bluuebunny/crossref_metadata_2025 huggingface dataset:
LEED, Auger spectroscopy, and contact potential studies of copper−gold alloy single crystal surfaces
Authors: Potter H. C. , Blakely J. M.
Published: July 2002

The (100), (111), and (110) surfaces of copper−gold alloy single crystals (Cu, Cu3Au, CuAu, Au3Cu, Au) have been studied. Results are presented for (i) the variation of relative Auger peak strengths with bulk composition, (ii) the variation of work function with orientation and bulk composition, and (iii) the occurrence of surface ordering. The average work function Φ increases as the bulk Au concentration increases from Cu to Au3Cu, with the orientation dependence in accord with the expected variation of surface dipole with ’’atomic roughness,’’ i.e., Φ (111) ≳ Φ (100) ≳ Φ (110); the surfaces of Au do not follow this simple rule. LEED indicates that Au(100), Au(110), Au3Cu(110), and CuAu(110) surfaces have complex structures. Observed differences in the kinetics of ordering of the Cu3Au (100) and (111) surfaces are discussed.
Chemical effects in the M4,5N
N Auger spectrum of Mo(110) due to adsorption of O2 and CO
Authors: Hooker M. P. , Grant J. T. , Haas T. W.
Published: July 2002

Chemical effects are observed in the M4,5NN Auger spectrum of Mo following adsorption of oxygen and carbon monoxide on clean Mo(110). This system is particularly interesting as Auger transitions involving only core electrons, one conduction band electron or two conduction band electrons are all present over the energy range 90−250 eV. On adsorption, Auger transitions involving only core electrons shift to lower energies, whereas those involving one or two conduction band electrons undergo changes in shape. Auger spectra are presented in both derivative form 𝒩(1)m(E) and following integration, 𝒩m(E).
Remarks on the use of perfluoropolyether fluids in particle accelerator vacuum systems
Authors: Luches A. , Perrone M. R.
Published: July 2002

A systematic series of tests was performed to investigate the advantages of using standard cuts of perfluoropolyether fluids (Fomblin Y) as vacuum fluids for the pumpdown of ion source and particle accelerator vacuum systems. Vacua in the low 10−3 and 10−7 Torr ranges were obtained by a rotary and an unbaffled diffusion pump, respectively. A residual gas analysis shows the presence of high molecular weight fractions, up to M=240. This fact advises against their use in heavy ion sources and accelerating systems where electron exchange processes are highly dangerous. The absence of tar and sludge formations even under high intensity electron bombardment is a very important feature for their use in high intensity electron beam accelerators.
Magnetron dc reactive sputtering of titanium nitride and indium–tin oxide
Authors: Clarke Peter J.
Published: July 2002

Magnetron dc reactive sputtering of TiN and ITO are sensitive to the design and operating parameters of the magnetron. Plasma confinement, current density, voltage, water cooling of the target, and the ratio of argon to the reactive gas are the important operating parameters. The TiN and ITO film composition was examined by x-ray diffraction. TiN fractional cross sections were examined by a SEM to determine film microstructure. The TiN films were thick enough to show a transition structure consisting of densely packed fibrous grains. The ITO films were too thin to show any structure.
Orbital identification in the INS and UPS spectra of chalcogens adsorbed on Ni(100)
Authors: Hagstrum H. D. , Becker G. E.
Published: July 2002

Orbital energy spectra of the c (2×2)Te structure on Ni(100) obtained by both UPS and INS show two Te-derived orbital peaks which we interpret as arising from the nonbonding and bonding orbitals of the surface Ni2Te molecular complex. These conclusions are suggested by the comparison of orbital peak shapes with those of the nonbonding 5d orbitals of Hg adsorbed on Ni(100) and by the energy positions relative to the p4 orbital energy level in free Te. Previously unpublished data on c (2×2)Se as well as considerations of relaxation energy indicate that this interpretation should also be carried over to the INS spectra for c (2×2)Se and c (2×2)S reported previously. Relative orbital intensity in the INS and UPS spectra support this interpretation if the chalcogen atom in the c (2×2) structure is bridge-bonded across the diagonal of the basic surface Ni square as previously proposed. INS and UPS spectra for c (2×4)Te show a single broad orbital peak requiring a different bonding configuration, probably of C4v symmetry involving four Ni atoms.
Large-capacity cryogenic pumping of D2 and H2 for fusion
Authors: Halama H. J. , Lam C. K. , Bamberger J. A.
Published: July 2002

We have investigated the pumping speed as well as the liquid helium and liquid nitrogen consumption of a large-capacity, all aluminum cryocondensation pump having a projected area of 0.9 m2 and real area of 1.15 m2. The liquid-helium-cooled surface was shielded from room-temperature thermal radiation by a black anodized aluminum chevron baffle held at 77 K. Deuterium pumping speed was nearly constant ∠80 000 l/s for gas flow rates up to 11 Torr l/s (1.47 Pa m3/s) and surface coverages up to 9×1020 molecules/cm2. The speed, however, increased slightly with coverage. Hydrogen pumping speed was also constant, i.e., 110 000 l/s. The boil off of liquid helium depended on the residual pressure and gas composition in the system. At low pressures boil off of liquid helium for D2 and H2 films was 0.53 and 0.85 W, respectively. Boil off of liquid helium increased linearly with the pumped gas load. The liquid nitrogen consumption was only weakly dependent on the pressure in the system.
Electrical properties of anodic and pyrolytic dielectrics on gallium arsenide
Authors: Zeisse C. R. , Messick L. J. , Lile D. L.
Published: July 2002

Capacitance–voltage and current–voltage measurements have been used to characterize dielectrics grown by anodization and by pyrolytic deposition on bulk n-type gallium arsenide. The anodic oxide is an ohmic insulator with a resistivity ≳1016 ohm cm and a breakdown field of 3×106 V/cm. Pyrolytically deposited SixOyNz films exhibited resistivities of 1015 ohm cm and breakdown fields between 5×106 and 1×107 V/cm. C–V data for the anodic and pyrolytic dielectrics are very similar, implying in each case: a fixed charge of more than 1012 electrons/cm2 in the dielectric, temporary trapping and release of 2–3×1010 electrons/cm2 at the semiconductor–dielectric interface for each volt of applied bias, and a U-shaped density of surface states in the upper half gap with a minimum value of 2–4×1012 cm−2 eV−1.
On the difference between true and net outgassing rates
Authors: Hobson J. P.
Published: July 2002

Measured outgassing rates are almost always net outgassing rates. Sometimes it is important to have information on true outgassing rates. This problem is discussed, with particular reference to the design of the wake shield experiment on the Space Shuttle.
Grease lubrication of turbomolecular vacuum pump bearings
Authors: Osterstrom G. E. , Knecht T.
Published: July 2002

Greases have been developed within the past five years which enable turbomolecular pumps of moderate rotor speeds to operate at least one year without regreasing. The relative imobility of grease as compared with lubricating oil greatly decreases the probability of contamination of the evacuated space by operator error. Low friction eliminates need for cooling most applications. Horizontal, vertical, and inverted positions are practical. Special problems of gas friction heating, hot degassing, and rough transport are discussed.
Ion and electron desorption of neutral molecules from stainless steel (304)
Authors: Edwards D.
Published: July 2002

The vacuum performance of both electron and proton storage rings (as well as certain types of fusion reactors) is expected to be sensitive to the desorption of neutral molecules from the vacuum chamber wall by ∠keV charged particles. In this study the desorption yields of H2, CO, CO2, and CH4 are reported from 1000-eV Ar+ and 500-eV e− impacting on SS (304) samples (∠ 1000 cm2 surface area) prepared by: (i) a degrease treatment, (ii) an acid cleaning (1/3 HF, 1/3 HNO3, 1/3 H2O), (iii) concentrated HF. Three separate samples were analyzed for the first two treatments allowing the sample-to-sample variation to be determined (10%–20% yield variations). The unit yield energy E0 (electron energy for which the total secondary electron emission is 1.0) has also been measured for each of the above treatments.
Measurements on the efficiency of acoustic delay lines in view of beam lines for synchrotron radiation
Authors: Betz H. , Hofbauer P. , Heuberger A.
Published: July 2002

Tests were run to study the propagation of a pressure wave as originated by the rupture of a beam exit foil window in the beam line of a synchrotron radiation storage ring. The measured velocities were approximately 1000 m/s for air and 2000 m/s for helium. The influence of various acoustic delay lines on the propagation of such waves was studied in detail by measuring the local dependence of the velocity in the pressure range of 10−6 to 10−3 mbar. It was found that the use of acoustic delay lines results in a drastic reduction of propagation velocity remaining at the same low level even in the part of the beam line behind the delay line. The efficiency of a delay line as defined by the ratio of inlet versus outlet velocity is determined mainly by its geometry and changes little with type of gas.
Dynamic properties of interface-state bands in GaAs anodic MOS system
Authors: Hasegawa Hideki , Sawada Takayuki
Published: July 2002

A capacitance transient study is performed on the n-type GaAs anodic MOS system, in order to clarify the dynamic properties of the interface states near midgap. A simple theory of capacitance transient and DLTS including the effect of time constant spread due to tunneling from the interfacial traps, is developed. Good agreements are obtained between the theory and experiment of capacitance transient, and between the transient analysis and the steady-state admittance analysis. The striking conclusion is that the states at midgap possess an activation energy of 0.38 eV. This is against the standard theory of surface-state continuum, and is explained by the interface-state-band (ISB) model in terms of partial formation of ’’band region’’ by interface states. The model resolves the previous question of anomalously large effective capture cross section of 10−8 cm2, giving a normal constant value of 1.5–2.9×10−15 cm2.
Ideal CdTe/HgTe superlattices
Authors: Schulman J. N. , McGill T. C.
Published: July 2002

In this paper we consider a new superlattice system consisting of alternating layers of CdTe and HgTe constructed parallel to the (001) zincblende plane. The tight-binding method is used to calculate the electronic properties of this system, in particular, band edge and interface properties. The energy gap as a function of layer thickness is determined. It is found to decrease monotonically with increasing HgTe layer thickness for a fixed ratio of CdTe to HgTe layer thicknesses. The symmetry of the valence band maximum state is found to change at certain HgTe layer thicknesses. This is explained by relating the superlattice states to bulk CdTe and HgTe states. The existence of interface states is investigated for the superlattice with 12 layers of CdTe alternating with 12 of HgTe. Interface states are found near the boundaries of the Brillouin zone, but none are found in the band gap.
Applications of a Kaufman ion source to low energy ion erosion studies
Authors: Sharp D. J. , Panitz J. K. G. , Mattox D. M.
Published: July 2002

The erosion of materials by low energy ions is of concern in fusion reactors since high Z impurities in the plasma cause radiation cooling. Ion bombardment of the fusion reactor chamber walls arises from ions of fuel (D, T) material, gaseous impurities (O, C), and impurities from eroded components (Fe, Co, Ni, C, Mo, etc.) being accelerated across the wall sheath potential (0.1 to 1 KeV). A Kaufman type ion source has been characterized for use with hydrogen, and subsequently used to determine the relative erosion rates of bulk Mo, C, Cu, coating of TiB2, B4C, Be, VBe12 and other materials. Ions of hydrogen (Z=1), argon (Z=18), and xenon (Z=54) at acceleration potentials of 250, 500, and 1000 V have been used to determine erosion yields.
X-ray lithographic patterning of magnetic bubble circuits with submicron dimensions
Authors: Hofer D. , Powers J. , Grobman W. D.
Published: July 2002

An x-ray process is described which permits the fabrication of submicrometer single level masking bubble devices. The process includes electron-beam patterning of the master x-ray mask followed by a CuLα x-ray copy to pattern a negative x-ray mask. Enhancements of electron-beam lithography are described which permit fabrication of 1/4 μm mask structures with 70 Å resolution. The x-ray process is applied to the SLM fabrication of 1 μm magnetic bubble devices with 1/2 μm features, and propagation characteristics of these devices are reported.
New design of modulated Bayard–Alpert gauge
Authors: Hua Z. Y. , Yang X. L. , Qiu S. X. , Zhuge J. L.
Published: July 2002

The fundamental equations of the modulated Bayard–Alpert gauge (MBAG) introduced by Redhead are briefly discussed. X-ray effects from the modulator may be weakened appreciably by using a ’’pin-to-pin’’ (PTP) collector–modulator structure; the figure-of-merit (Q), which measures the degree of extension of the lowest measurable pressure with respect to a Bayard–Alpert gauge (BAG), can be directly determined from the experimental results. A new operating mode is proposed such that the modulator potential does not switch from the grid potential to the collector potential, but varies always positively with respect to the cathode with an alternating voltage of very low frequency (typically 1 Hz) superimposed on a chosen dc potential. The collector current is then detected by a two-phase lock-in amplifier. The modulator–collector capacitance of the PTP gauge is only 1.7×10−5 F. The figure-of-merit Q calibrated is about 100 so that the lowest measurable pressure of this gauge is in the order of 10−10 Pa (10−12 Torr).
Surface diffusion of adsorbed species: A review
Authors: King David A.
Published: July 2002

Advances made in the study of the diffusion of adsorbed species on single crystal surfaces are summarized. An appraisal of the techniques and methods of data treatment which have been developed for both macroscopic (single crystals cut to expose a given crystal plane) and microscopic (field emitter) surfaces is presented, and a brief survey is made of the data obtained for precursor, molecularly chemisorbed, and dissociatively chemisorbed states. The influence of lateral interactions between adatoms on diffusion parameters is explicitly examined in relation to recent results for O adatoms on W{110}. Finally, a brief survey is given of the importance of diffusion in other surfaces processes, such as the formation of ordered overlayers and adsorption and desorption kinetics.
Thermal responses of first wall limiters in the Tokamak Fusion Test Reactor
Authors: Budny Robert
Published: July 2002

A model was used for the heat flux to estimate the thermal responses and the sublimation rates of several first wall limiters proposed for the Tokamak Fusion Test Reactor. The critical parameter is the thickness of the scrape-off layer, or outer skin of the plasma. The thinner this is, the hotter the limiter will become after repeated discharges. The minimum tolerable thickness is about 0.5 cm for copper or graphite tiles over Nitronic 33 steel backing plates. For thicknesses less than this the steel will be too hot; the sublimation rates of most of the proposed first wall coatings for the tiles are sufficiently low to not contaminate the plasma.
Helium scattering measurements of the Ag(111) surface phonon dispersion
Authors: Yerkes Steven C. , Miller David R.
Published: July 2002

Energy and intensity measurements have been performed on 23 meV He atoms scattered from 135 K Ag(111) to yield information on the surface dispersion relation. The preliminary results are in qualitative agreement with the linear Rayleigh phonon dispersion curve expected from continuum theory and experiment. The scattering probability falls exponentially with increasing phonon frequency but shows a distinct maximum at an angle dependent on incident beam angle and energy.
Extended appearance potential fine structure analysis of oxidized metal surfaces
Authors: den Boer M. L. , Einstein T. L. , Elam W. T. , Park Robert L. , Roelofs L. D. , Laramore G. E.
Published: July 2002

Like EXAFS, extended appearance potential fine structure (EAPFS) probes the immediate neighborhood of a particular element and thus, unlike most other structural probes, does not require long-range order. Furthermore, the use of low-energy electron makes the technique surface sensitive. Because no dipole selection rules apply to electron excitation, explicit calculation must determine the angular momentum of the outgoing final-state electron and thus the feasibility of Fourier inversion of the data. For excitation of the O 1s core, we find the outgoing electron is overwhelmingly s-wave. Reaction of Al(100) with about 1-1/2 equivalent monolayers of oxygen disorders the surface completely (i.e., extinguishes the LEED pattern). For this surface, analysis of the O 1s edge gives an O–Al distance of 1.98±0.05 Å, the longer of the two Al–O spacings in bulk Al2O3, which indicates that the oxygen goes under the top layer of Al. For a thick oxide layer on Ni(100), diffraction effects precluded use of the O 1s edge. From Ni 2p data, for which the angular momentum selection is weaker, we can extract the bulk Ni–O distance by using plausible phase shifts.
Microfabrication and microcharacterization techniques for laser fusion targets
Authors: Halpern G. M.
Published: July 2002

A review is presented of some recent accomplishments in the fabrication and characterization of laser fusion targets. These targets are used in a research program at the University of Rochester’s Laboratory for Laser Energetics whose goal is to demonstrate the scientific feasibility of laser fusion. Exploding pusher targets, consisting of deuterium–tritium filled glass microballoons, are discussed. Techniques are described for selecting high quality shells, filling them with D–T fuel by permeation, and characterizing their fuel content by nondestructive beta counting. More advanced targets have been employed in experiments designed to produce higher compressions using the six beam laser system ZETA. These consist of argon filled glass shells coated with plastic. A novel method is described for filling the shells with argon, which involves laser drilling a submicron hole in the balloon wall and sealing the gas with a meltable plug. Three methods are discussed for applying smooth and uniform plastic coatings to these targets. The thermal pyrolysis of di-paraxylene, plasma polymerization of organic monomers (e.g. p-xylene) and colloidal coatings of polyacrylates have all yielded excellent hydrocarbon coatings on glass microballons. Targets for upcoming experiments on the 24 beam laser system OMEGA involve multishell configurations. A new microfabrication molding and replication technique is being implemented to produce spherical and identical hemispherical shells used in the assembly of OMEGA targets. Details of this technique are provided, along with some preliminary examples of plastic and copper hemishells. A versatile physical vapor deposition system is also described which has the capability of coating levitated microballoons with metals and other materials amenable to sputtering. Finally, a unique method of examining opaque targets using contact microradiography is discussed. The x-ray source is generated by the focussed beam of a scanning electron microscope. Readout of the developed radiographic image is also performed in the SEM, using backscattered electrons from the silver grains in the emulsion. Edge resolution of 0.25 μm has been demonstrated in this radiography system. The characterization of localized defects and geometrical defects such as decentrations are possible with superior resolution in this system.
Molecular and radiation transmissivities of chevron type baffles for cryopumping
Authors: Benvenuti C. , Blechschmidt D. , Passardi G.
Published: July 2002

In the design of cryopumps, intermediate temperature (e.g. 77 K) baffles are interposed between the cold pumping surfaces and ambient temperature walls of the vacuum system. This intermediate baffle serves to reduce the effects of thermal radiation on the pumping surfaces. The introduction of the baffle, however, decreases the pumping speed, and therefore its design has to be optimized with respect to both molecular and radiation transparencies. We have studied the transmission probabilities for molecules and photons, assuming diffuse and specular reflection, respectively, as a function of the geometry and surface reflectivity of chevron type baffles, using the Monte Carlo method. The calculated figures are in good agreement with experimental results. Using a black paint which provides a reflectivity of ∠0.10, a molecular transmissivity of about 0.24 and a radiation transmissivity of ∠7×10−4 were achieved.
An electron-beam/optical-hybrid lithography approach to submicrometer electronic devices
Authors: Potosky J. C. , Higgins A. J. , Hoelke S. T. , Imerson R. G. , Kinoshita F. F. , Maddox R. L. , Reekstin J. P.
Published: July 2002

Submicrometer transistor gates have been fabricated in CMOS/SOS prototype VLSI circuits and GaAs digital integrated circuits. A hybrid lithography approach was used to take advantage of the rapid throughput of optical lithography and the high resolution capabilities of electron-beam lithography. The entire gate levels of these devices were defined with direct write electron-beam lithography. The six remaining lithographies in the CMOS/SOS device and the five remaining levels in the GaAs device were defined with various optical lithography systems. A unique electron-beam fiducial marker fabrication technique was required for each of the two devices. The goal of this approach was to substitute electron-beam lithography for optical lithography in the gate level only, leaving the remaining device process unaltered. Gate lengths as small as 0.6 μm were fabricated in the Si devices and 0.9 μm gates were achieved in GaAs. The CMOS/SOS gates were patterned in PMMA resist over MoSi2 and requires an Al liftoff and ion mill. The GaAs gates were patterned in AZ2400 resist which became an etch mask for underlying SiO2 and Si3N4 films. Circuits in both devices were sucessfully operated.
A simple technique for modifying the profile of resist exposed by holographic lithography
Authors: Efremow N. N. , Economou N. P. , Bezjian K. , Dana S. S. , Smith Henry I.
Published: July 2002

Holographic lithography is a rapid and convenient method of exposing low distortion periodic and quasi-periodic patterns over large areas. Spatial periods below 0.2 μm are readily achieved using commercial He:Cd lasers. However, many substrates of interest have significant reflectivity and, because the phase change on reflection is close to π, an intensity minimum occurs at the resist–substrate interface, leading to rounded ’’overcut’’ resist profiles. Such profiles are unsuitable for liftoff and undesirable for anisotropic dry etching. Moreover, the linewidth-to-period ratio is difficult to control and exposure latitude is limited. If a dielectric film is placed over a reflecting substrate, the intensity at the resist–dielectric interface can be maximized by proper choice of the optical thickness of the dielectric. We have developed a simple, operational, nondestructive method for precisely determining the angles of laser incidence that correspond to the condition of maximum interface intensity. The method uses the exposure laser and consists of measuring the total reflectivity from the dielectric/substrate combination as a function of incidence angle. Knowledge of the dielectric thickness and the optical constants of the dielectic and substrate are not required. We have used this method for the case of a He:Cd laser and a Si02/Si substrate. Chemical etching of the Si02 in buffered HF allowed us to maximize interface intensity at precisely the angles corresponding to preselected grating periods of 0.2 and 1 μm. Liftoff of evaporated chromium was achieved over cm2 areas with an exposure latitude of ∠200%. This, together with SEM analysis, indicated that resist sidewalls were vertical or slightly undercut, and improved control of linewidth-to-period ratio was feasible.
A new wide-range B–A gauge from UHV to 10−1 Torr
Authors: Ohsako N.
Published: July 2002

In a conventional B–A gauge, the ion collector current shows a strong nonlinearity with increasing pressure above about 10−3 Torr. This is considered to be due to the ion current to the filament becoming comparable to the electron emission from the filament. In this new gauge, an auxiliary electrode whose potential is kept lower than that of filament, is placed near the filament to eliminate such an undesirable ion current. By this modification, the linear region is extended up to 10−1 Torr N2 without sacrificing the sensitivity. Through the optimization study of electrode design parameters such as structure and potential, a gauge with a semicylindrical electrode kept at ground potential gives the best result. This new B–A gauge can cover the pressure range from 10−10 to 2×10−1 Torr with linear ion current–pressure characteristics.
Spinning rotor viscosity gauge: A transfer standard for the laboratory or an accurate gauge for vacuum process control
Authors: Reich G.
Published: July 2002

A new gauge has been developed that appears to be the ideal tool for measuring low pressures in both research and industrial vacuum processes where reliability and accuracy of measurement are of importance. In particular, it will be emphasized that the spinning rotor viscosity gauge (licensed by Kernforschungsanlage Jülich GmbH, Germany) is in fact a fundamental vacuum gauge because its ’’sensitivity’’ depends only on the mass and diameter of the ball. These quantities do not change and can be determined accurately by well-known fundamental methods. The new gauge excels the common vacuum gauges by the following features: long-term stability, instantly operational; high accuracy and repeatability; no hysteresis; no temperature stabilizing required. The new gauge is rugged and will perform well under both working and transfer conditions. The spinning rotor viscosity guage has inherent long-term reproducibility that will serve well should it be used as a transfer standard. The simplicity and accuracy of operation should offer applications in the area of process control.
Obtaining pressures in the 10−5 Pa range with oil-sealed rotary vacuum pumps
Authors: Kendall B. R. F.
Published: July 2002

Trapped oil-sealed rotary pumps are usually considered capable of ultimate pressures no lower than about 10−3 Pa. Experiments are described which confirm that most of this residual gas originates from air dissolved in the pump oil. Replacement of the air with a less soluble gas (helium) or an easily trapped gas (carbon dioxide) is shown to give a useful reduction in ultimate pressure and to reduce the oxygen partial pressure to essentially zero. Operation with completely degassed oil is shown to give ultimate pressures in the 10−5 Pa range. The design of pumps based on these principles is discussed.
Cryopump regeneration studies
Authors: Longsworth R. C. , Bonney G. E.
Published: July 2002

A cryopump (APCI Model HV202-8C) connected to a pump speed test dome was used to evaluate the time and effectiveness of its regeneration using alternate methods of purging and heating the pump. Regeneration effectiveness was determined by measuring the pumping speed and helium adsorption capacity of the charcoal after cool down. The pump was loaded with 8 g of water and 10 std.L of argon prior to regeneration. For all tested regeneration methods the helium speeds were within 80% of the maximum speed. Warm up and evacuation without extra heat or a purge followed by cooling can be done in 4 h and 15 min. Regeneration was accomplished in 2 h and 45 min using a heater on the outside of the housing and a nitrogen purge to bring the cryopump to 310 K, followed by evacuation with a mechanical pump to 100 mTorr without heat or purge, then closing the roughing valve and starting the cryopump. An initial water vapor pressure of 100 mTorr does not increase the cool-down time compared to a lower starting pressure. Tests with other gases showed that argon and nitrogen have to be pumped below 20 mTorr and hydrogen and helium have to be pumped below 4 mTorr to avoid long delays in cool down.
Properties of MBE grown InSb and InSb1−xBix
Authors: Noreika A. J. , Greggi J. , Takei W. J. , Francombe M. H.
Published: July 2002

Undoped homoepitaxial and heteroepitaxial films of MBE grown InSb display n-type bulklike semiconducting properties, e.g., high mobility at 77 K. Epitaxial films with p-type conductivity were grown by in situ doping with Be. Transmission electron microscopy of cross-sectioned films showed that the large lattice mismatch between InSb and GaAs is accommodated by both dislocations and stacking faults. Phase separation at, and near, the surface of InSb–InBi deposits was shown by a combination of scanning electron microscopy, and energy dispersive x-ray analysis.
Sealing mechanisms in bakeable vacuum seals
Authors: Roth A.
Published: July 2002

Bakeable seals have to maintain their leak tightness during and despite repeated heating/cooling cycles. An analysis of the mechanisms by which the leak rate of demountable bakeable seals is maintained (or lost) is presented. The mechanisms are studied by following the evolution of the strain in the gasket and/or flange during heating/cooling, as related to the strain developed during the processes of mechanical ‘‘tightening’’ and releasing. It is proposed to describe these processes by the relevant strain versus load curves, where the ‘‘operating position’’ of the seal is expressed by the intersection between the strain/load curve of the gasket and that of the flange. Typical curves and operating positions of commonly used seals are presented on a comparative ‘‘map’’. Heating modifies the strain by a combination of the effects of ‘‘softening’’ of the materials and variation of the load caused by the differential expansion of the parts. The mechanisms by which these effects may lead to the loss of the (elastic) strain and/or may increase the plastic deformation are discussed. The acceptable limits of the variation of the strain (expansion, yield point) for various bakeable seals are established. A method of recording the process, by measuring (on line) the strain at appropriate points on the surface of the gasket and/or the flange, is proposed.
Enhanced selective hydrogen desorption from metals
Authors: Knize R. J. , Cecchi J. L.
Published: July 2002

The thermal desorption of hydrogen isotopes from a metal is usually a second order process the rate for which becomes asymptotically slow. We present a method for enhancing the desorption rate of one particular isotope by maintaining a constant pressure of another molecular species. This results in an effective first order desorption and concommitant exponential decay of the concentration of the selected isotope. Data is presented for the enhanced desorption of deuterium from a Zr–Al getter. The results agree well with a theoretical model, which is discussed. This enhanced desorption method should be particularly useful for tritium operation in the tokamak fusion test reactor.
Pressure dependence of Zr–Al pumping speed for H2
Authors: Cecchi J. L. , Knize R. J.
Published: July 2002

We have measured the pumping speed of the Zr–Al alloy bulk getter over a pressure range of 10−5 to 10−2 Torr. The temporal evolution of the pumping speed closely follows the behavior predicted by a theoretical model for bulk gettering. In particular, for pressure P above ∼5×10−3 Torr, the pumping speed decreases as P−1/2. From the high pressure data, we have measured the bulk diffusivity of H in Zr–Al to be D=exp [−4.0(1.1)−9100(450)/T] cm2 s−1, with T the getter temperature in K. This is in good agreement with values obtained from desorption measurements.
Equilibrium pressures of H2 and D2 for different getter materials and the effect of CO impurities
Authors: Boffito C. , Ferrario B. , Martelli D.
Published: July 2002

The 84% Zr–16% Al nonevaporable getter alloy has been used for a long time in vacuum technology and, more recently, has been adopted in advanced applications such as fusion technology and particle accelerators. A new getter material consisting of a Zr–V–Fe ternary alloy having interesting characteristics for these applications has also been proposed. Particularly in fusion technology hydrogen and its isotopes must be sorbed in relatively large amounts. Therefore, the equilibrium pressures of H2 and D2 have been investigated for the above mentioned alloys as well as for the more traditional getter material, titanium. A temperature range from 500 to 800 °C at pressures less than about 100 Pa has been covered. Moreover, as the hydrogen isotopes will contain various gaseous impurities, of which carbon monoxide is usually the most important, the effects of this gas on the H2 and D2 equilibrium pressures have also been investigated.
A compact UHV rotary feedthrough
Authors: Silverman P. J.
Published: July 2002

A differentially pumped rotary feedthrough utilizing commercially available spring-loaded Teflon seals is described. The design is quite compact and allows rotation of a Conflat-type flange while maintaining ultrahigh vacuum.
The future of vacuum technology
Authors: Hobson J. P.
Published: July 2002

For 30 years vacuum technology has responded to spontaneous efforts to extend the limits of vacuum production and measurement and to the demands of diverse fields of application. In the future it is predicted that: vacuum pumps will see incremental improvements, particularly cryogenic pumps; more fundamental and less empirical research will take place on seals and outgassing leading to major improvements; vacuum gauges will improve incrementally; calibration will improve greatly and will be extended to 10−13 Pa (10−15 Torr); calibration methods will utilize cryogenics; leak detectors with sensitivities approaching 10−13 cm3 STP s−1 will appear commercially; a gauge to assess directly the interaction of ambient gases on surfaces will be developed; more special purpose vacuum facilities, such as storage rings and fusion reactors, will be built; portable systems at ultrahigh vacuum will multiply; microelectronics under vacuum will master the control of fabrication from 10 to 10 000 Å and new products will appear, in particular three-dimensional structures; there will be a synthesis of vacuum technology with lasers, superconductors, catalysis, and solar energy; pervading all these developments will be an ever-increasing application of microprocessors and computers to vacuum systems of all kinds.
Vacuum outgassing of various materials
Authors: Erikson E. D. , Beat T. G. , Berger D. D. , Frazier B. A.
Published: July 2002

A gas analytical system for measuring the evolved gases from materials during vacuum degassing is discussed. The outgassing data are based upon the throughput measurement and a computer-controlled quadrupole mass spectrometer allows the determination of residual gas species. A variety of materials have been tested in the ‘‘as-received’’ condition at room temperature vacuum exposure. Test results are presented for materials such as chlorinated polyvinylchloride (CPVC), low density carbon foam and Monel knitted wire mesh (both of which could be used for the attenuation of electromagnetic or radio frequency interference), polyethylene (in the form of black pipe, sheet of various thicknesses, and as an electrostatically applied coating to metal substrates), as well as Parylene-N■ conformal coatings applied to CPVC, polyethylene, and stainless steel substrates.
Plasma-enhanced CVD: Oxides, nitrides, transition metals, and transition metal silicides
Authors: Hess Dennis W.
Published: July 2002

Plasma-enhanced chemical vapor deposition (PECVD) of thin films has generated considerable interest in recent years. Much of this interest stems from the ability of high energy electrons in rf glow discharges (plasmas) to break chemical bonds and thereby promote chemical reactions at or near room temperature. Such considerations are particularly important when depositing films onto substrates which cannot withstand high temperatures. A further advantage, however, is that the highly reactive plasma atmosphere can result in the formation of materials with unique chemical, physical, and electrical properties. In this paper, the plasma-enhanced deposition of oxide, nitride, transition metal, and transition metal silicide films will be discussed. Emphasis will be placed upon the chemistry occurring in the glow discharge, and on the manner in which this chemistry controls the resulting film properties.
Influence of the metal–adsorbate interaction on secondary ion emission from UHV-prepared amino acid overlayers on metals
Authors: Holtkamp D. , Jirikowsky M. , Kempken M. , Benninghoven A.
Published: July 2002

Amino acid overlayers with controlled coverages were produced in situ using a molecular beam technique. The metal–adsorbate interaction was examined by monitoring the secondary ion emission and the desorption of neutral species during temperature-programmed target heating. Identification of the desorbing neutrals was possible by comparing the thermal desorption mass spectrum with the electron impact fragmentation pattern in the molecular beam measured in a cross-beam arrangement. Considering Au and Ni substrates, different binding sites could be distinguished, which are correlated with the emission of specific molecular secondary ions. The interaction between glycine and coadsorbed D2 was examined. Only on Pt significant hydrogen exchange rates were observed.
Pretreatment effects on the morphology and properties of aluminum oxide thermally grown on NiCoCrAlY
Authors: Prakash S. , Budhani R. C. , Doerr H. J. , Deshpandey C. V. , Bunshah R. F.
Published: July 2002

This report is part of the investigation on thin film temperature sensors for turbine blade applications. The effect of pretreatments on the morphology and properties of aluminum oxide thermally grown from NiCoCrAlY was investigated. The goal was to optimize process steps to produce a highly adherent, continuous, and insulating aluminum oxide. Two pretreatments were carried out, one in vacuum (∼10−4 Torr) at 1350 K for 5 h, and the other consisting of deposition of a 1 μm thick Al2O3 film by ARE (activated reactive evaporation). Samples were subsequently oxidized thermally at 1000 °C for 50 h at 0.5 Torr oxygen pressure. The two pretreatments were carried out on electron-beam evaporation NiCoCrAlY, ∼120 μm thick, deposited on a superalloy turbine blade substrate. The results showed that the thermally grown oxide was significantly different in microstructure, surface topography and in its adherence to the NiCoCrAlY for the two pretreatments. Optimum results were obtained by combining the two pretreatments to produce an adherent, continuous, and insulating oxide film on the NiCoCrAlY coated superalloy substrate.
Determination of film stresses during sputter deposition using an i
n s
i
t
u probe
Authors: Hoffman D. W. , Kukla C. M.
Published: July 2002

Previous work has established that the internal stresses and physical properties of sputter-deposited metals can be markedly affected by relatively small changes in the sputtering process. For instance, lowering the gas pressure or raising the discharge current can reverse the stress from tensile to compressive and, at the same time, produce more bulklike properties in the resultant coatings. Consequently, film stress observations can be utilized to map out the nature of the material produced in a given coating process and locate the boundary of the bulklike deposition regime as a function of process parameters. A principal obstacle to the implementation of this technique has been the laborious procedure of generating individual samples over a matrix of different process conditions. Residual film stresses were then determined by observing the resulting curvature of the thin substrates. In the present work substrate deflection was sensed capacitively using a miniature probe that was inserted into the deposition chamber and monitored in a remote manner. The probe signal was linear with film thickness, enabling detection of intrinsic stress in molybdenum layers as thin as 30 nm with sensitivity undiminished by multiple applications. The known compressive-to-tensile stress transition was accurately reproduced by the probe with significant additional detail. Effects of discharge current, source proximity, and argon flow conditions in shifting the stress transition were readily mapped out.
Surface analysis of diffusion zones in multiple chemical vapor deposition coatings
Authors: Moore R. L. , Salvati L. , Sundberg G. , Greenhut V.
Published: July 2002

In this investigation, a multilayer carbide coated cutting tool was examined. The cutting tool was produced through the sequential chemical vapor deposition (CVD) of TaC, TiC, Al2O3, and TiN layers over a WC/Co substrate. The purpose of this study was to characterize the interdiffusion of materials at each of the interfacial regions as a function of deposition conditions. To accomplish this, several surface analysis techniques were used including scanning Auger microscopy (SAM), scanning electron microscopy (SEM), and small spot x-ray photoelectron spectroscopy (XPS). The samples were prepared using a modified lapping technique. The lapping angle used was ∼0.25°, which yielded at least a 250× expansion of the interfacial regions. This allowed interface characterization without instrumental resolution limitations. Scanning AES and small spot XPS were performed on interfaces to investigate interface chemistry and interdiffusion. Argon sputter depth profiling was also used to further characterize diffusion zone composition and dimension.
Friction and wear properties of TiC–Al2O3 composite and Al2O3/TiC layered coatings
Authors: Memarian H. , Budhani R. C. , Karim A. A. , Doerr H. J. , Deshpandey C. V. , Bunshah R. F. , Doi A.
Published: July 2002

The measurement of wear, the coefficient of static and dynamic friction and the hardness of TiC–Al2O3, and Al2O3/TiC coatings deposited on stainless steel and TiC precoated stainless steel substrates are reported. The results of the studies are compared with similar studies on TiC coatings deposited by the activated reactive evaporation (ARE) process. It has been found that the wear in both types of TiC–Al2O3 and Al2O3/TiC coatings is a sum total of abrasive and adhesive contributions. The values of the coefficients of friction are higher compared to stainless steel TiC ARE wear couple.
Epitaxial growth of CeF3 and NdF3 on Si(111)
Authors: Sinharoy S. , Hoffman R. A. , Farrow R. F. C. , Rieger J. H.
Published: July 2002

We report the first epitaxial growth of two members of the rare earth lanthanide trifluoride family, namely cerium trifluoride (CeF3) and neodymium trifluoride (NdF3), on silicon (111). These materials are known to have superior physical and chemical properties in comparison with the group II fluorides for several potential applications including protective antireflection coatings and insulating layers in various semiconductor device structures. The films of thicknesses up to 3400 Å were grown under ultrahigh vacuum (UHV) conditions using a specially designed evaporator. They were characterized in situ by low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES), and ex situ by reflection high energy electron diffraction (RHEED) and Nomarski optical microscopy. Good quality epitaxial films were obtained on both the (1×1) and the (7×7) structures of Si(111). The optimum growth temperatures were found to be 600 °C for CeF3 and 500 °C for NdF3. In both cases, the c axis was parallel to the Si[111], consistent with the hexagonal symmetry of the trifluorides and the Si(111) surface. Cracking problems were encountered at nonoptimum growth temperatures.
A large aluminum alloy molecular beam epitaxy chamber with an ultimate pressure of 7.5×10−12 Torr
Authors: Chen J. R. , Narushima K. , Miyamoto M. , Ishimaru H.
Published: July 2002

An ultimate pressure of 7.5×10−12 Torr was reached in a large molecular beam epitaxy (MBE) chamber made of aluminum alloy A1050, after baking and after liquid nitrogen was introduced. Most of the components were made of aluminum alloys, except a gauge and the Ti-sublimation pump. For the seals between aluminum and stainless steel flanges, aluminum gaskets or helicoflexes were used and no problems resulted. It was also found that the Ti-sublimation pump was effective in the 10−10 Torr range but not in the lower 10−11 Torr range. The pressure limits of the turbomolecular pump used in the system was 6×10−11 Torr. Pumping speeds of the ion pump and the shroud cooled with liquid nitrogen were about 60 and 250 l/s, respectively. The outgassing rate of the chamber was estimated to be 1×10−13 Torr ⋅ l/s cm2. After a situation in which the ion pump was turned off at room temperature and in a second case in which the liquid nitrogen supply was stopped, surface conditions of the system were studied.
An effective background removal technique for inelastic electron tunneling spectra
Authors: Gajda G. J. , Weinberg W. H.
Published: July 2002

This report describes a simple, rapid, and effective computer algorithm for background removal in inelastic electron tunneling spectra.
Electron storage ring beam lifetime dependence on pressure and pumping speed
Authors: Halama Henry J.
Published: July 2002

The beam loss in electron storage rings depends to a large extent on the interaction of the beam with heavier residual gas molecules such as CO, CO2, and A due to bremsstrahlung and Coulomb scattering. The gas density inside the vacuum chamber is determined by the surface condition of the vacuum chamber, which is bombarded by photons (synchrotron radiation) generated by circulating electron beams, and by the installed pumping. During the initial commissioning severe limitations on the achievable beam current were observed due to large pressure rises. The x-ray ring was shut down for several months and its vacuum system was updated and baked out. Residual gas spectra obtained after the shut down were typical of a well baked out system, i.e., hydrogen constituted ∼95% of the gas and the average pressure was in the 10−10 Torr range. During initial operation the composition of desorbed gases was 43% H2, 25% CO, and 16% CO2 and CH4. After 3 months of beam conditioning the desorption rate dropped by a factor of 5 and the CO, CO2, and CH4 peaks represented smaller percentage of total desorbed gas. Beam lifetime did not, however, show a corresponding increase.
Zero stability of spinning rotor vacuum gages
Authors: McCulloh K. E. , Wood S. D. , Tilford C. R.
Published: July 2002

Spinning rotor vacuum gages measure pressure by determining the rate of slowing of a magnetically suspended spinning ball over and above the slowing caused by a pressure independent residual drag. For accurate measurement in the high vacuum range, this residual drag must be determined and subtracted as an offset correction. The stability of this residual drag, temperature induced changes of the ball’s moment of inertia, vibration, and random measurement noise will determine the limits of stability and hence, the lowest usable pressure of the gage. Selected balls in a quiet, stable environment have demonstrated instabilities as low as ±10−6 Pa (10−8 Torr) equivalent nitrogen pressure. However, instabilities as large as two orders of magnitude greater can occur. Examples are given of different types of instabilities and guidelines are presented for minimizing many of the sources of instability.