Browsing by Author "Hammond, Mark Stuart"

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    Investigations of surface electronic structure and surface-atom interactions with spin-polarized metastable atom de-excitation spectroscopy
    (1989) Hammond, Mark Stuart; Walters, G. King
    Metastable Atom De-excitation Spectroscopy (MDS) provides a powerful technique with which to investigate surface electronic structure with unparalleled surface specificity. In this technique a thermal energy beam of noble-gas metastable atoms is directed at the surface to be studied and the kinetic energy distribution of ejected electrons that result from metastable atom de-excitation is measured. Although the measured distribution contains information about the electronic structure of the outermost surface layer, its detailed analysis requires knowledge of the dynamics of the metastable atom-surface interaction. In the present work, these dynamics have been investigated directly by use of spin-labeling techniques. The electron spins on the incident metastable atoms are polarized and the spin-polarization of the ejected electrons is measured with a Mott polarimeter. Energy-integrated electron spin-polarization (ESP) measurements for Pd(110) and energy-resolved ESP measurements for Cu(100) surfaces under a variety of conditions indicate that metastable atom-surface interactions are more complex than has been assumed in past MDS studies. Spin-polarized MDS has also proven useful in the study of surface magnetism. The present work includes a study of the surface electronic and magnetic structure of the Fe(110) surface. Results indicate an interesting reversal of surface electron spin-polarization for Fe(110) surfaces exposed to oxygen.
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    Laser optical pumping of atomic beams
    (1985) Hammond, Mark Stuart; Dunning, F. Barry; Walters, G. King; Mutchler, Gordon S.
    Beams of heavy rare gas metastable atoms with a high degree of polarization have been produced by optical pumping using a variety of dye laser systems. Argon (Pa) metastable atoms were efficiently polarized. but frequency instabilities in the output of the simple, multimode Ozazine 75 dye laser used prevented stable, long-term polarizations from being achieved. Stable optical pumping of a Ne (P3) beam was achieved using a similar DCM dye laser. Frequency jitter due to low dye viscosity essentially broadened the narrow spectral components of the laser lineshape. allowing a large degree of polarization to be obtained for long periods of time. In order to insure controllable and reliable performance in the optical pumping of rare gas metastable atom beams, a frequency modulation technique has been developed. By creating sidebands between laser cavity modes. frequency modulation creates a broad qua si-continuous frequency spectrum. The negative effects of frequency drifts are thus eliminated by spreading radiation across the overall laser linewidth. A frequency modulated LD 7 dye laser was used to successfully polarize an argon metastable atom beam. High polarizations were routinely obtained for periods of several hours. The technique is suitable for use in optically pumping a wide variety of atomic species for the study of electron spin and orbital orientation dependencies in many collision processes.