bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of rf plasma generators for neutral beams
Authors: Vella M. C. , Ehlers K. W. , Kippenhan D. , Pincosy P. A. , Pyle R. V. , DiVergilio W. F. , Fosnight V. V.
Published: July 2002

The development of low frequency (1–2 MHz) rf plasma generators for high power neutral beam applications is summarized. Immersed couplers from one to three turns were used. Acceptable plasma profiles, ≤15% max/min, were obtained in a variety of field-free, magnetic bucket and magnetic filter-bucket sources, with 10×10 or 10×40 cm extraction areas. Hydrogen beam properties were measured with a 7×10 cm accelerator operated at 80 kV. Atomic fraction and power efficiency were at least as high as with arc plasmas in similar chambers. The potential advantages of an rf plasma source are: ease of operation; reliability; and extended service lifetime.
Ion source studies for particle beam accelerators
Authors: Bieg K. W. , Burns E. J. T. , Olsen J. N. , Dorrell L. R.
Published: July 2002

High power particle beam accelerators are being developed for use in inertial confinement fusion applications. These pulsed power accelerators require sources of low atomic number ions (e.g., protons, deuterons, carbon, or lithium). The sources must be of high purity for efficient accelerator operation and proper target coupling, must have a rapid ‘‘turn-on,’’ and must be compatible with ion diode configurations under development. A particular type of source presently being investigated is the flashover ion source which generates ions by means of the vacuum flashover of an insulating anode material when the high voltage pulse arrives at the diode. We have developed an applied-magnetic-field, extraction ion diode for the 0.03 TW Nereus accelerator specifically to investigate these sources. Extracted ion species are measured by means of a Thomson-parabola ion analyzer, dB/dt current monitors, and Faraday cups. Experiments have been performed to investigate the surface flashover mechanism and the effects of various dielectric source materials, anode preparation methods (including rf glow discharge cleaning), and vacuum conditions on ion species and diode operation.
The interaction of NO with a S-poisoned Rh(100) surface
Authors: Höchst H. , Colavita E. , Fisher G. B.
Published: July 2002

The poisoning effect of S on the dissociative adsorption of NO at 300 K on Rh(100) has been studied by work function measurements and photoemission spectroscopy using synchrotron radiation in the photon energy range hν=15–30 eV. Adsorption of S does not change the work function of Rh(100) but reduces the density of states at EF considerably. The 3p states of adsorbed S are at EB ∼5.3 eV. A sulfur overlayer of θs ∼0.08 ML inhibits the dissociative adsorption of NO and reduces drastically the amount of molecular adsorbed NO. The initial change in the work function with NO exposed to Rh(100) is Δφ/ΔL (NO)=270 meV/L (NO) with a saturation of Δφ=4.5 eV at ∼3 L NO. Sulfur covered Rh(100) with θs ∼0.08 ML reduces the initial change to Δφ/ΔL (NO)≂25 meV/L (NO) and saturates at ∼15 L NO with Δφ=80 meV.
The effect of low temperature annealing on defects, impurities, and electrical properties of (Hg,Cd)Te
Authors: Schaake H. F. , Tregilgas J. H. , Beck J. D. , Kinch M. A. , Gnade B. E.
Published: July 2002

Many methods for the preparation of (Hg,Cd)Te alloys rely on a low temperature processing step to convert the as-grown p-type material to n-type, or to otherwise adjust the concentration of native acceptors. During this anneal, tellurium precipitates in the material are annihilated by in-diffusing mercury, resulting in a substantial multiplication of dislocations. For substantially long anneals (>1 day at 270 °C) the depth of the p–n junction is found to vary as the square root of the anneal time and inversely as the square root of the excess tellurium concentration. Rapidly diffusing impurities such as silver are gettered out of the skin and into the remaining vacancy-rich core. The kinetics of these processes are analyzed for self-diffusion on the metal sublattice involving only vacancies, only interstitials, and for a mixed vacancy–interstitial model. Comparison with experimental data shows best agreement with the mixed interstitial–vacancy model.
AES and LEED study of the zinc blende SiC(100) surface
Authors: Dayan Moshe
Published: July 2002

Auger and LEED measurements have been carried out on the (100) surface of zinc blende SiC. Two different phases of the clean surface, in addition to two kinds of oxygen covered surfaces, have been obtained, identified, and discussed. In the oxygen covered surface, the oxygen is bonded to the Si. The carbon rich phase is reconstructed (2×1), similar to the (100) clean surfaces of Si, Ge, and diamond. The Si topped surface is reconstructed (×) R45°. A model of alternating Si dimers is suggested for this surface.
Interdiffusion at the polyimide–Cu interface
Authors: Tromp R. M. , Legoues F. , Ho P. S.
Published: July 2002

Interdiffusion at the polymide-Cu interface has been studied with high resolution medium energy ion scattering (MEIS) and cross section transmission electron microscopy (TEM). Cu was evaported on polyimide in UHV and studied in situ with ion scattering. In the temperature range from 293 to 593 K Cu is found to diffuse into polyimide and form small spherical particles. The size of these spheres and the depth at which they occur increase with increasing temperature. Once the Cu spheres have been formed they become relatively immobile. It is argued that the kinetics of Cu-polyimide interdiffusion is determined by atomic diffusion of Cu. Chemical effects do not appear to play an important role.
Flashover lithium ion source development for large pulsed power accelerators
Authors: Bieg K. W. , Burns E. J. T. , Gerber R. A. , Olsen J. N. , Lamppa K. P.
Published: July 2002

The Particle Beam Fusion Accelerator II (PBFA II), a light-ion pulsed power accelerator intended for inertial confinement fusion (ICF) applications, is currently under construction at Sandia National Laboratories. The accelerator will deliver a 30 MV, 5 MA lithium beam from an Applied-B diode to drive an ICF target. The ion source for this diode will require a thin (∼1 mm), dense (1016 cm−2) anode plasma layer of singly ionized lithium over an anode area of 103 cm2. One type of source being investigated is the flashover ion source, which generates the anode plasma via vacuum flashover of a lithium-bearing dielectric material. Experiments with a LiF flashover source on the 0.03 TW Nereus accelerator have shown that contaminant ions account for as much as 70% of the extracted ion beam current. To overcome this, we have explored in-diode cleaning of the externally prepared anode surface by glow discharge cleaning and vacuum baking as well as in-diode preparation of the anode surface by vacuum evaporation of the lithium dielectric. Lithium-bearing dielectric materials which have been investigated include LiF, LiI, LiNO3, and Li3N. These techniques have resulted in a two to threefold improvement in the extracted lithium ion purity. As a result, a glow-discharge cleaned LiF flashover source will be used for initial pulsed-power testing on PBFA II.
Silicon dioxide reactive ion etching dependence on sheath voltage
Authors: Fortuño Guadalupe
Published: July 2002

Previous experiments using different chlorinated Freons and CF4 have shown the etch rate of SiO2 to have a stronger dependence on the sheath voltage than on the nature or concentration of the chemical species, as if dominated by physical sputtering. To better understand the etching mechanism for SiO2, the etch rate, sheath voltage, and wafer temperature were measured as a function of the percentage of CF4 in Ar and as a function of the total pressure. The experiments were done in a reactive ion etching (RIE) system. It was observed that at high pressures or at high percentages of CF4 in Ar, the etch rate depended only on the sheath voltage. This is probably due to saturation of etching species on the surface. As the pressure and CF4 percentage are lowered, the system slowly becomes unsaturated. At low pressures, where the sheath voltage is nearly independent of the CF4 percentage, the etch rate steadily decreases with Ar addition, thus showing a dependence of the etching on the concentration of etching species. At low percentages of CF4, the etch rate depends on the pressure as well as on the sheath voltage. These results explain why physical sputteringlike behavior of the etching of SiO2 had been observed in other experiments in which saturation conditions predominated. A model for SiO2 etching that explains most of the results is proposed.
Photoreflectance study of Hg0.7Cd0.3Te and Cd1−xZnxTe: E1 transition
Authors: Amirtharaj P. M. , Dinan J. H. , Kennedy J. J. , Boyd P. R. , Glembocki O. J.
Published: July 2002

We present results of the first photoreflectance (PR) study in Hg0.7Cd0.3Te and MBE and bulk Cd1−xZnxTe and the first detailed measurement of the variation of E1 optical transition energy with x in Cd1−xZnxTe at 77 K. Photoreflectance is a completely contactless form of electroreflectance. The E1 optical transition line shapes were measured and analyzed using currently available models. The MBE Cd1−xZnxTe samples exhibited E1 features that could not be fit satisfactorily, which may be due to the presence of an electron-hole interaction that was not included. The results indicate that the dependence of E1 with x may be expressed as follows: E1(x)=3.523 eV−0.022 eV ⋅ x+0.267 eV ⋅ x2. The linewidths of the E1 feature measured at 77 K in all the samples were much smaller than those at 300 K owing to the reduction in temperature broadening. This suggests that, in addition to being contactless, the characterization accuracy available with PR may be significantly better than that available in techniques such as electrolyte electroreflectance that are confined to room temperatures.
Characterization of reactively evaporated SiOx thin films
Authors: O’Leary Michael J. , Thomas J. H.
Published: July 2002

Thin films of suboxides of silicon (SiOx, 1.4<x<2.0) were deposited by the well-known method of reactive evaporation of SiO in an oxygen ambient onto unheated substrates. The films were characterized by ellipsometry, Rutherford backscattering spectroscopy (RBS), Auger electron spectroscopy (AES), and x-ray photoelectron spectroscopy (XPS). Bulk compositions were provided by the RBS analysis and AES elemental depth profiles. XPS data indicate that the bonding of silicon in the deposits have both SiO and SiO2 coordination.
Reflectance–difference spectroscopy of (110) GaAs and InP
Authors: Aspnes D. E. , Studna A. A.
Published: July 2002

We report visible-near UV reflectance–difference (RD) spectra for (110) GaAs and InP. In contrast to those for (110) Si and Ge, chemisorption, physisorption, and surface many-body screening contributions are much weaker, or even absent. Aqueous solutions simply roughen the (110) GaAs surface on a few-Å scale, generating microstructural features whose net lengthwise orientation along 〈001〉 is consistent with the formation of pits with (111)A stop-etch-plane boundaries. The dominant RD contribution for both (110) GaAs and InP has the line shape of bulk spatial dispersion. A calculation of this effect for the E1 spectral regions in the standard two-dimensional M0 critical-point model (bands parallel along 〈111〉) yields results that have the wrong sign and are an order of magnitude too small. Both discrepancies can be eliminated if the full three-dimensional parabolic nature of these E1 critical points is included, provided, as expected, that they are of symmetry type M1. These results show that optical anisotropies are extremely sensitive to residual interband curvatures of nearly parallel bands.
Passive levitation of small particles in vacuum: Possible applications to vacuum gauging
Authors: Kendall B. R. F. , Vollero M. F. , Hinkle L. D.
Published: July 2002

Most techniques for levitating small objects in a vacuum employ fluctuating electric or magnetic fields, often controlled by feedback from a position-sensing device to obtain the desired stability. We describe an alternative technique, diamagnetic levitation, which is particularly useful where compactness and simplicity are important. Diamagnetic levitation is passive in that steady magnetic fields are used and no position sensing or feedback are required. The theoretical background and prior developments are summarized. Two basic configurations, in which the magnetic fields are either vertical or horizontal, are distinguished. Particles of graphite and bismuth in sizes down to the micron range have been levitated in experimental systems of these types. Observations of particle motion as a result of interactions with the surrounding gas molecules are discussed. Many of the observed effects are pressure dependent. Several types of vacuum gauges based on these principles are suggested.
Morphology of metal phthalocyanine thin films
Authors: Schoch Karl F. , Greggi James , Temofonte Thomas A.
Published: July 2002

Thin films of nickel phthalocyanine and copper phthalocyanine were deposited on substrates heated to 160 °C. These films were characterized by transmission electron microscopy, electron diffraction, and thickness and density measurements. The films were 1000–1500 Å thick and contained α phase crystallites with the stacking axis parallel to the substrate surface. Implications for electrical properties of the films are discussed.
A three-barrel repeating pneumatic pellet injector for plasma fueling of the Joint European Torus
Authors: Combs S. K. , Milora S. L. , Baylor L. R. , Foust C. R. , Gethers F. E. , Sparks D. O.
Published: July 2002

A three-barrel repeating pneumatic pellet injector has been developed for plasma fueling of the Joint European Torus (JET) tokamak. The versatile device consists of three independent machine-gun-like mechanisms that operate at cryogenic temperatures (10–20 K). Individual extruders provide a continuous supply of solid hydrogen isotope to each gun assembly, where a reciprocating breech-side cutter forms and chambers cylindrical pellets from the extrusion; the deuterium pellets are then accelerated in the gun barrels with compressed hydrogen gas (pressures up to 105 bar) to velocities ≤1.5 km/s. The injector features three nominal pellet sizes (2.7, 4.0, and 6.0 mm) and repetitive operation (5, 2.5, and 1 Hz, respectively) for quasi-steady-state conditions (>10 s). The design allows the gun barrels to be aligned mechanically for accurate aiming. A remote stand-alone control and data acquisition system is used for injector operation. The injector system has been installed on JET. The design features, operation, and performance characteristics of the injector are described.
Metal/semiconductor interfaces on SnO2(110)
Authors: Erickson J. W. , Fryberger T. B. , Semancik S.
Published: July 2002

Interfaces formed by tin and palladium deposition on the (110) face of tin dioxide, SnO2 (a semiconductor due to native defects), have been studied from coverages of 0.05 monolayer (ML) to over 10 ML. The structural, chemical, electronic, and electrical properties of the surfaces were characterized primarily by low-energy electron diffraction (LEED), x-ray photoelectron spectroscopy, ultraviolet photoemission spectroscopy, and a retractable four-point conductivity probe. Modifications of the substrate by oxidation, annealing, and ion bombardment treatments produced three different substrate structures which were used to examine the interface abruptness and the metallization due to Sn and Pd. The deposition of Sn produced an increased surface conductivity on the ordered substrates due to the formation of donor states (oxygen vacancies) at the surface. The deposition of Pd results in the growth of a metallic layer beginning at 1–5 ML, depending upon the surface oxygen concentration. The metallic conductivity rapidly increases with Pd coverage and by 10 ML, LEED reveals microcrystallites in azimuthal registry with the substrate. In contrast, the development of metallic conductivity is relatively slow for the disordered Sn multilayers.
Observation of microfabricated patterns by scanning tunneling microscopy
Authors: Okayama S. , Komuro M. , Mizutani W. , Tokumoto H. , Okano M. , Shimizu K. , Kobayashi Y. , Matsumoto F. , Wakiyama S. , Shigeno M. , Sakai F. , Fujiwara S. , Kitamura O. , Ono M. , Kajimura K.
Published: July 2002

A small-size scanning tunnel microscope (STM) developed to provide an easy operation for both tip and sample setting is applied to three-dimensional topographic measurements of microlithography patterns. The patterns having a grid structure with 160 nm in periodicity, 20–30 nm in groove width, and 40–50 nm in groove depth are fabricated on Si substrates using a technique of enhanced chemical etching by focused ion beam. The STM images are compared with two-dimensional scanning electron microscope images. Fairly good resolution of topographic maps for a large area is obtained for the fine groove structures. The large-area images are further processed to correct the piezoscanners’ nonlinearity, which becomes conspicuous for large-area scanning.
Metal oxides deposited using ion assisted deposition at low temperature
Authors: Williams Forrest L. , Reicher D. W. , Juang C.-B. , McNeil J. R.
Published: July 2002

We have investigated the use of ion assisted deposition (IAD) to deposit thin films of Al2O3, Ta2O5, and TiO2 at a low substrate temperature (Tsub≂100 °C). Refractive indices of films deposited using IAD initially increase for a corresponding increase in ion current density until the current density reaches a so-called ‘‘critical value.’’ Films deposited at bombardment levels greater than the critical value exhibit refractive indices that are less than those obtained at current densities below the critical value. The critical value is reduced by an increase in ion energy. We have compared the effects of using IAD at low temperature to our previous results from depositing thin films using IAD at an elevated substrate temperature (Tsub≂300 °C). This comparison shows that reducing the substrate temperature increases the critical value. The effects of IAD on optical scatter were also investigated. IAD increases the optical scatter characteristics of TiO2 thin films. Raman spectroscopy was used to correlate optical scatter in TiO2 thin films to the presence of anatase crystallites in the coatings.
Molecular-beam studies of the precursor-mediated dissociative chemisorption of N2 on W(100)
Authors: Rettner C. T. , Schweizer E. K. , Stein H. , Auerbach D. J.
Published: July 2002

Molecular-beam techniques have been employed to probe various aspects of the dynamics of the dissociative chemisorption of N2 on W(100). The dissociative chemisorption probability has been measured over a wide range of incidence energies Ei, angles θi, and surface temperatures Ts. This probability is found to fall rapidly with increasing Ei in the range 26–450 meV, where it is also found to fall rapidly with Ts, and to be relatively insensitive to surface coverage at low Ts. In addition, resu1ts are found to be surprisingly insensitive to the incidence angle over the range 0°–70°. This behavior has been interpreted in terms of a precursor model, noting that the trapping process must scale quite closely with the total incidence energy. Support for these conclusions comes from careful measurements of the angular and velocity distributions of scattered molecules which has also revealed that increasing Ts primarily serves to reduce the fraction of precursor molecules that go on to dissociate, by biasing the kinetics in favor of desorption. In contrast, the trapping probability into the precursor state is found to be relatively insensitive to Ts, accounting for ≲20% of the observed effects. Measurements have also been made of the trapping probability of N2 on the W(100) surface covered with N and N2 species. We find that while trapping is insensitive to coverage for Ei <0.1 eV, it varies appreciably with coverage at higher energies; being highest on the surface saturated with both atoms and molecules followed by the clean surface, with the lowest trapping probability on the surface saturated with atoms.
Structural and dynamical consequences of interactions in interfacial systems
Authors: Landman Uzi , Luedtke W. D. , Ribarsky M. W.
Published: July 2002

Basic understanding of the structure and dynamics of materials and their response to external perturbations requires knowledge on the microscopic level, of the underlying energetics and atomic dynamics, whose consequences we observe and measure. Coupled with the above is the everlasting quest to observe and understand natural phenomena on refined microscopic scales, which provides the impetus for the development of experimental and theoretical techniques for the interrogation of materials with refined spatial and temporal resolution. In this paper we review molecular dynamics simulations for studies of the energetics and dynamical response of materials to external mechanical perturbations. Applications to investigations of solid and liquid interfacial systems under stress and to studies of the consequences of tip–substrate interactions in atomic force microscopy are demonstrated.
Experimental study of the response of a liquid metal field ion source to short HV-extraction pulses
Authors: Schwieters J. , Zehnpfenning J. F. , Niehuis E. , Benninghoven A.
Published: July 2002

In order to gain a better understanding of the dynamics of the emitting cone in a liquid metal field ion source (LMIS), the response of a LMIS to an extraction voltage pulse when the emitter voltage is close to the threshold voltage has been investigated. A delay between the leading edge of the extraction pulse and the onset of ion emission, which is due to the formation of the emitting cone, has been observed for emitters with threshold voltages in the range of 3.5–5.5 kV. The formation time varied in the range of 0.5–2 μs depending on the amplitude and repetition rate of the extraction pulse. Stable pulsed operation of a LMIS with an ion pulse length down to 50 ns FWHM is demonstrated. In the case of emitters with low threshold voltages in the range of 1.5–2 kV, an extraction pulse amplitude of 6 V was sufficient to achieve stable pulsing and the formation time of the emitting cone was less than 20 ns.
Uniform liquid-fuel layer produced in a cryogenic inertial fusion target by a time-dependent thermal gradient
Authors: Gram R. Q. , Wittman M. D. , Immesoete C. , Kim H. , Craxton R. S. , Sampat N. , Swales S. , Pien G. , Soures J. M. , Kong H.
Published: July 2002

Targets for inertial confinement fusion are cooled by cryogenic helium gas jets in an environment of room-temperature thermal radiation in an effort to obtain uniform condensed deuterium–tritium (DT) layers. A time-dependent thermal gradient obtained by ohmic heating of the upper nozzle is found to produce a transient state of uniformity in liquid DT just above its freezing point. A replaceable assembly of nozzles with heaters and thermometers is designed to be implemented in the target chamber of the OMEGA laser. Targets are held between the nozzles by spider webs which are attached to an independently positioned fixture. A flow of He of 6×10−5 g/s is sufficient to obtain the uniform DT layer, producing a background pressure in a test chamber of 0.5 mTorr. Targets are characterized interferometrically in two orthogonal views. Interferograms are compared with computed templates to determine the thickness and uniformity of the condensed layer.
Infrared characterization of methanol adsorbed on Cu(110)
Authors: Peremans A. , Maseri F. , Darville J. , Gilles J.-M.
Published: July 2002

The density of the first chemisorbed monolayer of CH3OH on a Cu(110) at 90 K is determined by thermal desorption spectroscopy (TDS), to be equal to 1 molecule/ 16(±2) Å2. Photoelastic modulated infrared spectra of methanol submonolayers allow an accurate characterization of the adsorbate structure. At 90 K, the film formation is kinetically limited: a thermally activated reorganization occurs at 142 K. The methyl and hydroxyl group axes are inclined and quasiperpendicular to the surface normal, respectively. Both TDS and infrared results suggest that the first monolayer structure is similar to that of the reticular planes in the methanol crystal, except that all the methyl groups are puckered above the plane of the oxygens which are bonded to the substrate as previously observed for methanol on polycrystalline platinum. Films thicker than 2.5 monolayers are crystallizing into arbitrarily oriented small crystallites.
Molecular-beam study of gas-surface chemistry in the ion-assisted etching of silicon with atomic and molecular hydrogen and chlorine
Authors: Chuang Mei-Chen , Coburn J. W.
Published: July 2002

Modulated molecular-beam mass spectrometry and quartz crystal microbalance techniques were used to study the etching of Si by the combinations of H/H2, Cl/Cl2, HCl, and Ar+ ion bombardment at room temperature. Without ion bombardment, only H atoms etch Si spontaneously. While the addition of Cl or Cl2 stopped H etching instantaneously, the addition of HCl had no effect. With Ar+ ion bombardment at 2 keV, the addition of HCl to the etching of Si with H, Cl, or Cl2 did not influence the etch rates. No DCl was observed when D atoms and HCl molecules were incident on Si simultaneously. This confirms that HCl does not dissociatively chemisorb on Si instantaneously. During ion-assisted etching, the addition of fluxes of H atoms, Cl atoms or Cl2 molecules increased the Si etch rate significantly. The Si etch rate for Cl atoms and Cl2 molecules was identical within experimental error provided the total chlorine flux was kept constant. The etch products observed were primarily SiClx. The addition of H atoms to the ion-assisted etching of Si with Cl increased the etch rate the same amount as with Cl2 but four times more HCl was formed with Cl atoms. Several hydrogenated chlorosilane peaks were observed with the mass spectrometer and these peaks were larger with Cl2 than with Cl. The addition of either Cl or Cl2 to the H/Ar+/Si system decreased the etch rate. These observations suggest the recombination of H and Cl to form HCl is not rate limiting in these etching processes.
The operation of metalorganic bubblers at reduced pressure
Authors: Hersee S. D. , Ballingall J. M.
Published: July 2002

Operating a metalorganic (MO) bubbler at low pressure allows a high flux of MO reagent to be extracted without resorting to high carrier gas flows. This approach is particularly suitable for the MOMBE (metalorganic molecular beam epitaxy) growth of III–V compounds. Using a ‘‘see-through’’ water bubbler, we have compared the theory and practice of reduced-pressure bubbler operation, both with and without a carrier flow. We conclude that the small carrier approach offers a wider flexibility in the choice of reagent flow, and a better stability and day to day repeatability of reagent flow. The reduced pressure operation of triethylgallium (TEGa) and triethylaluminum (TEAl) bubblers is described, in the context of the MOMBE growth of GaAs and AlAs. We show that using the small carrier flow approach, the reagent flow can be accurately controlled and predicted over a wide range.
Deposition and properties of yttria-stabilized zirconia thin films using reactive direct current magnetron sputtering
Authors: Thiele E. S. , Wang L. S. , Mason T. O. , Barnett S. A.
Published: July 2002

Yttria-stabilized zirconia (YSZ) thin films were deposited by reactive magnetron sputter deposition from a composite Zr–Y target in Ar–O2 mixtures. Hysteresis was observed as a function of oxygen flow rate  f. For a discharge current of 0.4 A and a total pressure P of 5 mTorr, for example, the target oxidized at  f>2.3 ml/min, with the reverse transition from an oxidized to a metallic target surface occurring at 1.95 ml/min. The deposition rate was 2.7 μm/h in the metallic mode and 0.1 μm/h in the oxide mode. Fully oxidized (Y2O3)0.1(ZrO2)0.9 was obtained for f>2.0 ml/min, even in the metallic mode. While films deposited with P=3–20 mTorr were continuous, for P>20 mTorr crazing was apparent as expected for a ceramic film in a tensile stress state. For P<3 mTorr, the films delaminated due to excessive compressive stress. X-ray diffraction and electron microscopy results showed that the films were polycrystalline cubic YSZ with a columnar structure and an average grain diameter of 15 nm. Fully dense films were obtained at a deposition temperature of 350 °C. Temperature-dependent impedance spectroscopy analysis of YSZ films with Ag electrodes showed that the oxygen ion conductivity was as expected for YSZ.
A new ultrahigh vacuum single crystal sample transfer system with direct temperature control and measurement
Authors: Raval R. , Harrison M. A. , King D. A. , Caine G.
Published: July 2002

We report a new sample transfer system, developed for a combined reflection absorption infrared spectroscopy/low-energy electron diffraction/Auger apparatus, which enables single crystal samples to be transferred under ultrahigh vacuum (UHV) conditions while still retaining the facility for varying and monitoring the sample temperature. The important feature of this design is that direct temperature measurement at the sample is not sacrificed in order to gain sample transferability. This advance will allow single crystal samples to be moved from preparation chambers into reaction chambers where in situ studies may be carried out under catalytically relevant pressure and temperature conditions. Such research is vital in closing the ‘‘pressure gap’’ which exists at present between studies on characterized single crystals under low pressure conditions and those on uncharacterized catalysts under industrially relevant high pressure conditions.
Surface electrical properties of HF-treated Si(100)
Authors: Huang L. J. , Lau W. M.
Published: July 2002

The effects of hydrofluoric acid etching of SiO2/Si on surface band bending of p- and n-Si, and the thermal stability of such effects were studied by x-ray photoelectron spectroscopy and Raman spectroscopy. It was found that near flat band surfaces could be prepared on p- and n-Si by HF etching. However, a significant increase of surface band bending was found when p-Si was treated with an HF concentration of higher than 10%. Raman spectroscopy confirmed that excessive hydrogen incorporation deactivated the boron-dopant in Si by forming an H–B–Si complex. Nevertheless, the boron dopant could be reactivated by annealing at a temperature as low as 120 °C.
Compositional dependence of grain size in silver copper alloys prepared by direct current magnetron sputtering
Authors: Kazakos A. M. , Fahnline D. E. , Messier R. , Pilione L. J.
Published: July 2002

Cosputtering provides a simple, direct method of preparing alloy films across the entire compositional range, as an alternative to sputtering from diphasic targets of single compositions. Metal thin films were prepared by dc magnetron sputtering in an argon plasma at a pressure of 2.5 mTorr and ambient temperatures. Alloy films of Ag–Cu were deposited by simultaneous sputtering of the two elemental targets, as well as metal films of Ag and Cu by sputtering from the appropriate pure target. The low sputtering pressure utilized in this study insured the preparation of dense, smooth, highly reflective films, indicative of energetic ion bombardment. X-ray diffraction (XRD) was performed to identify the alloy phases present and estimate their crystallite size. Transmission electron microscopy (TEM) was utilized to observe the microstructure and estimate grain size. Electrical resistivity measurements were carried out at room temperature on 1500 Å thick, pure and alloy metal films to complement XRD and TEM results. A dramatic reduction in grain size from that of pure metal was detected when the second element was simultaneously sputtered. Electrical resistivity of the alloys increased from that of the pure films. A region of greatest resistivity was noted and found to correspond to the smallest grain size, which occurred between 40 and 70 at. % Cu.
Photon emission at metal/solution interface induced by electron injection from solvated electrons
Authors: Murakoshi Kei , Uosaki Kohei
Published: July 2002

Light emission from metal, induced by electron injection from solvated electrons, was observed in an electrochemical system. The efficiency of emitted light increases drastically as electrode potential becomes positive. The high energy threshold of the spectrum increases as the electrode potential becomes positive by 1 eV/V. The peak energy also shifts positively as the electrode potential becomes positive, although the degree of the shift is much smaller. Various processes are considered as a possible mechanism for a photon emission. From the qualitative comparison of the results at platinum and gold electrode, the contribution of the inverse photoemission process to the bulk band states at the light emission process in the electrochemical system is suggested. The feasibility of applying this phenomenon to a novel spectroscopy is discussed.
Structural anisotropy in oblique incidence thin metal films
Authors: Tait R. N. , Smy T. , Brett M. J.
Published: July 2002

A three-dimensional ballistic deposition model for thin film growth has been developed, incorporating the mechanisms of shadowing and relaxation which are essential to microstructure formation. In addition to generating columnar structure similar to that found in films deposited at low temperature, the simulation produces columns which become elliptic cylinders as the angle of incident vapor flux is increased. The model clearly confirms that this structural anisotropy which develops in the film plane is due to self-shadowing in the growing film. The anisotropy, originally revealed in magnetic and electrical properties of obliquely deposited alloys, appears as the elongation of column structure in a direction perpendicular to the plane of incidence. In agreement with titanium films sputtered using a planar magnetron at 65 mPa argon pressure, simulations show a maximum ratio of column major axis to minor axis of about 2 at a deposition angle of 60°. The effect is seen to decrease in both simulations and real films at higher angles of incidence.
Recommended practices for the calibration and use of leaks
Authors: Ehrlich Charles D. , Basford James A.
Published: July 2002

This document is the consensus view of the Calibrated Leak Subcommittee of the Recommended Practices Committee of the American Vacuum Society. It is divided into four main sections: Description, Calibration, Proper Usage, and Recommended Documentation of Leaks. Included in Sec. II are discussions of types of leaks, temperature effects, depletion rates, and units of leakage rate measurement. Section III addresses primary and secondary techniques for leak calibration, including uncertainties. Section IV addresses the proper handling and usage of leaks to achieve optimum results, recommendations of standardization of connections, and safety. The documentation to accompany and to be attached to each calibrated leak, recommended in Sec. V, is intended to provide the user with sufficient information about the leak for accurate and safe use. The appendices contain a glossary and a discussion of the use of throughput and flow rate units and conversions.
Anisotropic highly selective electron cyclotron resonance plasma etching of polysilicon
Authors: Gadgil P. K. , Dane D. , Mantei T. D.
Published: July 2002

High polysilicon etch rates have been obtained in combination with high etch selectivities with respect to SiO2 and photoresist in a microwave electron cyclotron resonance plasma etch reactor. The etch system is vacuum load locked, used Cl2–O2 chemistry, and employs backside helium substrate cooling with 150 mm wafer handling. Etch rates in excess of 4000 Å/min are obtained in undoped polysilicon with zero applied substrate bias, using Cl2 with 0.6% O2 at 3 mTorr total pressure and 700 W of 2.45 GHz input microwave power. The corresponding polysilicon-oxide selectivities are greater than 150, and the polysilicon-resist selectivity is 15–20. Half-micron polysilicon gates etched with zero applied substrate bias have vertical sidewalls and residue-free SiO2 floors. Electron and ion energy distribution measurements show that a high ion flux (≳10 mA/cm2) and simultaneous low ion bombardment energy are controlling parameters for high rate selective etching.
Atomic force microscopy and manipulation of living glial cells
Authors: Parpura V. , Haydon P. G. , Sakaguchi D. S. , Henderson E.
Published: July 2002

The atomic force microscope (AFM) is capable of imaging surfaces at very high resolution. The AFM has been used to image living glial cells in culture. Typical images reveal the three-dimensional shape of the cell and often internal cellular structures are visible. In this report, it is shown that by increasing the imaging force, cells can be removed from the surface on which they are grown. Although the forces involved in this process are complex, it is possible to compare relative adhesion of different types of living cells to a particular substrate.
Comparison of Mo–N and W–N synergism during passivation of stainless steel through x-ray photoelectron spectroscopy and electrochemical analysis
Authors: Halada G. P. , Clayton C. R.
Published: July 2002

In high nitrogen stainless steels and nitrogen surface-doped Mo-containing alloys, nitrogen has been shown to enhance passivity. The mechanism of this apparent Mo–N synergism appeared to be twofold. First, the formation of stable surface nitrides affects a reduction in active dissolution, and, second, reactions between the surface nitride and the electrolyte lead to an increase in interfacial pH, a condition favorable to the formation of an enhanced bipolar passive film. In this study, we compare and contrast the effect of surface nitriding of a Fe–19Cr–9Ni–2W on passivity to the effects previously reported for analogous systems alloyed with Mo. Electrochemical potentiodynamic polarization in deaerated 0.1 M HCl is used to examine the general effects on corrosion inhibition. Qualitative and quantitative analysis of the surface of each alloy following doping with nitrogen and passivation was conducted with variable angle x-ray photoelectron spectroscopy to provide depth-dependent information on the types and amounts of chemical species present. The synergism between W and N is found to be similar to that of Mo and N in enhancing the bipolar nature of the passive film by increasing the amount of tungstate incorporated into the outer layer of the passive film. The primary differences between the structures of the passive films in the two cases result from the passive nature in acidic media of the trioxide of tungsten as opposed to that of molybdenum.
Electronic and phonon mechanisms of vibrational relaxation: CO on Cu(100)
Authors: Tully John C. , Gomez Maria , Head-Gordon Martin
Published: July 2002

Stochastic dynamics simulations of vibrational relaxation rates are reported for a carbon monoxide molecule adsorbed on the (100) face of copper. A recently developed ‘‘molecular dynamics with electronic friction’’ scheme that self-consistently incorporates both phonon and nonadiabatic electron–hole (e-h) pair mechanisms of energy dissipation is employed. Lifetimes of the C–O stretch, the CO-surface stretch, the frustrated rotation, and the frustrated in-plane translation are examined as a function of temperature between 0 and 450 K. e-h pair dissipation plays a significant role for all modes above 150 K. For the C–O internal stretching mode, the e-h pair mechanism dominates and the lifetime depends weakly on temperature. The frustrated rotational (bending) mode is calculated to have the shortest lifetime at all temperatures, and the temperature dependence is weak. The e-h pair contribution is again largest although the phonon contribution is significant. The CO-surface stretch and the frustrated in-plane translation are the longest lived modes, but exhibit a dramatic decrease in lifetime with increasing temperature. The results suggest that e-h pair dissipation plays a significant role in adsorbate dynamics at metal surfaces when there are chemisorption interactions.
Deposition of amorphous hydrogenated silicon carbide films using organosilanes in an argon/hydrogen plasma
Authors: Maya Leon
Published: July 2002

Nearly stoichiometric, amorphous silicon carbide films with a relatively low hydrogen content were deposited from organsilanes on a variety of substrates in a microwave-generated plasma without external heating. The films undergo little weight loss upon pyrolysis to 800 °C. The effect of the different deposition parameters on the film composition and the exhaust gas was established through a battery of tests including infrared Fourier transform spectroscopy, Auger electron spectroscopy, x-ray photoelectron spectroscopy, ellipsometry, and mass spectroscopy. For a given power level there is a limiting feeding rate of the precursor under which operation of the system is dominated by thermodynamics and thus leads to the desired product. Beyond that limit, excessive hydrogen incorporation and carbosilane polymer formation takes place. The hydrogen content of the plasma is also an important parameter affecting the chemistry of the deposition. In the thermodynamically dominated regime the nature of the precursor has no effect on the quality of the film. It affects only the relative utilization efficiency.
Fluorinated diamondlike carbon films deposited from radio-frequency glow discharge in a triode reactor
Authors: d’Agostino Riccardo , Lamendola Ritalba , Favia Pietro , Giquel Alix
Published: July 2002

Diamondlike carbon thin films have been deposited by H2–C2F6 fed rf-glow discharges in a triode reactor. Raman spectroscopy and electron spectroscopy for chemical analysis have been utilized as diagnostic tools to investigate structural properties and chemical composition of deposited films. Transitions in film properties have been observed, from those typical of hydrogenated polymers to those of diamondlike and fluorinated polymers, by changing feed composition, substrate bias, and substrate temperature. In particular, it has been shown that the energy of the ions bombarding the growing films, as well as the fluorine contents in the films is the most critical parameter to obtain materials with diamondlike structure.
Redeposition kinetics in fluorocarbon plasma etching
Authors: Gray David C. , Mohindra Vivek , Sawin Herbert H.
Published: July 2002

The redeposition kinetics of plasma etching products have been measured as a function of ion and free-radical fluxes which are representative of the fluorocarbon etching environment. Silicon and SiO2 surfaces were exposed in a multibeam etching tool to energetic ions (Ar+), etchant radicals (F), and depositing carbonaceous species (CF2), the relative fractions of which were independently varied to alter the etching product distributions. The rate of product redeposition (i.e., the deposition rate on nonbombarded surfaces such as trench or via sidewalls) was measured using a quartz crystal microbalance (QCM) which could be rotated around the etching sample face. While redeposition rates of Ar+ sputtering products from Si and SiO2 were characteristically high, the addition of F suppressed redeposition by nearly an order of magnitude. The mechanisms for this reduction involve the passivation of the nonbombarded QCM surface by atomic F, the chemical etching of the redeposited material, and the production of volatile products which do not readily stick to sidewall surfaces. Redeposition rates during ion-enhanced F etching of Si and SiO2 surfaces are largely determined by the fraction of physical sputtering, which emits unsaturated ‘‘sticky’’ products. Accordingly, redeposition rates are observed to increase with decreasing F/Ar+ ratio and increasing ion energy. Addition of CF2 radicals during ion bombardment was observed to suppress redeposition rates measured during pure physical sputtering, but had no significant effect on redeposition in the presence of atomic F.
Mesostructure of photoluminescent porous silicon
Authors: Ruiz F. , Vázquez-López C. , González-Hernández J. , Allred David D. , Romero-Paredes G. , Peña-Sierra R. , Torres-Delgado G.
Published: July 2002

Scanning electron microscopy, atomic force microscopy, and Raman spectroscopy were used to characterize the microstructure of photoluminescent porous silicon (PS) layers formed by the anodic etching (HF:H2O:ethanol), at various current densities, of p-type (100) silicon wafers possessing resistivity in the range 1–2 Ω cm. Existing models for the origin of luminescence in PS are not supported by our observations. Cross-sectional as well as surface atomic force micrographs show the material to be clumpy rather than columnar; rodlike structures are not observed down to a scale of 40 nm. A three-dimensional model of the mesostructure of porous silicon is discussed. Room-temperature Raman scattering measurements show no evidence for a-Si:H or polysilanes and the material reported here is composed of 10 nm roughly spherical Si nanocrytallites rather than 3 nm wires postulated in standard quantum confinement models.
Ultrahigh vacuum in the semiconductor industry
Authors: O’Hanlon John F.
Published: July 2002

Vacuum processing equipment designed for high-end commercial silicon production does not operate in the ultrahigh vacuum region (10−9–10−12 Torr). However, for reasons of reducing process and gas impurities to the sub-part per billion level and increasing product throughput, UHV technology is required and is being incorporated into production equipment. This article reviews progress in the field of extremely clean device processing systems. It highlights progress in pump design, chamber design, operational procedures, and materials developments that have made today’s clean processes possible and suggests directions for improvements.
Adsorption site and the role of substrate reconstruction for the Mo(110) p(2×2)–S system
Authors: Toofan J. , Tinseth G. R. , Watson P. R.
Published: July 2002

Although the Mo(110) p(2×2)–S system has been widely studied, there have been no definitive studies that define the surface crystallography using modern methods. Sulfur was deposited on the clean Mo(110) surface from an in situ electrochemical source and the surface annealed to a coverage of 0.25 monolayer to produce a high-quality p(2×2) low-electron energy diffraction (LEED) pattern. Intensity–voltage curves from 13 nonequivalent beams were recorded at normal incidence using a video camera. These data were combined with tensor LEED calculations to produce an optimized surface structure. We allowed the coordinates of the Mo atoms in the first two substrate layers and the adsorbate S atom to vary until the Pendry R factor was minimized. There is evidence for adsorption-induced substrate reconstruction. The S adatom is located in a distorted central hollow (CH) site in which two of the top-layer Mo atoms have moved significantly outward. The top substrate layer is also rumpled on the order of 0.1–0.2 Å. The distortion is such that the final coordination of the S atom is somewhat closer to threefold coordination rather than the 2+2 coordination characteristic of of the undistorted CH site.