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  • 1
    Electronic Resource
    Electronic Resource
    Negative surface ionization of hydrogen atoms and molecules (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 2896-2901 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The total yield of H− ions, Y(Ein), produced in backscattering of low-energy H+ and H+2 ions from polycrystalline gold, tungsten, and molybdenum converter surfaces was measured at normal incidence in the energy range Ein=2–30 eV per nucleus. The yield per nucleus is independent of the ion mass. This indicates that the molecular ions are dissociated before colliding with the converter surface. A universal expression for Y(Ein) was developed by combining the electron tunneling theory with atomic scattering theory. This expression agrees well with measurements. The yield is completely characterized by two parameters, Eth/RE and RNη0, which can be determined experimentally: Y=0 for Ein=Eth/RE, and Y approaches the maximum yield Rη0 as Ein increases. These parameters were determined from measured H− yields in ion beam backscattering experiments, as well as for backscattering of thermal distributions of hydrogen atoms. For beam experiments, the maximum yield of 0.3 per nucleus was obtained for Mo/Cs converters with 1.5 eV work function. A higher maximum yield of 0.42 was obtained from experiments on backscattering thermal distributions of H atoms. This is attributed to high extraction fields. The universal yield formula made it possible to compare the results of the two different types of experiments. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361285
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  • 2
    Electronic Resource
    Electronic Resource
    Catalytic oxidation of silicon by cesium ion bombardment (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 452-458 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results for room-temperature oxidation of silicon using cesium ion bombardment and low oxygen exposure are presented. Bombardment with cesium ions is shown to allow oxidation at O2 pressures orders of magnitude smaller than with noble gas ion bombardment. Oxide layers of up to 30 A(ring) in thickness are grown with beam energies ranging from 20–2000 eV, O2 pressures from 10−9 to 10−6 Torr, and total O2 exposures of 100 to 104 L. Results are shown to be consistent with models indicating that initial oxidation of silicon is via dissociative chemisorption of O2, and that the low work function of the cesium- and oxygen-coated silicon plays the primary role in promoting the oxidation process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347684
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  • 3
    Electronic Resource
    Electronic Resource
    Source of low-energy hydrogen ions for measuring electron transfer in surface scattering experiments (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 5289-5293 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We present the design and performance of a beamline which is the source of 5–50-eV protons for surface scattering experiments. The beamline also incorporates a collector for measuring total secondary ion and electron yields. The beam forming optics are built around a commercially available gas discharge ion gun and produce a mass-selected, energy-filtered beam. Results of computer ray tracing are included to illustrate the operation of the beam optics. Tests have produced 50-pA proton beams 3.5-mm wide at 5 eV with an energy spread of about 1 eV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143441
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  • 4
    Electronic Resource
    Electronic Resource
    An arc discharge hydrogen atom source (1993)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 2746-2752 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A magnetically confined thermal electric arc gas heater of easy construction, handling, and maintenance has been designed, built, and tested as a suitable source of heat for dissociating hydrogen molecules. The plasma species in the gas discharge region are assumed to satisfy local thermodynamic equilibrium conditions. The average beam kinetic energy is determined to be 1.5 eV, leading to an arc temperature of approximately 8700 K; the dissociation rate is 0.5 atoms per molecule and the total atom beam intensity in the forward direction is 1018 atoms/sr s. This novel atom source has been successfully ignited and operated with pure hydrogen during several hours of continuous performance, maintaining its characteristics and overcoming some of the difficulties previously found by researchers using other arc sources. The hyperthermal hydrogen atom beam obtained from this source is identified by MoO3 chemical detectors, and analyzed and characterized by three different calorimetric sensors, Ni, Ta, and Teflon. The experimental results obtained with this dissociator agree with those published in the literature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144413
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  • 5
    Electronic Resource
    Electronic Resource
    Finite-size effects in ionization potentials and electron affinities of metal clusters (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 1295-1303 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Experimental ionization potentials (I) and electron affinities (A) of metal clusters MeN are compiled for a variety of systems and their size dependence is analyzed. In the theoretical part, we perform semiclassical density variational calculations using the spherical jellium model and the local density approximation. For alkali systems and, to some extent, also for some nonalkali systems, the calculated values of I and A reproduce very well the average size dependence of the measured quantities, if their common bulk limit W is adjusted to the experimental bulk work function. This holds even for rather small systems where I and A are no longer linear in N−1/3. We discuss the extent to which classical models for the energetics of charged metal spheres can account for the correct size dependence in the large-cluster limit. We point out that the deviation of the slope parameters α and β in the asymptotic expressions I∼W+α(e2/rs)N−1/3, A∼W−β(e2/rs)N−1/3 from the values (1)/(2) , which depends on the material via the Wigner–Seitz parameter rs, can be entirely accounted for by quantum-mechanical effects, namely the kinetic, exchange, and correlation energies and the diffuseness of the electron density.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461111
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  • 6
    Electronic Resource
    Electronic Resource
    Solid state cesium ion guns for surface studies (abstract) : International conference on ion sources (1990)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 658-658 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Three cesium ion guns covering the energy range of 5–5000 V are described. These guns use a novel source of cesium ions that combine the advantages of porous metal ionizers with those of aluminosilicate emitters. Cesium ions are chemically stored in a solid electrolyte pellet and are thermionically emitted from a porous thin film of tungsten at the surface. Cesium supply to the emitting surface is controlled by applying a bias across the pellet. A total charge of 10.0 C can be extracted, corresponding to greater than 2000 h of lifetime with an extraction current of 1.0 μA. This source is compact, stable, and easy to use, and produces a beam with 〉99.5% purity. It requires none of the differential pumping or associated hardware necessary in designs using cesium vapor and porous tungsten ionizers. It has been used in ultrahigh-vacuum (UHV) experiments at pressures of 〈10−10 Torr with no significant gas load. Three different types of extraction optics are used depending on the energy range desired. For low-energy deposition, a simple space-charge-limited planar diode with a perveance of 1×10−7 A/V3/2 is used. Current densities of 10.0 μA/cm2 at the exit aperture for energies ≤20 V are typical. This type of source provides an alternative to vapor deposition with the advantage of precise flux calibration by integration of the ion current. For energies from 50 to 500 V and typical beam radii of 0.5 to 0.2 mm, a high perveance Pierce-type ion gun is used. This gun was designed with a perveance of 1×10−9 A/V3/2 and produces a beam with an effective temperature of 0.35 eV. For the energy range of 0.5 to 5 keV, the Pierce gun is used in conjunction with two Einzel lenses, enabling a large range of imaging ratios to be obtained. Beam radii of 60 to 300 μm are typical for beam currents of 50 nA to 1.0 μA. Results are presented and discussed for UHV studies of ion implantation, electronic surface changes induced by adsorbates, and negative secondary-ion mass spectrometry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141896
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  • 7
    Electronic Resource
    Electronic Resource
    Solid state cesium ion guns for surface studies (1990)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 788-792 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Three cesium ion guns covering the energy range of 5–5000 V are described. These guns use a novel source of cesium ions that combine the advantages of porous metal ionizers with those of aluminosilicate emitters. Cesium ions are chemically stored in a solid electrolyte pellet and are thermionically emitted from a porous thin film of tungsten at the surface. Cesium supply to the emitting surface is controlled by applying a bias across the pellet. A total charge of 10.0 C can be extracted, corresponding to greater than 2000 h of lifetime with an extraction current of 1.0 μA. This source is compact, stable, and easy to use, and produces a beam with 〉99.5% purity. It requires none of the differential pumping or associated hardware necessary in designs using cesium vapor and porous tungsten ionizers. It has been used in ultrahigh-vacuum (UHV) experiments at pressures of 〈10−10 Torr with no significant gas load. Three different types of extraction optics are used depending on the energy range desired. For low-energy deposition, a simple space-charge-limited planar diode with a perveance of 1×10−7 A/V3/2 is used. Current densities of 10.0 μA/cm2 at the exit aperture for energies ≤20 V are typical. This type of source provides an alternative to vapor deposition with the advantage of precise flux calibration by integration of the ion current. For energies from 50 to 500 V and typical beam radii of 0.5 to 0.2 mm, a high perveance Pierce-type ion gun is used. This gun was designed with a perveance of 1×10−9 A/V3/2 and produces a beam with an effective temperature of 0.35 eV. For the energy range of 0.5 to 5 keV, the Pierce gun is used in conjunction with two Einzel lenses, enabling a large range of imaging ratios to be obtained. Beam radii of 60 to 300 μm are typical for beam currents of 50 nA to 1.0 μA. Results are presented and discussed for UHV studies of ion implantation, electronic surface changes induced by adsorbates, and negative secondary-ion mass spectrometry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141495
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  • 8
    Electronic Resource
    Electronic Resource
    A new solid-state cesium ion source (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 2704-2710 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A novel Cs+ion source combining the advantages of porous metal ionizers with those of zeolite emitters has been developed. Cesium ions are chemically stored in a cesium-mordenite solid electrolyte (Cs-M SE) pellet whose emitting surface is coated with a porous tungsten thin film. Cesium supply to the emitting surface is controlled by a voltage applied across the solid electrolyte pellet. Cs+ ion emission takes place on the surface of the porous tungsten electrode by surface ionization. The ionic conductivity of Cs+ ion in the Cs-M SE is of order of 10−5 Ω cm−1 at 1000 °C. The interface properties between electrolyte and electrodes play a major role in the cesium ion source. The cathode electrode interface (emitting electrode) determines the stability of the supply current density to the emitting surface. The lifetime of the source is found to depend on the anode interface. In a steady-state operation, an ion-emission current density of the order of 20 mA/cm2 has been extracted for 30 h at a total ion-emission current of 100 μA at 1000 °C. This corresponds to 10 C of extracted charge.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345458
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  • 9
    Electronic Resource
    Electronic Resource
    Sputtering of negative hydrogen ions by cesium bombardment (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 17-23 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The production of negative hydrogen ions sputtered from a low work function converter surface has been investigated. Hydrogen and cesium admitted into the vacuum chamber are chemisorbed on a polycrystalline molybdenum target. H−, Mo−, and e− are sputtered from this cathode by Cs+ ions in the energy range 150–1000 eV. Angular and parallel energy distributions of H−, Mo−, and e− are measured as a function of hydrogen gas pressure, cesium coverage, and incident ion energy. For optimum coverage, the H− ion temperature varies from 0.65% and 0.35% of the incident Cs+ bombarding energy for Cs+ ion energies of 250 and 1000 eV, respectively. The secondary electrons have a temperature of 0.04% of the bombarding energy almost independent of Cs+ energy. The spreads increase with decreasing target coverage and are independent of surface roughness. The optimum H−, Mo−, and e− yields are also measured as a function of hydrogen pressure and incident Cs+ bombarding energy. The optimum H− ion yield is 0.41 at a Cs+ ion energy of 750 eV. By extrapolating the H− ion yield at low Cs+ bombarding energy, a Cs+ ion threshold energy of 120 eV may be estimated. This indicates a binding energy of hydrogen smaller than 3.6 eV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.337800
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  • 10
    Electronic Resource
    Electronic Resource
    Surface production of H− ions by hyperthermal hydrogen atoms (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 2857-2859 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hyperthermal atomic hydrogen of energy in the range of 1–10 eV has been produced by electron impact dissociation in a cw 2.45 GHz microwave electron cyclotron resonance (ECR) discharge using a Lisitano-Coil. The flux and the energy of the hydrogen atoms have been measured by negative surface ionization of the atoms backscattered from pure and cesiated metal surfaces. A hyperthermal atomic hydrogen flux density equivalent to more than 0.5 A/cm2 and a temperature of about 5 eV has been produced for 420 W discharge power under cw condition. These hydrogen atoms can be directed onto an external converter located outside the discharge. This opens up new possibilities for H− ion source design.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.108056
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