THE EFFECT OF LASER ANNEALING OF THIN W(100) FILMS ON POSITRON TRANSMISSION REEMISSION PROPERTIES

Results on e+ transmission reemission properties are presented for three single-crystal W(100) films of thicknesses 1000, 2000, and 3100 Å for incident e+ energies of 1.4-16 keV. The films were first cleaned with a 10-s laser pulse, then annealed in O2 (10 -6 Torr), and finally heated in a vacuum (10 -9 Torr). Thereafter the films showed good reemission properties. The maximum transmitted yields of slow e+ were 38% (1000 Å), 27% (2000 Å), and 17% (3100 Å) at incident e+ energies of 4, 5.2, and 7.2 keV, respectively. The energy distributions of the reemitted e+ were characterized by a full width half maximum of 0.15-0.2 eV located at 2.8 eV containing 60%-70% of the e+ superimposed onto a nearly uniform distribution covering the energy interval 0-2.8 eV.