High-resolution angle-resolved positron reemission spectra from metal surfaces

Journal Article · Tue Apr 01 04:00:00 EST 1986 · Phys. Rev. B: Condens. Matter; (United States)

DOI:https://doi.org/10.1103/PhysRevB.33.4479· OSTI ID:5935553

Fischer, D A; Lynn, K G; Gidley, D W

An electrostatically focused beam of monoenergetic positrons is used with a hemispherical energy analyzer to acquire the first high-resolution (roughly-equal20 meV) total-energy spectra of positrons reemitted from metal single crystals. At 300 K the measured energy width of positrons elastically emitted (with kinetic energy corresponding to the magnitude of the negative positron work function) is roughly-equal75 +- 5 meV for all the samples investigated: Ni(100), Ni(100)+CO, Ni(100)+S, Ni(100)+O, W(110)+C, W(110)+Cu, W(110)+O, Cu(111), Cu(111)+S, and Cu(100)+S. These results, along with angular distribution measurements on W(110)+C, W(110)+O, and Cu(111), are completely consistent with energy and angular widths as determined by a beam Maxwell-Boltzmann distribution: i.e., thermal broadening alone. A much narrower peak is observed at sample temperatures of 23 K, but uncertainty in the analyzer resolution limits us to conclude that the observed broadening is consistent with a thermal distribution with effective temperature less than 100 K. Discrete energy-loss peaks due to vibrational excitations of adsorbed molecules on the sample surface, first reported by Fischer et al. (Phys. Rev. Lett. 50, 1149 (1983)), are further investigated for Ni(100)c(2 x 2)/CO. The first evidence for short-range positron ''impact'' scattering is found for OH adsorbed on NiO as a loss peak at 400 meV in the reemitted spectrum. Continuous inelastic scattering processes are also observed in the spectrum and a limit on wide-angle elastic scattering is determined from angular scans.

• Research Organization: Physics Department, Brookhaven National Laboratory, Upton, New York 11973
• OSTI ID: 5935553
• Journal Information: Phys. Rev. B: Condens. Matter; (United States), Journal Name: Phys. Rev. B: Condens. Matter; (United States) Vol. 33:7; ISSN PRBMD
• Country of Publication: United States
• Language: English

Related Subjects

640301* -- Atomic
Molecular & Chemical Physics-- Beams & their Reactions
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
COLLISIONS
COPPER
CRYSTALS
ELASTIC SCATTERING
ELECTRON SPECTROSCOPY
ELEMENTS
ENERGY RESOLUTION
ENERGY SPECTRA
ENERGY-LOSS SPECTROSCOPY
FUNCTIONS
INELASTIC SCATTERING
METALS
MONOCRYSTALS
NICKEL
POSITRON COLLISIONS
RESOLUTION
SCATTERING
SPECTRA
SPECTROSCOPY
TRANSITION ELEMENTS
TUNGSTEN
WORK FUNCTIONS