High-intensity variable-energy positron beam for surface and near-surface studies

Interaction of positron beams with surfaces, thin films, and interfaces

“…(6) assuming <p + =2.9 eV (from Fischer et al, 1986). berg et al, 1980a;Van House and Zitzewitz, 1984;Frieze, Gidley, and Lynn, 1985), axial magnetic fields (Costello et al, 1972;Lynn and Lutz, 1980b;Mills, 1981a;Hutchins et al, 1985Weiss, 1985;Lahtinen et al, 1986;Schultz, 1988), and hybridized electrostatic/magnetic systems (e.g., Rich, 1986). The fundamental difference between the electrostatic and magnetic system of beam transport is simply that some experiments require the measurement of scattering angles (and therefore are hindered by magnetic fields), whereas other experiments are simplified by the ability to confine all scattered charged particles.…”

“…The fraction of Ps being formed at a surface is determined by scaling the measured spectrum between these two extremes, using Eq. (9) (from Lahtinen et al, 1986). positron surface state as well as Ps velocity spectroscopy (see Sec.…”

Positron reflection from the surface potential

“…Since the initial e + energy is thermal, T vanishes at 0 K. Reemitted e + and Ps yields for a clean Cu(lll) surface were measured as a function of incident e + energy at temperatures down to 24 K with a beam of 5xl0 6 e + /s (Ref. 15) under UHV conditions having a base pressure of 5xl0~H Torr. The (99.9999% + )-purity single crystal was cleaned with standard Ar + sputtering and annealing cycles and the surface was monitored with LEED and Auger-electron spectroscopy (AES).…”

Vacancylike structure of theDXcenter in Te-dopedAlxGa1Laine1, Mäkinen2, Saarinen3 et al. 1996Phys. Rev. BSelf Cite

“…9 The 511-keV annihilation spectra were detected and recorded with a high-purity Ge detector and a digitally stabilized multichannel analyzer system. More than 3ϫ10 6 counts were collected to the annihilation peak in each measurement.…”