It was shown, using Mössbauer spectroscopy, that the electric field gradient which was associated with an atomic defect was very sensitive to the small changes in atomic distance which were introduced by bending ultra-thin wafers. A direct application of this was the determination of the orientation of defects that were associated with Mössbauer probe atoms, where normal Mössbauer experiments (and even electron paramagnetic resonance methods) could furnish no information. Provided that the defects were situated only in the surface region of the Si single crystal (as when introduced by ion implantation), bending in various crystallographic directions was observed to affect the hyperfine splitting and was sensitive to the defect orientation. Mössbauer spectroscopic measurements were made of Co dimers in (100)- and (l11)-oriented samples. It was found that Co dimers appeared after the heat treatment of low-dose 57Co-implanted material. Nothing was known concerning their configuration. On the basis of the results of bending along various crystallographic axes, a model for the defect orientation was proposed which revealed a <110> orientation of the pair axis.

A.M.Van Bavel, S.Degroote, A.Vantomme, A.Stesmans, G.Langouche: Materials Science Forum, 1995, 196-201, 1515-20