The nucleation and growth of {113} defects in float-zone material were observed  in situ  in an ultra-high vacuum transmission electron microscope. Intense irradiation with 200keV electrons was carried out, at 400 or 500C, under a pressure of 10-7Pa. It was found that defect development changed markedly when O2 (5 x 10-5Pa) was introduced into the chamber. This result constituted direct evidence for the effect of O2 upon the formation of the defects, since no other impurities were present in the ultra-high vacuum environment.

K.Koto, S.Takeda, T.Ichihashi, S.Iijima: Applied Physics Letters, 1997, 71[12], 1661-3