CONTRAST IN POSITRON REEMISSION MICROSCOPY DUE TO POSITRON TRAPPING BY DISLOCATIONS

Positron reemission microscope (PRM) images of 150 nm thick, self-supp orting, single crystal Ni(100) films were observed to exhibit high con trast band-like features on the few-mu m scale, with boundary definiti ons of similar to 0.1 mu m. Transmission electron microscope (TEM) ima ges of the films revealed no individual features on the mu m scale tha t would give rise to positron trapping or strong scattering by impurit ies. Also an examination of the surfaces with a scanning electron micr oscope (SEM) showed no surface composition variations that could be re lated to the PRM images. At 10 000 X magnification the TEM revealed mu m-scale domains containing large dislocation densities, similar to 10 (9)/cm(2) as distinct from domains having similar to 10(7)/cm(2) or le ss dislocation densities. Although the lateral size of the individual dislocations were observed to be less than 100 nm, the net effect of a high density of dislocations is proposed to be the contrast mechanism responsible for the mu m-scale dark regions observed in the PRM image s. The significance of correlating mu m-scale patterns in PRM images w ith dislocation densities is discussed in regard to providing focusing targets for future high magnification (similar to 50 000 x) PRM studi es of monovacancies.