Low temperature (<10 K) internal friction measurements have revealed a
contamination of silicon during annealing under all but the most care
ful conditions. A similar contamination occurs during ion-implantation
. Boron was suspected as a likely contaminant, but can be clearly rule
d out by combining low-temperature internal friction measurements and
secondary ion mass spectroscopy. (C) 1998 Elsevier Science B.V. All ri
ghts reserved.