Structural and IR studies on Cu-Ti mixed ferrite

The sensitivity of the positron to the internal electric fields in good quality thin (100 nm) Molecular Beam Epitaxy (MBE)-grown layers is experimentally demonstrated. Both a thin intrinsic layer grown on a p-type substrate and a highly n-doped profile buried in intrinsic silicon form effective barriers to positron diffusion although no defects can be detected. We also extract, from a full treatment of the positron diffusion, a quantitative estimate of the concentration, below the detection limits of other methods, of large vacancy clusters in a thick (680 nm) film.