RADIATION-DAMAGE AND TRAPPING OF HELIUM IN HOPG-GRAPHITE

Rutherford backscattering analysis in channeling geometry has been use d to measure the formation and annealing of radiation damage in highly oriented pyrolytic graphite (HOPG) implanted with 20 keV helium ions. The number of displaced atoms per incoming ion at room temperature wa s found to be more than four times greater for helium ions than for de uterium of equal damage profile and much greater than model calculatio ns. On the annealing of HOPG implanted with a low fluence of helium up to 800 K an increase of the disorder in the implanted region is obser ved which is attributed to the formation of blisters at the surface. T he desorption of helium implanted at 300 K was investigated by ion bea m analysis using the nuclear reaction He-3(D, p)alpha. Low fluence imp lanted helium (2 x 10(15) He/cm2) did not desorb below 950 K.