printed with the mask in contact to avoid alignment problems arising from wafer warpage. In this geometry the pattern to wafer distance is kept constant at 3 μm or less which allows the use of the large x-ray source and thus, the high x-ray flux.
UPS and LEED studies of GaAs (110) and (111) As surfaces
Authors: Skeath Perry , Saperstein W. A. , Pianetta P. , Lindau I. , Spicer W. E. , Mark Peter
Published: July 2002

By comparison of LEED intensity–voltage data on GaAs (110) surfaces prepared by cleaving and by chemical etch followed by sputter annealing, we find the surfaces to be essentially the same in atomic geometry within the limits of experimental error. However, we find that important distinctions can be made between (110) surfaces prepared by these two methods when Fermi-energy pinning and UPS data are considered. In this regard, we show that Fermi-energy pinning is a particularly sensitive indicator of the degree of surface perfection and that the UPS data gives valuable information about the degree of perfection achieved by the different surface preparation techniques used. As an example of this, we show differences in the spatial distribution of damage on sputter-annealed and heat-cleaned surfaces which are seen by UPS. The sputtered surface is extremely imperfect prior to annealing. Finally, we find no evidence for intrinsic filled surface states in the band gap on the (111) As surface when prepared by heat cleaning or sputter annealing.
Resolution of MOS one-transistor, dynamic RAM bit failures using SEM stroboscopic techniques
Authors: Gonzales A. J. , Powell M. W.
Published: July 2002

Stroboscopic techniques are used to allow the scanning electron microscope (SEM) to function as an electronic probe with a spatial resolution of 0.2 μm2 and a time resolution of 0.3 ns. The causes of ’’row’’ and ’’single-bit’’ failures in the one-transistor, dynamic random-access-memory (RAM) are resolved using the SEM electronic probe technique.
Annealing and rolling behaviors of concentration profiles of Cr and Cu implanted into mild steel
Authors: Iwaki M. , Namba S. , Yoshida K. , Soda N. , Sato T. , Yukawa K.
Published: July 2002

Concentration profiles of 52Cr and 63Cu implanted in mild steel have been measured by means of ion microprobe analysis in order to investigate annealing and rolling behaviors of implanted ions. Ion implantation has been performed with the dose of 1017 ions/cm2 at the energy of 150 keV. The concentration profile of as-implanted Cu exhibits the deeper penetration and its peak exists at the shallower region, compared with the depth distribution predicted by the LSS theory. The Cu maximum concentration after annealing decreases. It also decreases, being rolled, and its depth approaches near the surface. The concentration profile of as-implanted Cr has two peaks, of which the presence can not be predicted by the LSS theory. Chromium concentrations after annealing at 700°C decrease. The profile in the specimen rolled after ion implantation shows an exponential decrease inwards from the surface. These results are explained by sputtering, enhanced diffusion, thermodynamic, and rolling effects.
Theoretical study of the orientation dependence of heterojunction energy band lineups
Authors: Frensley W. R.
Published: July 2002

The orientation dependence of the energy band discontinuities at an abrupt heterojunction between lattice-matched zincblende semiconductors is studied by modeling the microscopic charge distribuion near the heterojunction. The model includes both ionic and bond charges, and assumes that each chemical bond contributes independently to the total charge distribution. The energy band lineups are derived by calculating the interface dipole. The results indicate that there should be no difference in the band lineups for heterojuncions on (100) and (111) faces of similar polarity, and that the (110) lineup should be equal to the mean of the lineups for the A and B polar faces. The lineup should be completely independent of orientation for heterojunctions which have an element common to both semiconductors, such as GaAs–AlAs. Any difference in band lineup between heterojunctions on nonpolar (110) planes and those on the (100) or (111) planes is related to deviations of the bond parameters from chemically systematic behavior, and thus is expected to be small.
Self-maintaining high-voltage ac vacuum system
Authors: Ames Elizabeth E. , Graneau Peter , Silevitch M. B.
Published: July 2002

This paper describes an experimental investigation of pumping characteristics of high-voltage ac Penning discharges. The investigation has focused on maintaining a vacuum in the 10−5 Torr pressure range while operating at a high ac voltage in the 10–100 kV rms range. It is intended that the pump will be an integral part of high-voltage ac power equipment and will thus ’’self-maintain’’ a vacuum in the equipment.
Resolution factors in the use of a double-pass CMA for ISS
Authors: Ellis W. P. , Taylor T. N.
Published: July 2002

A double-pass CMA with a 90° ion gun is limited for ISS by the angular-dependent ion scattering energies. A 90°±2.3° aperture mask significantly improves the peak resolution for He+/Au to 2% in ΔE/E from 7% in the unmasked mode. Although surface compositions of Ni/Cu alloys were still not resolvable with Ne+, Cu(amu 63.5) is separable from Fe(56) and As(75). As an adjunct to UPS studies, using the same analyzer, this approach is a valuable, additional capability .
Importance of argon pressure in the preparation of rf-sputtered amorphous silicon–hydrogen alloys
Authors: Anderson D. A. , Moddel G. , Paesler M. A. , Paul William
Published: July 2002

We report the influence of argon partial pressure pAr on the photoconductivity, four-probe conductivity and photoluminescence of rf-sputtered a-Si–H alloys. As pAr is increased from 5 to 30 mTorr, for fixed hydrogen partial pressure pH, photoconductivity increases by as much as three orders of magnitude and then saturates. Over this range the dark conductivity activation energy decreases, a plot of log conductivity versus inverse temperature becomes increasingly less linear and the photoluminescence intensity increases slightly and then drops back. We note that high pAr films become slowly contaminated upon exposure to air. These results are interpreted in terms of a reduction in energetic silicon atom bombardment of the growing film with increased pAr. For our sputtering arrangement, we show that silicon atoms ejected from the target become significantly more thermalized at pAr=10 mTorr than at 5 mTorr. Based primarily on the fact that the conductivity activation energy is more strongly dependent on pH for low pAr films, we develop a model which suggests that higher argon pressures reduce damage-related deep gap states exposing low density structure in the electronic density of states.
Milk-stool model for Si(111) surface reconstruction
Authors: Snyder L. C. , Wasserman Z. , Moskowitz J. W.
Published: July 2002

Quantum chemical ab initio computations have been used to characterize the molecular chemistry of silicon and hydrogen. It is concluded that the Lander vacancy model for the 7×7 reconstruction of the silicon (111) surface is endothermic by at least 46 kcal/vacancy with respect to the unreconstructed surface. It is proposed that a more stable silicon (111) surface corresponds to a ’’milk-stool’’ model in which neighboring triplets of silicon atoms on the unreconstructed silicon (111) surface are bonded to sila-cyclopropenyl rings, three member rings of silicon atoms having one dangling bond per silicon atom. The enhanced stability of the milk-stool is due to the greater coupling of these three dangling bonds, which are separated by the Si–Si single bond distance. A factor destabilizing this surface is strain within the milk-stool. Quantum chemical computations to evaluate these factors are presented. It is concluded that a milk-stool is 12 to 23 kcal endothermic with respect to the unreconstructed silicon (111) surface, and should be considered in models of the 7×7 reconstruction.
Accuracy requirements for adjusting variable-shaped beam systems for the production of submicron patterns
Authors: Binder H. J. , Hahmann P.
Published: July 2002

This paper deals mainly with accuracy requirements for adjusting the probe format in the variable shaped beam exposure system ZBA 10. The calibration of the probe format has to be performed in four steps: adjustment of the diaphragm edges with respect to parallelism and orthogonality, alignment of the coordinate system fixed by the diaphragm edges relative to the probe; deflection directions on the object; and calibration of the probe size. The admissible tolerance for each of the format setting parameters is smaller than 30 nm. This order of magnitude of the deviations can be measured and corrected by means of the highly magnifying projection system and the special probe format calibration program.
Nitridation of silicon (111): Auger and LEED results
Authors: Delord J. F. , Schrott A. G. , Fain S. C.
Published: July 2002

Clean silicon (111) (7×7) surfaces at up to 1050°C have been reacted with nitrogen ions and neutrals produced by a low energy ion gun. The LEED patterns observed are similar to those previously reported for reaction of silicon (111) (7×7) with NH3. The nitrogen KLL peak exhibits no shift or change in shape with nitride growth. At the same time the magnitude of the elemental silicon LVV peak at 92 eV decreases progressively as a new peak at 84 eV increases. The position of both peaks appears to be independent of the degree of nitridation. Since the Auger spectra are free of oxygen and other impurities, these features can be attributed only to silicon, nitrogen, and their reaction products. Characteristic features of the Auger spectra are related to LEED observations and to the growth of microcrystals of Si3N4.
Reconstructions of GaAs and AlAs surfaces as a function of metal to As ratio
Authors: Bachrach R. Z. , Bauer R. S. , Chiaradia P. , Hansson G. V.
Published: July 2002

The room temperature surface reconstructions of GaAs and AlAs have been investigated with angle integrated photoemission as a function of the metal to arsenic ratio. Detailed information on both the (110) and (100) surface as a function of reconstruction has been obtained from changes in the surface core level intensities, binding energy shifts, and changes in the surface valence band density of states. The GaAs(100) surface shows ordered reconstructions over a wide composition range. The ordering proceeds through a series of centered structures formed from As and vacancies in the outer layer in the As rich range to noncentered structures derived from As, Ga antisite defects, and vacancies on the Ga rich end. The AlAs(100) surface is predominantly disordered and only a 3×2 reconstruction was found in a narrow composition range. Aspects of the Al–Ga exchange reaction on GaAs(110) are discussed.
Directional reactive-ion-etching of InP with Cl2 containing gases
Authors: Coldren L. A. , Rentschler J. A.
Published: July 2002

Reactive ion etching (RIE) of InP with Cl2 containing gases is studied for a variety of system parameters. Using a shielded cathode configuration, the RIE is also studied as a function of substrate tilt angle. For normal ion incidence the etched walls generally slope away from the original mask edges. At lower pressures (∠1–2 mTorr) and higher temperatures and powers, the etch rate increases and the walls tend toward the vertical, but the surfaces become rougher. The shielded cathode results indicate little correspondence between the ion angle for maximum etch rate and the observed wall slopes, unlike analogous ion beam etching results. Vertical walls are possible by angling the substrates into the ion flux, and smoother walls are possible by rocking the substrate relative to the ion flux.
Interactions of residual gases with a barium getter film as measured by AES and XPS
Authors: Verhoeven J. , van Doveren H.
Published: July 2002

To arrive at a better understanding of barium getters, the interactions of a barium film with various gases has been measured with the aid of both AES and XPS techniques. The experimental results are interpreted in terms of the surface characteristics of the reaction, specific reaction rate, and interaction products. The interaction products involve both barium compounds (oxide, hydroxide, carbide, and carbonate) and adsorbates. The occurrence of the (carbon-containing) adsorbates is related to those gas exposures which are known to produce methane in actual tubes. Comparison between the measured characteristics of the gas–barium interactions and the properties of barium getters as observed in actual television picture tubes shows a good consistency.
The fast ion diagnostic’s neutral beam injector on the poloidal divertor experiment
Authors: Nudelman A. , Goldston R. , Kaita R.
Published: July 2002

Neutral beams, in conjunction with charge-exchange analyzers, have proved to be valuable diagnostic tools for studying high temperature tokamak plasmas. The PDX Fast Ion Diagnostic Experiment (FIDE) consists of a Diagnostic Neutral Beam (DNB) and spatially imaging charge-exchange analyzer. The DNB is built around a Lawrence–Berkeley Laboratory 40-kV, 10-A, 4-grid ion source. The power requirements are 0.5 MW in up to 10-ms-long pulse bursts. The accelerating grid is supplied from a 125-kJ, 50-kV capacitor bank with a hard-tube modulator for switching and pulse burst generation at up to 3 kHz. The filament and arc power is drawn directly from a 480-V ac line through multiphase controlled rectifiers, which provide a soft start for the filament and fast switching for the arc. Special attention was paid to the H–V transmission line, since the power supplies could not be located close to the ion source. The DNB has been tested under actual operating conditions and is now being used in experiments with the charge-exchange analyzer.
Deuterium flux measurements in the edge plasmas of PLT and PDX during auxiliary heating experiments
Authors: Wampler W. R. , Cohen S. A. , Dylla H. F. , Manos D. M. , Magee C. W.
Published: July 2002

The flux of deuterium in the plasma edge several centimeters outside the limiter has been measured using collector probes during neutral beam heating experiments on the PDX tokamak and rf heating experiments on the PLT tokamak. The dependence of the flux on the distance from the plasma was determined, and the time dependence of the flux was measured with a time resolution of 90 ms. In PDX the deuterium flux decreases rapidly with increasing distance from the plasma. The deuterium flux increased strongly when the beams came on and decreased when they turned off. The depth distribution of the deuterium in the samples, measured using SIMS, shows that when the beams are on, about 30% of the deuterium incident on the probe is superthermal deuterium from the beams. In PLT the deuterium flux decreased only slightly with increasing distance from the plasma. The ICRH heating in PLT caused an increase of about 30% in the flux of deuterium to the samples and in the plasma density. In both machines the deuterium fluxes were fairly low (≲1016 D/cm2s) at the positions sampled.
Formation of alternative surface oxide phases on GaAs by adsorption of O2 or H2O: A UPS, XPS, and SIMS study
Authors: Webb C. , Lichtensteiger M.
Published: July 2002

Adsorption of O2 and H2O on GaAs exhibits a sharp contrast in behavior: O2 bonds to As sites almost exclusively while H2O predominantly bonds to Ga sites. The formation of Ga–OH bonds due to dissociative adsorption of H2O preceded by a molecular adsorption step is inferred from UPS data. Corroboration of these findings is provided by SIMS data for positive Ga and negative As ions. The role of hydrogen is discussed in the formation of stable oxides on the GaAs surface.
Sputtering of multicomponent materials
Authors: Wehner G. K.
Published: July 2002

A survey is given of present, still rather sketchy, knowledge of (a) preferential sputtering of certain species in multielement materials, (b) the subsequent formation of a near surface layer with altered composition, (c) the total sputtering yields as a function of composition after steady-state conditions are established, and (d) the angular ejection distribution of different species. The basic differences between single phase alloys or compounds and multiphase alloys and materials with volatile species are described.
Modifications to the microhardness, adhesion, and resistivity of sputtered TiN films by ion implantation
Authors: Padmanabhan K. R. , Hsieh Y. F. , Chevallier J. , So/rensen G.
Published: July 2002

This study reports on modifications in surface mechanical and electrical properties of TiN films by heavy ion implantation. TiN films deposited by direct sputtering and reactive sputtering on different substrates were implanted with Kr+ to doses from 5×1014 to 5×1016/cm2. The energy of the implanted ions was chosen on the basis of calculated projected range of the ions in TiN and the film thickness. The thickness and composition of TiN films were measured by Rutherford backscattering and 14N(d,α)C12 nuclear reaction. Films directly rf-sputtered from TiN target had a deposition rate of 40 Å/min and showed no appreciable change of variation in N2 partial pressure, bias potential, and substrate temperature. However, the deposition rate and film composition of reactively sputtered films were found to change with N2 pressure and substrate temperature. The structure of the as-deposited films were determined by electron diffraction. Films implanted with Kr+ exhibited increase in microhardness, adhesion, and resistivity. These increases were found to be dependent on the initial film composition and implanted ion dose. It is suggested that the changes in the surface properties may be explained on the basis of ion-induced diffusion between the atoms from the substrate and that from the films.
Covalent interaction effects in electron/photon-stimulated desorption
Authors: Ramaker David E.
Published: July 2002

Recent results in electron/photon-stimulated desorption (ESD/PSD) from covalent systems are reviewed. This work has utilized Auger and photoelectron data, electron–electron and electron–ion coincidence data, and results from molecular orbital and configuration interaction calculations to provide an increased understanding of the desorption mechanisms in covalent systems. The systems reviewed include SiO2, Si3N4, H chemisorbed on Si, Ni, Pd, and W, and gas phase, condensed, and chemisorbed H2O and CO. Comparison of the ion desorption yields obtained from these systems reveals that atom–atom, adsorbate–adsorbate, adsorbate–substrate, and hydrogen bonding interactions can dramatically affect the ion yield. These covalent interactions are seen to increase the alternative decay rates of the excited states which initiate the desorption process.
Ground state and excited state sputtering Doppler-shift laser-fluorescence studies of Cr and Ca targets
Authors: Husinsky W. , Betz G. , Girgis I.
Published: July 2002

The recently much debated problem of excited state sputtering has been investigated for Cr and Ca targets using Doppler-shift laser-fluorescence spectroscopy (DSLFS). Using this sensitive and level selective method, sputtered densities for Ca and Cr atoms in the electronic ground and excited metastable states have been investigated as a function of oxygen background pressure. Furthermore, their velocity distributions have been measured for increasing oxygen coverage. In general the population of the ground state during sputtering of Cr and Ca decreases drastically by a factor greater than 50 for Cr or 20 for Ca, respectively, when the clean target is exposed to an oxygen partial pressure between 5×10−8 and 1×10−6 Torr. At the same time the maximum of the velocity distribution shifts from about 2 km/s to values between 3 and 5 km/s for Cr as well as for Ca. Thus, the velocity distribution of the Ca ground state becomes similar to the one obtained for metastable states of Ca. In addition, the light of short-lived excited states produced during the sputtering process has been monitored for different transition lines of Ca and Cr for different oxygen pressures. A quartz microbalance was used to monitor relative sputtering yields as a function of the oxygen partial pressure. For high oxygen coverage the total sputtering yield for Ca and Cr decreases by a factor of about 3. The contribution of charged particles remains below 20%. The majority of sputtered products are molecules or clusters.
A pattern edge profile simulation for oblique ion milling
Authors: Yamauchi Noriyoshi , Yachi Toshiaki , Wada Tsutomu
Published: July 2002

An oblique ion milling simulation method is proposed in which etching and redeposition at the pattern side wall are taken into account. The effective etching rate at the pattern side wall is determined as the difference between the etching rate given by the angular dependency and the redeposition rate. The redeposition rate is assumed to be proportional to the etching rate of the material to be etched at the flat surface. A pattern edge profile simulation is carried out for an oblique ion milling of silicon. The simulation results agreed well with the experimental results with a relatively large ion beam incident angle.
New ionization gauge geometries providing stable and reproducible sensitivities
Authors: Bills D. G. , Arnold P. C. , Dodgen S. L. , Van Cleve C. B.
Published: July 2002

A primary cause of inaccuracies in Bayard–Alpert (BA) gauges has been previously identified as the unstable and nonreproducible distribution of electron emission from hot cathodes. Because of uncontrollable variations and instabilities in electron emission density pattern along the length of a hot cathode, the assumptions required to apply the fundamental ionization gauge equation, p=i+/(Si−), are not well satisfied in BA gauges or other ionization gauges employing grids. A new class of ionization gauge geometries is described which avoids these difficulties by closely satisfying the assumptions. New geometries are defined so that regardless of where on the hot cathode an electron is emitted, the electron has the same probability of causing ionization as any other emitted electron. Computer simulated electron and ion trajectories are presented for an optimum simple geometry. Testing of hardware has shown that our computer model is a good predictor of actual electron trajectories. Extensive testing including life testing is being carried out but the limits of performance of this new design have not yet been ascertained. These data indicate it should be possible to duplicate the pressure range of the BA gauge in a simple ionization gauge that is fully compatible with existing gauge controllers and which provides considerably better stability and reproducibilty of gauge sensitivity than does a BA gauge.
Fabrication of electrically conductive metal oxide coatings by reactive ion plating
Authors: Hock V. F. , Stephenson L. D. , Givens J. H. , Rigsbee J. M.
Published: July 2002

Electrically conductive metal oxide (ceramic) coatings produced by reactive ion plating are being investigated at USA-CERL for potential application in cathodic protection systems. Ceramic materials are advantageous because of their very low dissolution rates (typically less than 1 g/A/yr in 3.5% NaCl solution) and ease of fabrication. Among the ceramic anode materials currently under investigation are two systems: (1) a mixture of titanium oxide and ruthenium oxide and (2) a mixture of titanium oxides ‘‘doped’’ with niobium, each ion plated on niobium substrates. The mixed oxide coatings were fabricated by a reactive ion plating process involving oxygen and dual electron beam evaporation sources. An enhanced plasma was used to increase reactivity. X-ray diffraction, scanning electron microscopy, and energy dispersive x-ray spectroscopy have been used for characterization of the microstructure, crystallography, and elemental composition of the coating.
The use of ion implantation techniques to study protective oxide scale adherence effects
Authors: Smeggil J. G. , Paradis E. L. , Shuskus A. J. , Bornstein N. S.
Published: July 2002

Data supporting a new mechanism to account for the beneficial effects of active elements such as yttrium on the adherence of protective alumina scales is presented. Previous work involving cast alloys had shown that, in the absence of yttrium, indigenous sulfur at tramp levels segregated to and weakened the bond between the scale and the underlying metal. Yttrium interacted with sulfur to form refractory compounds, thereby reducing the amount of sulfur available for segregation. In this study, the ion implantation of 27Al+ and 32S+ was used to modify alloy chemistries of Ni–Cr–Al–Y alloys. Results of oxidation tests on implanted alloys confirmed the role of yttrium in inhibiting interface segregation of sulfur. Al+ ion implantation did not modify the adherence of alumina scales on Ni–Cr–Al–Y alloys, thereby ruling out radiation damage effects. However, S+ implantation caused scale exfoliation.
Microstructural study of TiN-coated threading taps
Authors: Vuorinen S. , Niemi E. , Korhonen A. S.
Published: July 2002

Since the early 1980s TiN-coated high-speed steel (HSS) tools have become generally available in various cutting applications. Thin TiN-coating layers are mostly deposited by various physical vapor deposition (PVD) methods including ion plating, reactive evaporation, arc erosion, or sputtering. In this work commercially available TiN-coated taps were studied. Three series of different TiN-coated taps were chosen for cutting tests where both cast iron and quenched and tempered steel were used as work materials. Microstructural characterization of the coatings was mainly carried out using transmission electron microscopy (TEM). Nitrogen depth profiles were determined accurately using nuclear resonance broadening (NRB). The PVD TiN-coated tools showed distinctly different coating structures and thicknesses. Two of the coatings studied exhibited essentially stoichiometric TiN compositions throughout the whole coating layers. In the third coating the nitrogen content increased gradually, reaching the stoichiometric TiN in the immediate vicinity of the coating surface. These differences were clearly reflected in the microstructures of the coatings studied. The microstructural variations between individual coatings were, however, not clearly reflected in the performance of these coatings.
Transmission electron microscopy characterization of plasma sprayed TiC coatings
Authors: Fournier D. , Saint-Jacques R. G. , Brunet C. , Dallaire S.
Published: July 2002

In plasma spraying of high melting point materials like TiC, complete fusion is difficult to obtain and also not always desirable. This paper reports the transmission electron microscopy (TEM) study of the microstructure relation between the melted and the unmelted material in the coating. TEM samples were prepared by ion beam milling of mechanically ground coatings. We found that, under our spraying conditions from which sound coatings were obtained, the original grain structure of the powder was partially retained in the deposited coatings. The average particle size of the powder was ∼40 μm and scanning electron microscopy (SEM) observations indicated that these particles had a grain size of ∼10 μm. TEM study of the coatings showed two families of grain sizes. The first one is similar to that of the starting powder, i.e., 30 μm aggregates of ∼10 μm grains. This indicates that the core of many of the particles did not melt during the plasma spraying process. The second family consists of regions of ∼0.2 μm grains surrounding the 30–40 μm aggregates. This region has crystallized from the melted layer around the particles or from melted small particles. In addition, the plasma spraying process caused an important lowering of C/Ti. This was found by crystal lattice measurements using x-ray diffraction.
Structures and composition before and after annealing of coatings in the Cr–C binary system produced by reactive physical deposition
Authors: Cholvy G. , Derep J. L.
Published: July 2002

Coatings in the Cr–C binary system are deposited by reactive physical vapor deposition. Two types of deposition were used in an argon–methane atmosphere: chromium reactive evaporation by arc discharge and rf reactive sputtering. The objective of the study is to determine the nature and structure of the deposits as a function of deposition parameters before and after annealing. Phases are identified by x-ray diffraction. Deposit morphology is observed, both on the surface and in fractography, by scanning electron microscopy. A more particular study of coating structure, for a given configuration of deposition parameters, was conducted using transmission electron microscopy.
Mercury vapor streaming effect in McLeod gauges
Authors: Sharma J. K. N. , Sharma D. R.
Published: July 2002

In this paper the authors explain the experimental results, reported earlier, on the error made in measuring pressures below the vapor pressure of mercury with a McLeod gauge. Mercury vapor streaming effects the pressure measurement made by a cold trapped McLeod gauge. The percentage of errors in the pressure measured (i.e., Δp/P2%) agrees with Gaede’s transport theory and Takaishi’s kinetic theory of gas analysis of this problem. Below the vapor pressure of mercury the percentage error starts rising and rises to 10.3% forming a plateau and increases to 17%–19% below 2.67×10−3 Pa (2×10−5 Torr). This increase in pressure measurement error below 2.67×10−3 Pa (2×10−5 Torr) has been found to be in quantitative agreement with that predicted by Rambeau.
The adsorption and decomposition of water on Ni(110) studied by electron energy loss spectroscopy
Authors: Ollé L. , Salmerón M. , Baró A. M.
Published: July 2002

We present an electron energy loss spectroscopy (EELS) study of H2O adsorption on Ni(110). From the lowest exposures water clusters are formed. This is evidenced by the presence of two O–H stretching frequencies at 3350 and 3610 cm−1. The band at 3350 cm−1 is characteristic of hydrogen bonding between water molecules. The band at 3610 cm−1 corresponds to water molecules non-H-bonded. At 0.6 L H2O exposure, a third band at 2870 cm−1 is observed. We propose that this band belongs to a O–H ⋅ ⋅ ⋅ Ni stretching mode. From an analysis of the intensities we conclude that cyclic clusters are most probably formed at small coverages. After heating to 200 K we find that water decomposes to form hydroxyl (OH) groups. When the sample is heated to 415 K, the vibrational spectrum shows oxygen as the only product indicative of OH recombination.
A time-of-flight mass spectrometer for static SIMS applications
Authors: Steffens P. , Niehuis E. , Friese T. , Greifendorf D. , Benninghoven A.
Published: July 2002

A high performance time-of-flight secondary-ion mass spectrometer equipped with a mass selected pulsed primary ion source, an angle and energy focusing time-of-flight analyzer, and a high efficiency single-ion counting detector is described. The instrument can be applied for trace analysis of organic as well as inorganic material for the detection, identification, and structural analysis of large organic molecules in the pico- and femtomol range, as well as for the undisturbed SIMS investigation of surface structures very sensitive to ion bombardment. Spectra of Teflon, a fully protected tetranucleotide and a nonapeptide are reported.
New recycling model for light ions and atoms
Authors: Singer C. E. , Mann K. , Rauh K. , Heifetz D.
Published: July 2002

Recent theoretical studies and experimental results suggest a revision of light-ion reflection models used in simulation codes. Surface impenetrability leads to large reflection coefficients for hydrogen isotopes incident below 5–20 eV. Adsorption below 5–10 eV also depends on saturation of the surfaces. An effective surface roughness is included for all energy regimes. The fraction of nonreflected particles reemitted as molecules depends on the previous exposure of the surface and the incident flux. Simple models of these processes are collected in a form usable in neutral transport codes. The relevance of such models to tokamak design and interpreting divertor tokamak data is discussed and illustrated by numerical computation.
Crystal growth of Cd1−xZnxTe and its use as a superior substrate for LPE growth of Hg0.8Cd0.2Te
Authors: Bell S. L. , Sen S.
Published: July 2002

Cd1−xZnxTe (x=0.04) boules providing wafers with single crystal areas as large as 10 to 12 cm2 have been grown by the vertical modified-Bridgman (VMB) technique and evaluated as an alternative to CdTe for use as substrates for LPE growth of HgCdTe layers. The CdZnTe crystals, as compared with typical CdTe crystals, exhibit lower defect densities, increased mechanical strength, and significantly improved macro- and micromorphologies of LPE layers of HgCdTe grown on them. The surface morphology of LPE layers grown on CdZnTe substrates shows less orientation dependence than for layers grown on CdTe substrates, for orientations close to the {111} planes. The addition of Zn to the CdTe lattice may result in increased covalency and reduced ionicity, which in turn inhibit plastic deformation and generation of dislocations. These factors, combined with the ability to adjust the lattice constant to any desired value within the two extrema, allow the growth of low-defect density HgCdTe layers required for high-performance IR detector arrays. The quality of the substrates and epitaxial layers has been evaluated by defect etching, infrared microscopy, x-ray rocking curve analysis, and x-ray topography.
Surface analysis of TiC coated graphite limiters exposed to JIPPT-II
Authors: Kamada K. , Hori Y. , Sugiyama N. , Akaishi K. , Noda N. , Tanahashi S. , Fujita J. , Yamaguchi S. , Fujimori N. , Doi A.
Published: July 2002

Titanium carbide (TiC) coated carbon limiters, which suffered 1972 shots of tokamak discharge and 672 shots of stellarator discharge in JIPPT-II for about 3 months, are analyzed by AES and RBS. The stoichiometry and composition of a subsurface layer is found to be affected by the plasma exposure. In this region a large amount of oxygen and nitrogen are observed. These concentration profiles and the subsurface layer affected have systematic positional dependencies on the limiter, suggesting an inhomogeneous interaction between the plasma and limiter. The analysis of RBS data gave roughly 0.4 and 0.2 C and Ti atoms, respectively, being sputtered off for every impinging O atom.
Molecular beam study of the dissociative chemisorption of oxygen on W(110)
Authors: Rettner Charles T. , DeLouise Lisa A. , Auerbach Daniel J.
Published: July 2002

Molecular beam techniques have been used to study the dissociative chemisorption of oxygen on W(110). Chemisorption probabilities have been measured as a function of incidence angle, θi kinetic energy, Ei , and of surface coverage and temperature. In addition, angular scattering distributions have been measured for a range of conditions, and LEED has been used to examine surface structure. Sticking probabilities are determined as a function of coverage from the time dependence of reflected beam intensities, using Auger electron spectroscopy and LEED to calibrate the surface coverage. The initial (zero coverage limit) sticking probability is found to depend strongly on the incidence energy, scaling with En=Ei cos2 θi . This probability is ∼10% at En=0.1 eV, rising to essentially unity above En=0.4 eV. In most cases, the sticking probability is found to fall roughly linearly with increasing surface coverage. However, a less rapid falloff is observed for En≥1 eV and for En≤0.03 eV; the sticking probability actually rises with increasing coverage, reaching a maximum at ∼0.2 ML. For En≤0.3 eV, the chemisorption probability falls to <3% for a coverage of ∼0.5 ML; however, this apparent saturation coverage rises in a smooth step to 0.75 ML at ∼0.25 eV and to ∼1.0 ML in another step centered at ∼0.85 eV. These ‘‘favored’’ coverages of 0.5, 0.75, and 1.0 ML are found to be associated with p(2×1), p(2×2), and p(1×1) LEED patterns, respectively. Angular scattering distributions recorded with a differentially pumped rotatable mass spectrometer revealed predominantly quasispecular peaks. The energy dependence of the sticking probability and the observed falloff of the sticking probability with increasing coverage are not compatible with a classical precursor model, although such a process may indeed dominate for near-zero incidence energies at low surface temperatures.
Two-grid Auger–low energy electron diffraction system
Authors: Namba Yoshikatsu , Mōri Toshio
Published: July 2002

The characteristics of an Auger–low energy electron diffraction (LEED) system constructed with two grids have been studied. The modulation signal is fed to the sample, while the retarding field is applied to the collector instead of the grids; thus the energy analysis is made at the collector. The results show that (i) the system can give the Auger, elastic, and loss signals separately, (ii) the energy resolution for the Auger signal is almost constant (0.6 eV) and much better than that of the cylindrical mirror analyzer (CMA), and (iii) the LEED system shows high contrast compared with the typical four-grid configuration.