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A time-of-flight spectrometer has been developed for measuring velocity- and angle-resolved distributions of neutral and ionized alkali atoms in the range of several electron volts to several thousand electron volts. The spectrometer is mounted on a rotating platform inside a previously existing ultra-high-vacuum scattering chamber equipped with a low-energy ion beamline. A high work function platinum foil, placed after a pair of angle-defining apertures, is used to ionize the alkali atoms, regardless of their incident charge states. After striking the platinum foil, the alkali ions are accelerated and detected with a channel electron multiplier. Velocity resolution of the scattered flux is achieved using standard time-of-flight techniques. Neutral and ionized alkali atoms are detected with the same high efficiency. The ion flux can be rejected by biasing a pair of rejection elements, and therefore absolute ratios of the neutral to total flux can be determined. Such a spectrometer can be used to probe the role of charge transfer in a number of dynamical processes at surfaces. [ABSTRACT FROM AUTHOR]

We have constructed and tested an UHV beamline to produce beams of alkali metal and noble gas ions over the energy range <20 eV to 10 keV with energy resolution ΔE/E of 1% or better. At the sample position, we have attained tens of nanoamps of current for keV energy beams in a 1–2-mm beam spot with about ±1° angular divergence, and nanoamps of current at 25 eV in a 4-mm beam spot with ±2° angular divergence. By applying Liouville’s theorem to the beam’s emittance and using waist-to-waist transport through the beam optics, the current on the sample is maximized while limiting the spot size and angular divergence. To achieve useful current at the lowest energies, special attention was paid to minimizing space-charge effects. Beam emittances measured at the sample position are consistent with Liouville’s theorem. Equations for waist-to-waist transport are derived in the Appendix. [ABSTRACT FROM AUTHOR]

We have designed and constructed an apparatus that combines hyperthermal energy ion scattering (<100 eV) with low-energy ion scattering (a few hundred eV to several keV). The UHV scattering chamber possesses a full range of sample preparation and characterization capabilities, including LEED, Auger spectroscopy, a Kelvin probe for work function measurements, and facilities for gas or alkali-metal deposition. The differentially pumped beamline provides well-collimated, monoenergetic beams of gas or alkali-metal ions ranging in energy from <10 eV to 10 keV. To illustrate the qualitative changes in the scattering behavior observed over this range, we present experimental results for Na+ scattered off the Cu(110) surface with the incident ion energy ranging from 56 eV to 4 keV. We also show a comparison between 1 keV K+ and 1 keV Ar+ scattered from the same surface. [ABSTRACT FROM AUTHOR]