HELIUM-VACANCY CLUSTERING IN V-4CR-4TI AT ELEVATED-TEMPERATURES

Thermal Helium Desorption Spectrometry was used to investigate the hel ium-vacancy clustering in V-4Cr-4Ti at various implantation temperatur es. Samples were implanted with 1 keV helium to a dose of 10(14) cm(-2 ) at implantation temperatures ranging from 300 to 700 K. Helium trapp ing inside the sample was almost completely suppressed at implantation temperatures above 700 K. Helium-vacancy clustering at gas impurities was not observed at temperatures above 500 K. This result is consiste nt with the earlier proposed model where the helium-vacancy-oxygen com plex is unstable above 550 K. Helium trapping at 500-700 K is ascribed to pre-existing traps, e.g. fine-size precipitates. In a number of ex periments the implantation at elevated temperature was preceded by roo m temperature (RT) pre-implantation with doses varying from 1.8 x 10(1 3) to 10(14) cm(-2). It was observed that the clusters created during the RT implantation were stable enough to provide further cluster grow th during the subsequent high temperature (700 K) implantation. (C) 19 98 Elsevier Science B.V. All rights reserved.